The Rule of 5 says the HMA should be able to support 5 × 115 = 575 wild horses, not 115, with 460 horses denied a spot on their home range according to the Rule of 4. Let’s see how those estimates compare to figures determined the hard way.
The management plan allows 115 horses in an area covering 235,005 acres.
The stocking rate allowed by plan is 0.5 wild horses per thousand acres and the forage requirement is 115 × 12 = 1,380 AUMs per year. Recall from the post in April that fractional stocking rates may indicate large amounts of forage diverted to livestock.
The HMA intersects five grazing allotments per Section 3.2.1 of the draft environmental assessment for management actions on the HMA. All of the land is subject to permitted grazing. A map in Appendix D shows the arrangement.
Allotment data can be found in Table 3a of the EA. Although cattle and sheep are permitted, the livestock calculations pertain to cow/calf pairs only, as their resource requirements are said to be equivalent to those of wild horses.
The total estimated forage available to livestock inside the HMA is the sum of the forage amounts contributed by each allotment. For example, 78% of the HMA lies within the Thousand Peaks allotment, which is 183,304 acres (.78 × 235,005). The forage contributed by that allotment would be 6,785 AUMs per year (183,304 ÷ 332,022 × 12,289), assuming the resource is evenly distributed across the parcel.
The sum of these forage contributions is 9,805 AUMs per year. The number of cow/calf pairs that each contribution can support is equal to the forage amount divided by the grazing season. The Thousand Peaks ranchers would have to place 969 cow/calf pairs inside the HMA to graze off 6,785 AUMs in seven months.
The total estimated number of cow/calf pairs inside the HMA is 1,470, with a weighted average grazing season of 6.7 months (9,805 ÷ 1,470).
The estimated stocking rate allowed by plan is therefore 6.3 cow/calf pairs per thousand acres (1,470 ÷ 235,005 × 1,000). The stocking rates on individual allotments range from 5.3 to 12.6 cow/calf pairs per thousand acres.
These management indicators are compared in the following charts.
The forage assigned to livestock would support an additional 817 horses (9,805 ÷ 12), for a new AML of 932 (115 + 817). Both figures are larger than those estimated above by the Rule of 4 and Rule of 5.
The current population is thought to be around 550 wild horses, almost five times higher than AML but well within the capacity of the land to support them (550 < 932).
Roundups are symptoms, not causes. The Confusion wild horses will be forced off their home range not because there are too many of them but because the management plan gives priority to privately owned livestock, contrary to the original statute.
Management actions, such as roundups and fertility control, won’t occur until the EA is finalized, a Finding of No Significant Impact is issued and a Decision Record is signed.