Baja California peninsula oases: An agro-biodiversity of isolation and integration

• Oasis agro-biodiversity is a product of isolation and integration events through time and across space.
• Baja California oases harbor heritage crop species first introduced by Jesuit missionaries (1697–1768).
• These oases serve as agro-biodiversity refugia.
• The most isolated and the most integrated oases are unable to support agro-biodiversity over long time scales.

Agro-biodiversity in the desert oases of the Baja California peninsula, Mexico is a product of isolation and integration events through time and across peninsular spaces. Historic inventories of agricultural introductions provide a baseline from which to measure Mission-era crop persistence or genetic erosion in fifteen missions established during the Jesuit occupation (1697–1768). These mission-oases function as a network of interconnected sites supporting cultivated plant assemblages isolated from one another and the Mexican mainland by a desert matrix, by limited transportation infrastructure on the peninsula, and the surrounding sea. Garden surveys of perennial crop species and farmer interviews reveal that oases serve as refugia of Mission-era crop species and traditional knowledge. Isolation-connectivity analyses indicate that this agro-biodiversity disappears at the extremes: The most isolated and the fully integrated oases are unable to support heritage perennial crop species and traditional farming systems over long time scales. We describe how phases and processes of isolation and connectivity transform agro-biodiversity composition in this archipelago of peninsula oases and explore policy applications that could preserve this critical diversity and the rare and available oasis communities.