With the deer season right around the corner, it’s no surprise that the subject of our deer population and its struggles are a focus of more than a few conversations over a beer in our area.
Over the past several months, I’ve maintained a regular correspondence with Randall Tlachac, a former member of the DNR’s wildlife oversight committee with a solid scientific background, who has been pressuring the DNR for more than a year over what he sees as significant failings on several fronts, including far too limited research on the causes of deer mortality, a lack of follow-through on objectives identified during the agency’s various planning processes, and a deer population model that everyone seems to agree is of limited value. During our discussions, we have exchanged and discussed the few studies that have been done on the connection between wolves and deer mortality and the extent to which wolves are limiting the deer population in our region. Our discussions have also prompted me to undertake additional research on what I believe is another significant factor limiting deer recovery in our region, which is the decline in quality of deer habitat.
Over the next two weeks, I plan to address both of these issues in hopes of illuminating the discussion around our deer population going forward. This week, I’m focusing on the deterioration in habitat and the role it is almost certainly playing in slowing a deer population recovery in our region.
One of the most basic principles of wildlife management is the critical importance of habitat. For any species, quality habitat provides nutritious food sources and shelter that protects them from the weather.
Over the past 50 years in northern Minnesota, we’ve seen firsthand how the varying quality of habitat, even on the same acres, can impact the reproductive potential of white-tailed deer. Keep in mind, 120 years ago, there were no white-tailed deer in our region, because the habitat didn’t support them. It was only after intensive logging opened up the forest and created the right conditions that white-tailed deer moved in, replacing the woodland caribou that had lived here originally. Deer populations boomed for a time in the wake of logging, but as the second growth forests matured, deer numbers began to decline. By the 1970s, our region’s deer herd was at a low ebb as the mixed-aspen forest type, which then made up about 50 percent of the landscape here, had become overwhelmingly mature due to limited markets for timber.
In our region, the mixed-aspen cover type is generally considered prime deer habitat, but its value to deer depends largely on the age of the stand. Aspen stands are valuable to deer for a few years after harvest or other disturbance, because the elimination of the canopy allows sunlight to reach the forest floor, producing a flush of nutritious browse. But several years later, the regenerating aspen trees begin to shade the understory, reducing the availability and the quality of the available browse. For the next 30-40 years, those same stands provide little benefit to deer. Over time, as they near maturity, many aspen stands will develop a coniferous understory, primarily balsam fir, and at that point they begin to provide winter cover for deer, another key element of quality habitat.
In the 1960s and 70s, deer had plenty of winter cover, but quality browse was a limiting factor. Keep in mind, back then wolves were only a factor in a small portion of northeastern Minnesota, bordering the Boundary Waters. Due to bounties that had been in place for decades, wolves had largely been eliminated throughout most of northern Minnesota and were limited to several hundred near the border with northwestern Ontario. While those wolves had an impact in localized areas, their population impact across the entire region was minimal. Nonetheless, the deer population across virtually all of northern Minnesota was far less than today, and the DNR even canceled the deer season entirely in 1971 to allow for recovery. During this period, annual deer harvests ranged from 30,000-75,000, far less than the deer harvest in more recent years.
In the early 1980s, then Gov. Rudy Perpich made a pitch to paper and wood products manufacturers around the country to build plants in Minnesota to take advantage of the huge inventory of mature aspen. The manufacturers responded and new plants popped up across northern and central Minnesota. Timber harvesting increased significantly beginning in the mid-1980s and 1990s, and aspen clearcuts became a common sight in our region. The opening of the Potlatch OSB plant near Cook in 1983, which consumed about 400,000 cords of aspen a year, provided a steady market for wood right in our region.
The increase in timber cutting was a boon for deer and for deer hunters, and deer registrations increased steadily each hunting season. By 1992, the annual deer harvest fell just shy of 250,000 and wildlife managers feared that the deer population in northern Minnesota could grow out of control, with negative consequences for forest growth and agriculture.
The winters of 1995-1997 were a setback for deer as deep snow and intense cold in northern Minnesota provided a corrective. By then, federal protection of wolves had also allowed that species to expand its range, which meant they could exacerbate deer mortality during tough winters.
