Black spruce regeneration in Kalmia dominated sites : effects of mycorrhizal inoculation and forest floor mixing

Abstract

Study area : Terra Nova National Park, 90 km southeast of Gander, Newfoundland.

There can be a shift in vegetation from black spruce (Picea mariana Mill.) forests with the ericaceous shrub Kalmia angustifolia L. (Kalmia) in the understory to ericaceous dominated heath in some areas of Newfoundland. This occurs on low to medium fertility sites after forest fire, insect defoliation, or clear-cut harvesting. Kalmia spreads rapidly with the concomitant failure of black spruce regeneration. This is a serious and widespread problem for the forest industry, and for protected area management when human interventions to natural disturbance cause the formation of Kalmia heath. The objective of this thesis was to test two alternate methods of enhancing black spruce regeneration in Kalmia dominated sites. I examined the growth response and foliar nutrient concentration of black spruce seedlings inoculated with the ectomycorrhiza (EM) Paxillus involutus (Batsch. Ex Fr.) Fr, planted in mechanically-mixed forest floors dominated by Kalmia. Changes in soil physical and chemical properties following mechanical mixing (tilling) of the forest floor horizon were also studied. The experiment was conducted over two growing seasons in Kalmia dominated sites resulting from heavy insect defoliation by spruce budworm and natural fires in Terra Nova National Park, Newfoundland. I found that inoculated seedlings had higher levels of EM formation, but lower growth than control seedlings, suggesting that the effect of EM on host performance is likely related to the physiological performance of the specific EM isolate under the prevailing soil conditions. Control seedlings that were exposed to nutrient stress in the greenhouse had better growth than the commercial nursery grown seedlings that were cultured using standard levels of fertilization. This suggests that black spruce growth might be closely related to adaptations to tolerate nutrient stress. Seedlings in insect defoliated sites in general had higher growth and foliar nutrient concentrations than those in burned sites. This was likely due to increased decomposition. Seedlings in all of the mixed forest floors had higher foliar nutrient concentrations than those in non-mixed forest floors, likely due to decreased acidity and competition, and increased decomposition. However, my results did not explain why forest floor mixing resulted in increased growth of black spruce seedlings in insect defoliated sites, but not in burned sites. Most theories of the growth of black spruce in Kalmia dominated sites include only below ground effects, but above ground effects may also be important. One possibility is that partial canopy cover is an important factor due to its effects on extremes of soil temperature and moisture, decomposition, litter quality, light levels, and near ground microclimate. My results indicate that it is possible to restore black spruce forest in insect defoliated sites with partial canopy cover that are dominated by Kalmia by mixing the forest floor and planting seedlings grown at low soil nutrient levels. However, further research is required to establish a method for restoring black spruce forest in open canopy burned sites.