Can goats contribute to the management of invasive plants? Evidence from captive feeding trials

Abstract

In Mediterranean ecosystems, invasive woody species plants, such as Acacia and Hakea, threaten biodiversity, increase fire risk and raise forest management costs. Their fire-adapted traits and persistent seed banks make them difficult to control using conventional methods alone. Targeted goat browsing is a potentially cost-effective and sustainable alternative, with ecological and economic relevance in these fire-prone ecosystems, but its effectiveness for Acacia and Hakea control remains poorly understood. We conducted feeding trials with captive Serrana goats ( Capra hircus ) at the Biological Park of Lousã (Portugal) to evaluate their potential to assist in the management of Acacia and Hakea invasions. A cafeteria-style experiment tested goats preferences among six plant species (four invasive and two native). Acacia dealbata seeds (the most common invader in the region) were also fed to goats to examine ingestion, recovery from faeces and post-digestion fate. Goats demonstrated strong selective foraging preferences. Quercus robur (native) and A. dealbata (invasive) were the most preferred, whereas H. decurrens (invasive) was consistently avoided. Preferences varied for the invasives A. melanoxylon and H. salicifolia and the native Pterospartum tridentatum . Goats ingested 44 % of the 7500 A. dealbata seeds offered, of which 9% were excreted intact and germinated up to 70%. However, most seeds were not recovered, and seed fragments in faeces suggest substantial damage during digestion. This indicates limited, despite real, potential for seed dispersal via endozoochory. Our results suggest targeted goat browsing as a nature-based solution to manage plant invasions, particularly regeneration, providing ecosystem services by reducing invasive woody biomass and destroying most A. dealbata seeds. However, they may also cause disservices, such as the spreading of viable seeds and browsing on accessible Q. robur , hindering regeneration efforts. Goats had minimal effect on the spiny H. decurrens . To maximise benefits and limit risks, grazing should be confined to invaded areas, managing goat movement in space and time to prevent Acacia seed spread and the browsing of highly palatable native plants in sites under restoration. This approach may support the conservation of local goat breeds while contributing to invasive plant management programmes, fire risk mitigation and habitat management.