PS 39-109
The invasive potential of Centaurea stoebe ssp. micranthos (Asteraceae) in competition with the common native plant Lespedeza capitata (Fabaceae)
Spotted knapweed, Centaurea stoebe ssp. micranthos, long recognized as a problem in western North America, is an invader of increasing concern in the east. Broadly different environmental conditions between the regions invite consideration of different invasive dynamics and potential contrasts with patterns in the west. Changing patterns of land-use in eastern regions, as land that was once utilized for agriculture or industry returns to a more natural state or is actively restored, make this a critical time in understanding how invasive plants opportunistically exploit habitat availability. One of the most common native species occurring at sites of invasion in the Mid-Atlantic is Lespideza capitata or bush clover. Our goal was to examine the potential for knapweed to competitively displace the native through the use of competitive experiments in the greenhouse and census data collected in the field. We collected census data along the High Bridge Trail, a 50 kilometer greenway in Virginia developed from a recently decommissioned railway. These data are the beginning of a long-term record intended to document ecosystem changes along the naturalized habitat. Collections were made at the census sites from existing populations of knapweed and bush clover were sown in the greenhouse for competition experiments.
Results/Conclusions
Census data show the presence of both the invader and the native bush clover at sites along the restored area with higher light and peak-heat levels and the most well-drained soil types. While the bush clover thrives under these conditions, areas of greatest exposure and highest heat appear to be more supportive of the invading species. Invaders and native plants were grown in pairwise sets to observe the effects of competition. Measurements were taken of root length, shoot length, longest leaf length and leaf count, in addition to dried mass of roots and shoots at the end of the experiment. By the end of the experiment, C. stoebe was great than 2.5 times more likely to survive in the greenhouse pots in competition with the native Lespideza. Competitively dominant knapweed plants were smaller on average in size and mass than those in pots where the bush clover survived. The greater size of C. stoebe with living bush clover may be attributable great nutrient availability, either incidental in the soil from the clover or from AMF as are implicated in some western studies. A better understanding of competitive interactions between invaders and the dominant natives is timely in this natural system.