Plant community responses to disturbances in the western Canadian Arctic

Data are presented on several current studies being conducted in the Mackenzie Delta and the Arctic Archipelago in relation to oil and gas exploration. Tundra fires destroy most of the aboveground plant cover and result in significant increases in depth of the active layer. Fire stimulated the growth and flowering of Eriophorum vaginatum subsp. spissum and Calamagrostis canadensis. The recovery of dwarf heath shrubs from rhizomes was relatively rapid while lichens and mosses showed no early recovery. Crude oil spilled in different plant communities killed the leaves of all species, yet regrowth occurred on some woody species the same summer and more species showed regrowth the second summer. Oil spilled in early winter (October) and in wet sedge communities in summer appeared to be most detrimental.Percentage plant removal has been significantly reduced with changed seismic technology in the past 6 years. Native species, often from rhizomes, reinvade all lines though recovery on peats and by native grasses appears most rapid. Winter roads of compacted snow were less detrimental to wetland sedge communities than to upland dwarf shrub – sedge – heath ones. Upland sites, which were dry in summer, were more difficult to revegetate. The revegetation studies indicated that 100 kg/ha of elemental nitrogen and 200 kg/ha of phosphorus treatment was best and that early spring or late fall seeding was essential. About five perennial plus two annual grass species in varying mixtures grew best in the reseeding trials. The supply of available nitrogen appears to strongly limit plant growth of native species while phosphorus does not. Most of these nutrients are retained in the organic mat, thus any disturbance that destroys this mat will seriously modify normal nutrient cycling and greatly increase the need for fertilizer in revegetation.In the High Arctic most soils are wet during snow melt and thus subject to surface disturbance by vehicles. In the polar deserts, silty and sandy soils dry rather rapidly and show less evidence of disturbance later in summer. Lowland areas where there is a more complete cover of plants on wet shallow peats or silty soils are subject to rutting throughout the summer as in the Low Arctic. With surface disturbance there is much less thaw of the permafrost than occurs in the Delta.The different plant community – topographic – soil – ground ice landscape units or systems respond differentially to the different surface disturbances tested to date. This is true in both the Low and High Arctic.