On the Ecology of Mountainous Forests in a Changing Climate: A ...

152 Chapter 5
approaching the southwestern edge of the simulated geographical range. The increase of
total biomass simulated by FORCLIM, approaching 300 t/ha under mesic conditions in
the south, appears to be more realistic than the low-biomass forests simulated by FOR-
ENA (DeAngelis et al. 1981).
Second, FORCLIM produces plausible species compositions in eastern North America. It
performs best in the central part of the climate gradient explored in this study, where the
simulation results are more realistic than those obtained from FORENA. In the northern
part, an anomalous behaviour of some light-demanding species becomes evident, whereas
in the southwestern part of the gradient, FORCLIM reveals a larger deficiency than
FORENA to lose drought-intolerant species and to have total aboveground biomass constrained
by drought. In part this may be due to the generous assumption of 30 cm water
at field capacity in the present simulations. Soil moisture appears to be more important
throughout most of the deciduous forests of eastern North America than it is in the forests
of the European Alps. However, simulation results conducted with lower values of the
field capacity parameter suggest that the FORCLIM model is likely to encounter similar
problems along drought gradients as were revealed for European forests (cf. section 5.3).
Third, it should be noted that several of the FORCLIM parameters have a more differentiated
scale than their FORENA counterparts, such as those denoting the tolerance to browsing
(kBrow) and shading (kL y , kL a ). The simple assignments made in this study
(Tab. 5.5) could be improved considerably by using more precise descriptions of the
natural history of these tree species. The relative tolerance of the species was documented
e.g. by Baker (1949); data sources like this should allow one to define the tolerance of
the species with a differentiation appropriate for the FORCLIM model (cf. chapter 3).
Maybe such improvements could help to solve some of the problems mentioned above.
Finally, we may conclude that FORCLIM behaves fairly well with the set of species of
eastern North America and under climatic conditions characterized by much higher annual
temperature amplitudes than in Europe. The introduction of factors that are important for
providing a realistic picture of forest dynamics as observed in the landscape, such as
sandy soils and disturbance regimes (e.g. windthrow and fire) could be used to improve
the results obtained so far. Yet at some sites the present FORCLIM simulation results are
more plausible than those produced by the FORENA model (Solomon 1986). This study
suggests that FORCLIM has the potential to yield realistic results also when it is applied
with a set of species and under climatic conditions for which it has not been developed.