We investigated the use of sheep for controlling the spread of purple loosestrife in a wet meadow in upstate New York from June to August 2008. Changes in the purple loosestrife population and vascular plant community structure were monitored as a function of the grazing of two ewes, “rotated” through four “experimental” paddocks at 2- to 3-d intervals. Comparative data were collected in “reference” paddocks from which sheep were excluded. Purple loosestrife was heavily grazed and most plants did not flower in experimental paddocks. Purple loosestrife cover declined by 40.7% in the experimental paddocks but did not change significantly in the reference paddocks. After grazing, species richness was 20% higher in experimental than reference paddocks.
Nomenclature: Purple loosestrife, Lythrum salicaria L
Interpretive Summary: Although livestock is widely used to manage nuisance plant species on rangelands, little is known about the effectiveness of this approach, called “targeted grazing,” in wetlands, and controlled, systematic studies on the effectiveness of targeted grazing are scarce. We investigated the efficacy of using Romney sheep to control the spread of purple loosestrife in a wet meadow in upstate New York. We were interested in the impacts of the sheep on both the invasive population and on the larger plant community. The sheep were rotated through a system of small (200-m2) paddocks using a protocol, intensive rotational grazing (IRG), that employs high stocking densities, i.e., two to four times more livestock biomass than conventional grazing, and high frequency rotations (2 to 3 d per paddock). As such, IRG mimics the distribution, in time and space, of large, wild, herbivorous herding mammals on a landscape. The sheep fed on purple loosestrife (and other invasives), preventing flowering and reducing purple loosestrife cover by about 40%, relative to reference paddocks from which sheep were excluded. After the grazing phase of the study, species richness was 20% higher in the grazed paddocks than in the reference paddocks. Although a great deal remains to be learned about the impacts of targeted grazing and its underlying mechanisms, it appears that the technique can be used to help manage purple loosestrife, and perhaps other invasive plant species, in emergent wetlands and wet meadows.
