Thomas Lab Research

Current projects

To what extent can plant traits, phylogenetic history, and biogeography predict alpine climate change vulnerability?

Closely related alpine plant lineages have diversified in both the European Alps and North American Rockies. We're asking to what extent the shared and divergent elements of these groups' history influence their sensitivity to climate change (as estimated by climate niche models). Traits like plant height, habit, leaf chemistry, leaf and root economics, seed size, phenology, and life history can be important predictors of climate change responses, and may or may not reflect the phylogenetic structure of related lineages. Given shared traits and evolutionary history, how different are potential outcomes for lineages that have evolved in different geographical settings? How predictive are traits in each region? This project is under active development and, in addition to climate niche modeling, will involve collecting physical, phenological, and potentially genetic traits from herbarium specimens, databases, and alpine gradient plots.

Alpine specialists vs generalists

One observed consequence of warming temperatures in mountain regions is the tendency for plant populations to shift upward, bringing lower elevation species in contact with specialists adapted to high elevation habitats. Alpine specialists may also be facing disruptions to their temperature and phenological niches. As the broader tolerances of competitive generalist species allow them to colonize these habitats, will they have a competitive advantage over species that previously escaped these interactions through their specialized adaptations? Or will specialists still have an edge within their microhabitats that will allow them to coexist? We are currently developing ideas for how to test these interactions on alpine gradient plots, using techniques such as reciprocal alpine transplants (moving plants from higher to lower elevations and vice versa and testing their performance).

Predicting drivers of change in future mountain plant communities

European mountain biodiversity is already undergoing change as species and communities respond to multiple interacting global change drivers. Climate change may drive migration as temperature niches expand to higher elevations, while land use change, particularly patterns of mowing, grazing, and timber harvest, has the potential to restructure habitats and directly impact population sizes. Multiple possible future trajectories of these drivers could lead to divergent outcomes in ecosystem dynamics. The aim of this project is to use process-based model simulations (using a dynamic vegetation model, FATE-HD) to disentangle the potential impact of varying future climate and land use scenarios on plant functional diversity in the Alps, and to identify which functional types are more vulnerable to change. Among the many possible dimensions of biodiversity, this study examines a) indicators of positive and negative outcomes for plant functional groups, such as changes in overall abundance and extent, and b) changes in community-level diversity, such as changes in richness, across different elevational bands. By comparing experimental simulation outcomes, the relative impact of climate and land use change on each of these dimensions can be quantified.

Winners and losers under past and future climate change

Species vary in their vulnerability to climate change, experiencing more or less pressure to move or adapt depending on the narrowness of their environmental tolerances or habitat- and region-specific exposure to climate change. Some may even experience net expansion of potential range, thus potentially benefiting from climate change. An important goal of predicting future vulnerability to climate change is identifying what characteristics distinguish potential “winners” and “losers” under new conditions. At the same time, species have also responded to fluctuations in past climate over thousands of years, providing context for their current and future responses. Comparing reconstructions of past and future range shifts and niche shifts could help identify whether vulnerability to change can be consistently predicted by the same niche traits over time. This project uses a process-based species distribution model, TTR, which estimates plants' ideal physiological niche dimensions as well as predicting their possible ranges, to quantify past and future niche and range change in a large plant radiation endemic to New Zealand, Veronica sect. Hebe. The radiation consists of 124 species that occupy a wide variety of habitats, elevations, and range sizes. The size and shared history of the clade makes it an ideal case study for tracing the effects of climate change on range and niche stability across species with different environmental tolerances.