Alliance between invasive plants management and farming: Cutting and livestock browsing reduce resprout and fruit production in an invasive shrub

Abstract

Biological invasions and land use change for extensive livestock are among the main threats to biodiversity and ecosystem functioning in the Anthropocene. Mechanical management actions against invasive plants are important to restore some of nature’s contributions to people (e.g., water provisioning). Mountain Chaco Woodlands in central Argentina have been occupied by livestock production for centuries and during the last three decades invasive woody plants have been increasing their invaded surface. Pyracantha angustifolia is a thorny invasive shrub that facilitates other exotic species establishment and is rapidly invading many areas of this system. Moreover, the advance of the invasion is not uniform across the landscape (i.e., plant density is higher along water courses). The necessity to establish a low-cost, low-impact management strategy (e.g., without chemicals), motivates the integration of livestock production with mechanical actions against P. angustifolia advance. In this regard, we evaluate if livestock browsing complements mechanical control of invasive shrubs in mountain woodlands to reduce posterior resprout and fruit production. Using individual livestock exclusions we tested the effect of browsing and topography on P. angustifolia resprout and fruiting in a period of two years after mechanical cutting in an invaded basin of Mountain Chaco Woodlands. Our study demonstrates that the combined effect of plant cutting and subsequent livestock browsing on resprout contributes to reducing the propagule pressure of the targeted invasive shrub by temporarily limiting resprout and fruiting. Moreover, the livestock browsing on individuals located near the watercourse showed higher resprout and fruit production after the second year post-cutting compared to individuals on the slopes. This result highlights that the livestock effect is affected by topographic characteristics of the area (i.e., proximity to a watercourse). Furthermore, after two years of post-cutting, all the treatments showed a decrease in the effect of livestock browsing but the treatment with the highest fruit production remains much lower than the expected fruit production without management actions. Our study represents a contribution to the knowledge about how the interaction between human activity, such as livestock production, and invasive plant mechanical control can impact the invasion process of alien plants in mountain woodlands of central Argentina. The understanding of this relationship is an essential step for evaluating the success of a plant invasion management strategy in mountain systems.