Rising demands for forest biomass have raised concerns that the increased removal of organic residues and harvest impacts may reduce longer term site productivity. Replicated field experiments examining the effects of stem-only harvest with disc trenching (SO T ), whole-tree harvest with (WT T ) and without (WT) disc trenching, whole-tree harvest with forest-floor removal by blading (WT B ), and blading followed by compaction (WT BC ) were installed on nine sandy jack pine (Pinus banksiana Lamb.) sites in northern Ontario. At year 5, planted-tree diameters, dominant tree heights (H D ), and stand aboveground biomass (jP P Bio) were smaller without soil disturbance (the WT), but were otherwise similar among treatments. At year 15, planted-tree size and stand yield rankings were WT T = SO T = WT > WT B = WT BC . Biomass production by natural regeneration and total stand aboveground biomass (TotBio) treatment rankings were SO T ≥ WT T ≥ WT > WT B = WT BC . H D , jP P Bio, and TotBio showed increasing divergence over time in WT B vs. WT T -SO T response, whereas statistical equivalence of the WT T and SO T treatments was shown for most tree and stand growth responses. There was some evidence of increasingly negative impacts of WT B as site index declined. Overall, negative WT B effects on tree and stand productivity have become increasingly apparent.Résumé : La demande croissante de biomasse forestière soulève la question d'une possible réduction de la productivité des stations à long terme à la suite d'une augmentation du prélèvement des résidus organiques et des impacts de la récolte. Sur neuf stations sableuses de pin gris (Pinus banksiana Lamb.) du nord de l'Ontario, nous avons établi des expériences répétées sur le terrain pour étudier les effets de la récolte des tiges seulement avec scarifiage à disque (TS D ), de la récolte par arbre entier avec (AE D ) et sans (AE) scarifiage à disque, et de la récolte par arbre entier avec l'enlèvement de la couverture morte à l'aide d'une lame bineuse (AE L ) ou d'une lame bineuse suivie d'une compaction (AE LC ). Après 5 ans, le diamètre des arbres plantés, la hauteur des arbres dominants (H D ) et la biomasse aérienne des peuplements (jP P Bio) étaient plus faibles sans perturbation du sol (AE), mais similaires entre les autres traitements. Après 15 ans, le classement des traitements en ce qui concerne la taille des arbres plantés et la production étaient AE D = TS D = AE > AE L = AE LC . Dans le cas de la production en biomasse de la régénération naturelle et en biomasse aérienne totale des peuplements (BioTot), le classement des traitements était TS D ≥ AE D ≥ AE > AE L = AE LC . Nous avons observé une divergence croissante entre les réactions de AE L vs AE D et TS D en ce qui concerne la jP P Bio et la BioTot en fonction du temps, alors qu'une équivalence statistique des traitements AE D et TS D a été observée pour la plupart des réactions de croissance des arbres et du peuplement. Le traitement AE L tendait à avoir un impact négatif croissant avec une diminution de l...

Eight 5- to 15-year-old black spruce (Picectmariana (Mill.) BSP) plantations from each of the Northwestern Ontario Forest Ecosystem Classification treatment units B, C, D, E, and F were sampled for Armillaria root rot. All the plantations sampled were infected by Armillaria, with an infection rate ranging from slightly less than 1% to 32%. Some differences were observed among Northwestern Ontario Forest Ecosystem Classification treatment units but these differences were not statistically significant (p < 0.05). Plantations in treatment unit F had the highest average infection level (16.93%), while those in treatment unit B had the lowest (7.24%). Plantations in treatment unit F had significantly higher cumulative mortality levels than did those in treatment unit B (p < 0.05). The average ratio of infected healthy trees to infected dead trees was 3.28:1 across all treatment units. The total number and total basal area of all stumps and of all infected stumps were similar across the treatment units. Variations did exist in the ratio of conifer to hardwood stumps and reflected the differences in the species composition of the original stands. Infection levels based on trembling aspen (Populustremuloides Michx.) trap logs were not found to be a good indicator of percent infection in the trees. The use of colour and relative shoot growth was only moderately effective in identifying trees infected by Armillaria.

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Averages of 10, 10, 0 and 4% of white spruce, black spruce, balsam fir and jack pine saplings were killed by Armillaria Root Disease (ARD), after 10 years following planting around 50 infected stumps that had been prescribed burned. Comparable averages on an unburned control area of 8, 8, 0 and 6% were not significantly different from the burned area. ARD did not occur in any trees planted adjacent to five deeply burned stumps. However, no statistically significant relationship was found between ARD and intensity of burn on stumps. Significantly (p = .05) fewer balsam fir saplings were killed by ARD than of either white or black spruce. Jack pine heights were significantly greater (p = .05) than those of the other species on both locations after10 years, and on the unburned site after 17 years (experimental trees on the burned site were inadvertently cut during a silvicultural thinning in the year prior to measurements in the 17th year). Balsam fir heights were significantly less (p = .05) than those of the other three species on both sites after 10 years, and after 17 years on the unburned site. Key words: Root rot, Armillaria, burning, height growth, spruce, balsam fir, jack pine