MINIREVIEWS Neighborhood Effects, Disturbance Severity, and Community Stability in Forests

A theoretical framework and conceptual model for temporal stability of forest tree-species composition was developed based on a synthesis of existing studies. The model pertains primarily to time peri-ods of several tree lifetimes (several hundred to a few thousand years) at the neighborhood and stand spatial scales (0.01–10 ha), although a few exten-sions to the landscape scale are also made. The cusp catastrophe was chosen to illustrate compositional dynamics at the stand level for jack pine, northern hardwood, and white pine forests in the Great Lakes Region of the United States and for tropical rainfor-ests in the northern Amazon basin. The models feature a response surface (degree of dominance by late-successional species) that depends on two vari-ables: type of neighborhood effects of the dominant tree species and severity of disturbances. Neighbor-hood effects are processes that affect the chance of a species replacing itself at the time of disturbance (they can be positive, neutral, or negative) and are of two types: overstory–undestory effects, such as the presence of advanced reproduction; and distur-bance-activated effects, such as serotinous seed rain. Disturbance severity is the proportion of trees killed during a disturbance. Interactions between neighbor-hood effects and disturbance severity can lead to either punctuated stability (dramatic but infrequent change in composition, in those forests dominated by species with positive neighborhood effects) or succession (continuous change, in those forests dominated by species with neutral-negative neigh-borhood effects). We propose that neighborhood effects are a major organizing factor in forest dynam-ics that provide a link across spatial scales between individual trees and disturbance/patch dynamics at the stand and landscape scales. Key words: community stability; disturbance sever-ity; neighborhood effects; punctuated stability; suc-cession