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Ecological Impacts of a Widespread Frost Event Following Early Spring Leaf-Out
Abstract
In the spring of 2010, temperatures averaged ~3 °C above the long-term mean (March–May) across the northeastern United States. However, in mid-to-late spring, much of this region experienced a severe frost event. The spring of 2010 therefore provides a case study on how future spring temperature extremes may affect northeastern forest ecosystems. We assessed the response of three northern hardwood tree species (sugar maple, American beech, yellow birch) to these anomalous temperature patterns using several different data sources and addressed four main questions: (1) Along an elevational gradient, how was each species affected by the late spring frost? (2) How did differences in phenological growth strategy influence their response? (3) How did the late spring frost affect ecosystem productivity within the study domain? (4) What are the potential long-term impacts of spring frost events on forest community ecology? Our results show that all species exhibited early leaf development triggered by the warm spring. However, yellow birch and American beech have more conservative growth strategies and were largely unaffected by the late spring frost. In contrast, sugar maples responded strongly to warmer temperatures and experi- enced widespread frost damage that resulted in leaf loss and delayed canopy development. Late spring frost events may therefore provide a competitive advantage for yellow birch and American beech at the expense of sugar maple. Results from satellite remote sensing confirm that frost damage was widespread throughout the region at higher elevations (>500 m). The frost event is estimated to have reduced gross ecosystem productivity by 70–153 g C m␣2, or 7–14% of the annual gross productivity (1061 ± 82 g C m␣2) across 8753 km2 of high-elevation forest. We conclude that frost events following leaf out, which are expected to become more common with climate change, may influence both forest composition and ecosystem productivity.
... These extreme events often have larger and more adverse impacts on ecosystems and society than changes in mean climate alone (Ciais et al., 2005;Reichstein et al., 2013;Orsenigo et al., 2014;Frank et al., 2015). For example, heat waves, droughts, and spring frost defoliations have resulted in large declines in forest carbon uptake in Europe and North America (Ciais et al., 2005;Hufkens et al., 2012). Furthermore, ecosystem responses to extreme climate events often extend well beyond the duration of the event (Frank et al., 2015). ...
... However, earlier leaf out may also increase susceptibility to a late spring frost that causes defoliation of affected trees. While these events typically trigger production of a second cohort of leaves, the effective start of the growing season is delayed, which has the potential to reduce tree growth and forest canopy carbon uptake in temperate broadleaf forests (Hufkens et al., 2012;Wiley et al., 2017;Rubio-Cuadrado et al., 2021). ...
... Because mean leaf-level rates of oak tree photosynthesis were statistically the same in 2020 and 2021, even small changes in LAI from the defoliation event could have impacted total canopy carbon uptake. Delayed leaf expansion and reductions in maximum LAI following a defoliating spring frost have been estimated to reduce gross primary production in a northern hardwood forest by 7-14% (Hufkens et al., 2012). To the extent that defoliation in the oak dominated forests we studied impacted the timing of full leaf expansion and reduced LAI, we might expect the response of total canopy carbon uptake to be similar to what Hufkens et al. (2012) estimated for a northern hardwood forest. ...
Spring frosts can defoliate trees, reduce canopy carbon assimilation, and alter interspecific competition dynamics. These events may become more common with climate change, but our understanding of the associated ecological impacts is limited by the stochastic nature of their occurrences. In 2020, a late spring frost defoliated oak (Quercus spp.), but not co-occurring maples (Acer spp.) across temperate broadleaf forests of the Hudson Highlands in southern New York State, U.S.A. Defoliation impacted 60% of this region’s forests and delayed full leaf expansion of oaks by ∼17 days. We used this event as an opportunity to advance understanding of how leaf-level physiology, radial growth, and interspecific competition dynamics of mature trees respond to frost-induced defoliation. We quantified leaf-level photosynthetic capacity, stomatal conductance, and water-use efficiency (WUE), as well as basal area increment of defoliated red oak (Q. rubra) trees and non-defoliated red maple (A. rubrum) trees in 2020 (“defoliation year”) and 2021 (“reference year”). Oak defoliation provided red maple trees with a competitive edge in terms of photosynthetic capacity early in the growing season. However, the second cohort of red oak leaves that developed following defoliation had photosynthetic capacities that were 3–4 times higher than red maple trees by the second half of the growing season, likely facilitated by higher rates of stomatal conductance. The growing season mean photosynthetic capacities for the defoliation year were significantly higher for red oaks than red maples. Red oak basal area increment tended to be higher than red maple during both the defoliation and reference years. For both species basal area increment was significantly higher during the reference year than defoliation year, but the reasons remain unclear. Taken together, these findings demonstrate that temporal patterns of photosynthesis in temperate broadleaf forests are altered by defoliation events, but enhanced photosynthetic capacities of second cohort leaves can reduce the negative effects of delayed leaf expansion and mitigate competitive advantages conferred to undefoliated co-occurring tree species. We suggest that understanding a tree species’ ability to compensate for frost-induced defoliation is essential to accurately predict effects of extreme climate events on tree competition dynamics and ecosystem processes.
... An earlier phenology characterized as advanced sprouting and flowering increases the risk of frost damage on newly growing organs, which included sprouted buds, dehardened twigs, unfolded leaves, blooming flowers, and young fruits (Rodrigo 2000, Park 2016, Chmielewski et al. 2018, Vitasse et al. 2018. The loss of carbon (C) in a false spring was unlikely to be offset by post-spring continuous growth under a warming climate (Awaya et al. 2009, Hufkens et al. 2012, Chamberlain et al. 2020. The yearly productivity, however, may have been impaired in forests since the establishment of a late spring frost (Bascietto et al. 2018). ...
... To determine characteristics of a false spring depends on two conditions of dynamic change of temperature. The first condition is achieved with a significant thermal time that advances budburst and flower onset (Hufkens et al. 2012). A certain amount of days with thermal ranges between 0 and 5°C is required for bud burst and leaf unfolding closely following chilling (Cannell & Smith 1986, Heide 1993. ...
... A chronicle of ten years is long enough for analyzing and identifying temperature characters for a late spring frost event (Principe et al. 2017). Current literature indicates a gross period of late spring frost usually happens from a start on 1 March (61 days of year) to 30 April (121 days of years), when it is a time with frequent temperature fluctuations of alternative warming and freeze (Gu et al. 2008, Augspurger 2009, Hufkens et al. 2012, Weather of China 2020. Daily highest and lowest temperature points were recorded to describe the dynamics of extreme temperature in historical spring times as it was employed in former studies (Hufkens et al. 2012, Vitasse et al. 2018. ...
Information is highly scarce about the possible effect of a late spring frost on physiological response of buds in ornamental trees. In this study, spring temperature of Changchun at Northeast China was recorded to identify the characteristics of a false spring by detecting extraordinary warming and sudden freeze in early April of 2017. Buds of six local ornamental tree species were investigated for their dynamics in biomass, non-structural carbohydrates, frost resistance on days of 7, 14, 21, and 28 April 2017. According to a comparison with spring temperature records historically from 2007 to 2016, a false spring was determined. Black pine (Pinus tabuliformis var. mukdensis) had greater bud biomass than apricot (Prunus sibirica L.). Peach (Prunus persica L. var. persica f. rubro-plena Schneid.) reserved greater non-structural carbohydrate content in post-chilling buds than black pine, and apricot and willow (Salix babylonica L.) had greater soluble sugars and starch contents in buds, respectively. Cumulative number of days with temperature below 12°C had a negative relationship with relative conductance in sorbus (Sorbus pohuashanensis [Hance] Hedl.). Chokecherry (Padus virginiana ‘Canada Red’) had greatest bud starch content on 21 April. Overall, a late spring frost imposed interruption on carbohydrate metabolism rather than direct damage on buds of ornamental trees before late April. Advanced warming induced more pronounced negative impact of a false spring than the sudden decline of minimum temperature.
... Physiological and geological effects of climate change on sugar maple trees were compiled from an evaluation of The New England Regional Assessment of the Potential Consequences of Climate Variability and Change (Lauten et al. 2001), a study of sugar maple's geographical variation of reproductive capacity (Graignic et al. 2014), and reviews of the biophysical responses of plants to climate change effects (Blackwell 2020;Hufkens et al. 2012). ...
... Warmer minimum temperatures in January allow for thawing of snowpack, leading to a reduced snowpack volume and a higher occurrence of soil freezing, causing damage to roots (Oswald et al. 2018). Warmer winter temperatures also present a more frequent spring frost, triggering budbreak 2-3 weeks earlier (Hufkens et al. 2012). The more frequent frost causes leaf-dieback of the initial leaves, forcing sugar maples to expend extra energy to regrow leaves in June and reducing the tree's growing season (Hufkens et al. 2012). ...
... Warmer winter temperatures also present a more frequent spring frost, triggering budbreak 2-3 weeks earlier (Hufkens et al. 2012). The more frequent frost causes leaf-dieback of the initial leaves, forcing sugar maples to expend extra energy to regrow leaves in June and reducing the tree's growing season (Hufkens et al. 2012). ...
Intensifications in seasonal temperature variation, attributed to increased greenhouse gas concentrations, are having an adverse effect on the forest composition of the northeastern United States. New York’s temperate broadleaf forests are undergoing alterations including a decline of the native sugar maple (Acer saccharum), as the species’ population begins to decrease or migrate north to remain within its hospitable temperature zone. By the end of the 21st century, sugar maple’s presence in New York forests will be highly altered from its historical range and population size. The reduction of this species will incur negative effects on New York’s forest ecology, maple-based cultural activities and organizations, and sectors of the local economy. This study examines the primary causes of sugar maple decline and the subsequent ecological, social, and economic impacts of climate change on sugar maple. Potential management preparations, adaptations, and resources to minimize disruptions from sugar maple decline will also be included in this study.
... Phenology is a key component of fitness. Thus, a mismatch between plant phenology and local climate can affect the productivity of crops and forests and carbon uptake of terrestrial ecosystems (Augspurger, 2009;Hufkens et al., 2012), and challenging our strategies of sustainable resource management (Keenan, 2015;Marquis et al., 2022). ...
... Plants from cold and boreal ecosystems are advancing spring phenology (growth reactivation and flowering) due to climate warming (Menzel et al., 2006). The lengthening of the growing season could increase carbon uptake and forest productivity (Keenan et al., 2014), but an early growth reactivation can also expose the young tissues to late frost events (Hufkens et al., 2012). The impact of frosts on plants involves several factors, including a change in frost hardiness during bud break (Bigras and Hébert, 1996). ...
... As late frost damage can have dramatic consequences on plant growth and survival (Allevato et al., 2019;Girardin et al., 2022), late frost occurrence is expected to affect timing of bud break that is critical to determine local adaptation (Kreyling et al., 2014) and species distribution (Kollas et al., 2014). Populations with different sensitivity to climate have different bud phenology and risk of being exposed to late frosts and, consequently, different survival strategies to adapt to the local climate (Hufkens et al., 2012;Marquis et al., 2020a). In the long term, the reduction in fitness caused by recurrent frost damage could change the composition of forest ecosystems by lowering competitiveness and increasing mortality of phenotypes with early bud break and favoring the establishment of those with late bud break (Hufkens et al., 2012). ...
Global warming advances bud break, mismatches plant phenology from the local climate, and exposes the developing leaves to higher risks of frost damage. Bud break of sugar maple [Acer saccharum (Marsh.)], a species included in recent programs of assisted migration, is sensitive to nighttime spring temperatures. This suggests a link between frost events and leaf development. In this study, we raise the hypothesis that late frost is an evolutionary driver of growth reactivation in sugar maple provenances. We investigated the ecotypic variation of bud phenology in 30 provenances planted in two common gardens within and at the northern limit of the species range, in the Province of Quebec, Canada. Eight phases of bud break were assessed twice a week during 2020 on 252 and 272 seedlings in southern and northern sites, respectively. In the southern site, bud break occurred in May, starting on average 12 days earlier and ending 3 days earlier compared to the northern site. Logistic regression was used to estimate the probability of late frost and the results showed that regions located in the north, at higher elevations, and along the northeastern coast of the native maple range showed the latest occurrences of frost events in spring. This pattern mirrored the timing of bud break. When planted in the same common garden, provenances originating from sites with later spring frosts leafed out earlier. Such differences were maintained across the eight bud phenological phases and between the two common gardens, which indicates a similar response of the provenances to changing growing conditions. To avoid frost damage to sugar maple plantations, assisted migration should account for phenotypic traits in bud phenology, ensuring that the frost regime at the origin of the provenances is compatible with that of plantations.
... Thus, an earlier development of the vegetation in spring induced by warming may put plants at a higher risk of being damaged by frosts, particularly in Europe and Asia where tree species have lower freezing resistances (compared to North America) and are generally more responsive to temperature (Liu et al., 2018;Walde et al., 2022;Zohner et al., 2020). In fact, more damaging spring frosts have been observed in recent years, precisely because of the increased amount of heat energy that preceded leafout (Augspurger, 2009;Hufkens et al., 2012;Sangüesa-Barreda et al., 2021;. For instance in April 2017, after an extraordinary warm period in Western and Central Europe, the sudden arrival of cold air masses from the Arctic and the subsequent freezing events caused dramatic losses in fruit production in Central Europe and the amount of accumulated heat at the time of the frost was unprecedented in some stations since the beginning of meteorological records . ...
... Large-scale defoliations due to frost can have a significant impact on forest ecosystem functioning by affecting carbon uptake (Hufkens et al., 2012), water relations (Bréda & Granier, 1996) and by altering nutrient cycles (Estiarte & Peñuelas, 2015). In addition, populations of a vast variety of animal and fungal species, which depend on leaf tissue, fruits and seeds, may decline when frost damages occur (i.e. ...
1. Phenological shifts in response to changing climatic conditions is a key acclimation process for the persistence of perennial plants in temperate and boreal climates. The optimal time to leaf‐out is the result of an evolutionary processes determined by the trade‐off between minimizing the risk of freezing damages and herbivory pressure while maximizing resource uptake to increase competitiveness against the other plants. 2. We quantified the penalty exerted by frost exposure at the time of leaf emergence on plant development (reduction in leaf area, canopy duration, and growth) over the potential gains without frost (increased biomass and non‐structural carbohydrate reserves), depending on when leaf‐out occurs. To this purpose, we exposed 960 saplings of four temperate deciduous tree species with contrasting cold hardiness to two frost intensities shortly after leaf emergence, which was artificially induced at four occasions to reflect the whole range of natural leaf‐out dates. 3. One year above‐ground biomass (AGB) increments following the frost revealed a clear ranking among the species depending on their strategy to cope with damaging frosts. Prunus avium (‐41% of AGB‐increment compared to control saplings) resprouted from the stem base, Quercus robur (‐62%) rapidly produced new leaves from dormant reserve buds, Fagus sylvatica (‐98%) showed highest chlorophyll content in autumn and delayed senescence together with Carpinus betulus (‐105%), which overcompensated NSC reserves after the growing season but showed highest mortality (up to 32%). In all species, NSC reserves recovered rapidly their initial stage at the expense of growth. 4. The timing of leaf‐out (advanced and delayed artificially) significantly affected the performance and recovery (regreening and growth) of both frozen and non‐frozen saplings, with the lowest performance found at the most delayed leaf‐out date. We propose that the potential to recover from frost damages is an important component of a tree's performance, particularly at the juvenile stage. The ability to recover may become even more decisive in the future with the predicted increase of false springs in many extra‐tropical regions.
