EARLY SIGNS OF ECOSYSTEM TRANSITION: THIRTY YEARS OF SUBALPINE and ALPINE VEGETATION CHANGE IN YOSEMITE NATIONAL PARK

Abstract

Subalpine and alpine regions in California are rapidly warming. In response, high-elevation plants may acclimate or adapt to the new climate, move to higher elevations or latitudes, persist in refugia, or go extinct. Although shifts in high-elevation plant communities have been documented in other regions of the world, such changes have not yet been studied in Yosemite National Park. To assess high-elevation plant community shifts in Yosemite National Park, we resurveyed historic vegetation plots spanning 2800 to 3800 m from conifer forests to alpine fell-fields. Over the past 30 yr, in the subalpine zone, species richness declined by 7% on average. In the alpine zone, vegetation cover increased by 31% and species richness increased by 11% on average. Community composition shifted slightly towards lower-elevation assemblages, with no significant change in community climate affinity. Notably, Pinus albicaulis Engelm. appears to be transitioning from krummholz to upright growth, with 42.1% of previously alpine plots now supporting upright trees. These trends may indicate early stages of ecosystem transition under climate change.