A Comparison of Forest Survey Data with Forest Dynamics Simulators FORCLIM
and ZELIG along Climatic Gradients in the Pacific Northwest
By Richard T. Busing and Allen M. Solomon
This report is also available as a pdf.
July 2004
U.S. Geological Survey Scientific Investigation Report 2004-5078
Abstract
Two forest dynamics simulators are compared along climatic gradients
in the Pacific Northwest. The ZELIG and FORCLIM models are tested against forest
survey data from western Oregon. Their ability to generate accurate patterns
of forest basal area and species composition is evaluated for series of sites
with contrasting climate. Projections from both models approximate the basal
area and composition patterns for three sites along the elevation gradient at
H.J. Andrews Experimental Forest in the western Cascade Range. The ZELIG model
is somewhat more accurate than FORCLIM at the two low-elevation sites. Attempts
to project forest composition along broader climatic gradients reveal limitations
of ZELIG, however. For example, ZELIG is less accurate than FORCLIM at projecting
the average composition of a west Cascades ecoregion selected for intensive
analysis. Also, along a gradient consisting of several sites on an east to west
transect at 44.1oN latitude, both the FORCLIM model and the actual data show
strong changes in composition and total basal area, but the ZELIG model shows
a limited response. ZELIG does not simulate the declines in forest basal area
and the diminished dominance of mesic coniferous species east of the Cascade
crest. We conclude that ZELIG is suitable for analyses of certain sites for
which it has been calibrated. FORCLIM can be applied in analyses involving a
range of climatic conditions without requiring calibration for specific sites.
Contents
Abstract
Introduction
Methods
Models and Field Data
Parameterization of ZELIG
Parameterization of FORCLIM
Types and Sources of Field Data
Model Tests
West Cascades Test
Geographic Transect Test
Forested Ecoregion Test
Actual Vegetation along Test Gradients
Species Pool Effects
Results
Actual Vegetation Patterns
Simulated Vegetation Patterns
Western Cascade Range
Geographic Transect Gradient
Forested Ecoregions
Conclusions
Acknowledgements
References
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