... For example, the economic loss for agricultural crops after the 2007 late-spring frost in the U.S. was up to $112 million, with fruit crop loss of $86 million (Warmund et al., 2008). Further examples of late-spring frost damage include 1995 in France (Ningre & Colin, 2007); 2010 in the NE of U.S.A. (Hufkens et al., 2012); and 2011 and 2016 in Switzerland, south Germany, and northeastern France (Kreyling et al., 2012;. ...
... Late-spring frost can also exert substantial impacts on trees, including increased mortality, altered morphology, decreased growth, changes in primary nutrients for insects (e.g., N), and changes in leaf chemical defences (St. Clair et al., 2009;Hufkens et al., 2012;Man et al., 2013). Consequently, late-spring frost may also influence the susceptibility of plants to insects or pathogens, although the number of studies that have examined the connection between freeze damage and insect susceptibility in trees is limited. ...
• Global climate change affects the frequency of extreme weather events that can influence plant–insect interactions.
• We evaluated how the late‐spring frost and severe drought that occurred in Spain in 2017 affected interactions between the invasive gall insect, Dryocosmus kuriphilus, and the native tree, Castanea sativa. We assessed effects on insect survival, fertility, population growth, and effects through changes in tree palatability and in other pests and pathogens.
• Late‐spring frost reduced D. kuriphilus to 25–40% of previous abundance. Wasp populations recovered rapidly (>7‐fold in 3 years), consistent with density‐dependence in population dynamics.
• Larvae affected by freeze or drought were smaller. Female fecundity was affected by the freeze 1 year later.
• Late‐spring frosts and severe drought affected leaf size and physiology. Water content was higher within galls, but nitrogen was higher within galls in non‐freeze plots after weather conditions improved.
• Freezing also influenced the secondary chemistry of leaves. Phenol concentrations were lower, and terpenes higher, in frozen plots, while condensed tannins remained the same. Condensed tannins were reduced to half in the drought year.
• Freezing had limited effects on damage from other pests and pathogens.
• Our work expands understanding of how climate and weather affects forest pests.
... The results of our study showed immediate, negative effects on vegetative phenophases-although these effects were not significant. Although our findings were consistent with numerous other studies, e.g., [77][78][79][80][81][82][83][84][85], other studies found contradictory results, e.g., [86][87][88]. The reason for these differences may have been related to the dependence of the phenological cycle on environmental factors and stressors, such as drought, fire, soil erosion, and soil properties, as well as climatic and anthropogenic (e.g., land use and land cover change). ...
Wildfire has significant impact on plant phenology. The plants’ phenological variables, derived from time series satellite data, can be monitored and the changes in satellite imagery may be used to identify the beginning, peak, and end of the growing season. This study investigated the use of remote sensing data and land surface phenology (LSP) parameters to evaluate the impacts of fire. The LSP parameters included the start of growing season (SOS), the length of the growing season (LOS), the end of the growing season (EOS), maximum greenness of the season (Gmax), and minimum greenery in the season (Gmin) in the fire-impacted, semiarid oak forests of Iran. These LSP parameters were extracted from multitemporal normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI2) data, acquired from MODIS sensor images in Zagros of the Ilam province in western Iran. By extracting LSP indices from the NDVI and EVI2 data, the indices were compared between burned forest areas, areas surrounding the burned forests, and unburned areas and for timesteps representing pre-fire, fire (i.e., year of fire), and post-fire (i.e., 2 years) conditions. It was found that for the burned area, there were significant differences in Gmax and the day that Gmax occurred. Furthermore, there was also a significant difference in Gmin between the pre- and post-fire conditions when NDVI was used and a significant difference between Gmax when EVI2 was used. The results also showed that in both time series there was a significant difference between the burned and control area in terms of Gmax. In general, the results showed that the fire had a negative effect on LSP, but in the two years after the fire, there were signs of forest restoration. This study provides necessary information to inform forest and resource conservation and restoration programs.
... Different species have separate growth strategies, tolerances, and resilience, resulting in various levels of impact. For example, conservative growth strategies render yellow birch and American beech largely unaffected by late spring frosts, while sugar maple suffers from frost damage, resulting in leaf loss and delayed crown development [64]. In addition, European beech showed low resistance to late frost events but high resilience in radial growth [65]. ...
The response of vegetation spring phenology to climate warming has received extensive attention. However, there are few studies on the response of vegetation spring phenology to extreme climate events. In this study, we determined the start of the growing season (SOS) for three vegetation types in temperate China from 1982 to 2015 using the Global Inventory Modeling and Mapping Study’s third-generation normalized difference vegetation index and estimated 25 extreme climate events. We analyzed the temporal trends of the SOS and extreme climate events and quantified the relationships between the SOS and extreme climate events using all-subsets regression methods. We found that the SOS was significantly advanced, with an average rate of 0.97 days per decade in China over the study period. Interestingly, we found that the SOS was mainly associated with temperature extremes rather than extreme precipitation events. The SOS was mainly influenced by the frost days (FD, r = 0.83) and mean daily minimum temperature (TMINMEAN, r = 0.34) for all three vegetation types. However, the dominant influencing factors were vegetation-type-specific. For mixed forests, the SOS was most influenced by TMINMEAN (r = 0.32), while for grasslands and barren or sparsely vegetated land, the SOS was most influenced by FD (r > 0.8). Our results show that spring phenology was substantially affected by extreme climate events but mainly by extreme temperature events rather than precipitation events, and that low temperature extremes likely drive spring phenology.
... Early studies suggested that rapidly differentiating and actively growing leaves and flowers are most susceptible to frost (Augspurger, 2009;Hufkens et al., 2012;Sakai and Larcher, 1987). So the declining temperature sensitivity of spring phenology was beneficial for the plants since it reduced the risk of late spring frost damage (Fu et al., 2015). ...
Changes in the rate of spring green-up (RSP) caused by climate change can alter biosphere-atmosphere exchange of carbon, energy, and water cycles. Although the response of RSP to environmental conditions has been frequently discussed, little is known about the dynamic relationship between RSP and environmental variables over time. We investigated the interannual relationships between RSP and various environmental variables using the Ensemble Empirical Mode Decomposition (EEMD) detrending approach and partial correlation analyses. We then used 15-year moving windows to analyze the effects of accumulated green-up period temperature (AGT) on RSP and its temporal variation from 1982 to 2016.We found that: (1) AGT had a positive influence on RSP in 81.08% of the entire study regions and AGT dominated the interannual variation of RSP in 31.31% all pixels; (2) The percentage of moisture-controlled (vapor pressure deficit (VPD) and soil moisture) pixels was 28.71%, indicating that preseason moisture, especially vapor pressure deficit (negative correlations in 65.50% pixels), played critical roles in limiting RSP; (3) The linkage between RSP and AGT (RRSP–AGT) was significantly weakening over the Northern Extratropics with intensity decrease of −0.0017 year⁻¹ (p < 0.05) and extent reduction of −0.4 × 10⁵ km² year⁻¹ (p < 0.05), suggesting a decreasing influence of AGT on foliar development. (4) The decline in RRSP–AGT coincided with decreased chilling exposure (CE) and enhanced VPD during the preseason over the Northern Extrotrapics and Eurasia, but it only may be related to changes in VPD in the North America. Our findings highlighted the importance of the dynamic response of vegetation spring green-up to ongoing warming, for a better understanding of the vegetation seasonal cycle under climate change.
... In addition, climate warming could redistribute the optimal species growing in different regions, causing northward expansion of forest tree line and promote ecosystem species competition and succession ( Huang et al., 2017 ), and then influence the regional landcover type, land surface characteristics and soil carbon component ( Peñuelas et al., 2009 ). These phenology-related changes could alter the interactions between trophic levels and results in niche mismatch, biodiversity shifts, which could change the original carbon transport path of the ecosystem, even truncate some of the path, and consequentially affect the terrestrial carbon balance ( Augspurger, 2009 ;Hufkens et al., 2012 ;Trumbore et al., 2015 ). ...
The Earth is experiencing unprecedented climate change. Vegetation phenology has already showed strong response to the global warming, which alters mass and energy fluxes on terrestrial ecosystems. With technology and method developments in remote sensing, computer science and citizen science, many recent phenology-related studies have been focused on macrophenology. In this perspective, we 1) reviewed the responses of vegetation phenology to climate change and its impacts on carbon cycling, and reported that the effect of shifted phenology on the terrestrial carbon fluxes is substantially different between spring and autumn; 2) elaborated how vegetation phenology affects ecohydrological processes at different scales, and further listed the key issues for each scale, i.e. focusing on seasonal effect, local feedbacks and regional vapor transport for individual, watershed and global respectively); 3) envisioned the potentials to improve current hydrological models by coupling vegetation phenology-related processes, in combining with machine learning, deep learning and scale transformation methods. We propose that comprehensive understanding the climate-macrophenology-hydrology interactions are essential and urgently needed for enhancing our understanding of the ecosystem response and its role in hydrological cycle under future climate change.
... Although LSP observations can be influenced by several factors (e.g. spatial resolution, understorey, time series processing, metrics calculation; de Beurs and Henebry 2005), repeated evidence showed their ability to catch forest canopy dynamics (Liang et al. 2011;Hufkens et al. 2012;Richardson et al. 2018). ...
Calibrating land surface phenology (LSP) with tree rings is important to model spatio-temporal variations in forest productivity. We used MODIS (resolution: 250 m) NDVI, WDRVI and EVI series 2000-2014 to derive LSP metrics quantifying phenophase timing and canopy photosynthetic rates of 26 European beech forests covering a large thermal gradient (5-16 °C) in Italy. Average phenophase timing changed greatly with site temperature (e.g. growing season 70 days longer at low- than high-elevation); average VI values were affected by precipitation. An annual temperature about 12 °C (c. 1100 m asl) represented a bioclimatic threshold dividing warm from cold beech forests, distinguished by different phenology-BAI (basal area increment) relationships and LSP trends. Cold forests showed decreasing VI values (browning) and delayed phenophases and had negative BAI slopes. Warmer forests tended to increase VI (greening), and positive BAI slopes. NDVI peak, commonly used in global trend assessments, changed with elevation in agreement with changes in wood production. A cross-validation modelling approach demonstrated the ability of LSP to predict average BAI and its interannual variability. Merging sites into bioclimatic groups improved models by amplifying the signal in growth or LSP. NDVI had highest performances when informing on BAI trends; WDRVI and EVI were mostly selected for modelling mean and interannual BAI. WDRVI association with tree rings, tested in this study for the first time, showed that this VI is highly promising for studying forest dynamics. MODIS LSP can quantify forest functioning changes across landscapes and model interannual spatial variations and trends in productivity dynamics under climate change.
... B.S.P.] is a relevant model species to study this problem. The current scenario of increasing risk of late frost would entail negative impacts on growth, carbon uptake and survival of boreal species by loss of photosynthetic and reproductive tissue (Hufkens et al., 2012) and potentially increase the susceptibility to other stressors, such as drought . ...
Under climate change, the increasing occurrence of late frost combined with advancing spring phenology can increase the risk of frost damage in trees. In this study, we tested the link between intra-specific variability in bud phenology and frost exposure and damages. We analysed the effects of the 2021 late frost event in a black spruce (Picea mariana (Mill.) BSP) common garden in Québec, Canada. We hypothesized that the timing of budbreak drives the exposure of vulnerable tissues and explains differences in frost damage. Budbreak was monitored from 2015 to 2021 in 371 trees from five provenances originating between 48° and 53° N and planted in a common garden at 48° N. Frost damages were assessed on the same trees through the proportion of damaged buds per tree and related to the phenological phases by ordinal regressions. After an unusually warm spring, minimum temperatures fell to -1.9°C on May 28 and 29, 2021. At this moment, trees from the northern provenances were more advanced in their phenology and showed more frost damage. Provenances with earlier budbreak had a higher probability of damage occurrence according to ordinal regression. Our study highlights the importance of intra-specific variability of phenological traits on the risk of frost exposure. We provide evidence that the timings of bud phenology affect sensitivity to frost, leading to damages at temperatures of -1.9°C. Under the same conditions, the earlier growth reactivation observed in the northern provenances increases the risks of late frost damage on the developing buds. This article is protected by copyright. All rights reserved.
... Additionally, nighttime warming reduces the frost risk in spring ( Figure S11). Newly developed leaves lack the structural integrity to prevent frost damage (Hufkens et al., 2012), and frost during the early stage of vegetation greenup will directly affect subsequent leaf development and vegetation growth throughout the year (Deng et al., 2020). ...
Recent studies have revealed that the influence of diurnal temperature on spring phenology is asymmetric, and the faster nighttime warming in the Northern Hemisphere (NH) has a complex impact on spring phenology. Our understanding from the sensitivity of the start of the growing season (SOS) to daytime (ST_daytime) and nighttime temperatures (ST_nighttime) has urgently needs to be improved. In this study, the SOS sensitivity to diurnal temperature in the middle and high latitudes of the NH (>30°N) from 1982‐2015 is estimated. The results indicate that although SOS showed stronger sensitivity to daytime than nighttime temperature in most parts of the study areas, the influence of daytime temperature on SOS is decreasing, while the influence of nighttime temperature on SOS is increasing. The variations in ST_daytime and ST_nighttime along the latitude gradient were significantly correlated with the warming rate of the preseason diurnal temperature (p<0.01). The SOS between 40°N and 70°N was more sensitive to daytime temperature, while ST_nighttime was higher than ST_daytime at other latitudes due to topography and rapid nighttime warming. On the altitude gradient, the SOS was more sensitive to daytime temperature in areas below 800 m and 2000‐4000 m. ST_nighttime exceeded ST_daytime at other altitudes owing to nighttime warming relief of the severe restrictions on phenological processes and the reduction in frost risk. To reach a comprehensive characterization of the interaction between vegetation and climate systems, the current study suggests more investigation on the response of SOS to diurnal temperature on large scales. This article is protected by copyright. All rights reserved.
... Coping with frost requires adapted behaviours or elaborate physiological adaptations for both ecto-and endothermal organisms, and especially for non-migrating life forms that cannot escape, such as plants. Frost change frequency carries information about the occurrence frequency of freezing and thawing events and -indirectly -about their duration, both of which are crucial constraints determining the best-suited adaptation strategies, see e.g., Hufkens et al. (2012). We used a Bspline interpolation S(tasmax, t) and S(tasmin, t) to get both daily minimum (tasmini) and maximum (tasmaxi) near-surface 2 255 m air temperatures from monthly values, with t the sequence of Julian days marking the middle of each month, i.e., [349,15,45,74,105,135,166,196,227,258,288,319,349,15]. ...
