Abstract
Well site development associated with oil sands exploration is common in boreal mixedwood forests of northern Alberta, Canada, and necessitates reforestation to accommodate other land uses. Little is known about the impact of soil and debris handling strategies during well site construction on long-term forest regeneration. This study addresses the impact of soil disturbance intensity, debris treatment, soil storage, and planting on the reforestation of 33 well sites reclaimed prior to 2006. Data on the survival and growth of planted white spruce (Picea glauca (Moench) Voss) and the regeneration density of deciduous trees, including trembling aspen (Populus tremuloides Michx), are presented from 2014 to 2015. The survival of planted spruce increased from 81% to 88% at well sites with a high relative to low soil disturbance. The total tree densities were lower in most treatments (≤2.69 stems m−2) than those in clear cuts (5.17 stems m−2), with the exception of root salvage areas where clear cuts had greater balsam poplar (Populus balsamifera L.) densities (2.05 stems m−2 vs. <0.71 stems m−2 on all other treatments). Aspen densities were up to five times greater at well sites with low disturbance when compared to those with high disturbance, and this was further aided by shallow mulch at low disturbance sites. Spruce growth did not respond to well site treatments. Aspen growth (diameter and height) remained similar between well site disturbance regimes; aspen exposed to high disturbance underperformed relative to low disturbance well sites and clear cut controls. With high disturbance, progressive soil piling led to increases in the density of aspen and birch (Betula papyrifera Marshall). Few long-term changes in soil were found due to well site development, with a greater soil pH in high disturbance sites compared to low disturbance sites. Overall, these results indicate that the nature of well site construction, including the extent of soil removal, soil piling, and debris treatment, may collectively alter forest re-establishment, with associated implications for forest management.
Highlights
Large areas of boreal forest in northeastern Alberta are subject to oil sands exploration, with eight to 20 well sites, each approximately 0.7 ha2 in size, established per square mile across the landscape.These well sites are exploratory and do not lead to permanent infrastructure
Low disturbance methods were cost effective for industry and the environment, high disturbance methods may be necessary for site construction
Planted spruce growth was only favourable where soil mixing occurred, survival was greater at well sites with high soil disturbance
Summary
Large areas of boreal forest in northeastern Alberta are subject to oil sands exploration, with eight to 20 well sites, each approximately 0.7 ha in size, established per square mile across the landscape. These well sites are exploratory and do not lead to permanent infrastructure. It remains unclear whether and how reforestation on upland boreal oil sands exploration sites may be supported during the construction and/or reclamation phases of well site development to aid forest recovery. White spruce is commonly planted after disturbance as its natural regeneration patterns are temporally erratic
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