Nutrient Bioavailability for Black Spruce Establishment as Influenced by Elevation and Post-Fire Disturbance.

Black spruce (Picea mariana) forests are widespread across boreal North America and can be considered a climax species. These systems are consistently affected by fire disturbance and climatic factors. Four studies compared black spruce establishment potentials as influenced by climate change impacts on elevation ecotones and post-fire disturbances in eastern Newfoundland and Labrador, Canada. Plant Root Simulator (PRS)™-probes were used as a means to understand whether soil nutrient supply rates can support black spruce relocation and regeneration success. Soil bioavailable nutrients where measured along an elevation gradient from closed-crown forest, through shrub-tree-island transition zone, and into alpine tundra. In the alpine tundra soil nutrient supply rates were compared between two common black spruce seedbeds, Cladonia stellaris (fruticose lichen) and Pleurozium schreberi (feathermoss) to determine black spruce survival and recruitment potential above the current treeline. No significant differences in PRS™-N, P and S supply rates were found along the elevation gradient. However, differences in PRS™-Ca, Mg, K, and Mn supplies were significant (P<0.001) and show lowest levels in the tundra sites. Using principal component analyses the tundra ecotone explained 71% of the variation in soil nutrient supply rates indicating the lichen seedbeds are more nutrient-deficient for most nutrients compared to feathermoss seedbeds. Soil nutrient dynamics in black spruce forest following wildfire were investigated in conjunction with microsite soil mixing (MSM) as a technique for black spruce seedbed preparation in Kalmia angustifolia (sheep-laurel) dominated heath. Preliminary trends showed MSM had elevated PRS™-NO₃^--N, S, and K supply rates but lower PRS™-NH₄^--N, Ca, Mg, and Mn supply rates as compared to controls without microsite disturbance.  The authors concluded that black spruce seedlings are likely not limited by soil nutrient bioavailability alone in supporting establishments along the elevation gradient and in dominated sheep-laurel heath. Assessing black spruce seedbeds for soil nutrient bioavailability is one factor to consider in managing such ecosystems.