Planning for global change: Range-specific conservation and restoration recommendations from a study of cottonwood (Populus angustifolia)

Background/Question/Methods

Warming and drying trends associated with climate change are expected to result in major shifts in species distributions, altering community assemblages and trophic interactions. Conservation and restoration will face new challenges as focal species and organisms they interact with shift into and out of protected lands, requiring managers to adapt creative strategies as they work to preserve "moving targets." The goal of this study was to determine long-term vulnerability and risk assessment of narrowleaf cottonwood riparian habitats throughout the western U.S. As a foundation species, Populus angustifolia is intimately tied to the fate of numerous associated community members and ecosystem processes. By modeling the potential distribution of P. angustifolia under future climate change scenarios, we aim to provide managers with the resources they need to prepare for the impacts of climate change. We sampled 330 trees from 29 study locations from Arizona to Montana, including three national parks. Levels of genetic variation were analyzed using 14 microsatellite markers. We further assessed long-term vulnerability and risk of P. angustifolia riparian areas by modeling predicted habitat suitability under two future climate scenarios including time steps through 2099 to compare results using different assumptions of future population and CO² emissions.

Results/Conclusions

All stands showed moderate to high genetic variation, with unbiased expected heterozygosity (UH_E) ranging from 0.253 to 0.560; national parks were comparable to surrounding populations (Bandelier NM: UH_E = 0.406; Great Basin NP: UH_E = 0.536; Grand Teton NP: UH_E = 0.424). For the three parks surveyed, fixation indices (F) again did not stand out from the range for all study populations (overall F ranges from -0.311 to 0.289); Bandelier NM: F = 0.09; Great Basin NP: F = 0.039; Grand Teton NP: F = 0.179. Results from both climate scenarios predict that overall, P. angustifolia's range is predicted to increase; however each park has a unique story and will face its own challenges in planning for transitions over the next century. Of six protected lands included in climate models, we found a consistent pattern: cottonwood is predicted to lose habitat in southern latitudes and gain habitat in northern latitudes. We found precipitation of the warmest and wettest quarters as well as measures of temperature variability among the most important variables for predicting P. angustifolia occurrence. Results indicate that P. angustifolia may be relatively stable in a sea of change and a good conservation bet for maintaining regional biodiversity.