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White spruce expansion at the tree line and recent climatic change
Canadian Journal of Forest Research
Abstract
White spruce (Piceaglauca (Moench) Voss) populations at their northern limit of distribution, the tree line along the east coast of Hudson Bay, expanded significantly during the last 100 years in response to recent climatic warming. Expansion began around 1880 but was more important during the 20th century, especially between 1920 and 1965. Although no major change in the position of the forest limit and the latitudinal tree line occurred, local altitudinal tree lines rose a few tens of meters. The seed regeneration line increased to about 100 meters above the present altitudinal tree line during the same period. Tree density increased below the local tree lines at many sites. There, spruce expansion was stepwise, as indicated by widely distributed clustered cohorts belonging to the 10–29, 50–59, and 70–89 age-class groups. Although the expansion process was stimulated by nearby old seed bearers, long-distance seed dispersal did occur. The development of contagious dispersion during the formation of white spruce groves or forests caused important local ecological changes, particularly in snow patterns and tree growth. Fire selectively influenced tree regeneration during the past centuries. Black spruce krummholz were progressively decimated during the last 400 years before present, although the species was characterized by low postfire regeneration. Vigorous postfire white spruce regeneration was stimulated by favorable climatic conditions 100 years ago in the northernmost forest site. Conclusions from this study support the hypothesis that Holocene tree line displacements were of low magnitude in northern Québec, and that the primary influence of climatic change was on tree density.
... Despite these predictions, evidence from previous field research is mixed. A few regions show small shifts in response to warming (Suarez et al. 1999;Lloyd et al. 2002;Payette 2007;Mamet and Kershaw 2012), but the majority exhibit stability (Morin and Payette 1984;Payette and Filion 1985;Scott et al. 1987;Lescop-Sinclair and Payette 1995;Szeicz and Macdonald 1995;Lavoie and Payette 1996;MacDonald et al. 1998MacDonald et al. , 2008Gamache and Payette 2005;Wilmking et al. 2012). Studies at sites across the circumpolar also show that climate warming following the Little Ice Age and during the early to mid-20th century increased stand density at the northern edge of the Subarctic forest but did not change the position of northern boundary of the forest-tundra (Morin and Payette 1984;Payette and Filion 1985;Scott et al. 1987;Lescop-Sinclair and Payette 1995;Szeicz and Macdonald 1995;Lavoie and Payette 1996;MacDonald et al. 1998MacDonald et al. , 2008Wilmking et al. 2012). ...
... A few regions show small shifts in response to warming (Suarez et al. 1999;Lloyd et al. 2002;Payette 2007;Mamet and Kershaw 2012), but the majority exhibit stability (Morin and Payette 1984;Payette and Filion 1985;Scott et al. 1987;Lescop-Sinclair and Payette 1995;Szeicz and Macdonald 1995;Lavoie and Payette 1996;MacDonald et al. 1998MacDonald et al. , 2008Gamache and Payette 2005;Wilmking et al. 2012). Studies at sites across the circumpolar also show that climate warming following the Little Ice Age and during the early to mid-20th century increased stand density at the northern edge of the Subarctic forest but did not change the position of northern boundary of the forest-tundra (Morin and Payette 1984;Payette and Filion 1985;Scott et al. 1987;Lescop-Sinclair and Payette 1995;Szeicz and Macdonald 1995;Lavoie and Payette 1996;MacDonald et al. 1998MacDonald et al. , 2008Wilmking et al. 2012). ...
... Our analysis of a unique set of high-resolution repeat photographs shows that white spruce recruitment is altering the structure of the forest-tundra transition in the Tuktoyaktuk Coastlands but that the position of forest-tundra ecotone in this region has not changed in recent decades. This finding is consistent with the majority of studies at the latitudinal limit of trees, which show that multiple warm episodes over the last 200 years have not displaced the northern boundary of the forest-tundra ecotone (Morin and Payette 1984;Payette and Filion 1985;Scott et al. 1987;Lescop-Sinclair and Payette 1995;Szeicz and Macdonald 1995;Lavoie and Payette 1996;MacDonald et al. 1998MacDonald et al. , 2008Wilmking et al. 2012). Observed increases in stand density at forest tundra sites in the Tuktoyaktuk Coastlands are also consistent with previous research showing that recent and historic warming episodes have been associated with increased spruce density within the northern forest tundra (Morin and Payette 1984;Payette and Filion 1985;Scott et al. 1987;Lavoie and Payette 1994;Szeicz and Macdonald 1995;MacDonald et al. 1998MacDonald et al. , 2008Mamet and Kershaw 2012;Wilmking et al. 2012;Frost and Epstein 2014). ...
Shifts in the extent of the boreal forest during past warm intervals and correlations between climate and the position of the forest–tundra ecotone suggest that recent temperature increases will facilitate forest expansion into tundra ecosystems. In this study, we used a unique set of high-resolution repeat photographs to characterize white spruce (Picea glauca (Moench) Voss) populations in 1980 and 2015 at 52 sites across the forest–tundra transition in the Northwest Territories, Canada. We also conducted field inventories at eight sites to examine mapping accuracy, construct age distributions, and assess cone production and seed viability. Our analysis shows that stand density in the forest–tundra has increased significantly since 1980 but that the density of spruce at sites in the tundra has not changed. Age distributions constructed from field sampling also indicate that recent recruitment has occurred in the forest–tundra but not at tundra sites. The nonlinear relationship between summer temperature and seed viability suggests that recent warming has facilitated recruitment in the northern Subarctic but that cold temperatures still limit recruitment at higher latitude tundra sites. Additional research to determine the extent of changes in forest density across the northern Subarctic should be conducted to determine if similar changes are occurring across this ecotone.
... The tundra-taiga treeline in Alaska, U.S.A., has advanced between 80 to 100 m northward in the last 200 years (Suarez et al., 1999). Payette and Filion (1985) studied white spruce (picea glauca) expansion into northern Quebec, Canada, and found that the treeline has not changed substantially over the past centuries; however, below the treeline, its density has increased. Sturm et al. (2001) investigated shrub changes in Alaska using aerial photographs and found a significant increase between 1948 and 2000. ...
... The tundra-taiga treeline in Alaska, U.S.A., has advanced between 80 to 100 m in the last 200 years (Suarez et al., 1999). Payette and Filion (1985) studied white spruce (picea glauca) expansion into northern Quebec, Canada, and found that the treeline has not changed substantially over the past centuries; however, below the treeline, its density has increased. On the other hand, both shrub coverage and density have increased in the Arctic. ...
... Sniderhan and Baltzer (personal communication, January 31, 2018) argued that in the recent decades a significant increase in the forest basal area produced by infilling of trees below the treeline near Inuvik, Northwest Territories, Canada, has occurred; although this study has not been published yet, it provides the first evidence of changes in forest structure in the western Canadian Arctic. Payette and Filion (1985) found that white spruce treeline in northern Quebec, has not substantially changed over the past centuries, whereas Suarez et al (1999) found that the tundra-taiga treeline in Alaska advanced northward between 80 to 100 m north over the last 200 years. Gamache and Payette (2004) studied black spruce height near the Arctic treeline in eastern Canada and found that height growth has not significantly changed. ...
The Arctic has warmed rapidly, increasing shrub cover and density, and thawing permafrost. Understanding, quantifying and predicting the impact of these environmental changes on the hydrological regime of Arctic headwater basins represents a great scientific challenge, particularly due to the sparse monitoring network, limited understanding of governing physical processes and their interaction, and the uncertainty in future climate projections. The purpose of this research is to better understand the impact of climate and vegetation change on the hydrology of Arctic basins near the treeline. This thesis is divided into four sections with the following objectives: (1) to test the coupling of a ground freeze/thaw algorithm with a hydrological model at two research sites in northern Yukon; (2) to diagnose the hydrology of a small Arctic basin near the treeline using a physically based hydrological model; (3) to quantify its historical long-term changes and investigate the individual and combined effect of changing climate and vegetation on its hydrology; and (4) to use high-resolution climate simulations under a high gas concentration scenario along with expected vegetation changes, to investigate changes to hydrological processes and regime. Results revealed the importance of including vegetation dynamics such as changes in shrub extension and density in hydrological models, to capture their impact on blowing snow redistribution and sublimation, and canopy interception and sublimation of snow, something neglected by current studies. This study demonstrated that increasing shrub extension and density near the Arctic treeline slightly compensates the historical decrease in mean annual discharge produced by the decreasing precipitation, providing a small degree of hydrological resiliency. Historical change analysis revealed that hydrological processes are decelerating near the Arctic treeline, such as decreasing evapotranspiration, soil moisture, sublimation and streamflow, mostly driven by climate change. However, under sufficient climate change (38% and 6.1 °C increase in mean annual precipitation and temperature, respectively) significant hydrological changes are expected, reversing the simulated historical changes. Projections show a significant increase in mean annual streamflow discharge, shortening of the snowcover seasons, deepening of the active layer thickness, increasing peak snow accumulation and earlier and larger peak streamflow. Whilst specific to one basin, they indicate the nature of hydrological changes facing Arctic hydrology. These changes will have significant impacts on ecosystems, infrastructure, landscape evolution and atmospheric feedbacks, which are required to be properly understood and quantified to design sustainable and effective mitigation and adaptation plans. The analyses and discussions presented in this study to diagnose the past and predict future Arctic hydrology are relevant for the scientific community of hydrologists, engineers, water managers and policy makers, particularly those interested in cold regions. iii
... The correlative expansion of lowland tundra vegetation around the waning ice caps ceased with the arrival of boreal trees in most locations around 60°N and 58°N west and east of Hudson Bay (Fig. 1a). Only minor movements of tree line and forest limit positions associated with climate change occurred thereafter, during the late Holocene (Payette and Filion 1985;Ritchie 1987;Fig. 1. Location of study area among the boreal and the Arctic biomes (a) according to present (b at 0 m above sea level) and past shorelines (c, d, and e at 30, 60, and 100 m above sea level, respectively) at the junction of Hudson Bay and James Bay. Numbers refer to sampled sites from the tundra coast (1) to the innermost boreal forest established on sandy podzolic soils of the Sakami moraine (7). ...
... Suarez et al. 1999;Payette 2007;Trant and Hermanutz 2014). As an epicontinental sea of 1370 km long and 1050 km wide, Hudson Bay exerts a drastic cooling influence on the regional climate, particularly on the coastal environment where the treeline is located far south compared with that of inland environments (Payette and Filion 1985). The 1100 km long eastern coast of the bay is colonized today by Arctic and Subarctic ecosystems. ...
... Red "+" symbol corresponds to recent fire dated by fire scars. is <1% of the total population. No dead tree stems or stumps lie on the soil surface, much as in other coastal environments located farther north, along the Hudson Bay coast, indicating the young age of all the forest-limit stands (Payette and Filion 1985;Caccianiga and Payette 2006). A small number of charcoal remains were extracted from the surface compartment, whereas none was found in the mineral compartment (Table 1). ...
The Arctic tundra extends beyond the treeline north of 58°N in eastern North America and north of 66°N in western North America and Eurasia. A marked exception to this distribution is the azonal tundra situated as far south as 54°30′–45′N, in the Pointe-Louis-XIV area (JABA), along the fast-rising coasts of James Bay–Hudson Bay. The unusual position of JABA calls into question the influence of climate as the main causal factor for its existence. Macrocharcoal remains extracted from tundra and forest soils were used along a 105 km transect to date the onset of the boreal environment based on past occurrence of conifer fires. Assuming crustal uplift 1.3 m 100 year⁻¹ and 2.4 m 100 year⁻¹ over and before the last 1000 years, and after correcting site elevation at the time the oldest conifer fires occurred, trees established along the coast before 4000 cal. BP. Given charcoal distribution suggesting boreal vegetation in sites ≤13 m a.s.l., JABA was created after 4000 cal. BP when the flat, elongated peninsula emerged above marine waters. It is concluded that JABA origin was most likely caused by the synergistic impact of geophysical factors, isostatic uplift and topography, on a coastal environment already influenced by cold, wind-exposed conditions.
