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Abstract

The effects of short-term extreme events on tree functioning and physiology are still rather elusive. European beech is one of the most sensitive species to late frost and water shortage. We investigated the intra-annual C dynamics in stems under such conditions. Wood formation and stem CO2 efflux were monitored in a Mediterranean beech forest for 3 years (2015-2017), including a late frost (2016) and a summer drought (2017). The late frost reduced radial growth and, consequently, the amount of carbon fixed in the stem biomass by 80%. Stem carbon dioxide efflux in 2016 was reduced by 25%, which can be attributed to the reduction of effluxes due to growth respiration. Counter to our expectations, we found no effects of the 2017 summer drought on radial growth and stem carbon efflux. The studied extreme weather events had various effects on tree growth. Even though late spring frost had a strong impact on beech radial growth in the current year, trees fully recovered in the following growing season, indicating high resilience of beech to this stressful event.

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... While for northern and north-eastern part of beech distribution range, growth was limited by combination of spring frost and drought stress (Muffler et al., 2020). Finally, growth reduction in beech may also be associated with late spring frost, summer drought, or mast years, which are also strongly affected by temperature (Kolář et al., 2017;Hacket-Pain et al., 2018;Gazol et al., 2019;D' Andrea et al., 2020). Due to climate warming, a higher masting frequency of beech has been observed in recent decades in Central Europe (Bogdziewicz et al., 2021). ...
... Indeed, historical records show a largescale ice break disturbance at this site (Šifrer, 1977), which seems to have affected the growth of some trees. Recent studies showed that late spring frost essentially influenced beech foliage and TRW in the current year (D' Andrea et al., 2020;Decuyper et al., 2020;Sanguesa-Barreda et al., 2021). However, trees fully recovered in the following growing season, which indicates high resilience of beech to this stress event (D' Andrea et al., 2020). ...
... Recent studies showed that late spring frost essentially influenced beech foliage and TRW in the current year (D' Andrea et al., 2020;Decuyper et al., 2020;Sanguesa-Barreda et al., 2021). However, trees fully recovered in the following growing season, which indicates high resilience of beech to this stress event (D' Andrea et al., 2020). In contrast, no effect of summer drought was found on the radial growth of beech in the current year (D' Andrea et al., 2020), but it may be evident in the following year (Decuyper et al., 2020). ...
Article
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European beech ( Fagus sylvatica L.) adapts to local growing conditions to enhance its performance. In response to variations in climatic conditions, beech trees adjust leaf phenology, cambial phenology, and wood formation patterns, which result in different tree-ring widths (TRWs) and wood anatomy. Chronologies of tree ring width and vessel features [i.e., mean vessel area (MVA), vessel density (VD), and relative conductive area (RCTA)] were produced for the 1960–2016 period for three sites that differ in climatic regimes and spring leaf phenology (two early- and one late-flushing populations). These data were used to investigate long-term relationships between climatic conditions and anatomical features of four quarters of tree-rings at annual and intra-annual scales. In addition, we investigated how TRW and vessel features adjust in response to extreme weather events (i.e., summer drought). We found significant differences in TRW, VD, and RCTA among the selected sites. Precipitation and maximum temperature before and during the growing season were the most important climatic factors affecting TRW and vessel characteristics. We confirmed differences in climate-growth relationships between the selected sites, late flushing beech population at Idrija showing the least pronounced response to climate. MVA was the only vessel trait that showed no relationship with TRW or other vessel features. The relationship between MVA and climatic factors evaluated at intra-annual scale indicated that vessel area in the first quarter of tree-ring were mainly influenced by climatic conditions in the previous growing season, while vessel area in the second to fourth quarters of tree ring width was mainly influenced by maximum temperature and precipitation in the current growing season. When comparing wet and dry years, beech from all sites showed a similar response, with reduced TRW and changes in intra-annual variation in vessel area. Our findings suggest that changes in temperature and precipitation regimes as predicted by most climate change scenarios will affect tree-ring increments and wood structure in beech, yet the response between sites or populations may differ.
... Growth and non-structural carbohydrates (NSCs; i.e., sucrose, fructose, glucose and starch) dynamics are among the physiological processes most strongly affected by spring frost (D'Andrea et al. 2020b) and summer drought (Li et al. 2018). An increasing body of evidence has shown that NSCs do not represent a purely passive accumulation and depletion of recently synthesized C compounds. ...
... However, after the second green-up in July 2016, C allocation to cell wall thickening was extremely limited due to strong reduction of xylem cell Tree Physiology Online at http://www.treephys.oxfordjournals.org production (D'Andrea et al. 2020b), leading to the increase of both starch and soluble sugars in stemwood of beech trees at the end of August. The reduced sink activity (related to radial growth, wall thickening and lignification) during extreme weather events could be enough to prevent NSC depletion (Anderegg 2012, Dietrich et al. 2018. ...
Article
Extreme weather events are increasing in frequency and intensity due to global climate change. We hypothesized that tree carbon reserves are crucial for resilience of beech, buffering the source-sink imbalance due to late frosts and summer droughts, and that different components of non-structural carbohydrates (NSCs) play specific roles in coping with stressful situations. To assess the compound effects on mature trees of two extreme weather events, first a late frost in spring 2016 and then a drought in summer 2017, we monitored the phenology, radial growth and the dynamics of starch and soluble sugars in a Mediterranean beech forest. A growth reduction of 85% was observed after the spring late frost, yet not after the drought event. We observed a strong impact of late frost on starch, which also affected its dynamic at the beginning of the subsequent vegetative season. In 2017, the increase of soluble sugars, associated with starch hydrolysis, played a crucial role in coping with the severe summer drought. NSCs helped to counteract the negative effects of both events, supporting plant survival and buffering source-sink imbalances under stressful conditions. Our findings indicate a strong trade-off between growth and NSC storage in trees. Overall, our results highlight the key role of NSCs on beech trees response to extreme weather events, confirming the resilience of this species to highly stressful events. These insights are useful for assessing how forests may respond to the potential impacts of climate change on ecosystem processes in the Mediterranean area.
... Also, average climatic characteristics could influence species-mixing effect on drought reaction by changing the relative competitivity between species. For instance the high sensitivity of beech to late frosts (Pretzsch et al., 2015;D'andrea et al., 2020) could reduce its otherwise high dominance over less competitive tree species in late frosts prone climates. Lastly, spatial and temporal variations of environmental conditions influence species-mixing effect through their impacts on both resources and modulators. ...
... Numerous traits can influence tree growth response to climate, and thus determine the species-mixing effect. For instance, by their longer vegetation period, coniferous species could have more opportunity for compensatory growth (Seidel et al., 2019) during climatically favorable periods following a drought event than broadleaves (D'Andrea et al., 2020). If conifer compensatory growth happens after the end of the admixed broadleaves vegetation period, conifer could additionally benefit from lower interspecific competition in mixed stands compared to pure stands. ...
Article
Increasing species diversity is considered a promising strategy to mitigate the negative impacts of global change on forests. However, the interactions between regional climate conditions and species-mixing effects on climate-growth relationships and drought resistance remain poorly documented. In this study, we investigated the patterns of species-mixing effects over a large gradient of environmental conditions throughout Europe for European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.), two species with contrasted ecological traits. We hypothesized that across large geographical scales, the difference of climate-growth relationships and drought resistance between pure and mixed stands would be dependent on regional climate. We used tree ring chronologies derived from 1143 beech and 1164 pine trees sampled in 30 study sites, each composed of one mixed stand of beech and pine and of the two corresponding pure stands located in similar site conditions. For each site and stand, we used Bootstrapped Correlation Coefficients (BCCs) on standardized chronologies and growth reduction during drought years on raw chronologies to analyze the difference in climate-tree growth relationships and resistance to drought between pure and mixed stands. We found consistent large-scale spatial patterns of climate-growth relationships. Those patterns were similar for both species. With the exception of the driest climates where pure and mixed beech stands tended to display differences in growth correlation with the main climatic drivers, the mixing effects on the BCCs were highly variable, resulting in the lack of a coherent response to mixing. No consistent species-mixing effect on drought resistance was found within and across climate zones. On average, mixing had no significant effect on drought resistance for neither species, yet it increased pine resistance in sites with higher climatic water balance in autumn. Also, beech and pine most often differed in the timing of their drought response within similar sites, irrespective of the regional climate, which might increase the temporal stability of growth in mixed compared to pure stands. Our results showed that the impact of species mixing on tree response to climate did not strongly differ between groups of sites with distinct climate characteristics and climate-growth relationships, indicating the interacting influences of species identity, stand characteristics, drought events characteristics as well as local site conditions.
... At the same time, the Mediterranean basin is one of the main climate change hotspots on the planet (Diffenbaugh and Giorgi, 2012;Noce et al., 2017;Tuel and Eltahir, 2020). Indeed, the area is warming up 20 % faster than the global average, precipitations are projected to decrease up to 20 %, and extreme climatic events (e.g., heatwaves and droughts) are likely to increase both in frequency and intensity (D'Andrea et al., 2020;Lionello and Scarascia, 2018;Santini et al., 2014). These changing conditions could potentially reduce forest growth and prompt changes in forest dynamics (i.e., mortality and extensive dieback episodes) that, together with other disturbances, might limit the C-uptake capacity and the productivity of Mediterranean forests (Gentilesca et al., 2017;Klein et al., 2019;Matteucci et al., 2013;Resco De Dios et al., 2007). ...
Article
Mediterranean pine plantations provide several ecosystem services but are vulnerable to climate change. Forest management might play a strategic role in the adaptation of Mediterranean forests, but the joint effect of climate change and diverse management options have seldom been investigated together. Here, we simulated the development of a Laricio pine (Pinus nigra subsp. laricio) stand in the Bonis watershed (southern Italy) from its establishment in 1958 up to 2095 using a state-of-the-science process-based forest model. The model was run under three climate scenarios corresponding to increasing levels of atmospheric CO2 concentration and warming, and six management options with different goals, including wood production and renaturalization. We analysed the effect of climate change on annual carbon fluxes (i.e., gross and net primary production) and stocks (i.e., basal area, standing and harvested carbon woody stocks) of the autotrophic compartment, as well as the impact of different management options compared to a no management baseline. Results show that higher temperatures (+3 to +5°C) and lower precipitation (−20 % to −22 %) will trigger a decrease in net primary productivity in the second half of the century. Compared to no management, the other options had a moderate effect on carbon fluxes over the whole simulation (between −14 % and +11 %). While standing woody biomass was reduced by thinning interventions and the shelterwood system (between −5 % and −41 %), overall carbon stocks including the harvested wood were maximized (between +41 % and +56 %). Results highlight that management exerts greater effects on the carbon budget of Laricio pine plantations than climate change alone, and that climate change and management are largely independent (i.e., no strong interaction effects). Therefore, appropriate sil-vicultural strategies might enhance potential carbon stocks and improve forest conditions, with cascading positive effects on the provision of ecosystem services in Mediterranean pine plantations.
... This is in line with the global narrative, where extreme weather events are increasing globally and are mainly driven by global warming. Climate change is believed to be one of the key drivers of extreme weather events across the world (D'Andrea et al. 2020;Otto et al. 2017;Stott 2016 ...
Chapter
Access to drinking water remains a challenge in many rural areas in Sub-Saharan Africa. This situation is further compounded by frequent disasters such as floods, which affect water supply infrastructure. However, few scholarly works have examined access to drinking water for rural households vulnerable to floods in Southern Africa. This study analysed the extent to which the 2019 flooding induced by Cyclone Idai affected households’ access to water in Magalasi Village in Chikwawa District in Malawi. Data was collected and analysed following the mixed methods research design in which both quantitative and qualitative approaches were used. The results show that during the floods, households relocated to a nearby school which has solar powered tap water. However, the increased numbers at the camp resulted in a decline in the daily minimum water per capita of 20 L/c/d in about 60% of the households as each tap is meant to carter for 250 people only. Furthermore, the use of the taps was restricted to 8 h (6 am–2 pm during weekdays and 8 am–5 pm during weekends), which coincided with times for farming activities. Consequently, households had to fetch water from a village about 3 km away. However, the alternative water sources were also inaccessible during severe flooding conditions, with intermittent and contaminated water. Considering the health challenges associated with consumption of insufficient and contaminated water, this study proposes construction of more resilient deep boreholes for continuous water supply.
