Ecological Studies on Two Closely Related Chaparral Shrubs in Southern California

Abstract

• Also called grease wood and chamiso (or chamisal). See Cronemiller (1942) for derivation. a Also called redshanks, ribbon wood, bastard cedar, yerba del pasmo (Spanish), and palo amarillo (Mexican).

Factors Determining Mortality of Adult Chaparral Shrubs in an Extreme Drought Year in California

“…Measurements of ground water depth from wells less than 5 km from the study site show that ground water fluctuates between 6 m and 15 m below the surface (California Department of Water Resources 2006). Considering differential rooting depths observed in sprouting and non-sprouting chaparral species by Hellmers et al (1955) and Thomas and Davis (1989), and given the higher field water potentials we found for sprouters, it is reasonable to hypothesize that deeprooted sprouting species were accessing ground water, while the shallow-rooted non-sprouters were not, leading to dieback and mortality of non-sprouters. Arctostaphylos glauca is a very shallow rooted species, with roots occurring predominantly at 0.3 m depth (Miller and Ng 1977) and always less than 1 m deep (Hellmers et al 1955).…”

“…Considering differential rooting depths observed in sprouting and non-sprouting chaparral species by Hellmers et al (1955) and Thomas and Davis (1989), and given the higher field water potentials we found for sprouters, it is reasonable to hypothesize that deeprooted sprouting species were accessing ground water, while the shallow-rooted non-sprouters were not, leading to dieback and mortality of non-sprouters. Arctostaphylos glauca is a very shallow rooted species, with roots occurring predominantly at 0.3 m depth (Miller and Ng 1977) and always less than 1 m deep (Hellmers et al 1955). Like Arctostaphylos glauca, C. greggii is a shallow-rooted species with roots growing less than 1 m deep (Hellmers et al 1955;Miller and Ng 1977).…”

“…A total of four such wandering transects were used at each site beginning at 0 m, 10 m, 20 m, and 30 m along the base transect. To allow for intensive sampling of the two cooccurring congeners, Adenostoma fasciculatum and A. sparsifolium, we used the point quarter sampling method (Cox 1985) Hanes (1965), Stone and Juhren (1951), Nixon (2002), Keeley and Zedler (1978), and Keeley (1977 at one of the transects (site G, Table 2), instead of the wandering quarter sampling method described above. Each of 40 random points along a 500 m transect was divided into four quadrats (N, S, E, W) and the closest plant within each quadrat was sampled.…”

“…Changes in rainfall and temperature are predicted to impact the chaparral species at this ecotone, perhaps leading to local dieback and extinction of some species. Chaparral refers to the evergreen sclerophyllous shrub vegetation found in southwestern North America and is the most extensive vegetation type in California (Wieslander and Gleason 1954;Hanes 1995). Chaparral is a vegetation type found in one of five Mediterranean-type ecosystems of the world, each of which is characterized by winter rains and rain-free summers, high biodiversity, and risk of desertification.…”

“…This dieback coincided with several years of below-average rainfall between 1998 and 2002, culminating in an extreme drought year in the winter of [2002][2003]. We hypothesized that there would be species-specific differences in drought-induced mortality, with non-sprouting species exhibiting greater adult dieback and mortality because (1) non-sprouting species tend to be relatively shallow rooted (Hellmers et al 1955;Kummerow et al 1977;Thomas and Davis 1989) and (2) non-sprouting species normally exhibit lower water potentials than sprouting species, a discrepancy that is magnified during extreme drought years (Jacobsen et al 2007).…”