... Numerous studies on treeline dynamics have been conducted to explore climate-induced responses at community and population level during the past few decades (Payette and Filion 1985;Camarero and Gutierrez 1999;Danby and Hik 2007). A growing body of evidence has documented the upslope movement of treelines in response to global warming at many locations during the first half of the twentieth century, followed by increases in tree recruitment and tree density inside the ecotone and beyond treeline in the subsequent decades (Körner 1998;Kullman 2001;Camarero and Gutiérrez 2004;Harsch et al. 2009). ...
... The synchronous recruitment trends at these treeline stands imply that some common external factors (such as the warming climate) control subalpine fir regeneration on both the northern and southern slopes in spite of the different climate regimes. Although a few studies did not find increase trends in recruitment of treeline trees as a response to recent warming (Villalba and Veblen 1997;Wang et al. 2006), substantial densification in treeline ecotones seems to be a common phenomenon in both high-elevation and high-latitude sites during the twentieth century, and occurs more frequently than treeline advance (Payette and Filion 1985;Szeicz and Macdonald 1995;Kullman 2007;Hallinger et al. 2010). In fact, tree recruitment and density at treelines can respond rapidly to warming temperature (Camarero and Gutiérrez 2004;Danby and Hik 2007; Batllori and Gutiérrez 2008;Dang et al. 2009). ...
... In this study, the position of the subalpine fir treelines on the southern slope has not changed significantly over the past 200 years (Fig. 5), given the minimum criterion of a 10-m upslope shift for identifying a significant advance (Liang et al. 2011). Warming temperatures can bring about significant changes in structure and position of altitudinal treeline (Körner 2003;Holtmeier and Broll 2007), while ecological inertia of alpine vegetation due to site conditions may counteract the effects of climate warming on treeline position, causing increases in tree density rather than changes in the absolute elevation of treeline (Payette and Filion 1985;Lloyd and Fastie 2003;Danby and Hik 2007;Batllori and Gutiérrez 2008;Harsch et al. 2012). In contrast, the fir treelines on the northern slope displayed a significant upslope shift during the past 200 years (Fig. 4). ...
Key message
In the Qinling Mountains of north-central China, subalpine fir treelines exhibited a significant upward movement on the northern slope, but only a slight change on the southern slope over the past 200 years, supporting the idea that pattern and timing of treeline change are contingent on local environmental conditions.
Abstract
Variability in the response of altitudinal treelines to climate change might be contingent on species-specific characteristics and on different climate. The objective of this study was to examine the pattern, timing and variability in response of Abies fargesii treeline to climate warming among topographically similar, but climatically different sites. Rectangular plots were established across subalpine fir treeline ecotones on the northern and southern slopes of the Qinling Mountains. Dendroecological techniques were used to examine treeline patterns and dynamics at 50-year intervals. The results showed that despite the differences in regional climate, all the plots studied displayed a recent rapid recruitment trend. Tree recruitment was favored by high spring–summer temperatures on the northern slope and by high summer temperatures on the southern slope. Subalpine fir treelines exhibited a significant upward movement on the northern slope, but only a slight change on the southern slope over the past 200 years. The variability in changes of treeline position on the northern and southern slope can be attributed to the differences in regional climate conditions, supporting the idea that pattern and timing of treeline change is contingent on local environmental conditions.
... This is the case for latitudinal and altitudinal treeline ecotones, where low temperature limits tree growth (Tranquillini, 1979). Their value and reliability as monitors of the recent climate warming is based mainly on studies of tree growth and recruitment within these ecological boundaries (Tranquillini, 1979;Payette and Filion, 1985;Slatyer and Noble, 1992;Lescop-Sinclair and Payette, 1995;Paulsen et al., 2000). In this study, we define the alpine forest-tundra ecotone as the area bounded by the treeline (maximum elevation of live individuals with stems at least 2 m high) and the timberline (maximum elevation of a closed forest). ...
... A similar response at all the studied sites would indicate a common regional effect, most likely a climate factor. We were more interested in tree recruitment because of reports that it was more sensitive to climate variability than tree mortality was (Payette and Filion, 1985;Lloyd, 1997). We suggest that a greater variability in air temperature may be the ultimate climate factor favoring an upward shift of alpine mesic treelines. ...
... This is one of the few studies emphasizing the importance of climatic stability in understanding treeline dynamics. Some authors have reported an increase in tree density within treeline ecotones but minor treeline fluctuation in response to the recent climate warming (Kullman, 1979;Payette and Filion, 1985;Scott et al., 1987;Szeicz and MacDonald, 1995;MacDonald et al., 1998). It would suggest that tree abundance might be a more sensitive monitor of climate change than treeline position (Slatyer and Noble, 1992). ...
Spatial identifcation and description of ecological boundaries is fundamental to better understanding of treeline dynamics. Ecological boundaries across two contrasting subalpine Pinus uncinata forest-alpine grassland ecotones were delineated within the Central Pyrenees (Ordesa and Tessó sites). Boundaries were delineated using an edge detection algorithm for two-dimensional data (lattice-wombling). Tree density, size-structure, growth-form, and estimated age were used to reveal spatial location of boundaries for several size and growth-form tree classes. Overlap statistics were applied to quantify spatial relationships among boundaries determined for different sets of variables. The most significant and consistent boundaries were those for structural variables at the Ordesa site. At this site, the sequential disposition of bigger and unistemmed trees descending across the ecotone produced boundaries for size-structure and growth-form variables. These boundaries were located along an ordered spatial pattern (altitudinal diagonal). At the Tessó site, there were few consistent boundaries, most of which were developed along the slope. Overlap statistics showed that boundaries at the Ordesa site were more spatially related than were those at the Tessó site. This result held when any set of variables was considered. The studied ecotones describe sharp (Ordesa site) and gradual (Tessó site) structural changes in tree populations, related to situations similar to the ecotone and ecocline concepts, respectively. The possible environmental driving factors producing these patterns are the strong winds and reduced snow cover at higher altitudes at the Ordesa site, and snow avalanches at the Tessó site. Boundary detection through time in permanent plots might be a better tool for monitoring climate-change impact in the forest--alpine grassland ecotone than the subjective location of treelines.
... Por ejemplo, variables de forma de los árboles (altura, tamaño y forma de la copa, número de pies por cepa, etc.) pueden formar fronteras distintas de las delineadas por datos de densidad de árboles o de formas arbustivas o por las creadas por datos de edad. Sin embargo, todos estos aspectos muestran perpespectivas parciales y relacionadas de la dinámica del límite forestal (Kullman, 1979;Payette, Filion, 1985;Payette, Lavoie, 1994;Rochefort et al., 1994;Lloyd, 1996). ...
... La necesidad de considerar variables estructurales (tamaño y forma) y demográficas (densidad) por separado no es estadística sino que surge de enfoques recientes sobre la dinámica del ecotono bosque subalpino-pastos dirigidos bien hacia aspectos demográficos (cambios de densidad; Kullman, 1979;Payette, Filion, 1985) o bien hacia cambios estructurales (crecimiento vertical, paso de forma arbustiva a arbórea o viceversa, etc.; Lavoie, Payette, 1992;Hessl, Baker, 1997). Ambos grupos de enfoques se complementan y los cambios demográficos y estructurales y su interacción pueden provocar ascensos de los límites del árbol y del bosque. ...
We describe the spatial pattern of a subalpine forest-alpine pasture ecotone in the Central Pyrenees, that includes altitudinal timberline and treeline, and it is dominated by Pinus uncinata Ram. A rectangular (30 x 140 m) plot was located crossing the ecotone with its longest side parallel to the slope. We measured for each P. uncinata individual inside the plot: location (coordinates x, y), and structure (e. g. height) and growth form variables (number and type —living or dead, vertical or shrubby— of stems per individual). P. uncinata individuals were classified according to their size (adults, poles, saplings and seedlings) and growth form (krummholz —shrubby and multistemmed individuals— and krummholz with vertical stems). We described quantitatively the type of substrate (bare soil, organic matter, gravel and rock) and cover of herbs, shrubs and P. uncinata using transects parallel to the slope. The ecotone structure was described through: (1) point pattern (Ripley’s K) and (2) surface pattern analyses (spatial correlograms of height); (3) the detection and description of boundaries using density, size or growth form variables; (4) the synthesis of variations of presence and diversity of substrates and herbs and shrubs; and (5) the ordination of quadrats (the plot was previously subdivided into 115 6 x 6 m quadrats), according to their spatial position in the ecotone, the type of substrate, the cover of herbs and shrubs and the number, size and growth form of P. uncinata individuals. Most P. uncinata living individuals were krummholz, located above the timberline. Krummholz individuals showed significant and positive spatial interaction with seedlings. Bigger, vertical and unistemmed individuals predominated in the lower area of the ecotone, in the forest. The change of height with increasing elevation was abrupt and masked an underlying pattern of patches of trees with similar height in the forest. The structure variables were more sensitive because they produced a greater number of boundaries. These boundaries were arranged forming a “diagonal” (in the lower and upper areas of the ecotone for big and small individuals, respectively) because of the sequential location of progressively bigger unistemmed individuals descending across the ecotone. The shrubby individuals were associated with rocky substrates, that decreased in the forest, where organic matter predominated. The snow-wind interaction can explain the location of the studied timberline that could be considered a local phenomenon. Krummholz can buffer seedlings against the harsh climatic conditions of this ecotone (strong wind, reduced snowpack, low temperature). The spatial location of the different classes of individuals, the spatial interaction between seedlings and krummholz individuals, and changes of growth form (from shrubby to vertical growth form or vice versa) can cause some inertia in the response of ecotone P. uncinata populations to environmental changes.
... Recent warming at high latitude has created a disequilibrium, and the distribution of some tree species now lags the distribution of suitable climates 35 . Increased fire in a warmer and lightning-rich future near the treeline has the potential to accelerate the northward migration of trees 36 , mediated in part by landscape-scale factors that influence seed availability and seedling establishment 37,38 . High-severity wildfires contribute to the establishment of early successional tree species by exposing mineral soil 18 provided that seed sources are available 37,38 . ...
... Increased fire in a warmer and lightning-rich future near the treeline has the potential to accelerate the northward migration of trees 36 , mediated in part by landscape-scale factors that influence seed availability and seedling establishment 37,38 . High-severity wildfires contribute to the establishment of early successional tree species by exposing mineral soil 18 provided that seed sources are available 37,38 . ...
Changes in climate and fire regimes are transforming the boreal forest, the world’s largest biome. Boreal North America recently experienced two years with large burned area: 2014 in the Northwest Territories and 2015 in Alaska. Here we use climate, lightning, fire and vegetation data sets to assess the mechanisms contributing to large fire years. We find that lightning ignitions have increased since 1975, and that the 2014 and 2015 events coincided with a record number of lightning ignitions and exceptionally high levels of burning near the northern treeline. Lightning ignition explained more than 55% of the interannual variability in burned area, and was correlated with temperature and precipitation, which are projected to increase by mid-century. The analysis shows that lightning drives interannual and long-term ignition and burned area dynamics in boreal North America, and implies future ignition increases may increase carbon loss while accelerating the northward expansion of boreal forest.
... It usually only makes up about 10% of the forest cover of this bioclimatic sub-domain (Lafontaine and Payette, 2012). However, P. glauca is also a typical pioneer species in the colonization of mineral substrates during the primary succession in post-glacial and boreal habitats (Payette and Filion, 1985). The study of chronosequences of primary succession in northern Quebec, at the Hudson Bay, made it possible to find a link between the establishment of this species and the formation of podzols, the typical soil of boreal forests (Laliberté and Payette, 2008). ...
