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1.
The Canadian boreal forest covers 299.2 Mha which is two-thirds of Canada's forest and runs in a continuous belt from Newfoundland north and west to the Yukon. The major species are spruce, pines, balsam fir, white birch and trembling aspen often occurring in extensive monocultures. Wildfire is the driving successional force in the boreal forest and has remained so despite fire suppression activities and extensive harvesting. Insects and diseases also cause extensive damage. In order to ensure the sustainability of forests, it is necessary for the forest manager to know the condition of the health of these forests. The CFS established in 1984 the Acid Rain National Early Warning System in order to monitor the health of the forests. National results show that mortality is generally in the normal range of 1–3% and is caused by known stresses; insects, diseases and abiotic damage. No signs of pollution damage have been yet been detected in boreal forests by the system. An early warning system to detect and monitor conditions remains an essential part of our commitment to the sustainability of Canada's forests.  相似文献   

2.
Boreal regions contain more than half of the carbon in forested regions of the world and over 60% of the world’s surface freshwater. Carbon storage and the flood control and water filtration provided by freshwaters and wetlands have recently been identified as the most important ecosystem services provided by boreal regions, with a value many times greater than current resource exploitation. Ecosystem services and sensitive ways of detecting their impairment have so far not been fully included in boreal conservation planning. Climate warming, via its effect on permafrost melting, insect damage, and forest fire, threatens to trigger large positive carbon feedbacks that may enhance the concentrations of greenhouse gases in the atmosphere, further amplifying climate warming. In a water-scarce world, there is increasing pressure to divert and exploit boreal freshwaters, and devising conservation plans to protect boreal freshwaters and their catchments is urgent. We propose a catchment-based approach that includes water and chemical mass-balances as a sensitive means of detecting early degradation of many ecosystem services in both catchments and freshwaters, and give some examples of where this has been advantageous in the past. The necessary modifications to current conservation planning are simple ones, and the advantages are great.  相似文献   

3.
Forest management in temperate and boreal regions is often based on a strong foundation of applied ecological research. Increasingly, this has allowed the needs of saproxylic (dead wood associated) insects to be addressed. However, there has been very little equivalent research in tropical forests, where saproxylic insect faunas are likely to be much richer and where forestry is usually subject to weaker environmental controls. This study compares the saproxylic beetle fauna of old-growth, selectively logged and regrowth rainforest in the Daintree lowlands of northeastern Queensland, Australia. Old-growth levels of abundance, species richness, assemblage composition and guild structure were not maintained in logged and regrowth forest, suggesting that intact assemblages may not survive in the long-term in managed tropical rainforest. However, retaining a continuous supply of commercially overmature trees in the managed stand may prevent a repeat of the widespread extinctions of saproxylic insects witnessed in temperate and boreal forest regions.  相似文献   

4.
Predicted future changes in regional climate under a doubling of atmospheric CO2 concentrations were applied to the 1951–80 normals of 254 climate stations to examine future impacts on the boreal forest of western Canada. Previous analyses have indicated that in this region, the southern boreal forest is presently restricted to areas where annual precipitation (P) exceeds potential evapotranspiration (PET). The present analysis suggests that a predicted 11% increase in P would be insufficient to offset the increases in PET resulting from a predicted warming of 4–5°C. As a result, half of the western Canadian boreal forest could be exposed to a drier climate similar to the present aspen parkland zone (P < PET), where conifers are generally absent and aspen is restricted to patches of stunted trees interspersed with grassland. Future changes could result in permanent losses of forest cover following disturbance and an increase in the proportion of exposed edge habitat in remaining stands, where environmental conditions might induce additional stresses on tree growth. Thus if the predicted warming and drying occurs, productivity of aspen and other commercial species in the southern boreal forest would be greatly reduced.  相似文献   

