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1.
Over the last 100?years, Arctic warming has resulted in a longer growing season in boreal and tundra ecosystems. This has contributed to a slow northward expansion of the boreal forest and a decrease in the surface albedo. Corresponding changes to the surface and atmospheric energy budgets have contributed to a broad region of warming over areas of boreal forest expansion. In addition, mesoscale and synoptic scale patterns have changed as a result of the excess energy at and near the surface. Previous studies have identified a relationship between the positioning of the boreal forest-tundra ecotone and the Arctic frontal zone in summer. This study examines the climate response to hypothetical boreal forest expansion and its influence on the summer Arctic frontal zone. Using the Weather Research and Forecasting model over the Northern Hemisphere, an experiment was performed to evaluate the atmospheric response to expansion of evergreen and deciduous boreal needleleaf forests into open shrubland along the northern boundary of the existing forest. Results show that the lower surface albedo with forest expansion leads to a local increase in net radiation and an average hemispheric warming of 0.6°C at and near the surface during June with some locations warming by 1–2°C. This warming contributes to changes in the meridional temperature gradient that enhances the Arctic frontal zone and strengthens the summertime jet. This experiment suggests that continued Northern Hemisphere high-latitude warming and boreal forest expansion might contribute to additional climate changes during the summer.  相似文献   

2.
Changes in the duration of the photosynthetically active period strongly influence the changes in the carbon sequestration potential of boreal forests under climatic warming. In this paper, current theories on the effects of environmental variables such as spring air and soil temperature, photoperiod and chilling temperatures on the timing and initiation of photosynthesis in boreal deciduous and coniferous trees are discussed. Different dynamic phenological modeling approaches are reviewed, and model simulations are utilized to demonstrate model predictions under changing climatic conditions. A process-based forest ecosystem model is applied to estimate the relative importance of the duration of the photosynthetically active period on the amount of annual gross primary production and net primary production of boreal coniferous forests. All applied modeling approaches predict an increasing duration of the photosynthetically active period as a result of climatic warming. However, the magnitude of the response to increasing temperature varies between models and therefore affects the predictions of the changes in production.  相似文献   

3.
Human activities have altered the distribution and quality of terrestrial ecosystems. Future demands for goods and services from terrestrial ecosystems will occur in a world experiencing human-induced climate change. In this study, we characterize the range in response of unmanaged ecosystems in the conterminous U.S. to 12 climate change scenarios. We obtained this response by simulating the climatically induced shifts in net primary productivity and geographical distribution of major biomes in the conterminous U.S. with the BIOME 3 model. BIOME 3 captured well the potential distribution of major biomes across the U.S. under baseline (current) climate. BIOME 3 also reproduced the general trends of observed net primary production (NPP) acceptably. The NPP projections were reasonable for forests, but not for grasslands where the simulated values were always greater than those observed. Changes in NPP would be most severe under the BMRC climate change scenario in which severe changes in regional temperatures are projected. Under the UIUC and UIUC + Sulfate scenarios, NPP generally increases, especially in the West where increases in precipitation are projected to be greatest. A CO2-fertilization effect either amplified increases or alleviated losses in modeled NPP. Changes in NPP were also associated with changes in the geographic distribution of major biomes. Temperate/boreal mixed forests would cover less land in the U.S. under most of the climate change scenarios examined. Conversely, the temperate conifer and temperate deciduous forests would increase in areal extent under the UIUC and UIUC + Sulfate scenarios. The Arid Shrubland/Steppe would spread significantly across the southwest U.S. under the BMRC scenario. A map overlay of the simulated regions that would lose or gain capacity to produce corn and wheat on top of the projected distribution of natural ecosystems under the BMRC and UIUC scenarios (Global mean temperature increase of +2.5 °C, no CO2 effect) helped identify areas where natural and managed ecosystems could contract or expand. The methods and models employed here are useful in identifying; (a) the range in response of unmanaged ecosystem in the U.S. to climate change and (b) the areas of the country where, for a particular scenario of climate change, land cover changes would be most likely.  相似文献   

