Tom drew circles in the snow to show proper and improper crown spacing and railed against the foresters that marked the trees. “They should have known they would convert this stand to hardwoods.”
Soil moisture — that was a key. Different soil types hold more or less water. In sequence, dry to moist, jack pine grow on sandy soils, red pine on slightly coarser sands, white pine on sandy gravels, poplars and red maple on coarser gravels, and tolerant hardwoods on loams. The latter are found only in scattered patches on the east side of the park.
These soil-forest relationships prevail within the broad climate belt that runs across the east side of the Algonquin dome, where annual precipitation is a relatively low seventy-two to seventy-six centimetres per year. West of Algonquin Park, where annual precipitation is greater, even shallow, sandy soils are moist enough to grow tolerant hardwoods.
Within the dictates of soil moisture, shade often is the final arbiter of forest composition. Even on good soils for intolerants, if enough trees are left after logging to provide shade, pines will succeed where intolerants struggle and fail. However, if too few trees are left, the intolerants find both ideal soil moisture and sunlight and will outcompete the pines. Most of the Bonnechere Valley, logged over the previous eight years, intermediate in soil moisture, is coming back to intolerants because the cuts were excessive.
Ironically, despite plenty of sunlight, young pines often line the edges of the logging roads in the Bonnechere Valley like false-front western pioneer towns and fill the log landings where logs were loaded onto trucks. While they create an illusion of good pine regeneration, they present only a façade. The soil in these locations was compacted by heavy machinery, reducing soil moisture and thereby growing pines. But look behind the false front and you see a future deciduous forest.
The AFA is aware of the problem and has sent tree-planting crews out for a few days each spring, but they plant only a small percentage of the cut-overs. Unable to use herbicides in the park, maybe chain saws will be brought in for future “stand improvement.” Ecosystem mistakes are not easy to reverse, an argument for establishing parks and leaving them alone.
Moose, deer, and beaver do not share our concerns about the vanishing pines. Just the opposite is true. They quietly go about capitalizing on the increased food the intolerants provide, simultaneously levying their own impact on the forest. Again it took some years for us to recognize their effects. Several years ago, Mary and I were trapping in the Mathews Lake territory and running browse transects up near the Petawawa River. We set up camp in the pines beside an unused logging road. The cold black waters of Lone Creek slipped by into a foam-flecked pool below. As usual a scattering of hermit thrushes and winter wrens were practising their prelude to spring.
As we filled our notebooks with data, we noticed that in the pine cut-overs a greater percentage of regenerating poplars and red maples were browsed than we were used to seeing in the Bonnechere Valley. In some places browsing had been so heavy for so many years that the poplars had died. Without competition, small pines were doing well. Obviously browsing was holding back the poplars and red maples to the advantage of pines. Ironically, since moose do not eat pines, they were working against their own future, but neither natural selection nor moose can forecast the future.
After a week of trapping, we caught a Mathews wolf, so we left for the Bonnechere Valley to confirm our perception that a lower percentage of stems was being browsed there. We were right; in many places regenerating intolerant saplings were so dense you could hardly push your way through, but a lower percentage of them was browsed. Soil and sunlight were so favourable to the intolerants that the ungulate population could not keep all the saplings down. If they missed a red maple leader for three years in a row, it would spring up nine to twelve metres, beyond moose reach.
From this evidence, we realize that very subtle differences in soil moisture and shade can switch the direction of ecosystem control. In the Bonnechere Valley, moose and deer ride forest change, their browsing largely irrelevant; in the Petawawa Valley, however, they drive change by altering the upcoming forest stand. Somewhere between the dry sands and the moister soils, with just the right amount of shade, may be a more equal battlefield where ungulate browsing on the intolerants may balance annual growth. There, moose and deer, inadvertently, would be practising “sustainable forestry.” We have not found such a place; the system is just too dynamic. Ungulates have as much difficulty practising sustainability as we do.
Above the sun visor of our truck, and that of the two vans used by student crews, are file folders marked “Ungulate Observations.” On the forms we record every moose and deer we see, with its age and sex, location, and the number of kilometres driven that day or night. All the data, duly entered into the computer, provide an index of their changes in abundance, an important annual checkup.
Our most common view of a moose is from the rear as it thunders down a logging road to get out of our way. Sometimes at night a moose will refuse to leave the road. It will run ahead of us until we feel guilty, stop, and turn off the headlights. When we turn them on again, often the moose is still standing there, or if not, it is just around the next curve waiting to again show us its rear end and flying hooves.
Each summer there is a distinct peak in the number of moose and deer seen per one hundred kilometres driven in June, followed closely by May, but there is a big drop in July and another in August. The same seasonal pattern appears in both daytime and nighttime observations. We suspected that the decline was related to the end of the growing season and a rapid deterioration in food quality. With less to gain from browsing, and the ever-present wolves searching for scent trails, moose and deer may find it advantageous to switch from being energy maximizers feeding all the time to energy conservers.
Many studies have shown that protein, nitrogen, and phosphorus levels are highest in rapidly growing stems and leaves, and that they drop after new growth is complete. As well, unpalatable chemical compounds, plant defences against browsing, accumulate over time especially as the energy required for plant growth declines and can be shunted to their production.
