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Assessment of a model of forest dynamics under contrasting climate and disturbance regimes in the Pacific Northwest

By Richard T. Busing and Allen M. Solomon

U.S. GEOLOGICAL SURVEY

Scientific Investigations Report 2005-5242


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Abstract

     An individual-based model of forest dynamics (FORCLIM) was tested for its ability to simulate forest composition and structure in the Pacific Northwest region of North America. Simulation results across gradients of climate and disturbance were compared to forest survey data from several vegetation zones in western Oregon. Modelled patterns of tree species composition, total basal area and stand height across climate gradients matched those in the forest survey data. However, the density of small stems (<50 cm DBH) was underestimated by the model. Thus actual size-class structure and other density-based parameters of stand structure were not simulated with high accuracy. The addition of partial-stand disturbances at moderate frequencies (<0.01 yr-1) often improved agreement between simulated and actual results. Strengths and weaknesses of the FORCLIM model in simulating forest dynamics and structure in the Pacific Northwest are discussed.

CONTENTS

Introduction
     Background
     Purpose and Scope
     Acknowledgements
Description of Study Area
Methods
     The model
     Empirical data
     Model comparisons with field data
Results
     Geographic transect
     Forested ecoregions
          Composition by ecoregion
          Structure by ecoregion
Discussion
Summary
References


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