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1.
萌衍模块是植被生态动力学模式中群体动力学方案的重要组成部分,主要用于描述种子的生产、萌芽以及最终发展成新个体等一系列过程,对植被群落结构和演替起着至关重要的作用。然而,目前其参数化方案较不成熟,不同模式的方案差异较大,且存在众多不确定性。因此,为了提出更加合理的萌衍方案,作者首先从观测角度总结了影响种子生产和传播、种子库以及种子萌发和幼苗存活的各种因素;然后围绕森林林窗模型和全球植被动力学模式的萌衍方案进行较为全面的介绍和评述,重点关注对幼苗个体数增量的计算方案;最后讨论其中存在的不确定性和今后的发展方向。  相似文献   

2.
A comparison of forest gap models: Model structure and behaviour   总被引:4,自引:0,他引:4  
Forest gap models share a common structure for simulating tree population dynamics, and many models contain the same or quite similar ecological factors. However, a wide variety of formulations are being used to implement this general structure. The comparison of models incorporating different formulations is important for model validation, for assessing the reliability of model projections obtained under scenarios of climatic change, and for the development of models with a wide range of applicability. This paper reviews qualitative and quantitative comparisons of the structure and behaviour of forest gap models.As examples of qualitative model comparisons, the different formulations used for the heightdiameter relationship, for the maximum growth equation, and for the effects of temperature and drought on tree growth are reviewed. The variety of formulations currently in use has the potential to influence simulation results considerably, but we conclude that little is known on the sensitivity of the models in this respect.The quantitative model comparisons performed so far allow us to draw the following conclusions: (1) Gap models are quite sensitive to the formulation of climate-dependent processes under current climate, and this sensitivity is even more pronounced under a changed climate. (2) Adaptations of forest gap models to specific regions have required detailed sub-models of species life history, thus complicating model comparison. (3) Some of the complex models developed for region-specific applications can be simplified without hampering the realism with which they simulate species composition. (4) Attempts to apply the models without modification beyond the area for which they were developed have produced controversial results.It is concluded that the sensitivity of forest gap models to the exact process formulations should be examined carefully, and that more systematic comparisons of model behaviour at a range of test sites would be desirable. Such studies could improve our understanding of forest dynamics considerably, and they would help to focus future research activities with gap models.  相似文献   

3.
Three gap models, KOPIDE, NEWCOP, and ForClim, were compared with respect to their structure and behavior at four sites along an elevational gradient on Changbai Mt., northeastern China, under current climate and six climate change scenarios. This study intends to compare the three gap models under identical conditions, using a standardized simulation protocol. The three models were originally developed with different backgrounds and for different purposes. While they are relatively similar in the level of structural detail they include, they still differ in many respects regarding the assumptions that are made for representing specific ecological processes.The simulations showed that none of the three gap models provides satisfactory results in all situations; each gap model has strong and weak points in its behavior. While all models are fairly successful in simulating the composition of dominant species along the gradient under current climatic conditions, their projections under a set of hypothetical scenarios of climatic change diverge rather strongly. The analysis of these simulation results shows that several problem areas need to be addressed before any of the models can be used for a reliable impact assessment.Recommendations for improvements of the models are made, including the formulation of temperature and drought effects on tree establishment and tree growth, the size of the species pool, the appropriate choice of patch size and disturbance regimes, and allometric relationships. When aiming to use gap models under new environmental conditions, we propose to carefully reconsider their formulations based on our knowledge of the relevant processes in the region under concern, instead of using the models in an `as-is' mode.  相似文献   

