Tom K
Merchant.

Changing fire regimes

Fire impacts in the Great Basin

Fire is rapidly altering the historical sagebrush steppe ecosystem of the northern Great Basin. At the same time, climate projections predict an increase in precipitation variability — but we currently have a limited understanding of how these two drivers will interact.

Using satellite-based gridded datasets, we assessed how fire alters the relationship between net primary production and precipitation across a swath of northern Nevada. Drawing on quantitative methods from the causal inference literature, we found that as fire converts sagebrush ecosystems to annual-grass-dominated systems, this change in plant functional compostion leads to increased sensitivity of production to precipitation changes. Increased sensitivity can result in in larger inter-annual fluctuations, which in turn, have the potential to increase fire hazard, particularly under a more variable future precipitation regime. For more information see Merchant et al. 2026

Collaborators: Elisa Van Cleemput, Andrew Felton, Laura Dee, Peter Adler, Mike Koontz, Katie Suding

Fire-related plant traits

Historically, the Great Plains has been characterized by both grazing and fire — a history that may have shaped the strategies of plants in these grassland communities. We're quantifying grassland traits related to flammability and grazing, and testing whether there's a trade-off such that some species have fire-adaptive strategies while others are adapted to grazing. Can we use this information to understand the effects of land management decisions like grazing and perscribed fire?

Collaborators: Sam Ahler, Jon Henn, Advyth Ramachandran, Nancy Shackleford, Katie Suding

Fire probability forecasting

While wildland forest fires recieve much attention, fires in grasslands and shrublands acount for a large portion of the most destructive fires. Given the highly variable nature of fuels in grassland systems we expect that antecedent climate conditions can play a large role in the interannual variation in fire hazard across the Great Plains. Using seasonal climate and fuel estimates, I am applying machine learning techniques to better forecast fire proabibility in the Great Plains.

Collaborators: Jon Henn, Katie Suding

Drought impacts on plant communities

Droughts are becoming increasingly frequent and severe. I use a variety of experimental approaches to ask how droughts affect plant communities and ecosystem functioning — including how the spatial arrangement of communities interacts with drought, and how short-term extreme droughts shape rangelands.

Spatial patterns & ecosystem resilience

We implemented a long-term experiment in a Colorado grassland, simulating extreme precipitation shifts — drought (-66% of ambient) and wet periods (+66%), along with low-intensity grazing. Drought consistently reduced spatial vegetation aggregation but unexpectedly increased plant diversity, favoring stress-tolerant species. Less aggregated communities showed signs of recovery over time, suggesting a feedback mechanism where stress-adapted species influence ecosystem stability.

Collaborators: Julie Larson, Hunter Geist-Sanchez, Sarah Elizabeth Stockman, Meghan Hayden, Laura Dee, Katie Suding

Intra-season extreme droughts

To test how short-term extreme droughts affect above- and belowground processes, we used rain-out shelters to remove 100% of precipitation for five weeks in either spring or late summer. The impact of timing depended on plant community composition. Furthermore, while these droughts had only transient effects on aboveground production, effects on belowground production were stronger and more persistent. Indicating that we may be underestimating the effects of short-term droughts by focusing on aboveground responses.

Collaborators: Meghan Hayden, Katie Suding

Predicting variability in primary production

In semi-arid grasslands, landscape-level variability in primary production is critical for land management — particularly livestock grazing. Productivity can fluctuate widely across space and time, directly impacting forage availability.

Using a data-rich long-term dataset from a Colorado grassland, we investigated the drivers of spatio-temporal variability in aboveground net primary production (ANPP). Spatial variation in plant communities and soils interact to amplify these fluctuations, because different communities and soils respond to precipitation falling over different time periods — in some cases, even precipitation that fell two years ago. These effects are compounded by precipitation that varies sharply across the landscape due to localized convective storms.

Collaborators: Olivia Hajek, David Augustine, Lauren Porensky, Sean Kearney, David Hoover