Above and belowground resource patterns associated with sagebrush islands of fertility in the Intermountain West

Background/Question/Methods

Islands of fertility can be critical for the establishment and persistence of herbaceous seedlings in arid and semi-arid systems. The microenvironment created by big sagebrush (Artemisia tridentata) influences belowground resource availability and aboveground microclimate. Belowground, shrubs are associated with higher nutrient resource pools driven in large part by soil organic matter, and higher soil moisture. Aboveground, shrubs dampen the meteorological extremes characteristic of arid and semi-arid systems. Although the resource pools and microclimate associated with islands of fertility are well studied in the Intermountain West, they are typically conceptualized as a binary of canopy and interspace. Evidence from other arid and semi-arid systems across global rangelands indicates that many resources and nutrients associated with islands of fertility have complex attenuations and patterns of decay when measured and modeled at continuous distances from the shrub canopy. Here we ask whether microenvironments associated with sagebrush in the Intermountain West have patterns of decay that deviate from the binary canopy and interspace model. At four sites in the Intermountain West (two warm-dry and two cool-moist soil moisture-temperature regime sites), we measured soil organic matter, soil moisture, air temperature, and relative humidity at four distances from sagebrush canopies to understand the attenuation of above and belowground microenvironments and how this changes across a landscape gradient.

Results/Conclusions

We used mixed-effect generalized linear models to understand how these variables vary with distance from the sagebrush canopy. Our preliminary results indicate that relative humidity significantly decreased linearly with distance from sagebrush, while air temperature increased. Relative humidity had a more negative relationship with distance from sagebrush at the warmest and driest site than the others. Soil moisture varied by site, but not with distance from sagebrush canopy. This is likely due to different times since precipitation before sampling. Soil organic matter did not vary by site or distance from the sagebrush canopy. These preliminary results indicate that at these four sites, the aboveground microenvironment may be driving differences in the relationships between herbaceous cover and distance from sagebrush canopies, whereas belowground soil organic matter and soil moisture do not drive these patterns.