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EDGE Ecological and physical processes near beachfront and clearcut boundaries Terminology (Harper et al. in prep). 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). Terminology Cont. (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. light Structure Influences Growth Mortality Regeneration Predation Canopy Physical Env ironment Damages Community Processes Community Processes Energy Flow Ev aportranspiration Nutrient Cy cling Soil respiration Pollen & Seed dispersal Horizontal energy f low Inv asion Aerosols dispersal Sounds transf ormation Density Biomass Snaps CWD Litter Soil OM Roots Soil moisture Air temperature Productivity Humidity Habitat Quality Diversity Feedback Direct Changes Community Processes Function Direct and indirect of edge influences on ecological pattern and processes. Forest Exposure Processes What properties are really affected? Open 100 -100 -50 0 50 100 -100 -50 0 50 100 -100 -50 0 50 100 -100 -50 0 50 100 -100 -50 0 50 100 40 -50 0 50 100 -100 -50 0 50 100 -100 -50 0 50 100 -100 -50 0 50 100 -100 -50 0 50 100 -100 -50 0 50 100 RUAL 0 20 60 VAAN PRSE HIER PIBA 40 0 5 10 0 20 60 0 20 40 20 80 40 CAPE2 0 80 40 SAHU 0 VIOLA 10 20 30 0 10 15 0 5 0 ASSA -100 10 20 30 Species abundance across a jack pine edge in N. WI. 0 DASP 20 PRPU 0 50 60 0 20 ARUV 20 40 60 0 -50 0 COPE -100 -100 -50 0 50 Distance from the Edge (m) 100 (a) Edge Species Edge Vs Interior Species Distance from Edge (a) Interior Species Distance from Edge So what? Assuming the depth of edge influence is 240 m, a 50 ha (125 acre) forested patch surrounded by open area contains very little interior environment. Indeed, 84% of the forest is AEI. Interior Area of Edge Influence (AEI) (84%) 800 m Management Philosophies Leopold-Thomas-Harris/Yanher-Noss-… 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. -- Aldo Leopold (1933) The essential requirements of wildlife- food, cover, and water- will be maintained so as to provide optimum ‘edge effect’ and interspersion of habitat components in important wildlife areas. -- BLM Manual 1603 (1973) The law of dispersion and interspersion work together to show the forest manager how to increase wildlife populations associated with edge. -- Thomas et al. (1979) But increasing emphasis on plant and nongame wildlife conservation during the last two decades has revealed many characteristics of edges and ecotones are now considered undesirable. -- Larry Harris (1988) We must not conclude that creation of more edge in landscapes will always have a positive effect on wildlife … -- Richard H. Yahner (1988)