Overgrazing Effects on Vegetation Cover and Properties of Volcanic Ash Soil in the P ramo of Llangahua and La Esperanza (Tungurahua, Ecuador)

The p ramos (high altitude grassland ecosystems) of the northern Andes, Ecuador, is important to water availability in the inter-Andean valleys because of their high water retention. The p ramos have been intensively grazed by sheep in the last 20 yr, causing a serious decline in the number of plant species, a replacement of tussock grasses by short carpet grasses, and an increase in bare land area. The top 50 cm of the p ramo soils (a volcanic ash) are strongly affected by a convergent decline in aluminum and iron oxalate, pyrophosphate, carbon content, and water retention capacity. Overgrazed soils also show degraded macrostructure and development of a highly water repellent microstructure. These changes encourage aeolian erosion in dry areas, runoff in bare areas, and gully erosion on slopes. In particular, grazing has adversely influenced the water regulation role of the p ramos.