4.
Comparing the Performance of Forest gap Models in North America   总被引:6,自引:0,他引:6  
Forest gap models have a long history in the study of forest dynamics, including predicting long-term succession patterns and assessing the potential impacts of climate change and air pollution on forest structure and composition. In most applications, existing models are adapted for the specific question at hand and little effort is devoted to evaluating alternative formulations for key processes, although this has the potential to significantly influence model behavior. In the present study, we explore the implications of alternative formulations for selected ecological processes via the comparison of several gap models. Baseline predictions of forest biomass, composition and size structure generated by several gap models are compared to each other and to measured data at boreal and temperate sites in North America. The models ForClim and LINKAGES v2.0 were compared based on simulations of a temperate forest site in Tennessee, whereas FORSKA-2V, BOREALIS and ForClim were compared at four boreal forest sites in central and eastern Canada. Results for present-day conditions were evaluated on their success in predicting forest cover, species composition, total biomass and stand density, and allocation of biomass among species. In addition, the sensitivity of each model to climatic changes was investigated using a suite of six climate change scenarios involving temperature and precipitation. In the temperate forest simulations, both ForClim and LINKAGES v2.0 predicted mixed mesophytic forests dominated by oak species, which is expected for this region of Tennessee. The models differed in their predictions of species composition as well as with respect to the simulated rates of succession. Simulated forest dynamics under the changed climates were qualitatively similar between the two models, although aboveground biomass and species composition in ForClim was more sensitive to drought than in LINKAGES v2.0. Under a warmer climate, the modeled effects of temperature on tree growth in LINKAGES v2.0 led to the unrealistic loss of several key species. In the boreal forest simulations, ForClim predicted significant forest growth at only the most mesic site, and failed to predict a realistic species composition. In contrast, FORSKA-2V and BOREALIS were successful in simulating forest cover, general species composition, and biomass at most sites. In the climate change scenarios, ForClim was highly sensitive, whereas the other two models exhibited sensitivity only at the drier central Canadian sites. Although the studied sites differ strongly with respect to both the climatic regime and the set of dominating species, a unifying feature emerged from these simulation exercises. The major differences in model behavior were brought about by differences in the internal representations of the seasonal water balance, and they point to an important limitation in some gap model formulations for assessing climate change impacts.  相似文献   

5.
Gap models have been used extensively in ecological studies of forest structure and succession, and they should be useful tools for studying potential responses of forests to climatic change. There is a wide variety of gap models with different degrees of physiological detail, and the manner in which the effects of climatic factors are analyzed varies across that range of detail. Here we consider how well the current suite of gap models can accommodate climatic-change issues, and we suggest what physiological attributes and responses should be added to better represent responses of aboveground growth and competition. Whether a gap model is based on highly empirical, aggregated growth functions or more mechanistic expressions of carbon uptake and allocation, the greatest challenge will be to express allocation correctly. For example, incorporating effects of elevated CO2 requires that the fixed allometry between stem volume and leaf area be made flexible. Simulation of the effects of climatic warming should incorporate the possibility of a longer growing season and acclimation of growth processes to changing temperature. To accommodate climatic-change factors, some of the simplicity of gap models must be sacrificed by increasing the amount of physiological detail, but it is important that the capability of the models to predict competition and successional dynamics not be sacrificed.  相似文献   

6.
Predicting future changes in tropical rainforest tree communities requires a good understanding of past changes as well as a knowledge of the physiology, ecology and population biology of extant species. Climate change during the next hundred years will be more similar to climate fluctuations that have occurred in the last few thousand years and of a much smaller magnitude than the extent of climate change experienced during last glaciation or at the Pleistocene–Holocene transition. Unfortunately, the extent to which tropical rainforest tree communities have changed during the last few thousand years has been little investigated. As a consequence we lack the detailed evidence for population and range shifts of individual tropical species resulting from climate change analogous to the evidence available for temperate zone forests. Some evidence suggests that the rate of tropical forest change in the last several thousand years may have been high. If so, then CO2 increases and the likely alterations in temperature, forest turnover rate, rainfall, or severe droughts may drive substantial future forest change. How can we predict or model the effects of climate change on a highly diverse tree community? Explanations for the regulation of tropical tree populations often invoke tree physiology or processes that are subject to physiological regulation such as herbivory, pathology or seed production. In order to incorporate such considerations into climate change models, the physiology of a very diverse tree community must be understood. My work has focused on simplifying this diversity by categorizing the shade-tolerant species into functional physiological groups. Most species and most individual trees are shade-tolerant species, gap-requiring species being relatively uncommon. Additionally, in a regenerating gap most of the individuals are shade-tolerant species that established before gap formation. Despite the fact that the shade-tolerant species are of major ecological importance, their comparative physiology has received little attention. I have found that shade-tolerant species differ substantially in their responses to light flecks, treefall light gaps and drought. Furthermore, among phylogenetically unrelated species, these differences in physiology can be predicted from leaf lifetime. These results provide a general framework for understanding the mechanics of tropical rainforests from a physiological perspective that can be used to model their responses to climate change.  相似文献   

