A REPORT to The Williams Lake Conservation Company
Ecological Assessment of the Plant Communities of the Williams Lake Backlands
by Nick Hill (Fern Hill Institute of Plant Conservation, Berwick, Nova Scotia)
& David Patriquin (Professor of Biology, retired, Dalhousie University, Halifax, Nova Scotia)
February 12, 2014
The Williams Lake Backlands (WLB), covering approximately 200 ha, are the larger, undeveloped part of the Williams Lake Watershed which includes Colpitt Lake and Williams Lake. The WLB are part of "Purcell's Cove Backlands" (approximately the 1350 ha) which include the land between Purcell's Cove Road and Herring Cove Road from Williams Lake at the northwest end to Powers Pond at the southeast end. Lying only two kilometers from peninsular Halifax, the WLB are near pristine wilderness. We traversed various routes through the WLB on twelve separate days between May 13 and Nov. 8, 2013 to
The WLB present a mosaic of landscapes and plant communities associated with high variability on a fairly small scale in the topography, depth of soil/till, drainage and surface water storage and in the ages since disturbance of the associated plant communities. That variability in turn is related to the presence of glacially scoured hard granite outcrops of South Mountain Batholith, outcroppings of highly folded and metamorphosed Halifax Group black slates and siltstones of the Meguma Supergroup, a contact zone between the two rock types, and glacial till. Overall, the plant communities are those of nutrient-poor, acidic environments and of fire-, wind-, and pest-driven disturbance regimes within a moist temperate, coastal region. Exotic (non-native) species are found only close to roads and houses at the edge of the WLB. These are "old process" plant communities with a high degree of ecological integrity.
The fire dependent/fire adapted nature of the vegetation and carbon dating of charcoal from a core in a Jack Pine fen indicate that fires in the WLB are part of a long-term fire regime that predates European settlement. Indeed, the whole of the Purcell's Cove Backlands is one of the most fire-susceptible landscapes in Nova Scotia, the droughty, windswept high barrens acting as matchsticks. One result is the presence of an old process, fire dependent Jack Pine/Broom Crowberry Barrens community that is nationally unique to Nova Scotia, globally rare and of high conservation significance. In the northeastern U.S., this community transitions to the fire-dependent Pitch Pine/Broom Crowberry community which is well recognized as of high conservation value. The largest single patch of Jack Pine/Broom Crowberry Barrens within the Purcell's Backlands occurs within the WLB, and overall, the Jack Pine/Broom Crowberry Barrens in the Purcell's Cove Backlands are amongst if not the best, representatives of this community in Nova Scotia.
The water regime in the WLB has features of dryland systems, with intermittent stream courses probably accounting for a majority of the water flow. Critical components such as Mountain Holly washes, vernal pools and boulder fields are not currently protected under Nova Scotia wetland and stream course regulations but are vital to maintenance of the larger wetlands and water quality of both surface and groundwater in the area.
The undisturbed nature of this wilderness area, its mosaic of habitats with wetlands, lakes, streams, forest and barrens, and its location by the coast in the most urbanized area of the province make the WLB and the larger Purcell's Cove Backlands significant habitat for both breeding and migratory birds.
It is suggested that conserving the WLB and the larger Purcell's Cove Backlands as natural systems reduces fire risk to adjacent communities compared to allowing more intrusions into the backlands. Implementing strategies such as those promoted in the northeastern U.S. for living compatibly with fire structured pitch pine ecosystems would enhance both fire protection for neighbouring communities and conservation of biodiversity in our backlands.
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A SUMMARY VERSION, focus on fire ecology and fire management:
A Rare, Fire-Dependent Pine Barrens at the Wildland-Urban Interface of Halifax, Nova Scotia. Presentation to the Wildland Fire Canada 2014 Conference, Halifax, N.S. Oct 6-9, 2014 by Nick Hill and David Patriquin
12 page PDF (3 MB); includes 10 pages of annotated colour slides from the presentation.
Summary Given the appropriate geology and climate, fire barrens of high ecological integrity require space and fire, making them increasingly threatened systems. The Purcell's Cove Backlands (PCB), approximately 1350 ha on the Halifax south mainland, are an area of rough terrain with shallow soils and outcroppings of hard rock that have remained without roads or significant settlement except at their periphery until recently. There are many trails and several lakes are popular for swimming. There are frequent fires. The 2009 "Spryfield Fire" covered 800 ha and destroyed eight houses on a street recently developed in an area of Jack Pines. In 2013, we surveyed plant communities and wetlands of the Williams Lake Backlands which cover approximately 200 ha within the PCB. The fire dependent/fire adapted nature of plant species in seven upland vegetation types and carbon dating of charcoal from a Jack Pine Tussock Sedge fen indicate that fires within PCB are part of a long-term fire regime that predates European settlement. One result is the presence of a fire-dependent Jack Pine/Broom Crowberry Barrens community that is nationally unique to Nova Scotia and globally rare. The recent frequency of fire in the PCB appears sufficient to maintain this community. However settlement that impinges on Jack Pine/Broom Crowberry Barrens has involved either their complete destruction or subjected residents to highly elevated fire risk. No further development within the PCB would help to reduce fire threats to habitations, conserve a rare pine barrens and provide several other significant social and ecological benefits.