We had a hunch that the growth sequence of the plants was a factor in the changing behaviour of the ungulates. To assess whether this was the case, we had to determine if red maples and poplars stopped growing when deer and moose became scarce at the end of June. We spent a few hours each day measuring new growth, tying red flagging tape to the stems so we could find them again. When we remeasured at the end of August, we found that the red maples had not grown at all since the end of June, the poplars only by 30 per cent.
We repeated the measurements the next summer. Spring was late that year, 1996, and new growth on the red maples was not complete until mid-July. But the sudden drop in ungulate sightings, normally occurring at the end of June, occurred two weeks later too. We felt good; we had one piece of evidence that fit the hypothesis.
Research in Michigan helped us discount a general, weather-induced lethargy in late summer as the reason for less moose and deer activity then. Biologists P. Beier and D. McCullough showed that radio-collared deer increased their activity in August. This increase occurred in the absence of wolves, the one markedly different condition between our studies.
To further examine our hypothesis, we had to find out if wolves were less successful in catching deer and moose after the ungulates became less active. We analysed our collection of wolf scats in the expectation that the proportion of beaver would go up in the last half of the summer to compensate for a decline in deer and moose. Our guess was wrong; beaver in wolf scats peaked in early May, when beaver spend much of their time foraging on land immediately after the snow melts. There was no sudden increase in beaver in the latter half of the summer.
That could have nullified our hypothesis except one day while bumping along a logging road, Mary remarked that many of the wolves we catch in May and June appear to be in better shape than those caught later. We even have had a few
cases of wolf starvation in August and September. Perhaps the proportion of each prey species relative to one another does not change in the last half of the summer, but the total food intake drops.
With all our capture data on the computer, that possibility was easy to test. We found that average adult weights fell only slightly in the last half of the summer, not enough to be statistically significant, but we caught both smaller and larger wolves then, especially adult females. Yearling males in July and August, however, were 5.7 kilograms (12.5 pounds) lighter than earlier in the summer, although our sample size was small. So, we concluded that there was some evidence of food stress in Algonquin wolves in the last half of the summer.
The foolproof evidence in support of our hypothesis would be to find that wolves really are less successful in finding moose and deer in July and August. While that just seems reasonable, we have no data to inspect. Here our hypothesis rests, tantalizing us with some supporting evidence but not enough.
There is another intriguing relationship between ungulates and wolves. For years we have carefully noted whether stationary wolves were found in uplands or lowlands. Wolves move through all habitats, but in more than 90 per cent of the locations when we get three good cross-bearings on a stationary wolf, it is in lowlands, usually within fifty to one hundred metres of a lake, stream, or bog.
If wolves are predominantly creatures of the lowlands, you might expect their prey to be more abundant there too. Or, alternatively, natural selection and avoidance might work against deer and moose frequenting lowland areas.
Neither is true. Our data reveal no pattern in deer movements, day or night, early summer or late. Moose tend to be near water more often, but likely for the dual benefits of feeding on aquatic vegetation and cooling their big, black bodies.
Is natural selection on hold? Is there some balance between costs and benefits that we do not know? Is there some long-term cycle — wolves in lowlands, ungulates in uplands, switching to the reverse — that we are unable to recognize with short-term research? Or do wolves kill deer and moose everywhere and just for some reason prefer lowlands for lying around?
Anyone who disassembles and reassembles a machine usually has a few nuts and bolts left over. The machine may work fine without them, or does so until conditions change and the loss makes itself known. Parelaphostrongylus tenuis, a tiny roundworm parasite common in deer, is like that, an inconspicuous ecosystem component. Moose and deer both pick it up by accidentally ingesting snails that have crawled over the droppings of infected deer. In the spirit of being a good parasite, P. tenuis does not kill its deer host. Such an ideal relationship exemplifies evolutionary accommodation achieved over time.
The larvae show up on deer droppings. We collected them at the height of our interest in P. tenuis. One time we emerged from the trees onto a logging road with a plastic bag of droppings just as a pickup truck was going by. The driver jammed on his brakes and backed up. After chatting about the weather for a few minutes, he got to the point. “What have you got in that there bag?”
“Deer shit,” I replied.
“Deer shit?” I let him think about it for a few seconds, fully intending to tell him why, but waited a bit too long.
“Well,” he broke the silence, “to each his own,” and he stepped on the accelerator, leaving us in a cloud of dust.
Had he waited a second more, or had he asked, I would have explained the story of P. tenuis. A humble roundworm less than one centimetre long, it lives happily in deer brains. It gains access to them by tunnelling through a deer’s stomach to its spinal cord, then travelling up to the brain where it encysts, matures, and lays eggs. The eggs pass through the upper respiratory system, then the digestive tract, and are finally liberated in the deer’s droppings. There the eggs hatch into larvae and wait for a snail to ingest them and renew the cycle.