4.
The sensitivity of some high-latitude boreal forests to climatic parameters   总被引：1，自引：0，他引：1  
A gap model of environmental processes and vegetation patterns in boreal forests was used to examine the sensitivity of permafrost and permafrostfree forests in interior Alaska to air temperature and precipitation changes. These analyses indicated that in the uplands of interior Alaska, the effect of climatic warming on the ecology of boreal forests may not be so much a direct response to increased air temperature as it may be a response to the increased potential evapotranspiration demands that will accompany climatic warmings. On poorlydrained north slopes with permafrost, the drier forest floor reduced the flux of heat into the soil profile. This was offset by increased fire severity, which by removing greater amounts of the forest floor increased the depth of soil thawing and converted the cold black spruce forests to warmer mixed hardwood-spruce forests. On well-drained south slopes, the increased potential water loss reduced available soil moisture, converting these mesic sites to dry aspen forests, or if too dry to steppe-like vegetation. Increases in precipitation offset the effects of increased potential evapotranspiration demands and mitigated these forest changes.  相似文献   

5.
Tree populations located at the geographical distribution limit of the species may provide valuable information about the response of tree growth to climate warming across climatic gradients. Dendroclimatic information was extracted from a network of 10 silver-fir (Abies alba) populations in the south-western distribution limit of the species (Pyrenees, NE Iberian Peninsula). Ring-width chronologies were built for five stands sampled in mesic sites from the Main Range in the Pyrenees, and for five forests located in the southern Peripheral Ranges where summer drought is more pronounced. The radial growth of silver-fir in this region is constrained by water stress during the summer previous to growth, as suggested by the negative relationship with previous September temperature and, to a lesser degree, by a positive relationship with previous end of summer precipitation. Climatic data showed a warming trend since the 1970s across the Pyrenees, with more severe summer droughts. The recent warming changed the climate-growth relationships, causing higher growth synchrony among sites, and a higher year-to-year growth variation, especially in the southernmost forests. Moving-interval response functions suggested an increasing water-stress effect on radial growth during the last half of the 20th century. The growth period under water stress has extended from summer up to early autumn. Forests located in the southern Peripheral Ranges experienced a more intense water stress, as seen in a shift of their response to precipitation and temperature. The Main-Range sites mainly showed a response to warming. The intensification of water-stress during the late 20th century might affect the future growth performance of the highly-fragmented A. alba populations in the southwestern distribution limit of the species.  相似文献   

6.
We use a frame-based simulation model to estimate future rate of advance of the arctic treeline in response to scenarios of transient changes in temperature, precipitation, and fire regime. The model is simple enough to capture both the short-term direct response of vegetation to climate and the longer-term interactions among vegetation, fire, and insects that are important features of dynamic vegetation models. We estimate a 150–250 yr time lag in forestation of Alaskan tundra following climatic warming and suggest that, with rapid warming under dry conditions, there would be significant development of boreal grassland-steppe, a novel ecosystem type that was common during the late Pleistocene and today occurs south of the boreal forest in continental regions. Together, the time lag and grassland development would delay the positive feedback of vegetation change to climatic warming, providing a window of opportunity to control fossil fuel emissions, the primary cause of this warming.  相似文献   

7.
The response of terrestrial ecosystems to climate warming has important implications to potential feedbacks to climate. The interactions between topography, climate, and disturbance could alter recruitment patterns to reduce or offset current predicted positive feedbacks to warming at high latitudes. In northern Alaska the Brooks Range poses a complex environmental and ecological barrier to species migration. We use a spatially explicit model (ALFRESCO) to simulate the transient response of subarctic vegetation to climatic warming in the Kobuk/Noatak River Valley (200 × 400 km) in northwest Alaska. The model simulations showed that a significantly warmer (+6 °C) summer climate would cause expansion of forest through the Brooks Range onto the currently treeless North Slope only after a period of 3000–4000 yr. Substantial forest establishment on the North Slope didnot occur until temperatures warmed 9 °C, and only following a 2000 yr time lag. The long time lags between change in climate and change in vegetation indicate current global change predictions greatly over-estimate the response of vegetation to a warming climate in Alaska. In all the simulations warming caused a steady increase in the proportion of early successional deciduous forest. This would reduce the magnitude of the predicted decrease in regional albedo and the positive feedback to climate warming. Simulation of spruce forest refugia on the North Slope showed forest could survive with only a 4 °C warming and would greatly reduce the time lag of forest expansion under warmer climates. Planting of spruce on the North Slope by humans could increase the likelihood of large-scale colonization of currently treeless tundra. Together, the long time lag and deciduous forest dominance would delay the predicted positive regional feedback of vegetation change to climatic warming. These simulated changes indicate the Brooks Range would significantly constrain regional forest expansion under a warming climate, with similar implications for other regions possessing major east-west oriented mountain ranges.  相似文献   

