Human Activity and Geographical Factors Influence Vegetation and Plant Richness in Vanishing Oases of Baja California Peninsula

Abstract

The oases of the Baja California peninsula have served as biological refugia for unique and relict biological groups since the late Pleistocene. In this paper, we identified and analyzed the floristics associations in aquatic and riparian vegetation. We also investigated impacts of human activity and geographic factors on the oasis vegetation. A total of 248 species, including relic (e.g., Thelypteris puberula, Epipactis gigantea) and 56 nonnative species, were identified. Some exotic plants such as Cryptostegia grandiflora, Arundo donax, and Pennisetum ciliare were invasive. Species richness of the oasis plants exhibited a stronger correlation with oasis size (or area) but less with latitude, longitude, and elevation. Human activities, including introductions of exotic species, appeared as a threat to the oasis vegetation. Presence of the rare and relict species warrants a high-priority protection of these unique and vanishing mesic ecosystems from human threats.