Assessing growth response to climate controls in a Great Basin Artemisia tridentata plant community

An assessment of the growth response of key vegetative species to climatic variability is vital to identifying possible local impacts on ecosystems faced with imminent climate change. With current climate projections in Nevada predicting a shift to an even more arid climate with greater year-to-year variability, the imperative exists to identify the effects of specific climatic controls on plant growth and to research methods to assess large-scale vegetative changes, especially in more remote areas where readily available data sets may be lacking. This study utilized annual growth ring indices constructed from big sagebrush (Artemisia tridentata ssp. tridentata) stems collected in Spring Valley, NV as a measure of vegetative growth and compared standardized measures of ring growth to records collected from climate monitoring stations within the region. Growth ring indices had a strong, positive correlation with total hydrologic-year precipitation (Oct-Sep; r = 0.82, p < 0.001) with precipitation totals measured at the nearest climate station for the months of January, March, April, and June being the most highly related to ring growth (r = 0.48, 0.36, 0.47, and 0.41, respectively; p < 0.05). Mean maximum growing season temperatures were found to be negatively correlated to growth during the months of April, May, June, and October of the previous year (r = -0.40, -0.37, -0.50, and -0.30, respectively; p < 0.001). Multiple regression analyses between ring width measurements and relevant climate controls suggest that projected climate changes will be largely detrimental to the overall growth of big sagebrush in Spring Valley. Historical NDVI (Normalized Difference Vegetation Index), an indicator of plant canopy leaf area and photosynthetic activity, was regressed against sagebrush ring indices to examine growth response through time. NDVI values in May performed reasonably well as an indicator of sagebrush ring growth when measurements were integrated over all available sagebrush sites (r2 = 0.48, p < 0.01), but this relationship was inconsistent when assessed on a site-by-site basis when comparing single-pixel NDVI measurements against site-specific sagebrush growth ring chronologies. Overall, sagebrush growth ring chronologies were found to perform very well as a climate proxy and comparisons between sagebrush ring widths and a network of ring records from other species revealed that sagebrush growth in Spring Valley is representative of the larger region.