LFH salvaged with small amounts of upper horizon mineral soil for land reclamation (hereafter LFH mineral soil mix) has proven to be an important source of seeds and vegetative propagules for forest plant communities. Until recently in Canada, LFH mineral soil mix was not selectively salvaged from upland forest sites prior to disturbance and was mainly incorporated with deeper mineral soil horizons or subsoil as part of conventional salvage and placement practices. The Alberta government is beginning to require oil sands and mountain and foothills coal mines to salvage and store this material separately from underlying mineral soil and subsoil for use in reclamation. The potential of LFH as a source of native propagules for revegetation of disturbed landscapes and a source of organic matter and nutrients in soil reclamation has not been widely tested. This report summarizes available literature on potential use of LFH material in Alberta and provides an analysis of the current state of knowledge and future directions.
Although donor soil seed banks have been successfully used as a revegetation technique on mine sites and land disturbances in other ecosystems for some time, only recently has research been conducted using forest LFH for mine revegetation in Alberta. Most of this research has been conducted on a small scale with few operational scale studies and a rigorous experimental approach is often lacking. Currently there are only a few peer reviewed publications on the use of LFH as a propagule source or reclamation soil in Canada.
Recent research shows LFH mineral soil mix is a good source of propagules for native and woody species that are not readily available commercially or by wild collection. Most plants in LFH mineral soil mix establish from seed and resultant communities have greater plant cover, more upland species and fewer non-native species than with traditional peat mineral soil mix used in oil sands mines. Stockpiling before placement reduces seed viability and species diversity, thus direct placement is recommended although stockpiling still results in more diverse and abundant plant communities than peat mineral soil mix. Placement depth has greater effect on plant community development than salvage depth. Thresholds for salvage and placement have not been determined and are dependent on donor soil texture, ecosite, topography, forest type and substrate placed on.
Besides using LFH mineral soil mix to revegetate disturbed landscapes, it can be used to improve soil quality. Compared to conventional peat mineral soil mixes in the oil sands, LFH mineral soil mix has a texture and pH more similar to natural forest and provides greater available phosphorus and potassium. Soil microbial activity and diversity is also greater which may lead to a more productive and resilient plant community in the long term.
Recent research on LFH mineral soil mix for forest reclamation has led to development of regulatory requirements. Short term research results (< 10 years) clearly show benefits of LFH mineral soil mix for reclamation. However, whether short term effects will persist with time and lead to a more natural, diverse and sustainable plant community than conventional reclamation techniques is unknown. Enhanced soil properties and native regeneration strongly suggest reclaimed communities are on a trajectory towards the structure and function of self-sustaining natural forest. By researching a few key operational and ecological questions, benefits of LFH mineral soil mix can be maximized and ongoing reclamation costs reduced.