Potential Vegetation Modeling In The Chinese Loess Plateau

Human modifications of the natural environment profoundly affect biogeochemical processes of the Earth's climatic systems. These processes may bring about unpredictable changes of the natural eco-environment that supports our human socio-economic systems. To promote the sustainability of socio-economic developments, the need to assess the degree to which human activities can affect ecosystems is pressing. In other words, we need to know how much of the natural ecosystems have been altered. Or to simply put, what are the potential natural ecosystems. While nurturing the Chinese civilization, the Chinese Loess Plateau (CLP) has been radically changed in its visage of natural environments, as expressed by environmental issues such as ecological deterioration and soil degradation. After a long period of abusive economic over-exploration, the consensus has been recently reached by the government and the general public that the disrupted ecosystems need to be restored under scientific guidelines of potential ecology with a full consideration of current socio-economic status. To explore scientifically sounding ways of ecological restoration and to plan for a long-term socio-economic sustainability, we need to understand the maximum potentials of the widely-advocated ecological restoration in the Chinese Loess Plateau. This thesis is designed to explore the spatial patterns of the maximum potentials of various vegetation types both in the climate-vegetation scale and in the community-species scale by fully investigating the interacting and coupling relationships among ecological, hydrological and climatic processes in the plateau.Four aspects of work are involved in this thesis. First, distributed statistical models were constructed to spatially interpolate all of key environmental factors that contribute to the formation of ecological patterns. These key environmental factors include the following: precipitation, air temperature, surface temperature, minimal air temperature, maximal air temperature, air humidity, evaporation and potential solar radiation. These models first explore in detail the spatial structural functions and address spatially-distributed climate structure functions. Then, we conducted spatial analyses and model comparisons of the residues after removals of the structural components. Finally, the spatially-distributed climate factor models for the study area were constructed. Second, the Koppen, Kira, and HOLDRIDGE models were used to simulate the spatial distributions of climate-vegetation types in the study area. The normal HOLDRIDGE model was particularly used for further classifying HOLDRIDGE-defined major sub-climate-vegetation types, and a HOLDRIDGE transitional model was then used for delineating the spatial patterns of transitional climate-vegetation types. The normal HOLDRIDGE modeling results appear to be well acceptable and can be well compared with the results of the KSppen and Kira modeling. The latter model (HOLDRIDGE transitional model) seems to be quite effective in simulating the maximum potentials of vegetation distributions in the CLP, especially regarding the influences of regional climate conditions. Third, four algorithms (i.e. GARP, BIOCLIM, DOMAIN and the ENFA algorithms) were employed to simulate the potential distributions of 17 typical community-species out of 12 zonal vegetation types that dominate the study area. Among these simulations, GARP seems to well depict the spatial pattern of potential distributions of community-species. Although DOMAIN and BIOCLIM algorithms share some similar structural characteristics, the former depicts large-patch distributions of certain specieswhile the latter yields better results in simulating small-patch distributions of certain species. For species with characteristics of conspicuous vertical zonality, ENFA algorithm has unparalleled advantages over the other three algorithms. Finally, we propose that interventions of human activities can play a significant role in modifying the maximum potential distribution of vegetation-species in the study area according to the spatial trends of typical species distributions in different ecosystems. Human activities may results in reorganizations in the spatial distribution of vegetation-species in the context of modern climatic conditions. The results show that most parts of the Chinese Loess Plateau has the potential climatic conditions favoring forest development (forest and forest-steppes), but restoration and management of the eco-environment in the CLP require visionary and well-thought human interventions.