Chris J. Cieszewski, Michal Zasada, Mike Strub
Forest Science Volume 52, Number 2, pp. 187-197 April 2006
Abstract:
Using an example of averaged growth series data of Scots pine (Pinus
sylvestris L.), we examine several approaches to site-dependent height-age
model derivation. We consider several renowned base models (two-dimensional
equations, such as Y = f(t)) and derive from them
anamorphic and polymorphic dynamic site equations (three-dimensional
site-height-age models, such as Y = f(t, t 0,
y 0)) of different complexities. The considered base models
were selected previously as suitable for Scots pine in other studies, and are
different variations of exponential and fractional functions. We compare all of
the base models fit to individual site classes and the derived base-age
invariant anamorphic and polymorphic dynamic site equations fit to all sites
pooled together. All the fits of site equations to the pooled data from
different site productivity series were based on base-age invariant stochastic
regressions, in which the global model parameters that are common to all data
are estimated simultaneously with the site effects unique for each site
productivity series. The results show that: (1) choice of definition describing
changes across site qualities may be more important than the choice of base
equation defining changes over time; (2) a base model with high cost of
deriving self-referencing function may sometimes be better than a base model
with low cost of deriving the self-referencing function; and (3) superior base
models may not produce superior anamorphic or simple polymorphic site models,
but can produce superior advanced polymorphic site models, which can describe
the growth patterns in data better than either anamorphic or simple polymorphic
models.
Author Keywords:
Yield tables, site productivity, site
index model, growth model, dynamic equations
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Addresses:
Chris J. Cieszewski, Warnell School of Forest Resources, University of Georgia,
Athens, GA 30602
Michal Zasada, Warnell School of Forest Resources, University of Georgia, Athens, GA 30602 and Department of Dendrometry and Forest Productivity, Faculty of Forestry, Warsaw Agricultural University, Nowoursynowska 159, building #34, 00-776 Warsaw, Poland
Mike Strub, Warnell School of Forest Resources, University of Georgia, Athens, GA 30602 and Weyerhaeuser Company Inc., Hot Springs, AR
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