by: Zoe Lucas
SUMMER 1988
Shaped by atmospheric and oceanic influences, Sable Island is a sandy crescent some 160 km from the nearest landfall, Canso Head. The island's dune patterns reflect the prevailing westerly winds. Storm trends, ocean currents, waves and tides modify the width and contour of the beaches. Changing sea level inevitably affects the size and shape of the island- though recent research indicates that long-term sand movement may be cyclical. Sable may not be drifting inexorably eastward toward the deep Gully, or washing away as rapidly as once thought.
Topographic stability on Sable Island depends largely on the integrity of its vegetation. Records show that during the last several hundred years the island's vegetated area has been reduced. various studies suggest that following the establishment of the lifesaving station in 1901, destabilization of the dune systems accelerated. Such erosion was probably caused by intensive cultivation and pasturing. Then as now, damage to the vegetation allowed wind blown sand to advance over large areas.
The composition of Sable's plant communities also reflects human impact. During the 300 years of human presence, numerous species have been deliberately or accidentally introduced. Forty-four of the 179 plant species found in recent surveys were probably introductions. Most of the introduced plants, however, have been unable to survive the very demanding environment, and no persist only where buildings or debris afford some protection from wind. Many introduced species may have arrived during dune stabilization schemes at the beginning of this century.
During the years of the lifesaving station, island superintendents expressed concern about drifting sand and wasting dunes. Early attempts to control erosion were chiefly planting programs. Various species, including tussock grass from the Falkland Islands, were planted in hopes that would bind the sand. The most ambitious effort was a 19901 tree planting project. Using materials supplied by the Central Experimental Farm in Ottawa, 69,000 evergreens, 12,500 deciduous plants, 1,000 willow cuttings, 600 fruit trees and bushes and a collection of rhubarb roots were planted. About 25 kg (55 lbs) of Maritime pine seed were also sown. The project was a failure. By 1913 there were only 13 survivors; in 1927 one pine remained.
Today's terrain restoration projects, using native colonizing species such as marram (Ammphila breviligulata), sandwort (Honckenya peploides), and beach pea (Lathyrus maritimus) have made better progress. Efforts of the last decade have focused on areas affected by recent human activity such as unnecessary road building. Work has also been done at vulnerable sites such as dune lines protecting fresh water ponds, and the very narrow regions of the island. Protecting rare plant species and restricted habitats are of equal concern.
Between 1976 and 1984 terrain management work used conventional methods: dykes to reduce flooding, wood-slat snow-fences to encourage sand accumulation and marram grass plantings. While transplanting remains very important, the widespread use of wooden snow-fence has left a lot of metal debris (T-bar supports and wire) after deterioration. This debris is an eyesore; worse, it is a hazard to the island's wild horses.
In 1987 a new approach to restoration on Sable Island began with a program sponsored by Mobil Oil Canada Ltd. Preliminary work included experiments with surplus Christmas trees (balsam fir) as an alternative to snow-fence. Rows of tree were placed to capture sand and protect plantings. Trees have several advantages over snow-fencing. They leave no hazardous debris upon deteriorating. Moreover, they are very effective sand traps, presenting a three-dimensional surface which works well whatever the wind direction. In two months tree-fences have accumulated as much as 150 cm (5 ft.)of windblown sand in previously eroding areas.
The 1988 program continued in June 1988. At first it focused on stabilizing sand accumulated by the 1987 tree-fences. More than 8,500 clumps of marram grass were transplanted. These were carefully collected from areas of healthy growth and good cover, separated into clumps of 8 to 10 stems, and transplanted at the restoration site.
Marram grass thrives on sand accumulation Extra roots develop when sand accumulates around the nodes (areas of active cell division and growth) higher up the leafy stems. In fact, because the ability of marram roots to take up nutrients and water declines with age, the plant's continued vigour depends on developing new roots and thus upon the accumulation of new sand. Sand fences, whether made of wire and wood or trees, are important in transplant programs. While 900 surplus trees were used in the preliminary effort, 6,500 more were brought to Sable Island in June for the second phase of the 1988 program. These trees will trap more sand, protecting the areas of newly transplanted marram and sandwort from erosion or smothering.
Since 1987 we have learned a great deal about terrain management and conservation on Sable Island. Various current studies will increase our knowledge of erosion, sand dune development, and restoration techniques. There is continuing interest in the possible impact of the wild horses. It seems likely that heavy grazing in certain areas has increased erosion. But the horses recycle nutrients, and their minor disturbance probably creates habitat for certain species. thus any erosion they cause may be fully or partially compensated for.
Meanwhile, because of increased awareness and concern about the island's vulnerable vegetation, people working on Sable now take great care to prevent further damage. Each year we understand and appreciate this rare island environment better.
IMAGE: Landscape
IMAGE: Tree fences used to capture sand on Sable Island
IMAGE: Marram grass transplants
