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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146 Chapter 5<br />
100<br />
Tundra & nor<strong>the</strong>rn boreal sites<br />
Biomass (t/ha)<br />
80<br />
60<br />
40<br />
20<br />
Thuja, Juniperus, Larix<br />
Populus spp.<br />
Picea mariana/rubens<br />
Picea glauca<br />
Betula spp.<br />
Abies spp.<br />
0<br />
Churchill Shefferville Armstrong<br />
Site<br />
Fig. 5.10: Steady-state species composition at tundra and nor<strong>the</strong>rn boreal sites <strong>in</strong><br />
eastern North America as estimated by <strong>the</strong> FORCLIM-E/P model.<br />
<strong>in</strong>g to <strong>the</strong> tundra-forest transition zone typical <strong>of</strong> this area (Rowe 1972). While <strong>the</strong> occurrence<br />
<strong>of</strong> Picea glauca is plausible, <strong>the</strong> large fraction <strong>of</strong> Larix laric<strong>in</strong>a appears to be unrealistic<br />
(Rowe 1972). In eastern North America, L. laric<strong>in</strong>a is characteristic <strong>of</strong> cold-air<br />
dra<strong>in</strong>age situations and low peatlands, which are not simulated here. Although it may also<br />
grow <strong>in</strong> closed upland forests <strong>in</strong> <strong>the</strong> nor<strong>the</strong>rn half <strong>of</strong> its range, <strong>the</strong> large abundance simulated<br />
by FORCLIM represents an anomaly. However, <strong>the</strong> physiognomic characteristics <strong>of</strong><br />
<strong>the</strong> open woodland are reflected correctly <strong>in</strong> <strong>the</strong> simulation results.<br />
Typical species for real forests at boreal sites like Armstrong (Fig. 5.10) are Picea<br />
glauca, P. mariana, and Betula papyrifera (Rowe 1972). These species are correctly<br />
simulated as dom<strong>in</strong>ants, but o<strong>the</strong>r species atta<strong>in</strong> anomalous abundance: Aga<strong>in</strong>, L. laric<strong>in</strong>a<br />
should be <strong>of</strong> marg<strong>in</strong>al importance or should even be absent from <strong>the</strong> simulation. Maybe<br />
<strong>the</strong> description <strong>of</strong> its natural history is <strong>in</strong>appropriate <strong>in</strong> FORCLIM: In reality, its establishment<br />
from seeds is strongly limited by light availability; this was accounted for <strong>in</strong><br />
FORENA by prevent<strong>in</strong>g its establishment when LAI is above 0.05 m 2·m-2 , a factor that<br />
was not <strong>in</strong>cluded <strong>in</strong> FORCLIM because <strong>the</strong> important European tree species appear to be<br />
more shade tolerant. Moreover, L. laric<strong>in</strong>a grows more slowly than evergreen conifers<br />
because <strong>of</strong> <strong>the</strong> cost <strong>of</strong> develop<strong>in</strong>g new needles each year; thus, <strong>in</strong> reality it is outcompeted<br />
on uplands unless w<strong>in</strong>ter is cold enough to kill evergreen needles. However, competition<br />
is low <strong>in</strong> <strong>the</strong> simulated low-biomass forests (Fig. 5.10), which means that L. laric<strong>in</strong>a establishes<br />
and grows well.