After a mine is closed, waste rock storage areas must be revegetated to facilitate the return of ecosystem services and meet legal and social expectations. The restoration of forest ecosystems on waste rock through spontaneous colonization associated with primary succession can take decades and is still poorly studied. Adding a mulch of ramial chipped wood (RCW) could improve the physicochemical properties and microclimate conditions of waste rock, thus facilitating substrate colonization by plants. In 2016, a fully randomized block design was installed on waste rock from a closed gold mine located in the boreal forest in Abitibi-Témiscamingue, Quebec, Canada. The design included four treatments: scarified waste rock as the control (WR), 2 cm of RCW mulch on top of scarified waste rock (RCW/WR), and 10 cm layer of sand on top of scarified waste rock with or without 2 cm of RCW mulch (RCW/S and S, respectively). Over a period of five years, we followed the natural colonization of forest species as well as abiotic (substrate microclimate conditions and physicochemistry) and biotic (herbaceous plant colonization) factors influencing woody plant colonization success. Six boreal woody species spontaneously colonized the area (five individuals per m2, on average, all species combined). Salix sp. and Picea glauca seedlings were more abundant on substrates with RCW mulch (especially sand) than those without mulch, and P. glauca had greater aerial biomasses with RCW mulch. Substrate water content during the growing season and the presence of the weed species Tussilago farfara were determining environmental factors in substrate colonization by Abies balsamea. In the absence of Tussilago farfara, RCW mulch increased A. balsamea colonization. RCW mulch increased the total cover of colonizing herbaceous plants (23.3–58.2%) as compared to mineral substrates alone (4.78–52.3%), which negatively affected the number of A. balsamea individuals. The colonizing herbaceous species were mostly primary succession species, Pilosella caespitosa, Anaphalis margaritacea, and Tussilago farfara being dominant; no exotic species were observed. The results highlight the potential of RCW mulch in promoting forest recolonization on waste rock, including mid-successional species like Picea sp., which could be useful for facilitating ecosystem succession in post-mining landscapes.
... Here we address this issue by investigating how treelines in two climatically contrasting Russian subarctic regions (maritime vs. sharply continental) respond to climate conditions during the cold season, particularly to winter snowfall, which could represent a major, but underestimated, driver of treeline dynamics. Such high-altitude, remote territories located in subarctic regions have been little disturbed by local anthropogenic use (grazing, logging) and there, tree growth and regeneration are very sensitive to temperature changes [6,14,15]. For instance, in subarctic regions of Alaska, northern Canada and the Scandinavian Alps, treelines have positively responded to warmer growing-season conditions by showing enhanced tree growth and recruitment [16][17][18][19]. ...
Climate warming impacts on alpine treeline dynamics. However, we still lack robust assessments of the long-term impacts of climate on tree recruitment at the treeline, particularly in remote areas such as the subarctic regions of Russia subjected to different climate influences. We expected that the treelines in two regions may have different features and dynamics patterns. We analyzed climate variables and assessed treeline dynamics by quantifying recruitment using the tree rings of ca. 7000 trees of four species (Betula pubescens Ehrh. ssp. tortuosa, Pinus sylvestris L., Picea abies Ledeb. ssp. obovata, Larix gmelinii Rupr.) along 14 altitudinal transects (series of study plots). We compared the Khibiny Massif (Kola Peninsula) and the western Putorana Plateau, subjected to oceanic and continental influences, respectively. In both regions, summers became warmer, and winters became snowier during the past century. At the low part of the treeline ecotone, tree recruitment has slowly increased since the mid-18th century at the Putorana Plateau and the mid-19th century at the Khibiny but accelerated in the early 20th century at both regions and reached a maximum peak in the second half of the past century. Treeline encroachment intensified in the 1930s at the Khibiny and the 1950s at the Putorana Plateau. Trees encroached in the tundra leading to upward treeline shifts in the late 20th century. The slope exposure affected the rates of treeline shift with higher upward advances on southern-oriented slopes. Tree recruitment and early-winter precipitation were positively correlated. The differences in species composition, treeline altitude and influences of slope orientation on treeline dynamics can be explained primarily by differences in the degree of continentality. The abundance of saplings in both regions allows the future encroachment of trees into tundra and further treeline upward shifts to be forecast.
... This is especially relevant at large time scales, as Quaternary climatic oscillations prompted recurrent latitudinal or altitudinal range shifts of large amplitude (Hewitt 2000). Hence, current spruce distributions in boreal and subtropical zones mirror their idiosyncratic demographic trajectories, with ongoing climate change promoting range expansion in northern species (e.g., Payette and Filion 1985), and range contraction in southern species (Wright 1955;Jaramillo-Correa et al. 2006;Bodare et al. 2013). From a population genomics perspective, understanding the historical dynamics of species distributions is highly relevant since it strongly influences their extant natural genetic diversity and structure (Jaramillo-Correa et al. 2009;de Lafontaine et al. 2018). ...
Spruce (Picea spp.) species are the dominant component of the circumboreal forest and one of the most reforested species groups in the world. They have become a reference among conifers for fundamental and applied genomics research. This chapter reviews the compelling progress made in the field of spruce population genomics, from the supportive field trials established by tree breeders to the release of complete sequences of their cytoplasmic and nuclear genomes to most recent applications in forestry. Initial efforts focusing on sequencing the spruce gene space resulted in the development of extensive genomic resources such as expressed sequence tags libraries, gene and single nucleotide polymorphism catalogs, genotyping arrays, and high-resolution genetic maps. During the last decade, these resources allowed to gain insights into a variety of topics such as phylogeography and phylogeny, introgression and speciation processes, as well as association mapping. Thanks to the recent advent of high-throughput genotyping and sequencing technologies, population genomics data are now being produced at an exponential rate, which translates into new applications and opportunities in conservation genetics and spruce breeding, such as genomic prediction.
... Representing distributional margins of woody plants, these shrubby ecosystems often exhibit high sensitivity to climate change. Indeed, a shrub expansion caused by climate warming or wetter conditions has been reported recently for the Arctic tundra (Myers-Smith et al., 2011;Payette & Filion, 1985), alpine areas (Hagedorn et al., 2014;Hallinger et al., 2010) and dry regions (Caldeira et al., 2015). Moreover, shrub ecosystems host some of the most widespread woody plant species (Adams, 2008;Mao et al., 2010), whose climate-growth responses vary significantly along geographical gradients (Buchwal et al., 2020;Pellizzari et al., 2017;Shetti et al., 2018a). ...
Aim
Plant growth and phenology respond plastically to changing climatic conditions in both space and time. Species-specific levels of growth plasticity determine biogeographical patterns and the adaptive capacity of species to climate change. However, a direct assessment of spatial and temporal variability in radial growth dynamics is complicated, because long records of cambial phenology do not exist.
Location
Sixteen sites across European distribution margins of Juniperus communis L. (the Mediterranean, the Arctic, the Alps and the Urals).
Time period
1940–2016.
Major taxa studied
Juniperus communis.
Methods
We applied the Vaganov–Shashkin process-based model of wood formation to estimate trends in growing season duration and growth kinetics since 1940. We assumed that J. communis would exhibit spatially and temporally variable growth patterns reflecting local climatic conditions.
Results
Our simulations indicate regional differences in growth dynamics and plastic responses to climate warming. The mean growing season duration is the longest at Mediterranean sites and, recently, there has been a significant trend towards its extension of up to 0.44 days/year. However, this stimulating effect of a longer growing season is counteracted by declining summer growth rates caused by amplified drought stress. Consequently, overall trends in simulated ring widths are marginal in the Mediterranean. In contrast, durations of growing seasons in the Arctic show lower and mostly non-significant trends. However, spring and summer growth rates follow increasing temperatures, leading to a growth increase of up to 0.32 %/year.
Main conclusions
This study highlights the plasticity in growth phenology of widely distributed shrubs to climate warming: an earlier onset of cambial activity that offsets the negative effects of summer droughts in the Mediterranean and, conversely, an intensification of growth rates during the short growing seasons in the Arctic. Such plastic growth responsiveness allows woody plants to adapt to the local pace of climate change.
... There is positive greening trend and lengthening of the growing season in the current warming scenario (Singh et al., 2018;Mohapatra et al., 2019b). The response of vegetation to warming around the treeline has been reported as increased forest density and increased radial and vertical growth rather than advancing of treeline forests (Payette and Filion, 1985;Kullman, 2007;Zhang et al., 2009). ...
High elevation ecosystems of the Himalaya have warmed more rapidly in recent decades than other areas of the globe. Alpine life zones are areas lying between the elevational climatic treeline and the snow line. The limit of alpine treeline elevational position in Himalaya is temperature dependent. Satellite remote sensing of delineating Himalayan alpine treeline position and its dynamics can give insight regarding climatic variability. Resourcesat-1/2 Linear Imaging Self Scanning Sensor (LISS-III) and Landsat-1/2/3 Multispectral Scanner (MSS) were used to evaluate the long-term (1970s to 2014) treeline dynamics in high elevations (>3500 m) of Himalaya. The mean elevation of treeline position has shifted vertically 381 ± 73 m in over four decades at a rate of c. 95 m decade-1 in the entire Indian Himalaya. The highest shift (452 ± 74) in the treeline position was observed in Arunachal Pradesh Himalaya. We have also predicted through future climate model simulations, that there will be overall vertical shift in the niche area of treeline tree species (Betula utilis) in general and more towards eastern Indian Himalaya, in particular. The highest rate of upward shift in niche was observed in Sikkim Himalaya (c. 109.9 m decade-1) and the lowest magnitude of shift (c. 20.8 m decade-1) in Jammu and Kashmir Himalaya. The significant elevational shifts of the treeline ecotone is a fingerprint of climate change impact in Indian Himalayan alpine ecosystem.
... Understanding current forest dynamics is essential to realistically forecast the effects of climate variation on tree populations. Paleoecologists and forest ecologists have found evidence of range shifts of tree species in response to past climate variation, mostly upward or northward displacements in response to climate warmings (Payette and Filion, 1985;Kullman, 2002;Shiyatov, 2003;Bekker, 2005). Consequently, many forest ecologists have assumed that a species' actual niche is similar to its potential niche, which would happen if climate was the main determinant of the present tree species distribution. ...
To infer future changes in the distribution of tree species in response to climatic variability, we need an understanding of the recruitment dynamics and their climatic controls at the species’ distribution limit. We studied the recruitment processes in an isolated population of Pinus uncinata Ram. located at the southwestern limit of the species’ distribution in Europe (Iberian System, NE Spain). We assessed (1) the temporal patterns of pine recruitment, and (2) how climate influenced recruitment. To reconstruct the recent recruitment episodes and to assess the climatic influence on recruitment and radial growth we employed dendrochronological methods. We mapped, measured the size, and estimated the age of all P. uncinata individuals located within a 50 m × 40 m plot. Additional age data were obtained from individuals located in four nearby 20 m × 20 m plots. The main episodes of tree establishment (early 1960s, late 1980s) coincided with low radial growth during a period with reduced grazing pressure. Grazing pressure and tree recruitment were not related at the spatiotemporal scale of this study. High May, August, and September minimum temperatures and high April precipitation were positively associated with recruitment, whereas high maximum April and June temperatures were negatively associated with recruitment. The studied population was in equilibrium with climate until the late 1990s, one of the warmest decades in the 20th century, when recruitment decreased despite the availability of suitable sites for establishment and the presence of reproductive individuals. We suggest that late-summer temperatures might have a non-linear negative threshold effect on recruitment rather than a linear effect. Despite increasing evidence of climate-induced recruitment episodes in isolated cold mountain forests, threshold effects of temperature on recruitment may imply limited range shifts of these populations in response to climate warming.
