Shade coffee farms promote genetic diversity of native trees

Background

In the tropical Americas, coffee is typically cultivated under shade canopy cover. Unlike coffee grown in full sun, shade-grown coffee plays host to an increased diversity of vertebrates and invertebrates. However, the contributions of shade-grown coffee patches in tropical landscapes towards preserving genetic flows have not yet been studied.

Research goals & methods

This study reports on genetic analyses that reveal recent colonization and extensive gene flow of the native understory tree Miconia affinis (Melastomataceae), an obligate outcrosser, within a network of coffee farms and forest fragments in Chiapas, Mexico. M. affinis is bird-dispersed and relies on bee pollination. Farmers have allowed native understory trees, like M. affinis, to colonize the coffee plots because they help to reduce soil erosion. Strong spatial genetic structure of M. affinis found in the forest plots is similar to levels reported in species with extreme seed dispersal limitation; in contrast, no spatial genetic structure was detected for any distance class within the coffee farms, indicating more extensive gene flow across the shade coffee matrix.

Conclusions & takeaways

Levels of M. affinis genetic diversity within the coffee farms did not differ from forest populations. The high genetic diversity and overlapping deme structure of the colonizing trees show that traditional coffee farms maintain genetic connectivity with adjacent habitats and can serve as foci of forest regeneration.