Even so, the deer population rebounded quickly as more typical winters followed the mid-1990s cold snap. During the 1990s, the region’s deer population had the best of both worlds in terms of habitat, with plenty of clearcuts providing quality browse while sufficient mature timber still remained on the landscape for winter cover.
The good times for deer hunters quickly returned and by 2003 the annual harvest peaked at nearly 300,000 deer. Even here in the North Country, the DNR was offering hunters multiple permits. By then, wolf numbers had likely reached carrying capacity in our region and the range was expanding quickly, both as a result of continued federal protection as well as the burgeoning deer population. But with quality habitat, deer were clearly able to maintain exceptionally high numbers despite mortality from wolf predation and a significant increase in the hunter harvest of female deer.
Changing markets
But the good times for deer hunters wouldn’t last. By the mid-2000s, the region’s surplus of mature timber was mostly gone and stumpage prices spiked to unsustainable levels. Under financial pressure, some of the board plants began to close, including the former Potlatch plant near Cook, then owned by Ainsworth, which closed in 2007.
Harvest levels fell significantly, and even more precipitously in our region, since the Ainsworth plant had been the primary market for aspen wood in northern St. Louis and Lake counties. Stumpage prices fell dramatically and much of the wood that had been coming from private lands dried up as that happened (See Figure 1 on previous page).
The changes in markets had no immediate impact on the deer population, but as the acres cut in the early 2000s began to age, without as many new acres of clearcutting to replace them, access to quality browse for deer began to decline. And just as that was happening, the region began to experience a major infestation of spruce budworm, which has killed countless balsam fir, wreaking havoc on the cover that deer need to survive winters here.
Middle-age bulge
There are plentiful data to support this narrative. Inventory data (see Figures 2 and 3) produced by the DNR, shows how the age class distribution has changed. As Figure 2 shows, the age class distribution was like a pair of bookends by 2000, with 1.5 million acres in the 0-10 age class and about 1.3 million acres aged 51 years or older, with much lower acreage in those year classes in the middle. Compare that to Figure 3, from 2020, which shows the age class bulge on our aspen-type acres is now between 11 and 40 years of age— the exact ages of least value to deer.
It also shows that the total acreage in the 0-10 age class (the best for deer browse) has fallen from that 1.5 million acres across the region in 2000, to just 600,000 acres as of 2020. There is no way that’s not going to impact the productivity of the deer herd.
What’s more, Figure 4 shows that balsam fir mortality is now exceeding annual growth by a substantial margin, and that’s almost certainly impacting winter cover. So, even if we allow for a longer rotation age on aspen acres, it’s less likely that we’ll see the development of a spruce-fir understory.
While most folks are quick to blame the DNR for the current situation, it’s worth noting other data from Figure 3, including that the bulge in middle-aged aspen acres is occurring overwhelmingly on private land.
When stumpage prices dropped after the wave of plant closures, private landowners largely lost interest in selling timber (per Figure 1). And over the 15-20 years since the plant closures, all those aspen acres have grown up to the point where they offer little in the way of deer habitat.
The result has been a remarkably steady decline in the number of deer registered in Zone 1, which encompasses roughly the northeastern third of the state, where the aspen cover type is most dominant. That’s a solid correlation between the reduction of aspen harvesting, the decline in balsam fir, and a drop in deer numbers.
While wolves are a clear contributor to deer mortality, as we’ll discuss in next week’s installment in this series, there is no data (mostly because the research has not been done) to suggest that wolf numbers have changed as dramatically as deer harvests over the past 20 years, at least in our area. What research is out there points to range expansion as the primary cause of any growth in the state’s wolf population. Traditional wildlife biology research has shown that predator populations are closely tied to prey populations. Given the decline in deer numbers in our region over the past 20 years, it would be contrary to our traditional understanding of predator-prey relationships to think that wolves were increasing in density in our region at a time when their primary prey was declining.
What we know for sure is that habitat matters. There’s a reason hunters register a lot more deer in PA 177 than 119, for example. PA 177 has more agriculture in its western half (i.e. better habitat) so there are more deer found there. That concept applies across the northeastern Minnesota landscape. As the habitat changes, the ability of the land to produce enough deer to satisfy hunters is directly affected. We’re seeing the effects of that reality today.