Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2014
Publication Date: 5/1/2014
Publication URL: http://handle.nal.usda.gov/10113/59320
Citation: Sheley, R.L., James, J.J. 2014. Simultaneous intraspecific facilitation and interspecific competition between native and annual grasses. Journal of Arid Environments. 104:50-87. DOI: 10.1016/j.jariden.2014.01.019. Interpretive Summary: Competition from invasive plants can determine the success or failure of native plants during restoration. The size of native plants and precipitation are two very important factors that control the amount of competition occurring between annual grasses and desired native vegetation. We found that as the desired species get bigger it is better able to keep medusahead from growing and medusahead had a lower effect on native plants in dryer conditions. We also found the evidence that annual grasses and native plants have the ability to facilitate the establishment and growth of their own species, while simultaneously having a negative effect on their neighbor. Controlling annual grasses during restoration may allow desired plat to grow large enough to hinder invasion in moist condition, but may not be as necessary in droughty conditions.
Technical Abstract: Invasive annual grasses construct thinner and less dense root and leaf tissue than native perennial grasses. This allows invasive annuals to grow faster and produce more biomass in the arid grasslands of the United States. Based on these differences we tested the hypotheses that: 1) Competitive effects of the native perennial on the invasive annual will increase as plant developmental stage increases and as drought stress increases 2) Drought stress will reduce the competitive effect of invasive annuals on native perennials proportionately more than drought stress reduces the competitive effect of native perennials on the invasive annual 3) Facilitation among native perennial grass seedlings will decrease as developmental stage increases. The competitive effects of the squirreltail, a native perennial grass, on medusahead, an invasive annual grass, increased as the initial developmental stage of squirreltail increased, but not vice versa. Drought stress reduced the competitive effect of medusahead on squirreltail target biomass more than drought stress reduced the competitive effect of squirreltail on medusahead target biomass. While both squirreltail and medusahead displayed intraspecific facilitation, the net effect of their interspecific interaction was negative for both species. Habitat amelioration manifests itself differently depending on species traits, and can create conditions that simultaneously benefit one species while hindering another.