5.
Conservation planning is often based on static mapping of species’ ranges or habitat distributions. Succession and disturbance alter, however, habitat quality and quantity through time especially under global climate and land use change scenarios; hence, static protected areas may not ensure habitat persistence and species survival. Here, we examined the relative merits of static and dynamic (floating) protected areas for the conservation of American marten (Martes americana) habitat in a dynamic boreal forest of Québec (Canada). Forest dynamics were modeled using a spatially-explicit landscape disturbance model and protected areas were selected based on the quality and compactness of marten home ranges using MARXAN. Static protected areas were fixed in space during 200 year simulations of boreal forest dynamics, while dynamic protected areas were re-located every 50 years to track dynamic habitat. Dynamic protected areas supported more high quality home ranges through time than static protected areas. The locations of dynamic protected areas were constrained, however, by the highly fragmented forest patterns created through logging and fire in unprotected areas. Our findings emphasize the often-overlooked point that if dynamic conservation planning is to be successful in the long term, the landscape matrix quality surrounding protected areas must be managed in such a way that options remain when it comes to re-planning.  相似文献   

6.
The circumpolar boreal biomes coverca. 2 109 ha of the northern hemisphere and containca. 800 Pg C in biomass, detritus, soil, and peat C pools. Current estimates indicate that the biomes are presently a net C sink of 0.54 Pg C yr?1. Biomass, detritus and soil of forest ecosystems (includingca. 419 Pg peat) containca. 709 Pg C and sequester an estimated 0.7 Pg C yr?1. Tundra and polar regions store 60–100 Pg C and may recently have become a net source of 0.17 Pg C yr?1. Forest product C pools, including landfill C derived from forest biomass, store less than 3 Pg C but increase by 0.06 Pg C yr?1. The mechanisms responsible for the present boreal forest net sink are believed to be continuing responses to past changes in the environment, notably recovery from the little ice-age, changes in forest disturbance regimes, and in some regions, nutrient inputs from air pollution. Even in the absence of climate change, the C sink strength will likely be reduced and the biome could switch to a C source. The transient response of terrestrial C storage to climate change over the next century will likely be accompanied by large C exchanges with the atmosphere, although the long-term (equilibrium) changes in terrestrial C storage in future vegetation complexes remains uncertain. This transient response results from the interaction of many (often non-linear) processes whose impacts on future C cycles remain poorly quantified. Only a small part of the boreal biome is directly affected by forest management and options for mitigating climate change impacts on C storage are therefore limited but the potential for accelerating the atmospheric C release are high.  相似文献   

7.
Navjot Sodhi is best known for his advancement of tropical ecology and conservation science; however, his research origins were in fact based in the boreal forest ecosystem of Canada. Ironically, the less-studied ecosystems of the tropics have recently received much more conservation attention than northern biomes, despite the boreal forest (i) representing about one third of all remaining forest on the planet (and about 50% of the world’s remaining tracts of large, intact forest), (ii) sequestering about 30% of the Earth’s stored terrestrial carbon, and (iii) becoming increasingly fragmented with ecologically contiguous patches constituting only 44% of its entire area. These heightened threats of fragmentation and increasing fire frequency associated with expanding human industry in the boreal zone, along with climate change, mean that more international focus on the plight of the boreal ecosystem is warranted. Prior to his death, Navjot Sodhi had accepted a position at the University of Toronto where he planned to apply his keen, transdisciplinary approaches to boreal conservation science in an attempt to prevent the future destruction of planet Earth’s second ‘lung’. Although he never realised this dream, here we provide an overview and examples of how appropriate boreal forest management can be achieved.  相似文献   

8.
The Canadian boreal forest covers over 300 Mha of land area. Its dynamics are largely influenced by fires and insect-induced stand mortality and to a much lesser extent by forest management. This paper analyses six scenarios of future (1990–2040) carbon (C) budgets of the Canadian boreal forest, each based on different assumptions about natural disturbances, rates of reforestation of disturbed land, and conversion of non-stocked to productive forest stands. The objective of these scenarios is to explore the range of responses to different management options. The results indicate an overall inertia of a system whose dynamics are strongly influenced by a recent 20-year period (1970–1989) of large-scale forest disturbances by fire and insects. The 50-year C budget of the six scenarios ranges from an estimated net source of 1.4 Pg C to a net sink of 9.2 Pg C. These estimates indicate the range of response to the management of the Canadian boreal forest. Although a full-scale implementation of the management activities examined here is not likely given ecological and economic realities in the Canadian boreal forest, the analyses explore the relative merits of reducing forest disturbance rates, regeneration delays, and the area of non-stocked forest land.  相似文献   

