Balancing biodiversity and human land use? Interactive effects of leaf harvest, grazing and fire on plant populations and communities in the Western Ghats, India

The majority of the world’s remaining terrestrial biodiversity occurs in tropical areas, little of which has escaped modification by human activities. Studies in human-modified systems can contribute to understanding if, and under what conditions, human land use is compatible with the persistence of biodiversity. Fire, grazing and wild plant harvest commonly co-occur within tropical human-modified ecosystems but their interactive effects have rarely been considered. Determining the combined effects of – and interactions among – these multiple forms of disturbance is crucial to understanding their impacts on patterns and processes at multiple ecological scales, their relative importance within ecological systems and to managing the great number of tropical systems currently impacted by these activities. We examine interactions among leaf harvest, fire and grazing on a wild palm species (Phoenix loureiri) commercially harvested by indigenous communities in the Western Ghats, India. We combine data from ecological experiments with information from interviews with local harvesters to understand linkages between the social and ecological systems. Based on this data, we model palm population dynamics under different management histories using matrix models and quantify the diversity of the surrounding plant understory and canopy communities. We use multiple regression and information-theoretic approaches to model selection to determine the relationships between human management activities and plant community diversity, structure and composition. We find that leaf harvest and fire – set by local communities to manage palm populations and the production of livestock forage – each have a negative impact on palm populations. In addition, the interactive effect of harvest and fire on palm populations is greater that would be expected from the impact of either alone. We also find that levels of browsing on the palm are highest in areas with recent fire. This trend is due to the activity of wild animals such as elephant and gaur in addition to domestic livestock. Finally, we find evidence that human management activities, aimed at acquiring benefits from a subset of species present in the ecosystem, are affecting overall levels of plant diversity. The complex interactions we observe among human management activities, ecosystem service provision and ecosystem processes are likely common in other human-managed tropical landscapes, but remain poorly understood. Understanding these interactions is key to managing systems for the benefit of both local livelihoods and biodiversity.

Lead Investigator: 
Reciprocal Interactions
Temporal Scope: 
Natural System: 
tropical forest and savanna