Demand for ecosystem services in areas prone to landslides drive large-scale shifts in land-use in small mountainous watersheds in the tropics

Francisco-Javier Álvarez-Vargas and Angélica María Prado, Biology, Universidad del Valle, Cali, Colombia, María Angélica Villa Castaño, Fundación Ecovivero, Cali, Colombia, Carla Restrepo, Department of Biology, University of Puerto Rico Rio Piedras, San Juan, PR

Background/Question/Methods
An increasing frequency of extreme atmospheric events is challenging our basic understanding of how macrosystems, including the production of ecosystem services-ES, respond to such events. As part of a new reality, mountainous rural and exurb regions prone to landslides are becoming less heterogeneous and more connected, opening the possibility for the propagation of perturbations at multiple scales, and ultimately the sustainable production of ES. We hypothesize that an increasing demand for water-derived ES, translates into increases in forest cover and size of forest patches over time in ES-producing areas but that these changes are modulated by elevation (939-4306 masl) and steepness (0-74.5%). To test this hypothesis, we focused on four watersheds (13943 ha) in the Central Andes of Colombia and combined historical maps and Landsat imagery to reconstruct changes in water and land use, including disturbance. We used the Landsat images (2003-2019) offered through the Global Land Analysis and Discovery facility (GLAD) and GLAD Tools v1.1 for classification purposes. Two metrics, namely forest cover and forest aggregation, were used to examine regional and sub-regional trajectories.

Results/Conclusions
Historical documents revealed that one watershed (Nima) exhibited the longest and most complex history of water use dating back to the late 18th century. The relative importance of the various water uses, however, has changed over time. This together with the impacts of landslides and drought on the production of water-derived ES, has been reflected in a number of measures aimed at regulating land use, and ultimately guaranteeing the production of ES. Forest cover and degree of forest aggregation increased, or remained stable, throughout the region during the study period. Yet, this trend was not uniform across all elevation and steepness categories, nor across the four watersheds. Regionally, we observed a decreased in forest cover and forest aggregation at medium to low elevations in gentle slopes. In one watershed (Bolo), the two metrics consistently increased or remained constant across all elevation and steepness combinations. In a second watershed (Desbaratado) the two metrics decreased a low to medium elevations mostly in gentle slopes. In contrast, in the the Nima and Fraile watersheds the two metrics decreased at middle and very high elevations both in gentle and steep terrain. Road construction in the 1990s in the last two watersheds may explain their divergent trajectories, and possible conflicts with a number of measures at regulating land use.