Coupling microscale vegetation–soil water and macroscale vegetation–precipitation feedbacks in semiarid ecosystems

At macroscale, land–atmosphere exchange of energy and water in semiarid zones such as the Sahel constitutes a strong positive feedback between vegetation density and precipitation. At microscale, however, additional positive feedbacks between hydrology and vegetation such as increase of infiltration due to increase of vegetation, have been reported and have a large impact on vegetation distribution and spatial pattern formation. If both macroscale and microscale positive feedbacks are present in the same region, it is reasonable to assume that these feedback mechanisms are connected. In this study, we develop and analyse a soil‐vegetation‐atmosphere model coupling large‐scale evapotranspiration–precipitation feedback with a model of microscale vegetation–hydrology feedback to study the integration of these nonlinearities at disparate scales. From our results, two important conclusions can be drawn: (1) it is important to account for spatially explicit vegetation dynamics at the microscale in climate models (the strength of the precipitation feedback increased up to 35% by accounting for these microscale dynamics); (2) studies on resilience of ecosystems to climate change should always be cast within a framework of possible large‐scale atmospheric feedback mechanism (substantial changes in vegetation resilience resulted from incorporating macroscale precipitation feedback). Analysis of full‐coupled modelling shows that both type of feedbacks markedly influence each other and that they should both be accounted for in climate change models.     

Climate change has indirect effects on resource use and overlap among coexisting bird species with negative consequences for their reproductive success

Climate change can modify ecological interactions, but whether it can have cascading effects throughout ecological networks of multiple interacting species remains poorly studied. Climate‐driven alterations in the intensity of plant–herbivore interactions may have particularly profound effects on the larger community because plants provide habitat for a wide diversity of organisms. Here we show that changes in vegetation over the last 21 years, due to climate effects on plant–herbivore interactions, have consequences for songbird nest site overlap and breeding success. Browsing‐induced reductions in the availability of preferred nesting sites for two of three ground nesting songbirds led to increasing overlap in nest site characteristics among all three bird species with increasingly negative consequences for reproductive success over the long term. These results demonstrate that changes in the vegetation community from effects of climate change on plant–herbivore interactions can cause subtle shifts in ecological interactions that have critical demographic ramifications for other species in the larger community.     

荒漠化与气候变化间反馈机制研究进展

荒漠化和气候变化是全球关注的重大环境问题,两者间的反馈机制是目前科学研究的热点之一。从荒漠化与气候变化间的反馈机制和荒漠化及其防治对碳源／汇的影响两方面对其研究进展进行了评述。以往的研究表明,荒漠化对区域乃至全球气候变化的影响主要通过荒漠化过程中植被覆盖降低一地表反射率提高和(或)土壤含水量降低-降雨量降低-植被覆盖降低这样一个正反馈机制(荒漠化生物地球物理模型“Charney假说”及其衍生理论)来实现的,此外大气中悬浮的沙尘具有明显抑制降雨的作用,土地荒漠化所导致的沙尘暴频发及其影响范围之大也将对全球气候变化产生显著影响。气候变化对荒漠化的影响则表现在对荒漠化的范围、发展速度和强度以及潜在危险性及干旱生态系统的结构、功能及生产力的影响上。同时作为全球重要的碳贮存地,干旱区的变化从一定程度上影响到大气中CO2的收支．据估算全球荒漠化所导致的碳损失总量为18～28Pg C,其中中国近40a来因土地沙质荒漠化导致的CO2净释放量为91Mt C,如果UNEP建议的退化土地治理措施得以实施,每年可固定37Pg的碳,约占CO2年排放量的15％．其投入低于一些限制CO2排放的措施,因此具有很大的吸引力。从目前的研究进展来看,大多数研究尚处于定性描述阶段,虽然有一些量化的尝试,但多停留在低精度的外推或估算上,因此今后有关荒漠化与气候变化间反馈机制研究的重点应放在：(1)量化气候变化过程对干旱生态系统弹性、生物多样性、生物生产力和总体健康的影响。(2)模拟荒漠化发生发展对区域和全球的气候变化影响,(3)评价荒漠化防治对气候变化的可能影响及其程度,特别是一些大范围的生态建设工程在防治土地荒漠化方面的作用及其对气候变化的可能影响。简言之,从科学和政策的角度来看弄清荒漠化与气候变化间的反馈机制不仅有利于区域和全球尺度荒漠化防治的开展,而且也将为国际气候变化框架条约中相关部分的协商及谈判提供依据。     

