Foliar responses of black spruce to thinning and fertilization on a drained shallow peat

A thinning and fertilization experiment was established in 1987 in a 50- to 60-year-old black spruce (Picea mariana (Mill.) B.S.P.) stand growing on a shallow, boreal (central Alberta), minerotrophic peatland drained in 1986. The experiment was a split-split plot design with thinning as the main factor, fertilization as the subfactor, and distance from drainage ditch as the subsubfactor. Current and 1-year-old foliage, collected during late August 1988, was analysed for mass and N, P, and K. Black spruce responded to thinning, fertilization, and distance from a drainage ditch. Thinning alone increased foliar N and P concentration and unit needle mass by 12, 30, and 16%, and foliar N and P content by 30 and 41%, respectively. The relative increases in foliar mass and N concentration and content of current needles in N, NP, or NPK treated plots were generally higher in unthinned subplots and distant subsubplots than in thinned subplots and proximate subsubplots, suggesting that N was more limiting in unthinned plots and distant subsubplots. Although the addition of P and K alone or in combination elevated foliar P and K concentrations and contents, there were no concomitant significant changes in unit needle mass, suggesting that P and K were not limiting.