|JAMES, JEREMY - University Of California|
Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2015
Publication Date: 3/1/2016
Citation: Hardegree, S.P., Sheley, R.L., Duke, S.E., James, J.J., Boehm, A.R., Flerchinger, G.N. 2016. Temporal variability in microclimatic conditions for grass germination and emergence in the sagebrush steppe. Rangeland Ecology and Management. 69(2):123-128.
Interpretive Summary: Millions of acres of rangeland in the Intermountain western United States have been taken over by invasive annual weeds. These weeds reduce forage availability for livestock and wildlife, and produce fine fuels that increase the frequency and severity of wildfire across the region. Restoring these rangelands is very difficult and a primary reason for this is the extreme variability from year to year in the amount of rainfall to sustain establishment, growth and development of desirable planted species. Most of the published research on rangeland grass establishment only describes one or two years of field data. Given the high weather variability from year to year, one to two years is too short a time period to effectively interpret field research results. We analyzed long-term annual and seasonal patterns of rainfall and air temperature, and used a hydrologic model to estimate how weather variability affects the relative favorability of soil conditions for early plant establishment. We provide a modeling method that allows researchers to interpret short term field study results relative to longer-term site conditions. This methodology can also be used with seasonal forecasting to determine whether it is cost effective to attempt rangeland restoration in a given year, or whether one should wait for better conditions for plant establishment.
Technical Abstract: Sagebrush steppe ecosystems in the western United States are characterized by harsh environmental conditions with high annual and seasonal variability in both precipitation and temperature. Environmental variability contributes to widespread failure in establishing stands of desired species on degraded and invaded landscapes. To characterize seasonal microclimatic patterns and planting date effects on restoration outcomes we evaluated long-term simulations of seed germination response to soil temperature and moisture. Extremely high annual variability in both the conditions favorable for germination and in patterns of post-germination drought and thermal stress make it difficult to justify general inferences about seedbed treatment and planting date effects from individual, short-term field studies. We discuss the interpretation of individual-year and seasonal plant establishment factors and offer a mechanistic model for interpreting planting date and year effects on initial seedling establishment. Historical ranking and mechanistic descriptions of individual-year seedbed conditions may allow for expanded inferences through meta-analysis of limited-term field experiments.