Annual grass invasion in sagebrush steppe: the relative importance of climate, soil properties and biotic interactions

Authors: BANSAL, SHEEL - Us Forest Service (FS); Sheley, Roger

Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2016
Publication Date: 6/1/2016
Publication URL: http://handle.nal.usda.gov/10113/62972
Citation: Bansal, S., Sheley, R.L. 2016. Annual grass invasion in sagebrush steppe: the relative importance of climate, soil properties and biotic interactions. Oecologia. 181:543-557. doi: 10.1007/s00442-016-3583-8.

Interpretive Summary: Species distributions and abundances are constrained by climate factors (e.g., temperature, precipitation), soil properties (e.g., nutrients), biotic interactions (e.g., competition) and disturbances (e.g., fire). At macroecological scales, species distributions typically follow temperature or precipitation gradients, while biotic interactions have more influence on species abundance at smaller scales. However, biotic interactions may be relatively more important during a biological invasion, which is essential information for modeling and managing the spread of invasives. For example, attempts to control invasive annual grasses (AG) in sagebrush steppe ecosystems of the western USA have generally been unsuccessful due to a lack of consensus among ecologists as to the most important abiotic and biotic factors that are associated with the success of AGs. Therefore, we conducted a full spectrum, exploratory analysis of 100 climate, soil, biotic and disturbance factors along an AG invasion gradient (90 sites with 0-100% AG cover) across a sagebrush steppe landscape to identify which factors were most associated with the abundance of AG. We then used structural equation modeling to simultaneously integrate multiple abiotic and biotic factors as they relate to AG abundance. AG cover was negatively related to perennial grass cover, which was the strongest relationship of AGs to any of the measured abiotic or biotic factors. AG cover was also negatively related to perennial forb and biological soil crust cover, while annual forb, shrub and tree cover and microbial biomass were unrelated to AGs. AG cover was also positively related to temperature and negatively to precipitation, but had relatively few relationships with soil or disturbance factors. Resident functional groups had relatively more and stronger relationships to soil properties and climate factors compared to AGs. Our structural equation model confirmed the importance of perennial grasses and species diversity on AG cover while integrating the effects of climate and soil on resident biota. Overall, our exploratory analysis reveals an importance of biotic interactions during a biological invasion, questions the relative significance to soil properties and disturbance on AG invasion, and supports the notion that climate warming will favor the spread of AGs in sagebrush steppe ecosystems.

Technical Abstract: Species distributions and abundances are constrained by climate factors (e.g., temperature, precipitation), soil properties (e.g., nutrients), biotic interactions (e.g., competition) and disturbances (e.g., fire). At macroecological scales, species distributions typically follow temperature or precipitation gradients, while biotic interactions have more influence on species abundance at smaller scales. However, biotic interactions may be relatively more important during a biological invasion, which is essential information for modeling and managing the spread of invasives. For example, attempts to control invasive annual grasses (AG) in sagebrush steppe ecosystems of the western USA have generally been unsuccessful due to a lack of consensus among ecologists as to the most important abiotic and biotic factors that are associated with the success of AGs. Therefore, we conducted a full spectrum, exploratory analysis of 100 climate, soil, biotic and disturbance factors along an AG invasion gradient (90 sites with 0-100% AG cover) across a sagebrush steppe landscape to identify which factors were most associated with the abundance of AG. We then used structural equation modeling to simultaneously integrate multiple abiotic and biotic factors as they relate to AG abundance. AG cover was negatively related to perennial grass cover, which was the strongest relationship of AGs to any of the measured abiotic or biotic factors. AG cover was also negatively related to perennial forb and biological soil crust cover, while annual forb, shrub and tree cover and microbial biomass were unrelated to AGs. AG cover was also positively related to temperature and negatively to precipitation, but had relatively few relationships with soil or disturbance factors. Resident functional groups had relatively more and stronger relationships to soil properties and climate factors compared to AGs. Our structural equation model confirmed the importance of perennial grasses and species diversity on AG cover while integrating the effects of climate and soil on resident biota. Overall, our exploratory analysis reveals an importance of biotic interactions during a biological invasion, questions the relative significance to soil properties and disturbance on AG invasion, and supports the notion that climate warming will favor the spread of AGs in sagebrush steppe ecosystems.