植被变化对气候的反馈机制及调节效应

植被通过光合作用固定大气中的CO₂来减缓温室效应，同时植被也通过改变地表能量收支影响温室效应。在过去的气候-植被研究中，大多关注气候变化对植被的影响，而植被对气候反馈的研究相对较少。植被通过调节地表能量收支、水通量等重要地气过程影响局地、区域乃至全球气候，在气候变化中的作用十分重要。因此，需要厘清植被对气候的反馈效应机制及其结果，并识别其地域差异。从生物地球物理和生物地球化学过程两方面分析植被与气候之间的作用机制，对全球及关键区域内植被变化对局地、区域乃至全球的气候反馈效应进行了系统总结：（1）生物地球物理反馈的区域特征明显，生物地球化学反馈则表现在全球尺度上，二者相互作用但难以统一；（2）植被破坏带来的气候影响在气温效应方面与生态系统的类型及地理分布相关：热带森林破坏带来增温效应，北方森林破坏带来降温效应，温带森林破坏则会通过增加森林反照率抵消丢失的固碳降温效应，气温效应表现不明显；（3）当前研究对关键过程机制考虑不够完善，不同研究方法的结果差异较大，且缺乏高质量观测数据的验证；同时考虑生物地球物理和生物地球化学的净气候反馈研究尚无法支撑植树造林对气候变化单一减缓作用的常规理解。本文可为科学评估植树造林对气候变化作用的方向与强度提供理论依据。     

Climate Change Effects on Vegetation Distribution and Carbon Budget in the United States

The Kyoto protocol has focused the attention of the public and policymarkers on the earth's carbon (C) budget. Previous estimates of the impacts of vegetation change have been limited to equilibrium “snapshots” that could not capture nonlinear or threshold effects along the trajectory of change. New models have been designed to complement equilibrium models and simulate vegetation succession through time while estimating variability in the C budget and responses to episodic events such as drought and fire. In addition, a plethora of future climate scenarios has been used to produce a bewildering variety of simulated ecological responses. Our objectives were to use an equilibrium model (Mapped Atmosphere–Plant–Soil system, or MAPSS) and a dynamic model (MC1) to (a) simulate changes in potential equilibrium vegetation distribution under historical conditions and across a wide gradient of future temperature changes to look for consistencies and trends among the many future scenarios, (b) simulate time-dependent changes in vegetation distribution and its associated C pools to illustrate the possible trajectories of vegetation change near the high and low ends of the temperature gradient, and (c) analyze the extent of the US area supporting a negative C balance. Both models agree that a moderate increase in temperature produces an increase in vegetation density and carbon sequestration across most of the US with small changes in vegetation types. Large increases in temperature cause losses of C with large shifts in vegetation types. In the western states, particularly southern California, precipitation and thus vegetation density increase and forests expand under all but the hottest scenarios. In the eastern US, particularly the Southeast, forests expand under the more moderate scenarios but decline under more severe climate scenarios, with catastrophic fires potentially causing rapid vegetation conversions from forest to savanna. Both models show that there is a potential for either positive or negative feedbacks to the atmosphere depending on the level of warming in the climate change scenarios. Received 12 May 2000; accepted 22 November 2000.     

