A landscape approach to forecasting climate change impacts on geographic ranges and phenologies of plants in the Washington Cascades

Thesis (Ph.D.)--University of Washington, 2017-12As the pace of environmental change accelerates, biologists are transforming the discipline of ecology from a fundamentally descriptive science to one that can be used to generate skillful forecasts. Although important progress is being made, this work is stymied by (1) our limited understanding of the physical and biological processes involved, (2) our limited knowledge of how those processes vary across space, and (3) our ignorance of the feedbacks between ecological change and human society. In this work, we aim to contribute new process understanding, conceptual frameworks, and quantitative tools that help to alleviate these three limitations and advance our ability to forecast the impacts of climate change on plants in the Cascade Range (Washington, USA), where rapidly changing climate and hydrology pose unique risks to features of ecosystems that are economically and culturally important. Chapter one concerns the fundamental ecological processes that maintain the geographic range limits of plants, focusing on the role of climate and disturbance in setting contemporary range limits and mediating the response of those ranges to a warmer climate. As a study system, we used two species of yellow monkeyflower (Erythranthe spp.) that have similar habitat requirements, but strikingly different elevation ranges in Mt. Rainier National Park. We combined data from a large-scale transplant experiment and a multi-year observational study using a spatial population model. We found that the ranges of these two closely related and ecological similar species responded very differently to changes in climate, and we forecast that ranges will shift downhill for one species under some scenarios. This work illustrates the importance of accounting for landscape-scale processes in generating skillful forecasts of species range shifts. Chapter two focuses on forecasting how climate change will affect the landscape patterns of reproductive synchrony (landscape flowering phenology) in plants across networks of habitat patches. In this work, we use previously estimated relationships between climate and flowering time, as well as spatially extensive datasets on species distributions and microclimates, to predict spatial patterns of landscape phenology across Mt. Rainier throughout the growing seasons of 2009 - 2015. We found that unusually early snow melt in low elevation meadows in 2015 caused many species to bloom out of sync across their elevation ranges, decreasing the potential for pollen dispersal between meadows. Because 2015 conditions were similar to those expected by the late 21st century under unabated climate change (early low-elevation snow melt, warm spring temperatures), this raises the possibility that climate change could be an agent of population fragmentation in this system. Finally, chapter three considers how warming climates affect the relationships between ecosystems and their social and management context. Specifically, we use thousands of geolocated photos uploaded to the social media platform Flickr to track interactions between recreational visitors and the plant phenology of subalpine and alpine ecosystems in the Washington Cascades, where spectacular wildflower displays draw millions of visitors each year, and generate tens of millions of dollars of economic activity. We found that the timing of recreational visits to subalpine ecosystems at Mt. Rainier National Park was substantially less sensitive to variation in climate than the timing of wildflower displays. This led to pronounced mismatches between visitor and wildflower activity in the climate-change analog conditions experienced in 2015 at our sites. Overall, this work illustrates how a landscape approach can help to overcome the challenges associated with forecasting ecological responses to environmental change