... Natural disturbances have a key role in forest ecosystem dynamics [1], yet global changes in climate and land-uses have intensified disturbances rates in several biomes with important consequences on the ecosystems resilience [2]. Events like droughts and wildfires are becoming widespread phenomena in vast areas of the globe, potentially affecting the ecosystem services they provide [3,4] even in humid biomes with high rainfall rates, such as Amazonia [5][6][7]. ...
Article
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In recent decades, droughts, deforestation and wildfires have become recurring phenomena that have heavily affected both human activities and natural ecosystems in Amazonia. The time needed for an ecosystem to recover from carbon losses is a crucial metric to evaluate disturbance impacts on forests. However, little is known about the impacts of these disturbances, alone and synergistically, on forest recovery time and the resulting spatiotemporal patterns at the regional scale. In this study, we combined the 3-PG forest growth model, remote sensing and field derived equations, to map the Amazonia-wide (3 km of spatial resolution) impact and recovery time of aboveground biomass (AGB) after drought, fire and a combination of logging and fire. Our results indicate that AGB decreases by 4%, 19% and 46% in forests affected by drought, fire and logging + fire, respectively, with an average AGB recovery time of 27 years for drought, 44 years for burned and 63 years for logged + burned areas and with maximum values reaching 184 years in areas of high fire intensity. Our findings provide two major insights in the spatial and temporal patterns of drought and wildfire in the Amazon: (1) the recovery time of the forests takes longer in the southeastern part of the basin, and, (2) as droughts and wildfires become more frequent-since the intervals between the disturbances are getting shorter than the rate of forest regeneration-the long lasting damage they cause potentially results in a permanent and increasing carbon losses from these fragile ecosystems.
... We used the relative growth change method to identify potential growth reductions due to LFDs (Schweingruber et al., 1990). We defined a negative event year as a year with at least 40% of tree-ring growth reduction with respect to the average growth in the 4 preceding years (D'Andrea et al., 2020;Príncipe et al., 2017). In this first step, we identified negative event years as candidates for LFD events. ...
Article
Climate change is increasing the frequency of extreme climate events, causing profound impacts on forest function and composition. Late frost defoliation (LFD) events, the loss of photosynthetic tissues due to low temperatures at the start of the growing season, might become more recurrent under future climate scenarios. Therefore, the detection of changes in late-frost risk in response to global change emerges as a high-priority research topic. Here, we used a tree-ring network from southern European beech (Fagus sylvatica L.) forests comprising Spain, Italy and the Austrian Alps, to assess the incidence of LFD events in the last seven decades. We fitted linear-mixed models of basal area increment using different LFD indicators considering warm spring temperatures and late-spring frosts as fixed factors. We reconstructed major LFD events since 1950, matching extreme values of LFD climatic indicators with sharp tree-ring growth reductions. The last LFD events were validated using remote sensing. Lastly, reconstructed LFD events were climatically and spatially characterized. Warm temperatures before the late-spring frost, defined by high values of growing-degree days, influenced beech growth negatively, particularly in the southernmost populations. The number of LFD events increased towards beech southern distribution edge. Spanish and the southernmost Italian beech forests experienced higher frequency of LFD events since the 1990s. Until then, LFD events were circumscribed to local scales, but since that decade, LFD events became widespread, largely affecting the whole beech southwestern distribution area. Our study, based on in-situ evidence, sheds light on the climatic factors driving LFD occurrence and illustrates how increased occurrence and spatial extension of late-spring frosts might constrain future southern European beech forests' growth and functionality. Observed alterations in the climate-phenology interactions in response to climate change represent a potential threat for temperate deciduous forests persistence in their drier/southern distribution edge.
... Therefore, the evidence provided supports the fact that the Tree Physiology Volume 41, 2021 Downloaded from https://academic.oup.com/treephys/article/41/7/1171/6056328 by guest on 26 November 2022 autumn differences observed between 2017 and 2018 could not be explained solely by possible legacy effects due to interannual differences in the spring xylogenesis. In other words, the effect of summer conditions (drought) must have played a key role in any case (D'Andrea et al. 2020). ...
Article
Research on wood phenology has mainly focused on reactivation of the cambium in spring. In this study we investigated if summer drought advances cessation of wood formation and if it has any influence on wood structure in late successional forest trees of the temperate zone. The end of xylogenesis was monitored between August and November in stands of European beech and pedunculate oak in Belgium for two consecutive years, 2017 and 2018, with the latter year having experienced an exceptional summer drought. Wood formation in oak was affected by the drought, with oak trees ceasing cambial activity and wood maturation about three weeks earlier in 2018 compared to 2017. Beech ceased wood formation before oak, but its wood phenology did not differ between years. Furthermore, between the two years, no significant difference was found in ring width, percentage of mature fibers in the late season, vessel size and density. In 2018, beech did show thinner fiber walls, while oak showed thicker walls. In this paper, we showed that summer drought can have an important impact on late season wood phenology xylem development. This will help to better understand forest ecosystems and improve forest models.
... This hypothesis fed into the socalled boxer theory, suggesting the successive stresses may cause trees to decline (Wargo 1996;Bréda and Peiffer 2014). Wood growth has been used as an integrative marker following frost and drought stress (Vanoni et al. 2016;d'Andrea et al. 2020). However, due to the difficulty of conducting long-term studies through the development of project-based funding, few studies have been able to accurately characterize the affected ecophysiological processes. ...
Article
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• Key message The increase in climate variability is likely to generate an increased occurrence of both frost-induced and drought-induced damages on perennial plants. We examined how these stress factors can potentially interact and would subsequently affect the vulnerability to each other. Furthermore, we discussed how this vulnerability could be modulated by shifts in the annual phenological cycle. ContextThe edges of plant distribution are strongly affected by abiotic constraints: heat waves and drought at low latitude and elevation, cold and frost at high latitude and elevation. The increase in climate variability will enhance the probability of extreme events and thus the potential interaction of stress factors. The initial exposure to a first constraint may affect the vulnerability to a subsequent one.AimsAlthough three integrative physiological processes, namely water balance, carbon metabolism and the timing of phenological stages, have largely been studied in the response of trees to a single constraint, their interaction has rarely been investigated. How would the interaction of frost and drought constraints modulate the vulnerability to a subsequent constraint and how vulnerability to a given constraint and phenology interact?Conclusion We suggest that the interaction between frost and drought constraints should in the short-term influence water balance and, in the longer term, carbon metabolism, both consequently affecting further vulnerability. However, this vulnerability can be modulated by shifts in the annual phenological cycle. Significant gaps of knowledge are reported in a mechanistic framework. This framework can help to improve the current process-based models integrating the life history of the individual plant.
... This is possibly due to high soil water retention and tree rooting depth in the study site. In any case, previous studies have shown a reduced impact of summer drought on the growth of southern beech forests, probably resulting from a shortening of the radial growth period, so that most of the growth is concentrated in the wettest period (spring and early summer), thus reducing the possible impact of summer droughts (D'Andrea et al. 2020(D'Andrea et al. , 2021. These results would confirm that trees in rear-edge populations can display a high resistance to drought (Cavin andJump 2017, but see Camarero et al. 2021), although they could be particularly vulnerable to other climate extremes, such as spring frosts, particularly under continental conditions. ...
Article
Rear-edge tree populations forming the equatorward limit of distribution of temperate species are assumed to be more adapted to climate variability than central (core) populations. However, climate is expected to become more variable and the frequency of climate extremes is forecasted to increase. Climatic extreme events such as heat waves, dry spells and spring frosts could become more frequent, and negatively impact and jeopardize rear-edge stands. To evaluate these ideas, we analyzed the growth response of trees to successive spring frosts in a mixed forest, where two temperate deciduous species, Fagus sylvatica (European beech) and Quercus petraea (sessile oak), both at their southernmost edge, coexist with the Mediterranean Quercus pyrenaica (Pyrenean oak). Growth reductions in spring-frost years ranked across species as F. sylvatica > Q. petraea > Q. pyrenaica. Leaf flushing occurred earlier in F. sylvatica and later in Q. pyrenaica, suggesting that leaf phenology was a strong determinant of spring frost damage and stem growth reduction. The frost impact depended on prior climate conditions, since warmer days prior to frost occurrence predisposed to frost damage. Autumn Normalized Difference Vegetation Index (NDVI) data showed delayed leaf senescence in spring-frost years and subsequent years as compared with pre-frost years. In the studied forest, the negative impact of spring frosts on Q. petraea and especially on F. sylvatica growth was considerably higher than the impacts due to drought. The succession of four spring frosts in the last two decades determined a trend of decreasing resistance of radial growth to frosts in F. sylvatica. The increased frequency of spring frosts might prevent the expansion and persistence of F. sylvatica in this rear-edge Mediterranean population.
... This is in line with the global narrative, where extreme weather events are increasing globally and are mainly driven by global warming. Climate change is believed to be one of the key drivers of extreme weather events across the world (D'Andrea et al. 2020;Otto et al. 2017;Stott 2016 ...
Chapter
This study explores links between IKS and climate science for flood forecasting in a flood-prone area, affected by Tropical Cyclone Idai, in Malawi. Rural communities’ perceptions of flood trends and risks were collected using household interviews (n = 60), key informant interviews (n = 10) and mixed gender focus group discussions in Chikwawa District. Flood frequency analysis was performed using rainfall and discharge data from nearby weather stations and Mwanza and Shire Rivers. There is a decline in localised rainfall, but increase in flooding from rainfall in upstream catchment. Both communities highlighted reliable IKS (flora, fauna and atmospheric observations) used before the onset of and during the rainfall events for flooding forecasts. However, most of the IK indicators are threatened by environmental degradation and may not be suited to forecasts of patterns or intensity of rainfall at large spatial and temporal scales, such as floods from rainfall in upstream catchment. Therefore, IK indicators may not provide sufficient foreknowledge to respond to climate events such as cyclones. Scientific climate knowledge may provide forecasts at both small and large spatial and temporal scales. Therefore, integration of contextualised IK and scientific climate knowledge can produce robust flood forecasts in the poorly resourced settings.
... This is in line with the global narrative, where extreme weather events are increasing globally and are mainly driven by global warming. Climate change is believed to be one of the key drivers of extreme weather events across the world (D'Andrea et al. 2020;Otto et al. 2017;Stott 2016 ...
Chapter
Climate change is known to result in extreme weather events across the world. Concern has been increasing over the social, environmental and human costs of such extreme weather events. 2019 witnessed some of the most significant record cyclones in southern Africa due to the occurrence of two devastating cyclones, namely tropical cyclones Idai and Kenneth. These were followed by two more tropical cyclones, namely Chalane (2020) and Eloise (2021). The occurrence of these hydrometeorological hazards has raised various questions on the capacity of southern Africa to respond to these hazards, which are on the increase. The question regarding the state and capacity of early warning systems has been brought to the fore, challenging improvements to ensure climate resilience and regional sustainability. This book tackles issues of how southern Africa can view tropical cyclones in the context of climate change and develop early warning systems that can be used as a platform for disaster risk reduction and climate adaptation and resilience. This introduction sets the tone for the book and deals with various thematic issues, such as the meteorological and climatological occurrence of tropical cyclones, tropical cyclones as an emerging disaster risk and human response in the context of the Sendai Framework for Disaster Risk Reduction. A ‘building back better’ strategy is recommended for both infrastructure and disaster management institution and a de-risking approach to development anchored on clean development mechanisms to address climate change and its associated risks.
... This is in line with the global narrative, where extreme weather events are increasing globally and are mainly driven by global warming. Climate change is believed to be one of the key drivers of extreme weather events across the world (D'Andrea et al. 2020;Otto et al. 2017;Stott 2016 ...
