Life History Type and Water Stress Tolerance in Nine California Chaparral Species (Rhamnaceae)
Ecological Monographs, 77(2), 2007, pp. 239–253 Ó 2007 by the Ecological Society of America LIFE HISTORY TYPE AND WATER STRESS TOLERANCE IN NINE CALIFORNIA CHAPARRAL SPECIES (RHAMNACEAE) 1,5 2 3 4 2 3 R. B. PRATT, A. L. JACOBSEN, K. A. GOLGOTIU, J. S. SPERRY, F. W. EWERS, AND S. D. DAVIS 1Department of Biology, California State University, Bakersfield, 9001 Stockdale Highway, Bakersfield, California 93311 USA 2Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824 USA 3Natural Science Division, Pepperdine University, Malibu, California 90263 USA 4University of Utah, Department of Biology, Salt Lake City, Utah 84112 USA Abstract. Chaparral species of California, USA, exhibit three life history types in response to fire: non-sprouters (NS), facultative sprouters (FS), and obligate sprouters (OS). Adult non-sprouters are killed by fire; thus populations reestablish only through fire- stimulated seed germination and seedling recruitment. Facultative sprouters reestablish by both vegetative sprouting and seed germination. Obligate sprouters reestablish only by vegetative sprouting and do not recruit seedlings post-fire. Previous data suggest that post-fire NS and FS seedlings reestablish as open-canopy gap specialists, whereas OS seedlings primarily reestablish in deep shade during fire-free intervals. Their non-refractory seeds are killed by fire. We hypothesized that these differences in life history, compared within the same taxonomic group, would result in a range of relative resistance to water stress such that NS . FS . OS. To test our hypothesis, we estimated resistance to water stress using resistance to xylem cavitation (the water potential at 50% loss in hydraulic conductivity; W50) for stems and roots in nine species of the family Rhamnaceae: Ceanothus megacarpus, C.
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