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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Model applications 163<br />
At <strong>the</strong> site Bever (Fig. 6.5), <strong>the</strong>re is hardly any agreement among <strong>the</strong> simulated forests<br />
under climatic change. The projections under <strong>the</strong> various climate scenarios range from<br />
spruce-maple (Picea excelsa – Acer spp.) forests under <strong>the</strong> regionalized scenario, which<br />
resemble those typical <strong>of</strong> today's montane belt (Ellenberg & Klötzli 1972), to species<br />
compositions as surpris<strong>in</strong>g as silver fir-chestnut-oak (Abies alba – Castanea sativa –<br />
Quercus spp.) forests under <strong>the</strong> IPCC scenario. However, <strong>the</strong>re is one pattern that is<br />
common to all scenarios <strong>of</strong> future climate: All <strong>the</strong>se steady-state species compositions<br />
differ radically from <strong>the</strong> species composition simulated under current climatic conditions,<br />
which is also typical <strong>of</strong> <strong>the</strong> actual vegetation at Bever. Thus, sites like Bever are likely to<br />
undergo drastic changes, but it appears to be impossible to give an <strong>in</strong>dication <strong>of</strong> what <strong>the</strong><br />
exact changes will be, even if we optimistically assume that <strong>the</strong> forest model does not<br />
conta<strong>in</strong> any uncerta<strong>in</strong>ties.<br />
At <strong>the</strong> site St. Gotthard (Fig. 6.5), both scenarios agree (1) that <strong>the</strong> timberl<strong>in</strong>e will rise<br />
and this area would become afforested, and (2) that spruce (P. excelsa) would come to<br />
dom<strong>in</strong>ate <strong>the</strong>se forests. However, <strong>the</strong> two scenarios produce slightly diverg<strong>in</strong>g results<br />
concern<strong>in</strong>g <strong>the</strong> abundance <strong>of</strong> species such as silver fir (A. alba) and larch (Larix decidua).<br />
Compar<strong>in</strong>g <strong>the</strong>se f<strong>in</strong>d<strong>in</strong>gs to <strong>the</strong> results published by Kienast (1991), who used <strong>the</strong><br />
FORECE model, a large discrepancy becomes evident: In <strong>the</strong> Kienast study, P<strong>in</strong>us cembra<br />
was abundant after <strong>the</strong> first 100 years <strong>of</strong> climatic change, which most probably represents<br />
an anomaly (cf. section 5.3). Moreover, <strong>the</strong> forests simulated <strong>in</strong> that study had very low<br />
biomass (around 100 t/ha) irrespective <strong>of</strong> <strong>the</strong> magnitude <strong>of</strong> climatic change, whereas<br />
FORCLIM simulates an aboveground biomass <strong>of</strong> almost 300 t/ha (Fig. 6.5). The low<br />
biomass obta<strong>in</strong>ed from FORECE probably is an artifact <strong>of</strong> <strong>the</strong> aboveground carry<strong>in</strong>g capacity<br />
that was not adjusted, thus produc<strong>in</strong>g <strong>in</strong>consistent results under climatic change<br />
(cf. section 2.3.2).<br />
At <strong>the</strong> site Davos (Fig. 6.5), all three climate scenarios <strong>in</strong>duce a shift from <strong>the</strong> subalp<strong>in</strong>e<br />
spruce (P. excelsa) forests prevail<strong>in</strong>g today to forests where silver fir (A. alba), spruce,<br />
and beech (Fagus silvatica) are abundant. Thus, <strong>the</strong> model predicts an <strong>in</strong>vasion <strong>of</strong> species<br />
that are typical <strong>of</strong> today's montane belt (Ellenberg & Klötzli 1972). Aga<strong>in</strong>, <strong>the</strong>re are some<br />
differences among <strong>the</strong> various scenarios concern<strong>in</strong>g <strong>the</strong> abundance <strong>of</strong> s<strong>in</strong>gle species.<br />
Fig. 6.5 (fac<strong>in</strong>g page): Steady-state species composition simulated by <strong>the</strong> FORCLIM-E/P<br />
model under various climate scenarios at six locations along a climate gradient <strong>in</strong> <strong>the</strong> European<br />
Alps. The scenarios <strong>of</strong> future climate are described <strong>in</strong> more detail <strong>in</strong> Tab. 6.2.<br />
Symbols: Today – Current climate; IPCC – IPCC scenario <strong>of</strong> climatic change; Kienast –<br />
<strong>Climate</strong> scenario as used by Kienast (1991) for <strong>the</strong> year 2100; DS – Regionalized climate<br />
scenario obta<strong>in</strong>ed by <strong>the</strong> downscal<strong>in</strong>g methodology (Gyalistras et al. 1994).