Caribou, amongst many other species, are in rapid decline across the boreal forest and have become locally extinct in many areas (see Banff and Pukaskwa National Parks) or are likely to do so. The underlying reason for this decline is not disputed. Ecologists, the public and government alike agree that it’s a symptom of industrial habitat modification and loss. What is contentious is what, if any, our response should be.
Before wading into possible responses, it’s imperative to understand the reasons why caribou are declining. The #1 cited reason is “apparent competition”, which means that human modifications to the landscape are favouring other ungulates (deer), which aren’t problematically competing for resources (food, space) with the caribou but are supporting higher predator populations (wolves) which negatively affect caribou as well. The second mechanism is simpler. Roads built into formerly wild areas allow wolves to more efficiently access caribou refugia in the deep woods. Thus wolves become more efficient predators, particularly with regards to caribou which have low reproductive rates.
The core problem – industry – is indisputable but no one wants to curtail industry for fears that ecological preservation would come at the expensive of wealth. This is especially true because decision making parties (i.e. the Alberta government) are often some of the largest benefactors of industrial expansion (i.e. oil sands). Since the Canadian Species At Risk Act (SARA) mandates provincial governments not to allow species to go extinct, the popular “solution” is a wolf cull. Such a practice has been in place for several years in Alberta and the Yukon, and is being eminently considered in other areas (British Columbia). The lip service is that a wolf cull is a stop-gap measure while habitat is restored, but such restoration shows no signs of beginning, and would take decades. A good estimate is that large areas of forest would need to have the roads removed and allowed at least 50 years of recovery before caribou would have a positive growth rate (personal conversation with a wolf-caribou guru).
The ethics of a wolf cull are contentious, as wolves are either being shot inaccurately from a helicopter hovering over the thick forest or poisoned with strychnine, a truly undesirable way to go that involves hours of convulsions prior to death. Such poisoning is not species specific and has substantial side mortality on species ranging from ravens to endangered fishers to lynx. However, the logic of a wolf cull seems impeccable: less wolves = fewer caribou being eaten = larger caribou populations. But ecology is never that simple, as the folks who introduced the cane toad into Australia to combat beetles will surely tell you. Below are several reasons why a wolf cull is problematic.
1) The social structure of wolves typically involves one breeding pair per pack. As wolves are shot, packs become fragmented and form multiple, new, smaller groups. The outcome is that at up to 50% cull rates, wolf populations are capable of replenishing if not growing. Thus you get results like this paper, where wolf populations showed no decline despite an annual 50% cull. That’s why it took a truly fantastic effort to eradicate wolves from the lower 48.
2) If you do successfully reduce wolf populations, as the Yukon did with a 70% annual cull, then you hit several new problems. The first is commesurate a rise in other predators, such as the mesopredator release hypothesis. Mesopredator release is the phenomena where the removal of a top predator causes subordinate, secondary predators to increase in abundance. This is commonly seen by the proliferation of racoons in urban areas where apex predators are absent. For the woodland caribou, a drop in wolf populations would likely be offset by an increase in the populations of coyotes, which are equally adept at killing caribou since the vast majority of caribou kills in the boreal forest are on very young juveniles. Similarly, other competing apex predators like cougars would also experience reduced competition and would likely increase in number to maintain predation on caribou. Where there is an opportunity, someone is likely to fill it. Thus, a wolf cull may not generate the anticipated reduction in predation since they aren’t the only predators on the land.
3) If a wolf cull did successfully lead to a meaningful drop in predation on caribou, the next issue is an explosion of competing ungulates who would surely benefit as well. Other ungulates are already favoured in these modified landscapes and a drop in predation would enable even higher growth rates. Quite likely deer – with their high fecundity – but also moose and elk, would rise rapidly and begin to directly compete with caribou for food, breeding sites or overwintering habitat. As caribou have quite low fecundity, they are the least capable ungulate of exploiting a void in predation. Thus there is no reason to think that a void in predation would be a net positive for caribou. Furthermore, creating a landscape with a Smörgåsbord of ungulates would allow wolf populations to recover at amazing speeds if a successful culling program was halted.
Human modifications of the boreal forest have reached a threshold were caribou are no longer competitive. If we are okay with this, we can simply let them go locally extinct and accept the new deer ecosystem we have created. If we aren’t okay with this, we must begin substantial restoration efforts to start the long process of recreating viable caribou habitat. As most caribou populations aren’t on track to persist long enough to see this come to fruition, some intervention would be required to slow their decline. Massive wolf culls (~70% of the population annually) are a viable short term solution (1-5 years) but their efficacy will decline over the medium term due to rising populations of other predators and competitors. A more effective approach would be a simultaneous culling of both wolves and the competing ungulates that are supporting the wolf’s rise, followed by sustained culling of the other ungulates, and wolves as needed, to prevent wolf populations from rebounding and other predators from increasing. This could potentially work in the medium term (5 years to a few decades) but the complexities of ecology likely include many subtle reasons why this won’t work in the longer term and thus true restoration of the land is still required. The real question is are we serious about achieving this? Or are wolf culls just a token gesture as the caribou are on their way out?
My personal opinion is that there are a slew of reasons why we would should conserve large, functional examples of all habitat types including the boreal forest. The value provided by caribou (tourism, hunting, intrinsic value) is one such reason, but also important are the substantial ecosystem services (i.e. clean air, clean water, food, C02 sequestration) and recreation opportunities the boreal forest provides to humanity. By setting clear limits on our industrial activities in the boreal forest, we can preserve and restore functional examples and reap many benefits including the persistence of woodland caribou.