8.
The participation of different vegetation types within the physical climate system is investigated using a coupled atmosphere-biosphere model, CCM3-IBIS. We analyze the effects that six different vegetation biomes (tropical, boreal, and temperate forests, savanna, grassland and steppe, and shrubland/tundra) have on the climate through their role in modulating the biophysical exchanges of energy, water, and momentum between the land-surface and the atmosphere. Using CCM3-IBIS we completely remove the vegetation cover of a particular biome and compare it to a control simulation where the biome is present, thereby isolating the climatic effects of each biome. Results from the tropical and boreal forest removal simulations are in agreement with previous studies while the other simulations provide new evidence as to their contribution in forcing the climate. Removal of the temperate forest vegetation exhibits behavior characteristic of both the tropical and boreal simulations with cooling during winter and spring due to an increase in the surface albedo and warming during the summer caused by a reduction in latent cooling. Removal of the savanna vegetation exhibits behavior much like the tropical forest simulation while removal of the grassland and steppe vegetation has the largest effect over the central United States with warming and drying of the atmosphere in summer. The largest climatic effect of shrubland and tundra vegetation removal occurs in DJF in Australia and central Siberia and is due to reduced latent cooling and enhanced cold air advection, respectively. Our results show that removal of the boreal forest yields the largest temperature signal globally when either including or excluding the areas of forest removal. Globally, precipitation is most affected by removal of the savanna vegetation when including the areas of vegetation removal, while removal of the tropical forest most influences the global precipitation excluding the areas of vegetation removal.  相似文献   

9.
The impacts of year-to-year and decade-to-decade climatic variations on some of the Pacific Northwest's key natural resources can be quantified to estimate sensitivity to regional climatic changes expected as part of anthropogenic global climatic change. Warmer, drier years, often associated with El Niño events and/or the warm phase of the Pacific Decadal Oscillation, tend to be associated with below-average snowpack, streamflow, and flood risk, below-average salmon survival, below-average forest growth, and above-average risk of forest fire. During the 20th century, the region experienced a warming of 0.8 °C. Using output from eight climate models, we project a further warming of 0.5–2.5 °C (central estimate 1.5 °C) by the 2020s, 1.5–3.2°C (2.3 °C) by the 2040s, and an increase in precipitation except in summer. The foremost impact of a warming climate will be the reduction of regional snowpack, which presently supplies water for ecosystems and human uses during the dry summers. Our understanding of past climate also illustrates the responses of human management systems to climatic stresses, and suggests that a warming of the rate projected would pose significant challenges to the management of natural resources. Resource managers and planners currently have few plans for adapting to or mitigating the ecological and economic effects of climatic change.  相似文献   

10.
In the boreal biome, fire is the major disturbance agent affecting ecosystem change, and fire dynamics will likely change in response to climatic warming. We modified a spatially explicit model of Alaskan subarctic treeline dynamics (ALFRESCO) to simulate boreal vegetation dynamics in interior Alaska. The model is used to investigate the role of black spruce ecosystems in the fire regime of interior Alaska boreal forest. Model simulations revealed that vegetation shifts caused substantial changes to the fire regime. The number of fires and the total area burned increased as black spruce forest became an increasingly dominant component of the landscape. The most significant impact of adding black spruce to the model was an increase in the frequency and magnitude of large-scale burning events (i.e., time steps in which total area burned far exceeded the normal distribution of area burned). Early successional deciduous forest vegetation burned more frequently when black spruce was added to the model, considerably decreasing the fire return interval of deciduous vegetation. Ecosystem flammability accounted for the majority of the differences in the distribution of the average area burned. These simulated vegetation effects and fire regime dynamics have important implications for global models of vegetation dynamics and potential biotic feedbacks to regional climate.  相似文献   

