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Frelich, Lee and Peter Reich. 1999. Neighborhood effects, disturbance severity, and community
stability. Ecosystems 2:151-166.
Summary: The authors apply a conceptual model based on “catastrophe theory” (Thom 1975 and
Zeeman 1976) to explain temporal stability (or instability) of forest tree-species composition. They
“propose that neighborhood effects are a major organizing factor in forest dynamics that provide a link
across spatial scales between individual trees and disturbance/patch dynamics at the stand and landscape
scales…. The model is based on the idea that vegetation state can be explained as a nonlinear function of
disturbance severity and the strength of the neighborhood (feedback) effects of the dominant tree
species.”
Definitions: Neighborhood effects- any process mediated by canopy trees that affects the replacement
probability by the same or other species at the time of canopy mortality. Compositional catastrophesudden replacement of one species or group of species in a stand at the time of a severe disturbance which
generally initiates an episode of succession. Major fluctuation- shifts in relative abundance of 25% on
more among an existing group of species.
Model summary: Forests with strong positive neighborhood effects should be stable with rare jumps in
composition, whereas those with strong negative neighborhood effects should change continuously and
unidirectionally, and those with neutral neighborhood affects unstable and “wander” over time.
Model implications: Time lags are likely to be short (a few years) when the type of disturbances suddenly
changes from low to high severity. Changes from high to low severity are likely to leave a more
substantial legacy