... Tree crowns below the snowpack are sometimes mechanically damaged (Ishizuka, 1981;Minnich, 1984;Morin and Payette, 1986;Boivin and Bégin, 1997;Kajimoto et al., 2002). In general, the snowpack protects these crowns from cold air, wind-blown snow or ice particles, and desiccation in cold regions such as subarctic forest tundra or treeline (Hadley and Smith, 1986;Payette and Filion, 1985;Lavoie and Payette, 1992;Scott et al., 1993;Payette et al., 1996;Boivin and Bégin, 1997), but snowpack-induced damage also occurs in these regions (Morin and Payette, 1986;Boivin and Bégin, 1997). ...
On a gentle leeward slope in a snowy forest limit in northern Honshu Island, Japan, mechanical damage by snow settlement and creep on Abies mariesii trees buried below the snowpack was examined to detect signs of the snow-damage effect on future survival and crown development. Damage types were recorded based on direct observation of crowns in 1996, a year of high snow accumulation exceeding 4.5 m, and 1997, a year of moderate snow accumulation. Of 153 trees examined, 63% were damaged in 1996 and 15% were damaged in 1997. The most destructive damage type was breakage of stems ≥5 cm in diameter, which occurred on eight trees in 1996 and three in 1997, resulting in foliage loss and death of some trees. The prevalent damage type was branch tearing at branch-stem junctions primarily within a height range of 4–6 m, which occurred on 171 branches in 1996 and 5 in 1997. Under snowy and windy conditions, stem breakage and branch tearing, caused by forces active within restricted layers of the snowpack, may reduce the future survival and crown development of A. mariesii buried below the snowpack in years of heavy snowfall.
... In particular, the windward to leeward pattern of successively younger trees suggests that established trees improve the microenvironment for new seedlings. Variations in this expected pattern are not surprising, given the fact that the movement of ecotones is typically heterogeneous over both time and space (e.g., Payette and Filion, 1985;Kullman, 1986;Malanson, 1993;Lloyd and Graumlich, 1997;Payette et al., 2001). Nevertheless, many of the differences among the transects may be explained by the fact that the feedback-induced pattern is superimposed on other, spatially variable factors. ...
The development and maintenance of several types of visually striking vegetation patterns are controlled by positive feedback between pattern and process. These patterns are particularly common at ecotones, where the influence of positive feedback may affect the position and dynamics of the boundary between the adjacent biotic communities. In this study, I use dendrochronology to examine the role of feedback between existing trees and the establishment and survival of seedlings in the advancement of linear, finger-like strips of subalpine forest in Glacier National Park, Montana. A general upslope, windward to leeward pattern of older trees followed by progressively younger trees was evident in all sample transects, although in some cases this pattern repeated several times along the length of a transect, with each repetition originating leeward of boulders. Overall advancement rates varied from 0.28 to 0.62 m yr⁻¹. The oldest trees established in the early to mid-1700s, but establishment and advancement increased rapidly after 1850, and peaked in the early 1900s. In addition, almost all seedlings established within 5 m downwind of existing trees between 1700 and 1850, while establishment beyond this distance was common after 1850. These patterns suggest that existing trees facilitate leeward seedling establishment and survival, by depositing wind-blown snow. These seedlings in turn modify their leeward environment, thus allowing forest advancement in a linear pattern. Feedback was critical for the survival of seedlings before 1800, and strongly controlled advancement between about 1800 and 1850, but appears to have had little effect on establishment patterns since that time. The importance of feedback between pattern and process may change over time and space as a result of changes in climatic conditions or biotic surroundings.
... These broadscale greening trends have been corroborated by analysis of repeat photography and vegetation surveys, which show increases in the cover and density of upright shrubs and graminoids and decreases in moss and lichen (Elmendorf et al. 2012, Fraser et al. 2014, Myers-Smith et al. 2015, Moffat et al. 2016. Tree density in the sub-Arctic forest has also increased in some regions (Miller et al. 2017, Lantz et al. 2019), but many latitudinal treelines have been stable, exhibiting a slower climate response than other northern vegetation types (Payette and Filion 1985, Scott et al. 1987, Gamache and Payette 2005, Wilmking et al. 2012, Brown et al. 2018, Lantz et al. 2019. ...
Abstract The distribution and composition of Arctic vegetation are expected to shift with ongoing climate change. Global models generally predict northward shifts in high‐latitude ecotones, and analysis of remote sensing data shows widespread greening and changes in vegetation structure across the circumpolar Arctic. However, there are still uncertainties related to the timing of these shifts and variation among different plant functional types. In this paper, we investigate disequilibrium dynamics of green alder and white spruce in the Tuktoyaktuk Coastal Plain, NWT. We used high‐resolution air photographs captured in the 1970s and 2000s to quantify changes in the distribution and abundance of alder and spruce near their northern limits. We found increases in alder and spruce stem density over time, but no change in their range limits, indicating that both species are affected by leading‐edge disequilibrium. Low stand density and temperature limitation of reproduction along the northern margin likely contributed to observed disequilibrium in both species. We also observed the greatest change in species occupancy within a burned area, suggesting that the increased frequency of fire will play a significant role in the timing and magnitude of near‐term vegetation change.
... The vegetation belongs to the forest sub-zone of the forest-tundra, characterized by high spatial heterogeneity of lichen-dominated granitic outcrops, grassdominated sandy areas (nearby the coast) and scattered spruce or shrub stands in valleys or on raised beach deposits ( figure 1(b (Payette 1983(Payette , 1993). An increase in tree cover density (Payette and Filion 1985), a switch of the dominant growth form from stunted to erect (Caccianiga and Payette 2006) and an expansion of treelines northwards and towards the coast Filion 1985, Laliberté and, all resulting from climate change, have been observed over the last decades along the eastern coast of Hudson Bay. ...
Large spatial and between-tree variability has recently been observed in the response of boreal forests to ongoing climate change, spanning from growth stimulation by increasing temperatures to drought limitation. To predict future responses of boreal forests, it is necessary to disentangle the drivers modulating the temperature-growth interaction. To address this issue, we established two inventory plots (at a treeline and closed-canopy forest) and assembled site chronologies in Picea glauca stands at the transition between boreal forest and tundra in Northern Quebec, Canada. In addition to site chronologies, we established a set of chronologies containing, for each year, exclusive subsets of tree-rings with specific cambial age (young/old), tree dimensions (small/large) and tree social status (dominant/suppressed). All chronologies were correlated with climatic data to identify the course of climatic conditions driving variability in tree-ring widths. Our results show that the growth of P. glauca correlates significantly with summer temperature in tree-ring formation years and during up to two prior summers. Tree-ring width is positively influenced by summer temperatures in tree-ring formation year and two years prior to tree-ring formation. In addition, climate-growth correlations indicate a negative effect of summer temperature one year before tree-ring formation at the closed-canopy forest site. The pattern of climate-growth correlations is tightly synchronized with previously published patterns of climate-reproduction correlations of P. glauca, suggesting a growth-reproduction trade-off as a possible factor modulating the response of boreal forests to summer temperatures. Climatic signal does not differ between pairs of chronologies based on subsets of cambial ages, stem dimensions or tree competition status at the treeline site. However, the response to summer temperatures one year before tree-ring formation is significant only in mature (old, large and dominant) individuals at the closed-canopy site. The inverse pattern of temperature-growth correlations during a sequence of three years challenges predictions of how boreal forests respond to climate change.
... On the contrary, in regions where the levels of soil moisture on slopes differ depending on orographic conditions, tree regeneration is intensified during discrete or overlapping periods with different moisture conditions [10,11]. Periods of intense regeneration in areas where the amount of precipitation and snow depth are at a medium level (e.g., in zonal forest-tundra communities) coincide with periods of general warming; however, regeneration is locally intensified when snow depth increases, since the snow protects undergrowth against extremely low winter temperatures [12][13][14]. ...
... Global warming prolongs the growing season of the treeline ecotone (Grace, Berninger, and Nagy 2002). The response of vegetation to global warming around the treeline ecotone has been reported in terms of increased forest density and increased radial and vertical growth rather than advancing of treeline forests (Kullman 2007;Payette and Filion 1985). ...
Global warming is inducing the elevational alpine treeline ecotone (ATE) to migrate to higher elevations in the Himalaya. Prior research on ATE dynamics has been primarily based on field inventory and studied at the community level. The potential of using remote sensing and geographic information system for the delineation of the treeline ecotone has been explored. In this study, we used satellite-derived Normalized Difference Vegetation Index (NDVI) data from Landsat-1/2 Multispectral Scanner (MSS), Resourcesat-1/2 Linear Imaging Self Scanning Sensor (LISS-III), and National Oceanographic and Atmospheric Administration-Advanced Very High-Resolution Radiometer (NOAA-AVHRR) to investigate long-term ATE dynamics. Satellite remote sensing of treeline in Arunachal Pradesh Himalaya revealed an upward shift over the past four decades. The ATE has shifted c. 452 m ± 74 m upward in vertical dimension at a rate c. 113 m decade⁻¹. Furthermore, the land surface phenology along ATE and forest area has changed significantly over the past 33 years. The significant positive trend in length of the growing season (LOS; p < 0.05) and delay in the end of the growing season (EOS) was observed. The start of the growing season (SOS) had a negative tendency with non-significant linear trend. The treeline upward shift and significant lengthening of the growing season at ATE and forest area indicate changing climatic patterns and processes.
... However, there are no published studies investigating changes in the forest structure (i.e., density, height, and extension) over northwestern Canada. Payette and Filion (1985) found that white spruce tree lines in northern Quebec have not substantially changes over the past centuries, whereas Suarez et al. (1999) found that the tundra-taiga tree line in Alaska advanced northward between 80 and 100 m north over the last 200 years. Gamache and Payette (2004) studied black spruce height near the Arctic tree line in eastern Canada and found that height growth has not significantly changed. ...
The rapidly warming Arctic is experiencing permafrost degradation and shrub expansion. Future climate projections show a clear increase in mean annual temperature and increasing precipitation in the Arctic; however, the impact of these changes on hydrological cycling in Arctic headwater basins is poorly understood. This study investigates the impact of climate change, as represented by simulations using a high-resolution atmospheric model under a pseudo-global-warming configuration, and projected changes in vegetation, using a spatially distributed and physically based Arctic hydrological model, on a small headwater basin at the tundra-taiga transition in northwestern Canada. Climate projections under the RCP8.5 emission scenarios show a 6.1 °C warming, 38% increase in annual precipitation and a 19 W m−2 increase in all-wave annual irradiance over the 21st century. Hydrological modelling results suggest a shift in hydrological processes with maximum peak snow accumulation increasing by 70%, snowcover duration shortening by 26 days, active layer deepening by 0.25 m, evapotranspiration increasing by 18% and sublimation decreasing by 9%. This results in an intensification of the hydrological regime by doubling discharge volume, a 130% increase in spring runoff, and earlier and larger peak streamflow. Most hydrological changes were found to be driven by climate change; however, increasing vegetation cover and density reduced blowing snow redistribution and sublimation, and increased evaporation from intercepted rainfall. This study provides the first detailed investigation of projected changes in climate and vegetation on the hydrology of an Arctic headwater basin, and so it is expected to help inform larger scale climate impact studies in the Arctic.
... On the decadal scale, significant tree and shrub growth responses may be limited to moist climate zones with much slower changes expected in dry, continental climates (Frost and Epstein 2014). Subarctic spruce stands may respond to an ameliorating climate by increasing growth, height, reproduction, and stem density without a shift in position (Payette and Filion 1985;MacDonald et al. 1998). Site-specific factors such as soil types, moisture regime, topography, aspect, and existing plant cover influence both the rate of tree invasion into adjacent tundra and the response to fire (Payette et al. 2001). ...