White-tailed deer evolved in North America, presumably with P. tenuis. The two creatures worked things out so that P. tenuis could live as a free rider, neither harming nor helping the deer. But with moose, this little leftover part of the web takes on significance. Moose evolved in Eurasia and are comparative newcomers to North America. They have no signed agreement with P. tenuis. So P. tenuis kill moose, committing suicide in the process. Shakespearean tragedy. On the way from its entry point in the spinal cord to the moose’s brain, P. tenuis destroys nerve cells. Separating mind from body does a moose no good; infected animals run in circles until they die. Unwittingly, P. tenuis larvae must realize they are in trouble as the temperature falls around their spinal cord home — bad luck that their snail host was picked up by a moose instead of a deer. The parasites will rot with the moose in the spring.
In Murray Lancaster’s parasitology lab at Lakehead University, the droppings we collected were scrutinized microscopically to find the incidence of infection in Algonquin deer. The answer was about 90 per cent, with some uncertainty over identification. Its larval form is practically indistinguishable from other, nonpathogenic members of its genus.
We don’t know how many moose carry the parasite. Although we stockpiled moose heads for a time with the view to having them examined, we have observed disoriented moose in our telemetry flights too rarely to justify the cost of analysis.
Maybe something will trigger a P. tenuis epidemic some day, such as a greatly increased deer population infecting the range more heavily with larvae. If so, browsing pressure by moose will decline, balsam fir will grow unimpeded, and spruce will lose out for a while in competition with the fir. The web will adjust. Or P. tenuis may never rise to prominence and remain an insignificant ecosystem part.
Other seemingly insignificant players in the wolf web live as free riders inside wolves. We have participated in the autopsies of many wolves in the post-mortem room at the University of Guelph’s veterinary college, where Ian Barker and his pathologists Doug Campbell or, in the earlier years, Trent Bollinger presided. Many wolves we had come to know well in the wild ended up stretched out on the stainless-steel table with scalpels, scissors, saw, notebook all arranged around their heads. Mary and I, or Graham, usually attended to take measurements and collect the head and small pieces of heart, liver, kidney, and muscle in plastic bags and bring them back to our freezer in the ecology lab. Later the wolf bits and pieces would be shipped to McMaster University for DNA analysis. With the detachment of surgeons, Ian and colleagues made many interesting discoveries.
The intestines of many of our subjects harboured tapeworms, Taenia species, often about thirty centimetres long. Living a life of comfort and ease, so long as the wolf was eating, these tapeworms robbed the wolf of some nutrition, but not much. They caused little harm in a friendly if one-sided relationship that the textbooks call commensalism.
In the intestines of approximately one-quarter of the wolves was a tapeworm measuring only a couple of millimetres called Echinococcus granulosis. Under a microscope it looked like a slender bag distended with eggs. Usually the eggs were spilled out, crushed by the cover slip on top of the slide. The eggs made us shudder. If a human gets one under a fingernail and takes it in through mouth or eyes, the egg hatches in the host’s liver and destroys its functions, which can be dangerous. In moose or deer, however, the maturing egg causes little harm because disease and host have evolved together. A wolf, eating an infected moose or deer, picks up the immature tapeworm and offers it sanctuary for the rest of its life cycle, passing eggs out in its feces.
Even more insidious are viral diseases: rabies, canine distemper, canine parvovirus, and canine hepatitis. Tests were run on blood serum we took from wolves when we collared them. With no refrigeration, we had to drive out to the Pembroke Animal Hospital immediately to have the blood spun. Exposure to viruses is shown by antibodies — defences manufactured by animals — in the serum.
Algonquin wolves have been exposed to canine distemper, canine parvovirus, and canine hepatitis, shown by antibodies in 46, 83, and 76 per cent of animals tested, respectively. These results are not surp
rising, because all three viruses are common in North America; most domestic dogs get exposed and develop antibodies too. But the patterns and levels of exposure worked out by Ian and his colleagues revealed something of the viruses’ ecology. Canine distemper survives poorly outside a canine animal and, like the common cold, requires nose-to-nose transmission from one animal to another. Our samples showed that an epidemic occurred in 1989 and 1990, abating after that. Its occurrence was high in only a few packs, as expected for a disease that requires animal-to-animal contact. There is logically more contact within than between packs.
The other two viruses can live for years in wolf feces. They may even survive winter temperatures. All it takes is a good sniff by an investigating wolf to get infected. Before a wolf pup is eight weeks old, maternal antibodies to canine parvovirus from the mother’s milk will fend off the disease. These antibodies decline, however, leaving the animal susceptible between eight and twelve weeks of age, after which they normally build up enough to protect the young animal again.
Canine parvovirus was unknown before the late 1970s. Mutating from feline parvovirus, it quickly spread among dogs all across North America, possibly killing about 10 per cent of them. By the early 1980s, it was no longer a serious killer in older canines, however, because background, low-level exposure promoted antibody formation before the virus could kill. Pups exposed to a heavy infection during their susceptible period, though, still may die. Rolf Peterson suspects canine parvovirus caused the wolf population to decline on Isle Royale. Seven out of eight Algonquin pups tested were positive, but these animals, caught late in the summers, were the survivors. We have no way of knowing how many may have died.
Wolf Country Page 15