The Public Pressure Index

Of all the unique stats we offer up, the most confusing is probably the Public Pressure Index. I get a lot of questions on what the numbers mean, and I figured this article may help. The Public Pressure Index is something I came up with to reflect public land trophy potential, but it can also be used to indicate other problems with the unit you are looking at. I wrote an article on the trophy potential indices just a few months ago, and went into some detail about how to compute a buck’s chances of living to a specified age, so if you’d like a copy of that, just email me. I felt the Public Pressure Index deserved further examination and will do so here.
Ideally, the Public Pressure Index should indicate the % of available bucks or bulls harvested off of public land. In calculating the PPI, the game density and sex ratio is applied to just the public area, to extrapolate the number of public land bucks or bulls available. The total buck or bull harvest from the prior season is then divided by the available bucks or bulls, which equals the PPI. Computing the Public Pressure Index makes two assumptions: it assumes that game density is equal on public and private land and assumes that all males harvested came off of public land. Obviously, these two assumptions are not true 100% of the time, but without total knowledge of the hunter and harvest distribution within the unit, some assumptions have to be made. I think it’s fair to assume that most hunters are public land hunters and that most of the game harvested in a unit came off of public land in the West. Now, some people may argue the game density assumption, but when averaging out the unsuitable private land habitat throughout an entire area, and not looking at winter concentrations on private fields, the assumption shouldn’t be too far off in one direction or the other.
So the % harvest statistic measures the estimated % of available bucks or bulls harvested regardless of public or private lands and you may be more interested in that number if you have or are trying to gain private access. But the Public Pressure Index is another tool you can use to tease out the areas where the public lands are much more heavily hunted than the private lands. Because the PPI assumes 100% public land harvest, if a unit was 100% public land, the PPI should be the same as the % harvest, but in most cases it is not.
Let’s take a look at some examples. Unit 12 in Colorado is an extremely popular elk hunting unit, which is primarily private land, with some high elevation ranches that are outfitted. This past year, the DAU % bull harvest (which includes several additional units in the DOW’s post hunt population survey) fell to about 31%, which is much better than the mid 40s% of recent years. However, the PPI in unit 12 is 2.218. That indicates 221.8% of the available public land bulls were harvested in 2009. That’s impossible. What is likely occurring is significant private land harvest of the bulls, which also inflates the success rate. There is a similar phenomenon with the units northeast of Craig, units 4 and 441 with over 200% of the bulls available being harvested. Nearly every square inch of land outside of town is outfitted and/or in the Ranching For Wildlife program and it is likely that a disproportional number of bulls being harvested are coming from these lands, which also inflates the success rate. In contrast, in the Book Cliffs, which are almost entirely BLM land, have nearly the same % bull harvest and PPI. If one cares at all about trophy potential, you’d do well to discount any unit which has a PPI over 1.00, which indicates an impossibly high public bull harvest rate.
We all notice the number of nice bucks in the fields while driving through the lower elevation ranch lands, heading up to the Forest Service lands where we intend to hunt. Then when we get there and all we see are little yearling fork horns. This is typical of a unit that has a decent % buck or bull harvest, but the Public Pressure Index indicates a disproportional amount of public land harvest. While I’ve covered this before, I’ll use an up to date example on how to compute the age classes one might expect. Let’s look at unit 4: The DAU% buck harvest indicates about 24% of the available bucks were harvest in 2009. That’s not terrible, as the 2009 state average was about 18%. Remember, deer have a higher natural mortality rate than elk, so the bucks can’t be harvested quite as heavily. Since yearlings are legal, that means the chance of making it be a big forkhorn, or spindly 3 or 4 pointer at age 2 is 76% (100-24), assuming no significant natural mortality. To make it to age 3, deer in that DAU have a roughly 58% chance (0.76x0.76=0.5776). Still not bad and the chance of making it to four years old, at which point nearly anyone would consider harvesting this buck in a leftover tag unit would be about 44%. At 44%, he more than likely he wouldn’t make it to 4 years old, but it suggests there must be a fair number of older bucks out there. But that’s not the whole story. The Public Pressure Index is just 0.883. That suggests almost 90% of the available bucks were harvested on the public land in 2009. So the chance of a buck making it to just 3 years old is nearly incredibly low: 0.12x0.12= 0.0144, or 1.44%. Not impossible, but really, really unlikely.
Now, what about when the PPI is lower than the % buck or bull harvest? The only way that can happen is if the population estimate draws from more than one unit, as it frequently does in Colorado and Wyoming. You should expect some variation in the Public Pressure Index, which should be between half and twice the % harvest number. On occasion a PPI may be much less than half of the % harvest, and in these cases, it is likely that there is not anywhere near the number of deer or elk in that unit compared to surrounding units where the rest of the population came from. Staying with the DAU that makes up units 3,301,4,5,14,214, and 441, unit 14 has a PPI of just 0.069. It isn’t because unit 14 is completely ignored by hunters and the bucks get to live to a ripe old age. It’s because there is hardly any deer on public land to be harvested in that unit. Unit 14 has a 5 year average success rate of just 12.2% in 2nd season, and the hunter density (#hunters divided by sq. miles of public land) is almost 2.9 per sq. mile. There are lots of hunters running around those mountains, but no one is shooting deer. If look at the lower ranked units, you’ll see quite a few units with “good” Public Pressure Indices. Do not be fooled, the stat looks good because there is very little game to be harvested there.
So in review, use the Public Pressure Index to identify units that should be avoided. Avoid units with a PPI exceeding 1.0. The success rate that made you look at that unit in the first place is likely inflated by private land hunting, and if you have any sort of trophy standards at all, you will likely be disappointed. Avoid units where the PPI is half or less of the % harvest, the game density is likely less than it should be on the public lands.
Good luck.