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Elizabeth A. Pierson

Publications and source records attributed to Elizabeth A. Pierson.

3 recordsLinked to original sources
USGS2013

Regional demographic trends from long-term studies of saguaro ( Carnegiea gigantea ) across the northern Sonoran Desert

Ten saguaro ( Carnegiea gigantea ) populations in the northern Sonoran Desert were monitored from 1959 to 2005 to discriminate how climate influences plant growth, abundance, reproductive potential, survivorship, age structure and regeneration trends. Thousands of saguaros were measured to determine site-specific growth rates and survivorship through time. Observed growth rates were used to predict the ages of saguaros and reconstruct local and regional regeneration patterns back to the late 18th century. Both growth rates and degree of branching generally tracked temperature and moisture gradients. Site-specific age-height models explained 89-97% of variance in observed ages, with a slope of nearly one. Regeneration was more consistent at sites in the western (hotter/drier) than eastern (cooler/wetter) sites, which exhibited clear multidecadal variability in regeneration rates. Averaged across the region, saguaro regeneration rates were highest from 1780 to 1860, coincident with wet conditions and high Pinus ponderosa recruitment in the highlands. Milder and wetter winters and protection from livestock grazing likely promoted late 20th century regeneration surges at some sites. Predictions of saguaro population dynamics in the 21st century likely will be confounded by the saguaro's episodic and asynchronous regeneration, continued urbanization, ongoing grass invasions and associated wildfires, and changing climate.

Arizona↗
USGS1998

Effects of nutrient patches and root systems on the clonal plasticity of a rhizomatous grass

Clonal plant foraging has been examined primarily on individual clones exposed to resource-poor and resource-rich environments. We designed an experiment to examine the clonal foraging behavior of the rhizomatous grass Elymus lanceolatus ssp. lanceolatus under the influence of neighboring plant root systems in a heterogeneous nutrient environment. Individual Elymus clones were planted in large bins together with one of three neighboring grass species, Agropyron desertorum, Pseudoroegneria spicata, or Bromus tectorum, which differ in rooting density and growth activity. The position of Elymus clones was manipulated so rhizomes encountered a short-duration nutrient patch and subsequently root systems of the neighboring plants. Unexpectedly, the morphological plasticity of the perennial grass Elymus lanceolatus ssp. lanceolatus was influenced by the presence of the neighboring species much more than by the local nutrient enrichments, although nutrient patches did amplify some of the foraging responses. Elymus rhizomes branched readily and initiated large daughter plants as they encountered the low-density root systems of Pseudoroegneria. When Elymus encountered the fine, dense root systems of the annual Bromus, clonal expansion was initially reduced. Yet, after the short growing season of Bromus, Elymus resumed clonal expansion and produced several daughter plants. Elymus clones were most constrained by the fine, dense root systems of Agropyron desertorum. In this case, a few, long rhizomes avoided the densely rooted soil environment by growing aboveground as stolons crossing over the Agropyron tussocks. Elymus clonal biomass was largest in neighborhoods of Pseudoroegneria, intermediate in neighborhoods with Bromus, and smallest in neighborhoods with Agropyron. The latter were approximately half the size of those in the Pseudoroegneria environments. Elymus growth could not be explained by simple resource competition alone; other mechanisms must have been involved in the apparent differences in interference patterns of neighboring plants with Elymus.

Ecology↗