EDGE

Ecological and physical processes near beach- front and clearcut boundaries

Terminology There is a lack of consistent terminology in the literature on forest edges. Following consideration of past definitions and common usage in the literature, as well as ecological relevance and usefulness of terms, we propose the following terms and definitions as standard.  Edges: Relatively abrupt boundaries between different communities. Created edges form as a result of a natural or anthropogenic disturbance. Steep gradients in topography, soil type, microclimate and/or geomorphology result in inherent edges (Thomas et al. 1979).  Forest edge: Abrupt transition between forested and non-forested communities, or between two forests of contrasting structure or composition. In practice, a forest edge can be defined as the limit of the continuous canopy (Harper and Macdonald 2001) or the point of abrupt transition in canopy composition.  Forest interior: Area within a forest landscape that shows no detectable edge influence. Interior conditions are typically characterized using samples located in large blocks of unfragmented forest landscape or in the center of the largest patches available for study.  Edge influence (EI): The effect of processes (both abiotic and biotic) at the edge which result in a detectable difference in structure, composition or function of the edge community, as compared to the ecosystem on either side of the edge (e.g. both interior forest and non-forested area). Both 'edge influence' (Chen et al. 1992, Harper and Macdonald 2001) and 'edge effects' (Harris 1984, Murcia 1995) have been used extensively and interchangeably in the literature.  Significance of edge influence (SEI): The statistical significance of the edge influence (e.g. values at or near the edge, as compared to values in the interior forest, Saunders et al. 1999). (Harper et al. in prep).

 Magnitude of edge influence (MEI): A measure of the extent to which a given parameter differs at the edge, as compared to the reference ‘non-edge’ ecosystem. Both 'significance of edge influence' (Chen et al. 1995) and 'magnitude of edge influence' (Harper 1999) have been defined this way. To avoid confusion, we propose using MEI and SEI to distinguish between ecological effect and statistical significance. We recommend calculating MEI as (e-i)/(e+i) where e = value of the parameter at the edge, i = value of the parameter in the interior (non-edge) forest; MEI thus varies between -1 and +1 and is equal to 0 when there is no edge influence.  Distance of edge influence (DEI): The set of distances from the edge into the adjacent community over which there is a significant edge influence (Chen et al. 1992). Distance of edge influence may be considered to represent a zone of edge influence that extends to both sides of the edge, in which structure or composition is different from either of the adjacent communities. This zone may actually begin some distance into the forest or in the adjacent non-forested area (Cadenasso et al. 1997, Harper and Macdonald 2001, 2002); effects are not always monotonic (c.f. Murcia 1995).  Area of edge influence (AEI): The total area of a given landscape that is subject to significant edge influence; an extension of DEI in two dimensions. Since DEI varies with edge orientation, edge contrast, surrounding topography and other factors, AEI typically appears as a belt of variable width surrounding all edges in the landscape.  Core area: The total landscape area that is outside the zone of significant edge influence (e.g., total forested area - AEI).  Patch contrast: The difference in microclimate, structure, composition or function between adjoining ecosystems. Terminology Cont. (Harper et al. in prep).

Brief Review Game species (Leopold 1933) Biophysics in wind tunnels & fields (50s-70s) Vegetation responses (50s – present) Wildlife populations (30s – present) Microclimate (late 80s – present) Ecosystem processes: very rare

Game species (Leopold 1933) Biophysics in wind tunnels & fields (50s-70s) Vegetation responses 50s – present Wildlife population (30s – present) Microclimate (late 80s – present) Ecosystem processes: very rare Brief Review Create as much edge as possible because wildlife is a product of the places where two habitats meet. This has been the management principle for both public & private land owners until mid-90s. But increasing emphasis on plant and nongame wildlife conservation during the last 2 decades has revealed that many characteristics of edges and ecotones are now considered undesirable (Harris 1988). We must not conclude that creation of more edges in landscapes will always have a positive effects on wildlife …. (Yahner 1988)

Brief Review Game species (Leopold 1933) Biophysics in wind tunnels & fields (50s-70s) Vegetation responses 50s – present Wildlife population (30s – present) Microclimate (late 80s – present) Ecosystem processes: very rare

Edge effects normally extend to 2-3 tree heights (Franklin & Forman 1987); Neither empirical data, nor theoretical basis existed in the original FAO report. Insert Raynor 1972

Brief Review Game species (Leopold 1933) Biophysics in wind tunnels & fields (50s-70s) Vegetation responses (50s – present) Wildlife population (30s – present) Microclimate (late 80s – present) Ecosystem processes: very rare Since Gysel’s publication in 1953, dozens of empirical studies have been conducted to examine gradual changes of plants as functional groups, populations, or communities across forest-open edges; Each species/group responds to the same edge differently and some species are not affected at all.

Canopy Cover (%)Seedling Population

Brief Review Game species (Leopold 1933) Biophysics in wind tunnels & fields (50s-70s) Vegetation responses (50s – present) Wildlife population (30s – present) Microclimate (late 80s – present) Ecosystem processes: very rare Many excellent studies. See presentation today from Drs. Rolf Koford & Stanley Temple.

Brief Review Game species (Leopold 1933) Biophysics in wind tunnels & fields (50s-70s) Vegetation responses (50s – present) Wildlife population (30s – present) Microclimate (late 80s – present) Ecosystem processes: very rare Significant differences in all microclimatic variables, but edge width varies greatly among variables, ranging from a few to 300 m in the Douglas-fir forest of the PNW. Changes in major microclimatic variables from edges into mature forests in the PNW. Adopted by the FEMAT team.

Changes in light level from a south- and east- facing edge into the forest Edge exposure is a very important variable.