11.
Responses of vegetation distribution to climate change in China   总被引：1，自引：1，他引：0  
Climate plays a crucial role in controlling vegetation distribution and climate change may therefore cause extended changes. A coupled biogeography and biogeochemistry model called BIOME4 was modified by redefining the bioclimatic limits of key plant function types on the basis of the regional vegetation–climate relationships in China. Compared to existing natural vegetation distribution, BIOME4 is proven more reliable in simulating the overall vegetation distribution in China. Possible changes in vegetation distribution were simulated under climate change scenarios by using the improved model. Simulation results suggest that regional climate change would result in dramatic changes in vegetation distribution. Climate change may increase the areas covered by tropical forests, warm-temperate forests, savannahs/dry woodlands and grasslands/dry shrublands, but decrease the areas occupied by temperate forests, boreal forests, deserts, dry tundra and tundra across China. Most vegetation in east China, specifically the boreal forests and the tropical forests, may shift their boundaries northwards. The tundra and dry tundra on the Tibetan Plateau may be progressively confined to higher elevation.  相似文献   

12.
The effects of terrestrial ecosystems on the climate system have received most attention in the tropics, where extensive deforestation and burning has altered atmospheric chemistry and land surface climatology. In this paper we examine the biophysical and biogeochemical effects of boreal forest and tundra ecosystems on atmospheric processes. Boreal forests and tundra have an important role in the global budgets of atmospheric CO2 and CH4. However, these biogeochemical interactions are climatically important only at long temporal scales, when terrestrial vegetation undergoes large geographic redistribution in response to climate change. In contrast, by masking the high albedo of snow and through the partitioning of net radiation into sensible and latent heat, boreal forests have a significant impact on the seasonal and annual climatology of much of the Northern Hemisphere. Experiments with the LSX land surface model and the GENESIS climate model show that the boreal forest decreases land surface albedo in the winter, warms surface air temperatures at all times of the year, and increases latent heat flux and atmospheric moisture at all times of the year compared to simulations in which the boreal forest is replaced with bare ground or tundra. These effects are greatest in arctic and sub-arctic regions, but extend to the tropics. This paper shows that land-atmosphere interactions are especially important in arctic and sub-arctic regions, resulting in a coupled system in which the geographic distribution of vegetation affects climate and vice versa. This coupling is most important over long time periods, when changes in the abundance and distribution of boreal forest and tundra ecosystems in response to climatic change influence climate through their carbon storage, albedo, and hydrologic feedbacks.  相似文献   

13.
Most deciduous fruit trees need sufficient accumulated chilling, or vernalisation, to break winter dormancy. Inadequate chilling due to enhanced greenhouse warming may result in prolonged dormancy, leading to reduced fruit quality and yield. The potential impact of warming on chill accumulation has been analysed using the Utah vernalisation model and temperature data from over 400 climate stations in southern Australia. Two experiments were performed: (i) a sensitivity study where temperatures were increased at all sites by either 1, 2 or 3 °C; (ii) a scenario study for the year 2030 where temperatures were increased according to spatially- and seasonally-varying warming scenarios derived from five global climate models under enhanced greenhouse conditions.The sensitivity study shows that warming causes greater reduction in chilling at sites with a higher present mean temperature and/or a wider diurnal temperature range. In the scenario study, two warming scenarios for the year 2030 were considered: a low (high) warming scenario which assumes a low (high) rate of increase of greenhouse gas emission, a low (high) global climate sensitivity to increased emissions, and a low (high) regional temperature response. The low warming scenario is less than 1 °C in southern Australia and is unlikely to affect the vernalisation of high-chill fruit, except for pome-fruit grown in south-west Western Australia. The high warming scenario exceeds 1.5 °C and would significantly increase the risk of prolonged dormancy for both stone-fruit and pome-fruit at many sites.  相似文献   