Global climate change and soil carbon stocks; predictions from two contrasting models for the turnover of organic carbon in soil

Enhanced release of CO₂ to the atmosphere from soil organic carbon as a result of increased temperatures may lead to a positive feedback between climate change and the carbon cycle, resulting in much higher CO₂ levels and accelerated global warming. However, the magnitude of this effect is uncertain and critically dependent on how the decomposition of soil organic C (heterotrophic respiration) responds to changes in climate. Previous studies with the Hadley Centre's coupled climate–carbon cycle general circulation model (GCM) (HadCM3LC) used a simple, single‐pool soil carbon model to simulate the response. Here we present results from numerical simulations that use the more sophisticated ‘RothC’ multipool soil carbon model, driven with the same climate data. The results show strong similarities in the behaviour of the two models, although RothC tends to simulate slightly smaller changes in global soil carbon stocks for the same forcing. RothC simulates global soil carbon stocks decreasing by 54 Gt C by 2100 in a climate change simulation compared with an 80 Gt C decrease in HadCM3LC. The multipool carbon dynamics of RothC cause it to exhibit a slower magnitude of transient response to both increased organic carbon inputs and changes in climate. We conclude that the projection of a positive feedback between climate and carbon cycle is robust, but the magnitude of the feedback is dependent on the structure of the soil carbon model.     

Simulated responses of potential vegetation to doubled-CO2 climate change and feedbacks on near-surface temperature

Increases in the atmospheric concentration of carbon dioxide and associated changes in climate may exert large impacts on plant physiology and the density of vegetation cover. These may in turn provide feedbacks on climate through a modification of surface‐atmosphere fluxes of energy and moisture. This paper uses asynchronously coupled models of global vegetation and climate to examine the responses of potential vegetation to different aspects of a doubled‐CO₂ environmental change, and compares the feedbacks on near‐surface temperature arising from physiological and structural components of the vegetation response. Stomatal conductance reduces in response to the higher CO₂ concentration, but rising temperatures and a redistribution of precipitation also exert significant impacts on this property as well as leading to major changes in potential vegetation structure. Overall, physiological responses act to enhance the warming near the surface, but in many areas this is offset by increases in leaf area resulting from greater precipitation and higher temperatures. Interactions with seasonal snow cover result in a positive feedback on winter warming in the boreal forest regions.     

Indirect vegetation–soil moisture feedback with application to Holocene North Africa climate1

Using a fully coupled climate–terrestrial ecosystem model, we demonstrate explicitly that an initial perturbation on vegetation induces not only a direct positive vegetation feedback, but also a significant indirect vegetation–soil moisture feedback. The indirect feedback is generated through either fractional cover change or soil moisture depletion. Both indirect feedback mechanisms are triggered by a vegetation perturbation, but involve subsequent effects of soil moisture and evaporation, indirectly. An increase in vegetation tends to reduce bare‐ground evaporation through either the area reduction in bare ground or the depletion of soil moisture; the reduced evaporation may then counter the initial plant transpiration, favoring a negative net vegetation feedback. Furthermore, grasses are more effective in inducing the indirect vegetation–soil feedbacks, because of their limited plant evapotranspiration and shallower roots that tend to change surface soil moisture, and, in turn, evaporation, effectively. In comparison, trees favor a direct positive vegetation feedback due to their strong plant transpiration on subsurface soil moisture as well as a lower albedo.     

Vegetation cover—another dominant factor in determining global water resources in forested regions

Forested catchments provide critically important water resources. Due to dramatic global forest change over the past decades, the importance of including forest or vegetation change in the assessment of water resources under climate change has been highly recognized by Intergovernmental Panel on Climate Change (IPCC); however, this importance has not yet been examined quantitatively across the globe. Here, we used four remote sensing‐based indices to represent changes in vegetation cover in forest‐dominated regions, and then applied them to widely used models: the Fuh model and the Choudhury‐Yang model to assess relative contributions of vegetation and climate change to annual runoff variations from 2000 to 2011 in forested landscape (forest coverage >30%) across the globe. Our simulations show that the global average variation in annual runoff due to change in vegetation cover is 30.7% ± 22.5% with the rest attributed to climate change. Large annual runoff variation in response to vegetation change is found in tropical and boreal forests due to greater forest losses. Our simulations also demonstrate both offsetting and additive effects of vegetation cover and climate in determining water resource change. We conclude that vegetation cover change must be included in any global models for assessing global water resource change under climate change in forest‐dominant areas.     