Chapter
Extreme weather events have significantly affected human civilisation and development in recent periods. While COVID-19 has been the top news headline in 2020 and 2021, it is important to note that the additional impact of extreme weather events is catastrophic to human development. Tornadoes rank amongst the deadliest extreme weather events of global concern. This study seeks to assess the trend and impacts of tornadoes on the highveld area of Mpumalanga province, South Africa. The Mkhondo Local Municipality area was used in a case study to research primary and archival data from key informants and weather bureaus. The study found that high-impact tornadoes are on the increase in Mpumalanga. Tornadoes that occur mainly in summer months with a peak between November and January have led to loss of property, timber plantations, homes, schools, and health institutions and threaten the progress made in achieving the Sustainable Development Goals. The study noted a statistically significant (p = 0.015) increase in the frequency and severity of tornadoes in Mpumalanga, particularly in the last 5 years that coincide with probably the worst El Niño event experienced in Southern Africa. The study recommends a risk-adjusted approach to infrastructure development considering the increased frequency of tornadoes due to global warming and climate change. The risk-adjusted approach must encompass smart climate initiatives for rural and urban development to ensure climate resilience if sustainability is to be achieved.
... Once (and if) the minimum NSC threshold is reached, C is allocated preferentially for biomass growth for the different tree structural C-pools depending on the phenological phase as formerly described in Collalti et al. (2016). The only phenological phase during which NSC has no priority in allocation is during bud break (D'Andrea et al., 2020(D'Andrea et al., , 2021, when recent GPP is completely allocated for growth of leaves up to a maximum annual leaf area index (LAI, m 2 m -2 ), which is computed at the beginning of each year of simulation through the pipe-model (Shinozaki et al., 1964;Mäkelä, 1997), and growth of fine roots. This NSC allocation scheme reflects a quasi-active role of NSC, with NSC usually having priority over growth of new structural tissues, as described by Sala (2011), Merganičová et al. (2019 and Collalti et al. (2020a). ...
Article
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Forest management practices might act as nature-based methods to remove CO2 from the atmosphere and slow anthropogenic climate change and thus support an EU forest-based climate change mitigation strategy. However, the extent to which diversified management actions could lead to quantitatively important changes in carbon sequestration and stocking capacity at the tree level remains to be thoroughly assessed. To that end, we used a state-of-the-science bio-geochemically based forest growth model to simulate effects of multiple forest management scenarios on net primary productivity (NPP) and potential carbon woody stocks (pCWS) under twenty scenarios of climate change in a suite of observed and virtual forest stands in temperate and boreal European forests. Previous modelling experiments indicated that the capacity of forests to assimilate and store atmospheric CO2 in woody biomass is already being attained under business-as-usual forest management practices across a range of climate change scenarios. Nevertheless, we find that on the long-term, with increasing atmospheric CO2 concentration and warming, managed forests show both higher productivity capacity and a larger potential pool size of stored carbon than unmanaged forests as long as thinning and tree harvesting are of moderate intensity.
... This is in line with the global narrative, where extreme weather events are increasing globally and are mainly driven by global warming. Climate change is believed to be one of the key drivers of extreme weather events across the world (D'Andrea et al. 2020;Otto et al. 2017;Stott 2016 ...
Chapter
Natural hazard-related disasters have been progressively increasing across the globe over the last several decades. Notably, the frequency of floods and tornadoes has accelerated leading to the proliferation of related calamities over time. Although some significant amount of work has been done to understand flood risks on communities around the world, a lot more still needs to be researched given the evolving magnitude and frequency of the flood events. For tornadoes, the science still remains veiled in obscurity and their risks still need further scientific inquiry. It is in view of this that this chapter discusses the increasing risk of floods and tornadoes in different geographic and temporal contexts with a view to understand the consequences of increasing risks associated with both phenomena to society and the environment. The chapter presents this background and puts into context the various studies contained in this book. Generally, the chapter shows that floods and tornadoes are monstrous hazards that are seriously threatening societal progress and economic development around the globe. They are among the driving forces behind the slow progress towards the achievement of the 2030 Agenda for Sustainable Development and its associated sustainable development goals (SDGs). The need to build community preparedness and response capacity is also highlighted.
... This is in line with the global narrative, where extreme weather events are increasing globally and are mainly driven by global warming. Climate change is believed to be one of the key drivers of extreme weather events across the world (D'Andrea et al. 2020;Otto et al. 2017;Stott 2016 ...
Chapter
Hotel management is becoming more difficult in the face of increasing and repeated natural and human-induced disasters, particularly floods, cyclones and earthquakes. Hotel managers should come up with disaster risk reduction (DRR) and management plans that include early warning, search and rescue (evacuations) and relief and recovery. While there are numerous incidences of hotel infrastructure being razed to the ground, many hotels remain operational, but under the risk of repeat events. Through repeated direct observations, interviews and Geographical Information Systems, this chapter investigates the extent and potential causes of repeated flooding of The Centurion Hotel, South Africa. It further examines the DRR and management protocols put in place by the hotel and their effectiveness. The Centurion Hotel has been a victim of repeated flooding, with the most recent event in December 2019 being the worst, forcing it to close twice in 2020 affecting 84 employees. The flooding is aggravated by the heavily silted Centurion Lake and land use changes in the upper catchment of the Hennops River stretching across the three municipal jurisdictions of Ekurhuleni, Johannesburg and City of Tshwane metropoles. The results of this study further revealed that the hotel’s design originally took into account the possibility of flooding, although the flood lines have since shifted and high-impact floods have become more frequent. The hotel also put into place measures to counter the effects of flooding although these were overwhelmed by the 2019 floods. The hotel has a sound standard operating procedure for the evacuation of guests in the event of a disaster. Given that such extreme weather events will only increase in the future, we recommend that The Centurion Hotel continues adapting and building back better and smarter with lessons from each flood event, including carefully planning for possible seasonal operations in the future.
... In Europe, the recent climate variability significantly increased the frequency of extreme climate events such as LSFs (Augspurger, 2013;Bigler and Bugmann, 2018;Zohner et al., 2020;Lamichhane, 2021) and summer droughts (Spinoni et al., 2018;Gazol and Camarero, 2022;Dukat et al., 2022). In widely distributed species such as beech the combined effects of these extreme climate events pose several questions about forest productivity, tree growth and postdisturbance recovery Vitasse et al., 2019;D'Andrea et al., 2020). ...
... Depending on the research question, monitoring radial growth in trees can be performed on individual sites , at sites selected along an altitudinal or latitudinal gradient (Rossi et al., 2011), at sites with different soil types , and weather conditions (i.e., wet or dry sites) (Copini et al., 2016;Ren et al., 2019). Sampling can be conducted on young or old trees (Li et al., 2013), with different crown classes (Rathgeber et al., 2011b) or during extreme weather events (D'Andrea et al., 2020). In most studies between 4 and 10 trees are selected per site for statistical representation (e.g., Rossi et al. 2013). ...
Article
This technical note and its corresponding video show the procedure for optimal sample preparation to perform wood and phloem formation analyses.
... This is in line with the global narrative, where extreme weather events are increasing globally and are mainly driven by global warming. Climate change is believed to be one of the key drivers of extreme weather events across the world (D'Andrea et al. 2020;Otto et al. 2017;Stott 2016 ...
Article
This study aimed to simulate oak and beech forest growth under various scenarios of climate change and to evaluate how the forest response depends on site properties and particularly on stand characteristics using the individual process-based model HETEROFOR. First, this model was evaluated on a wide range of site conditions. We used data from 36 long-term forest monitoring plots to initialize, calibrate, and evaluate HETEROFOR. This evaluation showed that HETEROFOR predicts individual tree radial growth and height increment reasonably well under different growing conditions when evaluated on independent sites. In our simulations under constant CO2 concentration ([CO2]cst) for the 2071-2100 period, climate change induced a moderate net primary production (NPP) gain in continental and mountainous zones and no change in the oceanic zone. The NPP changes were negatively affected by air temperature during the vegetation period and by the annual rainfall decrease. To a lower extent, they were influenced by soil extractable water reserve and stand characteristics. These NPP changes were positively affected by longer vegetation periods and negatively by drought for beech and larger autotrophic respiration costs for oak. For both species, the NPP gain was much larger with rising CO2 concentration ([CO2]var) mainly due to the CO2 fertilisation effect. Even if the species composition and structure had a limited influence on the forest response to climate change, they explained a large part of the NPP variability (44% and 34% for [CO2]cst and [CO2]var, respectively) compared to the climate change scenario (5% and 29%) and the inter-annual climate variability (20% and 16%). This gives the forester the possibility to act on the productivity of broadleaved forests and prepare them for possible adverse effects of climate change by reinforcing their resilience.
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Anthropogenic activities have resulted in a significant increase of reactive nitrogen (N) compounds in the atmosphere and a rise in N deposition on forest ecosystems. Increasing N loads impact forest productivity and health, altering tree physiological status and nutrient balance with possible beneficial and detrimental consequences. The impact of N deposition has received considerable attention by scientific research, covering medium and high latitudes, while experimental studies in the Mediterranean area are almost absent. The present study used a manipulative approach, through replicated N additions (background deposition, 30, 60 kg N ha⁻¹ yr⁻¹) to simulate the cumulative effects of N deposition in two beech (Fagus sylvatica L.) forests located in contrasting climatic regions of Italy. Leaf nutrients and photosynthetic pigments were tested as monitoring indicators after four years of N fertilization. Foliar N and pigment concentrations indicated not limiting N conditions at both forest sites, although changes in chlorophylls and carotenoids showed an early response of the canopy to N additions. N-to-phosphorus (P) and sulfur (S) ratios increased under elevated N fertilization, which could be partly related to the relative enhancement of foliar N concentration, and partly associated with the reduction of foliar P and S. The two eutrophic beech forests monitored were not severely affected by chronic N addition, not showing critical nutritional and physiological impairments over the short to medium period. However, the modifications in leaf nutrient and pigment compositions showed an incipient stress response and accentuated the differences induced by climatic and soil characteristics at the two sites. The potential use of nutrients and photosynthetic pigments in monitoring forest N deposition under contrasting climatic conditions and the eventual limits of manipulative experiments are discussed.
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Mediterranean pine plantations provide several ecosystem services but are particularly sensitive to climate change. Forest management practices might play a strategic role in the long-term adaptation of Mediterranean forests, however the joint effect of climate change and alternative management options together in the near and far future must be investigated. Here, we developed a management options portfolio and simulated the development of a Laricio pine (Pinus nigra subsp. laricio) stand in the Bonis watershed (southern Italy) from its establishment in 1958 up to 2095 using a state-of-the-science process-based forest model. The model was run under three climate change scenarios corresponding to increasing levels of atmospheric CO2 concentration, and seven management options with different goals, including post-disturbance management, wood production and renaturalization purposes. We analyzed the effect of climate change on annual carbon fluxes (i.e., gross and net primary production) and stocks (i.e., basal area and potential carbon woody stocks), as well as the impact of different management options compared to no management. Results show that, while climate change (i.e. warming and enriched atmospheric CO2 concentration) seems to increase carbon fluxes and stocks in the first half of the century, both show a substantial decrease in the second half, along with higher temperatures (+3 to +5 °C) and lower precipitation (–20% to –22%). When compared to no management, alternative options had a moderate effect on carbon fluxes over the whole simulation (between –6% and +7%) but overall carbon stocks were maximized by thinning interventions and the shelterwood system (+54% to +55%). We demonstrate that the choice of management exerts greater effects on the features of Laricio pine plantations than climate change alone. Therefore, silvicultural strategies might enhance potential stocks and improve forest conditions, with cascading positive effects on the provision of ecosystem services in Mediterranean pine plantations.
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Extreme climate events such as late spring frosts (LSFs) negatively affect productivity and tree growth in temperate beech forests. However, detailed information on how these forests recover after such events are still missing. We investigated how LSFs affected forest cover and radial growth in European beech (Fagus sylvatica L.) populations located at different elevations at four sites in the Italian Apennines, where LSFs have been recorded. We combined tree-ring and remote-sensing data to analyse the sensitivity and recovery capacity of beech populations to LSFs. Using daily temperature records, we reconstructed LSF events and assessed legacy effects on growth. We also evaluated the role played by elevation and stand structure as modulators of LSFs impacts. Finally, using satellite images we computed Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI) and LAI (Leaf Area Index) to evaluate the post-LSF canopy recovery. The growth reduction in LSF-affected trees ranged from 36 % to 84 %. We detected a negative impact of LSF on growth only during the LSF year, with growth recovery occurring within 1–2 years after the event. LSF-affected stands featured low vegetation indices until late June, i.e. on average 75 days after the frost events. We did not find a clear relationship between beech forest elevation and occurrence of LSFs defoliations. Our results indicate a high recovery capacity of common beech and no legacy effects of LSFs.