9.
A consequence of isolation is increased susceptibility to catastrophe. Insect damage to fragmented and isolated forests has the potential to serve as a catastrophic force; such damage has increased worldwide due to climate change and fire suppression policies. We examined the response of endangered endemic Mt. Graham red squirrels to catastrophic insect damage due to moths, beetles, and introduced aphids. Insects changed the forest environment significantly for the endemic squirrel by reducing basal area and stem densities of live stems, while increasing number and basal area of standing dead stems. Availability of two major foods, fungi and tree seeds, declined in insect-damaged forests relative to trends in undamaged forests. Numbers of Mt. Graham red squirrels declined precipitously in insect-damaged forests suggesting a catastrophe. Conservation options are limited in such situations. Forest-insect induced catastrophes are likely to become more common in the near future as forest health declines due to past management tactics and climate change. Prudent conservation measures include the anticipation of insect outbreaks and effective forest treatments to decrease likelihood of such catastrophes to species of precarious conservation status, while avoiding abrupt changes to critical habitat.  相似文献   

10.
Range limits and broad-scale geographic variations in the productivity of boreal and northern deciduous tree species in Europe are simulated with a bioclimatic model (STASH). STASH is based on a small number of distinct mechanisms by which climate is thought to affect the survival, regeneration and growth of trees. Survival is limited by summer warmth requirements and winter cold tolerance; regeneration, additionally by winter chilling requirements; and growth rate by net assimilation, which in turn is related to photosynthetically active radiation, growing-season length, temperature (relative to species-specific optima) and soil moisture supply (relative to evaporative demand). These mechanisms are quantified either as thresholds (for survival and regeneration) or multipliers (for growth), based on bioclimatic variables computed from monthly climate normals interpolated three-dimensionally to a 10-minute grid. Growing-season and growing degree day calculations take into account the effects of chilling. The drought calculations also take into account the effects of soil-moisture storage by means of a physically based evapotranspiration calculation coupled to a one-layer soil hydrology model. STASH is used to examine changes in potential range limits under a 2xCO2 climate-change scenario. Associated transient responses at selected sites in the boreal and boreo-nemoral zones of Sweden are also simulated, using the forest gap model FORSKA2. The species-specific survival and regeneration constraints and growth responses of STASH modify the growth, establishment and mortality of trees in FORSKA2. The results obtained in this way differ sharply from the results of conventional forest gap models, where growth rates are assumed to decline to zero at minimum and maximum growing degree day limits. For example, towards the southern limit ofPicea abies (Norway spruce), STASH correctly shows no decline in productivity, but rather an abrupt cut-off corresponding to a chilling requirement during regeneration that is not met further south or west. In transient warming scenarios, this mechanism has the effect that natural regeneration can be blocked due to the warm winters even as yield is increasing due to the longer and warmer summers. STASH predicts drastic changes in species distributions in response to the large climate changes (especially winter warming) expected for northern Europe. Some of the common boreal species (e.g.,Picea abies; Pinus sylvestris; Alnus incana) are unlikely to survive in much of their present range, withdrawing to the far north. Other species already widespread may be able to occupy some of the few sites that are today unavailable to them (e.g.,Betula spp.;Corylus avellana). Other temperate deciduous species such asFagus sylvatica could have dramatic range expansions, potentially occupying large tracts of the present boreal zone. FORSKA2 transient simulations illustrate some of the possible routes towards different types of forest in a changed climate. Some sites in the north show little change in species composition, but sites towards the southern boundary of the boreal zone could develop a new suite of dominants. The degree of sensitivity of a particular site depends both on the climate change prediction and on the transient dynamics of the forest community. Many types of transient behaviour are shown to be possible. Coupled with uncertainties about the future role of dispersal and changes in disturbance rate, the complexity and variety of these transient responses imply a highly uncertain future for the north European boreal forests.  相似文献   

