Natural grasslands

States and transitions model proposal to characterize its degradation under grazing condition and its satellite monitoring: Doctoral thesis abstract

Abstract

Natural grasslands (NG) are being progressively degraded around the world due to human-induced action. In Uruguay where livestock production based on NG is an important economic activity, this takes on real importance. The general objective of this thesis was to detect degradation of NG using remote sensing (RS) techniques. To achieve this, we worked on: 1) a conceptual framework to approach degradation studies and a clear definition of what “NG degradation” is; 2) definition of a structural characteristics of NG, essential to support national policies and decisions at the farm level. Regarding topic 1, we propose a comprehensive framework with different conceptual categories, for monitoring NG degradation, and a new definition based on current ones. We identified “drivers” as external forces that cause degradation; “processes” as measurable changes in NG conditions (evaluated using indicators); and “consequences” as the impacts or results of NG degradation process. Topic 2 was based on RS (MODIS) due to its ability to quantify large areas in a relative short time, at low cost and with the possibility of analyzing annual evolution. The NG height (available biomass estimator) was selected as a variable to be evaluated as an indicator of degradation, as long as it remained in low ranges for a long time frame or in critical periods (spring or autumn). Variability within each paddock was extremely large in field observations (CV: 70%) and smaller than expected when considering MODIS (CV: 4%-6%) and Landsat information (CV: 12%). Correlations between RS info. and field measurements were low, but Red band showed some potential and justifies further exploration. Additional work is needed to find a RS method that can be used to monitor the "instantaneous" condition of NG. The results of this thesis are expected to contribute to promoting and improving sustainable management, monitoring and decision-making, in this very important and often neglected ecosystem.