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The effects of short‐term extreme events on tree functioning and physiology are still rather elusive. European beech is one of the most sensitive species to late frost and water shortage. We investigated the intra‐annual C dynamics in stems under such conditions. Wood formation and stem CO2 efflux were monitored in a Mediterranean beech forest for three years (2015–2017), including a late frost (2016) and a summer drought (2017). The late frost reduced radial growth and, consequently, the amount of carbon fixed in the stem biomass by 80%. Stem carbon dioxide efflux in 2016 was reduced by 25%, which can be attributed to the reduction of effluxes due to growth respiration. Counter to our expectations, we found no effects of the 2017 summer drought on radial growth and stem carbon efflux. The studied extreme weather events had various effects on tree growth. Even though late spring frost had a strong impact on beech radial growth in the current year, trees fully recovered in the following growing season, indicating high resilience of beech to this stressful event. This article is protected by copyright. All rights reserved.
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The FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.
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The FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.
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Process-based vegetation models are widely used to predict local and global ecosystem dynamics and climate change impacts. Due to their complexity, they require careful parameterization and evaluation to ensure that projections are accurate and reliable. The PROFOUND Database (PROFOUND DB) provides a wide range of empirical data on European forests to calibrate and evaluate vegetation models that simulate climate impacts at the forest stand scale. A particular advantage of this database is its wide coverage of multiple data sources at different hierarchical and temporal scales, together with environmental driving data as well as the latest climate scenarios. Specifically, the PROFOUND DB provides general site descriptions, soil, climate, CO2, nitrogen deposition, tree and forest stand level, and remote sensing data for nine contrasting forest stands distributed across Europe. Moreover, for a subset of five sites, time series of carbon fluxes, atmospheric heat conduction and soil water are also available. The climate and nitrogen deposition data contain several datasets for the historic period and a wide range of future climate change scenarios following the Representative Concentration Pathways (RCP2.6, RCP4.5, RCP6.0, RCP8.5). We also provide pre-industrial climate simulations that allow for model runs aimed at disentangling the contribution of climate change to observed forest productivity changes. The PROFOUND DB is available freely as a “SQLite” relational database or “ASCII” flat file version (at https://doi.org/10.5880/PIK.2020.006/; Reyer et al., 2020). The data policies of the individual contributing datasets are provided in the metadata of each data file. The PROFOUND DB can also be accessed via the ProfoundData R package (https://CRAN.R-project.org/package=ProfoundData; Silveyra Gonzalez et al., 2020), which provides basic functions to explore, plot and extract the data for model set-up, calibration and evaluation.
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Late-spring frosts (LSFs) affect the performance of plants and animals across the world's temperate and boreal zones, but despite their ecological and economic impact on agriculture and forestry, the geographic distribution and evolutionary impact of these frost events are poorly understood. Here, we analyze LSFs between 1959 and 2017 and the resistance strategies of Northern Hemisphere woody species to infer trees' adaptations for minimizing frost damage to their leaves and to forecast forest vulnerability under the ongoing changes in frost frequencies. Trait values on leaf-out and leaf-freezing resistance come from up to 1,500 temperate and boreal woody species cultivated in common gardens. We find that areas in which LSFs are common, such as eastern North America, harbor tree species with cautious (late-leafing) leaf-out strategies. Areas in which LSFs used to be unlikely, such as broad-leaved forests and shrublands in Europe and Asia, instead harbor opportunistic tree species (quickly reacting to warming air temperatures). LSFs in the latter regions are currently increasing, and given species' innate resistance strategies, we estimate that ∼35% of the European and ∼26% of the Asian temperate forest area, but only ∼10% of the North American, will experience increasing late-frost damage in the future. Our findings reveal region-specific changes in the spring-frost risk that can inform decision-making in land management, forestry, agriculture, and insurance policy.
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Tree stems are an overlooked source of volatile organic compounds (VOCs). Their contribution to ecosystem processes and total VOC fluxes is not well studied, and assessing it requires better understanding of stem emission dynamics and their driving processes. To gain more mechanistic insight into stem emission patterns, we measured monoterpene, methanol, and acetaldehyde emissions from the stems of mature Scots pines (Pinus sylvestris L.) in a boreal forest over three summers. We analysed the effects of temperature, soil water content, tree water status, transpiration, and growth on the VOC emissions, and used generalized linear models to test their relative importance in explaining the emissions. We show that Scots pine stems are considerable sources of monoterpenes, methanol, and acetaldehyde, and their emissions are strongly regulated by temperature. However, even small changes in water availability affected the emission potentials: increased soil water content increased the monoterpene emissions within a day, whereas acetaldehyde and methanol emissions responded within two to four days. This lag corresponded to their transport time in the xylem sap from the roots to the stem. Moreover, the emissions of monoterpenes, methanol, and acetaldehyde were influenced by the cambial growth rate of the stem with six‐ to ten‐day lags. This article is protected by copyright. All rights reserved.
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The tree belowground compartment, especially fine roots, plays a relevant role in the forest ecosystem carbon (C) cycle, contributing largely to soil CO2 efflux (SR) and to net primary production (NPP). Beyond the well-known role of environmental drivers on fine root production (FRP) and SR, other determinants such as forest structure are still poorly understood. We investigated spatial variability of FRP, SR, forest structural traits, and their reciprocal interactions in a mature beech forest in the Mediterranean mountains. In the year of study, FRP resulted in the main component of NPP and explained about 70% of spatial variability of SR. Moreover, FRP was strictly driven by leaf area index (LAI) and soil water content (SWC). These results suggest a framework of close interactions between structural and functional forest features at the local scale to optimize C source-sink relationships under climate variability in a Mediterranean mature beech forest.
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Process-based vegetation models are widely used to predict local and global ecosystem dynamics and climate change impacts. Due to their complexity, they require careful parameterization and evaluation to ensure that projections are accurate and reliable. The PROFOUND Database (PROFOUND DB) provides a wide range of empirical data to calibrate and evaluate vegetation models that simulate climate impacts at the forest stand scale. A particular advantage of this database is its wide coverage of multiple data sources at different hierarchical and temporal scales, together with environmental driving data as well as the latest climate scenarios. Specifically, the PROFOUND DB provides general site descriptions, soil, climate, CO2, nitrogen deposition, tree and forest stand-level, as well as remote sensing data for nine contrasting forest stands distributed across Europe. Moreover, for a subset of five sites, time series of carbon fluxes, atmospheric heat 10 conduction, and soil water are also available. The climate and nitrogen deposition data contain several datasets for the historic period and a wide range of future climate change scenarios following the Representative Concentration Pathways (RCP2.6, RCP4.5, RCP6.0, RCP8.5). We also provide pre-industrial climate simulations that allow for model runs aimed at disentangling the contribution of climate change to observed forest productivity changes. The PROFOUND DB is available freely as a ‘SQLite’ relational database or ‘ASCII’ flat file version (at http://doi.org/10.5880/PIK.2019.008, Reyer et al., 2019). The data policies of the individual, contributing datasets are provided in the metadata of each data file. The PROFOUND DB can also be accessed via the ProfoundData R-package (https://github.com/COST-FP1304-PROFOUND/ProfoundData, Silveyra Gonzalez et al., 2019), which provides basic functions to explore, plot, and extract the data for model set-up, calibration and evaluation.
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Carbon allocation plays a key role in ecosystem dynamics and plant adaptation to changing environmental conditions. Hence, proper description of this process in vegetation models is crucial for the simulations of the impact of climate change on carbon cycling in forests. Here we review how carbon allocation modelling is currently implemented in 31 contrasting models to identify the main gaps compared with our theoretical and empirical understanding of carbon allocation. A hybrid approach based on combining several principles and/or types of carbon allocation modelling prevailed in the examined models, while physiologically more sophisticated approaches were used less often than empirical ones. The analysis revealed that, although the number of carbon allocation studies over the past 10 years has substantially increased, some background processes are still insufficiently understood and some issues in models are frequently poorly represented, oversimplified or even omitted. Hence, current challenges for carbon allocation modelling in forest ecosystems are (i) to overcome remaining limits in process understanding, particularly regarding the impact of disturbances on carbon allocation, accumulation and utilization of nonstructural carbohydrates, and carbon use by symbionts, and (ii) to implement existing knowledge of carbon allocation into defence, regeneration and improved resource uptake in order to better account for changing environmental conditions.
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A major component of climate change is an increase in temperature and precipitation variability. Over the last few decades, an increase in the frequency of extremely warm temperatures and drought severity has been observed across Europe. These warmer and drier conditions may reduce productivity and trigger compositional shifts in forest communities. However, we still lack a robust, biogeographical characterization of the negative impacts of climate extremes, such as droughts on forests. In this context, we investigated the impact of the 2017 summer drought on European forests. The normalized difference vegetation index (NDVI) was used as a proxy of forest productivity and was related to the standardized precipitation evapotranspiration index (SPEI), which accounts for the temperature effects of the climate water balance. The spatial pattern of NDVI reduction in 2017 was largely driven by the extremely warm summer for parts of the central and eastern Mediterranean Basin (Italian and Balkan Peninsulas). The vulnerability to the 2017 summer drought was heterogeneously distributed over Europe, and topographic factors buffered some of the negative impacts. Mediterranean forests dominated by oak species were the most negatively impacted, whereas Pinus pinaster was the most resilient species. The impact of drought on the NDVI decreased at high elevations and mainly on east and north‐east facing slopes. We illustrate how an adequate characterization of the coupling between climate conditions and forest productivity (NDVI) allows the determination of the most vulnerable areas to drought. This approach could be widely used for other extreme climate events and when considering other spatially resolved proxies of forest growth and health. This article is protected by copyright. All rights reserved.
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Limited knowledge about vertical variation in wood CO2 efflux (Rwood) is still a cause of uncertainty in Rwood estimates at individual and ecosystem scales. Although previous studies found higher Rwood in the canopy, they examined several tree species of similar size. In contrast, in the present study, we measured vertical variation in Rwood for 18 trees including 13 species, using a canopy crane for a more precise determination of the vertical variation in Rwood, for various species and sizes of trees in order to examine the factors affecting vertical variation in Rwood and thus, to better understand the effect of taking into account the vertical and inter-individual variation on estimates of Rwood at the individual scale. We did not find any clear pattern of vertical variation; Rwood increased significantly with measurement height for only one tree, while it decreased for two more trees, and was not significantly related with measurement height in 15 other trees. Canopy to breast height Rwood ratio was not related to diameter at breast height or crown ratio, which supposedly are factors affecting vertical variation in Rwood. On average, Rwood estimates at individual scale, considering inter-individual variation but ignoring vertical variation, were only 6% higher than estimates considering both forms of variation. However, estimates considering vertical variation, while ignoring inter-individual variation, were 13% higher than estimates considering both forms of variation. These results suggest that individual measurements at breast height are more important for estimating Rwood at the individual scale, and that any error in Rwood estimation at this scale, due to the absence of any more measurements along tree height, is really quite negligible. This study measured various species and sizes of trees, which may be attributed to no clear vertical variation because factors causing vertical variation can differ among species and sizes.
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The ratio of CO2 efflux to O2 influx (ARQ, apparent respiratory quotient) in tree stems is expected to be 1.0 for carbohydrates, the main substrate supporting stem respiration. In previous studies of stem fluxes, ARQ values below 1.0 were observed and hypothesized to indicate retention of respired carbon within the stem. Here, we demonstrate that stem ARQ < 1.0 values are common across 85 tropical, temperate, and Mediterranean forest trees from nine different species. Mean ARQ values per species per site ranged from 0.39 to 0.78, with an overall mean of 0.59. Assuming that O2 uptake provides a measure of in situ stem respiration (due to the low solubility of O2 ), the overall mean indicates that on average 41 % of CO2 respired in stems is not emitted from the local stem surface. The instantaneous ARQ did not vary with sap flow. ARQ values of incubated stem cores were similar to those measured in stem chambers on intact trees. We therefore conclude that dissolution of CO2 in the xylem sap and transport away from the site of respiration cannot explain the low ARQ values. We suggest refixation of respired CO2 in biosynthesis reactions as possible mechanism for low ARQ values.