11.
Because of successive forest fires, closed-canopy black spruce forests are susceptible to a shift towards open lichen-spruce woodlands in parts of the boreal forest of eastern North America. The shift from dark black spruce canopies to pale lichen ground cover offers a dramatic contrast in reflectance that may compensate for the CO2 emissions from forest fires in terms of radiative forcing. We have therefore looked at the climate change feedback that would result from the generation of lichen woodlands through changes in albedo and in stored carbon. Using albedo estimates based on MODIS imagery and incoming solar radiation for the period between 2000 and 2008 along with forest biomass estimates for eastern Canada, we have estimated that net radiative forcing for the conversion from closed-canopy coniferous forests to open lichen woodlands would be about −0.12 nW m−2 ha−1, and would therefore generate a cooling effect in the atmosphere. Based on current estimates of area in open lichen woodlands within the closed-canopy black spruce-moss forests of eastern Canada, we estimate that a current net forcing of −0.094 mW m−2 has already arisen from such conversions. As projections of future climate have been linked to increased probability of forest fires, the generation of open lichen woodlands provides a possible negative feedback to climate change. Results also suggest that carbon sequestration through the afforestation of boreal lichen woodlands may not provide a climate change mitigation benefit.  相似文献   

12.
Broad-scale monitoring in Alaska has become of increasing interest due to uncertainty about the potential impacts of changing climate on high-latitude ecosystems. The Forest Inventory and Analysis (FIA) program is a national monitoring program for all public and private forestlands in the US, but the program is not currently implemented in the boreal region of Alaska. We provide an overview of the strengths and weaknesses of the FIA system for monitoring the potential impact of climate change on Alaska’s species, communities, and ecosystems. The primary strength of the system is a scientifically rigorous design-based statistical estimation method that produces estimates of forest attributes with known sampling error and quantifiable measurement error. The weaknesses of the system include low power for small area estimates, lack of spatial context and contiguity, and difficulty in inferring causality of factors when changes in monitored attributes are detected.Climate change is expected to impact many components of boreal ecosystems, but for most indicators the direction and magnitude of change are difficult to predict because of complex interactions among system components. Status and trend information provided by FIA monitoring that could be helpful to conservation decisions includes abundance and rarity of vascular plants, invasive species, biomass and carbon content of vegetation, shifting vegetation species distribution, disturbance frequency, type, and impact, and wildlife habitat characteristics. Because of unique factors such as the low level of infrastructure, modifications to the FIA monitoring system used in the conterminous US have been proposed for Alaska. Remote sensing data would play a greater role in meeting monitoring objectives, and sampling intensity of field plots would be reduced. Coordination with other national, regional, and local monitoring efforts provides potential for increased understanding of change in boreal ecosystems at multiple scales.  相似文献   

13.
Mycetophilids is a species-rich insect group for which the ecological requirements in temperate forests are poorly understood. This study of mycetophilids was based on trap samples from 15 oak-dominated sites in the boreonemoral zone of southern Sweden. Species richness and composition were analysed in relation to environmental variables at a local and at larger scales (multiple regression), and compared to results from similar studies in spruce-dominated sites in the boreal zone of Norway (PCA and two-sample t tests). Regressions showing a dominance of regional factors over local in-site variables agree with species-richness models assuming that local communities most often are unsaturated. Precipitation (inter-correlated with elevation) was the strongest factor for explaining the variation in species-richness, which is consistent with previous results indicating that mycetophilids are disfavoured by drought. In addition to precipitation, the area of mixed forest with high biodiversity values (woodland key habitats and protected areas) was a positive factor for species-richness, probably because such habitats combine elements of both coniferous and deciduous forests. PCA ordination revealed a clear separation of the species composition between boreal and boreonemoral forests. Species-richness in boreal forest was significantly higher than in boreonemoral forest, indicating a preference for boreal habitats in many of the species. For mycetophilids and other drought-sensitive insects, it is suggested that (partial) cutting in some dense successional oak stands should be avoided, and that some invading spruces should be tolerated.  相似文献   