14.
我国冬半年局地气温对北半球增暖响应的特征分析   总被引：2，自引：2，他引：2  
采用主分量分析与回归分析相结合的方法，研究北半球气候变化与我国区域气候变化的一些统计学关系。根据北半球平均增暖的条件，推求我国各地气温变化的统计估计模型，借助某些一般大气环流模式数值试验结果，计算并分析了在ＣＯ２浓度倍增时，我国各地增温幅度及其置信区间。结果表明：我各区域与北半球平均增暖趋势基本同步、但幅度不一；我国增暖敏感区主要在西北，华北和东北，南方部分地区的增温趋势有较大的不确定性。  相似文献   

15.
Northeast China (NEC) is one of the major agricultural production areas in China and also an obvious region of climate warming. We were motivated to investigate the impacts of climate warming on the northern limits of maize planting. Additionally, we wanted to assess how spatial shifts in the cropping system impact the maize yields in NEC. To understand these impacts, we used the daily average air temperature data in 72 weather stations and regional experiment yield data from Jilin Province. Averaged across NEC, the annual air temperature increased by 0.38 °C per decade. The annual accumulated temperature above 10 °C (AAT10) followed a similar trend, increased 66 °C d per decade from 1961 to 2007, which caused a northward expansion of the northern limits of maize. The warming enabled early-maturing maize hybrids to be sown in the northern areas of Heilongjiang Province where it was not suitable for growing maize before the warming. In the southern areas of Heilongjiang Province and the eastern areas of Jilin Province, the early-maturing maize hybrids could be replaced by the middle-maturing hybrids with a longer growing season. The maize in the northern areas of Liaoning Province was expected to change from middle-maturing to late-maturing hybrids. Changing the hybrids led to increase the maize yield. When the early-maturing hybrids were replaced by middle-maturing hybrids in Jilin Province, the maize yields would increase by 9.8 %. Similarly, maize yields would increase by 7.1 % when the middle-maturing hybrids were replaced by late-maturing hybrids.  相似文献   

16.
Recent efforts to project vegetationresponses to climatic warming have emphasized thetight linkages between climate and vegetationdistribution. Here we provide several examplesindicating that the direct effects of climatic warmingon boreal vegetation can be qualitatively differentthan the indirect effects mediated by climaticresponses of herbivores. These herbivore-mediatedvegetation responses to climatic warming will likelyvary regionally. In southern Fennoscandia, we projectthat the climatically induced changes in animalpopulations should enhance the density of spruce atthe expense of pine and broadleafed trees. In northernFennoscandia we project reduced herbivory onbroadleafed trees and increased herbivory on pine,leading to an increase in broadleafed trees and spruceand a reduction in pine. Climatic warming in interiorAlaska may reduce herbivory on broadleafed trees andincrease herbivory on evergreen spruce, thusreinforcing the impact of increased fire frequency.  相似文献   

17.
We used an individual-based forest simulator (a gap model) to assess the potential effects of anthropogenic climatic change on conifer forests of the Pacific Northwestern United States. Steady-state simulations suggested that forest zones could be shifted on the order of 500–1000 m in elevation, which could lead to the local extirpation of some high-altitude species. For low-elevation sites, species which currently are more abundant hundreds of kilometers to the south would be favored under greenhouse scenarios. Simulations of transient responses suggested that forest stands could show complex responses depending on initial species composition, stand age and canopy development, and the magnitude and duration of climatic warming. Assumptions about species response to temperature, which are crucial to the model's behaviors, were evaluated using data on species temperature limits inferred from regional distributions. The high level of within-species variability in these data, and other confounding factors influencing species distributions, argue against over-interpreting simulations. We suggest how we might resolve critical uncertainties with further research.  相似文献   

