Overpopulation means more horses than allowed by plan, not necessarily more horses than the land can support.
AMLs, which represent the number of horses allowed by plan, are small relative to the authorized forage, because most of it has been assigned to privately owned livestock.
The authorized forage may correspond to half of the available forage, a safety factor that allows for natural variations in climate.
To determine if the area is really overpopulated, compare the current population to the True AML, which requires a few calculations as previously explained.
For example, the current population at Roberts Mountain HMA is 1,132, including foals, according to Table 1 of the Draft EA for resource enforcement actions in the Complex.
The True AML is 678, computed earlier today, to be achieved by confining the ranchers to their base properties. (What do you think happens during the off season?)
The HMA is overpopulated because the current population exceeds the True AML.
The footnote in the table says the current population includes horses outside the HMA, and the number of foals was based on a 19% growth rate (24% birth rate, assuming a 5% death rate), so the situation inside the HMA may not be as bad as originally thought.
Western Horse Watchers Association 