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).