Vegetation structure and soil properties in Ecuadorian páramo grasslands with different histories of burning and grazing

Abstract

High-altitude grasslands in the north Andes (páramos) are subject to frequent fires that are usually set by farmers to support traditional cattle-raising systems. Apparently, this practice has caused dramatic changes in the structure and composition of native vegetation, but the mechanisms, magnitude, and direction of these changes still need to be documented for a broader range of conditions. This paper describes the differences in selected soil properties, ground cover, grass tussock structure, and populations of giant Andean rosettes (Espeletia pycnophylla) in four páramo sites in northwestern Ecuador, characterized by contrasting patterns of burning and grazing. The only differences between the soil properties of the sites were the higher pH in the least disturbed site, and the high concentration of P in the more recently burned site. Along the sequence of least impacted to most impacted sites, we observed a decrease in grass tussock cover, and an increase in the amount of bare ground and number of fragments per tussock. In the most undisturbed site tussock coverage was extremely low due to the dominance of shrubs. The density of giant Andean rosettes was higher in the sites with intermediate disturbance regimes, while the mortality of adult stem rosettes was significantly higher at the more recently burned site. The significance of these differences is discussed in the context of the regeneration of páramo vegetation after burning and grazing disturbance.