Abstract
In the Chihuahuan Desert of Mexico and New Mexico, shrub invasion is a common problem, and once-abundant grassland ecosystems are being replaced by shrub-dominated habitat. The spatial arrangement of grasses and shrubs in these arid grasslands can provide better insight into community dynamics and can provide information on grass shrub interactions. To better understand the dynamics of the Chihuahuan Desert ecosystem and to provide information regarding the interactions between grasses and shrubs, we examined the spatial patterns of grasses and shrubs in remaining grass-dominated areas, interspersed with some shrubs. We developed 18, 10 × 20 m vegetation distribution plots by mapping the location of all grasses and shrubs on each and repeating the measurements three years later. Spatial patterns were then assessed for each plot using a second-order spatial statistic, Ripley's K-function, as well as any observed changes in the spatial patterns over a three-year period. We observed clumped grass distributions, indicating a lack of competition among grasses; random shrub distributions; and even grass distribution with respect to shrub locations, indicating competition between grasses and shrubs. We also observed a tendency for grass distributions to become more even over time, and grasses to become less even with respect to shrub locations over time. These changes occurred during a period of greater than average rainfall, indicating that greater water availability may lead to increased competition among grasses and decreased competition between grasses and shrubs.
Highlights
Arid grassland ecosystems, such as those found in North America throughout the Chihuahuan Desert, are able to support some mixed grass and shrub vegetation growth, but with low net primary production (McClaran 1995)
In order to better understand the dynamics of this ecosystem, and to provide insight into the interactions among grasses and shrubs that may dictate eventual loss of grassland habitat, we developed detailed vegetation distribution maps in grass-dominated areas, interspersed with some shrubs, to observe spatial patterns
Study area We examined spatial patterns of vegetation on grass-dominated plots located at the Jornada Basin Long Term Ecological Research (LTER) station
Summary
Arid grassland ecosystems, such as those found in North America throughout the Chihuahuan Desert, are able to support some mixed grass and shrub vegetation growth, but with low net primary production (McClaran 1995). Research in these arid grasslands has largely focused on grassland degradation and invasion of woody species (Schlesinger et al 1990, Larney et al 1998, Schlesinger et al 2000, Okin et al 2001, Okin and Gillette 2001, Geist and Lambin 2004, Laliberte et al 2004, Gibbens et al 2005, Browning et al 2008); many of the community dynamics of these ecosystems are still not well understood. Much research has been conducted on the importance of competition in unproductive environments and results have been inconsistent (Kadmon 1995, Goldberg and Novoplansky 1997)
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