Climate-vegetation models predict rapid northward advance of the subarctic forest-tundra in the coming century, although modelled responses may not be congruent with field data. This study aimed to determine how forest-tundra vegetation has responded to climate change in north-central Canada. Vegetation cover and gradients were mapped and compared to changes in climate parameters between 1955 and 2006. Increased aridity and annual and July warming corresponded to spatial isotherm shifts of one-half the width of the forest-tundra transition. Over the 51-year period, the areal extent of live trees decreased 26% (5227 km²) while the areal extent of recently-burned trees increased 16-fold (7768 km²). Changes in the areal extent of treeless wetland, tall shrubs, and upland tundra were non-significant. There was significant forest loss in the southern forest-tundra and modest forest gain in the northern forest-tundra. Overall, forest loss outpaced forest gain. The forest-tundra increased in areal extent by ~6% via an overall broadening of the transition region. Contrary to model predictions, no appreciable northward migration of the forest-tundra was detected over the 51-year period despite significant climate change. Increased wildfire activity and moisture stress may limit the potential of tree vegetation to expand northward under a warming climate.
... Its elevational distribution ranges from sea level to 1520 m (Burns and Honkala 1990). While the tree line in eastern North America is mainly formed by black spruce (Lavoie and Payette 1992;Gamache and Payette 2004), white spruce takes over as the primary treeline-forming species in western North America (Payette and Filion 1985;Lloyd et al. 2005). This species is widely favored for timber production in Canada and the United States and is one of the most important commercial species in the boreal forest (Burns and Honkala 1990). ...
Many plant species reproduce by cloning if environmental conditions are unfavorable for sexual reproduction. To test the alternative hypotheses, whether cloning is an “exit strategy” or caused by selection, clonal growth in white spruce (Picea glauca (Moench) Voss) was investigated in three stands in Alaska, each consisting of a core (closed forest) plot and an edge (tree-line) plot. In total, 2571 trees were mapped and genotyped with 11 single sequence repeat (SSR) markers. The proportion of clonal trees follows a moisture gradient and was lowest in the dry Interior basin (4.5%), followed by the sites at the Alaska Range (9.0%) and the Brooks Range (21.7%). At the two latter sites, clonal growth was more frequent in the edge plot. A comparison among 960 aged trees revealed that clonal growth becomes more likely with increasing age and continues over the life span of a tree. Genetic data do not indicate any genetic predisposition for cloning. Clonal growth in white spruce most likely takes place via layering and depends on environmental conditions. Because performance of the trees, and therefore likely plant reproductive success, is lower in plots with a high proportion of clones, selection for clonal growth seems to be highly unlikely.
... There is positive greening trend and lengthening of the growing season in the current warming scenario. The response of vegetation to warming around the treeline has been reported as increased forest density and increased radial and vertical growth rather than advancing of treeline forests (Payette and Filion 1985;Kullman 2007;Zhang et al. 2009). The SOS dates widely ranged between the 260th and the 298th Julian day. ...
Mountain ecosystems of the Himalaya have warmed more rapidly in recent decades than other areas of the globe. Landscape-level delineation of treeline position and its dynamics can give insight regarding climatic variability. Landsat-2 Multispectral Scanner (MSS), Resourcesat-2 Linear Imaging Self Scanning Sensor (LISS-III) and National Oceanic and Atmospheric Administration- Advanced Very High Resolution Radiometer (NOAA-AVHRR) derived normalized difference vegetation index (NDVI) was used to study the long-term treeline dynamics. The treeline has shifted vertically 301 ± 66 m upward in 37 years at a rate of c. 81 m decade⁻¹. The minimum air temperature has increased at a rate of 0.3 °C decade⁻¹ (p < 0.001) depicting the favourable scenario for treeline growth in this temperature limited ecosystem. The annual cumulative precipitation has decreased at a rate of 206.5 mm decade⁻¹. The length of growing season (LOS) has increased and the start (SOS) and end of growing season (EOS) has got earlier in the 1977 treeline. The elevation shifts and phenological changes of the treeline were observed in the warming scenario. © 2018
... The tundra-taiga treeline in Alaska, USA, has advanced from 80 to 100 m in the last 200 years (Suarez et al., 1999). Payette and Filion (1985) studied white spruce (picea glauca) expansion into northern Quebec, Canada, and found that the treeline has not changed substantially over the past centuries; however, below the treeline, its density has increased. On the other hand, both shrub coverage and density have increased in the Arctic. ...
The impact of transient changes in climate and vegetation on the hydrology of small Arctic headwater basins has not been investigated before, particularly in the tundra–taiga transition region. This study uses weather and land cover observations and a hydrological model suitable for cold regions to investigate historical changes in modelled hydrological processes driving the streamflow response of a small Arctic basin at the treeline. The physical processes found in this environment and explicit changes in vegetation extent and density were simulated and validated against observations of streamflow discharge, snow water equivalent and active layer thickness. Mean air temperature and all-wave irradiance have increased by 3.7 ∘C and 8.4 W m-2, respectively, while precipitation has decreased 48 mm (10 %) since 1960. Two modelling scenarios were created to separate the effects of changing climate and vegetation on hydrological processes. Results show that over 1960–2016 most hydrological changes were driven by climate changes, such as decreasing snowfall, evapotranspiration, deepening active layer thickness, earlier snow cover depletion and diminishing annual sublimation and soil moisture. However, changing vegetation has a significant impact on decreasing blowing snow redistribution and sublimation, counteracting the impact of decreasing precipitation on streamflow, demonstrating the importance of including transient changes in vegetation in long-term hydrological studies. Streamflow dropped by 38 mm as a response to the 48 mm decrease in precipitation, suggesting a small degree of hydrological resiliency. These results represent the first detailed estimate of hydrological changes occurring in small Arctic basins, and can be used as a reference to inform other studies of Arctic climate change impacts.
... The tundra-taiga treeline in Alaska, U.S.A., has advanced between 80 to 100 m in the 15 last 200 years (Suarez et al., 1999). Payette & Filion (1985) studied white spruce (picea glauca) expansion into northern Quebec, Canada, and found that the treeline has not changed substantially over the past centuries; however, below the treeline, its density has increased. On the other hand, both shrub coverage and density have increased in the Arctic. ...
The impact of observed changes in climate and vegetation on the hydrology of Arctic basins is often considered to be most sensitive at the tundra-taiga transition where the region is warmest and sub-arctic vegetation is nearest. This study uses weather and land cover observations and a cold regions hydrological model to investigate historical changes in modelled hydrological processes driving the streamflow response of a small Arctic permafrost-underlain basin at the tundra-taiga transition. The physical processes found in this environment and explicit changes in vegetation type and density were simulated and validated against observations of streamflow discharge, snow water equivalent and active layer thickness. Mean air temperature and all-wave irradiance have increased by 3.7 °C and 8.4 W m−2, respectively, while precipitation has decreased from 369 to 321 mm since 1960. Two modelling scenarios were created to separate the effects of changing climate and vegetation on hydrological processes. Results show that over 1960–2016 most hydrological changes were driven by climate changes, such as decreasing snowfall by 7.8 mm decade−1, deepening active layer thickness by 1.8–4.2 cm decade−1, earlier snowcover depletion and ground thaw initiation dates from 1.5 to 3 and by 1 to 3 days decade−1, respectively, and diminishing annual sublimation and soil moisture by 1.3 and 5.9 mm decade−1, respectively. Evapotranspiration decreased by 2.5 mm decade−1, due to decreasing irradiance and soil moisture. Shrub expansion and densification decreases blowing snow redistribution by 20 to 40 mm and sublimation by 1 to 10 mm. Streamflow dropped by 40 mm as a response to the 48 mm decrease in precipitation, suggesting a small degree of hydrological resiliency. These results represent the first detailed estimate of hydrological changes occurring in small Arctic basins, and can be used as a reference to inform other studies of Arctic climate change impacts.
... Plant population shift up when seeds are dispersed and establish above the current range (Corlett & Westcott, 2013). Various studies clearly indicate an upward shift of woody vegetation at the alpine treeline ecotone (Payette & Filion, 1985;Harsch et al., 2009). The rate of shift varies among different species and it is location specific. ...
The increase in temperature due to global warming is affecting forest ecosystems worldwide. At the treeline ecotone growth is usually restricted by low temperatures. Recently, the impacts of climate change have been visible with the upward shift of the Himalaya fir (Abies spectabilis) in Nepal. Rhododendron campanulatum D. Don grows at the treeline ecotone and subalpine forest. Hardly any studies have been carried on this species in Nepal. The local people have reported that this species has been seen colonizing upper altitude in recent years, however, these needs to be verified with dendroecological studies. The study aims to assess the response of R. campanulatum to climatic variability and to evaluate the relationship of its basal diameter (Groundline) and age using dendroecological methods. Results reveal that the basal diameter was found to be significantly correlated with age (r2= 0.824, p<0.00001). Using the basal diameter age equations, attempts were made to study the age distribution along the altitudinal gradient. The species limit was observed at 4090 m asl. The age structure differed along the altitudinal gradient with multi age cohorts below the treeline and younger cohorts above the treeline. Results show that this species is migrating up at a rate of 24.7m per decade.
... Picea glauca (Moench) Voss (White spruce) is one of the signature tree species of the North American boreal forest. It occurs across the entire continent from Newfoundland and Labrador in the east to Alaska in the west, forming the northern treeline in the western part of North America (Lloyd et al., 2005;Payette and Filion, 1985). Its vertical distribution ranges from sea level to 1520 m (Burns and Honkala, 1990), often forming the elevational treeline. ...
Northern and elevational treelines are classic sites for dendroclimatological studies. At these marginal sites only one climate parameter is usually considered growth limiting and trees from these sites are therefore used to reconstruct that parameter back in time. Marginal sites are also those sites within a species range, where clonal reproduction is most frequent. Clonal growth can ensure plant species survival and growth under stressful conditions or if the environmental conditions do not allow sexual reproduction, e.g. by layering, by stems resprouting after damage, or through the exchange of resources between different clone ramets (“stems”). We literally stumbled across clonal and non-clonal growth forms of White spruce growing intermingled with each other at two Alaskan treeline sites. The two growth forms could not be distinguished a priori in the field. After sampling and detection of clones we thus asked whether clonal ramets and non-clonally grown trees (singletons) showed similar growth patterns. Clones were identified by identical multilocus genotypes in a SSR microsatellite genotyping analysis and radial growth was analyzed using traditional tree ring width methods High-frequency growth patterns were very similar between singletons and clonal ramets in Alaskan treeline White spruce, thus posing no problem in including both reproductive strategies in a classic dendroclimatological investigation.
... Although the method used to detect the changes in cover classes along the timberline ecotone is fairly reliable, explanation of the causes of such changes would require in-depth and long-term studies along the high-altitude forest-grassland interfaces. The results of the present study support the finding of field researchers that timberline ecotones have shifted slightly towards higher altitudes during recent decades in response to current warming (Payette and Filion 1985) at both regional and local scales (Masek 2001). ...
... Alpine treeline ecotones are considered to be sensitive to temperature increments because long-lived tree species growing at the treeline ecotone are more sensitive to climate variability (Chen et al. 2011). This relationship between climate and tree growth at the treeline was identified nearly 30 years ago in North America (LaMarche et al. 1984;Payette and Filion 1985;Cooper 1986;Salzer et al. 2009), the Alps (Nicolussi et al. 1995;Paulsen et al. 2000), and Patagonian Andes (Villalba et al. 1997;Körner 2012). These dendrochronological studies have emphasized that strong radial growth signals occurring in trees near the treeline are the result of temperature increase during the late twentieth century (Körner 2012). ...
