Submitted to: Rangeland Ecology and Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/8/2007
Publication Date: 7/1/2007
Citation: James, J.J., Drenovsky, R.E. 2007. A basis for relative growth rate differences between native and invasive forbs. Rangeland Ecology and Management 60(4):1-7. Interpretive Summary: While the ability of invasives species to achieve higher growth rates than their native counterparts has been demonstrated, the underlying mechanisms driving these differences are not known. Leaves and roots of six native and six invasive forbs grown in a greenhouse were sampled four times over a two month period. Our results suggest invasive forbs achieved higher growth rates than natives by constructing leaves more efficiently, not by allocating more biomass to leaves or by having higher rates of photosynthesis. These results indicate there may be a greater chance of successfully restoring weed infested areas with natives by selecting native plants with the most efficient leaf production.
Technical Abstract: ABSTRACT The ability of invasives species to achieve higher relative growth rate (RGR) than their native counterparts has been widely documented. Little is known, however, about the underlying mechanisms driving RGR differences between native and invasive species. The objective of this study was to determine the basis for RGR differences between native forbs adapted to nutrient-poor soils of the intermountain west and exotic forbs that have widely invaded these systems. Six perennial native forbs and six perennial invasive forbs were randomly selected from a list of 12 potential native forbs and 12 potential invasive forbs. Species were seeded in pots in a greenhouse and four harvests were conducted over a two month period. These four harvests were used to calculate RGR and the components of RGR, net assimilation rate (NAR, rate of dry matter production per unit leaf area), leaf area ratio (LAR, leaf area per unit total plant mass), leaf mass ratio (LMR, the proportion of biomass allocated to leaves) and specific leaf area (SLA, leaf area per unit leaf biomass). Mean RGR of the 12 study species ranged between 0.04 and 0.15 g g-1 d-1 but was significantly higher for invasive forbs compared to native forbs (P = 0.036). The higher RGR achieved by invasive forbs compared to natives mainly was due to a greater SLA and LAR. This indicates that invasive forbs achieved higher RGR than natives primarily by creating more leaf area per unit leaf mass, not by allocating more biomass to leaf tissue or by having a higher net rate of dry matter production. A high degree of variation in RGR, SLA and LAR was observed in native forbs suggesting the ability to design weed-resistant plant communities may be improved by managing for specific functional traits as opposed to functional groups.