ABSTRACT
Global climatic change is expected to affect
growth and survival of trees and will likely change the geographical
distribution of many temperate and boreal tree species. Models
that calculate the
effects of environmental factors, as well as biotic factors, such as
intra-
and interspecific competition, on growth and survival of trees have
been
widely used to calculate the potential effects of temperature changes
on
tree populations. The methods to calculate thermal effects in
such
models are described and analyzed for the soundness and consistency of
underlying
assumptions. They are compared to the evidence from studies of
tree
physiology, growth, and biogeography. The use of thermal indices,
especially
temperature sums, in studies of tree growth and development is
discussed.
It is concluded that the majority of modeling
studies
to date have been based on faulty and internally inconsistent
assumptions and/or do not utilize basic findings from more than a
century of tree research. Only a small number of recent studies
are based on assumptions that are consistent
with such findings. Because of a lack of mechanistic explanations
for
many observations regarding tree growth and development, only empirical
modeling
approaches are currently available for these aspects of tree
ecology. Hybrid approaches, partly mechanistic, partly empirical,
are a promising alternative
to purely empirical models, as long as the different aspects are well
defined
in the models. Several aspects of modeling studies remain
problematic.
Future studies will have to find methods of parameterization that do
not
infer fundamental growth and survival limits from the geographical
distribution
of tree species. A consideration of intraspecific genetic
variation
in trees will greatly improve models of tree growth and survival.