PARENT SESSION
Contributed Oral Session 132: Invasive Species: Management and Indicator Species
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 516 A, Level 5, Palais des congrès de Montréal

Comparative demography of an invasive and native Rubus in two deciduous forest habitats.

Innis, Anne^{*,1, 2}, Forseth, Irwin ¹, Whigham, Dennis², ¹ University of Maryland, College Park, MD² Smithsonian Environmental Research Center, Edgewater, MD

ABSTRACT- Management actions that prevent the spread and impacts of invasive species require knowledge of their ecological characteristics. The interaction between an invasive species and its habitat can be investigated through demographic studies across habitats. We examined demographic characteristics of the invasive wine raspberry (Rubus phoenicolasius) and the native sawtooth blackberry (Rubus argutus) in two forest habitats on the Coastal Plain of Maryland. Yearly change in stem density and fruit production were monitored in permanent plots from 2002-2004. Stem density decreased in both forests for both species in the second year of the study and did not return to initial levels by the end of the study. Stem mortality occurred in 2002, a drought year, and recovery was slow in 2003, a year with record high precipitation. There was significantly less stem mortality for both species in the lower light, lower nutrient forest. In the high light forest only stem densities of the invasive species recovered to levels close to those measured in the first year of the study. The number of flowering stems and number of mature fruits produced was significantly higher for R. phoenicolasius in both forests. In all three years R. phoenicolasius produced significantly more seeds per fruit than R. argutus and seeds of R. phoenicolasius had significantly higher germination rates. Overall mortality was lower for both species in the study site with lower light and nutrient levels indicating the importance of habitat conditions for plant performance. The invasive R. phoenicolasius had significantly lower mortality than R. argutus at the high light and high nutrient site. The combination of lower mortality, higher fruit production with greater germination and habitat characteristics favorable to invasion may explain the success R. phoenicolasius.

Key words: invasive species, Rubus, demography