HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text Free Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (4) Citing Articles via Google Scholar Google Scholar Articles by Wood, Y. A. Articles by Allen, E. B. Search for Related Content PubMed PubMed Citation Articles by Wood, Y. A. Articles by Allen, E. B. Agricola Articles by Wood, Y. A. Articles by Allen, E. B. Related Collections Dryland Soils Watershed and Landscape Processes Hillslope Analysis Plant and Environment Interactions Soil Hydrology Nitrogen

Altered Ecohydrologic Response Drives Native Shrub Loss under Conditions of Elevated Nitrogen Deposition

^a Department of Environmental Sciences
^b Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721
^c USDA-ARS George E. Brown, Jr. Salinity Laboratory, Riverside, CA 92507-4617
^d Department of Botany and Plant Sciences, University of California, Riverside, CA 92521

View larger version (110K): [in a new window]   Fig. 1. Repeat photographs of the foothills of the Box Springs Mountains illustrating the decline of coastal sage scrub (CSS). Arrows in each photograph point to same hill adjacent the UC Riverside campus. (a) Photograph taken in 1958, courtesy of the Botanic Gardens of UC Riverside (photograph taken by Dr. Frank Vasek). (b) Photograph taken in 2005 of the same site. Note distinctive textural differences across the landscape as shrub cover has been lost.

View larger version (165K): [in a new window]   Fig. 2. Location of study sites. The generally trapezoidal-shaped Perris Plain is fault-bounded (strong linear features at the base of southern California mountain ranges) to the northeast and southwest. The Box Springs Mountains (shown in photographs of Fig. 1) have lost most of their coastal sage scrub (CSS) shrub cover. The site at Lake Skinner remains predominantly CSS.

View larger version (29K): [in a new window]   Fig. 3. (a) Mean monthly precipitation and air temperature based on data from California Irrigation Management Information System (CIMIS) stations within 3.2 km of each site (+CSS, healthy coastal sage scrub site at Lake Skinner; –CSS, degraded coastal sage scrub site at the base of the Box Springs Mountains). (b) Precipitation (from same sources) recorded over the two years of this study. Arrows indicate time of quarterly soil samplings.

View larger version (29K): [in a new window]   Fig. 4. Percent regolith water, by volume, for quarterly soil cores taken in the extreme drought of 2001–2002, and the following wet year of 2002–2003. An arrow indicates the region of the regolith (on average) that is weathered bedrock (WBR) at each site. (a) Data from the healthy coastal sage scrub site at Lake Skinner (+CSS). (b) Data from the degraded coastal sage scrub site at the base of the Box Springs Mountains (–CSS).

View larger version (27K): [in a new window]   Fig. 5. Regolith chloride (µg g–1 based on oven dry soil weight) for quarterly samples taken in the extreme drought of 2001–2002, and the following wet year of 2002–2003. An arrow indicates the region of the regolith (on average) that is weathered bedrock (WBR) at each site. (a) Data from the healthy coastal sage scrub site at Lake Skinner (+CSS). Note the dynamic distribution over time of chloride throughout the regolith depth. (b) Data from the degraded coastal sage scrub site at the base of the Box Springs Mountains (–CSS). Note the L-shape to the curves indicating the strong stratification of soil chloride within the top 25 cm of the regolith, which overlies the static distributions over time of soil chloride beneath the 50-cm depth.

View larger version (29K): [in a new window]   Fig. 6. Regolith nitrate N (µg g–1 based on oven dry soil weight) for quarterly soil cores taken in the extreme drought of 2001–2002, and the following wet year of 2002–2003. An arrow indicates the region of the regolith (on average) that is weathered bedrock (WBR) at each site. (a) Data from the healthy coastal sage scrub site at Lake Skinner (+CSS). Note the distribution of nitrate N that is mainly concentrated within the surface 25 cm. However, there is not as strong an L-shape to the distribution as is evident at the –CSS site. (b) Data from the degraded coastal sage scrub site at the base of the Box Springs Mountains (–CSS). Note the L-shape to the curves indicating the strong stratification of nitrate N within the top 25 cm of the regolith.

View larger version (19K): [in a new window]   Fig. 7. Schematic of the negative feedback between physical and biotic processes associated with additions of anthropogenic nitrogen that drives coastal sage scrub (CSS) decline over time.