Black spruce growth and understory species diversity with and without sheep laurel

Growth and understory species diversity of black spruce [Picea mariana (Mil ler) B,S.P,] planted in central Newfoundland at contiguous sites with and w ithout dense cover of sheep laurel (Kalmia angustifolia L.) were compared. Black spruce stem density and volume per hectare were calculated by samplin g 10 circular quadrats (50 m(2)), and the cover of all plant species was de termined by sampling 20 quadrats (1 m(2)) in each site. Ln addition, 10 ran domly sampled planted black spruce samplings from each site were analyzed f or stem height, basal diameter, and foliar chemistry. Results showed a sign ificantly lower stem height and basal diameter (65 and 51%, respectively) a t the site with dense sheep laurel cover (36%) compared with the site with sparse sheep laurel cover (<1% sheep laurel cover, and henceforth referred to as the non-sheep laurel site for simplicity). Black spruce grown at the sheep laurel dominated site contained significantly higher quantities of Ca , Al, Fe, and K in the needles than that grown at the non-sheep laurel site , The sheep laurel dominated site also had a significantly higher mean orga nic matter depth of 8.3 cm compared with 5.6 cm at the non-sheep laurel sit e. Canonical correspondence analysis (CCA) of the species cover data clearl y separated the sheep laurel dominated plots from the non-sheep laurel plot s. The sheep laurel dominated site had reduced species richness of vascular plants but increased species richness for lichens compared with the non-sh eep laurel site. Allelopathy associated with phenol-induced soil nutrient i mbalance and nutrient stress is a possible cause for black spruce growth in hibition at the sheep laurel dominated site.