Introduction

Information Sources

Stop #1
Stop #2
Stop #3
Stop #4
Stop #5 
Stop #6
Stop #7
Stop #8
Stop #9
Stop #10

Appendix 1

Bibliography

Stop # 2. Timber Creek, at the Headwaters

Descending from the height of land and the mountains, we leave the alpine tundra with its discontinuous and sparse vegetation, and enter the arctic tundra. It is a gradual change. Only in the human need for classifying is there really a boundary between the two types. Arctic tundra features continuous cover, in this area usually low to medium height sedge tussocks, with shrubs and heath of similar height.

The type and amount of tundra vegetation depends in part on the soil available. Like soils everywhere, the characteristics of tundra soils are dependent upon the original material it was formed from (see Soils). Within the Old Crow Basin there are a variety of parent materials. Soil can develop on weathered bedrock (the most common surficial sediment), lake-formed sediments, deposits originally formed on ocean floors, and those deposited by rivers. Arctic soils are usually high in organic content, because of the slow rate of decomposition in the cold, and high in silt content as a result of the water transport of the products of glacial erosion.

Permafrost is continuous throughout the basin, with an active layer varying from over 1 m in mineral soils to less than 1/2 m in organic soils. In some areas the soil is only a veneer and active layer depth exceeds 60 cm.

The main type of vegetation in this ecodistrict is the tussock-shrub tundra, characterized by the sedges, Labrador tea, alpine bearberry, Lapland rosebay, dwarf birch, netted and beautiful willows, and mosses. The striking pattern of the streams and drainageways is accentuated by the contrast between the dark green sedge and willow vegetation that follows them and the lighter yellow-brown and orange of the tussock-shrub tundra that occurs between them. The lower part of the gentle mountain slopes are well-vegetated while the upper slopes have patches and stripes of vegetation.

Timber Creek is quite distinctive. It has some flow all summer and meanders its way to the Old Crow Flats to join the Old Crow River. Some of the smaller creeks feeding Timber Creek dry up in summer (these are known as ephemeral streams) and others have what is termed a "beaded" drainage (small round ponds joined by a meandering stream). The small ponds on the Timber Creek floodplain remain water-filled all summer. Wiken et al. (1981) suggest melting ground water as the source of this water. They also suggest that there is an absence of limestone aquifers (permeable underground rock strata which hold water) in the area.

Timber Creek, like others found partly above the treeline, has extensive riffle areas, with shallow water flowing over a rough bottom, causing turbulence. Both riffles and pools normally have a rocky bottom. Alpine creeks are usually clear and contain large numbers of invertebrate animals. Sampling in Timber Creek and others in the Old Crow Basin has shown that the most abundant life forms in these creek bottoms are the insects (in larval form); midges or chironomids, stoneflies, caddisflies, and mayflies (Brunskill et al. 1973). Smaller numbers of other insects such as blackflies, and craneflies are expected to be present in some creeks. The only invertebrates other than insects to be expected in most alpine creeks are water mites (Hydracarina), and possibly snails (gastropod molluscs).

In Ivvavik National Park, open water and stream channels near river icings (aufeis) support spawning, rearing, and overwintering populations of arctic char and year-round populations of arctic grayling (Steigenberger et al. 1974). The higher temperatures of the groundwater sources probably keep these areas ice-free for some distance below the upwelling. In Vuntut National Park there are no arctic char, but there are populations of grayling overwintering in Timber Creek that appear to be associated with the river icings in that area, but this needs field confirmation.

Areas of open water at the headwaters of many streams in this area often have enough dissolved oxygen in the water to allow overwintering of some fish species. Timber Creek supports large numbers of arctic grayling and slimy sculpins in October (Steigenberger et al. 1974). Arctic grayling may move upstream in the fall to open water areas. During sampling in April the only fish captured in Timber Creek were grayling and slimy sculpin (Bryan et al. 1973).

