Examining Temporal Patterns of Water Cycling and Plant-Fog Interactions Across Microclimatic Zones in the Galapagos Islands

Abstract:

Changes in land use pose an incredible threat to the fragile ecosystems in the tropics. One such consequence of land use change in the tropics is the propagation of invasive plant species. The Galapagos Islands, an ecosystem subject to significant anthropogenic pressure by both increasing tourism and a growing native population, are especially threatened by invasive plant species. More than 800 plant species have been introduced in Galapagos, comprising over 60% of the total flora. To investigate the impact of invasive plants on water cycling in different microclimates, we examined water use by both native and invasive plant species across different microclimatic zones using stable isotope analysis of cloud water interception, surface water, and plant xylem water. We conducted these measurements starting at the end of the rainy season and through the middle of the dry season, and again during the peak of the current El Nino. To date, we observed a clear isotopic rainout effect in precipitation from windward to leeward sides of the island. Furthermore, our results suggest that invasive guava consistently utilizes water with a similar isotopic signal while native species use water with a larger isotopic range in all microclimatic zones. Our results represent an initial effort to characterize the effects of a changing vegetative cover on the water cycling of tropical islands and provide insight into the interactions between plants, surface water, and groundwater at various spatial and temporal scales.