A dendroclimatic study was conducted in the treeline ecotone of Barun Valley, eastern Nepal, to determine the tree-ring climate response and ring width trend of Abies spectabilis. A 160-year-old chronology, from 1850 to 2010, was developed from 38 tree-ring samples. No higher growth in recent decades was observed in tree-ring width in this area. The mean temperature of the current year in February and in the combined winter months of December, January, and February showed significant positive correlation with tree-ring width, although no significant correlation was found between tree-ring width and the precipitation pattern of the region. This tree-ring climate response result is different from that in other studies in Nepal, which could be attributed to location and elevation. © 2016 Northeast Forestry University and Springer-Verlag Berlin Heidelberg
... Despite some shortcomings (e.g., the degradation of dead trees or the sporadic presence of seedlings after recruitment pulses) (Szeicz and Macdonald 1995), field data and dendrochronogical methods allow quantifying and reconstructing treeline dynamics by providing age, growth rate and recruitment tree data with annual to decadal resolutions (Lloyd and Fastie 2003;Camarero and Gutiérrez 2004;Liang et al. 2011). Thus, how plots are surveyed is of vital importance to reach a suitable characterization of structure and to adequately infer treeline dynamics (Payette and Filion 1985;Hofgaard et al. 2009). Nevertheless, few studies have evaluated how different plot sizes and shapes affect the inferences on treeline dynamics, even though field sampling protocols considerably affect the quality, precision, and reliability of forest inventory data (Cherubini et al. 1998;Kangas and Maltamo 2006;Nehrbass-Ahles et al. 2014). ...
Key message
Field survey methods influence the assessment of treeline structure and inferences on reconstructed treeline dynamics.
Abstract
Numerous field studies have described the structure of alpine treeline ecotones encompassing the forest limit and treeline to infer their dynamics in response to climate warming. However, the inferred treeline dynamics may be biased due to the selection of different plot sizes and shapes. Rectangular large plots including the whole treeline ecotone, i.e., encompassing the forest limit and the treeline, and square small plots located at current treeline have been widely used. Nevertheless, little is known about how large a plot must be to capture the main features of treeline structure and dynamics. Here, we investigate this question at Smith fir treelines located in the Sygera Mountains, southeastern Tibetan Plateau. Six rectangular large treeline plots (30 × 150 m) were sampled and compared with six square small treeline plots (30 × 30 m). Six rectangular plots with lengths shorter than the treeline ecotone span (100–135 m) were also sampled and compared with the other two plot types. Dendrochronology was used to reconstruct the recruitment dynamics of treelines, which were related to summer mean minimum temperatures. Rectangular large plots better captured the main features of recent treeline dynamics such as the abundance of recruits from the 1950s onwards and the establishment of old trees. Therefore, large plots allowed reaching more robust conclusions on treeline dynamics as compared to small plots. On the other hand, smaller rectangular plots revealed similar findings to those inferred from large rectangular plots but with a much lower survey cost. We propose using smaller rectangular plot with its longest side being shorter than the ecotone span as the most reliable and practical method to characterize alpine treeline dynamics.
... To date, the focus of climate change research at the forest-tundra ecotone has been on trees (Harsch and Bader, 2011) and their responses to increased summer and winter temperatures, growing season length, and changes in duration of snow cover. At the tree line, relationships between temperature and range limits of tree species across gradients, both latitudinal (Payette and Filion, 1985;Hobbie and Chapin, 1998;MacDonald et al., 2000) and altitudinal (Körner and Paulsen, 2004;Körner, 2012) are well known. How tree species are responding to recent global change (e.g., increased summer temperatures) is less clear. ...
As climate warms, abiotic factors, as well as plant community and biodiversity structure, may constrain or promote the movement of ecotone boundaries. Our study sought to examine how plant communities change across the tree-line ecotone of the Mealy Mountains in Labrador, Canada. We established eight transects (50–100 m in length) along an elevation gradient in three tree-line zones (forest, forest-tundra, and alpine-tundra) and recorded all species and cover of vegetation in contiguous 1 × 1 m quadrats. Companion abiotic parameters of nutrients and soil temperature were also measured. The absence of abrupt changes in important soil nutrients and growing season temperatures suggests that these factors do not limit tree species establishment beyond the current tree line. Vegetation cover and richness, however, were highly variable and in some cases changed non-linearly across the tree-line ecotone. Tree cover and species density generally decreased with elevation, while some field layer species (< 25 cm in height) increased; the latter change seems to be influenced by ground shrubs rather than herbaceous species. As expected, transects separated by the greatest difference in elevation were the least similar (higher beta diversity/species turnover); however, species turnover between the forest and forest-tundra transects was higher than it was between forest-tundra and alpine-tundra transects, even though the latter were separated by a greater elevation. Community structure and species turnover vary greatly across a tree line with the greatest differences between the forest and the forest-tundra, suggesting a biotic or abiotic barrier. While our ability to predict how the tree line will respond to continued climate change is complicated by these patterns in plant communities, the potential barriers investigated and others identified will be a useful focus for future studies.
... It was believed that the following rapid rising of temperature and drought in spring were the main reason resulted in the high mortality of seedlings and juveniles. Recruitment and mortality patterns may be closely tied to climatic fluctuations, with periods of abundant regeneration coinciding with periods of favorable weather conditions (Franklin et al., 1971;Payette & Filion, 1985;Kullman, 1986). Further regeneration will be suppressed once a vigorously growing cohort of young plants has monopolized available resources (Hett & Loucks, 1976;Peet, 1981;Agren & Zackrisson, 1990). ...
Haloxylon ammodendron C.A. Mey Bunge is a desert shrub with ecological and economic importance. Because of the severe drought and the over-exploitation for firewood and livestock, the species is threatened. The survivor and mortality were studied in six populations distributed along the margin of Gurbatunggut desert. The size structures, life tables and survivor curves were constructed for the studied populations. Populations were dominated by juvenile individuals and the seedling recruitment was extremely limited. Size distributions were skewed towards larger size classes in all populations. The survivorship curves approached Deevey type III in which the highest mortality occurs in the early life stages. The results indicated that the populations of H. ammodendron are threatened and efforts are required to minimize uncontrolled exploitation. Due to the very limited seedling recruitment, conservation efforts are required to protect and develop the extant populations. For this purpose, in situ and ex situ conservation of H. ammodendron populations are strongly recommended.
... Snowmelt changes led to earlier flowering and appearances of plants and arthropods in Greenland between 1996 and 2005 (Høye et al., 2007) and earlier flowering in an alpine plant in the Rocky Mountains, USA, between 1975(Hülber et al., 2010Lambert et al., 2010). Earlier snowmelts decreased floral resources and hence affected insect population dynamics in mountain ranges in the USA in the years 1980, 1985, 1986, and 1989(Boggs and Inouye, 2012. In Colorado, USA, the yellow-bellied marmot emerged earlier from hibernation due to snowmelts becoming earlier over 1976(Ozgul et al., 2010 while in Alberta, Canada, Columbian ground squirrels emerged later over 1992-2012 owing to delayed snowmelts associated with increased late-season snowstorms (Lane et al., 2012). ...
Past Assessments The topics assessed in this chapter were last assessed by the IPCC in 2007, principally in WGII AR4 Chapters 3 (Kundzewicz et al., 2007) and 4 (Fischlin et al., 2007), but also in WGII AR4 Sections 1.3.4 and 1.3.5 (Rosenzweig et al., 2007). The WGII AR4 SPM stated "Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases," though they noted that documentation of observed changes in tropical regions and the Southern Hemisphere was sparse (Rosenzweig et al., 2007). Fischlin et al. (2007) found that 20 to 30% of the plant and animal species that had been assessed to that time were considered to be at increased risk of extinction if the global average temperature increase exceeds 2°C to 3°C above the preindustrial level with medium confidence, and that substantial changes in structure and functioning of terrestrial, marine, and other aquatic ecosystems are very likely under that degree of warming and associated atmospheric CO2 concentration. No time scale was associated with these findings. The carbon stocks in terrestrial ecosystems were considered to be at high risk from climate change and land use change. The report warned that the capacity of ecosystems to adapt naturally to the combined effect of climate change and other stressors is likely to be exceeded if greenhouse gas (GHG) emission continued at or above the then-current rate. 4.2. A Dynamic and Inclusive View of Ecosystems There are three aspects of the contemporary scientific view of ecosystems that are important to know for policy purposes. First, ecosystems usually have imprecise and variable boundaries. They span a wide range of spatial scales, nested within one another, from the whole biosphere, down through its major ecosystem types (biomes), to local and possibly short-lived associations of organisms. Second, the human influence on ecosystems is globally pervasive. Humans are regarded as an integral, rather than separate, part of social-ecological systems (Gunderson and Holling, 2001; Berkes et al., 2003).
... Important climatic variations have occurred in the northern hemisphere throughout the twentieth century (Jones et al., 1982). Several investigations in the boreal zone, and along the altitudinal and the latitudinal tree line, have indicated a causal relationship between tree regeneration rates and twentieth century climatic changes (Kullman, 1979, 1986, 1987; Morin and Payette, 1984; Payette and Filion, 1985; Steijlen and Zackrisson, 1987). However, there has been little assessment of the effects of climatic fluctuation for population located well into the forested area. ...
The age structure of two mixed red pine (Pinus resinosa Ait.) and jack pine (Pinus banksiana Lamb.) forests located at Lac Duparquet, northwestern Quebec, were correlated with mean annual temperature and total precipitation recorded at Iroquois Falls for the period between 1913 and 1986. The age structures of both pine species showed a common pattern of regeneration characterized by low regeneration before 1930, an important regeneration peak starting around the 1930s, a dip in the age structure around 1950, a second, though less important, regeneration peak in the 1960s, and an important drop, especially for red pine, after 1970. In general, high regeneration rates were positively correlated with precipitation and negatively with temperature, suggesting that pine recruitment is negatively affected by low snow cover and/or drought. The absence of correlation with temperature suggests that the red pine northern limit may be controlled more by a change in the fire regime than by increasing temperature.
... As a result, tree-line movement and infilling due to climate change have been extensively studied (e.g., Holtmeier and Broll, 2005;Holtmeier, 2009;Mamet and Kershaw, 2012). Although tree-line movement has not been widespread, many studies have found an increase in tree density within the forest-tundra ecotone (Payette and Filion, 1985;Scott et al., 1987;Lavoie and Payette, 1994). Tree-line movement is a long-term process: an initial change in growth of current trees causes reduced wind velocities, increased snow accumulation, more favourable soil conditions, altered vegetation cover (more luxuriant species) and eventually a greater nutrient supply (Holtmeier and Broll, 2010a). ...
The forest-tundra ecotone is expected to experience some of the initial effects of climate change. At the forefront of this transition zone, we find clonal growth forms of stunted and deformed trees with and without taller erect trees, called tree islands and krummholz, respectively. We sought to assess the potential effects of expansion of these growth forms on tundra plant species at two Canadian locations, one in the Mealy Mountains of Labrador and the other near Churchill, Manitoba. Our objectives were 1) to analyze the structure (height distribution and shape) of these clonal growth forms to determine whether they are expanding; 2) to compare tree cover on the leeward and windward sides of these growth forms and 3) to assess patterns in individual plant species across these growth forms. Cover of trees and other plant species was measured at both locations, while tree stems were mapped near Churchill only. The presence of seedlings and symmetric patterns of tree height suggest that half of the tree islands near Churchill may be expanding. The edges of tree islands and krummholz may harbour safe sites for tundra plant species, as shown by peaks in cover of individual species at these edges. Our results suggest that expansion of tree islands and krummholz would affect the abundance of tundra plant species, which could lead to changes in species composition and biodiversity.
