Areas influenced by multiple edges and their implications in fragmented landscapes

Abstract

We introduced a new approach for delineating areas of multiple edge influence (AMEI) within a fragmented landscape using a geographic information system (GIS). AMEI was defined as the interface that is affected by more than two neighboring patch types. We decomposed AMEI into three components: AMEI 1, the area where one patch type meets a different patch type; AMEI 2, the area where one patch type meets two different patch types; AMEI 3, the area where one patch type meets three or more other different patch types. This approach provides a direct measure of the complexities of multiple edge effects that may occur at a spatial location, and also measures the amount of the affected area at the patch and landscape levels. Using the Chequamegon National Forest (CNF), USA, as a case study, we found that the total AMEI was approximately 48, 74, 86, and 92% of the landscape with depth of edge influence (DEI) at 30, 60, 90, and 120 m, respectively. The more complicated components of the area of multiple edge influence (AMEI 2 and AMEI 3) ranged from 5% (at 30 m DEI) to 60% (at 120 m DEI) of the studied landscape. Most empirical and modeling studies miss this additional edge complexity if they only consider a single edge structure. In general, AMEI 1 is greater than AMEI 2; AMEI 2 is greater than AMEI 3. Three indices – AMEI to patch area ratio (APAR), AMEI to patch edge area ratio (APEAR), and AMEI to landscape area ratio (ALAR) – were introduced to explain the relative importance of AMEI at the edge, patch, and landscape levels. This approach has the potential to improve model predictions and better inform us about ecological processes that are influenced by multiple edge effects at patch and landscape scales.