Characterizing and Comparing Landscape Diversity Using GIS and a Contagion Index

Abstract

The purpose of this study was to examine the pattern and changes in forest cover types over the last two decades on three landscape level physiographic provinces of the state of Alabama, USA: (i) The Great Appalachian Valley Province, (ii) The Blue Ridge Talladega Mountain Province, and (iii) The Piedmont Province. Studies of spatial patterns of landscapes are useful to quantify human impact, predict wildlife effects or describe various landscape features. A robust landscape index should quantify two distinct components of landscape diversity: composition and configuration. Composition refers to both the total number of “patch” types (i.e., forest cover types) and their relative proportions in the landscape, whereas configuration refers to the spatial pattern of patches in the landscape. The U.S. Forest Service conducts periodic surveys of forest resources nationwide from plots distributed on a 3 mile by 3 mile (4.8 km by 4.8 km) grid randomly established within each county using forest inventory and analysis survey data stratified by physiographic province, a relative contagion (RC) diversity value and its variance were calculated for each province for the survey years 1972, 1982, and 1990. One-way analysis of variance was used for hypothesis testing of RC values across time and between provinces. A view of each landscape at each point in time was generated with GIS software using Thiessen or proximal polygons of the forest cover types identified at each survey point on the landscape.