Tom K
Merchant.

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, the sensitivity of production to precipitation changes — leading to far more inter-annual fluctuations. These fluctuations, in turn, have the potential to increase fire hazard, particularly under a more variable precipitation regime.

Collaborators: Elisa Van Cleemput, Andrew Felton, Laura Dee, Peter Adler, Mike Koontz, 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 — and while these droughts had only transient effects on aboveground production, effects on belowground production were stronger and more long-lived. As ecologists, 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

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.

Collaborators: Sam Ahler, Jon Henn, Advyth Ramachandran