|Wu, X Ben - TEXAS A&M UNIVERSITY|
Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 21, 2003
Publication Date: July 1, 2004
Citation: Derner, J.D., Wu, X. 2004. Spatial patterns of light gaps in mesic grasslands. Journal of Range Management. 57(4):393-398. Technical Abstract: Invasions by non-resident species into grasslands are a global phenomenon that can affect ecosystem structure and function, and dramatically alter vegetation composition. Predictive capacity for assessing invasibility of grasslands, however, has been hindered by the complex interaction of several factors. Here, we assessed the invasibility of mesic grasslands with contrasting disturbance histories using the model species honey mesquite (Prosopis glandulosa var. glandulosa Torr.), an invasive woody plant of southern North America. Patch metrics, with the exception of edge density, were significantly different between annually-disturbed (i.e., haying) and non-disturbed grasslands on all sample dates, suggesting that dynamics of light gaps in mesic grasslands are driven by the current disturbance regime. The structure, arrangement and configuration of light gaps were distinctly different between annually-disturbed and non-disturbed grasslands: a low density of large patches characterized light gaps in annually-disturbed grassland, while non-disturbed grasslands had a high density of small patches. Although available gap area for invasion by honey mesquite was 2-3 times greater in annually-disturbed than non-disturbed grasslands, successful establishment of this plant is likely prevented by the annual disturbance, which removes accumulated standing crop. Invasion potential appears to not be restricted to a specific "window of opportunity" in these grasslands, as the patch metrics exhibited high temporal stability. Rather, successful invasion of these grasslands by non-resident species depends on the concurrence of viable propagules and desirable environmental conditions specific to the emergence and survival that individual species. Our data support emerging theory that identifies fluctuating resources as the key factor controlling invasibility.