Effects of spotted knapweed (Centaurea maculosa) density, biomass, and removal on the growth of blueberry (Vaccinium angustifolium) and strawberry (Fragaria virginiana).

Abstract

Centaurea maculosa, commonly known as spotted knapweed, is an allelopathic invasive plant species rapidly increasing across rangelands and meadows throughout North America. Such invasions have notable impacts on soil chemistry and biodiversity loss, though the differential responses of native plant species to increasing C. maculosa densities or to the removal of C. maculosa following population establishment remain unknown. This study sought to determine (1) relationships between the density of C. maculosa and those of two native plant species: Vaccinium angustifolium (low-bush blueberry) and Fragaria virginiana (strawberry); and (2) whether the removal of C. maculosa differentially affects the growth of V. angustifolium and F. virginiana by comparing density and percent cover of the species of interest along with other commonly found species in the plots. In order to measure the difference in the growth of V. angustifolium and F. virginiana in the absence of C. maculosa, manual removal of C. maculosa was performed on a series of paired plots. Density and percent cover of C. maculosa had no influence on the density and percent cover of V. angustifolium or F. virginiana. The results suggest that C. maculosa density does not affect V. angustifolium or F. virginiana density within the study site. The removal of C. maculosa did not affect the growth of either V. angustifolium or F. virginiana, indicating that C. maculosa does not have short-term effects on either native species, and that manual removal of C. maculosa may not be an effective removal method.