Long-term experiences for the management of a grassland invasive herb: The case of <em>Hieracium pilosella</em> L. in the Fuegian Steppe

Abstract

Ecología Austral 24:135-144 (2014)

Long-term experiences are generally rare in studies on management of invasive species, and they are the key to understand the effectiveness of controls. In this work, we revisited a field experiment set seven years ago to evaluate the effects of four control measures (pasture sown + fertilizer, fertilizer and selective/non-selective herbicide applications) under two different grazing conditions (grazed and ungrazed) in rangelands from northern grasslands of Tierra del Fuego Island in Southern Patagonia (Argentina) invaded by the exotic weed Hieracium pilosella L. (mouse-ear hawkweed, Asteraceae). To evaluate the effects of the treatments applied seven years ago, we measured the cover of the invasive species, the dominant growth forms, and bare soil. The effects of fertilization depended on the grazing conditions; H. pilosella cover decreased by more than 82% and it was replaced by naturalized herbs with high forage value in the ungrazed-fertilized plots, while it exhibited no decrease in the grazed-fertilized plots after seven years since the application. Both herbicides (selective and non-selective) reduced H. pilosella cover by ca. 90% independently of grazing. However, the non-selective herbicide application resulted in an increase in bare soil cover (15%) independently of grazing. In contrast, the selective broadleaf herbicide application increased the graminoids cover up to a 60% and the bare soil cover was below the 2%. According with the results, we suggest a control strategy based on the local application of selective herbicides and/or fertilizers in conjunction with a transient ban on sheep grazing because it is able to reduce the invader’s cover at midterm and local scale.