Stand structure, growth, and mortality of residual overstory trees after partial harvests: A comparison of full tree and tree length harvesting

Harvesting traditionally unmerchantable biomass (harvest residues) to use as a bioenergy feedstock provides an opportunity to increase bioenergy fuel sources without increasing the land area impacted by partial harvesting. However, the effects of removing nutrient dense harvest residues on residual overstory trees remains unclear. We assessed the effects of 2 harvesting treatments (as well as an unharvested Control) on residual overstory stand structure, growth, and mortality in 81 plots across 4 sites in the Great Lakes-St. Lawrence forest region of Ontario, Canada. Treatments occurred in single-tree selection or uniform shelterwood systems and included conventional tree length (TL) harvests removing only merchantable roundwood and full tree (FT) harvests removing merchantable roundwood and harvest residues. Overall, 10-years post-harvest there were few differences between harvesting methods; individual tree growth, mortality, injuries, and presence of stem defects did not consistently differ between TL and FT plots. Trees with defects were generally more likely to grow slower and were more likely to die compared to unaffected trees, particularly for sugar maple. However, mortality did not differ between major and moderately defected trees, and trees with moderate defects tended to grow slower than trees with major defects. While there were few differences in residual overstory trees between the two harvesting treatments, 10-years may not be a sufficient study period to fully assess the effects of nutrient loss on long-term tree health particularly considering the slow-release nature of nutrients stored in harvest residues. • Few differences in residual overstory between full tree and tree length harvests. • Individual tree growth did not differ between harvest types 10-years post-harvest. • Stand structure, stem defects, injuries, and mortality comparable between harvests. • Trees with defects more likely to grow slower and more likely to die.