A multitude of physical and biological processes on which ecosystems and human societies depend are governed by climatic conditions. Understanding how these processes are altered by climate change is central to mitigation efforts. Based on mechanistically downscaled climate data, we developed a set of climate-related variables at yet unprecedented spatiotemporal detail as a basis for environmental and ecological analyses. We created gridded data for near-surface relative humidity (hurs), cloud area fraction (clt), near-surface wind speed (sfcWind), vapour pressure deficit (vpd), surface 15 downwelling shortwave radiation (rsds), potential evapotranspiration (pet), climate moisture index (cmi), and site water balance (swb), at a monthly temporal and 30 arcsec spatial resolution globally, from 1980 until 2018 (time-series variables). At the same spatial resolution, we further estimated climatological normals of frost change frequency (fcf), snow cover days (scd), potential net primary productivity (npp), growing degree days (gdd), and growing season characteristics for the periods three shared socioeconomic pathways (SSP126, SSP370, 20 SSP585) and five Earth system models (projected variables). Time-series variables showed high accuracy when validated against observations from meteorological stations. Projected variables were also highly correlated to observations, although some variables showed notable biases, e.g., snow cover days (scd). Together, the CHELSA-BIOCLIM+ data set presented here (https://doi.org/10.16904/envidat.332, Brun et al., 2022) allows improving our understanding of patterns and processes that are governed by climate, including the impact of recent and future climate changes on the world's ecosystems and 25 associated services to societies.
... Atmospheric phenomena, especially frost, are among the costliest natural hazards in the world (Guan et al., 2015), which have a massive effect on agriculture (Xiao et al. 2018), horticulture (Moonen et al. 2002;Kamali et al. 2008;Chmielewski et al. 2018), and forestry (Gu et al. 2008;Hufkens et al. 2012;Sangüesa-Barreda et al. 2021;Lhotka Brönnimann, 2021;Kollas et al. 2014;Meier et al. 2018). Frost is defined in various ways, including a decline in temperature below the freezing point of water during the growing period, a reduction in temperature below 0 °C during the positive numbers of temperature in 24 h, and a fall in air temperature below 0° C during a 24-h period with a maximum positive temperature (Niedzwied, 2003). ...
Occurrence of extreme climatic phenomena such as frost will cause significant risks and costs to many sectors, especially agriculture, horticulture, and forests. Frost will cause the worst damage when it occurs at the critical stages of crops, especially in spring. The frost phenomena are one of the important climatic and environmental hazards that cause a lot of damage to the agricultural sector of Iran every year. In this respect, the present study intends to highlight the projection of late spring rost by global circulation models (GCMs) from Coupled Model Intercomparison Project Phase 6 (CMIP6). For this purpose, minimum temperature data of 17 synoptic stations were used in the period 1985-2014 in cold regions of Iran. For projecting the changes of LSF, the ACCESS-ESM1-5 and Nor-ESM2-LM Models were used under three (Shared Socioeconomic Pathway (SSP)) scenarios SSP1-2.6, SSP2-4.5, and SSP5-8.5 for the next three periods (i.e., 2020-2049, 2050-2079, and 2080-2099). Then, the changes were compared to the historical period (1985-2014). The root mean square error (RMSE), mean bias error (MBE), correlation coefficient (CC), and Nash-Sutcliff efficiency (NSE) indices evaluated the models' performances. The results revealed that the latest and earliest dates of LSF during the base period occurred in the western and central parts of Iran, respectively. The model evaluation indicated that the performance of ACCESS-ESM1-5 (MBE = 0.3, CC = 0.87, and NSE = 0.68) exhibited a higher accuracy than the NorESM2-LM model. Based on both GCM under all three SSP scenarios, the projection of changes in future periods (compared to the base period) indicated that the date of occurrence of LSF would be earlier than the base period, with the highest and lowest changes projected based on NorESM2-SSP5-8.5 and ACCESS-ESM1-5-SSP1-2.6 in Arak, Isfahan, Khorramabad, Sabzevar, Shahrekord, and Shahroud stations. In general, depending on the model and climate scenario, the LSF phenomenon occurs earlier or later in cold regions of Iran, and its changes would be between − 76 and + 19 days in the future period.
... Meanwhile, air Gordo and Sanz (2009) suggested the 1 • C warming in early spring was observed to bring an advance of spring phenology by up to 7 days for the Spanish populations of European beech. Hufkens et al. (2012) indicated that the low temperature events in the late spring of 2010 contributed to a 14% ∼ 33% decreasing in the leaf area index over the northeastern United States. Therefore, it is reasonable to examine whether the winter North Atlantic SST influences the spring NDVI by regulating the local temperature. ...
In this study, the single value decomposition method was used to analyze the covariation between the winter (December, January, and February) North Atlantic sea surface temperature (SST) and spring (April and May) normalized difference vegetation index (NDVI) over mid‐high‐latitude Eurasia for the period 1982–2015. The results show that the first paired mode explains 32.8% of the total squared covariance, and the correlation of time coefficients is +0.67 (p < 0.01), suggesting that the meridional tripole structure of the winter North Atlantic SST is significantly associated with the three zonally anomalous centers of the spring mid‐high‐latitude Eurasian NDVI. Surface air temperature (T2m) is the most important factor related to spring NDVI changes. The tripole pattern of the winter North Atlantic SST can persist until the following spring, triggering an eastward anomalous Rossby wave train in the middle troposphere, which features two negative geopotential height anomalies centers near northwestern Europe and eastern Siberia and one positive center over central Eurasia. Surface temperature anomalies are well consistent with these anomalous pressure centers. This implies that the winter North Atlantic SST could be a robust driver and potential precursor for spring vegetation prediction over the mid‐high latitudes of Eurasia.
... In a hardwood Mediterranean forest in southwest Australia, tree canopy frost damage increased with declining elevation because of cold-air pooling (Matusick et al., 2014). In temperate deciduous forests, frost damage could be especially devastating for species like sugar maple, which tends to leaf out early in the season to optimize carbon gain but is particularly vulnerable to frost damage and temperature anomalies (Hufkens et al., 2012), as well as for saplings that experience earlier budbreak than conspecific canopy trees (Augspurger, 2009;Pederson et al., 2014). In other cases, deciduous species could respond to cold stress in these areas by delaying spring phenology (e.g., later budburst and leaf emergence) and shedding leaves earlier in fall (Vitasse et al., 2014), shortening the growing season and window for carbon capture. ...
Cold‐air pooling is a global phenomenon that frequently sustains low temperatures in sheltered, low‐lying depressions and valleys and drives other key environmental conditions, such as soil temperature, soil moisture, vapor pressure deficit, frost frequency, and winter dynamics. Local climate patterns in areas prone to cold‐air pooling are partly decoupled from regional climates and thus may be buffered from macroscale climate change. There is compelling evidence from studies across the globe that cold‐air pooling impacts plant communities and species distributions, making these decoupled microclimate areas potentially important microrefugia for species under climate warming. Despite interest in the potential for cold‐air pools to enable species persistence under warming, studies investigating the effects of cold‐air pooling on ecosystem processes are scarce. Because local temperatures and vegetation composition are critical drivers of ecosystem processes like carbon cycling and storage, cold‐air pooling may also act to preserve ecosystem functions. We review research exploring the ecological impacts of cold‐air pooling with a focus on vegetation, and then present a new conceptual framework in which cold‐air pooling creates feedbacks between species and ecosystem properties that generate unique hotspots for carbon accrual in some systems relative to areas more vulnerable to regional climate change impacts. Finally, we describe key steps to motivate future research investigating the potential for cold‐air pools to serve as microrefugia for ecosystem functions under climate change.
... adjusting phenology to new climatic conditions) can lead to greater growth and/or reproduction in some species (Cleland et al., 2012). However, early leaf out can also be problematic if it occurs during a period of warming followed by a hard frost, known as a false spring (Inouye, 2008;Hufkens et al., 2012). In the end, what matters is the 'match' between phenology and the environment, and this 'match' is influenced by species-specific differences in anatomy and physiology (Cooke et al., 2012;Panchen et al., 2014;Flynn & Wolkovich, 2018). ...
There is a long‐standing idea that the timing of leaf production in seasonally cold climates is linked to xylem anatomy, specifically vessel diameter because of the hydraulic requirements of expanding leaves. We tested for a relationship between the timing of leaf out and vessel diameter in 220 plants in three common gardens accounting for species’ phylogenetic relationships. We investigated how vessel diameter related to wood porosity, plant height and leaf length. We also used dye perfusion tests to determine whether plants relied on xylem produced during the previous growing season at the time of leaf out. In all three gardens, there was later leaf out in species with wider vessels. Ring‐porous species had the widest vessels, exhibited latest leaf out and relied less on xylem made during the previous growing season than diffuse‐porous species. Wood anatomy and leaf phenology did not exhibit a phylogenetic signal. The timing of leaf out is correlated with wood anatomy across species regardless of species’ geographic origin and phylogenetic relationships. This correlation could be a result of developmental and physiological links between leaves and wood or tied to a larger safety efficiency tradeoff.
... Climate change not only results in elevated mean temperatures in spring, but also increases the risk of late spring frost events, particularly in Europe and Asia [25][26][27]. Late spring frosts are rare but may heavily impact forest ecosystems as they can negatively affect, both directly and indirectly, tree survival, growth, regeneration and stem form [28,29]. For instance, radial growth in central European beech was reduced by 90% due to late spring frosts [30]. ...
Global change increases the risk of extreme climatic events. The impact of extreme temperature may depend on the tree species and also on the provenance. Ten provenances of Fagus sylvatica L. were grown in a common garden environment in Belgium and subjected to different temperature treatments. Half of the one year old seedlings were submitted to a high thermal stress in the spring of the first year, and all plants were exposed to a late spring frost in the second year.
The high-temperature treated plants displayed reduced growth in the first year, which was fully compensated (recovery with exact compensation) in the second year for radial growth and in the
third year for height growth. Frost in the spring of the second year damaged part of the saplings and reduced their growth. The frost damaged plants regained the pre-stress growth rate one year
later (recovery without compensation). The high temperature treatment in the first year and the frost damage in the second year clearly influenced the phenological responses in the year of the event
and in the succeeding year. Little population differentiation was observed among the provenances for growth and for phenological responses. Yet, a southern provenance, a non-autochthonous
provenance (original German provenance that was planted in Belgium about a century ago) and a more continental provenance flushed earlier than the local Atlantic provenances in the year of the frost event, resulting in more frost damage. Some caution should therefore be taken when translocating provenances as an anticipation of the predicted climate warming.
... Sugar maple is generally healthy across its range, though declining growth and crown dieback have been noted in selected stands in the last 40 years (Bauce and Allen 1992;Payette et al. 1996). The specific drivers of decline, often termed sugar maple decline disease, are diverse and often locally specific but well studied (Horsley et al. 2002;Hufkens et al. 2012). Given the species' specific environmental (Sullivan et al. 2013;Bauce and Allen 1992;Duchesne et al. 2002) and climate (Gavin 2008) tolerances, climate change is likely to be the largest threat to the species in the future (Bishop et al. 2015). ...
Unabated anthropogenic greenhouse gas emissions have resulted in an unprecedented rise in global atmospheric CO2 (Ca) levels and a perhaps irreversible shift in the dynamics of global carbon cycling. Given that C3 plants are likely to be carbon limited at current Ca levels, there was previous optimism regarding the potential for increased carbon storage and water-use efficiency (WUE) in global forests. To address this question, scientists have turned to tree ring series to investigate long-term trends in growth and resource use in global forests. Unfortunately, our ability to draw accurate conclusions regarding the fate of forests from tree ring studies alone is limited by our inability to control for the multitude of environmental and developmental variables that confound long-term, climate-related signals in tree ring series. In this thesis I use principles of forest ecology to select forest types where long-term changes in growth and WUE can be estimated independently of the effects of stand and individual tree development, namely, chronosequence jack pine and self-replacing sugar maple forests in Ontario.
To do so a novel tree ring standardization model is presented that uses tree diameter in the year of ring formation as the primary determinant of the underlying developmental trend. This method is shown to be superior to current models in separating developmental trends from long-term environmental/climatic signals in tree ring series from shade-tolerant species.
In chronosequence jack pine stands I show increases in stand-level WUE but progressive growth decline. Water-use efficiency was negatively associated with tree growth, suggesting that warming- and drought-induced stomatal closure has likely led to deviations from expected Ca enhanced growth. In self-replacing sugar maple, I show that the response of neither growth or WUE to increasing Ca is conserved across the site- or landscape-levels. While it is evident that variability in soil moisture controls this response at the site-level, the drivers of variation across the landscape are unclear. Further, high-frequency climate sensitivity is not conserved across stands near the species northern range limit, nor is climate an important predictor of growth in these stands. These findings have important implications for range prediction of the species, as current distribution models are climate driven.
... Although the timing of leaf senescence is controlled to some extent by leaf age (Reich et al. 1992;Lim et al. 2007) and is thus endogenous, environmental factors and biotic interactions can alter the relationship between spring and autumn phenology in several ways. Individuals with early spring phenology may have greater exposure to frost (Bennie et al. 2010;Hufkens et al. 2012) or insect attack (Wesolowski and Rowinski 2008;Jepsen et al. 2011), which are both linked with earlier senescence. Abiotic and biotic factors may also affect phenological correlations by altering photosynthetic or carbon assimilation rates, which are known to influence senescence timing (Zani et al. 2020). ...
Seasonal life history events are often interdependent, but we know relatively little about how the relationship between different events is influenced by the abiotic and biotic environment. Such knowledge is important for predicting the immediate and evolutionary phenological response of populations to changing conditions. We manipulated germination timing and shade in a multi-factorial experiment to investigate the relationship between spring and autumn phenology in seedlings of the pedunculate oak, Quercus robur, and whether this relationship was mediated by natural colonization of leaves by specialist fungal pathogens (i.e., the oak powdery mildew complex). Each week delay in germination corresponded to about 2 days delay in autumn leaf senescence, and heavily shaded seedlings senesced 5–8 days later than seedlings in light shade or full sun. Within seedlings, leaves on primary-growth shoots senesced later than those on secondary-growth shoots in some treatments. Path analyses demonstrated that germination timing and shade affected autumn phenology both directly and indirectly via pathogen load, though the specific pattern differed among and within seedlings. Pathogen load increased with later germination and greater shade. Greater pathogen load was in turn associated with later senescence for seedlings, but with earlier senescence for individual leaves. Our findings show that relationships between seasonal events can be partly mediated by the biotic environment and suggest that these relationships may differ between the plant and leaf level. The influence of biotic interactions on phenological correlations across scales has implications for understanding phenotypic variation in phenology and for predicting how populations will respond to climatic perturbation.
... SFD is a well-known worldwide risk for overwintering crops, tree species, and some early spring orchards in temperate climate regions [8,50,51] and Mediterranean areas [49,52] at northern latitudes, and also for tea plantations in humid areas around the equator [14]. The distribution characteristics of SFD risk were systematically analyzed at three scales, including temporal scale, spatial scale, and terrain scale, over the MLRYR in China. ...
