Rethinking Rangeland Health Analysis on the Navajo Nation

Abstract

The ranching industry in the American West has long been both an integral and romanticized part of our nation’s history and culture. It is also recognized as a way of life that has been detrimental to native ecological communities and a contributor to land degradation. Over 70% of the American west is grazed, making the disturbance to natural systems brought by livestock perhaps the most ubiquitous force shaping western landscapes today. Thus, it is important to have an appropriate tool to assess rangeland condition, to better determine areas that are susceptible to degradation, lands that are degraded and regions that might be more resilient to livestock use. Currently, the Natural Resource Conservation Service (NRCS) uses a combination of ranked indicators and vegetation surveys in their rangeland condition analysis, which can be expensive and time consuming. For this project, I analyze data from an NRCS-based rangeland health survey from the Navajo Nation in Northern New Mexico; a region marked by its marginal resource base and depressed economy. Using an NMS ordination and a cluster analysis, I assess the three rangeland health indicators that the NRCS uses to assess ecological condition. Building upon this analysis, an indicator species analysis for groups defined by rangeland health show that for the poorest range, an invasive species, cheatgrass (Bromus tectorum) is an indicator of poor health, while native forbs such as Townsendia incana and Scarlet Globemallow are indicators of areas in good biotic health. Species scores calculated from a weighted average ordination are another tool to be used in a monitoring plan, where scores can be used to calculate range health scores at certain sites. Assessment of a CART model of environmental variables associated with the groups provide a map of areas that could be prioritized for monitoring. Even though results of this analysis show that this study site might be too recently disturbed by overgrazing to show a wide range of ecological condition, these methods are an improved rangeland assessment tool that is less costly for natural resource managers on the Navajo Nation. This will allow for rapid immediate assessment in years between major rangeland health surveys, and can use range-condition indicator species, species weights and corresponding environmental variables created in this study to prioritize areas to monitor and manage. In having a better assessment technique, it is the hope that new and more efficient monitoring strategies can be implemented in areas that are affected by overgrazing in the American Southwest.