Aquatic Food Chains

The functioning of an ecosystem depends on links among species. Because of the relatively low number of species present in the north, the nature of these links is particularly important. In tracing the movement of energy and nutrients from one feeding group of organisms to another, ecologists use the concept of food chains. A food chain usually begins with plants and ends with carnivores. Semi-aquatic insects, especially midges (chironomids), both adults and larvae are the most important food for fish in these northern streams.

Figure 1.2c  Click photo to enlarge.

Insects and Wildlife

Insects have another powerful impact on life in northern regions. Black flies and mosquitoes that depend on blood from vertebrates (animals with a backbone) can influence or even determine the movements, activity, and location of caribou (and humans!). If we were standing here in the spring and early summer (late June, July) when the biting insects are most bothersome, we would see caribou moving to higher elevations north of the treeline in Vuntut National Park, in particular the cool pediments area, in an effort to escape the mosquitos and other biting pests. This method of avoiding insect harassment is linked to a specific climate effect which results in cooler temperatures at higher elevations. The insects remain more abundant and active in the warm sheltered lowlands (Russell et al. 1993).

As well as moving to higher ground, caribou also escape insect harassment by seeking out late-lying snowbeds. There the cool air and mountain winds double to decrease the efficiency of the insects. These snowbeds also have an impact on other aspect of the northern ecosystem. They are important to the life cycles of many small mammals and insects. In some mountains snowbeds may harbour a very specialized fauna and flora, including the red algae known as "red snow." Snowbeds can be the source of water for smaller streams and can play a role in slope stability and active layer development (Peterson 1974).

In order to survive in the short, cool summer season of the northern Yukon, insects are equipped with many adaptations that separate them from their southern relatives. These include the early emergence of all adults at the same time, early reproduction, long life cycles, resistance to shortage of resources, feeding on a variety of foods, and the selection of discrete habitats, especially those with favourable microclimates (Danks 1981). Insects meet winter conditions by cold-hardiness, tolerance of freezing and selection of specific sites for overwintering.

The activities of mosquitoes (such as egg-laying, emergence and host-seeking) show daily peaks that appear to be related to air temperature. In the high arctic these activities occur at approximately solar noon, depending on cloud cover, rather than in the early evening as in the south (Corbet 1966). Because of the very short summer, the emergence of mosquitoes and other insects, is condensed into a very brief period.

Wolves and the Ecology of Predation

As we continue down Timber Creek, we may be lucky enough to see members of one of the local wolf packs. The valley of Timber Creek is the site of one of several wolf dens in Vuntut National Park. Several wolf packs travel through the Park area and two packs, known as the Thomas Creek Pack and the Blow River Pack, have their home den within the Park (Figure 1.2d) (Hayes et al. 1997). Wolves are of major importance in terms of visitor interest and management concerns.

The gray wolf, one of the two major predators found in the Park, occupies the position at the top of the food chain along with the grizzly bear. Wolves are opportunist feeders and may feed on carrion, and on unfledged birds and eggs, as well as preying on a variety of mammals from small rodents, to snowshoe hare, to caribou and muskoxen. Along with other species, such as the grizzly bear, red fox and many birds, wolves also cross habitat boundaries and feed from both freshwater and land habitats.

Studies of the ecology of predation and the relationships between caribou and wolves in the northern Yukon indicate that wolves are not an important factor in regulating the size of the caribou herd (Hayes et al. 1997). Wolf packs prey on caribou during the fall migration near Old Crow, following and killing caribou as they move along and cross the Porcupine River (Hayes et al. 1997). Predation by wolves (along with grizzly bears and golden eagles) is the primary cause of death for Porcupine caribou calves between 3 and 30 days old (Fancy et al. 1994). Wolves prefer caribou to moose and travel seasonally to keep in contact with caribou herds. The absence of caribou (and moose in the Old Crow Flats in winter means that tundra wolves do not establish and defend territories. Although muskoxen are a major prey species of wolves elsewhere, there is no information on the relationship between wolves and the few muskoxen that have recently moved into the Old Crow Basin area from the north.