Fine-scale stand structure mediates drought-induced tree mortality in pinyon-juniper woodlands
Eleven mountain ranges between the Desatoya and Diamond mountains in central Nevada.
Description of Site
Elevation – variable; Ppt – 230-414 mm; Soils – variable with depths ranging from 7.3-43 cm (2.8-17 in); Plant communities – singleleaf pinyon (Pinus monophylla), Utah juniper (Juniperus osteosperma), sagebrush (Artemisia sp.), rabbitbrush (Ericameria sp.), mormon tea (Ephedra viridis), Sandberg bluegrass (Poa secunda), Thurber needlegrass (Achnatherum thurberianum), and Idaho fescue (Festuca idahoensis).
Drought-Mortality and Responses Measured
Influence of 1) climate, 2) insect herbivory, 3) aridity gradients, 4) tree attributes such as size, and 5) spatial structure of stands (density) on drought-mortality; Time Period – 2005-2015; Measurements – tree mortality and change in live canopy, height, and diameter.
Tree mortality at coarse scales was largely driven by climate, specifically long-term average climate and severity of recent droughts. Elevated mortality occurred on hot dry sites. At finer scales, results indicated that competition resulting from the density and size of neighboring trees was related to mortality, especially for singleleaf pinyon on the hot dry sites. Pests were also found to be closely associated with singleleaf pinyon drought-related mortality. Mortality and canopy dieback were 0.6% and 10% in Utah juniper and 11% and 23% singleleaf pinyon, respectively.
In reviewing the literature, both Flake & Weisberg 2019 and Miller et al. 2019 (pg 128, 3rd P) reported the role of tree density in drought-related mortality across semi-arid woodlands in the Intermountain West is inconsistent ranging from minimal to significant. The inconsistencies are likely linked to characteristics of the site including climate, soils, topography, stand structure, tree size, and scale. Flake and Weisberg also found drought related mortality of juniper and pinyon in the Great Basin (central Nevada) was considerably lower than in the Colorado Plateau, which is also supported by other literature.