Spring frost damage (SFD), defined as the disaster during the period of newly formed tea buds in spring caused by lower temperature and frost damage, is a particular challenge for tea plants (Camellia sinensis), whose capacity to adapt to extreme weather and climate impacts is limited. In this paper, the region of the Middle and Lower Reaches of the Yangtze River (MLRYR) in China was selected as the major tea plantation study area, and the study period was focused on the concentrated occurrence of SFD, i.e., from March to April. By employing the standard lapse rate of air temperature with elevation, a minimum temperature (Tmin) estimation model that had been previously established was used based on reconstructed MYD11A1 nighttime LST values for 3 × 3 pixel windows and digital elevation model data. Combined with satellite-based Tmin estimates and ground-based Tmin observations, the spatiotemporal characteristics of SFD for tea plants were systematically analyzed from 2003 to 2020 in the MLRYR. The SFD risks at three scales (temporal, spatial, and terrain) were then evaluated for tea plants over the MLRYR. The results show that both SFD days at the annual scale and SFD areas at the daily scale exhibited a decreasing trend at a rate of 2.7 days/decade and 2.45 × 104 ha/day, respectively (significant rates at the 0.05 and 0.01 levels, respectively). The period with the highest SFD risk appeared mainly in the first twenty days of March. However, more attention should be given to the mid-to-late April time period due to the occurrence of late SFD from time to time. Spatially, areas with relatively higher SFD days and SFD risks were predominantly concentrated in the higher altitude areas of northwestern parts of MLRYR for both multi-year averages and individual years. Fortunately, in regions with a higher risk of SFD, the distribution of tea plants was relatively scattered and the area was small. These findings will provide helpful guidance for all kinds of people, including government agencies, agricultural insurance agencies, and tea farmers, in order that reasonable and effective strategies to reduce losses caused by spring frost damage to tea plants may be recommended and implemented.
... Previous work in the UK revealed a tendency for host alternating aphids to delay their autumn return journey to primary host plants in warm years (Bell et al., 2015), which might narrow the window of opportunity for mating and egg laying on primary host plants before the onset of winter. Increasing climate variability and extreme weather events might also disproportionately affect host alternating aphids, for example, when a warm spell in the spring induces egg hatch only to be followed by a period of lethally cold low temperatures (Augspurger, 2013;Hufkens et al., 2012). Host alternation might also increase vulnerability to climate change by constraining poleward range expansion as aphids follow their thermal optima, if either winter or summer host plants do not also shift their ranges poleward (Bell et al., 2012). ...
Many animals change feeding habits as they progress through life stages, exploiting resources that vary in space and time. However, complex life histories may bring new risks if rapid environmental change disrupts the timing of these switches. Here, we use abundance times series for a diverse group of herbivorous insects, aphids, to search for trait and environmental characteristics associated with declines. Our meta dataset spanned three world regions and >300 aphid species, tracked at 75 individual sites for 10-50 years. Abundances were generally falling, with median changes of -8.3%, -5.6%, and -0.1% per year in the central USA, northwestern USA, and United Kingdom, respectively. Aphids that obligately alternated between host plants annually and those that were agricultural pests exhibited the steepest declines, relative to species able to persist on the same host plant year-round or those in natural areas. This suggests that host alternation might expose aphids to climate-induced phenology mismatches with one or more of their host plant species, with additional risks from exposure to insecticides and other management efforts. Warming temperatures through time were associated with milder aphid declines or even abundance increases, particularly at higher latitudes. Altogether, while a warming world appeared to benefit some aphid species in some places, most aphid species that had time-sensitive movements among multiple host plants seemed to face greater risk of decline. More generally, this suggests that recent human-induced rapid environmental change is rebalancing the risks and rewards associated with complex life histories.
... Globally, too, time-lapse cameras have been deployed for analysing plant phenophases (Richardson et al. 2018a), crop productivity (Moriondo et al. 2016), natural resource conservation (Bater et al. 2011), experimental ecology (Pennekamp Fig. 2 Classification of pixels into the 'snow' and 'no snow' categories based on their blue digital numbers using the threshold limit (left side) along with photograph of that particular day (right side); amaximum snow cover, bpartial snow cover, and cno snow. and Schtickzelle 2013) and frost damage (Hufkens et al. 2012b). However, the present study is amongst the pioneer works from a global biodiversity hotspot that is highly heterogeneous. ...
The use of time-lapse camera setups for characterizing phenology is fast emerging because of their advantages in offering continuous unbiased data. We therefore installed a camera setup in the Western Himalaya to monitor temporal patterns of Betula utilis phenology and also to document snow cover patterns. Digital images (N = 653) of two growing seasons (2017 and 2018) captured through the setup were used for the same. Images hold information in the red, green and blue channels (RGB) and relative changes in RGB indicate canopy colouration. We categorized the phenophases into greenup, leaf maturity, senescence and dormancy. The RGB analyses revealed that during both the years, greenup in B. utilis started during early May [128th and 124th day of the year (DOY) in 2017 and 2018, respectively] and continued till mid-June when the canopy attained maturity. On the other hand, senescence started in early September and by mid-October, the trees became leafless (288th and 289th DOY in 2017 and 2018, respectively). A four-day earlier greenup and dormancy delayed by one day were noted in 2018 when compared to 2017. Thus, the length of the growing season was five days longer in 2018. The snow cover ratio revealed that snowmelt occurred eigth days earlier in 2018 than in 2017. Though this is preliminary, seasonal phenological patterns are evident and call for continued monitoring of B. utilis. The installed setup will provide continuous long-term data from the Himalayan region which had been lacking until now. The present setup for phenological monitoring is pioneering in the Indian Himalaya and needs to be replicated.
... The risk of false springs was identified early in our understanding of the effects of climate change on species' phenology [13]. Since then, there have been numerous documented instances of freeze-induced plant death and damage due to premature budding and shooting (e.g., in the winters of 2007 [26] and 2010 [36]). ...
Background
Increases in temperature variability associated with climate change have critical implications for the phenology of wildlife across the globe. For example, warmer winter temperatures can induce forward shifts in breeding phenology across taxa (“false springs”), which can put organisms at risk of freezing conditions during reproduction or vulnerable early life stages. As human activities continue to encroach on natural ecosystems, it is also important to consider how breeding phenology interacts with other anthropogenic stressors (e.g., pollutants). Using 14 populations of a widespread amphibian (wood frog; Rana sylvatica ), we compared 1) growth; 2) tolerance to a common wetland contaminant (NaCl); and 3) the ability of tadpoles to acclimate to lethal NaCl exposure following sublethal exposure earlier in life. We evaluated these metrics across two breeding seasons (2018 and 2019) and across populations of tadpoles whose parents differed in breeding phenology (earlier- versus later-breeding cohorts). In both years, the earlier-breeding cohorts completed breeding activity prior to a winter storm and later-breeding cohorts completed breeding activities after a winter storm. The freezing conditions that later-breeding cohorts were exposed to in 2018 were more severe in both magnitude and duration than those in 2019.
Results
In 2018, offspring of the later-breeding cohort were larger but less tolerant of NaCl compared to offspring of the earlier-breeding cohort. The offspring of the earlier-breeding cohort additionally were able to acclimate to a lethal concentration of NaCl following sublethal exposure earlier in life, while the later-breeding cohort became less tolerant of NaCl following acclimation. Interestingly, in 2019, the warmer of the two breeding seasons, we did not detect the negative effects of later breeding phenology on responses to NaCl.
Conclusions
These results suggest that phenological shifts that expose breeding amphibians to freezing conditions can have cascading consequences on offspring mass and ability to tolerate future stressors but likely depends on the severity of the freeze event.
... Current climate model forecasts suggest that events such as air temperatures that increase faster in the spring could be more frequent with global warming (Príncipe et al. 2017), and theoretically, late spring frost damage occurs more severely as a result of the early opening of the buds in such conditions (Delpierre et al. 2016). In the last 15 years, indeed, it has been reported that late spring frost events cause significant yield losses in different countries, including the USA in 2012 (Kistner et al. 2018;Hufkens et al. 2012) and 2007 (Augspurger 2009), and France in 1995 (Ningre and Colin 2007); and southern Germany, Spain, Switzerland, and northeastern France in 2016 and 2011 (Vitasse and Rebetez 2018), after the onset of early vegetation in the spring. An unusually warm period in these regions has caused bud burst earlier than normal time. ...
To boost our understanding of recent frost damage events in apricot trees, we focused on estimating the cell death point in the receptacle and pistil organs of apricots by simulating the unexpected temperature changes occurring in early spring under laboratory-based freezing experiments. The hypothesis also that organic acids (oxalic, propionic, tartaric, butyric, malonic, malic, lactic, citric, maleic, fumaric and succinic acids) and soluble sugar compositions (glucose, fructose, sucrose and total sugar) may directly stimulate the change of the frost tolerance in apricot receptacle and pistil organs was investigated using two apricot (Prunus armeniaca L.) cultivars, one tolerant to frost (‘Iğdır Şalak’) and the other sensitive to frost (‘Mihralibey’). Our results indicated that the mean the cell death point (CDP) of flower pistil (from −13.26 to −14.18 °C) was at lower temperatures than those of flower receptacle (from −6.28 to −8.65 °C) in both apricot cultivars during the full blooming stage. In both apricot cultivars, receptacle organs showed more sensitive changes to the frost tolerance in response to low temperatures compared with pistil organs. In terms of organic acid and soluble sugar contents, significant differences were determined for both apricot cultivars and between the pistil and the receptacle organs of the flowers. Organic acid content was higher in the freezing-tolerant apricot cultivar (‘Iğdır Şalak’) than the freezing-sensitive apricot cultivar (‘Mihralibey’), but it was lower in the freezing-tolerant organ (pistil) in comparison with the freezing-sensitive organ (receptacle). Moreover, fructose concentrations for both ‘Mihralibey’ and ‘Iğdır Şalak’ were significantly higher in the receptacle compared to the pistil. A significant negative correlation was also observed between the mean CDP values and both all organic acids and sucrose contents in the pistil and the receptacle organs for both apricot cultivars. There was a positive relationship between the CDP values and fructose content in ‘Iğdır Şalak’. Additionally, there was a negative correlation between the CDP values and sucrose in 'Mihralibey'. Overall, the data presented suggest that the high level of sucrose and organic acid content of receptacle and pistil organs contributes to support frost tolerance of organs. The results of this study could help in the understanding of how receptacle and pistil organs of two different apricot cultivars react to frost stress, and how they modulate their soluble sugar and organic acid metabolism.
... Sugar maple is generally healthy across its range, though declining growth and crown dieback have been noted in selected stands in the last 40 years (Bauce and Allen 1992;Payette et al. 1996). The specific drivers of decline, often termed sugar maple decline disease, are diverse and often locally specific but well studied (Horsley et al. 2002;Hufkens et al. 2012). Given the species' specific environmental (Sullivan et al. 2013;Bauce and Allen 1992;Duchesne et al. 2002) and climate (Gavin 2008) tolerances, climate change is likely to be the largest threat to the species in the future (Bishop et al. 2015). ...
Given the large contribution of forests to terrestrial carbon storage, there is a need to resolve the environmental and physiological drivers of tree-level response to rising atmospheric CO 2 . This study examines how site-level soil moisture influences growth and intrinsic water-use efficiency in sugar maple (Acer saccharum Marsh.). We construct tree-ring, δ ¹⁸ O, and Δ ¹³ C chronologies for trees across a soil moisture gradient in Ontario, Canada, and employ a structural equation modelling approach to ascertain their climatic, ontogenetic, and environmental drivers. Our results support previous evidence for the presence of strong developmental effects in tree-ring isotopic chronologies — in the range of −4.7‰ for Δ ¹³ C and +0.8‰ for δ ¹⁸ O — across the tree life span. Additionally, we show that the physiological response of sugar maple to increasing atmospheric CO 2 depends on site-level soil moisture variability, with trees only in relatively wet plots exhibiting temporal increases in intrinsic water-use efficiency. These results suggest that trees in wet and mesic plots have experienced temporal increases in stomatal conductance and photosynthetic capacity, whereas trees in dry plots have experienced decreases in photosynthetic capacity. This study is the first to examine sugar maple physiology using a dendroisotopic approach and broadens our understanding of carbon–water interactions in temperate forests.
... Whether APV-induced spring vegetation variability has negative or positive seasonal compensation effects in the subsequent summer and autumn is another important issue to address. Previous studies have shown that the spring environmental stresses, such as low temperatures and drought lasting several months, can greatly reduce vegetation productivity (Noormets et al. 2008;Hufkens et al. 2012). However, Buermann et al. (2018) demonstrated that contrasting lagged productivity responses to spring environmental change exist widely in northern ecosystems, which indicates that spring vegetation variability may not result in the reduction of vegetation productivity. ...
The Arctic polar vortex (APV) system plays an important role in controlling winter and spring atmospheric circulation pattern in China. Here, we evaluate the anomalous APV-induced spring vegetation variability and lagged productivity responses in China. We found that both strong and weak APV conditions have almost equally negative impacts on spring vegetation growth in China, e.g., negative NDVI anomalies occurred in 48.6 and 53.2% of China’s vegetated areas under strong and weak APV conditions, respectively. However, large seasonal compensation effects were associated with weak APV conditions, and beneficial lagged vegetation productivity responses occurred in 67.2% of China’s vegetated areas, whereas adverse responses occurred in only 32.8% of vegetated areas. Under a strong APV, adverse lagged vegetation productivity responses occurred in 54.5% of China’s vegetated areas, whereas beneficial responses occurred in only 45.5% of vegetated areas. The temperature, precipitation, and solar radiation changes caused by anomalous APV-induced changes in circulation patterns are the main reasons for spring vegetation variability. The lagged vegetation productivity responses were attributed to anomalous APV-related precipitation and air temperature anomalies in the following summer and autumn. This improved understanding of the strong links between APV anomalies and vegetation dynamics in China should facilitate early warning of vegetation productivity reductions under anomalous APV conditions.
... Specifically, a positive relationship of interannual variations of EOS against SOS was found in this study (Fig. 12), which is supported by previous research Liu et al., 2016b). An earlier EOS could result from the risks of spring frost and summer drought that are increased by an earlier SOS (Buermann et al., 2013;Hufkens et al., 2012;Lian et al., 2020). The within-year relationship of a later SOS and EOS maintains a relatively stable growing season length and may reduce the effect of climate warming on terrestrial carbon sequestration . ...
Land surface phenology (LSP) characterizes the seasonal dynamics of vegetation communities that compose individual satellite pixels and its interannual and spatial variations have been widely associated with climate. However, increasing evidence shows an effect of land cover composition within a pixel on LSP, but it remains unclear the extent of impacts relative to other drivers. To fill this gap, this study quantitatively assessed the contributions of land cover composition, climate, and topography on the spatial and interannual variation in LSP throughout the 2002 Ponil Complex Fire in New Mexico, USA, using a machine learning approach of Boosted Regression Trees (BRT). As the fire mainly converted ponderosa pine and Douglas-fir (evergreen tree) to soil ground and Gambel Oak (deciduous shrub), we computed both the proportion of tree cover to all vegetation cover (PTV) and vegetation fractional cover (VFC) as the metrics of land cover composition from high-resolution images in 2018 and from MODIS growing season greenness from 2001-2018. Start (SOS) and end (EOS) of growing season were derived from 500-m MODIS data from 2001-2018 and 30-m Harmonized Landsat Sentinel-2 data in 2018. BRT models showed that PTV was the most important predictor of spatial variations in SOS and EOS in 2018, despite the different contributions (20.3%-42.9%) at 30-m and 500-m spatial scales. Although the growing degree days (28.6%) and the first freeze date (19.6%) were the most important predictors of interannual variations in SOS and EOS from 2001-2018, respectively, VFC also presented an important contribution for SOS (8.4%) and EOS (12.2%). This study demonstrates the utility of machine learning in modeling phenology and highlights the essential role of land cover composition in understanding the spatial and interannual variations of LSP that have been widely associated with topography and climate.
