A 10-year demographic study of rabbitbrush (Chrysothamnus nauseosus): growth, survival and water limitation

Abstract

A population of 126 adult rabbitbrush (Chrysothamnus nauseosus var. consimilis) was followed for 10 consecutive years from 1983 through 1992 in a sanddune ecosytem on the north shore of Mono Lake, California. The study area received an average (1981-1992) of 160 mm total annual precipitation of which 55 mm fell from April through October, making this site drier than other known sites in the Great Basin desert where C. nauseosus occurs. Cover of all shrubs was 18.0%, and that of C. nauseosus 7.5%, in the 3077 m study plot. Water was limiting for this population of C. nauseosus, exerting large effects on new canopy growth and reproductive effort in a given year, on survival, and on establishment of juveniles into the adult population. Growth and survivorship of the adult shrubs were significantly correlated with the depth to ground water, which varied from 3.6 to 6.0 m below the surface during the study, and not with any measure of precipitation in a given year or adjacent years. Shrubs in this population exhibited a net decrease in size between 1983 and 1992. The region experienced a significant drought from 1987 onwards, with some increase in precipitation after 1990. Mortality of shrubs began in 1987 and reached 22% by 1992. Individuals that died were smaller on average initially than individuals surviving throughout the study: 50% or more of the individuals having 4000 cm of canopy or less at the start of the study died by 1992. Elevation (m msl) of each shrub in the study area, presumably correlated with depth to ground water, had no effect on growth but a weak effect on survival during the study period. Specific microsite had significant effects, with shrubs on steep slopes being smaller, having more negative "growth" slopes, and being more likely to die during the drought compared to individuals occurring on flatter gradients. Recruiment of juveniles into the population did not occur after 1985. Competition between shrubs could not be definitively demonstrated during the study, but only indirect tests for competition were used. Adult C. nauseosus and adults of all species combined (Sarcobatus vermiculatus with 9.6% cover, Tetradymia tetrameres with 0.8% cover and Chrysothamnus viscidiflorus with 0.02% cover) were randomly distributed, failing to support the hypothesis of competition if competition for water results in a uniform distribution of shrubs. Moreover, comparison of the spatial dispersion of C. nauseosus individuals before (1985) and after (1992) mortality did not reveal competitive thinning toward uniformity. On the other hand, larger individuals were farther from their nearest neighbor than were smaller individuals, an effect postulated to result from competitive thinning.

Differential use of large summer rainfall events by shrubs and grasses: a manipulative experiment in the Patagonian steppe

“…Unfortunately, the few manipulative experiments available are not sucient to answer this question either, because the penetration depth of water was smaller than the rooting depth of the unresponsive shrubs (MontanÄ a et al 1995;Lin et al 1996). In the experiment of Lin et al (1996), simulated rainfall only reached 45 cm, while at least one of the two unresponsive shrubs ± Chrysothamnus nauseosus ± in some cases behaves as a phreatophyte (Toft 1995). The experiment performed by MontanÄ a et al (1995) in Southern Chihuahua, Mexico has the same problem because water penetrated 40 cm, but 40% of the roots of the unresponsive shrub ± Prosopis glandulosa ± are below 67 cm (Heitschmidt et al 1988).…”

Predawn disequilibrium between plant and soil water potentials in two cold-desert shrubs

“…Seeds of Sarcobatus (from 13 plants) and Chrysothamnus (from 10 plants) were collected from Mono Dunes Ecosystem Research Site north of Mono Lake, Calif. (Toft 1995;Donovan et al 1996, air dried, and refrigerated until use. In autumn 1996, after scarifying Sarcobatus seeds with sandpaper, seeds of both species were germinated on wet ®lter paper in petri dishes.…”

Seasonal variations in plant nitrogen relations and photosynthesis along a grassland to shrubland gradient in Owens Valley, California

“…E. nauseosa, formerly known as Chrysothamnus nauseosus, is a winter deciduous, C 3 phreatophytic shrub that depends predominantly on groundwater (Donovan and Ehleringer 1994;Leffler et al 2004). When the watertable drops below the rooting zone, E. nauseosa is susceptible to significant dieback and mortality (Toft 1995). Finally, D. spicata is a C 4 perennial halophytic grass commonly found in salt marshes and areas with relatively shallow watertables (Dahlgren et al 1997;Elmore et al 2006).…”