Snow Season Variability and Community Dynamics in the Western Hemlock-True Fir Ecotone of Western Oregon, USA

Keywords: climate change, snowpack, community dynamics, range shift, western hemlock-true fir ecotone, HOBO
Abstract Type: Poster Abstract

Abstract

Global climate change is expected to significantly alter abiotic factors on mountain gradients, causing warmer temperatures and decreased snowpack at higher elevations. Community dynamics are likely to shift significantly as species attempt to adapt to these changes. The goal of this research is to evaluate the extent to which spatial (elevation, temperature, and canopy cover) and temporal (decadal trend and ENSO/PDO cycles) factors impact seasonal snowmelt and community dynamics in the western hemlock-true fir ecotone region of the Oregon Cascades. To conduct this study, western hemlock (Tsuga heterophylla) and true fir (Abies spp.) seedling data were collected from 5 sample plots over 20 years in the H.J. Andrews Experimental Forest Long-Term Ecological Research site. Additionally, daily temperatures and light intensity for the 5 plots were collected using over 60 HOBO data loggers over the same period. Time lapse cameras were used to validate the HOBO data loggers, which proved highly reliable for estimating below-canopy snow metrics. The resulting analyses revealed snow season variability was most significantly impacted temporally by cyclical ENSO/PDO climate patterns and spatially by differences in canopy cover within the ecotone. However, neither the 20-year global temperature increase nor fine-scale elevation differences had significant impacts on snow season variability in the plots. Community analysis did identify clear sorting of seedlings by elevation within the ecotone, but reflected this lack of long-term trend as species dominance in the seedling strata did not vary significantly over the 20-year study.