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 Little Bluestem (Schizachyrium scoparium) is one of several plant species rarely seen on grazed lands adjacent to Chaco Culture Park. A recent study looked at the relationship of park plants to protection from grazing.
James Ramakka
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 By James M. Ramakka The scenic canyons of northwestern New Mexico hold prehistoric ruins from the Chaco Culture. In 1907 those ruins came under the protection of the National Park Service at Chaco Canyon National Monument. The Park Service began fencing monument boundaries in 1933 to protect the resource from erosion and damage by domestic livestock. By 1948, approximately 21,000 acres were enclosed by fences. In 1980 the National Park Service acquired an additional 12,000 acres and Chaco Canyon National Monument became known as Chaco Culture National Historical Park. As funds became available, these lands were also fenced. Thus, the park now contains plant communities that have been protected from livestock grazing for both long and relatively short periods of time. These protected parcels make Chaco Culture National Historical Park one of the largest living laboratories on the Colorado Plateau. The impact of livestock grazing on rangelands has long been a controversial topic. Antigrazing proponents state that livestock cause long-term damage to plant communities and soils and adversely affect biodiversity. Grazing advocates believe that livestock are a substitute for native grazers, such as bison, that are no longer present and therefore, grazing is essential to maintain rangeland health. Often, both sides rely on anecdotal evidence to support their arguments, and at least one grazing consultant has stated, without data, that the protected area of Chaco is a classic example of the detrimental effects of prolonged rest from grazing. The contrast in ground cover between the park and surrounding multiple-use lands shows clearly in aerial photographs and satellite imagery. However, other than one study in the mid-1980s, which examined the effects of grazing on soil and vegetation, the park had no quantitative data to evaluate the contention that rest from grazing was causing a decline in health of plant communities and biodiversity within the park. In 1998 the park partnered with the Environmental Studies Program of Prescott College, Arizona, to study the effects of historic livestock grazing on vegetation. The study examined differences in plant species richness, capacity for nutrient cycling, and vegetation structure and composition between three grazing treatments: long-term protection (50-plus years), recent protection (5 years or less), and currently grazed. The park accepted the final report of the researchers in early 2001. The results of the study contradict the assertion that long-term protection from grazing has been detrimental to park plant communities. Researchers found significantly greater plant species richness in areas protected from grazing. Although shrub cover and grass cover were also greater in the majority of protected areas, there was enough variation between sample sites to indicate that physical characteristics, such as soil type and water infiltration capacity, can affect the trajectory of plant succession after the removal of grazing. In addition to the park making land management agencies aware of this study, the researchers will publish their results in a peer-reviewed journal. Prescott College began a new study in 2001 that will analyze historic changes in riparian plant communities using the 12-mile Chaco Wash as their study site. Conservation biologists advocate the establishment of large reserves to conserve community and species diversity, while land management agencies occasionally cite the lack of control areas as one problem affecting their analysis of long-term planning efforts. To help address these issues, park personnel are conducting outreach efforts with other agencies and universities to make them aware of the potential use of the park as an ecological reference site for regional biodiversity assessments and planning efforts. |
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This material is from Natural Resource Year in Review--2001, published by the National Park Service, U.S. Department of the Interior, in May 2001 (publication D-2255) /YearInReview/yir/yir2001/03_laboratories/03_4_ramakka.html Last Updated: |
