Baseline Studies of Invasive African Buffelgrass (Cenchrus ciliaris) in Big Bend National Park, Texas

Date

2008-05

Authors

Malone, Dawnelle

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Abstract

Buffelgrass is a highly invasive weed that is becoming a management concern in Big Bend National Park, which protects over 324,000 hectares of Chihuahuan Desert habitat. The potential problems with this pest include displacement of native species, reduction in species diversity; increased fire hazard, and alteration of ecosystem functions. Baseline studies were conducted to learn about the species in the park, including where it occurs, what habitat it prefers to establish in, and how it may impact other species once established. In the 2001 and 2002 field seasons, 2485 buffelgrass locations were mapped in the southeastern part of the park. Vegetation transects were established in four monitoring units to compare characteristics of buffelgrass and adjacent non-buffelgrass plots. The amount of bare ground in buffelgrass plots is significantly lower than in non-buffelgrass plots (p < 0.001). Buffelgrass fills in the typically open spaces between desert plants, creating fuel for fire. Diversity indices, although not statistically significant, indicate the species is slowly impacting biodiversity. Soil samples taken from the monitoring units show that most of the buffelgrass seeds appear in the litter of buffelgrass plots (p < 0.001), with few seeds in the top 2 cm of soil, and no seeds in the non-buffelgrass plots. Seed viability using Tetrazolium staining techniques indicate higher viability in one-year old seeds (83 percent) than 3-month old seeds (64 percent). The vast area and often rugged nature of Big Bend National Park make field mapping of all buffelgrass-infested areas both cost and time prohibitive. A predictive habitat map showing areas where buffelgrass is most likely to occur in the park could reduce the time and effort required to locate infestations, and could aid in guiding management decisions and in prioritizing control efforts. A baseline predictive model was built using geographic information systems (GIS), nine environmental data layers, and characteristics of the 7400 buffelgrass points mapped between 1998 and 2005. The model rates the suitability of the habitat on a scale from 1 to 5, with 1 indicating where buffelgrass is most likely to occur and 5 indicating where it is least likely to occur. The original model predicted 57.61 percent of the known buffelgrass points in value 1, and an additional 38.54 percent in value 2, with 96.15 percent of the 7400 known locations occurring in the two highest values. The original model was then validated in the field, and the results were used to improve the predictability of the model. The improved model predicted 80.07 percent of the known buffelgrass points in value 1, and an addition 16.8 percent in value 2, with 96.87 percent of the 7400 known locations occurring in the two highest values.

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Keywords

Buffelgrass, Invasive plants, Big Bend National Park, Controls

Citation

Malone, D. (2008). <i>Baseline studies of invasive African buffelgrass (Cenchrus ciliaris) in Big Bend National Park, Texas</i> (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.

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