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Forest carbon use efficiency (CUE, the ratio of net to gross primary productivity) represents the fraction of photosynthesis that is not used for plant respiration. Although important, it is often neglected in climate change impact analyses. Here, we assess the potential impact of thinning on projected carbon-cycle dynamics and implications for forest CUE and its components (i.e. gross and net primary productivity and plant respiration), as well as on forest biomass production. Using a detailed process-based forest-ecosystem-model forced by climate outputs of five Earth System Models under four Representative- climate scenarios, we investigate the sensitivity of the projected future changes in the autotrophic carbon budget of three representative European forests. We focus on changes in CUE and carbon stocks as a result of warming, rising atmospheric CO 2 concentration and forest thinning. Results show that autotrophic carbon sequestration decreases with forest development and the decrease is faster with warming and in unthinned forests. This suggests that the combined impacts of climate change and changing CO2 concentrations, lead the forests to grow faster mature earlier but also die younger. In addition, we show that under future climate conditions, forest thinning could mitigate the decrease in CUE, increase carbon allocation into more recalcitrant woody-pools and reduce physiological-climate-induced mortality risks. Altogether, our results show that thinning can improve the efficacy of forest-based mitigation strategies and should be carefully considered within a portfolio of mitigation options.
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The magnitude and frequency of Extreme Weather Events (EWEs) are increasing, causing changes in species distribution. We assessed the short-term effects of a late spring frost on beech forests, using satellite images to identify damaged forests and changes in vegetation phenology, as well as to support the analyses on associated moth communities. The EWE caused crown dieback above 1400 m of altitude, recovered only after several weeks. Nine stands for moth sampling, settled in impacted and non-impacted forests, allowed us to study changes in moth communities and in the wingspan of the most impacted species. The EWE modified community structures, reducing the abundance of beech-feeder species, but leaving species richness unaltered. Operophtera fagata and Epirrita christyi, dominant before the EWE, lost 93% and 89% of their population, respectively. We found a general increase in the average wingspan for these species, caused by the loss of small specimens in most impacted forests, suggesting a re-colonization from non-impacted forests. According to our results, populations of some species could be more resilient than others after an EWE due to their different dispersal ability. Forest ecosystems appear to be dynamic entities able to cope with extreme weather events but, likely, only if they continue to occur in the future at the current rate.
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In the last decade, the pervasive question of climate change impacts on forests has revived investigations on intra-annual dynamics of wood formation, involving disciplines such as plant ecology, tree physiology and dendrochronology. This resulted in the creation of many research groups working on this topic worldwide and a rapid increase in the number of studies and publications. Wood-formation-monitoring studies are generally based on a common conceptual model describing xylem cell formation as the succession of four differentiation phases (cell division, cell enlargement, cell wall thickening and mature cells). They generally use the same sampling techniques, sample preparation methods and anatomical criteria to separate between differentiation zones and discriminate and count forming xylem cells, resulting in very similar raw data. However, the way these raw data are then processed, producing the elaborated data on which statistical analyses are performed, still remains quite specific to each individual study. Thereby, despite very similar raw data, wood-formation-monitoring studies yield results that are still quite difficult to compare. CAVIAR-an R package specifically dedicated to the verification, visualization and manipulation of wood-formation-monitoring data-can help to improve this situation. Initially, CAVIAR was built to provide efficient algorithms to compute critical dates of wood formation phenology for conifers growing in temperate and cold environments. Recently, we developed it further to check, display and process wood-formation-monitoring data. Thanks to new and upgraded functions, raw data can now be consistently verified, standardized and modelled (using logistic regressions and Gompertz functions), in order to describe wood phenology and intra-annual dynamics of tree-ring formation. We believe that CAVIAR will help strengthening the science of wood formation dynamics by effectively contributing to the standardization of its concepts and methods, making thereby possible the comparison between data and results from different studies.
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Beech is one of the most important forest tree species in Europe, hence possible adverse factors affecting its physiology and productivity can have strong ecological and economic impacts. In this context, four beech forests along a latitudinal gradient from southern Apennines to middle European lowlands were selected for chronological determinations of carbon isotope composition (δ13C) in tree-ring cellulose. The main objectives of this study were to assess (i) the effect of climate on the carbon signature of tree-ring cellulose (δ13C); (ii) the physiological response to recent CO2 concentration increment and to climatic variation; and (iii) the relationship between intrinsic water-use efficiency (iWUE, here the average long-term ratio of net photosynthesis to stomatal conductance) and growth of trees in different sites since 1950. Our results demonstrated that site climatic conditions peculiarly affect δ13C. In northern sites, a climatic control of summer precipitation and temperature on stomatal conductance was demonstrated by their opposite correlations with δ13C, negative and positive, respectively. Furthermore, an 'earliness effect' was suggested by a significant relationship between spring temperature and δ13C in the coldest sites and by a positive one between winter temperature and δ13C in the warmest ones. In all the study sites, during the maturity phase, a positive correlation between the increment of CO2 and iWUE was observed, due to an active response of trees to CO2 increment. This increment of CO2 was the main driver of the long term increasing trend of iWUE, resulting by an active response of trees to CO2 fertilization. Moreover, precipitation mostly influences positively and negatively the inter-annual variations of iWUE of the southernmost and northernmost sites, respectively. Overall, we observed a mean increment of 40% of iWUE. Moreover, the sensitivity of iWUE to the increase of CO2 was different between the northernmost and southernmost sites. Increasing iWUE was correlated to growth in the two sites during the release phase and we hypothesize a positive effect of silvicultural treatments.
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It has been known for a long time that drought intensity is a critical variable in determining water stress of Mediterranean tree species. However, not as much attention has been paid to other drought characteristics, for example the timing of the dry periods. We investigated the impact of the timing and intensity of extreme droughts on growing season length, growth and water-use efficiency of three tree species, Pinus nigra ssp. Salzmannii J.F. Arnold, Quercus ilex ssp. ballota (Desf.) Samp. and Quercus faginea Lam. coexisting in a continental Mediterranean ecosystem. Over the study period (2009–13), intense droughts were observed at annual and seasonal scales, particularly during 2011 and 2012. In 2012, an atypically dry winter and spring was followed by an intense summer drought. Quercus faginea growth was affected more by drought timing than by drought intensity, probably because of its winter-deciduous leaf habit. Pinus nigra showed a lower decrease in secondary growth than observed in the two Quercus species in extremely dry years. Resilience to extreme droughts was different among species, with Q. faginea showing poorer recovery of growth after very dry years. The highest intra- and inter-annual plasticity in water-use efficiency was observed in P. nigra, which maintained a more water-saving strategy. Our results revealed that the timing of extreme drought events can affect tree function to a larger extent than drought intensity, especially in deciduous species. Legacy effects of drought over months and years significantly strengthened the impact of drought timing and intensity on tree function.
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Understanding the dynamics of organic carbon mineralization is fundamental in forecasting biosphere to atmosphere net carbon ecosystem exchange (NEE). With this perspective, we developed 3D‐CMCC‐PSM, a new version of the hybrid process based model 3D‐CMCC FEM where also heterotrophic respiration (R h ) is explicitly simulated. The aim was to quantify NEE as a forward problem, by subtracting ecosystem respiration (R eco ) to gross primary productivity (GPP). To do so, we developed a simplification of the soil carbon dynamics routine proposed in the DNDC (DeNitrification‐DeComposition) computer simulation model. The method calculates decomposition as a function of soil moisture, temperature, state of the organic compartments, and relative abundance of microbial pools. Given the pulse dynamics of soil respiration, we introduced modifications in some of the principal constitutive relations involved in phenology and littering sub‐routines. We quantified the model structure‐related uncertainty in NEE, by running our training simulations over 1000 random parameter‐sets extracted from parameter distributions expected from literature. 3D‐CMCC‐PSM predictability was tested on independent time series for 6 Fluxnet sites. The model resulted in daily and monthly estimations highly consistent with the observed time series. It showed lower predictability in Mediterranean ecosystems, suggesting that it may need further improvements in addressing evapotranspiration and water dynamics.
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Key message European beech showed low resistance but high resilience in radial growth after an extreme late frost event. Site-specific growth reductions correlated with absolute minimum temperature in May. Abstract Late spring frost events occurring after the early leaf unfolding (“false spring”) can result in severe leaf damages in deciduous trees. With climate warming, such damages may occur more frequently due to an earlier start of the growing season. While affected, mature trees usually survive, but radial and height growth after the late frost has rarely been quantified in relation to the magnitude of the frost events. The effects of a severe late frost event in the early May 2011, following a warm spring and early bud break, was quantified for European beech (Fagus sylvatica L.) at 7 forest stands in Bavaria, Germany. Resistance and resilience of tree growth were quantified based on tree-ring widths of 135 trees. Resistance to the late frost event (comparing tree-ring width in the frost year with the previous 5 years) was on average reduced by 46%. Resistance was positively correlated with May minimum temperature at the study sites, indicating a relationship between growth reduction and frost severity. Partial least-square linear models based on monthly climate data (precipitation, temperature, potential evapotranspiration, and the Standardized Precipitation Evapotranspiration Index) could not explain the growth reduction in 2011, thereby providing evidence for the importance of frost damages on annual growth. F. sylvatica showed high resilience after the frost year, with tree-ring widths in the subsequent years being comparable to the previous years. This study suggests that frost events may strongly reduce growth of F. sylvatica in the event year, but that carry-over effects on the radial growth of subsequent years are not likely.
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This study evaluates the performances of the new version (v.5.1) of 3D-CMCC Forest Ecosystem Model (FEM) in simulating gross primary productivity (GPP), against eddy covariance GPP data for 10 FLUXNET forest sites across Europe. A new carbon allocation module, coupled with new both phenological and autotrophic respiration schemes, was implemented in this new daily version. Model ability in reproducing timing and magnitude of daily and monthly GPP fluctuations is validated at intra-annual and inter-annual scale, including extreme anomalous seasons. With the purpose to test the 3D-CMCC FEM applicability over Europe without a site-related calibration, the model has been deliberately parametrized with a single set of species-specific parametrizations for each forest ecosys- tem. The model consistently reproduces both in timing and in magnitude daily and monthly GPP variability across all sites, with the exception of the two Mediterranean sites. We find that 3D-CMCC FEM tends to better simulate the timing of inter-annual anomalies than their magnitude within measurements’ uncertainty. In six of eight sites where data are available, the model well reproduces the 2003 summer drought event. Finally, for three sites we evaluate whether a more accurate representation of forest structural characteristics (i.e. cohorts, forest layers) and species composition can improve model results. In two of the three sites results reveal that model slightly increases its performances although, statistically speaking, not in a relevant way.
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Stem CO2 efflux (ES ) plays an important role in the carbon balance of forest ecosystems. However, its primary controls at the global scale are poorly understood and observation-based global estimates are lacking. We synthesized data from 121 published studies across global forest ecosystems and examined the relationships between annual ES and biotic and abiotic factors at individual, biome, and global scales, and developed a global gridded estimate of annual ES . We tested the following hypotheses: (1) Leaf area index (LAI) will be highly correlated with annual ES at biome and global scales; (2) There will be parallel patterns in stem and root CO2 effluxes (RA ) in all forests; (3) Annual ES will decline with forest age; and (4) LAI coupled with mean annual temperature (MAT) and mean annual precipitation (MAP) will be sufficient to predict annual ES across forests in different regions. Positive linear relationships were found between ES and LAI, as well as gross primary production (GPP), net primary production (NPP), wood NPP, soil CO2 efflux (RS ) and RA . Annual ES was correlated with RA in temperate forests after controlling for GPP and MAT, suggesting other additional factors contributed to the relationship. Annual ES tended to decrease with stand age. Leaf area index, MAT and MAP predicted 74% of variation in ES at global scales. Our statistical model estimated a global annual ES of 6.7 ± 1.1 Pg C yr(-1) over the period of 2000-2012 with little interannual variability. Modelled mean annual ES was 89 ± 53, 248 ± 127 and 506 ± 262 g C m(-2) yr(-1) for boreal, temperate, and tropical forests, respectively. We recommend that future studies report ES at a standardized constant temperature, incorporate more manipulative treatments, such as fertilization and drought, and whenever possible, simultaneously measure both aboveground and belowground CO2 fluxes. This article is protected by copyright. All rights reserved.
