%0 Research article
%T Thinning effects on jack pine and black spruce photosynthesis in eastern boreal forests of Canada
%A Goudiaby, Venceslas
%A Brais, Suzanne
%A Grenier, Yvon
%A Berninger, Frank
%D 2011
%J Silva Fennica
%V 45
%N 4
%R doi:10.14214/sf.95
%U https://silvafennica.fi/article/95
%X A decrease in the average diameter of commercially harvested tree  species in the Eastern boreal forest of Canada has led to a decrease in  availability of quality wood for the forest industry. Commercial  thinning has been proposed as a means to increase stem diameter growth.  However, little is known about physiological responses underlying  species responses to thinning. We assessed the effect of canopy opening  on the photosynthetic response of mature jack pine (Pinus banksiana  Lamb.) and black spruce (Picea mariana (Mill.) BSP) trees. Two years  after thinning and for each species, light response curves and the  diurnal course of photosynthesis were characterized from measurements  taken in a completely randomized block experiment on current-year and  one-year-old needles of 12 trees from stands subjected to different  levels of canopy opening. Soil water content, air and soil temperatures,  and needle N concentration were not affected by thinning for either  species. However, light availability increased with basal area removed  and could explain the significantly positive relationship between  thinning intensity and diurnal course of photosynthesis for one-year-old  needles of jack pine. Black spruce photosynthesis did not respond to  increases in light. Light-saturated rate of net photosynthesis (A<sub>max</sub>), photosynthetic efficiency (α), light compensation point (LCP), and diurnal respiration (R<sub>d</sub>)  did not vary with thinning for either of the species. Jack pine and  black spruce responses to thinning should be interpreted in light of  species autecology.