Submitted to: Journal of Arid Environments
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/26/2001
Publication Date: 3/1/2002
Citation: Krogh,S.N., Zeisset, M.S., Jackson, E., Whitford, W.G. Presence/absence of a keystone species as an indicator of rangeland health. Journal of Arid Environments. 2002. v. 50(3). p. 513-519. Interpretive Summary: One of the most pressing problems in assessing and monitoring rangeland health is the ability to determine the threshold degradation state of ecosystems that represents a virtually irreversible state. In Chihuahuan Desert grasslands, bannertail kangaroo rats have been described as ¿keystone¿ species because of their effects on nutrient-rich patches, water infiltration and soil water storage, some plant species and on soil formation. The abundance of occupied and/or abandoned bannertail kangaroo rat mounds was assessed at 117 sites (random sites) in south-central New Mexico. Bannertail kangaroo rats did not survive at sites with shrub cover greater than 20% of the vegetative cover. It was concluded that 20% shrub cover represents the degradation threshold for irreversible change in state from desert grassland to degraded shrubland.
Technical Abstract: We examined the relationship between a Chihuahuan Desert grassland keystone species (banner-tailed kangaroo rat, Dipodomys spectabilis) and several vegetation and soil indicators of rangeland health in order to define a threshold indicator value for irreversible change in ecosystem structure and function. The abundance of occupied and/or abandoned D. spectabilis burrow-mounds was assessed at 117 sites in south central New Mexico where previous studies had reported vegetation cover and composition. The most robust indicator for presence/absence of D. spectabilis was shrub cover. D. spectabilis did not occur at sites with shrub cover greater than 20%. It was concluded that a threshold value of 20% shrub cover could be applied to assessment and monitoring of Chihuahuan Desert rangelands because higher shrub cover results in the local extinction of this keystone species. The combination of data on the presence/absence of a keystone species with vegetation and soil indicators provides a method for identifying thresholds of degradation that may be irreversible.