Extreme weather events such as hurricanes and tornadoes have been found to change the spatial and temporal abundance of raptors by decreasing survival and forcing the emigration of individuals, or by increasing habitat heterogeneity and facilitating recolonization of disturbed areas. Nonetheless, little is known about how extreme weather events could affect raptors’ movements and their space use in areas disturbed by large-scale weather events. We studied how extreme weather affected the movements of black and turkey vultures (Coragyps atratus and Cathartes aura, respectively) in Mississippi, USA, facing Hurricane Zeta in November 2020, winter storm Viola in February 2021, and tornados MS-43 and MS-44 in May 2021. We GPS-tracked 28 vultures in the paths of these events. We compared movement rates, net-squared displacements, and use of forest cover, before, during, and after the events. Since storm avoidance behavior has been observed in other birds, we expected that vultures would shift their movements out of the path of these events before storms hit. Further, we forecasted that vultures would make greater use of forested areas as protection against harsh conditions such as strong winds and heavy rain. Vultures responded differently to each weather event; they shifted their movements out of the predicted path of the hurricane and tornadoes but not the snowstorm. These findings reveal that both species use avoidance behavior and adjust their navigation and hazard detection accordingly. Avoidance behavior was more pronounced in turkey vultures than in black vultures. In general, vultures did not make greater use of forest areas as we expected, but turkey vultures did select forest areas during the snowstorm. We propose that olfaction and audition may be key in vultures’ response to extreme weather events.
Although phenology is a key indicator of climate change, the effects of phenological change under the background of climate change remain unexplored in arid and semi-arid region. We studied the phenological change of Populus euphratica during 1960–2019, and investigated the relationships between phenological change and climate change. The results showed that the annual average temperature in the Lower reaches of Heihe River was increased significantly over the past 58years, which directly led to the flower bud opened early, and delayed the time when the leaves turn yellow of Populus euphratica. The growth season of Populus euphratica was significantly prolonged after 1990, and the mean growth season length were 230, 236, 245 days in 1960–1969,1990–1999,2010–2019, respectively. Temperature is the major environmental factor affecting phenological change, and the length of growing season was prolonged with the increase of annual average temperature and accumulated temperature. Phenological changes have an important effect on plant growth. Our study showed that the frost days of Populus euphratica increasing from 1990 to 2019, and the frost days was increased with the growth season length. The accumulated frost days were 19, 21, 23 days in 1990–1999, 2000–2009, 2009–2019. The results also indicated that phenological changes also affect socioeconomic, especially the delay of leaf yellow period maybe has an important impact on tourism due to the best viewing period is postponed. This study of phenological change law and its relationships with climate changes could guide the government formulates tourism policies and help tourists to arrange best viewing time.
Climate change is causing a shift to earlier spring budburst in deciduous temperate trees, which may predispose them to greater risk of damage from growing season frosts. Populus tremuloides may be particularly vulnerable to growing season frosts, which can defoliate entire canopies and damage woody tissue. These growing season frost events may shift in frequency under continued climate change and alter a disturbance regime that disproportionately impacts deciduous, cold-sensitive vegetation. We used Populus tremuloides tree cores from 14 sites across the montane and subalpine forests of Utah, USA, to identify characteristic tree rings, namely ‘white rings’, associated with growing season frost damage over the period 1767–2016. Early growing season frost was estimated using a frost intensity index using local data sourced from 22 long-term weather stations and was correlated with white ring occurrence. Over the last 150 years, the frequency of white rings was between 5 and 6% of all years. Growing season frost occurrence was similar in northern and southern Utah and highly synchronous across stands indicating widespread defoliation. Populus tremuloides radial growth declined nearly 40% during years of frost-associated defoliation. Our results highlight a severe disturbance that disproportionately impacts Populus tremuloides. Our methods are broadly applicable in identifying historical frost-induced defoliation in deciduous trees and emphasize the potential for discrete weather events to impact tree health
Graphical Abstract
Vegetation phenology is one of the most sensitive indicators to environmental and climate changes. In order to characterize the seasonal variation in relatively pure or homogenous vegetation types, fine spatial resolution satellite data (≤ 30 m), such as Landsat, Sentinel-2, PlanetScope, or Harmonized Landsat and Sentinel-2 (HLS), have been increasingly applied to detect land surface phenology (LSP). However, the most critical challenge in LSP detections is the gaps in temporal satellite observations caused by noise and persistent cloud/snow cover. Therefore, this study presented a novel algorithm for generating synthetic gap-free time series at the field scale (30 m) for LSP detections. Specifically, we first developed a framework to establish a large collection of temporal shapes of vegetation growth with as many as 100 grid-based Green Chromatic Coordinate (GCC) time series in a single PhenoCam site. For a given HLS pixel, the two-band Enhanced Vegetation Index (EVI2) time series was matched and fused with the most comparable temporal GCC shape selected from the collection of PhenoCam GCC time series to generate a synthetic gap-free HLS-PhenoCam EVI2 time series, which was used to detect the 30 m phenometrics. The detected phenometrics were evaluated using manually selected and spatially matched GCC observations as well as phenology detections from HLS alone. The result indicates that the HLS-PhenoCam phenometrics are very close to the observations from PhenoCam network with a correlation coefficient (R) of 0.82–0.97, a mean absolute difference (MAD) of 2.8–3.5 days, a root mean squared error (RMSE) of 3.5–4.0 days, and a mean systematic bias (MSB) of 0.1–2.2 days. The HLS-PhenoCam detections are significantly improved relative to the HLS phenometrics that have a statistic accuracy of R = 0.57–0.78, MAD = 6.4–9.3 days, RMSE = 8.8–13.9 days, MSB = -5.2–5.9 days. The difference between HLS-PhenoCam and HLS alone LSP detections over a HLS tile could be on average larger than two weeks if high-quality observation (HQO) proportion in the annual HLS time series is <10%, which exponentially reduces with the increase of HQO in HLS observations. The analyses in this study suggest that the gap-free HLS-PhenoCam time series is able to be generated for producing high-quality phenology datasets across a local and regional scale, to bridge near-surface PhenoCam observations with satellite observations data at various scales, and to be used as a scalable phenology dataset for the validation of global MODIS and VIIRS LSP products.
Leaf angle distribution (LAD) is an essential canopy element that controls the foliage projection function (G-function), which is a parameter for estimating the plant area index (PAI). In recent studies, digital cover photography (DCP) has been applied to estimate the PAI (PAIDCP) in many terrestrial ecosystems. However, few studies related to this topic have been performed in mixed forests, where LAD features differ among multiple species. This study sought to evaluate the PAIDCP in a cool temperate mixed deciduous-coniferous forest in western Japan using a field-based G-function that was estimated from digital images captured by using a small uncrewed aerial vehicle (UAV; a quadcopter). The intensive UAV observations showed that measured throughout a vertical canopy profile of the deciduous broadleaved tree species, LAD was plagiophile-planophile for Fagus crenata, but was planophile throughout the canopy for Carpinus tschonoskii. Meanwhile, for the other dominant coniferous Abies firma species, we assumed either plagiophile or spherical for LAD and the G-function based on previous studies instead of measuring the parameters directly using the small UAV. With the species-specific LAD and G-function of dominant tree species, we compared the four-year PAIDCP time series with those based on a direct method using litter-trap inventories (PAIlit). The results indicate that PAIDCP provided more suitable representation of the canopy than that obtained assuming the spherical LAD for all tree species in the forest, although estimations of PAIlit includes uncertainties, mainly associating with measurements of specific leaf area (SLA). Our study highlights that in mixed forests with a tall canopy and multiple species it is important to ascertain species-specific LAD values for accurate estimation of the PAI using digital cover photography. Overall, we argue that the combined UAV–DCP photographic approach serves as a powerful tool for estimating the PAI.
This chapter describes the impact of some nonbiotic factors on forest health in Europe during the past decades. Storms, floods, and fires, as well as anthropogenic factors, were taken into consideration as primary disturbances predisposing trees to biotic damage. Data and information on the main harmful factors in a few countries obtained since 1950 are presented. These damage agents negatively influence forest health, reducing the survival of trees, and lead to biomass losses. The consequences of abiotic stress for the tree in the final balance are reduced photosynthesis efficiency, weakened plant immunity, increased susceptibility to infections, reduced tolerance to fungi, and increased opportunities for polycyclic diseases. The impact of these abiotic environmental elements is further discussed in relation to climate change.
Effectively managing large, forested landscapes for multiple goals has proven to be a challenging endeavour. Forest landscapes are large complex systems that are driven along development trajectories by tremendous solar energy inputs. In this chapter, we use the concept of momentum from physics as a conceptual framework for thinking about forests and forest development and a valuable tool for understanding the complexities and the potential for unanticipated outcomes associated with managing large, forested landscapes and regions over long-time frames. Lessons learned from forest landscapes are compared to those found in the management of another massive momentum system, piloting giant ships. Dr. Chad Oliver identified the value of simulating forest landscape scenarios so that cumulative impacts of management approaches over many decades meet goals.KeywordsConversion efficiencyDisturbance regimesMassive momentum systemsNew England
Climate change affects timings, frequency, and intensity of frost events in northern ecosystems. However, our understanding of the impacts that frost will have on growth and survival of plants is still limited. When projecting the occurrence of frost, the internal variability and the different underlying physical formulations are two major sources of uncertainty of climate models. We use 50 climate simulations produced by a single-initial large climate ensemble and five climate simulations produced by different pairs of global and regional climate models based on the concentration pathway (RCP 8.5) over a latitudinal transect covering the temperate and boreal ecosystems of western Quebec, Canada, during 1955–2099 to provide a first-order estimate of the relative importance of these two sources of uncertainty on the occurrence of frost, i.e. when air temperature is < 0 °C, and their potential damage to trees. The variation in the date of the last spring frost was larger by 21 days (from 46 to 25 days) for the 50 climate simulations compared to the 5 different pairs of climate models. When considering these two sources of uncertainty in an eco-physiological model simulating the timings of budbreak for trees of northern environment, results show that 20% of climate simulations expect that trees will be exposed to frost even in 2090. Thus, frost damage to trees remains likely under global warming.
Remote sensing of vegetation phenology has long been used to characterize ecosystem functions and responses to climate at spatial and temporal scales unfeasible to field surveys. However, the potential of remote sensing to elucidate mechanistic drivers of phenology and the underlying plant community processes at such scales remains under‐discussed. This review synthesizes possibilities to advance this knowledge using multi‐temporal remote sensing and discusses remaining challenges and progress in instruments and analytical tools. Recent evidence indicates that, besides documenting vegetation seasonality and responses to climate, remote sensing of phenology can help meet emerging needs for indicators of plant diversity, vegetation structure, and ecosystem change. Responses of phenological metrics to stressors over large, heterogeneous regions may provide clues on ecological resilience manifested in asynchronies, recovery of vegetation cycles, and stable microrefugia. At the same time, important barriers persist in relation to choosing among phenological estimation methods and paradigms, characterizing phenological events beyond changes in photosynthetically active biomass, and mechanistic interpretation of phenological patterns. Synthesis. Increasing temporal frequency of products, opportunities for multi‐sensor data fusion, and advances in historically less available hyperspectral, active microwave, and lidar instruments promise to help navigate these barriers and enable more comprehensive assessments of seasonality. Progress in customizable local platforms such as unoccupied aerial vehicles and phenocams may further enrich ground‐level understanding of phenology and validate satellite‐based assessments. However, remote sensing analyses alone are insufficient for mechanistic interpretation of phenology, which can be challenged by artifacts in remote sensing data and sensitivity of estimated metrics to landscape structure and spatial resolution of the inputs. Robust and informative phenological assessments call for rigorous collaborations with field ecological studies, strategic selection of ancillary environmental and geographic data, and wider adoption of causal inference approaches to address these needs and support novel explorations in plant ecology.
Phenology is a key indicator of climate change. We studied the phenological change of Populus euphratica during 1960–2019, and investigated the relationships between phenological change and climate change. The results showed that the annual average temperature in the Lower reaches of Heihe River was increased significantly over the past 58years, which directly led to the germination of Populus euphratica was advanced, and the leaf yellowing delayed. The growth season of Populus euphratica was significantly prolonged after 1990, and the mean growth season length were 230, 236, 245 days in 1960–1969,1990–1999,2010–2019, respectively. Temperature is the major environmental factor affecting phenological change, and the length of growing season was prolonged with the increase of annual average temperature and accumulated temperature. Phenological changes have an important effect on plant growth. Our study showed that the frost days of Populus euphratica increasing from 1990 to 2019, and the frost days was increased with the growth season length. The accumulated frost days were 19, 21, 23 days in 1990–1999, 2000–2009, 2009–2019. Our studies also indicated that phenological changes also affect socioeconomic, especially the delay of leaf yellow period maybe has an important impact on tourism due to the best viewing period is postponed. Our study of phenological change law and its relationships with climate changes could guide the government formulates tourism policies and help tourists to arrange best viewing time.
Trees are bioindicators of global climate change and regional urbanization, but available monitoring tools are ineffective for fine-scale observation of many species. Using six accelerometers mounted on two urban ash trees (Fraxinus americana), we looked at high-frequency tree vibrations, or change in periodicity of tree sway as a proxy for mass changes, to infer seasonal patterns of flowering and foliage (phenophases). We compared accelerometer-estimated phenophases to those derived from digital repeat photography using Green Chromatic Coordinates (GCC) and visual observation of phenophases defined by the USA National Phenology Network (NPN). We also drew comparisons between two commercial accelerometers and assessed how placement height influenced the ability to extract seasonal transition dates. Most notably, tree sway data showed a greenness signal in an urban environment and produced a clear flowering time-series and peak flowering signal (PF), marking the first observations of a flower phenophase using accelerometer data. Estimated start of spring (SOS) from accelerometers and time-lapse GCC were more similar than start of autumn (SOA); accelerometers lagged behind the time-lapse camera dates by three and four days for SOS and 13 and 14 days for SOA for each tree. Estimates for SOS and SOA from accelerometers and time-lapse cameras aligned closely with different NPN phenophases. The two commercial accelerometers produced similar season onset: a difference of 2.4 to 3.8 days for SOS, 2.1 days for SOA, and 0.5 to 2.0 days for PF. Accelerometers placed at the main crown branch point versus higher in the canopy showed a difference of 0.2 to 4.9 days for SOS and -1.5 to 1.7 days for PF. Our results suggest accelerometers present a novel opportunity to objectively monitor reproductive tree biology and fill gaps in phenology observations. Furthermore, widely available accelerometers show promise for scaling up from individual trees to the landscape level to aid forest management and assessing climate change impacts to tree phenology.
