Heather L. McFarland and Scott J. Meiners

Biological Sciences Department, Eastern Illinois University, Charleston, IL

Exotic plant invasions are a major threat to biodiversity, however the mechanisms of these impacts are poorly understood.  Rosa multiflora Thunb. was introduced into the United States from Asia in the1860’s and has since become a problematic invader of fields in the eastern and central United States.  We used data from a long term succession study to assess the impact of Rosa multiflora invasion on species richness and community dynamics.

We used permanent plot data from the Buell-Small Succession Study, to look for changes in community composition from the beginning (T₁) to the midpoint (T₂) of the Rosa multiflora invasion.

Figure 1. We used these data to investigate dynamics associated with an invasion.  From these data we quantified: 1. Change in Rosa multiflora cover 2. Change in species richness 3. Number of new species colonizations 4. Number of local species extinctions

	Figure 2. Successional field of the BSS
	Figure 3. Rosa multiflora in fruit.
	Figure 4. Entrance to the Hutcheson Memorial Forest, site of the BSS.
	Figure 5. Rosa multiflora thicket in the BSS.

Does Rosa multiflora impact diversity?
	Figure 6. As Rosa multiflora cover increases, species richness declines.
Changes in species richness could be caused by decreased rates of colonization or by increased rates of species extinction in invaded plots.

 

Why does richness decrease?
	Colonizations Figure 7. As Rosa multiflora cover increases, the number of new species colonizations decreases.
	... and  Extinctions Figure 8. As Rosa multiflora cover increases, the number of local species extinctions increases.

Conclusions

Invasion of Rosa multiflora caused a decrease in species richness.  Both colonization and extinction are mechanisms for change in species richness.  Rosa multiflora caused an increase in the number of species lost, and a decrease in the number of species that colonized plots.  Rosa multiflora has a stronger effect on colonization rates than it does on species extinction rates.  This is contrary to the traditional competitive exclusion view, which would predict primarily species extinctions.

Figure 9. Buell-Small Succession Study. (Image courtesy Buell-Small Succession Study)

This is a long term ecological study designed to document old field succession. The study includes ten fields abandoned from agriculture beginning in 1958. Vegetation dynamics have been followed in 48 permanently marked 0.5 x 2.0 m plots in each field.  For more information go to http://www.ecostudies.org/bss/

Funded by: The Council on Faculty Research, Eastern Illinois University