Seeing through the clouds - Mapping desert fog oasis ecosystems using 20 years of MODIS imagery over Peru and Chile

Abstract

The desert fog oasis ecosystem of Peru and Chile comprises numerous oases along 3000 km of the Pacific coastal belt, it hosts a highly endemic flora, providing vital ecosystem services and genetic resources. However, due to their marked seasonality and fog cover they are poorly mapped, greatly compromising their conservation. Here we redress this using 479 images from the MODIS (MOD13Q1 V6 product) data/algorithm for the period 2000–2020, permitting the mapping of ephemeral vegetation, herbaceous and woody fog oases vegetation. In addition, we examine the main drivers of productivity in this unique ecosystem using generalised linear models, assess human pressures, conservation efforts, and summarise present plant diversity knowledge. The resultant map (https://gistin.users.earthengine.app/view/fogoasis) extends existing mapped areas by more than four-fold to over 17,000 km2

, revealing extensive little-known vegetation habitats with few or no collection records. Tillandsia (‘air plants’) fog oases were mapped manually due to poor spectral discrimination and were found to cover an area of approximately 1,900 km2 the majority of which is in Peru (96%). Fog oasis productivity is significantly related to aridity and distance to the coast, as well as elevation and slope angle. Most fog oases peak in productivity during August-September, although productivity is highly variable between August and December with different oases reacting to inter-annual and annual climate fluxes.

Only 4% of fog oases are protected, most are threatened by mining, urban development, air pollution and off- road 4 × 4 driving. Urgent action is needed to protect these areas, which we estimate support around 1200

ecosystem-specific flowering plant species with approximately 30% endemism in Peru and 67% in Chile. By presenting a comprehensive map and catalogue of Peruvian and Chilean fog oases, we hope to catalyse increased conservation and research towards a better understanding of these exceptional ecosystems within South America.