Leaf abundance of trees plays a dominant role in energy, water and nutrient flux of forest ecosystems, in defining the habitat structure of entrained biota and in mediating interspecific competition among tree species. We quantified leaf abundance of three dominant tree species (Acer saccharum Marsh.; Fagus grandifolia Ehrh.; Betula alleghaniensis Britt.) for 27 years in mature northern hardwood forest at the Hubbard Brook Experimental Forest, New Hampshire, USA using annual counts of leaves of each species collected in 117 litter traps (0.1 m², each). We hypothesized that variation in leaf abundance would reflect known disturbance events and canopy dieback episodes. No significant trend in leaf abundance of the three species over 27 years (1993–2019) was observed in seven reference stands despite known canopy dieback of sugar maple and American beech in these stands, indicating that 1) maple decline preceded our sampling interval and 2) expansion of beech understory compensated for canopy dieback caused by beech bark disease. Leaf abundance temporarily declined significantly in response to known disturbances (ice storm, 34 to 47%; late-spring frost, 13 to 16%). Increased leaf abundance, especially for sugar maple (30%), on a watershed where calcium addition restored acidified soils, was probably associated with increased soil pH, Ca availability and decreased Al. The temporal sequence of decline of paper birch at higher elevations following a severe drought in 2002 also was apparent. Leaf abundance based on leaf litterfall in deciduous forests provides a useful indicator of forest ecosystem function and forest health.
Under global warming, advances in spring phenology due to rising temperatures have been widely reported. However, the physiological mechanisms underlying the warming-induced earlier spring phenology remain poorly understood. Here, using multiple long-term and large-scale phenological datasets between 1951 and 2018, we show that warmer temperatures during the previous growing season led to earlier spring phenology in the Northern Hemisphere, with an average advancement of 2.5 days °C − 1 . Correspondingly, we observed an earlier spring phenology with the increase in photosynthesis of previous growing season. Furthermore, we found a significant decline in the advancing effect of warming in previous growing season on spring phenology from cold to warm periods. These findings reveal that the observed warming-induced earlier spring phenology is driven by increased photosynthetic carbon assimilation in the previous growing season, while the slowdown in the advanced spring phenology may arise from decreased carbon assimilation when warming exceeds optimal temperatures for photosynthesis. Therefore, the vital role of warming-induced changes in carbon assimilation should be considered to accurately project spring phenology and carbon cycling under future climate warming conditions.
This chapter assesses climate information relevant to regional impact and risk assessment. It complements other WG1 chapters which focus on the physical processes determining changes in the climate system and on methods for estimating regional changes.
This chapter is new in the IPCC WGI assessment reports, in that it represents a contribution to the “IPCC Risk Framework”. Within this framework, climate-related impacts and risks are determined through an interplay between the occurrence of climate hazards and their consequences depending on the exposure of the affected human or natural system and its vulnerability to the hazardous conditions. In Chapter 12, we are assessing climatic impact-drivers that could lead to hazards or to opportunities, from the literature and model results since AR5. This will particularly support the assessment of key risks related to climate change by WGII (Chapter 16). Despite the fact that impacts may also be induced by climate adaptation and mitigation policies themselves, as well as by socioeconomic trends, changes in vulnerability or exposure, and external geophysical hazards such as volcanoes, the focus here is only on ‘climatic’ impacts and risks induced by shifts in physical climate phenomena that directly influence human and ecological systems.
As a sensitive indicator of climate change, forest phenology (e.g., the start of season (SOS)) has profound impacts on the global carbon cycle. Traditional phenological observations are based on surface observation networks. Generally, the outcomes of this manner are less representative and hard to implement in wide forested regions. Remote sensing based observation of forest SOS has currently been a popular way. Those sensors with coarse spatial resolution have been widely used to estimate forest SOS, but they create serious estimation errors in areas of high heterogeneity. Medium-resolution sensors, such as Landsat, face significant challenges in SOS monitoring due to the long revisit period. In this study, we aimed to develop a new method to estimate forest SOS from 2013 to 2019. First, we collected all available Landsat and Sentinel-2 images, and then redefined the linear regression coefficients for the bandpass adjustment to weaken the surface reflectance (SR) differences in different sensors. Subsequently, we improved and developed the modified continuous change detection and classification (MCCDC) model to generate daily vegetation index curves. Finally, we adopted the logistic regression model to test the potential of the enhanced vegetation index (EVI), normalized difference vegetation index (NDVI) and land surface water index (LSWI) in evaluating the annual SOS. The reduced root mean square error (RMSE) for all bands after the integration indicated that the adjustment was successful. We visually compared Landsat’s synthetic images with the actual acquired images and found that their respective false-colour composites were highly similar. Assessing the SOS from the EVI, NDVI and LSWI showed different estimated results. By comparing the annual SOS derived from the three indices with the field observations, it was found that the SOS based on the EVI maintained a low consistency with the field observations. The SOS accuracy from LSWI was the highest and most forest SOS from LSWI in the study area were mainly concentrated in 80–150 days. These three indices all showed that the SOS always fluctuated by ± 4 days from 2013 to 2019. Facing the lack of clear remote sensing images with medium spatial resolution in cloudy and rainy areas, this study proposes an improved method to generate clear daily vegetation index images at a spatial resolution of 30 m, making annual SOS monitoring promising and feasible.
Changes in climate are leading to modifications in the timing of seasonal events such as migrations and flowering. Erythronium americanum (trout lily) can break bud early in response to warming, but changes to its growing season may be limited by early shade from canopy trees and frost. I experimentally assessed the impact of shade and frost on senescence in E. americanum and descriptively monitored the response of E. americanum to vernal air and soil temperatures in a garden setting. Early shade did not affect the timing of senescence. Experimental exposure to frost resulted in increased leaf damage, earlier senescence, and greater corm death than in control plants. Despite ten days in which the air temperature dropped below freezing, there was no evidence of leaf damage in the field. These results suggest that early shade from canopy trees will not hasten the end of the future growing season for E. americanum, but that late frost could bring about early senescence if that frost is sufficiently hard.
Climate change is having many effects in the agricultural sector, which are being studied worldwide. Undoubtedly, warmer winters and earlier springs produce changes in frost regimes and severity that will affect the sustainability of agricultural production in the area. The Mediterranean region and the Iberian Peninsula (IP) are among the areas where the greatest impact of climate change is expected. Daily data from 68 weather stations of the IP belonging to the European Climate Assessment and Dataset (1975–2018) were used to conduct a spatiotemporal study of the frost regime. The variables calculated include the probability of three frost types according to their severity, frost day, mean absolute minimum yearly temperature, first frost day, last frost day, and frost-free period. These variables were integrated into a geographic information system, which allowed the graphical visualization of their patterns using of geostatistical interpolation techniques (kriging). Changes in frost variables were investigated using the Mann–Kendall test and Sen’s slope estimator. A general reduction in the number of frosts per year is observed (values between −0.04- and −0.8-day frosts per year), as well as an increase in the mean absolute minimum temperature (values between 0.04 and 0.10 °C per year), with very high significant trends throughout the territory. The reduction in the number of frosts is more pronounced at a higher elevation. Frost dates vary greatly due to the orographic characteristics of the IP. The generalized trend is of a significant delay of the autumn frosts (values between 0.4 and 1.06 days/year), as well as early spring frosts (between −0.429 and −1.29 days/year), and as a consequence a longer frost-free period, all changes were much stronger than those found in other regions of the world. These effects of climate change must be mitigated by modifying species, varieties, and cultivation techniques to guarantee sustainable agriculture.
Climate widely influences the geographical patterns of wildfires in terrestrial ecosystems. Understanding climate-fire relationships is crucial in exploring the response of wildfires to climatic conditions in different ecogeographic environments. However, how climate affects regional wildfires and which factors dominate the spatial patterns of climate-fire relationships are still poorly understood. Using satellite-based burned area data and climate datasets of the Mongolian Plateau, we analyzed the concurrent and antecedent climate-fire relationships; evaluated the spatial change characteristics of the climate-fire relationships along gradients of moisture, fuel, topography, and human activity; and estimated the ability of climate to explain fire dynamics to identify key factors mediating the spatial patterns of climate-fire relationships at ecoregion scales. The results showed that concurrent hot and dry and antecedent warm climatic conditions widely facilitated larger burned areas, and humid conditions increased the amount of burned areas in most arid ecoregions by controlling fuel accumulation. The strength of the climate-fire relationships changed along the environmental factor gradients, and the nature of climate-fire relationships shifted when variation in drivers exceeded the gradient thresholds. Wildfires respond differently to climatic conditions, and ecoregion-based models revealed that climate explained 21.53% of the variation in burned areas on average. These findings suggested that under universal arid environments, climate across multiple time scales shapes distinct local fire regimes by controlling fuel flammability and fuel accumulation, and vegetation productivity and moisture mediate the spatial patterns of climate-fire relationships across ecoregions. This study provides knowledge of climate-fire interactions in mid-latitude regions at ecoregion scales and facilitates policies for regional fire suppression.
Spring phenology is advancing with warming but late spring freezes may not advance at the same rate, potentially leading to an increase in freezes after trees initiate budburst. Research suggests warming winters may delay budburst through reduced chilling, which may cause plants to leaf out more slowly, thus decreasing spring freeze tolerance. Here, we assessed the effects of late spring freezes and reduced over-winter chilling on sapling phenology, growth and tissue traits, across eight temperate tree and shrub species in a laboratory experiment. We found that spring freezes delayed leafout-extending the period of greatest risk for freeze damage-and increased damage to the shoot apical meristem, decreased leaf toughness and leaf thickness. Longer chilling accelerated budburst and leafout, even under spring freeze conditions. Thus chilling compensated for the adverse effects of late spring freezes on phenology. Despite the effects of spring freezes and chilling on phenology, we did not see any major re-ordering in the sequence of species leafout. Our results suggest climate change may impact forest communities not through temporal reassembly, but rather through impacts on phenology and growth from the coupled effects of late spring freezes and decreased over-winter chilling under climate change.
At the time of leaf emergence in deciduous forests, markedly enhanced evapotranspiration leads to a rapid drop in the Bowen ratio. A small fraction of this surface flux alteration converges into the boundary layer, and this can be detected in the mean temperature and humidity daily increments at the surface. A simple technique is presented for identifying this response in surface climate data and extracting time series for the date of spring onset and for the `spring intensity,' a measure of surface energy budget partition change in spring. A tendency Bowen ratio B is found from changes in the daily increment of temperature and humidity in multidecadal averages. The spring date determined using this criterion for stations along the U.S. east coast corresponds to the date at which the normalized difference vegetation index (NDVI) reaches 80% of its seasonal maximum. Northward movement of the vernal front is similar to that obtained using Hopkins' empirical rule; it is linearly related to leaf emergence and flowering dates from the North American lilac phenology network. Spring intensity increases northward; the states from Virginia north exhibit distinctly higher values. There has been a trend in the most recent decades toward earlier spring dates, except for regions in Virginia and North Carolina. The same analyses performed using the small subset of stations with longer-term records indicate that a trend toward an earlier spring date is confined to recent decades. An inverse relationship between the spring date and spring average temperature was found for the Midwest but is inadequate for the northeast. Spring intensity has generally increased in northeastern North America throughout the twentieth century. However, large oscillations with an approximate 20-yr period distinguish the northeastern United States from the Midwest, indicating that the intensity of spring is not a simple function of spring temperature or of forest cover fraction.
Projected climate warming will potentially have profound effects on the earth's biota, including a large redistribution of tree species. We developed models to evaluate potential shifts for 80 individual tree species in the eastern United States. First, environmental factors associated with current ranges of tree species were assessed using geographic information systems (GIS) in conjunction with regression tree analysis (RTA). The method was then extended to better understand the potential of species to survive and/ or migrate under a changed climate. We collected, summarized, and analyzed data for climate, soils, land use, elevation, and species assemblages for .2100 counties east of the 100th meridian. Forest Inventory Analysis (FIA) data for .100 000 forested plots in the East provided the tree species range and abundance information for the trees. RTA was used to devise prediction rules from current species-environment relationships, which were then used to replicate the current distribution as well as predict the future potential distri- butions under two scenarios of climate change with twofold increases in the level of at- mospheric CO2. Validation measures prove the utility of the RTA modeling approach for mapping current tree importance values across large areas, leading to increased confidence in the predictions of potential future species distributions. With our analysis of potential effects, we show that roughly 30 species could expand their range and/or weighted importance at least 10%, while an additional 30 species could decrease by at least 10%, following equilibrium after a changed climate. Depending on the global change scenario used, 4-9 species would potentially move out of the United States to the north. Nearly half of the species assessed (36 out of 80) showed the potential for the ecological optima to shift at least 100 km to the north, including seven that could move .250 km. Given these potential future distributions, actual species redistributions will be controlled by migration rates possible through fragmented landscapes.
In the last two decades the availability of global remote sensing data sets has provided a new means of studying global patterns and dynamics in vegetation. The vast majority of previous work in this domain has used data from the Advanced Very High Resolution Radiometer, which until recently was the primary source of global land remote sensing data. In recent years, however, a number of new remote sensing data sources have become available that have significantly improved the capability of remote sensing to monitor global ecosystem dynamics. In this paper, we describe recent results using data from NASA's Moderate Resolution Imaging Spectroradiometer to study global vegetation phenology. Using a novel new method based on fitting piecewise logistic models to time series data from MODIS, key transition dates in the annual cycle(s) of vegetation growth can be estimated in an ecologically realistic fashion. Using this method we have produced global maps of seven phenological metrics at 1-km spatial resolution for all ecosystems exhibiting identifiable annual phenologies. These metrics include the date of year for (1) the onset of greenness increase (greenup), (2) the onset of greenness maximum (maturity), (3) the onset of greenness decrease (senescence), and (4) the onset of greenness minimum (dormancy). The three remaining metrics are the growing season minimum, maximum, and summation of the enhanced vegetation index derived from MODIS. Comparison of vegetation phenology retrieved from MODIS with in situ measurements shows that these metrics provide realistic estimates of the four transition dates identified above. More generally, the spatial distribution of phenological metrics estimated from MODIS data is qualitatively realistic, and exhibits strong correspondence with temperature patterns in mid- and high-latitude climates, with rainfall seasonality in seasonally dry climates, and with cropping patterns in agricultural areas.
In this study we seek empirical relationships among canopy resistance to water vapor transport, the time-varying leaf area index (LAI), in situ radiative flux observations, and a satellite-based estimate of leaf state (NDVI, the normalized difference vegetation index) from a leafless deciduous forest to a covered canopy and vice versa. These relationships can be used in numerical models such as verification in global climate models. They also can be useful tools for developing remote sensing techniques.LAI was found through analysis of frequent video images of canopy evolution in spring and autumn during 1992 and 1993 at a deciduous forest in central Massachusetts. We examined the impact of leaf presence on water vapor transport during spring and autumn using an LAI time series during leaf emergence and leaf fall for the four study seasons. The canopy resistance to water vapor transport (rc) decreased abruptly at leaf emergence in each year but then also continued to decrease slowly during the remaining growing season, owing to slowly increasing LAI. One remarkable result is that a single linear relationship between rc. and LAI during leaf emergence can be used to estimate the minimum seasonal rc associated with the maximum foliage cover. Canopy resistance and PAR-albedo (albedo from photosynthetically active radiation (PAR) instruments) began to increase about 1 month before leaf fall with the diminishment of CO2 gradient above the canopy as well, at which time evaporation began to be controlled as if the canopy were leafless. We present empirical linear regressions relating NDVI, rc, and PAR-albedo. The NDVI linear regressions with surface measurements indicate that tower-based measurements can represent at least a satellite pixel region. These results reinforce the notion that relationships among these parameters are scale independent from tower-based measurements spatial scale to a satellite pixel resolution (1.1 km X 1.1 km area)., at least.