The role of ice dynamics in shaping vegetation in flowing waters

Ice dynamics is an important factor affecting vegetation in high‐altitude and high‐latitude streams and rivers. During the last few decades, knowledge about ice in streams and rivers has increased significantly and a respectable body of literature is now available. Here we review the literature on how ice dynamics influence riparian and aquatic vegetation. Traditionally, plant ecologists have focused their studies on the summer period, largely ignoring the fact that processes during winter also impact vegetation dynamics. For example, the freeze‐up period in early winter may result in extensive formation of underwater ice that can restructure the channel, obstruct flow, and cause flooding and thus formation of more ice. In midwinter, slow‐flowing reaches develop a surface‐ice cover that accumulates snow, protecting habitats under the ice from formation of underwater ice but also reducing underwater light, thus suppressing photosynthesis. Towards the end of winter, ice breaks up and moves downstream. During this transport, ice floes can jam up and cause floods and major erosion. The magnitudes of the floods and their erosive power mainly depend on the size of the watercourse, also resulting in different degrees of disturbance to the vegetation. Vegetation responds both physically and physiologically to ice dynamics. Physical action involves the erosive force of moving ice and damage caused by ground frost, whereas physiological effects – mostly cell damage – happen as a result of plants freezing into the ice. On a community level, large magnitudes of ice dynamics seem to favour species richness, but can be detrimental for individual plants. Human impacts, such as flow regulation, channelisation, agriculturalisation and water pollution have modified ice dynamics; further changes are expected as a result of current and predicted future climate change. Human impacts and climate change can both favour and disfavour riverine vegetation dynamics. Restoration of streams and rivers may mitigate some effects of anticipated climate change on ice and vegetation dynamics by, for example, slowing down flows and increasing water depth, thus reducing the potential for massive formation of underwater ice.     

Sensitivity of Siberian larch forests to climate change

The Northern Hemisphere's boreal forests, particularly the Siberian boreal forest, may have a strong effect on Earth's climate through changes in dominant vegetation and associated regional surface albedo. We show that warmer climate will likely convert Siberia's deciduous larch (Larix spp.) to evergreen conifer forests, and thus decrease regional surface albedo. The dynamic vegetation model, FAREAST, simulates Russian boreal forest composition and was used to explore the feedback between climate change and forest composition at continental, regional, and local scales. FAREAST was used to simulate the impact of changes in temperature and precipitation on total and genus‐level biomass at sites across Siberia and the Russian Far East (RFE), and for six high‐ and low‐diversity regions. Model runs with and without European Larch (Larix decidua) included in the available species pool were compared to assess the potential for this species, which is adapted to warmer climate conditions, to mitigate the effects of climate change, especially the shift to evergreen dominance. At the continental scale, when temperature is increased, larch‐dominated sites become vulnerable to early replacement by evergreen conifers. At the regional and local scales, the diverse Amur region of the RFE does not show a strong response to climate change, but the low‐diversity regions in central and southern Siberia have an abrupt vegetation shift from larch‐dominated forest to evergreen‐conifer forest in response to increased temperatures. The introduction of L. decidua prevents the collapse of larch in these low‐diversity areas and thus mitigates the response to warming. Using contemporary MODIS albedo measurements, we determined that a conversion from larch to evergreen stands in low‐diversity regions of southern Siberia would generate a local positive radiative forcing of 5.1±2.6 W m^?2. This radiative heating would reinforce the warming projected to occur in the area under climate change.     