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Wood is the main terrestrial biotic reservoir for long-term carbon sequestration, and its formation in trees consumes around 15% of anthropogenic carbon dioxide emissions each year. However, the seasonal dynamics of woody biomass production cannot be quantified from eddy covariance or satellite observations. As such, our understanding of this key carbon cycle component, and its sensitivity to climate, remains limited. Here, we present high-resolution cellular based measurements of wood formation dynamics in three coniferous forest sites in northeastern France, performed over a period of 3 years. We show that stem woody biomass production lags behind stem-girth increase by over 1 month. We also analyse more general phenological observations of xylem tissue formation in Northern Hemisphere forests and find similar time lags in boreal, temperate, subalpine and Mediterranean forests. These time lags question the extension of the equivalence between stem size increase and woody biomass production to intra-annual time scales. They also suggest that these two growth processes exhibit differential sensitivities to local environmental conditions. Indeed, in the well-watered French sites the seasonal dynamics of stem-girth increase matched the photoperiod cycle, whereas those of woody biomass production closely followed the seasonal course of temperature. We suggest that forecasted changes in the annual cycle of climatic factors may shift the phase timing of stem size increase and woody biomass production in the future.
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The role of forest ecosystems in the carbon cycle is a central problem of global ecology and has important, practical implications from the points of view of global change and production of woody raw material. Furthermore, in forest ecosystems the bio-geochemical cycles of carbon and mineral nutrients, particularly nitrogen, are intimately related because foliage nutrient content strongly controls carbon assimilation by forests and, therefore, their primary productivity (Waring and Running 1998).
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Extreme droughts, heat waves, frosts, precipitation, wind storms and other climate extremes may impact the structure, composition, and functioning of terrestrial ecosystems, and thus carbon cycling and its feedbacks to the climate system. Yet, the interconnected avenues through which climate extremes drive ecological and physiological processes and alter the carbon balance are poorly understood. Here we review literature on carbon-cycle relevant responses of ecosystems to extreme climatic events. Given that impacts of climate extremes are considered disturbances, we assume the respective general disturbance-induced mechanisms and processes to also operate in an extreme context. The paucity of well-defined studies currently renders a quantitative meta-analysis impossible, but permits us to develop a deductive framework for identifying the main mechanisms (and coupling thereof) through which climate extremes may act on the carbon cycle. We find that ecosystem responses can exceed the duration of the climate impacts via lagged effects on the carbon cycle. The expected regional impacts of future climate extremes will depend on changes in the probability and severity of their occurrence, on the compound effects and timing of different climate extremes, and on the vulnerability of each land-cover type modulated by management. Though processes and sensitivities differ among biomes, based on expert opinion we expect forests to exhibit the largest net effect of extremes due to their large carbon pools and fluxes, potentially large indirect and lagged impacts, and long recovery time to re-gain previous stocks. At the global scale, we presume that droughts have the strongest and most widespread effects on terrestrial carbon cycling. Comparing impacts of climate extremes identified via remote sensing vs. ground-based observational case studies reveals that many regions in the (sub-)tropics are understudied. Hence, regional investigations are needed to allow a global upscaling of the impacts of climate extremes on global carbon-climate feedbacks. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
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The temporal variability of ecosystem respiration (RECO) has been reported to have important effects on the temporal variability of net ecosystem exchange, the net amount of carbon exchanged between an ecosystem and the atmosphere. However, our understanding of ecosystem respiration is rather limited compared with photosynthesis or gross primary productivity, particularly in Mediterranean montane ecosystems. In order to investigate how environmental variables and forest structure (tree classes) affect different respiration components and RECO in a Mediterranean beech forest, we measured soil, stem and leaf CO2 efflux rates with dynamic chambers and RECO by the eddy-covariance technique over 1 year (2007-2008). Ecosystem respiration showed marked seasonal variation, with the highest rates in spring and autumn and the lowest in summer. We found that the soil respiration (SR) was mainly controlled by soil water content below a threshold value of 0.2 m(3) m(-3), above which the soil temperature explained temporal variation in SR. Stem CO2 effluxes were influenced by air temperature and difference between tree classes with higher rates measured in dominant trees than in co-dominant ones. Leaf respiration (LR) varied significantly between the two canopy layers considered. Non-structural carbohydrates were a very good predictor of LR variability. We used these measurements to scale up respiration components to ecosystem respiration for the whole canopy and obtained cumulative amounts of carbon losses over the year. Based on the up-scaled chamber measurements, the relative contributions of soil, stem and leaves to the total annual CO2 efflux were: 56, 8 and 36%, respectively. These results confirm that SR is the main contributor of ecosystem respiration and provided an insight on the driving factors of respiration in Mediterranean montane beech forests.
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Seasonal and inter-annual dynamics of growth, non-structural carbohydrates (NSC) and carbon isotope composition (δ(13)C) of NSC were studied in a beech forest of Central Italy over a 2-year period characterized by different environmental conditions. The net C assimilated by forest trees was mainly used to sustain growth early in the season and to accumulate storage carbohydrates in trunk and root wood in the later part of the season, before leaf shedding. Growth and NSC concentration dynamics were only slightly affected by the reduced soil water content (SWC) during the drier year. Conversely, the carbon isotope analysis on NSC revealed seasonal and inter-annual variations of photosynthetic and post-carboxylation fractionation processes, with a significant increase in δ(13)C of wood and leaf soluble sugars in the drier summer year than in the wetter one. The highly significant correlation between δ(13)C of leaf soluble sugars and SWC suggests a decrease of the canopy C isotope discrimination and, hence, an increased water-use efficiency with decreasing soil water availability. This may be a relevant trait for maintaining an acceptable plant water status and a relatively high C sink capacity during dry seasonal periods. Our results suggest a short- to medium-term homeostatic response of the Collelongo beech stand to variations in water availability and solar radiation, indicating that this Mediterranean forest was able to adjust carbon-water balance in order to prevent C depletion and to sustain plant growth and reserve accumulation during relatively dry seasons.
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The temperature coefficient, Q 10 (fractional change in rate with a 10°C increase in temperature) describes the temperature sensitivity of soils, roots, and stems, as well as their possible performance in global warming processes. It is also a necessary parameter for the estimation of total CO2 efflux from each element. A number of studies have focused on Q 10 values to date; however, their conclusions are not universal and do not always agree. A review of these reported Q 10 values therefore becomes necessary and important for a global understanding of the temperature sensitivity of different forest types and elements. The aims of our present paper are, first, to find the frequency distribution pattern of soils, roots, and stems (branches) and compare their temperature sensitivity; then, to find the Q 10 differences between conifer and deciduous tree species and the effect of methodology on Q 10 values; finally we want to give a perspective on future Q 10-related studies. We found that most Q 10 values of each element were concentrated in a relatively narrow range despite a total data distribution over quite a wide range. For soil respiration, the median Q 10 value was 2.74 and the center of the frequency distribution was between 2.0 and 2.5 with a percentage of 23%. Most of the data (>80%) were within the range from 1.0 to 4.0. The median Q 10 value for root respiration was 2.40 and the center of the frequency distribution was from 2.5 to 3.0 with a percentage of 33%. Most of the results (>80%) ranged from 1.0 to 3.0. For stem respiration, the median Q 10 value was 1.91 and the frequency distribution was concentrated between 1.5 and 2.0. Over 90% of the data ranged from 1.0 to 3.0. Obvious differences in Q 10 value were found between different elements, stem < root < soil including root < soil excluding root. The differences between woody organisms of stems, roots, and soils excluding roots were statistically significant (p0.10). CO2 analytical methods (soda lime absorption method, IRGA (Infra-read gas analysis), and chromatograph analysis) and root separation methods (excised root and trenched box) slightly affected the Q 10 values of soil and root respiration (p>0.10), but an in vitro measurement of stem respiration yielded a significantly higher Q 10 value than an in vivo method (pQ 10 values of non-photosynthetic organisms stayed within a relatively conservative range, considerable variation between and within elements were still detectable. Accordingly, attention should be paid to the quantitative estimation of total CO2 efflux by Q 10-related models. In future studies, the biochemical factors and the environmental and biological factors controlling respiration should be emphasized for precise estimation of total CO2 efflux. The difficulty is how to clarify the underlying mechanism for fluctuations of Q 10 values for one specific habitat and element (e.g. temperature acclimation or adaptation of Q 10 values) and then allow the Q 10 values to be more conservative for representation of temperature sensitivity in global warming processes.
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Late-spring frosts (LSFs) affect the performance of plants and animals across the world’s temperate and boreal zones, but despite their ecological and economic impact on agriculture and forestry, the geographic distribution and evolutionary impact of these frost events are poorly understood. Here, we analyze LSFs between 1959 and 2017 and the resistance strategies of Northern Hemisphere woody species to infer trees’ adaptations for minimizing frost damage to their leaves and to forecast forest vulnerability under the ongoing changes in frost frequencies. Trait values on leaf-out and leaf-freezing resistance come from up to 1,500 temperate and boreal woody species cultivated in common gardens. We find that areas in which LSFs are common, such as eastern North America, harbor tree species with cautious (late-leafing) leaf-out strategies. Areas in which LSFs used to be unlikely, such as broad-leaved forests and shrublands in Europe and Asia, instead harbor opportunistic tree species (quickly reacting to warming air temperatures). LSFs in the latter regions are currently increasing, and given species’ innate resistance strategies, we estimate that ∼35% of the European and ∼26% of the Asian temperate forest area, but only ∼10% of the North American, will experience increasing late-frost damage in the future. Our findings reveal region-specific changes in the spring-frost risk that can inform decision-making in land management, forestry, agriculture, and insurance policy. – https://www.dora.lib4ri.ch/wsl/islandora/object/wsl:23373 – https://doi.org/10.1073/pnas.1920816117
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A substantial portion of locally respired CO2 in stems can be assimilated by chloroplast‐containing tissues. Woody tissue photosynthesis (Pwt) therefore plays a major role in the stem carbon balance. To study the impact of Pwt on stem carbon cycling along a gradient of water availability, stem CO2‐efflux (EA), xylem CO2‐concentration ([CO2]) and xylem water potential (Ψxylem) were measured in 4‐year‐old Populus tremula L. trees exposed to drought‐stress and different regimes of light‐exclusion of woody tissues. Under well‐watered conditions, local Pwt decreased EA up to 30 %. Axial CO2‐diffusion (Dax) induced by distant Pwt caused an additional decrease in EA of up to 25 % and limited xylem [CO2] build‐up. Under drought stress, absolute decreases in EA driven by Pwt remained stable, denoting that Pwt was not affected by drought. At the end of the dry period, when transpiration was low, local Pwt and Dax offset 20 and 10 % of stem respiration on a daily basis, respectively. These results highlight (i) the importance of Pwt for an adequate interpretation of EA measurements and (ii) homeostatic Pwt along a drought stress gradient, which might play a crucial role to fuel stem metabolism when leaf carbon uptake and phloem transport are limited. Woody tissue photosynthesis remains constant during drought, highlighting its importance as reliable carbon source when leaf assimilation is compromised. In addition, stem CO2 efflux was substantially lowered by local woody tissue photosynthesis, altering its temperature sensitivity. This article is protected by copyright. All rights reserved.
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This article is a Commentary on Salomón et al. (2020), 225: 2214–2230.
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Two simplifying hypotheses have been proposed for whole‐plant respiration. One links respiration to photosynthesis; the other to biomass. Using a first‐principles carbon balance model with a prescribed live woody biomass turnover, applied at a forest research site where multidecadal measurements are available for comparison, we show that if turnover is fast the accumulation of respiring biomass is low and respiration depends primarily on photosynthesis; while if turnover is slow the accumulation of respiring biomass is high and respiration depends primarily on biomass. But the first scenario is inconsistent with evidence for substantial carryover of fixed carbon between years, while the second implies far too great an increase in respiration during stand development – leading to depleted carbohydrate reserves and an unrealistically high mortality risk. These two mutually incompatible hypotheses are thus both incorrect. Respiration is not linearly related either to photosynthesis or to biomass, but it is more strongly controlled by recent photosynthates (and reserve availability) than by total biomass.
