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Decay following pruning of Balsam fir in the Maritime Provinces of Canada Van Sickle, Gordon Allan


As management of forests and parks intensifies, pruning of conifers becomes more common. Thus understanding the role of wounds as possible entry courts for decay fungi is vital. In order to study some aspects of this, three natural stands, one in New Brunswick and two in Nova Scotia, which had been pruned 4 to 7 years earlier by industrial or displaced workers, were examined. Five pruned and two unpruned balsam fir (Abies balsamea (L.) Mill.) trees from each stand were dissected; cultural isolations were taken from 207 knots where pruning had caused little or no apparent damage to the bole, and from 169 blazes resulting from less careful prunings. All 15 pruned trees, ranging in age from 23 to 42 years, had decay attributable to pruning which averaged 1.7% of the stem volume. This incidence and volume of decay exceeds that recorded in unpruned trees 40 to 60 years old in New Brunswick. Axe blazes were the major entry court for decay-causing fungis basidiomycetes were associated with 12% of the blazes and with 5% of the more carefully pruned knots. Neither stem nor butt decay was found in the unpruned trees. In a further study, 7 branches on each of 30 balsam fir trees near Fredericton, N. B. were experimentally axe pruned; some carefully, some carelessly; both during tree dormancy and during wet and dry periods of active growth. Thirty additional branches were saw pruned. At periods of 2 to 3 weeks, 5 to 7 months and 17 to 19 months after pruning, cultures were made in the field from 70 of the pruning wounds. Within 2 weeks of the latter period, the trees were dissected, measured and further cultures were made in the laboratory from the same 70 wounds. Eighteen months after pruning, 28 of 30 trees had decay averaging 3.9% of stem volume and basidiomycetes were isolated from 22 (31%) of 70 wounds. In the controls butt decay only occurred in 4 of 10 trees. These studies show: (l) that blazes into sapwood (careless pruning) were more frequently infected than those where little or no sapwood was exposed; (2) the incidence of infection was least in branches pruned during the dry period and about equal for those pruned in the wet-active and dormant periods; and (3) the successional pattern began with imperfect fungi and bacteria, and terminated with decay fungi.

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