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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178<br />
8 . Conclusions<br />
Explor<strong>in</strong>g <strong>the</strong> mechanisms <strong>of</strong> forest dynamics with forest gap models<br />
The complexity <strong>of</strong> forest ecosystems toge<strong>the</strong>r with <strong>the</strong> large temporal and spatial scales<br />
<strong>in</strong>volved <strong>in</strong> successional processes render experimental approaches to study forest succession<br />
extremely difficult (chapter 1; Shugart 1984). Forest gap models (Botk<strong>in</strong> et al.<br />
1972a,b) have been used successfully to syn<strong>the</strong>size <strong>the</strong> exist<strong>in</strong>g knowledge on successional<br />
dynamics <strong>of</strong> forests. However, <strong>the</strong> complexity <strong>of</strong> <strong>the</strong>se models <strong>in</strong> turn bears problems,<br />
e.g. because <strong>the</strong>ir properties are ill-known. The analyses performed <strong>in</strong> chapter 2 toge<strong>the</strong>r<br />
with <strong>the</strong> re-implementation <strong>of</strong> FORECE with<strong>in</strong> RAMSES yielded several systems<br />
<strong>the</strong>oretical, statistical and ecological <strong>in</strong>sights <strong>in</strong>to <strong>the</strong> structure and function<strong>in</strong>g <strong>of</strong> <strong>the</strong><br />
FORECE gap model (Kienast 1987), which provided a safer basis for improv<strong>in</strong>g and <strong>in</strong>terpret<strong>in</strong>g<br />
<strong>the</strong> model.<br />
Forest gap models are capable <strong>of</strong> depict<strong>in</strong>g <strong>the</strong> successional characteristics <strong>of</strong> many forest<br />
ecosystems <strong>in</strong> a realistic way (Shugart 1984). The analyses performed <strong>in</strong> <strong>the</strong> present<br />
study and <strong>the</strong> subsequent changes to <strong>the</strong> model, such as <strong>the</strong> update <strong>of</strong> state variables and<br />
<strong>the</strong> structural simplification, did still lead to realistic model behaviour for a wide range <strong>of</strong><br />
sites <strong>in</strong> <strong>the</strong> European Alps (chapter 4 & section 5.3) and even <strong>in</strong> eastern North America<br />
(section 5.4). Moreover, <strong>the</strong> factors that turned out to be most important <strong>in</strong> <strong>the</strong> model<br />
conform to ecological expectations, e.g. light availability. <strong>On</strong> <strong>the</strong> o<strong>the</strong>r hand, <strong>the</strong> factors<br />
that contributed little to <strong>the</strong> simulated dynamics <strong>in</strong> FORECE and thus could be omitted are<br />
those that are also considered to be less important <strong>in</strong> ecology (Shugart 1984, Ellenberg<br />
1986), or <strong>the</strong>ir use <strong>in</strong> a forest gap model is debatable for pr<strong>in</strong>cipal reasons, e.g. <strong>in</strong>dicator<br />
concepts.<br />
These results support <strong>the</strong> hypo<strong>the</strong>sis that forest gap models are powerful tools for explor<strong>in</strong>g<br />
<strong>the</strong> dynamics <strong>of</strong> forest ecosystems on scales that are not directly observable, and that<br />
<strong>the</strong> models can be used successfully to <strong>in</strong>terface <strong>the</strong> ecological knowledge from various<br />
discipl<strong>in</strong>es (cf. Lev<strong>in</strong> 1992).