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work remained sub rosa to most ecologists. The forestry models were mostly, but
certainly not entirely, in sources not frequently read by forest ecologists. Addition-
ally, some of the forestry models were seen as sufficiently useful that the models
drifted into the realm of “industrial secrets” as their developers found employment
in the timber industry.
In 1980, a paper reviewing some of this work [ 66 ] coined the term, “gap model,”
to describe this class of models. The gap-model designation was originally devel-
oped to emphasize that a principal simplifying assumption in these models (the
assumption that the competition among individual trees on a small patch of land
was homogeneous in the horizontal over a small area of land but spatially explicit in
the vertical dimension) fitted well with the classic “gap dynamics” concept of A.S.
Watt [ 39 , 67 ]. At the time the term gap model was coined, Watt's concept had been
significantly reintroduced to American ecologists by Frank Bormann and Gene
Likens [ 68 , 69 ]. A generation of forest ecologists have made numerous extensions
of “gap models” and the term, nowadays, refers to a broad class of individual-based
models of forests and other ecosystems of a natural character (mixed-age, mixed-
species, natural disturbance regimes, etc.).
An Application of an Individual-Based Model on Sustainability
of Russian Forests under Climate Change
Global climate model simulations indicate that the Northern Hemisphere's boreal
forests and, in particular, the Siberian boreal forest zone, may not only respond to
climate change but may affect the Earth's climate through feedbacks involving
changes in the regional surface albedo, the degree to which the surface reflects
incoming radiation. Bonan and his colleagues [ 70 ] altered surface albedo in order to
simulate the clearing of the boreal forest in the National Center for Atmospheric
Research (NCAR)'s Community Climate System Model version 1.0 (CCSM1).
This substantially cooled the Earth not only in the boreal zone but across the
Northern Hemisphere. Betts [ 71 ] used the Hadley Center Atmosphere Model
(HadAM3) to simulate the climatic consequences of albedo changes from growing
more trees, worldwide. He found that the surface albedo changes associated with
the growth of coniferous evergreen trees in boreal regions led to significant
increases in the average global temperature. These increases were large enough to
overshadow the effect of the carbon storage that occurred as a result of growing
evergreen forest in that region.
Field observations provide further evidence that changes in the boreal forest
may impact the global climate. Larch forest, dominated by both Larix sibirica and
L. gmelinii , covers extensive regions in Siberia. Shifts from larch to dark-conifer
forests, dominated by trees such as spruce or fir that are tolerant of higher
temperatures, have been documented [ 72 , 73 ]. Because larch is a deciduous
conifer, this shift in forest composition wouldleadtothesimilaralbedochanges
as the evergreen tree growth simulation presented by Betts. This reduction of
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