Ecological compatibility and trade-offs between wild plant harvest and conservation of plant diversity in a seasonally dry tropical ecosystem

Background/Question/Methods

Developing a better understanding of the compatibility between human land management and biodiversity conservation is critical to achieving effective conservation while meeting current human needs. Harvest of non-timber forest products (NTFP) is thought to be more compatible with biodiversity conservation relative to conversion for agriculture or pasture because NTFP harvest does not involve land clearing but still provides economic benefits to local people. However, few ecological studies have assessed the degree to which management for NTFP harvest also maintains biodiversity. In the Western Ghats, India, leaves of a wild understory palm, mountain date palm (Phoenix loureiri), are harvested from savanna woodland ecosystems to make brooms. In this study, we ask if leaf harvest is compatible with conservation of plant diversity. To address this question, we carried out a regional study across 5 sites and 14 palm populations and surrounding plant communities from 2009-2011. Because fire is a common management tool in the study area, as throughout much of the tropics, our study sites included areas with differing histories of fire and palm leaf harvest. We combine results from integral projection models of mountain date palm population dynamics with models of plant taxonomic and functional diversity with differing land management.

Results/Conclusions

Our models of mountain date palm population dynamics suggest populations are resilient to harvest of up to ~20% of leaves/population and to the observed ~3 year fire return interval. There is therefore a high potential for sustainable harvest of palm leaves at the population level. Harvest is best suited to areas with more open canopies due to increased palm growth and flowering under these conditions. At the community level, areas with and without harvest had similar levels of plant species diversity and functional diversity. However, areas with fire in the past 1-2 years had a lower diversity of tree species compared to areas without fire for 3 or more years. In addition, areas with more open canopies had lower tree diversity but higher diversity of understory forbs. In combination, our results suggest that palm leaf harvest is compatible with the maintenance of a high degree of plant diversity. However, we also found a trade-off between maximizing mountain date palm population growth and maximizing tree diversity, mediated by fire and canopy openness. Harvest of understory species, like mountain date palm, may be most compatible with conservation of plant diversity in more open ecosystems where most plant diversity occurs in the understory.