Current Research Projects
We have three long-term climate change experiments in the Sevilleta National Wildlife Refuge here in New Mexico. These projects are associated with but independent from the Sevilleta Long-term Ecological Research Program. These projects are separately funded by an NSF Long-term Research in Environmental Biology award to Scott Collins and Renée Brown
The first long-term field experiment is the Monsoon Rainfall Manipulation Experiment, affectionately known as MRME (started in 2007). This experiment is located in black grama grassland and addresses two key ecological theories about the structure and functioning of dryland ecosystems: pulse dynamics and the bucket model. MRME is the longest on-going experiment designed to test the bucket model and pulse dynamics.
The second experiment is the Warming-El Niño-Nitrogen Deposition Experiment (WENNDEx). WENNDEx started in 2006 with funding from the NSF Ecology Program and includes the following experimental treatments: increased winter precipitation during El Niño years and N addition (n=5 replicates per treatment combination). All plots originally contained both blue and black grama. We supplement ambient winter precipitation during El Niño years by adding four 5 mm events, one 10 mm event, and one 20 mm event between January-March to intensify El Niño events. We add 2 g N m-2 y-1 as NH4NO3 prior to the monsoon season to reflect future N deposition rates (Báez et al. 2007 J Arid Environment).
The third experiment is the Extreme Drought in Grasslands Experiment (EDGE). EDGE started in 2012 with funding from NSF Macrosystems Biology program and is located in both blue grama and black grama grassland. The black grama grassland is just north of the shrub boundary and just south of MRME. EDGE includes two components: (1) Extreme drought - from 2013-2019 rainout shelters removed 66% of growing season precipitation (April through mid-September) to reflect decadal droughts predicted in the future (Cook et al. 2015, Science Advances). The drought treatment ended after seven growing seasons and monitoring of recovery started in 2020. This platform has also been used for research on microbial contributions to drought recovery by the Rudgers Lab at UNM. (2) Delayed monsoon – starting in 2013 rainout shelters have been deployed in July and August each year to capture, remove and store all precipitation. Stored water is then reapplied to the plots via several watering events in September and October delaying the onset of the monsoon without changing total seasonal rainfall amount. This design reflects predicted changes in monsoon seasonality under climate change (Cook & Seager 2013, JGR-Atmospheres).
Results from these experiments can be integrated to address overarching questions about the impact of climate change, particularly rainfall variability and seasonality, on the potential for reordering among dominant species and the consequences of reordering on ecosystem processes. A better understanding of long-term drivers of community and ecosystem dynamics can inform future management decisions in drylands. Furthermore, our long-term experiments provide platforms for additional research on dryland processes. Over the next five years we hope to more fully integrate results from these experiments into a conceptual model of community reordering and state change in dryland ecosystems.
In addition to these experiments at Sevilleta we have been monitoring grassland community composition and net primary production in grazed and ungrazed areas under three different fire frequencies in Kruger National Park, South Africa, since 2006.
Long-term Research in African savanna, Kruger National Park, South Africa