Rangeland Invasive Plant Management

Abstract

lands provide a valuable resource for wildlife and recreational activities, as well as livestock grazing. The establishment and spread of invasive plants on rangeland are often symptomatic of long-term cultural practices.3 Invasion of many rangeland sites by non-native plants has been facilitated by multiple factors including overgrazing by domestic livestock, purposeful introduction of non-native plants for agricultural purposes, unintentional introduction of non-native plant seeds as a contaminate in crop seed, changes in fire frequency and intensity, and climatic changes that converge to cause shifts in plant community composition. There are over 300 rangeland weeds in the United States, but perhaps 30 have significant negative impact in the western United States.2 Of these, some of the most problematic include downy brome or cheatgrass {Bromus tectorum), medusahead {Taeniatherum caput-medusae), leafy spurge {Euphorbia esula)> perennial pepperweed {Lepidium latifolium), Dalmatian toadflax {Linaria dalmatica), and several members of the Asteraceae, including yellow starthistle {Centaurea solstitialis), diffuse knapweed (C. diffusa), spotted knapweed {C. stoebe subsp. micranthos), musk thistle {Carduus nutans), Canada thistle {Cirsium arvense), hawkweeds {Hieracium spp.), and Russian knapweed {Acroptilon repens). These and other invasive plants can have adverse effects on rangeland and pastures by disrupting vegetation dynamics and reducing ecosystem capacity to recover after disturbance.3 The financial impacts of invasive plants in rangelands are substantial and have been estimated to cost ranchers US$5 billion annually just for control.4 Other impacts to the livestock industry not included in the estimate are the negative effects of invasive plants on yield and quality of forage, livestock poisoning, interference with grazing, supplemental costs associated with managing and producing livestock, and land values. In addition to the livestock industry, invasive rangeland species can decrease wildlife habitat and forage, deplete soil and water resources, and reduce plant and animal diversity. Mechanical, cultural, biological, and chemical methods have been developed to manage rangeland invasive plants. These methods include mowing, prescribed burning, appropriate grazing management, herbicides, biocontrol agents, and revegetation with desirable plants.1 The merits of each control measure and potential for complementary or synergistic interactions when applied in appropriate sequences and combinations should be considered when developing integrated weed management programs. For example, summer burning resulted in a dramatic increase in yellow starthistle germination the following fall and winter.5 Thus, using an herbicide treatment in the year following a prescribed burn gave far better control of yellow starthistle compared with an herbicide treatment followed by prescribed burning. Successful integrated strategies require careful planning that incorporates a long-term approach consisting of prevention programs, education activities, and management approaches. These are designed to diminish negative impacts of invasive plants by improving the invaded plant community to increase its ecosystem function, niche occupation, and competitiveness. These qualities can increase the communities' resistance to reinvasion by other invasive plants.3