18.
Abundant evidence indicates the growing season has been changed in the Alaskan terrestrial ecosystems in the last century as climate warms. Reasonable simulations of growing season length, onset, and ending are critical to a better understanding of carbon dynamics in these ecosystems. Recent ecosystem modeling studies have been slow to consider the interactive effects of soil thermal and hydrological dynamics on growing season changes in northern high latitudes. Here, we develop a coupled framework to model these dynamics and their effects on plant growing season at a daily time step. In this framework, we (1) incorporate a daily time step snow model into our existing hydrological and soil thermal models and (2) explicitly model the moisture effects on soil thermal conductivity and heat capacity and the effects of active layer depth and soil temperature on hydrological dynamics. The new framework is able to well simulate snow depth and soil temperature profiles for both boreal forest and tundra ecosystems at the site level. The framework is then applied to Alaskan boreal forest and tundra ecosystems for the period 1923–2099. Regional simulations show that (1) for the historical period, the growing season length, onset, and ending, estimated based on the mean soil temperature of the top 20 cm soils, and the annual cycle of snow dynamics, agree well with estimates based on satellite data and other approaches and (2) for the projected period, the plant growing season length shows an increasing trend in both tundra and boreal forest ecosystems. In response to the projected warming, by year 2099, (1) the snow-free days will be increased by 41.0 and 27.5 days, respectively, in boreal forest and tundra ecosystems and (2) the growing season lengths will be more than 28 and 13 days longer in boreal forest and tundra ecosystems, respectively, compared to 2010. Comparing two sets of simulations with and without considering feedbacks between soil thermal and hydrological dynamics, our analyses suggest coupling hydrological and soil thermal dynamics in Alaskan terrestrial ecosystems is important to model ecosystem dynamics, including growing season changes.  相似文献   

19.
We have used the BIOME4 biogeography–biochemistry model and comparison with palaeovegetation data to evaluate the response of six ocean–atmosphere general circulation models to mid-Holocene changes in orbital forcing in the mid- to high-latitudes of the northern hemisphere. All the models produce: (a) a northward shift of the northern limit of boreal forest, in response to simulated summer warming in high-latitudes. The northward shift is markedly asymmetric, with larger shifts in Eurasia than in North America; (b) an expansion of xerophytic vegetation in mid-continental North America and Eurasia, in response to increased temperatures during the growing season; (c) a northward expansion of temperate forests in eastern North America, in response to simulated winter warming. The northward shift of the northern limit of boreal forest and the northward expansion of temperate forests in North America are supported by palaeovegetation data. The expansion of xerophytic vegetation in mid-continental North America is consistent with palaeodata, although the extent may be over-estimated. The simulated expansion of xerophytic vegetation in Eurasia is not supported by the data. Analysis of an asynchronous coupling of one model to an equilibrium-vegetation model suggests vegetation feedback exacerbates this mid-continental drying and produces conditions more unlike the observations. Not all features of the simulations are robust: some models produce winter warming over Europe while others produce winter cooling. As a result, some models show a northward shift of temperate forests (consistent with, though less marked than, the expansion shown by data) and others produce a reduction in temperate forests. Elucidation of the cause of such differences is a focus of the current phase of the Palaeoclimate Modelling Intercomparison Project.  相似文献   

20.
水热的合理配置为农业生产提供了有利的气候条件,明确热量和水分的匹配及变异规律对指导农业生产具有重要意义。本文利用东北农业区1961—2014年的逐日降水和气温资料,分析了东北农业区降水年内分配不均匀性的变异规律及其对区域增暖的响应,结果表明：(1)近54年来,该区表现为全区一致性的降水年内分配不均匀性降低、年际变化幅度增大和降水集中期提前的变化趋势;(2)降水年内分配不均匀性降低速率表现为中间大,南、北小的区域间差异;(3)降水年内分配不均匀性对气温具有很强的响应,表现出明显的不同步和区域间差异性,大致表现为在短周期上降水集中度落后气温、而长周期上超前气温的响应特征。气候增暖背景下,降水集中期的提前使得该区雨热同期的气候要素匹配关系保持稳定,但降水年内分配不均匀性的降低及年际间变化幅度的增大可能会增加该区夏季发生干旱的风险。研究结果可为制定科学的农田水管理策略提供参考。  相似文献   

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