SpruceRoots Magazine - July 2004
|The Pontoons, Tlell River, Haida Gwaii|
a rare ecosystem
|from the Tlell River Watershed Legacy Project
By Erica Thompson
|8 kilometers west of Lawn Point lies one of Haida Gwaiis most distinctive wetlands and it is a landscape rarely encountered along BCs northern coast. This area known as the Pontoons sweeps across 690 hectares, a mere 30 metres above sea level. Here exists the literal heart of the watershed, where the Tlells major tributaries converge and drop their sediment loads before proceeding as one body through forest, towards the sea.
Hans Roemer, a plant ecologist working for the BC provincial government, first surveyed the Pontoons in 1979, with field assistance from Keith Moore. The research was in effort to secure ecological reserve status for the wetland the project was designed to protect rare and endangered species, critical and unique habitat areas.
The Pontoons exhibits the only ecosystem on Haida Gwaii where extensive meso- and eutrophic wetland ecosystems, or shallow waters rich in nutrients and plant diversity, occur away from the coastal shorelines. Nearly nine kilometres long and three wide, this shallow inland depression, is bordered by gentle slopes, forest and bog. All major tributaries of the Tlell River, except Geike Creek, converge at the Pontoons where flooding is common and known to be furiously fast. The Pontoons feature braided river channels, sloughs, ponds, swamps, marshes, raised peat bogs, surrounded by sparsely treed wet forests and the local topographic diversity and nutrient rich sediment transported form the tributaries produces a dramatic mural of plant species. Open, wet meadows, mud bottomed depressions, dense shrub areas, found mainly along the river and sloughs, openly treed sedge meadow with scattered shrub, forest bog, oxbows, and open peat bog house species, such as Sitka Sedge, Bog Orchids, Marsh Violets, Bog Bean and the perennial herb Great Burnet. The wet forests house sparse stands of Western Hemlock, Western Red Cedar, Sitka Spruce and Red Alder.
In the Pontoons, Roemer noted plants rarely found on-Island, such as marsh speedwell (Veronica scutellata), tufted loosestrife (Lysimachia thyrsiflora) as well as the provincially rare water plantain buttercup (Rannanculus alismaefolius). Wildlife observed within this area were sandhill cranes (probably nesting), trumpeter swans, black bear, beaver, muskrat, Oregon junco, Stellers Jay, Rocky Mountain Elk, Canada Goose and common snipe.
Twenty years ago, Roemer and Moores report noted that traces of human activity had all but vanished from the inland area, with the exception of a skid road and remnants of a bridge and several cabins. One of the most influential factors in landscape modification noted by Roemer were the introduced species inhabiting the area.
However, the introduced elk, black tail deer, and beaver are present and presumably will have a strong influence on vegetation in the long run, he noted.
Though the area has not been designated a protected area to date, the Pontoons remains as ecologically unique and largely unvisited as in the times of Roemer and Moores field work. An examination of the area, prepared for the Tlell Watershed Society, indicates little has changed in the heart of Tlell. The earliest aerial photographs of the area available date back to 1939. Additional photographic records from 1966 and 1997 indicate relative stability of the forests and vegetation around the Pontoons perimeter, and on adjacent small elevated slopes. No obvious sediment deposition in the Pontoons was observed from any of the sub-basins, says the report.
The topography of the area is the result of either historic glacial scour or ice stagnation. Large historic glacial outwash fans from the Upper Tlell and Survey sub-basins, which may have originated as deltas building into Hecate Strait, have prograded into the Pontoons area, says the hydrology report
For the community of Tlell, the Pontoons function as natural flood prevention insurance, mediating an average 155-cm of precipitation a year, absorbing high water events by flooding into one wide and shallow lake. Local residents say there is an average two-day lag between high rainfalls and the Tlells peak flows past the community; a natural safeguard against frequent flash floods.
|Wetland Habitat Types
Fens: These wetlands are characterized by a high water table with slow internal drainage by seepage down low gradients. Their surface waters may be acidic or alkaline. Fens have more nutrients than bogs and are consequently more productive and although sedges dominate fens, they may contain shrubs and trees. Like bogs, they are more common in the north.
Bogs: Bogs are peat-covered wetlands in which the vegetation shows the effects of a high water table and a general lack of nutrients. Due to poor drainage and the decay of plant material, the surface water of bogs is strongly acidic. Although they are dominated by sphagnum mosses (peat) and heath shrubs, bogs may support trees bogs are the least productive of all wetland types.
Marshes: These wetlands are periodically or permanently covered by standing or slowly moving water. Marshes are rich in nutrients and are characterized by emergent vegetation of reeds, rushes, cattails, and sedges. Water remains within the rooting zone of these plants for most of the growing season. Marshes are the most productive wetlands habitat.
Environment Canada, Habitat Types & Species Protected, Click here for more info.