Impact of tussock grass removal on the soil water dynamics of a tropical mountain hillslope

Abstract

Soil water content (SWC) is related to the ecohydrological processes and environmental services of ecosystems. However, SWC studies are scarce in mountain humid ecosystems, such as the Andean páramos, where human activities can alter their SWC dynamics and perhaps their water regulation capacity. Our objective was to analyze the influence of extensive grazing in the SWC of an Andean páramo hillslope with native tussock grass vegetation. The SWC of a hillslope was monitored through paired water content reflectometers (WCRs) placed at different soil depths (10 – 75 cm) in eight soils profiles along two parallel transects. After 5 years the vegetation was cut out from one transect – as an emulation of extensive grazing – and both transects were monitored for 10 months. Changes in SWC were explored through differences in SWC between the paired WCRs during three subperiods after the experiment, selected according to the precipitation characteristics (amount, intensity and distribution). Immediately after the vegetation cut out (2 months) and during the dry subperiod (2 months) we noticed that in the superficial soil layer (10 cm depth) at the top and middle-top of the hillslope the SWC increased and decreased respectively, while their SWC spatio-temporal variability decreased. No impact was detected during the rainy subperiod, 8 months after the experiment. Nevertheless, these few changes were attributed to changes in interception and to grassroots death-regrowth. Results suggest that the impact of extensive grazing is low as long as the soils are not destroyed, especially during rainy periods.