Impacts of recent climate change on terrestrial flora and fauna: Some emerging Australian examples

The effects of anthropogenic climate change on biodiversity are well known for some high‐profile Australian marine systems, including coral bleaching and kelp forest devastation. Less well‐published are the impacts of climate change being observed in terrestrial ecosystems, although ecological models have predicted substantial changes are likely. Detecting and attributing terrestrial changes to anthropogenic factors is difficult due to the ecological importance of extreme conditions, the noisy nature of short‐term data collected with limited resources, and complexities introduced by biotic interactions. Here, we provide a suite of case studies that have considered possible impacts of anthropogenic climate change on Australian terrestrial systems. Our intention is to provide a diverse collection of stories illustrating how Australian flora and fauna are likely responding to direct and indirect effects of anthropogenic climate change. We aim to raise awareness rather than be comprehensive. We include case studies covering canopy dieback in forests, compositional shifts in vegetation, positive feedbacks between climate, vegetation and disturbance regimes, local extinctions in plants, size changes in birds, phenological shifts in reproduction and shifting biotic interactions that threaten communities and endangered species. Some of these changes are direct and clear cut, others are indirect and less clearly connected to climate change; however, all are important in providing insights into the future state of terrestrial ecosystems. We also highlight some of the management issues relevant to conserving terrestrial communities and ecosystems in the face of anthropogenic climate change.     

Recent vegetation changes at the high‐latitude tree line ecotone are controlled by geomorphological disturbance,productivity and diversity

Aim We test how productivity, disturbance rate, plant functional composition and species richness gradients control changes in the composition of high‐latitude vegetation during recent climatic warming. Location Northern Fennoscandia, Europe. Methods We resampled tree line ecotone vegetation sites sampled 26 years earlier. To quantify compositional changes, we used generalized linear models to test relationships between compositional changes and environmental gradients. Results Compositional changes in species abundances are positively related to the normalized difference vegetation index (NDVI)‐based estimate of productivity gradient and to geomorphological disturbance. Competitive species in fertile sites show the greatest changes in abundance, opposed to negligible changes in infertile sites. Change in species richness is negatively related to initial richness, whereas geomorphological disturbance has positive effects on change in richness. Few lowland species have moved towards higher elevations. Main conclusions The sensitivity of vegetation to climate change depends on a complex interplay between productivity, physical and biotic disturbances, plant functional composition and richness. Our results suggest that vegetation on productive sites, such as herb‐rich deciduous forests at low altitudes, is more sensitive to climate warming than alpine tundra vegetation where grazing may have strong buffering effects. Geomorphological disturbance promotes vegetation change under climatic warming, whereas high diversity has a stabilizing effect.     

Changes in the avifauna in a high Andean cloud forest in Colombia over a 24‐year period

The upper altitude ecosystems of the Andes are among the most threatened by climate change. Computer models suggest that a large percentage of species in these ecosystems will be at risk of extinction and that avian communities will suffer disruption and impoverishment. Studies in other Andean countries lend some support to these predictions, but there are no quantitative data from Colombia appropriate to test these models. In 1991–1992, we conducted a bird survey in a high Andean cloud forest to gather information about the species present and their abundance. We attempted to replicate this earlier study 24 yr later to detect any changes in the avifauna and determine possible causes for those changes. From June 2015 to May 2016, we made bimonthly trips to the study site and identified all birds detected either visually or by voice along a number of trails. We supplemented our observational data by also capturing birds in mist‐nets. Community species richness and composition as well as the overall abundance of birds changed little from 1991–1992 to 2015–2016, but nearly 30% of bird species changed in abundance. Changes in the presence or abundance of nine or 10 species reflected upward shifts in elevational limits potentially due to climate change. However, most changes in abundance appeared to reflect changes in the vegetation of the study area due to successional changes in forest and subparamo habitats and a large number of relatively recent treefalls of old canopy trees with heavy epiphyte loads and subsequent changes in the understory vegetation. Our results suggest that the effects of climate change on the avifauna in our study area at a high‐altitude site in Colombia are apparently occurring more slowly than predicted by recent computer models, although we conclude that the possible effects of climate change should definitely be considered in future studies. However, single‐site studies such as ours have limitations in documenting elevation shifts; the most conclusive and quantitative evidence for elevational shifts comes from long‐term studies conducted over a wide range of elevations. As such, we recommend establishment of such a monitoring program in Colombia because data obtained from such a program might be important in designing measures to mitigate the effects of climate change and conserve biodiversity.     