The boreal forest covers about one-third of the world’s forested area. Ecosystem creation and ecosystem collapse are common components of the long-term evolution of the boreal forest fueled by the ever-changing climatic and geophysical conditions since the last glacial period. After the late Pleistocene characterized by abrupt climatic changes, ecosystem building of the boreal biota prevailed from early- to mid-Holocene times (from 10,000 to 4000 years before present), including forest and peatland growth and expansion from south to north towards the Arctic tundra. Large-scale collapse of the dominant terrestrial ecosystems occurred after the mid-Holocene caused by the progressive decrease of orbitally forced solar radiation. Post-fire deforestation during the late Holocene, especially during the Little Ice Age (particularly from the end of the sixteenth century to the mid-nineteenth century), occurred in the northern part of the boreal forest with the creation of subarctic tundra covering the exposed summits and snow-patch environments on downwind side of ridges. Permafrost also expanded in wetlands with the creation of palsas and extensive peat plateaus. Human-induced post-Little Ice Age warming is unparalleled at the scale of the Holocene and is now significantly impacting the cold-prone ecosystems of the northern part of the boreal forest. Their changes and replacement by novel ecosystems adapted to the new climate are already detectable. Variable tree line advances and shrubification of forest-tundra and Arctic tundra environments across North America and Eurasia are presently the main ecosystem responses, with large-scale permafrost decay in subarctic and Arctic wetlands, to the continuous and increased warming of the twentieth and the twenty-first centuries. Fire, the principal disturbance factor of ecosystems after climate is bound to affect profoundly the integrity of most mesic and dry plant communities. It is expected that the fire regime of the northern part and southern part of the boreal forest will cause extensive changes and severe damage to northern ecosystems, more so if precipitation amounts are reduced during this century. Greater damage to the forest is anticipated if this change of the fire regime is accompanied by an increase of human impact.
Spatial identifcation and description of ecological boundaries is fundamental to better understanding of treeline dynamics. Ecological boundaries across two contrasting subalpine Pinus uncinata forest-alpine grassland ecotones were delineated within the Central Pyrenees (Ordesa and Tessó sites). Boundaries were delineated using an edge detection algorithm for two-dimensional data (lattice-wombling). Tree density, size-structure, growth-form, and estimated age were used to reveal spatial location of boundaries for several size and growth-form tree classes. Overlap statistics were applied to quantify spatial relationships among boundaries determined for different sets of variables. The most significant and consistent boundaries were those for structural variables at the Ordesa site. At this site, the sequential disposition of bigger and unistemmed trees descending across the ecotone produced boundaries for size-structure and growth-form variables. These boundaries were located along an ordered spatial pattern (altitudinal diagonal). At the Tessó site, there were few consistent boundaries, most of which were developed along the slope. Overlap statistics showed that boundaries at the Ordesa site were more spatially related than were those at the Tessó site. This result held when any set of variables was considered. The studied ecotones describe sharp (Ordesa site) and gradual (Tessó site) structural changes in tree populations, related to situations similar to the ecotone and ecocline concepts, respectively. The possible environmental driving factors producing these patterns are the strong winds and reduced snow cover at higher altitudes at the Ordesa site, and snow avalanches at the Tessó site. Boundary detection through time in permanent plots might be a better tool for monitoring climate-change impact in the forest-alpine grassland ecotone than the subjective location of treelines.
Global warming may accelerate nitrogen (N) transformations in the soil, with potentially large effects in N‐poor high‐elevation ecosystems. To gain insight into the partitioning of inorganic and organic N inputs within the plant–soil system and how warming influences these patterns, we applied a ¹⁵ N label ( ¹⁵ NH 4 Cl or ¹⁵ N‐glycine) shortly after snowmelt during the sixth year of experimental soil warming (+4 °C) at treeline in the Swiss Alps.
Seven weeks after labelling, approximately 60% of the applied label remained in the soil organic layer to 10 cm depth, whereas label recovery summed over all measured plant pools was <10% of the added label. Soil warming led to a weaker Δ ¹⁵ N signal in plants and no change in the amount of added label recovered in plants. This ¹⁵ N dilution resulted from a greater N pool size of some plant species in warmed plots as well as enhanced availability of (unlabelled) N under warming. Temporal dynamics of foliar Δ ¹⁵ N in dominant dwarf shrub species suggested that these plants primarily take up N early in the season. In a subset of plots labelled with ¹³ C‐enriched glycine (U‐ ¹³ C 2 ‐ ¹⁵ N‐glycine), the labelled glycine was mineralized rapidly, with approximately 50% of the applied ¹³ C respired as CO 2 during the first 99 h, suggesting that effects of warmer soils on N dynamics in this treeline system are only slightly modulated by the preferences of different plant species for inorganic and organic N forms.
Synthesis . Plants growing in warmer soils acquired more unlabelled, soil‐derived N in the sixth year of treatment, implying a sustained increase in N mineralization and availability in alpine treeline ecosystems with higher soil temperatures predicted for the future. Wide variation in the ability of plant species and functional groups to compete for early‐summer N inputs means that there is a feedback between plant community shifts and N dynamics under environmental change at the treeline.
We tested the hypothesis considering old‐growth subarctic woodlands, free of fire, insect and stand‐scale blowdown disturbances, to be at equilibrium with the climate. To do so, we explored the status of Hudsonian woodlands based on the natality/mortality ratio.
The gap history of the woodland was reconstructed based on mapping and dating of dead gap‐spruces ( Picea mariana ). Among the 25 gaps studied, 763 dead trees and only 14 saplings were recorded. The center of some gaps remained treeless over the last 1000 yr, and gap area doubled over the last 100 yr. The status of the tree population is in a demographic disequilibrium caused by the small replacement of dead spruces in all of the gaps.
Episodes of ‘mass’ mortality occurred during several decades corresponding to years of favorable tree‐ring growth. The natural process of gap‐filling appears to be ineffective under current conditions. Good tree‐ring growth of dying trees suggests abundant precipitation during the mortality episodes, but precipitation appears to be involved indirectly in the mortality process.
The main cause of the widespread tree mortality during the last centuries of gap expansion appears to be biotic in origin. The impact of pathogenic fungal disease linked to late‐lying snow cover is proposed for the mortality events.
This chapter discusses patterns of coniferous forest response to climatic variation at two temporal scales: (1) the Late Quaternary and (2) the last millennium. The individualism of the behavior of a species with respect to physiological attributes is mirrored in long-term and large-scale vegetation dynamics. Weather and climate vary on timescales from seconds to millions of years. The climatic changes marking the transition from the last glaciation to the current interglacial period caused major reorganization of coniferous forests worldwide. For example, boreal forests covered substantially less area during full glacial times as compared to today, whereas conversely, the coniferous forest cover in southwestern North America expanded during full glacial times. Temperature fluctuations in the last millennium have accrued two broad classes of response in coniferous species: (1) at several arctic and alpine tree lines, range limits have shifted as a result of altered reproductive and establishment rates, and (2) in areas where climatic limitations to growth have changed, established trees have undergone phenotypic adjustments to the altered climate. Long-term records of vegetation change indicate that altered seasonality such as that associated with the glacial/interglacial transition is commonly associated with vegetation types without analogs on the modern landscape. The individualism of species physiological attributes is also reflected in long-term vegetation dynamics. Seasonality effects are also relevant to considerations of future climate change because general circulation models predict independent changes in seasonal climates. Also, short-term extreme events can have long-term implications on forest populations.
Mediterranean areas are considered particularly sensitive to climate change. Two questions are asked in this context: what is the nature and magnitude of regional climate change (climate and snow cover) in central Chile, since the 70's? What are the changes in mountain vegetation (in the altitude range of 1,500-2,500 m), especially at the upper limit of Kageneckia angustifolia forest? The first part of the thesis shows the characteristics of mountain environments and observed climate change at global and Chilean local level. It also presents the study area, from the standpoint of biogeography and climate. The second part refers to the data and methodology. We used a multiscale approach to the confrontation and the application of several complementary techniques: remote sensing, climatic data and field measurements. The third part presents the results. Climate data recorded in the last 30 years in the stations of El Yeso (2,500 m) and Los Bronces (3,500 m), shows an increase of about 1° C in mean annual temperature, been the sharpest increase in El Yeso, especially in average of low temperatures. In relation to snow cover, it shows high variation and a rise up in the limit of snowline in recent decades, about 300 m. These results are accompanied by a slight increase in NDVI. In the Yerba Loca valley, the diachronic study of Kageneckia angustifolia forest ecotone shows changes towards an increase forest areas and densification. Finally, the experience of germination in Yerba Loca indicates a significant difference between the percentage of germination of the seeds under protection from snow and the ones without treatment, with a negative effect of snow cover on the germination.
Four communities, formed as a result of locally varying site conditions, were identified and studied along the timberline ecotone in part of Kedarnath Wildlife Sanctuary (KWS). Communities on the vicinity of pilgrimage site and along gentler slopes were highly disturbed having sharp timberlines, while those located far and in the steep slopes were less affected, forming a little broader transition. The tree density ranged from 340 to 780 trees/ha, while the basal cover of communities varied greatly and ranged from 6.4 to 55.1 m 2 /ha. Birch dominated community had lowest basal area among all the communities, while mixed community had the highest. In all the respective communities, from subalpine zone, density and basal area was higher than that of timberline zone. The Importance Value Index (IVI), which used to determine the overall importance of each species in the community structure, of dominant species at timberline was more than 200 in all the communities, except in the mixed community. Influence of the anthropogenic disturbances was apparent on the regeneration performance of all the studied tree species. Rhododendron campanulatum was the dominant shrub species of the area and formed krummholz, while distribution of other species varies greatly with forest type. The shrub density decreased from high to low disturbance, while the herbaceous species density increased with prevalence of a few species favoring the high disturbance (grazing). The shrub and herb species richness was higher in the ecotone zone. Some uncommon species like Balanophora involucrata and Aralia cissifolia were also found at timberline. Three species of Lady's Slipper orchid were reported together from Betula utilis community at timberline ecotone.
Climate is the state factor that most strongly governs the global distribution of terrestrial biomes. This chapter provides a general background on the functioning of the climate system and its interactions with atmospheric chemistry, ocean, and land.
Seedling recruitment is a critical life history stage for trees, and successful recruitment is tightly linked to both abiotic factors and biotic interactions. In order to better understand how tree species' distributions may change in response to anticipated climate change, more knowledge of the effects of complex climate and biotic interactions is needed. We conducted a seed-sowing experiment to investigate how temperature, precipitation and biotic interactions impact recruitment of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) seedlings in southern Norway. Seeds were sown into intact vegetation and experimentally created gaps. To study the combined effects of temperature and precipitation, the experiment was replicated across 12 sites, spanning a natural climate gradient from boreal to alpine and from sub-continental to oceanic. Seedling emergence and survival were assessed 12 and 16 months after sowing, respectively, and above-ground biomass and height were determined at the end of the experiment. Interestingly, very few seedlings were detected in the boreal sites, and the highest number of seedlings emerged and established in the alpine sites, indicating that low temperature did not limit seedling recruitment. Site precipitation had an overall positive effect on seedling recruitment, especially at intermediate precipitation levels. Seedling emergence, establishment and biomass were higher in gap plots compared to intact vegetation at all temperature levels. These results suggest that biotic interactions in the form of competition may be more important than temperature as a limiting factor for tree seedling recruitment in the sub- and low-alpine zone of southern Norway.
Le developpement et la croissance d'une population cotiere d'epinette blanche ( Picea glauca [Moench] Voss) ont ete etudies sur le littoral en emersion du detroit de Manitounuk situe sur la cote est de la baie d'Hudson. Cette region subit un relevement glacio-isostatique a un taux des plus eleves au monde (1,2 a 1,5 m/siecle). La recherche vise a determiner la relation entre le developpement d'une frange d'arbustes et l'expansion de l'epinette blanche et a mettre en evidence les changements environnementaux survenus au cours du dernier siecle et menant a une population forestiere ouverte. La colonisation des rivages par l'epinette blanche est sous l'etroite dependance de l'etablissement prealable d'une frange arbustive. Les arbustes forment une bande etroite dans la zone suprariveraine encore humide, alimentee par le drainage hypodermique des terres avoisinantes. En hiver, ils retiennent la neige poudree par le vent et protegent ainsi du froid les semis d'epinette blanche qui s'y etablissent en abondance. Avec l'emersion des terres, la nappe phreatique s'abaisse et la frange d'arbustes hygrophiles se deplace vers le plan d'eau. La degradation des arbustes change le regime d'accumulation de la neige au sol a l'emplacement des epinettes preetablies. Seules les epinettes les plus developpees, qui avaient initialement une croissance rapide, survivent. Il en resulte une population clairsemee en milieu tres expose, qui n'a de possibilite d'expansion que derriere les buttes de pergelisol et les plages soulevees ou s'accumule la neige. Les etapes du processus de colonisation sont mises en evidence par la distribution des arbustes et des arbres selon leur âge, par l'elongation et l'accroissement radial de l'epinette blanche et les macrofossiles identifiables laisses depuis la fin du XIXe siecle.
