The Alpine Tundra Zone occurs on mountains throughout British Columbia, but especially along the Coast Mountains, in the north of the province

Authors Avatar

The Alpine Tundra Zone occurs on mountains throughout British Columbia, but especially along the Coast Mountains, in the north of the province, and in the southeast corner. It also extends beyond the borders of British Columbia to the north, east, and south. In southeastern British Columbia, alpine elevations start at about 2250 m, in the southwest at 1600 m, in the northeast at about 1500 m, and in the northwest at about 1500 to 1000 m.

with limited areas of continuous vegetation cover. Soils are typically shallow and derived from weathered bedrock. Since cold retards the process of weathering, soils develop slowly in this zone. Occasional areas of permafrost also occur here.

Terrain

At the high altitudes typical of this zone, the terrain is often steep and rugged, with tall cliffs and rocky, snow-capped peaks. Much of the landscape is rock, ice, and snow, but some areas have stretches of flatter, gently rolling terrain, probably smoothed by glacial action. Glaciers also scoured out valleys and shaped steep cliffs and valley walls. When they melted, glaciers left a variety of special alpine landforms such as basin-like cirques. Talus slopes occur where gravity has caused frost-shattered fragments of rock to slide or fall down the slope. In alpine regions, the physical environment dictates the vegetation. Whether the terrain is gentle or extremely rough, the smallest differences in the microenvironment are important. In the open and windy places typical of the alpine tundra, even a few centimeters difference in topography have a pronounced effect on factors that influence plants – soil temperature, depth of thaw, exposure to wind, and drifting snow. The result is a complex mosaic of vegetation and soil types. At the middle and lower elevations of the zone, depending on the topography, there is a mix of patchy or patterned vegetation, along with limited areas of continuous vegetation cover. Soils are typically shallow  and derived from weathered bedrock. Since cold retards the process of weathering, soils develop slowly in this zone. Occasional areas of permafrost also occur here.

Spruce, willow, Birch

Ecology

At lower elevations, the landscape of the Spruce–Willow–Birch Zone is mostly forested. The trees of old forests are primarily a mixture of white spruce and sub alpine fir. In many of the valleys in this zone, the forest cover is made up of white spruce with variable amounts of lodge-pole pine and trembling aspen in the valley bottoms and on lower slopes. Higher on the slopes sub alpine fir dominates the forest. Sub alpine fir commonly forms open forest and woodland on steep, moist, cold, middle slopes, especially on northern and eastern exposures, where it often forms nearly pure stands. Black spruce occurs infrequently on nutrient-poor sites at lower elevations. West of the Rocky Mountains, wildfires have had comparatively low impact in this zone. As a result, extensive seral stands of lodge pole pine are not common here, though they do occur in places such as the upper Jennings and Little Rancheria rivers. From the Rocky Mountains east, large-scale burning to enhance wildlife range has resulted in extensive young aspen stands and grasslands.

Climate

The Spruce–Willow–Birch Zone has the harshest climate of all the forested zones in British Columbia, second only to the Alpine Tundra. Winters here are long and cold, and summers are brief and cool. The mean annual temperature ranges between-0.7° and -3°C. Average temperatures remain above 10°Cfor only about a month in most parts of the zone and up to 3 months in some medium-elevation areas such as Muncho Lake in the drier, eastern portion. Moist Pacific air frequently causes sudden, often violent, local storms during summer. The weather is more settled in winter, but Chinook winds sometimes disrupt the cold spells. Balsam poplar is also uncommon throughout most of the zone, but in Alsek-Tatshenshini it is widespread and often forms the

timberline. Engelmann spruce, paper birch, and tamarack are absent from the Spruce–Willow

–Birch Zone. Shrub-dominated ecosystems are widespread, ranging from swamps and fens to dry colluvial scrub. On some of the driest, poorest sites, usually rapidly drained out wash deposits, an open woodland of lodge pole pine, scrub birch, and ground lichens occurs. Aspen stands are fairly common on drier sites along the major valleys. At upper elevations, the landscape of his zone is essentially scrub/park land that is dominated by fairly tall (1– 4 m high) deciduous shrubs. These are primarily scrub birch and willows such as gray  leaved willow, Barclay’s willow, tea-leaved willow, Barratt’s willow, Alaska willow, and woolly willow. In some areas, groves of stunted aspen and balsam poplar occur at the timberline, usually on steep south slopes. It may be that deciduous shrubs dominate in this zone because they grow quickly during the short, intense growing season, then shed their leaves in late summer, thus avoiding the killing autumn frosts. In some of the high, wide valleys where cold air masses settle, a non-forested mosaic of shrub fields, fens, and dry to moist grassland occupies the valley floor and lowermost slopes. The lower slopes have a skirt of forest, and above the intermediate forested belts, shrubs dominate again. This “double tree line” phenomenon is particularly well developed and striking on the northern plateaus. Some of these valleys also contain permafrost, especially above 1200–1400 m. Elsewhere in the zone, pockets of permafrost occur sporadically, mainly on north slopes. Wetlands in the Spruce– Willow –Birch Zone are usually the richer types, including white spruce and tall willow swamps, sedge fens, and sedge marshes. Acid, nutrient- poor bogs are uncommon. Although sub alpine grasslands occur frequently in this zone, they are usually not extensive.

Boreal, white and black Spruce

Fire and Forest Succession

wildfires are frequent here, especially in the drier areas. Usually started by lightning, these fires are often intense enough to kill most of the trees over a large area. This triggers a process of forest succession where the burned site is quickly occupied by plants well adapted to surviving fires ortorecolonizing burned over habitats. The first plants to grow back after fires are

Join now!

often herbs, shrubs, and deciduous trees such as aspen and willow. Although these plants may dominate the region for a long time, conifers such as white spruce and black spruce often overtake them. In other places, conifers such as lodge-pole pine and black spruce may reseed and dominate an area directly after afire, bypassing the deciduous stage. Because upland forests have many fires, the landscape is a mosaic of stands of various types and ages.

 climate and Terrain

Winters in this zone are long and extremely cold. The summer growing season is warm, but short. The zone receives relatively little ...

This is a preview of the whole essay