Spatial, functional and genetic characteristics of field-planted and naturally-regenerated populations of white spruce (Picea glauca (Moench) Voss)

The spatial structure of white spruce populations was studied in 52 stands. White spruce tree density increased with age in the 200-year chronosequence after fire. Tree height and DBH peaked at about 120 years after fire. Sapling density along the chronosequence after clearcutting exhibited similar pattern to that after fire, but peaked earlier. White spruce seedlings were present in various densities and heights along the chronosequence after fire, producing uneven-aged stands. Seedling regeneration was mostly on the LFH layer (72%) in younger plots and on logs (97%) in old plots. Seedlings in both regeneration types were evenly spaced at a young age. This pattern changed to random and clumped in older stands. Artificially planted clearcuts formed more even-aged stands. Physiological, morphological and growth responses to sun and shade treatments in the greenhouse were examined in white spruce seedlings collected from three naturally-regenerated (N1, N2 and N3) and three field-planted (P1, P2, and P3) stands. Dark respiration and light compensation points declined by 70 and 81% respectively, in shade- compared to sun-acclimated seedlings. Quantum yield, total chlorophyll content, specific leaf area and absolute water content increased by 45, 33, 32 and 50% respectively, in response to shade treatment. Height was not affected by light regime. Fewer and longer secondary branches were noticed in the shade compared to full sun. At light saturation, populations P1 and N3 showed similar photosynthetic responses under both light regimes (around 6 [mu]mol m-2 s-1). Populations P2, P3 and N2 performed more poorly in the sun than in the shade (8.2, 8.7 and 9.1 in shade, versus 5.1, 4.1 and 5.5 in full sun, respectively). Photosynthetic rate in N1 was greater in full sun than in shade (14.7 and 11.1 [mu]mol m -2 s-1, respectively). Differences in physiological responses to light among populations suggest the presence of more than one ecotype. The variation in physiological and morphological parameters within field-planted and naturally-regenerated populations was large, and did not show any obvious differences among populations. RAPD analysis showed abundant polymorphism in all populations. The naturally-regenerated arid the field-planted populations demonstrated similar within and among regeneration-type variation. Of the total genetic variation 82.9% was due to intra-population variation, while inter-population variation and regeneration type accounted for 16.7 and 0.4% of the total variation, respectively. It appears that selection pressure during reforestation was not great enough to cause a significant decline in the genetic diversity of field-planted compared to naturally-regenerated white spruce