The ‘Missing’ Deer

If you follow the news or social media in New Brunswick you might have the impression that white-tailed deer are vanishing from this Province. These ‘disappearing deer stories‘ are usually associated with condemnations of current and past forest management policies in New Brunswick. If you are interested in forest management, the 2008 Erdle Report provides a comprehensive review of alternative forestry management policies. While management of Crown forest lands in New Brunswick might be far from optimal, the evidence that those practices are having a decisive impact on deer populations is mixed.  Data available from the New Brunswick Department of Natural Resources (DNR) and published by the CBC show that deer populations in the 1970s are similar to those that we have seen in more recent years:

Note that the title in the CBC story referred to above is ‘New Brunswick deer herd down 70% in 30 years, DNR numbers show’; it could just as well have been titled ‘Deer populations revert to 1970s levels, DNR numbers show’. That would have been less-alarming and generated fewer clicks, I suppose.

[If graph cannot be seen, try this]
An interesting observation from this graph is that, while purchase of deer licenses increased as deer populations jumped upwards during late 70s and into the 1980s, the proportionate increase in licenses was far less. That means that while there were more folks hunting, there were many more deer to hunt. Hunters likely saw more deer then, and had more success. Young folks hunting then would be ‘boomers’ today (“Hardly any deer left, nowadays. Damn Irvings! No point in goin’ out now, I sold my gun. Maybe bow-hunting will be more fun. Or turkey”). It should also be noted that the deer population estimates are, in part, based on deer harvest data. That means there is some confounding in the data – we should not read to much into them, and use the data for trends and not much else.

The main take-away from the above graph, however, is that populations of white-tailed deer have fluctuated tremendously over the past few decades, peaking in the mid 1980s at levels over three times the current population. So, the real question in my mind is, why are deer populations fluctuating so much?  Why do they go up and down to such an extent?

First, let’s look at some historical perspective. The white-tailed deer is an invasive species; prior to the 1800s, it was not particularly common in New Brunswick. Reports from early European settlers, such as Nicolas Denys, refer to First Nations people hunting moose, beaver and bear, but not deer. From an article published at the Elements NB website, Stephen Clayden notes:

Although caribou numbers in northeastern North America were already much reduced by the late 1800s from those of previous centuries, the ultimate extinction of the species in New Brunswick, Nova Scotia, and adjoining mainland regions appears to have coincided with the influx and explosive population growth of white-tailed deer. Deer were rare in the Maritimes in the early 1600s, and remained so for most of the next three hundred years. A scarcity of immature forest cover and clearings, their principal habitat, was probably the main factor limiting expansion of the white-tail’s range. But as deer spread northward in the wake of European settlement, both caribou and moose populations were affected. In areas with a high density of deer, many moose succumbed to a mysterious sickness. However, while moose and deer established a somewhat precarious coexistence, caribou perished.”

In other words, the old-growth mature forest habitat that dominated New Brunswick until European settlers began clearing the land was NOT habitat that favoured white-tailed deer. Deer prefer the more open habitat of either natural clearings (along rivers, flood plains, mixed prairie/woodlands, etc) or clearings created by farming – provided that there are wooded areas nearby where they can hide from predators and seek shelter from harsh weather. Clearings support the small herbaceous perennials, grasses and grains that provide excellent deer food. As Europeans cleared the land, the deer population in New Brunswick grew markedly, and the caribou and moose that dominated the old growth forest declined. Again, from Clayden:

A telling glimpse of the reversal in fortunes of caribou and deer in New Brunswick is contained in a reminiscence by guide and outfitter Bert Moore (1883-1972), published in the Winter 1996-1997 issue of the magazine New Brunswick Tree and Forest: “In 1900,” wrote Moore, “there were very few deer in the Tobique–Nepisiguit country, but caribou were there in great numbers.” He attributed the precipitous subsequent decline of the caribou to a rapid increase in the deer population. This, he assumed, led to competition between the two species for a limited food supply, and to the caribou, now supposedly under-nourished and weakened, becoming more susceptible to disease.”

