The use of degradation gradients for the assessment and ecological interpretation of range condition

Abstract

Multivariate procedures were used to subdivide the southern African climatic climax grasslands of the 700–800‐mm rainfall zone into relatively homogeneous grazing areas. A degradation gradient was constructed for each of these areas. This was done by means of centred PCA ordination, using static data representing compositional differences induced mainly by grazing. The first axis of these ordinations represented a gradient of degradation. The second and higher axes were combined in a single value, namely, the Euclidean distance from the first axis. The degradation gradients were then used as a basis for ordinating new sites into the old ordinations, assessing their condition in an objective and quantitative way. The Euclidean distances from the first axis were used to determine the appropriateness of the degradation gradients for the assessment of the condition of a particular site. Knowledge of species response to grazing, community dynamics and recovery potential obtained through the ordination and regression studies was used to interpret the condition assessments.