COMPARING NATURAL AND PLANTED BLACK SPRUCE SEEDLINGS .1. WATER RELATIONS AND GROWTH

Container-grown black spruce (Picea mariana (Mill.) B.S.P.) seedlings were planted during 2 consecutive years alongside natural black spruce seedlings of similar initial height on an upland boreal forest clearc ut. Acclimation of the planted seedlings to site conditions was follow ed by comparing needle conductance, shoot water potential, and growth of the planted seedlings to values obtained on the natural seedlings. Relative growth rates of the newly planted seedlings were significantl y lower than those of the natural seedlings, but the difference was sm aller during their second season in the field. Predawn and midday shoo t water potential as well as midday needle conductance showed signific ant but relatively small differences between planted and natural seedl ings during both years. On any given date of measurement, no clear rel ation could be found between water status and growth in planted seedli ngs. Seasonal midday averages of shoot water potential, needle conduct ance, and soil-plant resistance to water movement were related to the relative growth rates of all seedling types over the course of the two growing seasons. Seasonal averages of midday shoot water potential ap peared to best reflect the acclimation of the planted seedlings to sit e conditions.