Abstract
Fire is thought to profoundly change the ecology of the sagebrush steppe. The Idaho National Laboratory provides an ideal setting to compare the effects of fire and physical disturbance on plant diversity in high-native-cover sagebrush steppe. Seventy-eight 1-hectare transects were established along paved, green-striped, gravel, and two-track roads, in overgrazed rangeland, and within sagebrush steppe involving different fire histories. Transects were sampled for the diversity and abundance of all vascular plants. Alpha, beta, and phylogenetic beta diversity were analyzed as a response to fire and physical disturbance. Postfire vegetation readily rebounds to prefire levels of alpha plant diversity. Physical disturbance, in contrast, strongly shapes patterns of alpha, beta, and especially phylogenetic beta diversity much more profoundly than fire disturbance. If fire is a concern in the sagebrush steppe then the degree of physical-disturbance should be more so. This finding is probably not specific to the study area but applicable to the northern and eastern portions of the sagebrush biome, which is characterized by a pulse of spring moisture and cold mean minimum winter temperatures. The distinction of sagebrush steppe from Great Basin sagebrush should be revised especially with regard to reseeding efforts and the control of annual grasses.
Highlights
Sagebrush vegetation embodies the wide-open spaces of western North America, yet it is better known for its state of decline (e.g., Carson 1962; Welch 2005; Davies et al 2011)
Sites dominated by Artemisia tridentata ssp. tridentata and Artemisia cana were not included because they involve a disturbance and soil-moisture regime that precluded the characteristic plant diversity found in the semi-arid short-statured sagebrush steppe
Species accumulation curves suggest that physical disturbance more than fire disturbance affects alpha diversity (Fig. 3; intercept) and that both kinds of disturbance may lower beta diversity (Fig. 3; slope)
Summary
Sagebrush vegetation embodies the wide-open spaces of western North America, yet it is better known for its state of decline (e.g., Carson 1962; Welch 2005; Davies et al 2011). Pinyon–juniper (Pinus monophylla and Juniperus osteosperma) encroachment is blamed for losses of sagebrush vegetation in the Great Basin (e.g., Suring et al 2005), but cheatgrass invasion via fire is considered generally most threatening (e.g., Suring et al 2005; Mack 2011). Repeated fires may cause a change in sagebrush vegetation and eventually a change in state where the degraded state comprises a number of grass-dominated or invasive-dominated plant communities from which restoration to sagebrush vegetation is difficult (e.g., Jones and Monaco 2009; Davies et al 2012). Postfire reseeding efforts that cause physical disturbance can be counterproductive to the reestablishment of plant cover, density, and diversity in the sagebrush steppe (Ratzlaff and Anderson 1995)
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