The impact of feral camels (Camelus dromedarius) on woody vegetation in arid Australia

Data on the extent of feral camel damage on trees and shrubs in inland Australia are scarce, and there is currently no universally accepted theoretical framework for predicting the impact of a novel large mammal browser on arid vegetation. In other (mainly mesic) grassy systems, large mammal browsers can strongly suppress woody biomass across landscapes by limiting the transition of saplings to adulthood and by significantly thinning adult tree canopies. The recent Australian Feral Camel Management Project provided an opportunity to assess the impacts of camel browsing on woody vegetation in inland Australia. We examined browsing intensity and severity (stunting and canopy loss) in 22 species of woody plants in camel-affected regions across inland Australia prior to camel removal operations. The severity of plant damage increased with camel density as both trees and shrub growth were strongly suppressed where camel densities exceeded 0.25km(-2). In most tree and shrub species tested, camel browsing significantly stunted plants, suggesting that camel browsing has long-term impacts on plant populations. Browsing also reduced canopy volume in several species, including the structurally important Acacia aneura F.Muell. ex Benth. Thus, in this dryland ecosystem, camels can curtail the regeneration and growth of woody species enough to threaten ecosystem health. To avoid adverse impacts on woody plant populations, camel densities should be maintained at 0.25 camels km(-2) or less over as much of inland Australia as possible.