Research
TRANSFORMATION OF LARCH-DOMINATED FORESTS AND WOODLANDS INTO MIXED TAIGA
Administrative Information - Larch
OBJECTIVES
The objective of this proposed work is to extend recent findings of the co-Investigators that southern forest species in Siberia are “invading” traditional larch forests and to understand the implications of this to biodiversity and feedbacks to climate and soil. The major hypothesis to be tested is that the historical area of larch dominance in eastern Russia is transforming into a zone of mixed taiga in areas of disturbance. We plan to identify the extent of the evergreen conifer invasion and understand whether it is widespread or limited to specific regional areas as controlled by disturbances using a combination of well-calibrated satellite data, ground measurements, and coupled forest gap and soil process models. We also propose to use these tools to forecast trends of biodiversity in the region. This work is designed to provide a prototype for future missions aimed at quantifying ecosystem change due to disturbance and the resulting impacts on biodiversity. Specific objectives of the study are: 1) Couple existing forest growth and soil moisture and energy flux models to simulate ecosystem dynamics of the Siberian region subject to known temperature, precipitation, soil properties, and disturbance patterns; and use forward modeling with this information to guide remote sensing analysis. 2) Augment an existing field measurement database across a wide area of forest within eastern Russia. 3) Use high spatial and spectral resolution imagery to help quantify forest composition and structure biodiversity in traditional larch taiga for areas in eastern Russia based on field observations. 4) Validate modeling results with field and remotely sensed observations. 5) Use the combined remote sensing and modeling approach to forecast disturbance effects on biodiversity with the expansion of plant functional type characteristic of mixed taiga into the larch forest within the larger study area of eastern Russia. 6) Assess potential consequences of the future functioning of these ecosystems based on model forecasts. These objectives meet the NASA Strategic Objectives of quantifying global land cover change and improving ecosystem modeling as well as advancing Earth observation from space.
UVA Responsibility:
Forest Ecosystem Modeling FAREAST Gap Model Forest gap models simulate forest dynamics by computing the establishment, diameter growth, and mortality of each tree on a small plot, usually equivalent to a gap or opening formed by a dominant tree’s death (see Shugart, 1984, 1998, 2003 for more details and a history of this modeling approach). Gap models require relatively simple demographic parameters for tree species, which often can be obtained from typical inventory and forestry study. The models are driven by readily available climate variables and other environmental variables such as soil physical and chemical properties, slope, and aspect. Because of their straightforward parameterization, gap models have been applied widely to study forest management, climate/ vegetation interrelations and forest succession (Shugart, 1998) At an elementary level, eastern Eurasian forests can be divided into two categories: boreal forests and temperate mixed forests. In this project, we plan to use the FAREAST model (Xiandong and Shugart 2005) to simulate the composition, physical stature, and successional pattern of the forest across our study area. FAREAST has been developed and tested across a wide range of sites in eastern Russia and was shown to reproduce broad compositional and structural forest patterns in about 75-87% of the cases it was subject to (Xiaodong and Shugart, 2005) (Fig 6.) Like other forest gap models, FAREAST simulates a forest stand as a summation of trees on many independent plots. The dimensions of each tree on any plot are updated annually based on the tree growth by a GROWTH sub-model; species and initial dimension of each tree are determined when it is established, based on the seedling bank and size and environmental condition by a REGENERATION sub-model. Finally the death of each tree within each plot is determined by a MORTALITY sub-model. All these sub-models are impacted by annual updated bio-environmental condition: ENVIRON. These four main sub-models are linked together as annual ENVIRONGROWTH- MORTALITY-REGENERATION cycles (Shugart, 1984; Botkin, 1993). The Hydro-Thermodynamic Soil Vegetation Model-HTSVS We propose to use the Hydro-Thermodynamic Soil Vegetation Scheme (HTSVS) (Kramm et al., 1996; Mölders et al., 2003a) to compute change in permafrost depth, surface runoff, drainage, evapotranspiration, available water, and soil thermal flux. HTSVS is a multi-layer soil model which presents advanced soil physics parameterizations which are simplified in forest models. The model includes a multi-layer snow model which introduces an insulating effect and the retardation of infiltration (Mölders and Walsh, 2004). It models the heat conduction and water diffusion (including the Richards equation) within the soil as well as the cross-effects (the Ludwig-Soret effect and the Dufour effect) generated by soil moisture and temperature gradients as postulated by the linear thermodynamics of irreversible processes. The model also simulates soil freezing and thawing, and the related release and consumption of latent heat and the effects of frozen soil layers on vertical fluxes of heat and moisture and water vapor fluxes within the soil. The water uptake by plants includes a vertically variable root distribution dependent on vegetation type and a variable ground water depth depending upon previous meteorological conditions. Soil albedo as well as albedo and emissivity of snow vary with time (e.g., Kramm et al., 1996; Mölders et al., 2003a, b). HTSVS also takes into account moss and lichen, which are of special relevance for the moisture distribution within soils and for permafrost dynamics (e.g., Beringer et al., 2001). HTSVS has been successfully evaluated in a number of field studies (e.g., Kramm, 1995; Mölders, 2000; Narapusetty and Mölders, 2005, 2006) including long-term permafrost observations at Barrow, Alaska (Mölders and Romanovsky, 2006). Coupled Modeling We intend to use the coupled forest gap and soil moisture and energy flux model to assess the implications of land cover disturbance on permafrost extent, active layer thickness, and the consequences on soil temperature flux, water storage, infiltration, runoff and evapotranspiration and their effect on forest succession and biodiversity. We will develop data-driven scenarios using soils and land cover information to forecast changes in biodiversity. In order to accomplish this, one- way and two-way coupling will be performed using parameters shared and required by the FAREAST and HTSVS models. For one way coupling, HTSVS will be driven by observed meteorological conditions. Soil moisture and heat flux, soil temperature, and permafrost, and moisture conditions predicted by HTSVS will serve as input to FAREAST to simulate changes in forest growth. In two-way coupling simulations, FAREAST and HTSVS will be run so that the changes in forest growth and can feedback on incoming climate and effect soil conditions simulated by HTSVS. Comparison of results obtained with one- and two-way coupling will provide a means for sensitivity testing of the feedback processes between soil and forest growth.
Department of Environmental Sciences
376 Clark Hall
The University of Virginia
Charlottesville, Virginia 22903
Telephone: 434-924-7642
Fax: 434-924-4761
email: hhs@virginia.edu
