Effects of patch size and basal area on avian taxonomic and functional diversity in pine forests: Implication for the influence of habitat quality on the species-area relationship.

Myung‐Bok Lee,John P Carroll

doi:10.1002/ece3.4208

Abstract

Relationships between avian diversity and habitat area are assumed to be positive; however, often little attention has given to how these relationships can be influenced by the habitat structure or quality. In addition, other components of biodiversity, such as functional diversity, are often overlooked in assessing habitat patch value. In the Sandhills Ecoregion of Georgia, USA, we investigated the relationship between avian species richness and functional diversity, forest basal area, and patch size in pine forests using basal area as a surrogate for overstory structure which in turn impacts vegetation structure and determines habitat quality within a patch. We conducted bird surveys in planted mature pine stands, during breeding season of 2011. We used three classes of stand basal area (BA): OS, overstocked (BA ≥ 23 m2/ha); FS, fully/densely stocked (13.8 m2/ha ≤ BA < 23 m2/ha); and MS, moderately stocked (2.3 m2/ha ≤ BA < 13.8 m2/ha). MS patches showed more structural diversity due to higher herbaceous vegetation cover than other two pine stocking classes of patches. Total species richness and functional richness increased with the size of MS patches, whereas functional divergence decreased with the size of OS patches (p < 0.05). Functional richness tended to be lower than expected as the size of OS patches increased. Greater richness of pine–grassland species was also found at MS patches. Percent cover of MS patches within a landscape influenced positively the richness of pine–grassland species (p < 0.05). Our results suggest that (a) avian species–habitat area relationship can be affected by habitat quality (structural diversity) and varies depending on diversity indices considered, and (b) it is important to maintain moderate or low levels of pine basal area and to preserve large‐sized patches of the level of basal area to enhance both taxonomic and functional diversity in managed pine forests.

Highlights

Planted pine forests comprise the dominant forest type in the Southeastern United States
Our results demonstrated that habitat quality of a pine patch, which was based on structural diversity represented by the level of basal area, can influence the relationship between avian diversity and patch size in pine forests
Dissimilarity in functional traits between abundant species and other species decreased with increasing the size of patches with high level of basal area (OS patches)

Summary

| INTRODUCTION

Planted pine forests comprise the dominant forest type in the Southeastern United States. Our goal was to determine (a) what levels of basal area are necessary for pine forest management to conserve avian diversity in the region and (b) how patch size and basal area interplay and affect avian diversity, that is, how habitat quality represented by levels of basal area can influence the species–area relationship in birds. We expected that both taxonomic and functional diversity would decrease with increasing basal area because high basal area could reduce structural diversity of vegetation (i.e., habitat quality) within a stand, especially the amount of understory herbaceous vegetation cover by creating too dense canopy cover. We expected that the effect of patch size on avian diversity would vary with the level of basal area, namely habitat quality of the patch

| METHODS

Findings

| DISCUSSION