FIELDWORK: dynamics of degradation and recovery in arid rangelands
Recovery after desertification Desertification, the degradation of arid rangelands due to overgrazing and climate change, is occurring in aridlands around the globe and threatens the livelihoods of millions of people. This degradation causes a shift in vegetation from productive grasslands to desert shrublands, and is often considered irreversible. However, grass recovery has been reported at four sites worldwide, all after nearly 40 years of livestock exclusion. I have developed and am testing a new theoretical model to account for perennial grass recovery in desertified sites.
My research is focused on potential mechanisms for a reversal of desertification, specifically focused on the role of livestock in transforming soil properties and the impacts that change has on vegetation. I am examining patterns in soil physical and chemical properties across a series of long-term livestock exclosures.
Our most recent project uses geostatistical methods to examine the spatial patterns of soil nutrients inside a series of long-term livestock exclosures. We're finding striking differences in the distribution patterns of different nutrients after long-term rest from grazing.
Publications: Allington and Valone. 2010. Reversal of desertification: The role of physical and chemical soil properties. Journal of Arid Environments 74: 973-977. (pdf) Allington and Valone. 2011. Long-term livestock exclusion in an arid grassland alters vegetation and soil. Rangeland Ecology and Management 64 (4), 424-428. (pdf)
photo credit: Morgan Ernest
Invasive species & biotic resistance.
Although many factors influence the ability of exotics to invade successfully, most studies focus on only a few variables to explain invasion; attempts at theoretical synthesis are largely untested. The niche opportunities framework proposes that the demographic success of an invader is largely affected by the availability of resources and the abundance of its enemies. Here, we use a 31-year study from a desert ecosystem to examine the niche opportunities framework via the invasion of the annual plant Erodium cicutarium. While the invader remained rare for two decades, a decline in granivory combined with an ideal climate window created an opportunity for E. cicutarium to escape control and become the dominant annual plant in the community. We show that fluctuations in consumption and resources can create niche opportunities for invaders and highlight the need for additional long-term studies to track the influence of changing climate and community dynamics on invasions.
Allington, G.R.H., D. Koons, S.K.M. Ernest, M. Schutzenhofer, and T.J. Valone, (2013). Biotic resistance, niche opportunities and the reorganization of an annual plant community by an exotic invader. Ecology Letters 16: 158-166. (pdf)