Grass-shrub spatial patterns over moisture and grazing gradients in Great Basin sagebrush communities: Insights into restoration and climate change

Restoration efforts in the highly disturbed Great Basin ecosystem have historically focused on re-establishing the native herbaceous understory after sagebrush removal. A more effective approach may be to target areas where canopies are left intact and seeds/seedlings are planted in shrub interspaces or shrub canopies. In this context, shrub canopies may facilitate the growth of native perennial species, or alternatively seeds/seedlings may thrive in interspaces due to reduced woody competition. In the Great Basin, there is some evidence that positive perennial grass-shrub associations occur between Wyoming big sagebrush and native grasses. We are investigating the response of these grass-shrub spatial associations to moisture and grazing gradients in the Great Basin. We hypothesized that grass-shrub spatial associations would become more pronounced as rainfall level decreased and grazing intensity increased. Specifically, we wanted to determine how the spatial association between Wyoming big sagebrush and two Great Basin perennial grasses, Poa secunda and Elymus elymoides, changed in response to a landscape-scale rainfall gradient and a grazing gradient. We sampled 29 sites in three states (Utah, Idaho, and Nevada) with different annual rainfall levels (low, medium and high) and grazing intensities (low and high). We used an individual shrub sampling method to determine percent cover of Poa secunda and density of Elymus elymoides in shrub canopies and interspaces. We used a regression approach to model the response of percent cover of Poa secunda in canopy, interspace, and edge regions to rainfall level. Preliminary results show that as rainfall increases, percent cover of Poa secunda in canopies remains relatively constant at 6%. However, the response of percent cover in the interspace is much stronger; as rainfall level increases, percent cover of Poa secunda increases from 2% at low rainfall levels to 10% at high rainfall levels. Analyses regarding the grazing gradient are pending. Better understanding of plant spatial patterns over stress gradients can aid in determining appropriate microsite planting locations for perennial grasses in ecological restorations and help predict vegetation responses to climate change