Past, present, and future suitable habitat of yellow pine saplings in southern California

Anne-Marie Parkinson and Leana Goetze, Bren School of Environmental Science & Management, University of California, Santa Barbara, Santa Barbara, CA, Bruce Kendall, Bren School of Environmental Science & Management, University of California Santa Barbara, Santa Barbara, CA

Background/Question/Methods
Vegetation in California is expected to move towards higher elevations by the end of the century due to strong climatic influences on vegetation distribution. However, southern California yellow pine mixed conifer forests already exist near top elevations in relatively isolated sky islands, which puts them at risk of being severely limited in extent or lost indefinitely. We used MaxEnt to model the historic, current, and projected habitat suitability of yellow pine (P. jeffreyi and P. ponderosa) saplings across the Transverse Ranges in southern California. Future projections of suitable habitat were done using 8 climate scenarios: 4 wet and 4 dry. Additionally, we compared suitable habitat of modern day yellow pine saplings and adults to determine if there is currently a range disconnect between the two life stages of these species. We chose to focus on yellow pines as they are well adapted to drought and fire. These important adaptations make yellow pines critical to the long-term persistence of conifer forests under climate change.
While most tree species distribution models use adult presences as occurrence data, we chose to use sapling presences. The conditions in which adult conifers germinated hundreds of years ago are not indicative of today’s climate. Thus, using adult presences to project future distributions would not be unrepresentative of future ranges. However, areas where conifer saplings can survive gives insight into the future distribution of these long-lived species, making modeling sapling suitable habitat a more practical approach.

Results/Conclusions
Our results show that suitable habitat of yellow pine saplings is shrinking in southern California as the climate warms and precipitation becomes more variable. Preliminary results indicate that habitat at lower elevations is becoming less suitable, and the suitable habitat for the species is shifting upward in elevation under both wet and dry climate scenarios. When comparing the suitable habitat of both current saplings and adults, we observed a range disconnect between the two life-stages of yellow pines.