14.
针对林业信息监测方式实时性差、监测范围有限等问题,为更加实时、准确地对林业虫害信息进行监测并计算监测样地中虫害区域比例,该文在搭建面向林区虫害监测的多旋翼无人飞行器航拍监测系统基础上,提出了一种基于复合梯度分水岭算法的图像分割方法。该方法引入全局直方图均衡化消除了图像暗纹理的影响,并采用形态学混合开闭重构滤波完成了图像样本的去噪处理。计算灰度图像各像素点的复合梯度实现了非相关区域(道路及裸地)的提取,最终利用分水岭算法实现了监测图像虫害区域的分割提取。利用该文所提算法对8幅虫害侵蚀程度不同的监测图像进行分割,并与传统分水岭算法、K-means聚类算法进行对比试验。试验结果表明,该文算法虫害区域提取的平均相对误差率分别降低6.56%、3.17%,平均相对极限测量精度分别改善7.19%、2.41%,能够相对准确地将虫害区域从监测图像中分割出来,可为后续林业虫害监测与防护提供参考。  相似文献   

15.
气候变暖对陆地生态系统的影响   总被引:3,自引:0,他引:3  
人类活动引起的温室效应导致全球气候变暖,气候变暖对全球生态环境的影响越来越受到人们的关注.作为人类赖以生存的环境主体,陆地生态系统对气候变暖将做出何种响应,更是人们关注的重点.植物物候的变化可以直观地反映某些气候变化,尤其是气候变暖.气候变暖影响植物的生长节律,进而引起植物与环境关系的改变及生态系统物质循环(如水和碳的循环)的改变.不同种类植物对气候变化的差异响应,会使植物间和动植物间的竞争与依赖关系发生深刻的变化,如北半球中高纬度地区植被生长季延长、植物提早开花、昆虫提早出现、鸟类提早产蛋以及冰川退缩、永冻土带融化、江河湖泊结冰推迟而融化提早等.本文主要从陆地生态系统的分布和演替两方面着眼,以植物和动物作为考察对象,系统论述了森林、草原、荒漠、湿地及农田等陆地生态系统在气候变暖背景下产生的变化,并从微观和宏观尺度上提出陆地生态系统变化的生态学机制,最后在技术和政策层面给出若干对策.  相似文献   

16.
Although an increasing frequency of forest fires has been suggested as a consequence of global warming, there are no empirical data that have shown climatically driven increases in fire frequency since the warming that has followed the end of the “Little Ice Age” (~1850). In fact, a 300-year fire history (AD 1688–1988) from the Lac Duparquet area (48°28′N, 79°17′W) shows a significant decrease both in the number and extent of fires starting 100 years ago during a period of warming. To explore this relationship between climatic change and fire frequency we used daily data from the Canadian Atmospheric Environment Service's General Circulation Model to calculate components of the Canadian Forest Fire Weather Index (FWI) System for the 1xCO2 and 2xCO2 scenarios. The average FWI over much of eastern Canada, including the Lac Duparquet region, decreased under the 2xCO2 simulation, whereas FWI increased dramatically over western Canada. According to these results, fire frequency would decrease over the southeastern boreal forest which is in agreement with the empirical data from the fire history. Our results stress the importance of large regional variability and call into question previous generalisations suggesting universal increases in the rate of disturbance with climate warming.  相似文献   

17.
针对小蠹虫对森林的危害隐蔽强,症状滞后性明显,在其早期发生时进行遥感识别非常困难。该文基于干旱和虫害存在一定的时滞相关性的假设,提出基于温度植被干旱指数(temperature vegetation dryness index,TVDI)预报小蠹危害的方法。以遭受大面积连续干旱和小蠹危害的云南省中部的石林县为案例区,利用Landsat数据,建立归一化植被指数(normalized difference vegetation index,NDVI)-地表温度(land surface temperature,Ts)特征空间,估算逐像元TVDI。基于地面小班调查的虫害等级数据(健康、轻度、中度和重度4个等级),比较不同虫害等级斑块TVDI差异。同时,以持续干旱2011年轻度受害区为例,结合受害前后云南松林NDVI差值(difference of NDVI before and after the forest attacked by bark beetles,d NDVI)表征实际受害程度的方法,建立TVDI与d NDVI的关系,对2012年进行预测。结果表明,2010-2015年,受害区整体呈下降趋势,TVDI由西向东逐渐变大。健康云南松林TVDI显著高于虫害云南松林(P0.05),且虫害越严重,TVDI越小;2011年,TVDI与d NDVI呈显著负相关(P0.05),可以用线性模型进行拟合,拟合决定系数R2为0.322。采用模型对2012年实际发生情况进行预测,得到预测与实测d NDVI均方根误差RMSE为0.237。在整体干旱的环境下,相对湿润的地方小蠹虫害更严重。因此,可以根据TVDI空间分布特征,找出TVDI相对较小的区域,作为虫害可能发生的重点关注区域,该研究对及时发布虫情监测信息有建设性的意义。  相似文献   