Predicting insect phenology across space and time

Many species appear to be undergoing shifts in phenology, arising from climate change. To predict the direction and magnitude of future changes requires an understanding of how phenology depends on climatic variation. Species show large‐scale spatial variation in phenology (affected by differentiation among populations) as well as variation in phenology from year‐to‐year at the same site (affected predominantly by local plasticity). Teasing apart spatial and temporal variation in phenology should allow improved predictions of phenology under climate change. This study is the first to quantify large‐scale spatial and temporal variation in the entire emergence pattern of species, and to test the relationships found by predicting future data. We use data from up to 33 years of permanent transect records of butterflies in the United Kingdom to fit and test models for 15 butterfly species. We use generalized additive models to model spatial and temporal variation in the distribution of adult butterflies over the season, allowing us to capture changes in the timing of emergence peaks, relative sizes of peaks and/or number of peaks in a single analysis. We develop these models using data for 1973–2000, and then use them to predict phenologies from 2001 to 2006. For six of our study species, a model with only spatial variation in phenology is the best predictor of the future, implying that these species have limited plasticity. For the remaining nine species, the best predictions come from a model with both spatial and temporal variation in phenology; for four of these, growing degree‐days have similar effects over space and time, implying high levels of plasticity. The results show that statistical phenology models can be used to predict phenology shifts in a second time period, suggesting that it should be feasible to project phenologies under climate change scenarios, at least over modest time scales.     

Convergent ecosystem responses to 23‐year ambient and manipulated warming link advancing snowmelt and shrub encroachment to transient and long‐term climate–soil carbon feedback

Ecosystem responses to climate change can exert positive or negative feedbacks on climate, mediated in part by slow‐moving factors such as shifts in vegetation community composition. Long‐term experimental manipulations can be used to examine such ecosystem responses, but they also present another opportunity: inferring the extent to which contemporary climate change is responsible for slow changes in ecosystems under ambient conditions. Here, using 23 years of data, we document a shift from nonwoody to woody vegetation and a loss of soil carbon in ambient plots and show that these changes track previously shown similar but faster changes under experimental warming. This allows us to infer that climate change is the cause of the observed shifts in ambient vegetation and soil carbon and that the vegetation responses mediate the observed changes in soil carbon. Our findings demonstrate the realism of an experimental manipulation, allow attribution of a climate cause to observed ambient ecosystem changes, and demonstrate how a combination of long‐term study of ambient and experimental responses to warming can identify mechanistic drivers needed for realistic predictions of the conditions under which ecosystems are likely to become carbon sources or sinks over varying timescales.     

Vegetation controls on northern high latitude snow‐albedo feedback: observations and CMIP5 model simulations

The snow‐masking effect of vegetation exerts strong control on albedo in northern high latitude ecosystems. Large‐scale changes in the distribution and stature of vegetation in this region will thus have important feedbacks to climate. The snow‐albedo feedback is controlled largely by the contrast between snow‐covered and snow‐free albedo (Δα), which influences predictions of future warming in coupled climate models, despite being poorly constrained at seasonal and century time scales. Here, we compare satellite observations and coupled climate model representations of albedo and tree cover for the boreal and Arctic region. Our analyses reveal consistent declines in albedo with increasing tree cover, occurring south of latitudinal tree line, that are poorly represented in coupled climate models. Observed relationships between albedo and tree cover differ substantially between snow‐covered and snow‐free periods, and among plant functional type. Tree cover in models varies widely but surprisingly does not correlate well with model albedo. Furthermore, our results demonstrate a relationship between tree cover and snow‐albedo feedback that may be used to accurately constrain high latitude albedo feedbacks in coupled climate models under current and future vegetation distributions.     

