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Title: Rainfall interception by Singleleaf Piñon and Utah Juniper: implications for stand-level effective precipitation

item STRINGHAM, TAMZEN - University Of Nevada
item Snyder, Keirith
item SNYDER, DEVON - University Of Nevada
item LOSSING, SAMUEL - University Of Nevada
item CARR, CRAIG - Montana State University
item Stringham, Bennett

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2017
Publication Date: 5/31/2018
Citation: Stringham, T.K., Snyder, K.A., Snyder, D.K., Lossing, S.S., Carr, C.A., Stringham, B.J. 2018. Rainfall interception by Singleleaf Piñon and Utah Juniper: implications for stand-level effective precipitation. Rangeland Ecology and Management. 71(3):327-335.

Interpretive Summary: Pinyon and Juniper are native species that are encroaching into areas formerly dominated by sagebrush steppe. These two species are tall-statured trees in comparison to the shrubs and grasses that should dominate the sagebrush steppe. This study examined how much rainfall was intercepted by these larger tree canopies. The results showed that on average, 44% of rainfall was intercepted by the tree canopy and did not reach the soil surface. Therefore, tree canopies effectively reduce the water that is available to shorter-statured grasses and shrubs.

Technical Abstract: The expansion of piñon and juniper trees into sagebrush steppe and the infilling of historic woodlands has caused a reduction in the cover and density of the understory vegetation. Competition for limited resources between understory vegetation and trees is a plausible cause of this degradation. Water is the limiting factor in these systems, therefore redistribution of water resources by tree species is critical to understanding the dynamics of these formerly sagebrush dominated rangelands. Tree canopy interception may have a significant role in reducing the amount of rainfall that reaches the ground beneath the tree, thereby reducing the amount of available soil moisture. We measured rainfall redistribution that results from canopy interception by singleleaf piñon (Pinus monophylla Torr. & Frém.) and Utah juniper (Juniperus osteosperma (Torr.) Little) across a gradient of storm sizes. Simulated rainfall was used to quantify interception and effective precipitation during 133 rainfall events ranging in size from 2.2 to 25.9 mm hr-1 on 19 trees of each species, varying in size and shape. Effective precipitation was defined as the sum of throughfall and stemflow beneath tree canopies but above the litter layer. Results indicated that canopy interception averaged 44.6% with no significant difference between the two species. Tree allometrics including height, diameter at breast height, stump diameter and live crown height and width were measured and tree canopy area was calculated. The best fit predictive model of effective precipitation under canopy was described by stump diameter and gross precipitation (R2=0.74, p<0.0001). An alternative model predicted effective precipitation from tree canopy area and gross precipitation (R2=0.74, p<0.0001). Canopy area can be derived from various remote sensing techniques allowing these results to be extrapolated to larger spatial scales to illuminate the effect of increasing tree canopy cover on rainfall interception loss and the potential implications for the water budget.