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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Introduction 3<br />
1.2 Methods for <strong>the</strong> analysis <strong>of</strong> forest ecosystems<br />
The term “forest dynamics” spans huge ranges both <strong>in</strong> time and space: The enzymatic reactions<br />
<strong>of</strong> photosyn<strong>the</strong>sis operate with<strong>in</strong> fractions <strong>of</strong> a second; foliage development takes<br />
a few weeks, while tree growth lasts decades to centuries, and <strong>the</strong> dynamics <strong>of</strong> soil organic<br />
matter span millennia. <strong>On</strong> <strong>the</strong> o<strong>the</strong>r hand, <strong>the</strong> germ<strong>in</strong>ation <strong>of</strong> a seed takes place on a<br />
few square centimetres, a sunfleck mov<strong>in</strong>g over <strong>the</strong> forest floor covers a few square meters;<br />
a dom<strong>in</strong>ant tree <strong>in</strong> <strong>the</strong> canopy occupies 0.01-0.1 ha, and <strong>the</strong> quasi-equilibrium <strong>of</strong> a<br />
forest landscape may be reached on <strong>the</strong> scale <strong>of</strong> several hectares only (Shugart & Urban<br />
1989). Lev<strong>in</strong> (1992) hypo<strong>the</strong>sized that <strong>the</strong> central problem <strong>in</strong> ecology is that <strong>of</strong> pattern<br />
and scale, and that <strong>the</strong> various temporal, spatial, and organizational scales should be <strong>in</strong>terfaced<br />
<strong>in</strong> order to understand <strong>the</strong> dynamics <strong>of</strong> ecosystems.<br />
Due to <strong>the</strong> size <strong>of</strong> trees, even <strong>the</strong> measurement <strong>of</strong> simple <strong>in</strong>dices <strong>of</strong> forest ecosystems,<br />
such as allometric relationships or total biomass, requires much personnel, time, and<br />
money (Burger 1945-1953, K<strong>in</strong>g 1991, Woods et al. 1991, Smith et al. 1991, Wang et<br />
al. 1991). <strong>On</strong> <strong>the</strong> o<strong>the</strong>r hand, <strong>the</strong> longevity <strong>of</strong> <strong>the</strong> dom<strong>in</strong>ant organisms makes measurements<br />
on a temporal scale appropriate for <strong>the</strong> whole ecosystem practically impossible<br />
(Botk<strong>in</strong> 1981, Shugart 1990). Not surpris<strong>in</strong>gly, empirical studies <strong>of</strong> forests typically<br />
cover a few years and a few ares at most. For example, many <strong>in</strong>vestigations on <strong>the</strong> direct<br />
effects <strong>of</strong> carbon dioxide on vegetation (Eamus & Jarvis 1989) dealt with <strong>the</strong> short-term<br />
<strong>in</strong>crease <strong>of</strong> photosyn<strong>the</strong>sis (Oechel & Stra<strong>in</strong> 1985), growth rates <strong>of</strong> tree seedl<strong>in</strong>gs<br />
(Bazzaz & Williams 1991), or competition <strong>in</strong> model ecosystems (Miao et al. 1992,<br />
Körner & Arnone 1992). The effects on natural forest ecosystems can not be estimated<br />
simply by extrapolat<strong>in</strong>g <strong>the</strong>se f<strong>in</strong>d<strong>in</strong>gs across scales (O'Neill et al. 1986), and <strong>the</strong>ir <strong>in</strong>compatibility<br />
makes it difficult to deal with several scales simultaneously on an empirical<br />
basis (Shugart & Urban 1989). Thus, o<strong>the</strong>r methods are required to <strong>in</strong>vestigate <strong>the</strong> coupl<strong>in</strong>gs<br />
and feedbacks between scales <strong>in</strong> ecosystems. The present study is based on <strong>the</strong> assumption<br />
that ecological models provide an opportunity to do so.<br />
Unfortunately, ecologists cont<strong>in</strong>ue to be substantially separated <strong>in</strong>to those who build and<br />
use quantitative models, and those who don't (Botk<strong>in</strong> 1981). In fact, ecological models<br />
can be nei<strong>the</strong>r built nor tested without a sound empirical basis. The “empirical” (fieldoriented)<br />
and <strong>the</strong> “<strong>the</strong>oretical” (model-oriented) approaches have complementary functions<br />
and depend on each o<strong>the</strong>r (Fischl<strong>in</strong> 1982): Field data serve as a basis for develop<strong>in</strong>g<br />
and test<strong>in</strong>g an ecological model; on <strong>the</strong> o<strong>the</strong>r hand, sensitivity analyses conducted with<br />
<strong>the</strong> model can be used to test our understand<strong>in</strong>g <strong>of</strong> <strong>the</strong> system and to identify research