On the Ecology of Mountainous Forests in a Changing Climate: A ...
On the Ecology of Mountainous Forests in a Changing Climate: A ...
On the Ecology of Mountainous Forests in a Changing Climate: A ...
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150 Chapter 5<br />
species <strong>of</strong> <strong>the</strong> former two genera, agrees well with descriptions <strong>of</strong> <strong>the</strong> near-natural forests<br />
<strong>of</strong> <strong>the</strong> area. The overall performance <strong>of</strong> FORCLIM thus is fairly good.<br />
Major differences between <strong>the</strong> two models become evident with <strong>the</strong> Arkansas climate<br />
(Fig. 5.12): While <strong>the</strong> FORENA simulation is dom<strong>in</strong>ated by sou<strong>the</strong>rn oaks, FORCLIM<br />
produces stands dom<strong>in</strong>ated by Carya spp. and nor<strong>the</strong>rn oaks. However, <strong>the</strong> most<br />
important oak species simulated by FORCLIM are also prom<strong>in</strong>ent on <strong>the</strong> landscape: Q.<br />
alba and Q. velut<strong>in</strong>a (Küchler 1975). Carya spp. is a warmth and drought-adapted genus,<br />
as are many <strong>of</strong> <strong>the</strong> oak species, which makes <strong>the</strong> FORCLIM simulation results quite<br />
realistic. The decrease <strong>of</strong> <strong>the</strong> total aboveground biomass as compared to Missouri<br />
(Fig. 5.12) is due to drought stress; yet <strong>the</strong> real forests <strong>of</strong> <strong>the</strong> area are less dense, and<br />
biomass should be lower (DeAngelis et al. 1981). If <strong>the</strong> field capacity <strong>in</strong> <strong>the</strong> FORCLIM<br />
model is reduced to 10-15 cm, total aboveground biomass decreases below 200 t/ha,<br />
which may be more plausible.<br />
SOUTHEASTERN DECIDUOUS FORESTS<br />
The simulation results from Georgia, <strong>the</strong> sou<strong>the</strong>rnmost site along <strong>the</strong> transect, are given<br />
<strong>in</strong> Fig. 5.13. Sou<strong>the</strong>rn oaks and Carya spp. dom<strong>in</strong>ate this forest. However, <strong>the</strong>re is a<br />
large discrepancy between real and simulated forests both <strong>in</strong> FORCLIM and <strong>in</strong> FORENA:<br />
<strong>On</strong> <strong>the</strong> landscape, sou<strong>the</strong>rn p<strong>in</strong>es (P<strong>in</strong>us spp. <strong>in</strong> Fig. 5.13) dom<strong>in</strong>ate <strong>the</strong> forests, which<br />
is due to <strong>the</strong> occurrence <strong>of</strong> extr<strong>in</strong>sic disturbances such as fire and <strong>the</strong> drought<strong>in</strong>ess <strong>of</strong> <strong>the</strong><br />
sandy soils prevail<strong>in</strong>g <strong>in</strong> that area. However, on <strong>the</strong> clay soils <strong>of</strong> <strong>the</strong> piedmont, for which<br />
<strong>the</strong> simulation results are more representative, oaks and hickories dom<strong>in</strong>ate. Thus, as a<br />
statement about <strong>the</strong> potential natural forest vegetation <strong>in</strong> <strong>the</strong> absence <strong>of</strong> disturbance, <strong>the</strong><br />
FORCLIM model is ra<strong>the</strong>r successful.<br />
Similar simulation results are obta<strong>in</strong>ed for Cumberland Plateau, Tennessee (not shown).<br />
Although <strong>the</strong> annual precipitation sum is high, <strong>the</strong> area is subject to considerable drought<br />
because <strong>of</strong> <strong>the</strong> sandy soils, lead<strong>in</strong>g to low-biomass forests. However, at Cumberland<br />
Plateau FORCLIM produces <strong>the</strong> largest amount <strong>of</strong> aboveground biomass along <strong>the</strong> transect.<br />
The FORENA model also misrepresents <strong>the</strong> effects <strong>of</strong> drought at this site. It is clear<br />
that <strong>the</strong> assumption <strong>of</strong> 30 cm water at field capacity does not represent sandy soils; unfortunately,<br />
<strong>the</strong> large amount <strong>of</strong> aboveground biomass simulated by FORCLIM is by and<br />
large <strong>in</strong>dependent <strong>of</strong> <strong>the</strong> value <strong>of</strong> <strong>the</strong> field capacity parameter that is used <strong>in</strong> <strong>the</strong> simulations.<br />
These anomalies may constitute a serious problem for both models.