Several large-scale climate patterns influenced climate conditions and weather patterns across the globe during 2010. The transition from a warm El Nino phase at the beginning of the year to a cool La Nina phase by July contributed to many notable events, ranging from record wetness across much of Australia to historically low Eastern Pacific basin and near-record high North Atlantic basin hurricane activity. The remaining five main hurricane basins experienced below-to well-below-normal tropical cyclone activity. The negative phase of the Arctic Oscillation was a major driver of Northern Hemisphere temperature patterns during 2009/10 winter and again in late 2010. It contributed to record snowfall and unusually low temperatures over much of northern Eurasia and parts of the United States, while bringing above-normal temperatures to the high northern latitudes. The February Arctic Oscillation Index value was the most negative since records began in 1950. The 2010 average global land and ocean surface temperature was among the two warmest years on record. The Arctic continued to warm at about twice the rate of lower latitudes. The eastern and tropical Pacific Ocean cooled about 1 C from 2009 to 2010, reflecting the transition from the 2009/10 El Nino to the 2010/11 La Nina. Ocean heat fluxes contributed to warm sea surface temperature anomalies in the North Atlantic and the tropical Indian and western Pacific Oceans. Global integrals of upper ocean heat content for the past several years have reached values consistently higher than for all prior times in the record, demonstrating the dominant role of the ocean in the Earth's energy budget. Deep and abyssal waters of Antarctic origin have also trended warmer on average since the early 1990s. Lower tropospheric temperatures typically lag ENSO surface fluctuations by two to four months, thus the 2010 temperature was dominated by the warm phase El Nino conditions that occurred during the latter half of 2009 and early 2010 and was second warmest on record. The stratosphere continued to be anomalously cool. Annual global precipitation over land areas was about five percent above normal. Precipitation over the ocean was drier than normal after a wet year in 2009. Overall, saltier (higher evaporation) regions of the ocean surface continue to be anomalously salty, and fresher (higher precipitation) regions continue to be anomalously fresh. This salinity pattern, which has held since at least 2004, suggests an increase in the hydrological cycle. Sea ice conditions in the Arctic were significantly different than those in the Antarctic during the year. The annual minimum ice extent in the Arctic reached in September was the third lowest on record since 1979. In the Antarctic, zonally averaged sea ice extent reached an all-time record maximum from mid-June through late August and again from mid-November through early December. Corresponding record positive Southern Hemisphere Annular Mode Indices influenced the Antarctic sea ice extents. Greenland glaciers lost more mass than any other year in the decade-long record. The Greenland Ice Sheet lost a record amount of mass, as the melt rate was the highest since at least 1958, and the area and duration of the melting was greater than any year since at least 1978. High summer air temperatures and a longer melt season also caused a continued increase in the rate of ice mass loss from small glaciers and ice caps in the Canadian Arctic. Coastal sites in Alaska show continuous permafrost warming and sites in Alaska, Canada, and Russia indicate more significant warming in relatively cold permafrost than in warm permafrost in the same geographical area. With regional differences, permafrost temperatures are now up to 2 C warmer than they were 20 to 30 years ago. Preliminary data indicate there is a high probability that 2010 will be the 20th consecutive year that alpine glaciers have lost mass. Atmospheric greenhouse gas concentrations continued to rise and ozone depleting substances continued to decrease. Carbon dioxide increased by 2.60 ppm in 2010, a rate above both the 2009 and the 1980-2010 average rates. The global ocean carbon dioxide uptake for the 2009 transition period from La Nina to El Nino conditions, the most recent period for which analyzed data are available, is estimated to be similar to the long-term average. The 2010 Antarctic ozone hole was among the lowest 20% compared with other years since 1990, a result of warmer-than-average temperatures in the Antarctic stratosphere during austral winter between mid-July and early September.
Several large-scale climate patterns influenced climate conditions and weather patterns across the globe during 2010. The transition from a warm El Niño phase at the beginning of the year to a cool La Niña phase by July contributed to many notable events, ranging from record wetness across much of Australia to historically low Eastern Pacific basin and near-record high North Atlantic basin hurricane activity. The remaining five main hurricane basins experienced below- to well-below-normal tropical cyclone activity. The negative phase of the Arctic Oscillation was a major driver of Northern Hemisphere temperature patterns during 2009/10 winter and again in late 2010. It contributed to record snowfall and unusually low temperatures over much of northern Eurasia and parts of the United States, while bringing above-normal temperatures to the high northern latitudes. The February Arctic Oscillation Index value was the most negative since records began in 1950.
The 2010 average global land and ocean surface temperature was among the two warmest years on record. The Arctic continued to warm at about twice the rate of lower latitudes. The eastern and tropical Pacific Ocean cooled about 1°C from 2009 to 2010, reflecting the transition from the 2009/10 El Niño to the 2010/11 La Niña. Ocean heat fluxes contributed to warm sea surface temperature anomalies in the North Atlantic and the tropical Indian and western Pacific Oceans. Global integrals of upper ocean heat content for the past several years have reached values consistently higher than for all prior times in the record, demonstrating the dominant role of the ocean in the Earth's energy budget. Deep and abyssal waters of Antarctic origin have also trended warmer on average since the early 1990s. Lower tropospheric temperatures typically lag ENSO surface fluctuations by two to four months, thus the 2010 temperature was dominated by the warm phase El Niño conditions that occurred during the latter half of 2009 and early 2010 and was second warmest on record. The stratosphere continued to be anomalously cool.
Annual global precipitation over land areas was about five percent above normal. Precipitation over the ocean was drier than normal after a wet year in 2009. Overall, saltier (higher evaporation) regions of the ocean surface continue to be anomalously salty, and fresher (higher precipitation) regions continue to be anomalously fresh. This salinity pattern, which has held since at least 2004, suggests an increase in the hydrological cycle.
Sea ice conditions in the Arctic were significantly different than those in the Antarctic during the year. The annual minimum ice extent in the Arctic—reached in September—was the third lowest on record since 1979. In the Antarctic, zonally averaged sea ice extent reached an all-time record maximum from mid-June through late August and again from mid-November through early December. Corresponding record positive Southern Hemisphere Annular Mode Indices influenced the Antarctic sea ice extents.
Greenland glaciers lost more mass than any other year in the decade-long record. The Greenland Ice Sheet lost a record amount of mass, as the melt rate was the highest since at least 1958, and the area and duration of the melting was greater than any year since at least 1978. High summer air temperatures and a longer melt season also caused a continued increase in the rate of ice mass loss from small glaciers and ice caps in the Canadian Arctic. Coastal sites in Alaska show continuous permafrost warming and sites in Alaska, Canada, and Russia indicate more significant warming in relatively cold permafrost than in warm permafrost in the same geographical area. With regional differences, permafrost temperatures are now up to 2°C warmer than they were 20 to 30 years ago. Preliminary data indicate there is a high probability that 2010 will be the 20th consecutive year that alpine glaciers have lost mass.
Atmospheric greenhouse gas concentrations continued to rise and ozone depleting substances continued to decrease. Carbon dioxide increased by 2.60 ppm in 2010, a rate above both the 2009 and the 1980–2010 average rates. The global ocean carbon dioxide uptake for the 2009 transition period from La Niña to El Niño conditions, the most recent period for which analyzed data are available, is estimated to be similar to the long-term average. The 2010 Antarctic ozone hole was among the lowest 20% compared with other years since 1990, a result of warmer-than-average temperatures in the Antarctic stratosphere during austral winter between mid-July and early September.
Plant ecologists have long been concerned with a seemingly paradoxical scenario in the relationship between plant growth and
climate change: warming may actually increase the risk of plant frost damage. The underlying hypothesis is that mild winters
and warm, early springs, which are expected to occur as the climate warms, may induce premature plant development, resulting
in exposure of vulnerable plant tissues and organs to subsequent late-season frosts. The 2007 spring freeze in the eastern
United States provides an excellent opportunity to evaluate this hypothesis and assess its large-scale consequences. In this
article, we contrast the rapid prefreeze phenological advancement caused by unusually warm conditions with the dramatic postfreeze
setback, and report complicated patterns of freeze damage to plants. The widespread devastation of crops and natural vegetation
occasioned by this event demonstrates the need to consider large fluctuations in spring temperatures a real threat to terrestrial
ecosystem structure and functioning in a warming climate.
Studies of the effects of climate change on forests have focused on the ability of species to tolerate temperature and moisture changes and to disperse, but they have ignored the effects of disturbances caused by climate change (e.g., Ojima et al. 1991).Yet modeling studies indicate the importance of climate effects on disturbance regimes (He et al. 1999). Local, regional, and global changes in temperature and precipitation can influence the occurrence, timing, frequency, duration, extent, and intensity of disturbances (Baker 1995, Turner et al. 1998). Because trees can survive from decades to centuries and take years to become established, climate-change impacts are expressed in forests, in part, through alterations in disturbance regimes (Franklin et al. 1992, Dale et al. 2000). yes
Near-record warmth over much of the United States during March 2007 promoted early growth of crops and vegetation. A widespread arctic air outbreak followed in early April, resulting in extensive agricultural losses over much of the south-central and southeastern US. This 'false spring' event also resulted in widespread damage to newly grown tissues of native deciduous forest species, shown by previous researchers to have had measurable effects on the terrestrial carbon cycle. The current study reconstructed the historical occurrence of false springs over most of the southeastern quarter of the conterminous US (32–39°N; 75–98°W) from 1901 to 2007 using daily maximum and minimum temperature records from 176 stations in the Global Historical Climatology Network database, and enhanced vegetation index (EVI) data derived from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations. A false spring index was derived that examined the timing of the start of the growing season (SGS), or leaf emergence, relative to the timing of a potentially damaging last hard freeze (minimum temperature ≤ − 2.2 °C). SGS was modeled for the domain by combining EVI data with ground-based temperature 'degree day' calculations reflecting the rate of springtime warming. No significant area-wide, long-term SGS trend was found; however, over much of a contiguous region stretching from Mississippi eastward to the Carolinas, the timing of the last hard freeze was found to occur significantly later, this change occurring along with increased frequency of false springs. Earlier last hard freeze dates and decreased frequency of false springs were found over much of the northwestern part of the study region, including Arkansas and southern Missouri.
In mountain forest ecosystems where elevation gradients are prominent, temperature gradient-based phenological variability can be high. However, there are few studies that assess the capability of remote sensing observations to monitor ecosystem phenology along elevation gradients, despite their relevance under climate change. We investigated the potential of medium resolution remotely sensed data to monitor the elevation variations in the seasonal dynamics of a temperate deciduous broadleaf forested ecosystem. Further, we explored the impact of elevation on the onset of spring leafing. This study was based on the analysis of multi-annual time-series of VEGETATION data acquired over the French Pyrenees Mountain Region (FPMR), in conjunction with simultaneous ground-based observations of leaf phenology made for two dominant tree species in the region (oak and beech). The seasonal variations in the perpendicular vegetation index (PVI) were analyzed during a five-year period (2002 to 2006). The five years of data were averaged into a one sole year in order to fill the numerous large spatio-temporal gaps due to cloud and snow presence – frequent in mountains – without altering the temporal resolution. Since a VEGETATION pixel (1 km²) includes several types of land cover, the broadleaf forest-specific seasonal dynamics of PVI was reconstructed pixel-by-pixel using a temporal unmixing method based on a non-parametric statistical approach. The spatial pattern of the seasonal response of PVI was clearly consistent with the relief. Nevertheless the elevational or geographic range of tree species, which differ in their phenology sensitivity to temperature, also has a significant impact on this pattern. The reduction in the growing season length with elevation was clearly observable from the delay in the increase of PVI in spring and from the advance of its decrease in the fall. The elevation variations in leaf flushing timing were estimated from the temporal change in PVI in spring over the study area. They were found to be consistent with those measured in situ (R2 N 0.95). It was deduced that, over FPMR, the mean delay of leaf flushing timing for every 100 m increase in elevation was estimated be approximately 2.3 days. The expected estimation error of satellite-based leaf unfolding date for a given elevation was approximately 2 days. This accuracy can be considered as satisfactory since it would allow us to detect changes in leafing timing of deciduous broadleaf forests with a magnitude equivalent to that due to an elevation variation of 100 m (2.3 days on average), or in other words, to that caused by a variation in the mean annual air temperature of 0.5 °C. Although averaging the VEGETATION data over five years led to a loss of interannual information, it was found to be a robust approach to characterise the elevation variations in spring leafing and its long-term trends.
brought frigid temperatures to parts of Europe, Russia, and the U.S. We analyzed regional and Northern Hemispheric (NH) daily temperature extremes for these two consecutive winters in the historical context of the past 63 years. While some parts clearly experienced very cold temperatures, the NH was not anomalously cold. Extreme warm events were much more prevalent in both magnitude and spatial extent. Importantly, the persistent negative state of the North Atlantic Oscillation (NAO) explained the bulk of the observed cold anomalies, however the warm extremes were anomalous even accounting for the NAO and also considering the states of the Pacific Decadal Oscillation (PDO) and El Niño Southern Oscillation (ENSO). These winters' widespread and intense warm extremes together with a continuing hemispheric decline in cold snap activity was a pattern fully consistent with a continuation of the warming trend observed in recent decades.
1] We analyzed 13 years (1992À2004) of CO 2 flux data, biometry, and meteorology from a mixed deciduous forest in central Massachusetts. Annual net uptake of CO 2 ranged from 1.0 to 4.7 Mg-C ha À1 yr À1 , with an average of 2.5 Mg-C ha À1 yr À1 . Uptake rates increased systematically, nearly doubling over the period despite forest age of 75–110 years; there were parallel increases in midsummer photosynthetic capacity at high light level (21.5À31.5 mmole m À2 s À1), woody biomass (101À115 Mg-C ha À1 from 1993À2005, mostly due to growth of one species, red oak), and peak leaf area index (4.5À5.5 from 1998–2005). The long-term trends were interrupted in 1998 by sharp declines in photosynthetic capacity, net ecosystem exchange (NEE) of CO 2 , and other parameters, with recovery over the next 3 years. The observations were compared to empirical functions giving the mean responses to temperature and light, and to a terrestrial ecosystem model (IBIS2). Variations in gross ecosystem exchange of CO 2 (GEE) and NEE on hourly to monthly timescales were represented well as prompt responses to the environment, but interannual variations and long-term trends were not. IBIS2 simulated mean annual NEE, but greatly overpredicted the amplitude of the seasonal cycle and did not predict the decadal trend. The drivers of interannual and decadal changes in NEE are long-term increases in tree biomass, successional change in forest composition, and disturbance events, processes not well represented in current models.
Although trees have responded to global warming in the past – to temperatures higher than they are now – the rate of change predicted in the 21st century is likely to be unprecedented. Greenhouse gas emissions could cause a 3–6°C increase in mean land surface temperature at high and temperate latitudes. Despite this, few experiments have isolated the effects of temperature for this scenario on trees and forests. This review focuses on tree and forest responses at boreal and temperate latitudes, ranging from the cellular to the ecosystem level. Adaptation to varying temperatures revolves around the trade-off between utilizing the full growing season and minimizing frost damage through proper timing of hardening in autumn and dehardening in spring. But the evolutionary change in these traits must be sufficiently rapid to compensate for the temperature changes. Many species have a positive response to increased temperature – but how close are we to the optima? Management is critical for a positive response of forest growth to a warmer climate, and selection of the best species for the new conditions will be of vital importance.
