Angle Cover Class: A Variable Plot Technique for Estimating Shrub Quantities in Rangeland Areas

Abstract

Woody species have a discontinuous influence on their immediate vicinity and beyond. Most sampling methods record mean values over the area being sampled, not accounting for information at the scale of pattern created by individual woody plants. This article outlines development and testing of a field technique to quickly assess woody plant influence at a single point or small herbaceous vegetation sample area. The angle cover class method (ACC) is plotless. At each sampling point, woody plants were judged within quadrants by species as nondominant (0), dominant (1), or highly dominant (2), resulting in total scores ranging from 0 to 8 per sample point. The communities sampled were dominated by mesquite alone or by mesquite and juniper trees together, ranging from low growing, sparsely populated forms to mixed species old growth. Total aerial cover ranged from 2 to 75%. Seven evaluators were used to test for repeatability between evaluators. The ACC method was highly correlated to woody plant quantities of line-intercept cover (r2 = 0.963), cover based on ellipse (r2 = 0.965), volume (r2 = 0.936), and estimated leaf weight (r2 = 0.986). Analysis of covariance indicated that ACC accounted for >90% of variation in line-intercept cover with sampling error accounting for approximately 6% of model r2. Approximately 4% of variation was ACC method error, primarily for woody plant types and species. Variation associated with evaluators was <1.3%. Generally, three conversion factors were required for evaluator ACC scores to accurately predict species woody plant cover over this wide range of woody plant types.