HR: 1340h
AN: B43B-1163 [WITHDRAWN]    [Abstracts]
TI: Potential mechanisms for fine-scale variation in desertification thresholds
AU: * Duniway, M C
EM: mduniway@nmsu.edu
AF: Jornada Experimental Range, USDA Agricultural Research Service P.O. Box 30003, MSC 3JER, Las Cruces, NM 88003, United States
AU: Peters, D P
EM: debpeter@nmsu.edu
AF: Jornada Experimental Range, USDA Agricultural Research Service P.O. Box 30003, MSC 3JER, Las Cruces, NM 88003, United States
AU: Herrick, J E
EM: jherrick@nmsu.edu
AF: Jornada Experimental Range, USDA Agricultural Research Service P.O. Box 30003, MSC 3JER, Las Cruces, NM 88003, United States
AB: The process of desertification includes many interactions and feedbacks occurring at multiple spatial scales, often resulting in nonlinear dynamics and threshold behavior. These interactions and feedbacks have been observed in the broad-scale transition of former black grama grasslands to mesquite dominated shrublands (desertification) in the Chihuahuan Desert of southern New Mexico, USA. Heterogeneity in soil properties at the landscape scale can increase resistance to change, thereby reducing the probability of crossing a threshold at some sites due to small scale, within patch processes. Observational studies indicate that grass communities occurring in sandy soils shallow to well-developed petrocalcic horizons are more resistant to drought than those growing on similar soils without a this horizon. To assess the mechanism for this observed resistance, water availability dynamics were monitored in a multiyear, landscape scale study across soils with differing degrees of petrocalcic development. Results show that petrocalcic horizons absorbed and retained much greater amounts of available soil water for several months following an extremely wet winter and summer than similar depths in a deep sandy soil. Wetting and drying dynamics indicate the mechanism for the observed resistance of grasses to drought on these soils is the slow release of petrocalcic water into the grass rooting zone. The petrocalcic soil- water dynamics observed during these extreme events indicate that the high water holding capacity of these soils can potentially buffer effects of increased variability in precipitation expected to occur as a result of climate change. In water limited systems, water holding capacity of the entire profile, including rock-like material such as calcium carbonate, should be considered when evaluating the potential resistance of sites to crossing a threshold, particularly in a changing climate. Areas that are inherently more resistant to patch-scale shrub invasion processes could present a management opportunity for restoration or conservation--if they can be protected from broad-scale feedbacks and drivers pushing the system towards a desertification threshold.
DE: 0429 Climate dynamics (1620)
DE: 0486 Soils/pedology (1865)
DE: 1809 Desertification
DE: 1813 Eco-hydrology
DE: 1866 Soil moisture
SC: Biogeosciences [B]
MN: 2007 Fall Meeting