Abstract : 3N.19
Bioclimatic concept for assessment of atmosphere and forest land-cover coupling at a regional scale

Julia Stoyanova
National Institute of Meteorology and Hydrology

The aim of this study is to identify quantitavely the main physical mechanisms that maintain the equilibrium between vegetated land cover and atmosphere as a dynamic coupled system in mountain environment at a regional-scale. The relevant boundary conditions of this equilibrium and related distribution of Plant Functional Types (PFT) are defined. Applying a process-based approach, the specific problems to be addressed include: (i) to develop a framework of the relation between the physical climate and forest land cover; (ii) to delineate the driving forces on the long-term coupling between climate and Forest Vegetation Types (FFTs) at mountain environment; (iii) to specify the threshold levels of the main descriptors that might be used to distinguish FFTs on a regional scale.

A conceptual bioclimatic approach for differentiation of potential natural forest cover that accounts for the regional-scale environmental specific features (climate, relief, forest cover type) is proposed. This is a bi-dimensional biosphere-atmosphere equilibrium scheme that defines the forest-cover classes into functional units. It is based on two bioclimatic indicators: index of dryness of Budyko and potential evapotranspiration of forested-land surface (net radiation estimates) during the growing season. In other words, biogeophysical long-term coupled processes of water- and energy- exchange are the criteria used to define the climatic limits of FFTs stable equilibrium.

Forest-vegetated land cover of south and southeastern Bulgaria is considered. National vegetation maps and descriptors are used to derive the dominant forest cover types. Modeling scheme is developed for the presentday climate (1961-1990) and uses meteorological information from the national network stations that cover space- and altitudinal-environmental differences of studied region. On this basis, the functional units are delineated and the threshold levels of water-limited equilibrium conditions (bouth soil media and atmospheric demands) are obtained. Above these threshold limits, environmental pressure is directed towards disturbance of the site water balance optimality. An example of disrupted land surface-atmosphere coupling is illustrated by simulating the land cover change and evaluation its potential impacts and forest-atmosphere feedbacks.