Some HMAs are managed for horses and burros. Some allotments are permitted for cattle and sheep. Sometimes you know the number of animals allowed by plan and other times you know the active AUMs and grazing seasons.
An HMA may fit within an allotment or intersect a large portion of it, resulting in a common area.
What do the resource allocations tell you about the management priorities in that area?
The trick is to put everything on a consistent basis. Don’t try to compare burros to cattle and horses to sheep.
Convert burros to horses and sheep to cattle. The resource requirements of horses and cattle are said to be equivalent, allowing a direct comparison.
Consider this example. The HMA and allotment occupy the same 88,000 acre parcel.
- AML for horses: 42
- AML for burros: 92
- Grazing season in months: 12
- Cattle on permit: 224
- Sheep on permit: 640
- Grazing season in months: 6
Start by converting burros to horses and sheep to cattle.
Two burros are equivalent to one horse and five sheep are equivalent to one cow, so the equivalent number of horses allowed in the area is 42 + (92 ÷ 2) = 88 and the equivalent number of cattle is 224 + (640 ÷ 5) = 352.
The horses require 88 × 12 = 1,056 AUMs per year and the cattle require 352 × 6 = 2,112 AUMs per year.
Horses receive one third of the authorized forage, neglecting wildlife, and cattle receive two thirds.
The stocking rate for horses is 88 ÷ 88,000 × 1,000 = 1 animal per thousand acres and the stocking rate for cattle is 352 ÷ 88,000 × 1,000 = 4 animals per thousand acres.
The HMA is managed primarily for livestock. The forage assigned to cattle would support an additional 2,112 ÷ 12 = 176 wild horses, for a True AML of 264.
The new AML could be distributed any number of ways among horses and burros, for example, 150 horses and 114 × 2 = 228 burros, as long as the total AUMs are 3,168.