What Do Stocking Rates Tell You About HMAs?

As noted earlier this month, the stocking rate allowed by plan for the Spruce-Pequop HMA is a miniscule 0.3 wild horses per thousand acres, which is what you’d expect for an area where livestock receive almost nine times as much forage as the horses.

Does that pattern hold for other areas?  Would it be a reliable indicator of management priorities on lands set aside for wild horses?

Let’s add another column to the dataset used last month to test an assertion about the number of wild horses in long-term holding.  The new column is on the far right, wild horses per thousand acres.

Stocking Rate and Forage Allocation Data-1

Now, let’s plot the forage allocated to livestock as a function of the stocking rate.

All of the data points are in the upper third of the chart, meaning that none of the areas are managed primarily for horses.  Most of the data fall below the target stocking rate of one wild horse per thousand acres (across all HMAs).

The highest forage allocations to livestock occur at the lowest stocking rates for horses, the same pattern observed at Spruce-Pequop.  This is called an inverse relationship, denoted by a line with negative slope.

Stocking Rate and Forage Allocation Chart B-1

The line, known as the ‘least-squares fit,’ is of the form y = mx + b.

There are no outliers in the data (remote values in the y-space) and no influential observations (remote values in the x-space), but there could be an issue involving the scatter of the data around the line.

That problem might go away with more data.  But how many areas would you have to review to find larger numbers of horses (higher stocking rates) and permitted livestock grazing?

A few of the lower forage allocations to livestock appear at lower stocking rates, so the relationship is not ironclad.  But coming across stocking rates below 1.0 should prompt you to dig a little deeper to find out how bad things are for the horses.

PSA 12-15-19

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