Deciphering rangeland transformation—complex dynamics obscure interpretations of woody plant encroachment
Woody plant encroachment—the conversion of grasslands to woodlands—is among the greatest challenges faced by rangelands worldwide. Yet this phenomenon is poorly understood, and complex land use dynamics make interpreting the timing and extent of land cover changes a global challenge.
For many regions, the true degree and rate of historical change in woody cover and cropland remain unknown. We quantify these processes and explore the effects of prior cultivation on woody plant distribution.
In the Lampasas Cut Plain, USA, we measured rangeland transformation using digital classification of aerial imagery 1937–2012. Our study is the first to use data of such high spatial and temporal resolution to address this question at this scale. We also provide some of the first documentation of dramatic regional cropland abandonment.
Although total woody cover remained almost unchanged (1937: 28%, 2012: 27 %), woody cover underwent a major redistribution across the landscape. Formerly open areas attained much greater levels of woody cover, and previously wooded areas lost woody cover. As cropland area declined by 78 %, woody plants invaded former croplands more slowly than the rangeland portions of the area (0.1 % year−1 vs. 0.3 % year−1, respectively).
These findings conflict with widely held assumptions and suggest that woody plant encroachment is more nuanced than often recognized. Multiple dynamics and past conditions interact in complex ways to produce landscape change. Because perceptions of encroachment determine how we respond to this challenge, great care should be taken in interpreting observed woody plant encroachment of the world’s rangelands.
KeywordsCropland abandonment Ecological invasion Great Plains Historical imagery Juniper Land cover Land use Remote sensing Shrubs Succession trajectories
We thank J. McAlister for supplying local landscape information and other technical support. This work was supported by USDA-NIFA Managed Ecosystems grant 2011-68002-30015, USDA-NIFA National Needs Program grant 2009-38420-05631, NSF-CNH grant 413900, and a Tom Slick Graduate Research Fellowship from the Texas A&M University College of Agriculture and Life Sciences.
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