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Monday, April 9 • 5:30pm - 7:00pm
POSTER: Spatial Pattern of Upper and Lower Pinyon-Juniper Treelines in the Great Basin, Nevada

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AUTHORS: Matteo Garbarino*, University of Torino, IT; Malandra Francesco, Marche Polytechnic University, IT; Tom Dilts, University of Nevada, Reno; Sam Flake, University of Nevada, Reno; Fabio Meloni, University of Torino, IT; Peter J Weisberg, University of Nevada, Reno

ABSTRACT: Pinyon-Juniper woodlands expanded considerably in the last century across the western USA. The presence of anthropogenic biotic and abiotic disturbances (grazing, logging, fire) contributed to shape the structure of this ecosystem. We established 20 plots (10 along the upper and 10 along the lower treeline) in the Toyabe range, Great Basin National Park, NV. Tree canopies were photo-interpreted in a GIS and the accuracy was assessed through GCPs. PPA (pair-correlation function) analyses was used to compare the spatial arrangement of trees at upper and lower treelines. We used LANDSAT images to do a 30-year NDVI trend analysis to describe treeline dynamics. Upper treeline plots were located around 2500 m a.s.l. on steep slopes (22°) and were characterized by a mean density of 106 tph. Lower treelines were denser (124 tph) and on gentler slopes (7°) at a mean elevation of 2096 m a.s.l. Combining the spatial pattern 10 by 10 replicates we obtained a clumped distribution of trees for both upper and lower treelines. Nevertheless, upper treeline ecotone resulted more grouped than the lower one. The NDVI and the tree size distribution analyses support previous observations of recently active expansion at both treelines in the Great Basin. The increasing trend of NDVI was significantly higher at lower than at upper treeline. At higher elevation tree recruitment was limited to favorable microsite due to energy limitation. Conversely, at lower elevation water limitation led to a less aggregated pattern at small scale due to competition between trees. This different pattern between upper and lower treelines could also be explained by the higher level of topographic variability observed at the upper treeline. Further studies are needed to determine whether the observed fine-scale patterns of tree distribution reflect fundamental differences in limiting factors that control tree distributions at upper and lower forest ecotones globally.

Monday April 9, 2018 5:30pm - 7:00pm CDT
Monroe Room

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