Several summers ago, while exploring one of the large coastal peatlands in Gros Morne National Park in western Newfoundland, I was struck by the signs of intensive caribou grazing and trampling of the ground-inhabiting lichens. It occurred to me for the first time that the similar lichen carpets in many of New Brunswick’s drier peat bogs, especially those of the east and northeast coasts, are unusually pristine. Caribou must have frequented these areas up to the late 1800s. They are unlikely to do so again, however, on this side of the next Ice Age. Unless, of course, we allow the province to revert to old-growth wilderness and thereby exclude the beautiful but fatal white-tail …

So, OK, there were relatively few deer in New Brunswick until the last couple of hundred years, then deer populations increased significantly as farmers cleared land and settlements grew. But why the ups and downs in populations since then? There can be many explanations. A series of very cold winters with deep snow will reduce deer overwintering survival; mild winters with little snow may promote survival; over-hunting may place too much pressure on populations; etc. Unregulated hunting, in fact, nearly wiped out deer in much of the United States by the early 1900s:

“…unregulated year-round harvests of deer, often aided by packs of dogs, night hunting with fire torches, or hunting from boats, coupled with extensive habitat losses during the mid to late 1800s, led to a dramatic decrease in the number of deer…..By the end of the nineteenth century, an estimated 300,000–500,000 deer remained in North America (Downing 1987). Remnant deer populations were small, isolated, and typically confined to mountainous areas, coastal marshes and swamps, and river bottoms that were inaccessible to hunters.

[As an aside, note in the above graph that deer herd estimates and numbers of licenses issued were similar in the early 1970s to current numbers. I wonder if perhaps there were too many licenses being issued in the 1960s and 70s and whether that may have driven the deer population below what available habitat would have otherwise supported. Did the same occur during the late 1980s and 90s when deer populations were falling?]

Habitat changes in New Brunswick over the past 50-60 years have also been significant. In the 1930s, farming in New Brunswick was near its peak:

Early in the last century, farmers in the province worked on a large number of small farms. In 1931 there were 34,025 farms, with an average of 122 acres per farm. By 2006, the number had decreased to 2,776 farms, with an average of 352 acres per farm. However, the total farm area in New Brunswick had gone down, from 4.2 million acres in 1931 to 976,629 acres in 2006.”

That’s a decline in farmed land of over 70%.

Much of that land has reverted to forest – either managed or unmanaged woodlots. Some of that farmland has been converted to suburban development, and some of those suburbs (low density housing on large wooded lots) provide reasonable deer habitat. But many suburbs in large towns and cities do not provide good deer habitat – there is insufficient tree cover, food, or shelter for deer. As forest replaced what was once farmland, deer were deprived of the herbaceous plants and grasses they feed upon. Deer populations thus may fall in extensively re-forested areas and may remain healthy only in ‘one-acre lot’ suburbs, or in areas where there are natural open spaces. Ironically, deer populations have likely declined in many rural areas of the province as farms were abandoned and converted to woodland. We’ve gone from being a Province where a large proportion of residents were both employed and living in rural areas to one where most rural residents are really suburbanites commuting to urban areas for work.

But what about clear-cutting? If you have a large area of woodland where there are few open spaces to provide good habitat for deer, then clear-cuts can provide those habitats. Absent farmland then, clear-cuts can be essential to maintaining large deer populations in forested areas. The huge growth in deer populations in the late 1970s and 1980s (when the deer herd increased to over three times the 1970 population) can, at least in part, be attributed to the spruce budworm epidemics of the 1950s – 1970s. (for some interesting comments on spray programs to control budworm in New Brunswick, see here – “By 1952, large patches of forest in the northern part of the province were grey, i.e., they had been completely denuded”). Those epidemics killed millions of conifers and created natural clear-cuts of a sort, allowing light to reach the lower levels of the canopy and thereby promoting growth of herbaceous plants upon which deer browse. Natural regeneration of such stands can also be adversely affected by deer, if deciduous forests are the desired outcome.

In addition, many budworm-killed trees were no doubt mechanically harvested in order to save the wood from decay or prepare land for re-stocking. Those actions also created large clear-cuts. Although such areas may have been treated with herbicides, it’s important to note that it is only economical to apply herbicides a limited number of times (once per year or less during early years of regeneration) to clear-cuts. The role of herbicide application is not to eliminate competitors but to suppress the growth of competing plants such that the planted conifer seedlings have a growth advantage. These products are not persistent and herbicidal activity is short-lived. Thus, even with herbicide application, there is likely sufficient food for deer. In fact, in some parts of North America, herbicides are an integral part of deer-stewardship programs operated by hunters. In order for herbicide application to significantly affect deer food supply, the deer population would need to be at or near the carrying capacity of the clear-cut – that seems unlikely (and undesirable if your goal is to promote hardwoods).

