Threats to persistence of the rare orchid Erasanthe henrici in Madagascar

Background/Question/Methods

Plant and animal species face many threats to survival including land use changes, disruption of mutualisms, and climate change. However, some species face further complications from human harvest.  We focused on the harvest of the Malagasy orchid, Erasanthe henrici, which is collected for the horticultural market.  This species is already restricted to highly fragmented forest patches and suffers from low reproduction. We built demographic models for six populations based on field observations from 2007-2010 and projected the population growth rates 25, 50 and 100 years into the future.  We then incorporated varying levels of harvest (1, 3, or 5 plants per year) into the models and either allowed any plant to be harvested at random or restricted the harvest to reproductive individuals.

Results/Conclusions

Our data show that reproduction is infrequent in southern populations, but relatively common in northern populations although neither region has high seedling recruitment. Legal protection of forest reserves reduces not only the rate of forest destruction but also the frequency with which plants are collected for the horticultural market.  Populations declined under all harvest scenarios, but most severely under those where only reproductive plants were being harvested.  Since reproductive plants are more likely to be harvested, sustainable quotas should be set to ensure survival of this species.