7.
An integrated program of ecosystem modeling and field studies in the mountains of the Pacific Northwest (U.S.A.) has quantified many of the ecological processes affected by climatic variability. Paleoecological and contemporary ecological data in forest ecosystems provided model parameterization and validation at broad spatial and temporal scales for tree growth, tree regeneration and treeline movement. For subalpine tree species, winter precipitation has a strong negative correlation with growth; this relationship is stronger at higher elevations and west-side sites (which have more precipitation). Temperature affects tree growth at some locations with respect to length of growing season (spring) and severity of drought at drier sites (summer). Furthermore, variable but predictable climate-growth relationships across elevation gradients suggest that tree species respond differently to climate at different locations, making a uniform response of these species to future climatic change unlikely. Multi-decadal variability in climate also affects ecosystem processes. Mountain hemlock growth at high-elevation sites is negatively correlated with winter snow depth and positively correlated with the winter Pacific Decadal Oscillation (PDO) index. At low elevations, the reverse is true. Glacier mass balance and fire severity are also linked to PDO. Rapid establishment of trees in subalpine ecosystems during this century is increasing forest cover and reducing meadow cover at many subalpine locations in the western U.S.A. and precipitation (snow depth) is a critical variable regulating conifer expansion. Lastly, modeling potential future ecosystem conditions suggests that increased climatic variability will result in increasing forest fire size and frequency, and reduced net primary productivity in drier, east-side forest ecosystems. As additional empirical data and modeling output become available, we will improve our ability to predict the effects of climatic change across a broad range of climates and mountain ecosystems in the northwestern U.S.A.  相似文献   

8.
Cloud microphysical processes occur at the smallest end of scales among cloud-related processes and thus must be parameterized not only in large-scale global circulation models(GCMs) but also in various higher-resolution limited-area models such as cloud-resolving models(CRMs) and large-eddy simulation(LES) models. Instead of giving a comprehensive review of existing microphysical parameterizations that have been developed over the years, this study concentrates purposely on several topics that ...  相似文献   

9.
The development of atmospheric mesoscale models from their early origins in the 1970’s until the present day is described. Evolution has occurred in dynamical and physics representations in these models. The dynamics has had to change from hydrostatic to fully nonhydrostatic equations to handle the finer scales that have become possible in the last few decades with advancing computer power, which has enabled real-time forecasting to go to finer grid sizes. Meanwhile the physics has also become more sophisticated than the initial representations of the major processes associated with the surface, boundary layer, radiation, clouds and convection. As resolutions have become finer, mesoscale models have had to change paradigms associated with assumptions related to what is considered sub-grid scale needing parameterization, and what is resolved well enough to be explicitly handled by the dynamics. This first occurred with cumulus parameterization as real-time forecast models became able to represent individual updrafts, and is now starting to occur in the boundary layer as future forecast models may be able resolve individual thermals. Beyond that, scientific research has provided a greater understanding of detailed microphysical and land-surface processes that are important to aspects of weather prediction, and these parameterizations have been developing complexity at a steady rate. This paper can just give a perspective of these developments in the broad field of research associated with mesoscale atmospheric model development.  相似文献   

10.
Summary The importance of linking measurements, modeling and remote sensing of land surface processes has been increasingly recognized in the past years since on the diurnal to seasonal time scale land surface–atmosphere feedbacks can play a substantial role in determining the state of the near-surface climate. The worldwide Fluxnet project provides long term measurements of land surface variables useful for process-based modeling studies over a wide range of climatic environments.In this study data from six European Fluxnet sites distributed over three latitudinal zones are used to force three generations of LSMs (land surface models): the BUCKET, BATS 1E and SiB 2.5. Processes simulating the exchange of heat and water used in these models range from simple bare soil parameterizations to complex formulations of plant biochemistry and soil physics.Results show that – dependent on the climatic environment – soil storage and plant biophysical processes can determine the yearly course of the land surface heat and water budgets, which need to be included in the modeling system. The Mediterranean sites require a long term soil water storage capability and a biophysical control of evapotranspiration. In northern Europe the seasonal soil temperature evolution can influence the winter energy partitioning and requires a long term soil heat storage scheme. Plant biochemistry and vegetation phenology can drive evapotranspiration where no atmospheric-related limiting environmental conditions are active.  相似文献   

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