Inferring Processes From Stand Characteristics and Soil Nutrient Patterns In Reclaimed Boreal Forests.

Oil sands surface mining has currently disturbed over 650km² of boreal ecosystems in northern Alberta (Canada) and the disturbed area is projected to increase to 1500 km² in the next 10-15 years.  Forest land reclamation after the complete removal and replacement of soil and geologic materials represents a major ongoing challenge that is partially contingent on re-establishing soil development and biogeochemical cycles. Soil development was quantified as forest floor mass, and along with canopy type, canopy area, season, and pH, the spatial heterogeneity of nutrient availability, was examined with a spatially explicit sampling protocol.  We assessed nutrient availability in three different reclaimed canopy types (Populus tremuloides, Pinus banksiana, and Picea abies), measured using three sets of plant root simulator probes (PRS, Western Ag Innovations^TM) placed in August 2008, November 2008, and May 2009.  Tree locations were mapped on each site in 2009 and canopy area was recorded for each tree.  Spatial patterns in soil nutrient availability were generally patchy at scales of 3 to 20 m and nutrients varied among seasons.  Fine scale patterns (~3 m) were reminiscent of natural forest structure, but large scale patterns (~20 m) were similar to those observed in agricultural settings.  In the aspen stand, canopy area was the dominant factor leading to increased nitrogen, sulphur, and calcium, while it was only related to potassium concentration in the spruce stand.  Forest floor mass, a partial indicator of soil development, was only related to P and K availability in the aspen stand.  SPACE, a quantified surrogate for unmeasured variables, and season were significantly related to nitrogen cycling in the conifer stand types. These results provide evidence that soil-plant relations are re-establishing differently in aspen and conifer stands, with aspens more dominated by canopy dynamics and conifers dominated by soil nutrient availability likely mediated by microorganisms.