Survival of three cool-temperate tree species in shade with lime and NPK applications

Knowledge of the site specificity of plastic reactions and shade tolerance of tree species within the complexity of natural forests is limited but critical to understanding forest regeneration. Paper birch (Betula papyrifera), yellow birch (B. alleghaniensis), and eastern hemlock (Tsuga canadensis) were planted in a randomized block design under natural deciduous canopy and within small canopy gaps with a single application of lime and NPK at time of planting in 2003. Saplings were excavated in 2004 and 2008 for analysis of biomass allocation and testing of foliar N. In 2008, mean survival rate differed significantly among species at 0.14 for paper birch, 0.57 for yellow birch, and 0.76 for eastern hemlock, respectively. Yellow birch emerged as a species of intermediate shade tolerance associated with a sharp decline in shoot development after two growing seasons, high leaf allocation of biomass, and foliar plasticity. Foliation and physiological adaptation of leaves appeared N-limited in yellow birch. Biomass allocation analysis revealed strong allometric growth in yellow birch and eastern hemlock across experimental treatments imposed. Increased soil reaction from pH 4.7 to 6.3 following lime applications had no discernable effect on the juvenile growth and survival of the three species during six growing seasons. The experiment underlined the need for experimental testing of species under natural forest canopy. Cyclical cutting of forests with moderate canopy opening is recommended for sustainable management of yellow birch and eastern hemlock.