Although the creation of edges during forest fragmentation can have im
portant abiotic and biotic impacts, especially under conditions of fut
ure climate change, mechanistic models of edge effects have not been f
orthcoming. A simple numerical model of two-dimensional heat flow is d
eveloped and applied to a vertical forest/clearcut edge profile and to
simulated fragmented landscapes. Height-specific thermal diffusivity
and conductivity in the forest were assumed to vary in proportion to f
oliage densities measured in the central Amazon. In the edge profile,
the clearcut that abutted the edge served as a heat source and its tem
perature was maintained at a constant value higher than in the initial
ly cooler forest. In the fragmented landscapes, simulated treefall gap
s were heat sources whose temperature varied with sun movements during
the day. Gap frequency was varied so as to approximate the gap covera
ge observed in selectively logged forests. In one set of simulations,
temperature in the openings was systematically varied; in another, the
rmal diffusivity of the forest was varied. Along the edge profile, hig
h temperatures in the clearcut were rapidly transmitted into the upper
canopy due to additive edge effects. Temperatures in the forest under
story were also very sensitive to clearcut temperatures due to relativ
ely sparse understory foliage. An overall increase in forest diffusivi
ty led to markedly higher temperatures close to the edge and a more ev
en temperature distribution among height strata. In fragmented landsca
pes, total gap coverage and additivity from neighboring gaps strongly
influenced forest temperatures. At low conductivities, heat flowed onl
y into the forest close to the gaps and hence forest temperature incre
ased almost linearly with gap area. However, at high conductivities, h
eat flowed far into the forest and forest temperature varied as a func
tion of gap density in the surrounding neighborhood. Because of these
additive effects, slight increases in total gap area led to disproport
ionate changes in the thermal profile of the landscape. These results
have important implications for the conservation of forest ecosystems.