1 Black spruce (Picea mariana) experienced increased radial growth and stem height over the last 100 years at treeline in subarctic Quebec, suggesting warmer and snowier conditions. We tested if recent climate change also induced a shift from forest to krummholz during the Little Ice Age and stand reversion from krummholz to forest during the 1900s. Whether the shifts caused measurable displacements of the forest limit were also examined. 2 Growth forms of living and dead spruces were compared in five lichen-spruce stands located 0, 2, 4, 6 and 8 km south of the krummholz limit. The age structure of supranival shoots (stems standing above the snow cover) at each site was also determined. 3 A reversion from lichen-spruce forest to krummholz probably occurred during the mid-1800s. Since the late 1800s, the forest limit moved 4 km northward most likely in response to milder winter conditions. Krummholz changed progressively to forest as spruce height and frequency of the tree growth form increased. Thus the northward advance of the forest limit resulted from structural changes of pre-established spruces, whereas there was no evidence for a recent spruce establishment in the tundra.
I investigated the dates of origin of riparian forests dominated by Populus angustifolia James, and recent interannual fluctuation in P. angustifolia seedling abundance on a relatively undisturbed 6-mile reach of the Animas River in southwestern Colorado. The goal was to develop plausible hypotheses about the roles of floods and interannual climatic fluctuation in structuring these forests. I determined the year of origin 242 recently-established seedlings and fifty-seven forest stands, and then developed empirical models relating seedling abundance and stand-origin events to climatic and hydrologic fluctuations. Seedlings were most abundant in years with cool winters, wet springs, and cool, wet falls (R2 adj=0.98). Both good seedling years and stand-origin years were associated with winter blocking in the North Pacific and a persistent late-summer Arizona Monsoon. Extant stand originated in ten to thirteen discrete periods between 1848 and 1976, in years with both high spring and fall peak discharges. Expected seedling abundance and stand-origin dates since 1914 were reconstructed using climate data, and were extended to 1556 using tree-ring chronologies. Model results suggest good seedling years occurred more frequently (about ever 3.4 years) than stand-origin years (about every 10-15 years). Good seedling years were 2-3 times, and stand-origin years were 5 times more common from 1848 to 1985 than from 1556 to 1848. Recent expansion of P. angustifolia may have been favoured by more frequent cool, wet years since 1848.
The Campbell-Dolomite uplands comprise a small area (140km2) of outcropping, faulted dolomite, limestone, and shale E of the Mackenzie River Delta c40km S of the northern limit of trees. The major landforms are bedrock ridges and plateaux, steep colluvium, stable slopes, shorelines, and depressions. A principal component anlaysis of vegetation-cover data from 150 stands suggest that much of the variation within the heterogeneous vegetation is correlated with these broad habitat categories. A glacially modified karstic (solution) depression contains a small (8 ha), relatively deep (22m) apparently meromictic lake, which yielded a 12 000 yr core of sediment. The pattern of change in pollen spectra suggest an initial phase of migration of willow and herbs from adjacent unglaciated Megaberingia (North Yukon and Alaska), followed rapidly by dwarf birch and later poplar. Slow soil development (humus accumulation, rising permafrost table) probably favoured the spread of the palynologically 'silent' elements - lichens, ericads, and Dryas (the dominants of the modern ground vegetation). Changes in the influx values of Picea suggest a climatically induced increase in tree density and/or pollen production during the period 9 000-7 000 BP.-from Author
In the forest-tundra ecotone region of the Washington and Oregon Cascades, massive invasion into subalpine meadows by a variety of tree species, especially Abies lasiocarpa and Tsuga mertensiana, has been noted. The most intense period of establishment in most areas was during 1928 to 1937. Little invasion has been noted in the Cascade Range since about 1945. We consider fire, grazing, and forest edge effect as possible factors influencing the massive establishment of trees during this time but suggest that climatic change is the most probable causative factor. At Paradise Valley on the slopes of Mount Rainier, trees invaded meadows during the period when the mass budget of the Nisqually Glacier was generally negative; after 1945, this mass budget was positive or balanced. The snow-free period in certain subalpine meadow communities is probably the most critical factor affecting tree establishment. Invasion densities were low on tall-forb-dominated (Valeriana sitchensis) and grass (Festuca viridula) communities and were high on low-forb-dominated (Potentilla flabellifolia) and shrub (Phyllodoce empetriformis-Vaccinium deliciosum) meadow types. However, growth rates of established trees appeared greatest on the tall-forb and grass communities.
Earlier studies in Alaska and northwest Canada have shown inconsistent evidence for the expected northward extension of the Arctic tree line during the Hypsithermal Interval. Only megafossil evidence has supported this suggestion; the palynological findings have been inconclusive. The Tuktoyaktuk Peninsula, in the Northwest Territories of Canada, offers critical sites for studies of late-Pleistocene ecology, because of its geological, biotic, and climatological features. Palynological and megafossil evidence is presented from sites on the Tuktoyaktuk Peninsula, indicating northward advance of the Arctic tree line during the period 8500-5500 B.P. Relative pollen frequencies of a core of lake sediment suggest a late-Pleistocene sequence as follows: 12,900-11,600 dwarf birch tundra; 11600-8500 forest tundra; 8500-5500 closed-crown spruce-birch forest; 5500-4000 tall shrub tundra; 4000-present dwarf birch heath tundra. These results suggest that during the Hypsithermal Interval the Arctic Front (July position) was further north, over the Beaufort Sea, a displacement from its present position of about 350 km. The Tuktoyaktuk Peninsula, presently occupied by tundra, and dominated by the Arctic airstream in July, was apparently under forest, with warm, moist Pacific air during the Hypsithermal Interval.
The morphology of paleosols and radiocarbon-dated charcoal from buried surface horizons of soils provide evidence to suggest that between periods of northward forest encroachment tundra climate has dominated areas at least 50 km south of the present forest/tundra border in southwest Keewatin. The present forest/tundra border climate is nearly as severe as any climate that has prevailed in the area since deglaciation.
A nested quadrat pattern analysis suggests that the adult members of early seral tree species exhibit maximal clumping at a quadrat size corresponding to the sizes of natural lightgaps created by treefalls. However, the dominant species show a pattern of randomness at nearly all quadrat sizes. Some seral characteristics of forest trees support the idea that the beech-maple forest is a mosaic of species of different seral stages.
Indicators of large-scale climate developments show that the oscillatory cooling observed in the past 30 yr in the Northern Hemisphere has not yet reversed. This conclusion was reached by updating our data on the month-to-month, season-to-season, and year-to-year variations of selected zonally averaged meteorological parameters.
During the past 5,000 yr BP the Tropics have experienced an increase in aridity and aeolian activity in both maritime and continental areas1–4. In contrast the onset and subsequent development of post-Hypsithermal climates in northern latitudes were primarily conducive to global cooling. It is suggested here that aeolian activity in cold environments represents a direct response to this long-term cooling trend that began after 6,000–5,000 yr BP, at the end of the climatic optimum5–9. This study establishes the Holocene chronology of sand dunes near the outer forest limit in northern Quebec (Fig. 1). I show here that fires initiate the aeolian activity, and that the fire–dune relationship is typical of cooling period. On this basis, a palaeoclimatic reconstruction since the climatic optimum is proposed.
Fluctuations of the surface air temperature averaged globally are presented for 16 years from 1957 to 1972 by objective analysis of the global network data. The results show appreciable effects of large eruptions of volcanoes on the hemispheric and/or global mean temperatures.Schwankungen der Lufttemperatur in Bodennhe, global gemittelt, wurden fr die 16 Jahre von 1957 bis 1972 auf Grund objektiver Analysen des globalen Beobachtungsnetzes ermittelt. Die Resultate zeigen beachtliche Effkete starker Vulkanausbrche auf hemisphrische sowie globale Mitteltemperaturen.
Remains of dead bristlecone pine (Pinus longaeva Bailey) are found at altitudes up to 150 m above present treeline in the White Mountains. Standing snags and remnants in two study areas were mapped and sampled for dating by tree-ring and radiocarbon methods. The oldest remnants represent trees established more than 7400 y.a. Experimental and empirical evidence indicates that the position of the treeline is closely related to warm-season temperatures, but that precipitation may also be important in at least one of the areas. The upper treeline was at high levels in both areas until after about 2200 B.C., indicating warm-season temperatures about 3.5°F higher than those of the past few hundred years. However, the record is incomplete, relative warmth may have been maintained until at least 1500 B.C. Cooler and wetter conditions are indicated for the period 1500 B.C.-500 B.C., followed by a period of cool but drier climate. A major treeline decline occurred between about A.D. 1100 and A.D. 1500, probably reflecting onset of cold and dry conditions. High reproduction rates and establishment of scattered seedlings at high altitudes within the past 100 yr represents an incipient treeline advance, which reflected a general climatic warming beginning in the mid-19th century that has lasted until recent decades in the western United States. This evidence for climatic variation is broadly consistent with the record of Neoglacial advances in the North American Cordillera, and supports Antevs' concept of a warm “altithermal age” in the Great Basin.
Complex glacier and tree-line fluctuations in the White River valley on the northern flank of the St. Elias and Wrangell Mountains in southern Alaska and Yukon Territory are recognized by detailed moraine maps and drift stratigraphy, and are dated by dendrochronology, lichenometry, 14C ages, and stratigraphic relations of drift to the eastern (1230 14C yr BP) and northern (1980 14C yr BP) lobes of the White River Ash. The results show two major intervals of expansion, one concurrent with the well-known and widespread Little Ice Age and the other dated between 2900 and 2100 14C yr BP, with a culmination about 2600 and 2800 14C yr BP. Here, the ages of Little Ice Age moraines suggest fluctuating glacier expansion between ad 1500 and the early 20th century. Much of the 20th century has experienced glacier recession, but probably it would be premature to declare the Little Ice Age over. The complex moraine systems of the older expansion interval lie immediately downvalley from Little Ice Age moraines, suggesting that the two expansion intervals represent similar events in the Holocene, and hence that the Little Ice Age is not unique. Another very short-lived advance occurred about 1230 to 1050 14C yr BP. Spruce immigrated into the valley to a minimum altitude of 3500 ft (1067 m), about 600 ft (183 m) below the current spruce tree line of 4100 ft (1250 m), at least by 8020 14C yr BP. Subsequent intervals of high tree line were in accord with glacier recession; in fact, several spruce-wood deposits above current tree line occur bedded between Holocene tills. High deposits of fossil wood range up to 76 m above present tree line and are dated at about 5250, 3600 to 3000, and 2100 to 1230 14C yr BP. St. Elias glacial and tree-line fluctuations, which probably are controlled predominantly by summer temperature and by length of the growing and ablation seasons, correlate closely with a detailed Holocene tree-ring curve from California, suggesting a degree of synchronism of Holocene summer-temperature changes between the two areas. This synchronism is strengthened by comparison with the glacier record from British Columbia and Mt. Rainier, Likewise, broad synchronism of Holocene events exists across the Arctic between the St. Elias Mountains and Swedish Lappland. Finally, two sequences from the Southern Hemisphere show similar records, in so far as dating allows. Hence, we believe that a preliminary case can be made for broad synchronism of Holocene climatic fluctuations in several regions, although further data are needed and several areas, particularly Colorado and Baffin Island, show major differences in the regional pattern.
Radiocarbon dating of charcoal on podzols along a transect reaching 280 kilometers north of the present tree line from Ennadai Lake indicates that former forests were burnt about 3500 years ago and again about 900 years ago. These forests probably were associated with periods of relatively mild climate.