Plant invasions differentially affected by diversity and dominant species in native- and exotic-dominated grasslands

Authors: XU, XIA - Iowa State University; Polley, Herbert; HOFMOCKEL, KIRSTEN - Iowa State University; DANESHGAR, PEDRAM - Monmouth University; WILSEY, BRIAN - Iowa State University

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2015
Publication Date: 10/21/2015
Publication URL: https://handle.nal.usda.gov/10113/62107
Citation: Xu, X., Polley, H.W., Hofmockel, K., Daneshgar, P.P., Wilsey, B.J. 2015. Plant invasions differentially affected by diversity and dominant species in native- and exotic-dominated grasslands. Ecology and Evolution. 5(23):5662-5670.

Interpretive Summary: Weeds are undesirable and often exotic plants that reduce the quality and quantity of grassland forage for livestock. Weed invasion of grasslands could be promoted by the changes in precipitation patterns that are anticipated as Earth’s climate warms. However, it remains unclear as to whether weed invasion is regulated primarily by long-term climate patterns or shorter-term trends in precipitation commonly referred to as weather. Also unclear is the extent to which weed responses to precipitation depend on the species composition of grassland vegetation. We explored the importance of precipitation patterns (long-term vs. short-term trends) and the geographic origin of vegetation (native vs. non-native or exotic perennial species) in regulating weed invasion of experimental grassland plots in central Texas, USA. Weed invasion tracked the long-term (100-year) seasonal pattern of precipitation more closely than precipitation trends during the measurement year. Weed invasion was greatest early in the growing season before resident perennial species began growth. Invasion was greater in existing communities of native than exotic plants because growth began later in the season for native than exotic species. Summer irrigation marginally decreased weed invasion despite having little effect on the date at which the grassland canopy was estimated to have surpassed 50% cover. Our results indicate that weed invasion tracks long-term precipitation patterns reaching maximum values early in the season when soils typically are wet, but resident perennial species are just beginning growth. Introducing desirable plants that grow early in the season would appear a viable option to reduce weed invasion of grasslands.

Technical Abstract: Precipitation is anticipated to vary greatly under global climate change. However, little is known about the role of precipitation in shaping weed invasion of established grassland ecosystems. Here, we explored how weed invasion was influenced by precipitation and how this pattern was modified by grassland origins (native- vs novel exotic-dominated perennial species) and species diversity under ambient and elevated summer precipitation in Texas in 2009. Weed invasion tracked long-term dynamics of climatic precipitation more closely than the precipitation in 2009. Summer irrigation marginally decreased weed invasion and had little effect on the date at which the canopy of perennial species was estimated to have surpassed 50% cover. In comparison to exotic communities, weeds invaded native communities more in the early growing season (February and March), although invasion did not differ significantly between native and exotic communities across the six sampling times in 2009. More weed invasion in natives was consistent with the phenomenon that exotics greened up and surpassed 50% canopy cover earlier than natives by an average of 18 days. Weed invasion was negatively influenced by species richness in native communities but by dominant species in exotic communities. Weed invasion tracked long-term climatic precipitation. Our results indicate that matching between long-term climate and invasion may constrain responses to fluctuations in precipitation expected with climate change.