Long-term Perspectives on Lagged Ecosystem Responses to Climate Change: Permafrost in Boreal Peatlands and the Grassland/Woodland Boundary

Changes in climate could have far-reaching consequences for ecosystems sensitive to changes in temperature and precipitation, such as boreal permafrost peatlands and grassland/woodland boundaries. The long-term data from our studies in these ecosystems suggest that transient responses of permafrost and vegetation to climate change may be difficult to predict due to lags and positive feedbacks related to vegetation and disturbance. Boreal permafrost peatlands comprise an ecosystem with strong local controls on microclimate that influence the formation and thaw of permafrost. These local controls may preserve permafrost during the transient stages of climate warming, producing lagged responses. The prairie–forest border region of the northern Great Plains has experienced frequent change and has complex dynamics involving transitions in the grassland composition of prairie and in the degree of woodiness in bordering forests. Fire frequency interacts with fuel loading and tree recruitment in ways that affect the timing and direction of change. Lags and thresholds could lead to sudden large responses to future climate change that are not readily apparent from current vegetation. The creation of adequate models to characterize transient ecosystem changes will require an understanding of the linkages among processes operating at the scale of 10s of meters and over long time periods. Received 14 December 1999; accepted 7 July 2000.     

Fire severity mediates climate‐driven shifts in understorey community composition of black spruce stands of interior Alaska

Question: How do pre‐fire conditions (community composition and environmental characteristics) and climate‐driven disturbance characteristics (fire severity) affect post‐fire community composition in black spruce stands? Location: Northern boreal forest, interior Alaska. Methods: We compared plant community composition and environmental stand characteristics in 14 black spruce stands before and after multiple, naturally occurring wildfires. We used a combination of vegetation table sorting, univariate (ANOVA, paired t‐tests), and multivariate (detrended correspondence analysis) statistics to determine the impact of fire severity and site moisture on community composition, dominant species and growth forms. Results: Severe wildfires caused a 50% reduction in number of plant species in our study sites. The largest species loss, and therefore the greatest change in species composition, occurred in severely burned sites. This was due mostly to loss of non‐vascular species (mosses and lichens) and evergreen shrubs. New species recruited most abundantly to severely burned sites, contributing to high species turnover on these sites. As well as the strong effect of fire severity, pre‐fire and post‐fire mineral soil pH had an effect on post‐fire vegetation patterns, suggesting a legacy effect of site acidity. In contrast, pre‐fire site moisture, which was a strong determinant of pre‐fire community composition, showed no relationship with post‐fire community composition. Site moisture was altered by fire, due to changes in permafrost, and therefore post‐fire site moisture overrode pre‐fire site moisture as a strong correlate. Conclusions: In the rapidly warming climate of interior Alaska, changes in fire severity had more effect on post‐fire community composition than did environmental factors (moisture and pH) that govern landscape patterns of unburned vegetation. This suggests that climate change effects on future community composition of black spruce forests may be mediated more strongly by fire severity than by current landscape patterns. Hence, models that represent the effects of climate change on boreal forests could improve their accuracy by including dynamic responses to fire disturbance.     

Projected climate change effects on Alberta's boreal forests imply future challenges for oil sands reclamation

Climate change will drive significant changes in vegetation cover and also impact efforts to restore ecosystems that have been disturbed by human activities. Bitumen mining in the Alberta oil sands region of western Canada requires reclamation to “equivalent land capability,” implying establishment of vegetation similar to undisturbed boreal ecosystems. However, there is consensus that this region will be exposed to relatively severe climate warming, causing increased occurrence of drought and wildfire, which threaten the persistence of both natural and reclaimed ecosystems. We used a landscape model, LANDIS‐II, to simulate plant responses to climate change and disturbances, forecasting changes to boreal forests within the oil sands region. Under the most severe climate forcing scenarios (representative concentration pathway [RCP] 8.5) the model projected substantial decreases in forest biomass, with the future forest being dominated by drought‐ and fire‐tolerant species characteristic of parkland or prairie ecosystems. In contrast, less extreme climate forcing scenarios (RCPs 2.6 and 4.5) had relatively minor effects on forest composition and biomass with boreal conifers continuing to dominate the landscape. If the climate continues to change along a trajectory similar to those simulated by climate models for the RCP 8.5 forcing scenario, current reclamation goals to reestablish spruce‐dominated boreal forest will likely be difficult to achieve. Results from scenario modeling studies such as ours, and continued monitoring of change in the boreal forest, will help inform reclamation practices, which could include establishment of species better adapted to warmer and drier conditions.