Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2006
Publication Date: 7/1/2006
Citation: Peters, D.P.C., Mariotto, I., Havstad, K.M., Murray, L.W. 2006. Spatial variation in remnant grasses after a grassland-to-shrubland state change: Implications for restoration. 2006. Rangeland Ecology & Management. 59:343-350. Interpretive Summary: Degraded rangelands that have converted from grassland to shrubland are notoriously resistant to restoration efforts. We examined the potential for recovery by remnant black grama grasses in a degraded area. Vegetation maps from 1858 showed that black grama was the historic dominant on this site, although current vegetation is dominated by the shrub, creosotebush. Field surveys in 2002-2003 located a total of 3335 individual black grama plants in the 29 ha area. High spatial variation was found in the occurrence and basal area of black grama plants that was related to water availability rather than livestock grazing: most plants were found in or adjacent to an arroyo at a northern aspect and outside a historic exclosure dating to 1930. These remnant plants can be used as propagule sources in restoration efforts. Information on microsite conditions for black grama survival can be used to improve the restoration potential for sites on similar vegetation and soils.
Technical Abstract: Rangelands that have been degraded, such as perennial desert grasslands now dominated by woody shrubs, are notoriously resistant to restoration efforts. Very slow recovery of black grama following cattle and lagomorph exclusion combined with periodic shrub removal since the 1930s at the Jornada Experimental Range exemplifies the difficulties associated with grass restoration. The goal of this research was to examine the potential for recovery by remnant plants in a degraded area as a function of plant location across a landscape. Our objectives were: (1) to determine the historical dominant vegetation and change in dominance through time; (2) to examine relationships between fine scale variation in black grama presence and basal area with variation in environmental condition; and (3) to identify the landscape positions more favorable for restoration. Historical vegetation maps starting in 1858 were combined with a field survey in 2002-2003 of the location of all individual black grama plants in a 29 ha area and spatial data layers in a geographic information system. Results showed that upland grasses, including black grama, dominated the study site in 1858, although tarbush was the dominant species by 1915, and creosotebush is the current dominant. A total of 3335 black grama plants were found for an average density of 0.01 plants/m2. High spatial variation was found in the occurrence and basal area of black grama plants that was related to water availability rather than livestock grazing: most plants were found in or adjacent to an arroyo (67%), at a northern aspect (47%), and outside the 1930 experimental exclosures (43%).These remnant plants can be used as propagule sources in restoration efforts, and information on microsite conditions for black grama survival can be used to improve the restoration potential for sites on similar vegetation and soils.