It seems reasonable to conclude that the clear-cutting that followed the budworm epidemics of the 1950s, 60s and 70s provided, via promotion of large populations of herbaceous plants and grasses, a large increase in good deer habitat, and this likely contributed to the boom in deer populations that began in the mid-1970s. That boom is reflected in the sharp upward direction of the population curve in the above graph. Clear-cuts are generally thought to provide good browse conditions for white-tailed deer.

By contrast, as those planted conifers grew and matured, deer food declined and deer populations eventually fell back to their previous levels of the early 1970s. By the 1990s, however, farmland acreage had collapsed. Consequently, the population distribution of deer has changed from the early 1970s (there are fewer  ‘rural’ deer and more ‘suburban’ deer) while the total population is now at about the same level as it was then. In addition, deer that reside close to ‘one-acre lot’ rural suburbs are often ‘out-of-bounds’ to hunters – that further reduces the hunter’s success rate, relative to the total population of deer. In other words, a smaller percentage of the total deer population is accessible to hunters than was the case prior to the collapse of farming.

Clear-cuts are not always a positive for deer, however. For example, the maintenance of winter deer yards are vital to protect deer during harsh winters. Conifer stands in such yards tend to have lower snow depths than open or deciduous stands; this makes it less difficult for deer to move about. Over-harvesting of conifers in such locations (and thus creation of clear-cuts) would likely be harmful to deer populations. Proper deer herd management would include protection of conifer stands in deer wintering yards. Not all clear-cuts have the same impact on deer.

Bottom line: while weather patterns and hunting regulations influence deer populations, the major determinant is habitat. The loss of farmland and its conversion to forest has greatly decreased deer habitat in the rural parts of New Brunswick. The nature of the forest may have changed from old-growth forest dominated by a mix of deciduous trees and conifers to predominantly a highly-managed forest of relatively young conifers, but, from the perspective of white-tailed deer, the New Brunswick forest is just not that attractive. Given the role that the deer play with respect to Lyme disease and other zoonotic diseases, perhaps that is not entirely a bad thing.

Sources:

  1. http://www.cbc.ca/news/canada/new-brunswick/deer-herd-in-new-brunswick-decline-population-1.3532002
  2.  http://www.cbc.ca/news/canada/new-brunswick/deer-population-new-brunswick-1.3339977
  3. Erdle Report (2008) – Management Alternatives for New Brunswick’s Public Forest – Report of the New Brunswick Task Force on Forest Diversity and Wood Supply.
  4. http://nbdatapoints.ca/another-day-another-new-forestry-policy-for-new-brunswick/
  5. http://www.elements.nb.ca/theme/endangeredspecies/caribou/sclayden.htm
  6. http://www.parl.ns.ca/nicolasdenys/pages1_4.htm
  7. http://www.hww.ca/en/wildlife/mammals/white-tailed-deer.html?referrer=https://www.google.ca/
  8. Paddock, CD; Yabsley, MJ. 2007. Ecological Havoc, the Rise of White-Tailed Deer, and the Emergence of Amblyomma americanum -Associated Zoonoses in the United States. Curr. Top. Microbiol. Immunol. (2007) 315:289–324
  9. http://www.statcan.gc.ca/ca-ra2006/agpop/nb-eng.htm
  10. MacLean, DA; Andersen, AR. 2008. Impact of a spruce budworm outbreak in balsam fir and subsequent stand development over a 40-year period. For. Chron 84: 60-69.
  11. https://forestprotectiontbmavengers.wordpress.com/history-of-the-spray-program-in-new-brunswick-2/history-of-the-spray-program-in-new-brunswick/
  12. Alverson, WS; Waller, DM; Solheim, SL. 1988. Forests Too Deer: Edge Effects in Northern Wisconsin. Conservation Biology 2: 348-358.
  13. Lautenschlager, RA. 1993. Response of wildlife to forest herbicide applications in northern coniferous ecosystems. Can J. For Res. 23:2286-2299
  14. http://www.outdooralabama.com/managing-wildlife-habitats-herbicides
  15. http://www.clemson.edu/extension/natural_resources/wildlife/handbook/white_tailed_deer.html
  16. Vreeland, JK; Servello, FA; Griffith, B. 1998. Effects of conifer release with glyphosate on summer forage abundance for deer in Maine. Can J For Res. 28: 1574-1578, 10.1139/x98-144
Facebooktwitterby feather