Woody plant encroachment of grassland and the reversibility of shrub dominance: Erosion, fire and feedback processes

Authors: LI, JUNRAN - University Of Tulsa; RAVI, SUJITH - Temple University; WANG, GUAN - University Of Tulsa; Van Pelt, Robert - Scott; GILL, THOMAS - University Of Texas - El Paso; SANKEY, JOEL - Us Geological Survey (USGS)

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2021
Publication Date: 3/9/2022
Citation: Li, J., Ravi, S., Wang, G., Van Pelt, R.S., Gill, T.E., Sankey, J.B. 2022. Woody plant encroachment of grassland and the reversibility of shrub dominance: Erosion, fire and feedback processes. Ecosphere. 13(3). Article e3949. http://doi.org/10.1002/ecs2.3949.
DOI: https://doi.org/10.1002/ecs2.3949

Interpretive Summary: Throughout the southwestern United States, desert grasslands are being invaded and replaced by invasive shrub communities. This transition has resulted in increased erosion by water and wind, resulting in nutrient accumulation at the base of the shrubs and nutrient depletion in the areas between shrubs. Shrub invaded grasslands are also more emissive in terms of fugitive dust which impairs human and environmental health. Environmental causes of this transition have included climate change, overgrazing, and the control of wildfire. Scientists from Tulsa University, Temple University, USDA-ARS Wind Erosion and Water Conservation Research Unit, and USGS Grand Canyon Monitoring and Research Center teamed to compare and contrast the results from several long-term field investigations they conducted together and individually at the USDA Jornada Experimental Range in southern New Mexico and at the USFWS Sevilleta National Wildlife Refuge in central New Mexico as well as other related studies to look at the factors affecting the degree and rate of transition. Although many of the sites at the Jornada Experimental Range no longer provide the mass and continuity of fuel to support wildfires or control burns, most of the sites in transition at the Sevilleta National Wildlife refuge will support wildfires and control burns. At the Sevilleta site, repeated control burns and occasional wildfires have been shown effective in slowing shrub encroachment.

Technical Abstract: The desert grasslands of the southwestern U.S. have undergone extensive woody shrub encroachment over the last 150 years. Although this process has been initiated and reinforced by several mechanisms including climate change, CO2 increase, fire, and grazing among others, their relative importance has rarely been studied. The northern Chihuahuan Desert provides different stages of shrub encroachment from the south (middle-late) to the north (early), along with an intensity gradient for many biophysical processes including erosion and fire. Since the early 2000s, a series of studies has been conducted in the south (Jornada Basin LTER) and in the north (Sevilleta LTER), to untangle feedbacks and drivers of ecosystem changes in this area. In the Jornada LTER, a number of studies were conducted to investigate the role of wind in the formation and reinforcement of shrub islands and associated soil resources heterogeneity in the shrubby grassland. In the Sevilleta LTER, a group of experimental and modeling studies have been performed to reveal the wind-soil-vegetation interactions in this grass-shrub transition area. Despite the fact that many of these studies have been conducted in the same overall context of ecosystem dynamics, they were largely conducted independently. We consider the controlling factors and make management suggestions to maintain the grasslands where it is still possible.