18.
The development of forests in Pukaskwa National Park, Ontario, Canada, was simulated over 150 years to investigate boreal carbon dynamics and to test the feasibility of simulating large tracts of heterogeneous boreal forest. Pukaskwa National Park, located on the north shore of Lake Superior, encompasses 1835 km2 of the Superior Section of the boreal forest. We developed a patch model, called BOPAS (BOreal PAtch Simulator), to simulate the development of carbon pools as a function of environmental parameters. Using GIS techniques, we divided the park into patches defined by a unique combination of forest type, age, climatic variables, soil type and topography, then used a forest gap model to develop biomass-over-time relationships for each patch type. BOPAS uses these relationships to simulate the development of carbon pools for trees, moss and litter/humus. We report results for constant climate, but BOPAS can be easily adapted to changing climate scenarios. Good results were obtained for predictions of carbon storage in trees. The initial value was 3.61 kg C m?2, which agrees closely with literature values. With no disturbance, tree carbon increased to a maximum of 3.97 kg C m?2 at 30 years then slowly declined. Carbon storage was stabilized by introducing fire as a disturbance with a return interval of 100 years. Predicted forest floor carbon density, however, was much lower than expected, being less than half that of trees. It was anticipated to be substantially higher than tree carbon density based on a preliminary survey in the park and values reported in the literature. Published data, however, are very limited in coverage and give such a wide range of values that it was impossible to draw any firm conclusions about the validity of the model. BOPAS also showed that the forest floor carbon pool was relatively constant over the timescales of the simulation, but no published data were available to test this prediction. In summary, this work has demonstrated the feasibility of the BOPAS approach, but has high-lighted the necessity for more extensive data on forest floor carbon storage and dynamics.  相似文献   

19.
This paper reviews the effects that windstorm-induced drastic changes (micro-climate, soil, vegetation, and ground structural heterogeneity) have on forest insect communities. In the current context of shady and CWD-deprived managed forests, windthrow gaps act as regional biodiversity hotspots by maintaining habitat continuity in a mosaic landscape, and by facilitating the breeding and population growth of clearing specialists and saproxylic species. Windthrow gaps are dead-wood islands where forest protection and habitat conservation goals may stand against each other. Besides the quantitative effect of dead wood on bark beetle outbreaks and saproxylic diversity, the latter is favoured by key dead-wood micro-habitats such as large logs, snags and sun-exposed coarse woody debris. The role of natural enemies and sanitation operations in regulating pest outbreaks is discussed. Heterogeneous openings provide many micro-habitats favouring flower-visiting insects, phytophages on saplings, on fallen tree crowns, and on diverse understory flora, as well as ground insects on specific micro-sites.  相似文献   

20.
Amazonia (sensu lato) is by far the largest tropical forest region, but has succumbed to the highest absolute rates of tropical deforestation and forest degradation, driven by rapid frontier expansion, road-building, and spontaneous or government-subsidized migration. The large area-through-time and paleo-climatic stability of Amazonian forests may help explain the high regional to local scale plant and animal species diversity of true forest specialists and high ecological sensitivity to contemporary land-use change. We describe the prevailing forms of anthropogenic disturbance that affect forest organisms in the context of the geographic and evolutionary background that has shaped the degree to which forest species may be resilient to environmental change. The fate of Amazonian biodiversity will partly depend upon the interaction between land-use and climate change, and the extent to which seasonally-dry forests can retain immunity against catastrophic recurrent wildfires. This review illustrates the importance of considering interactions between different forms of forest disturbance to develop effective conservation policy. We conclude with some considerations of the policy agenda necessary to protect forest cover and forest biodiversity at a meaningful scale across the Amazonian biome.  相似文献   

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