The timing of phenological events varies both among species, and also among individuals of the same species. Here we use a
12-year record of spring and autumn phenology for 33 woody species at the Harvard Forest to investigate these differences.
Specifically, we focus on patterns of leaf budburst, expansion, coloration and fall, in the context of differences between
canopy and understory species, and between canopy and understory individuals of the same species. Many understory species
appear to adopt a strategy of “phenological escape” in spring but not autumn, taking advantage of the high-light period in
spring before canopy development. For all but a few of these species, the spring escape period is very brief. Relationships
between canopy and understory conspecifics (i.e. individuals of the same species) varied among species, with leaf budburst
and leaf fall occurring earlier in understory individuals of some species, but later in other species. We fit standard models
of varying complexity to the budburst time series for each species to investigate whether biological responses to environmental
cues differed among species. While there was no clear consensus model, Akaike’s Information Criterion (AIC) indicated that
a simple two-parameter “Spring warming” model was best supported by the data for more than a third of all species, and well
supported for two-thirds of all species. More highly-parameterized models involving various chilling requirements (e.g., Alternating,
Parallel or Sequential chilling) were less well supported by the data. Species-specific model parameterization suggested that
responses to both chilling and forcing temperatures vary among species. While there were no obvious differences in this regard
between canopy and understory species, or between early- and late-budburst species, these results imply that species can be
expected to differ in their responses to future climate change.
Understanding spatial patterns of net primary production (NPP) is central to the study of terrestrial ecosystems, but efforts are frequently hampered by a lack of spatial information regarding factors such as nitrogen availability and site history. Here, we examined the degree to which canopy nitrogen can serve as an indicator of patterns of NPP at the Bartlett Experimental Forest in New Hampshire by linking canopy nitrogen estimates from two high spectral resolution remote sensing instruments with field measurements and an ecosystem model. Predicted NPP across the study area ranged from less than 700 g m−2 year−1 to greater than 1300 g m−2 year−1 with a mean of 951 g m−2 year−1. Spatial patterns corresponded with elevation, species composition and historical forest management, all of which were reflected in patterns of canopy nitrogen. The relationship between production and elevation was nonlinear, with an increase from low- to mid-elevation deciduous stands, followed by a decline in upper-elevation areas dominated by evergreens. This pattern was also evident in field measurements and mirrored an elevational trend in foliar N concentrations. The increase in production from low-to mid-elevation deciduous stands runs counter to the generally accepted pattern for the northeastern U.S. region, and suggests an importance of moisture limitations in lower-elevation forests.
Field measurements of foliar N, wood production and leaf litterfall were also used to evaluate sources of error in model estimates and to determine how predictions are affected by different methods of acquiring foliar N input data. The accuracy of predictions generated from remotely sensed foliar N approached that of predictions driven by field-measured foliar N. Predictions based on the more common approach of using aggregated foliar N for individual cover types showed reasonable agreement in terms of the overall mean, but were in poor agreement on a plot-by-plot basis. Collectively, these results suggest that variation in foliar N exerts an important control on landscape-level spatial patterns and can serve as an integrator of other underlying factors that influence forest growth rates.
Information related to land cover is immensely important to global change science. In the past decade, data sources and methodologies for creating global land cover maps from remote sensing have evolved rapidly. Here we describe the datasets and algorithms used to create the Collection 5 MODIS Global Land Cover Type product, which is substantially changed relative to Collection 4. In addition to using updated input data, the algorithm and ancillary datasets used to produce the product have been refined. Most importantly, the Collection 5 product is generated at 500-m spatial resolution, providing a four-fold increase in spatial resolution relative to the previous version. In addition, many components of the classification algorithm have been changed. The training site database has been revised, land surface temperature is now included as an input feature, and ancillary datasets used in post-processing of ensemble decision tree results have been updated. Further, methods used to correct classifier results for bias imposed by training data properties have been refined, techniques used to fuse ancillary data based on spatially varying prior probabilities have been revised, and a variety of methods have been developed to address limitations of the algorithm for the urban, wetland, and deciduous needleleaf classes. Finally, techniques used to stabilize classification results across years have been developed and implemented to reduce year-to-year variation in land cover labels not associated with land cover change. Results from a cross-validation analysis indicate that the overall accuracy of the product is about 75% correctly classified, but that the range in class-specific accuracies is large. Comparison of Collection 5 maps with Collection 4 results show substantial differences arising from increased spatial resolution and changes in the input data and classification algorithm.
With the launch of NASA's Terra satellite and the MODerate Resolution Imaging Spectroradiometer (MODIS), operational Bidirectional Reflectance Distribution Function (BRDF) and albedo products are now being made available to the scientific community. The MODIS BRDF/Albedo algorithm makes use of a semiempirical kernel-driven bidirectional reflectance model and multidate, multispectral data to provide global 1-km gridded and tiled products of the land surface every 16 days. These products include directional hemispherical albedo (black-sky albedo), bihemispherical albedo (white-sky albedo), Nadir BRDF-Adjusted surface Reflectances (NBAR), model parameters describing the BRDF, and extensive quality assurance information. The algorithm has been consistently producing albedo and NBAR for the public since July 2000. Initial evaluations indicate a stable BRDF/Albedo Product, where, for example, the spatial and temporal progression of phenological characteristics is easily detected in the NBAR and albedo results. These early beta and provisional products auger well for the routine production of stable MODIS-derived BRDF parameters, nadir reflectances, and albedos for use by the global observation and modeling communities.
Projected climate warming will potentially have profound effects on the earth's biota, including a large redistribution of tree species. We developed models to evaluate potential shifts for 80 individual tree species in the eastern United States. First, environmental factors associated with current ranges of tree species were assessed using geographic information systems (GIS) in conjunction with regression tree analysis (RTA). The method was then extended to better understand the potential of species to survive and/or migrate under a changed climate. We collected, summarized, and analyzed data for climate, soils, land use, elevation, and species assemblages for >2100 counties east of the 100th meridian. Forest Inventory Analysis (FIA) data for >100 000 forested plots in the East provided the tree species range and abundance information for the trees. RTA was used to devise prediction rules from current species-environment relationships, which were then used to replicate the current distribution as well as predict the future potential distributions under two scenarios of climate change with twofold increases in the level of atmospheric CO2. Validation measures prove the utility of the RTA modeling approach for mapping current tree importance values across large areas, leading to increased confidence in the predictions of potential future species distributions. With our analysis of potential effects, we show that roughly 30 species could expand their range and/or weighted importance at least 10%, while an additional 30 species could decrease by at least 10%, following equilibrium after a changed climate. Depending on the global change scenario used, 4-9 species would potentially move out of the United States to the north. Nearly half of the species assessed (36 out of 80) showed the potential for the ecological optima to shift at least 100 km to the north, including seven that could move >250 km. Given these potential future distributions, actual species redistributions will be controlled by migration rates possible through fragmented landscapes.
Several large-scale climate patterns influenced climate conditions and weather patterns across the globe during 2010. The transition from a warm El Niño phase at the beginning of the year to a cool La Niña phase by July contributed to many notable events, ranging from record wetness across much of Australia to historically low Eastern Pacific basin and near-record high North Atlantic basin hurricane activity. The remaining five main hurricane basins experienced below- to well-below-normal tropical cyclone activity. The negative phase of the Arctic Oscillation was a major driver of Northern Hemisphere temperature patterns during 2009/10 winter and again in late 2010. It contributed to record snowfall and unusually low temperatures over much of northern Eurasia and parts of the United States, while bringing above-normal temperatures to the high northern latitudes. The February Arctic Oscillation Index value was the most negative since records began in 1950.
The 2010 average global land and ocean surface temperature was among the two warmest years on record. The Arctic continued to warm at about twice the rate of lower latitudes. The eastern and tropical Pacific Ocean cooled about 1°C from 2009 to 2010, reflecting the transition from the 2009/10 El Niño to the 2010/11 La Niña. Ocean heat fluxes contributed to warm sea surface temperature anomalies in the North Atlantic and the tropical Indian and western Pacific Oceans. Global integrals of upper ocean heat content for the past several years have reached values consistently higher than for all prior times in the record, demonstrating the dominant role of the ocean in the Earth's energy budget. Deep and abyssal waters of Antarctic origin have also trended warmer on average since the early 1990s. Lower tropospheric temperatures typically lag ENSO surface fluctuations by two to four months, thus the 2010 temperature was dominated by the warm phase El Niño conditions that occurred during the latter half of 2009 and early 2010 and was second warmest on record. The stratosphere continued to be anomalously cool.
Annual global precipitation over land areas was about five percent above normal. Precipitation over the ocean was drier than normal after a wet year in 2009. Overall, saltier (higher evaporation) regions of the ocean surface continue to be anomalously salty, and fresher (higher precipitation) regions continue to be anomalously fresh. This salinity pattern, which has held since at least 2004, suggests an increase in the hydrological cycle.
Sea ice conditions in the Arctic were significantly different than those in the Antarctic during the year. The annual minimum ice extent in the Arctic—reached in September—was the third lowest on record since 1979. In the Antarctic, zonally averaged sea ice extent reached an all-time record maximum from mid-June through late August and again from mid-November through early December. Corresponding record positive Southern Hemisphere Annular Mode Indices influenced the Antarctic sea ice extents.
Greenland glaciers lost more mass than any other year in the decade-long record. The Greenland Ice Sheet lost a record amount of mass, as the melt rate was the highest since at least 1958, and the area and duration of the melting was greater than any year since at least 1978. High summer air temperatures and a longer melt season also caused a continued increase in the rate of ice mass loss from small glaciers and ice caps in the Canadian Arctic. Coastal sites in Alaska show continuous permafrost warming and sites in Alaska, Canada, and Russia indicate more significant warming in relatively cold permafrost than in warm permafrost in the same geographical area. With regional differences, permafrost temperatures are now up to 2°C warmer than they were 20 to 30 years ago. Preliminary data indicate there is a high probability that 2010 will be the 20th consecutive year that alpine glaciers have lost mass.
Atmospheric greenhouse gas concentrations continued to rise and ozone depleting substances continued to decrease. Carbon dioxide increased by 2.60 ppm in 2010, a rate above both the 2009 and the 1980–2010 average rates. The global ocean carbon dioxide uptake for the 2009 transition period from La Niña to El Niño conditions, the most recent period for which analyzed data are available, is estimated to be similar to the long-term average. The 2010 Antarctic ozone hole was among the lowest 20% compared with other years since 1990, a result of warmer-than-average temperatures in the Antarctic stratosphere during austral winter between mid-July and early September.
A causal relationship between Holocene patterns of plant distributions in the American Southwest and shifts in atmospheric flow structure has been inferred, but has yet to be demonstrated. To investigate this inferred relationship, seedlings of Quercus gambelii were transplanted along various local microhabitat gradients and regional air mass gradients and assessed for patterns of seedling establishment. The primary cause of seedling mortality appeared to be summer drought stress, which paralleled the latitudinal gradient of the `Arizona monsoon'. The `Arizona monsoon' air mass gradient produces an increasing probability of summer drought stress with increasing latitude, while the `polar front' air mass gradient produces an increasing probability of winter and spring cold stress with increasing latitude. We hypothesize that the two gradients produce, as a function of increasing latitude, convergent upper and lower elevational limits of Q. gambelii. The results of this elevational convergence appear to be a virtual absence of oak seedling establishment near the species' northern limits and a gradual senescence of long-lived clones from spring freeze stress when followed by summer drought stress. These conclusions have been extended to the biogeography of Q. turbinella through growth chamber experiments on the comparative drought physiology of seedlings of the two species and through previous work on their associated biogeographic patterns. Thus, the northern ecotones of Q. gambelii and Q. turbinella, appear to be primarily caused by the combination of spring freeze stress and summer moisture stress, rather than freeze stress alone, as previously proposed. We report systematic temporal and spatial shifts in the two air mass gradients, between warming and cooling trends, which can account for the Holocene biogeographic history of the two oak species and, in part, the observed spatial and temporal variations in oak morphology and oak/pine community structure.
(1) The dates of budhurst of lateral shoots on 2- to 10-year old trees of Picea sitchensis were recorded on fourteen occasions at sites near meteorological stations in lowland and upland Britain between 1960 and 1980. (2) The following relationship accounted for 92% of the variation in thermal time from 1 February to the date of budburst among the fourteen observations: thermal time = 67.4 + 4401.8 exp (-0.042 x chill days) where thermal time was day degrees >5 ⚬C accumulated from 1 February, and chill days were the number of days ⩽5 ⚬C counted from 1 November, both based on mean daily air temperature ((max. + min.)/2). This model may be used to estimate the date of budburst on young P. sitchensis of most provenances growing in upland Britain. (3) The following features or assumptions of the model were examined with reference to the literature and/or by experimentation: the small effect of provenance; linearity in the relationship between bud growth rate and temperature; the large effect of chilling on thermal time to budhurst; the omission of daylength and soil temperature as variables; the choice of starting dates for effective chilling and thermal time; and the use of simple fixed base temperatures. (4) The model was applied to mean daily temperatures at Eskdalemuir for the period 1912-82. The predicted dates of budburst ranged from 23 April in 1961 to 30 May in 1923, with a mean date of 12 May.
PREFACE TO THE SECOND EDITION LIST OF SYMBOLS 1. SCOPE OF ENVIRONMENTAL PHYSICS 2. GAS LAWS Pressure, volume and temperature Specific heats Lapse rate Water and water vapour Other gases 3. TRANSPORT LAWS General transfer equation Molecular transfer processes Diffusion coefficients Radiation laws 4. RADIATION ENVIRONMENT Solar radiation Terrestrial radiation Net radiation 5. MICROCLIMATOLOGY OF RADIATION (i) Interception Direct solar radiation Diffuse radiation Radiation in crop canopies 6. MICROCLIMATOLOGY OF RADIATION (ii) Absorption and reflection Radiative properties of natural materials Net radiation 7. MOMENTUM TRANSFER Boundary layers Wind profiles and drag on uniform surfaces Lodging and windthrow 8. HEAT TRANSFER Convection Non-dimensional groups Measurements of convection Conduction Insulation of animals 9. MASS TRANSFER (i) Gases and water vapour Non-dimensional groups Measurement of mass transfer Ventilation Mass transfer through pores Coats and clothing 10.MASS TRANSFER (ii) Particles Steady motion 11.STEADY STATE HEAT BALANCE (i) Water surfaces and vegetation Heat balance equation Heat balance of thermometers Heat balance of surfaces Developments from the Penman Equation 12.STEADY STATE HEAT BALANCE (ii) Animals Heat balance components The thermo-neutral diagram Specification of the environment Case studies 13.TRANSIENT HEAT BALANCE Time constant General cases Heat flow in soil 14.CROP MICROMETEOROLOGY (i) Profiles and fluxes Profiles Profile equations and stability Measurement of flux above the canopy 15.CROP MICROMETEOROLOGY (ii) Interpretation of measurements Resistance analogues Case studies: Water vapour and transpiration Carbon dioxide and growth Sulphur dioxide and pollutant fluxes to crops Transport within canopies APPENDIX BIBLIOGRAPHY REFERENCES INDEX