2.3 Anthropogenic disturbances
Next, three subplots were chosen in each vegetation plot by drawing lots to measure pressure metrics by domestic herbivores. We used the fecal pellets of these animals (goats, sheep, cows, and horses) as evidence of their presence in the plot in question. All pellets in the selected subplots were counted, and three of these were collected and weighed to calculate average biomass of each pellet. Finally, the total fecal biomass of each of these animals in the plot was calculated (Martorel and Peters 2005).
The fecal biomass from goats, sheep, cattle, and horses were entered as individual metrics in a Principal Component Analysis (PCA). The metrics were correlated with the first two axes of the PCA, and then we determined a single measure through the sum of their coordinates, which we called the Herbivory Pressure Index (Martorel and Peters 2005).