Influence of directional side of sagebrush canopies and interspaces on microhabitats

Abstract

Shrubs can contribute to spatial heterogeneity in plant communities by creating distinct microsites under their canopies compared to between their canopies (interspaces). This results in distinct microhabitats that differ in understory vegetation characteristics and ground cover. However, microhabitats may also differ under the north and south side of canopies because of differences in shading and other microsite characteristics. We investigated if microhabitats varied among north and south sides of sagebrush canopies, and interspaces in 16 plant communities. Several understory vegetation characteristics and most ground cover variables varied among north sides, south sides, and interspaces. Moss and litter cover were greatest and bare ground was lowest in north sides. Moss and litter cover decreased and bare ground increased from north to south sides and from south sides to interspaces. Exotic annual grass cover and abundance was less in north side microsites compared to south side and interspace microsites, implying that sagebrush creates heterogeneity in resistance to invasion. This may be critical in allowing native herbaceous vegetation to persist under annual grass invasion pressure. Our results provide evidence that sagebrush creates distinct microhabitats. This highlights the pivotal role of shrubs in creating heterogeneity in shrub steppe communities and indicates that preventing the loss of shrubs in these communities should be a management priority. This also suggests that it is critical to restore sagebrush, and potentially other shrubs in similar ecosystems, after they are lost to maintain differences in microhabitats that promote diversity and coexistence.