RELATIONSHIPS BETWEEN FORAGE PLANT DIVERSITY AND WEEK INVASION IN PASTURE COMMUNITIES

Authors: TRACY, B - UNIV. OF ILLINOIS; Sanderson, Matt

Submitted to: Agriculture Ecosystems and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2003
Publication Date: 4/20/2004
Citation: Tracy, B.F., Sanderson, M.A. 2004. Relationships between forage plant diversity and week invasion in pasture communities. Agriculture Ecosystems and the Environment. 102(2):175-183.

Interpretive Summary: Weeds can lower the yield and quality of forage available for grazing, which, in turn, affects animal weight gain, health and ultimate product (e.g., meat, wool, milk). One type of biological control that has received little attention in managed pastures and rangelands is the potential manipulation of forage species diversity to control the invasion of weeds. We used data from three separate studies to determine whether forage diversity was related to weed abundance in pasture communities. Results from the three studies support the concept that increased forage plant diversity may repress weed invasion in pastures. Our data suggest maintaining consistently productive pasture communities and an evenly distributed array of forage species may effectively reduce weed invasion. Managing for increased forage species diversity could be a potentially useful biological control method for weeds in pasture ecosystems.

Technical Abstract: A long standing ecological paradigm suggests that diverse plant communities should be more resistant to invasion by non resident plants (i.e., weeds) compared with plant communities that have few species. In this paper, we used data from three separate studies conducted from 1998 to 2000 to determine whether forage diversity in pasture plant communities was related to weed abundance. The first study involved measuring weed abundance in experimentally constructed pasture communities ranging from 1 to 15 species. A second complementary study was conducted under greenhouse conditions and involved sowing of a common perennial weed species, curly dock (Rumex crispus L.), into forage mixtures containing 5 and 10 different species and three monocultures. Lastly, we investigated the relationship between weed abundance and forage diversity across 37 pastures that were surveyed across the northeast United States. Overall, we found consistent negative relationships between forage species diversity and weed abundance in all three studies supporting the notion that increased forage diversity may repress weed invasion in pastures. Although the specific causal mechanisms for these patterns remain unknown, they likely involve complementary resource use among different forage species that creates an unfavorable environment for weed invasion. We concluded that maintaining consistently productive pasture communities (> 100 gm-2 of aboveground biomass) and an evenly distributed array of forage species could effectively reduce weed abundance. Our findings suggest managing pastures for increased forage species diversity could be a potentially useful biological control method for weeds.