Muscling into Meadows: A Preliminary Dendrochronological Analysis of Recent Conifer Encroachment in Mount Rainier’s Subalpine Meadows

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A dramatic reconfiguration of the subalpine ecotone is underway in many mountainous regions. One of the changes occurring in subalpine ecosystems is the shrinking and fragmentation of subalpine meadows. In July 2016, we investigated the encroachment of conifers into a subalpine meadow on the south side of Mount Rainier as part of the North American Dendroecological Fieldweek, a unique experiential learning program dedicated to training participants in the theories and techniques of dendrochronology. We collected increment cores and cross-section disks from conifers in a subalpine meadow to determine their dates of establishment. We compared these establishment dates with climatic and environmental variables to assess potential drivers of encroachment. Our results show that the establishment of conifer seedlings occurred in distinct pulses over the twentieth century coinciding with periods of low summer snowfall. We found that seedling establishment rates were much higher on locally convex micro-topographic settings and in areas with a dense cover of woody shrubs. The spatiotemporal patterns of seedling establishment we observed appear to be the result of the complicated and highly scale-dependent interplay between climatic fluctuations and both biotic and abiotic microsite conditions. While our results should be considered a preliminary analysis, they reveal a compelling story of the spatiotemporal patterns of conifer encroachment and suggest potential causal mechanisms that warrant further investigation.