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Climate warming has lengthened the growing season by advancing leaf unfolding in many temperate tree species. However, an earlier leaf unfolding increases also the risk of frost damage in spring which may reduce tree radial growth. In equatorward populations of temperate tree species, both late frosts and summer droughts impose two constraints to tree growth, but their effects on growth are understudied. We used a tree-ring network of 71 forests to evaluate the potential influence of late frosts and summer droughts on growth in two tree species that reach their southern distribution limits in northeastern Spain: the deciduous European beech (Fagus syl-vatica L.) and the evergreen Silver fir (Abies alba Mill). The occurrence of late frost events and summer drought was quantified by using a high-resolution daily temperature and precipitation dataset considering the period 1950-2012. Late frosts were defined as days with average temperature below 0 °C in the site-specific frost-free period, whereas drought was quantified using the 18 month-long August Standardized Precipitation Evapotranspiration Index (SPEI). The growth of European beech and Silver fir was reduced by the occurrence of both late frost events and summer drought. However, we did not find a significant interaction on growth of these two climate extremes. Beech was more negatively impacted by late frosts, whereas Silver fir was more impacted by summer drought. Further studies could use remote-sensing information or in situ phenological records to refine our frost index and better elucidate how late frosts affect growth, whether they interact with drought to constrain growth, and how resilience mechanisms related to post-frost refoliation operate in beech.
Article
Late frost can destroy the photosynthetic apparatus of trees. We hypothesized that this can alter the normal cyclic dynamics of C‐reserves in the wood. We measured soluble sugar concentrations and radiocarbon signatures (Δ14C) of soluble non‐structural carbon (NSC) in woody tissues sampled from a Mediterranean beech forest that was completely defoliated by an exceptional late frost in 2016. We used the bomb radiocarbon approach to estimate the time elapsed since fixation of mobilized soluble sugars. During the leafless period after the frost event, soluble sugar concentrations declined sharply while Δ14C of NSC increased. This can be explained by the lack of fresh assimilate supply and a mobilization of C from reserve pools. Soluble NSC became increasingly older during the leafless period, with a maximum average age of 5 years from samples collected 27 days before canopy recovery. Following leaf re‐growth, soluble sugar concentrations increased and Δ14C of soluble NSC decreased, indicating the allocation of new assimilates to the stem soluble sugars pool. These data highlight that beech trees rapidly mobilize reserve C to survive strong source/sink imbalances, e.g. due to late frost, and show that NSC is a key trait for tree resilience under global change. This article is protected by copyright. All rights reserved.
Article
Given the importance of carbon allocation for plant performance and fitness, it is expected that competition and abiotic stress influence respiratory costs associated to stem wood biomass production and maintenance. In this study, stem respiration (R) was measured together with stem diameter increment in adult trees of eight co-occurring species in a sub-Mediterranean forest stand for two years. We estimated growth R (Rg), maintenance R (Rm) and the growth respiration coefficient (GRC) using two gas exchange methods: 1) estimating Rg as the product of growth and GRC (then Rm as R minus Rg) and 2) estimating Rm from temperature dependent kinetics of basal Rm at the dormant season (then Rg as R minus Rm). In both cases, stem basal-area growth rates governed intra-annual variation in R, Rg and Rm. Maximum annual Rm occurred slightly before or after maximum Rg. The mean contribution of Rm to R during the growing season ranged from 56 to 88% across species using method 1 and 23 to 66% using method 2. An analysis accounting for the phylogenetic distance among species indicated that more shade-tolerant, faster growing species exhibited higher Rm and Rg than less shade-tolerant, slower growing ones, suggesting a balance between carbon supply and demand mediated by growth. However, GRC was not related to species growth rate, wood density, or drought- and shade-tolerance across the surveyed species, nor across 27 tree species for which GRC was compiled. GRC estimates based on wood chemical analysis were lower (0.19) than those based on gas exchange methods (0.35). These results give partial support to the hypothesis that wood production and maintenance costs are related to species ecology, and highlight the divergence of respiratory parameters widely used in plant models according to the methodological approach applied to derive them.
Article
Late spring frost plays a major role in the structure and function of forest ecosystems with potential consequences on species distribution at both local and regional scales. Paradoxically, in a warmer world the incidence and impact of frost is increasing because of earlier leaf unfolding and flowering as a response to warmer temperatures. In this regard, European Beech (Fagus sylvatica L.), a native tree species widely distributed in European forests, is considered particularly sensitive to changes in spring temperature regimes associated with climate change and thus especially subject to the risk of frost damage. Although several studies concerning F. sylvatica frost damage have been conducted in northern and central Europe, no extensive studies are available for the southern part of its range, i.e. central and southern Italy as well as Greece. In this paper the effect of a late spring frost occurring at the end of April 2016 is extensively documented with high spatial detail all along the Apennine Chain through satellite image data. Three different remote-sensing greenness indexes, namely the normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), and the greenness index (GI) derived from Landsat-8 satellite images acquired from May to July in the years 2014, 2015, and 2016 at a spatial resolution of 30 m, were used to gauge the spatial response of common beech forests to this late frost event with relation to latitude, altitude and slope exposure. Frost damage was evaluated as a difference (Δ) of NDVI, GI and EVI between the mean of years 2014 and 2015 (i.e. MRY, mean of reference years), and 2016 (i.e. FEY, frost reference year). The three satellite remote-sensing indexes were efficient at detecting leaf damage with detailed spatial resolution and proved consistent with one another. The greatest damage occurred in the middle altitudinal range between 1500 and 1700 m a.s.l. with a decreasing trend toward both lower and higher elevations due to warmer temperatures below, and delayed phe-nology above. Exposure also influenced frost injury, with south-facing slopes of the mountain more damaged than the north. This difference was due to earlier spring leaf phenology of southern beech trees in response to a greater heat sum in the warm weeks preceding. Less damage in the northern Apennines is consistent with the spatial extent of minimum freezing temperatures. To sum up, frost damage is strongly related to site-specific conditions, i.e. on the one hand to minimum temperatures, and on the other to the phenological stage of the trees involving both altitude and exposure. Hence focusing on detailed sub-regional studies can be helpful for predicting future consequences of climate change on forests.
Article
To quantify stem respiration (RS) under elevated CO2 (eCO2), stem CO2 efflux (EA) and CO2 flux through the xylem (FT) should be accounted for, because part of respired CO2 is transported upwards with the sap solution. However, previous studies have used EA as a proxy of RS, which could lead to equivocal conclusions. Here, to test the effect of eCO2 on RS, both EA and FT were measured in a free‐air CO2 enrichment experiment located in mature Eucalyptus native forest. Drought stress substantially reduced EA and RS, which were unaffected by eCO2, likely as a consequence of its neutral effect on stem growth in this phosphorus‐limited site. However, xylem CO2 concentration measured near the stem base was higher under eCO2, and decreased along the stem resulting in a negative contribution of FT to RS, whereas the contribution of FT to RS under ambient CO2 was positive. Negative FT indicates net efflux of CO2 respired below the monitored stem segment, likely coming from the roots. Our results highlight the role of nutrient availability on the dependency of RS on eCO2 and suggest stimulated root respiration under eCO2 that may shift vertical gradients in xylem [CO2] confounding the interpretation of EA measurements.
Article
The phenology of wood formation is a critical process to consider for predicting how trees from the temperate and boreal zones may react to climate change. Compared to leaf phenology, however, the determinism of wood phenology is still poorly known. Here, we compared for the first time three alternative ecophysiological model classes (threshold models, heat‐sum models and chilling‐influenced heat‐sum models) and an empirical model in their ability to predict the starting date of xylem cell enlargement in spring, for four major Northern Hemisphere conifers (Larix decidua, Pinus sylvestris, Picea abies and Picea mariana). We fitted models with Bayesian inference to wood phenological data collected for 220 site‐years over Europe and Canada. The chilling‐influenced heat‐sum model received most support for all the four studied species, predicting validation data with a 7.7‐day error, which is within one‐day of the observed data resolution. We conclude that both chilling and forcing temperatures determine the onset of wood formation in Northern Hemisphere conifers. Importantly, the chilling‐influenced heat‐sum model showed virtually no spatial bias whichever the species, despite the large environmental gradients considered. This suggests that the spring onset of wood formation is far less affected by local adaptation than by environmentally‐driven plasticity. In a context of climate change, we therefore expect rising winter‐spring temperature to exert ambivalent effects on the spring onset of wood formation, tending to hasten it through the accumulation of forcing temperature, but imposing a higher forcing‐temperature requirement through the lower accumulation of chilling. This article is protected by copyright. All rights reserved.
Article
Key message A remote sensing-based approach was implemented to detect the effect of a late spring frost on beech forests in the Mediterranean mountain region. The analysis of spatio-temporal variability of frost effects on normalised difference vegetation index (NDVI) highlighted the distribution of the canopy damage across the forest according to geomorphic factors such as slope, aspect, and altitude. Context Increased intensity and frequency of extreme temperatures such as late spring frosts and heat waves represent the main drivers affecting forest ecosystem structure and composition in the Mediterranean region. Aims The main objective of this study was to evaluate the effects of a late spring frost disturbance, which occurred during spring 2016 in southern Italy, through the assessment of the spatial pattern of the damage to the beech forest canopy associated with the peak decrease in normalised difference vegetation index (NDVI), and the analysis of the NDVI temporal recovery after this frost disturbance. Methods The forest areas affected by frost were detected through the NDVI differencing technique based on Landsat 8 (OLI/TIRS) imagery time series. The influence of local geomorphic factors (i.e., aspect, elevation, and slope) on forest NDVI patterns was assessed by means of a generalized additive model (GAM). Results A rather counterintuitive NDVI patterns emerged according to the forest exposition, with NDVI significantly higher on the north facing areas than the southerly ones. The main canopy damage occurred at about 1250 m and reached up to 1500 m asl, representing the altitudinal range affected by the frost disturbance. Finally, the full canopy recovery occurred within 3 months of the frost event. Conclusion The analysis of seasonal Landsat 8 image time series related to local geomorphic factors, such as aspect, slope, and altitude, and plant phenology on a frost event date, contributed to highlight the NDVI spatio-temporal variation and canopy recovery of a Mediterranean mountain beech forest.
Article
Current methods to study relations between stem respiration and stem growth have been hampered by problems in quantifying stem growth from dendrometer measurements, particularly on a daily time scale. This is mainly due to the water-related influences within these measurements that mask growth. A previously published model was used to remove water-related influences from measured radial stem variations to reveal a daily radial growth signal (ΔˆGm). We analysed the intra- and inter-annual relations between ΔˆGm and estimated growth respiration rates (Rg) on a daily scale for 5 years. Results showed that Rg was weakly correlated to stem growth prior to tracheid formation, but was significant during the early summer. In the late summer, the correlation decreased slightly relative to the early summer. A 1-day time lag was found of ΔˆGm preceding Rg. Using wavelet analysis and measurements from eddy covariance, it was found that Rg followed gross primary production and temperature with a 2 and 3 h time lag, respectively.This study shows that further in-depth analysis of in-situ growth and growth respiration dynamics is greatly needed, with a focus on cellular respiration at specific developmental stages, its woody tissue costs and linkages to source-sink processes and environmental drivers.
Article
We investigated the dynamics of xylem differentiation processes and vessel characteristics in Fagus sylvatica L. to evaluate the plasticity of xylem structures under different environmental conditions. In 2008–10, analyses were performed on microcores collected weekly from two temperate sites: Menina planina (1200 m above sea level (a.s.l.)) and Panska reka (400 m a.s.l.). The duration between the onset and end of major cell differentiation steps and vessel characteristics (i.e., density, VD; mean diameter, MVD; mean area, MVA; and theoretic conductivity area, TCA) were analysed in the first and last quarters of the xylem rings, also in respect of local weather conditions (precipitation, temperature). Although the onset, duration and end of xylem formation phases differed between the two sites, the time spans between the successive wood formation phases were similar. Significant differences in MVD, MVA and TCA values were found between the first and last quarters of xylem increment, regardless of the site and year. Vessel density, on the other hand, depended on xylem-ring width and differed significantly between the sites, being about 30% higher at the high elevation site, in beech trees with 54% narrower xylem rings. Vessel density in the first quarter of the xylem ring showed a positive correlation with the onset of cell expansion, whereas a negative correlation of VD with the cessation of cell production was found in the last quarter of xylem increment. This may be explained by year-to-year differences in the timing of cambial reactivation and leaf development, which effect hormonal regulation of radial growth. No significant linkage between intra-annual weather conditions and conduit characteristics was found. It can thus be presumed that precipitation is not a limiting factor for xylem growth and cell differentiation in beech at the two temperate study sites and sites across Europe with similar weather conditions.
