The effect of sample area on heterogeneity and plant species richness in coastal barrens

Abstract

Spatially varying environments are expected to provide more niche breadth than homogeneous areas, and should thus support a larger number of plant species. The observed sample area, or spatial scale, can also influence the relationship between this environmental heterogeneity and plant species richness. Few studies have been conducted at a multi-scalar level and none have been conducted in coastal barrens habitats. This study looked at two types of environmental variation: 1) Spatial heterogeneity and 2) Average conditions, at Chebucto Head, NS, at three different scales: subplot (0.5 m x 0.5 m), plot (1 m x 1 m), and transect (25 m x 2 m). Spatial heterogeneity was calculated as the standard deviation of substrate depth, substrate moisture, and topographic elevation as well as the Shannon-Weiner diversity index of six cover type variables. Average conditions were calculated as the mean of substrate depth, substrate moisture, and topographic elevation. Results of a multivariate linear regression analysis indicated that the strongest environmental predictor of plant species richness varied with sample area and also showed a general trend towards an increase in the strength of the relationship between environmental heterogeneity and plant species richness with increasing sample area. This study is one of the first to assess environmental heterogeneity and plant species richness on a multi-scalar level in coastal barrens and underlies the importance of how spatially varying environments can influence the diversity of plant species and how vegetation sampling design can affect the strength of predictor variables.