Why Are We Restoring Burns Bog?
The ecological integrity of Burns Bog faces a range of challenges resulting from many decades of peat extraction, drainage, filling, conversion to agriculture, and adjacent urban and industrial uses. Drainage ditches and survey lines were cut through Burns Bog in the early 1900s, but the most significant drainage activity is associated with peat harvesting (1940s-1980s).
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Archival photos from a Western Peat Brochure |
Before peat mining and conversion, the Bog covered about 48 km2 with much of the peat mass 4-5 m above sea level and the adjacent delta surface. During the 20th century, the Bog’s area was reduced to about 30 km2 and an average elevation closer to 2-3 m above sea level, with west and south portions remaining unexcavated.
Draining, peat extraction, and clearing radically altered the hydrology and plant communities of the Bog. The centre was extensively mined for peat using various methods and resulting in the creation of many large ponds, large bare and recovering scraped fields, and ditch and ridge topography. After disturbance in the middle of the Bog, Sphagnum recolonized depressions, pine growth increased on ridges, and many sites were widely invaded by native and non-native bog species such as paper birch (Betula papyrifera) and European birch (Betula pendula). The result is a patchwork of regenerating plant communities of various ages.
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Historic vegetation map and example of historic bog plant community (Photo: Paul Whitfield) |
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Current vegetation map and example of recently established forested plant community (Photo: Paul Whitfield) |
One hundred years of peripheral drainage and lowering of the surface in the bog centre favoured widespread expansion of pine (Pinus contorta var.contorta)-salal (Gaultheria shallon) forest and invasion of non-bog trees such as western hemlock (Tsuga heterophylla). Extensive birch woodland arose and expanded particularly on burned and cleared sites. The lagg zone was especially impacted by filling and conversion to agriculture such that little of it remains intact today either ecologically or hydrologically. The water table near the bog margins was sharply lowered, and it now declines to more than one metre below below the surface in the pine-salal woodland zone.
The lower water tables result in drier surface vegetation and a higher fire risk. Fires in the last two decades consumed about 20% of the bog vegetation, including previously undisturbed peat-forming plant communities. In response to a large bog fire in 2005, The Corporation of Delta developed a Burns Bog Fire Management Plan, which is updated annually. Delta also worked with Metro Vancouver to put staff protocols in place to minimize the risk of fire caused by human error.
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2005 fire in Burns Bog (Photos: Tony Hemsley) |
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