Book
The storage of carbon in forest ecosystems has received special attention in the Kyoto protocol of the Climate Convention, which attempts to equilibrate fossil fuel emissions with biological sinks. This volume quantifies carbon storage in managed forest ecosystems not only in biomass, but also in all soil compartments. It investigates the interaction between the carbon and nitrogen cycles by working along a north-south transect through Europe which starts in northern Sweden, passes through a N-deposition maximum in central Europe and ends in Italy. Surprisingly, C storage in soils increases with N deposition; in addition, not young reforestations, but old growth forests have the highest rate of carbon sequestration. For the first time biogeochemical processes are linked to biodiversity on a large geographic scale and with special focus on soil organisms. The enclosed CD-ROM provides a complete database of all flux, storage and species observations for modellers.
Article
In common beech forests the most damaging frosts are those that occur at the end of spring. At that time the fresh new leaves are at a vulnerable stage and risk to be readily killed by the freezing temperatures. The ability to identify late spring frost spatial dynamics is a key issue for understanding forest patterns and processes linked to such extreme event. The aim of this study is to detect, map and quantify the vegetation anomalies that occurred in the mono-specific beech forest of the Lazio, Abruzzo and Molise National Park (Italy) after an exceptional spring frost recorded on the 25th of April 2016. Results showed that, beech forests at lower elevations that had an early greening process were subject to spring frost damage (SFD pixels) and their productivity performance strongly decreased with respect to the previous 15 years; to the contrary the beech forests located at higher elevations did not suffer the spring frost effects (NSFD pixels) thanks to their delayed leaf unfolding phase. The duration of the effects of freezing stress for the SFD pixels was about two months, until the end of June, confirmed by Net Ecosystem Exchange measurements. This greening hiatus led to an average 14% loss of productivity compared to the previous 15 years. Elevation had a significant role on the probability of occurrence of SFD pixels. Productivity loss in SFD pixels was more severe at elevations in the range 1500–1700 m, on steeply terrains and North aspects. This study represents a step forward the systematic use of automated techniques to study areas subject to stress or anomalies from multitemporal satellite imagery and to identify break points and recovery of the greening process.
Article
Daytime decreases in temperature-normalised stem CO2 efflux (EA_D ) are commonly ascribed to internal transport of respired CO2 (FT ) or to an attenuated respiratory activity due to lowered turgor pressure. The two are difficult to separate as they are simultaneously driven by sap flow dynamics. To achieve combined gradients in turgor pressure and FT , sap flow rates in poplar trees were manipulated through severe defoliation, severe drought, moderate defoliation and moderate drought. Turgor pressure was mechanistically modelled using measurements of sap flow, stem diameter variation, and soil and stem water potential. A mass balance approach considering internal and external CO2 fluxes was applied to estimate FT . Under well-watered control conditions, both turgor pressure and sap flow, as a proxy of FT , were reliable predictors of EA_D . After tree manipulation, only turgor pressure was a robust predictor of EA_D . Moreover, FT accounted for < 15% of EA_D . Our results suggest that daytime reductions in turgor pressure and associated constrained growth are the main cause of EA_D in young poplar trees. Turgor pressure is determined by both carbohydrate supply and water availability, and should be considered to improve our widely used but inaccurate temperature-based predictions of woody tissue respiration in global models.
Article
Winters and early springs are predicted to become warmer in temperate climates under continued global warming, which in turn is expected to promote earlier plant development. By contrast, there is no consensus about the changes in the occurrence and severity of late spring frosts. If the frequency and severity of late spring frosts remain unchanged in the future or change less than spring phenology of plants does, vulnerable plant organs (dehardened buds, young leaves, flowers or young fruits) may be more exposed to frost damage. Here we analyzed long-term temperature data from the period 1975–2016 in 50 locations in Switzerland and used different phenological models calibrated with long-term series of the flowering and leaf-out timing of two fruit trees (apple and cherry) and two forest trees (Norway spruce and European beech) to test whether the risk of frost damage has increased during this period. Overall, despite the substantial increase in temperature during the study period, the risk of frost damage was not reduced because spring phenology has advanced at a faster rate than the date of the last spring frost. In contrast, we found that the risk of frost exposure and subsequent potential damage has increased for all four species at the vast majority of stations located at elevations higher than 800 m while remaining unchanged at lower elevations. The different trends between lower and higher elevations are due to the date of the last spring frost moving less at higher altitudes than at lower altitudes, combined with stronger phenological shifts at higher elevations. This latter trend likely results from a stronger warming during late compared to earlier spring and from the increasing role of other limiting factors at lower elevations (chilling and photoperiod). Our results suggest that frost risk needs to be considered carefully when promoting the introduction of new varieties of fruit trees or exotic forest tree species adapted to warmer and drier climates or when considering new plantations at higher elevations.
Article
Extreme climate events are of key importance for forest ecosystems. However, both the inherent infrequency, stochasticity and multiplicity of extreme climate events, and the array of biological responses, challenges investigations. To cope with the long life cycle of trees and the paucity of the extreme events themselves, our inferences should be based on long-term observations. In this context, tree rings and the related xylem anatomical traits represent promising sources of information, due to the wide time perspective and quality of the information they can provide. Here we test, on two high-elevation conifers (Larix decidua and Picea abies sampled at 2100 m a.s.l. in the Eastern Alps), the associations among temperature extremes during the growing season and xylem anatomical traits, specifically the number of cells per ring (CN), cell wall thickness (CWT) and cell diameter (CD). To better track the effect of extreme events over the growing season, tree rings were partitioned in 10 sectors. Climate variability has been reconstructed, for 1800-2011 at monthly resolution and for 1926-2011 at daily resolution, by exploiting the excellent availability of very long and high quality instrumental records available for the surrounding area, and taking into account the relationship between meteorological variables and site topographical settings. Summer temperature influenced anatomical traits of both species, and tree-ring anatomical profiles resulted as being associated to temperature extremes. Most of the extreme values in anatomical traits occurred with warm (positive extremes) or cold (negative) conditions. However, 0% - 34% of occurrences did not match a temperature extreme event. Specifically, CWT and CN extremes were more clearly associated to climate than CD, which presented a bias to track cold extremes. Dendroanatomical analysis, coupled to high-quality daily-resolved climate records, seems a promising approach to study the effects of extreme events on trees, but further investigations are needed to improve our comprehension of the critical role of such elusive events in forest ecosystems.
Article
Understanding whether tree growth is limited by carbon gain (source limitation) or by the direct effect of environmental factors such as water deficit or temperature (sink limitation) is crucial for improving projections of the effects of climate change on forest productivity. We studied the relationships between tree basal area (BA) variations, eddy covariance carbon fluxes, predawn water potential (Ψpd ) and temperature at different timescales using an 8-yr dataset and a rainfall exclusion experiment in a Quercus ilex Mediterranean coppice. At the daily timescale, during periods of low temperature (< 5°C) and high water deficit (< -1.1 MPa), gross primary productivity and net ecosystem productivity remained positive whereas the stem increment was nil. Thus, stem increment appeared limited by drought and temperature rather than by carbon input. Annual growth was accurately predicted by the duration of BA increment during spring (Δtt0-t1 ). The onset of growth (t0 ) was related to winter temperatures and the summer interruption of growth (t1 ) to a threshold Ψpd value of -1.1 MPa. We suggest that using environmental drivers (i.e. drought and temperature) to predict stem growth phenology can contribute to an improvement in vegetation models and may change the current projections of Mediterranean forest productivity under climate change scenarios. © 2015 CNRS-ADEME New Phytologist © 2015 New Phytologist Trust.
Article
We investigated the anatomical structure of phloem and xylem growth rings as well as the dormant cambium in relation to vitality in 81 adult silver fir trees (Abies alba Mill.). Specifically, we investigated the number of cells produced in the current phloem growth ring (PR), xylem growth ring (XR) and their ratio, the number of cells in the dormant cambium (CC), and the structure of the PR, which included characterisation of the early phloem (EP), the late phloem (LP), and the presence, absence, and continuity of tangential bands of axial parenchyma (AP). EP was relatively stable with respect to number and types of cells as PR width changed, but LP was quite variable. The CC of more vital trees produced more xylem than phloem cells. The ratio of XR to PR number decreased with decreasing vitality of trees and in the most severely affected trees (4% of the study group), more cells were formed in the PR than in the XR. The number of cells in phloem, xylem and dormant cambium is positively correlated. The use of width and structure of phloem and the ratios be-tween PR, XR and CC can provide information on tree conditions and, consequently, can be a useful tool for forest management.
Article
There is recent clear evidence that an important fraction of root-respired CO2 is transported upward in the transpiration stream in tree stems rather than fluxing to the soil. In this study, we aimed to quantify the contribution of root-respired CO2 to both soil CO2 efflux and xylem CO2 transport by manipulating the autotrophic component of belowground respiration. We compared soil CO2 efflux and the flux of root-respired CO2 transported in the transpiration stream in girdled and nongirdled 9-yr-old oak trees (Quercus robur) to assess the impact of a change in the autotrophic component of belowground respiration on both CO2 fluxes. Stem girdling decreased xylem CO2 concentration, indicating that belowground respiration contributes to the aboveground transport of internal CO2. Girdling also decreased soil CO2 efflux. These results confirmed that root respiration contributes to xylem CO2 transport and that failure to account for this flux results in inaccurate estimates of belowground respiration when efflux-based methods are used. This research adds to the growing body of evidence that efflux-based measurements of belowground respiration underestimate autotrophic contributions.
Article
Xylem and phloem formation, as well as cambium and leaf phenology, and their relation to weather factors, were studied from 2008 to 2010 in beech (Fagus sylvatica L.) trees from two sites in Slovenia with different elevations and weather conditions: Panˇska reka (PA) (400 m a.s.l.) and Menina planina (ME)(1200 m a.s.l.). During the vegetation periods leaf phenology and dynamics of xylem as well as phloem formation were monitored. Leaf unfolding, onset of cambial cell production and increased number ofactive phloem cells occurred simultaneously for each site: in mid-April at PA and in the first week ofMay at ME; all three events were positively related to temperature in the first part of the growth season. Maximum rate of xylem cell production occurred at PA from 20 May until 9 June and about two weekslater at ME. Maximum phloem cell production occurred more than 1 month earlier at both sites. Cessation of xylem and phloem cell production was observed at PA around 19 August and around 10 days earlier at ME. Differentiation of the last-formed xylem cells was concluded by mid-September at both plots. The differences in xylem and phloem formation phases were smaller in the second part of the growth season and can be ascribed to similar temperatures at both plots. Year to year variability of the observed phases was not statistically significant but the differences between the sites were. Phloem formation seems to be less subjected to fluctuations in environmental conditions since the growth ring widthswere comparable at both sites. Temperature and growing degree days before the occurrence of mostof the observed phenological phases significantly differed between the sites. This demonstrates that the observed differences in xylem and phloem formation between the sites can be attributed to highintra-specific plasticity of beech.
Article
Past carbon (C) storage trends were estimated using dendroecological methods in a beech chronosequence in central Germany. Raw-ring-width chronologies, sensitivity curves, and carbon uptake trends were developed for 70-, 110-, and 150-year-old (S70, S110, and S150), even-aged stands. Ecosystem C stock and net ecosystem productivity (NEPC) were computed as the sum of the C stock and fluxes of the soil, the aboveground compartment, and the esti- mated belowground compartment. The ecosystem C stock ranged from 216 t C·ha-1 in S150, to 265 t C·ha-1 in S70, to 272 in S110. NEPC values followed ecosystem C stocks, ranging from 1.7, to 2.4, to 5.1 t C·ha-1·year-1 for S150, S70, and S110, respectively. Stem C-stock uptake rate in S110 showed an increase in growth rate over the first 110 years of S150. We estimate that this increase in stem C stock was 6.2%. Given the constancy of forest management among the stands of the chronosequence, we hypothesize that the increase in C stock shown by S110 is due to indirect human- induced effects. We conclude that managed young forests can take advantage of increased resources and counteract the C losses at harvest that are seen in the old forests.