Balsam fir trees established from advanced regeneration following a clear-cut in 1970 were pruned in June 1985 to live crown ratios of 0.6, 0.4, and 0.2 compared with control trees, which had live crown ratios of 0.8. After two growing seasons, we investigated the homeostatic adjustment of these trees to the loss of their foliage. The height growth, basal area growth, sapwood cross-sectional area, heartwood area, and sapwood saturated permeability of the trees that were pruned to a 0.6 live crown ratio were not significantly different from those of the controls. On the other hand, height growth increment following pruning was reduced 16.7 cm (23%) and 19.5 cm (27%) for the trees pruned to 0.4 and 0.2 live crown ratios, respectively. Furthermore, basal area growth following pruning was reduced 3.2 cm2 (30%) and 6.5 cm2 (61%), respectively. While trees in both the 0.4 and 0.2 live crown ratio pruning treatments did adjust their breast height sapwood area in response to the removal of foliage, the nature of this adjustment differed between the two treatments. For the trees with the 0.4 live crown ratio, sapwood area was reduced because of a reduction in basal area growth but the area of heartwood remained unchanged. For the trees with the 0.2 live crown ratio, the changes in sapwood area were due both to a reduction in basal area growth and an expansion of the heartwood. The saturated permeability of sapwood was not significantly affected by pruning. The adaptive implications of balsam fir's response to the loss of foliage are discussed in terms of the optimizing the allocation of a limited amount of available carbon.
Balsam fir (Abiesbalsamea (L.) Mill.) and white spruce (Piceaglauca (Moench) Voss) mortality was measured in five areas of the province of Quebec severely affected by spruce budworm (Choristoneurafumiferana (Clem.)) defoliation. Mortality was compared for different combinations of soil texture and drainage. For balsam fir, two vulnerability classes, based on combinations of soil texture and drainage, were defined. In the first class, mortality reached 74% of the preoutbreak volume, as compared with 86% in the second class. For white spruce, three vulnerability classes were defined based on soil texture and drainage combinations. In the low, moderate, and high vulnerability classes, white spruce mortality reached 10, 26, and 52%, respectively. Soil moisture regime is an important factor in determining vulnerability. From these results, we propose an ecosystem classification based on vulnerability to spruce budworm. Particular reference is made to what significance the findings may have for forest integrated pest management.
Leaf area is commonly estimated as a function of sapwood area. However, because sapwood changes to heartwood over time, it has not previously been possible to reconstruct either the sapwood area or the leaf area of older trees into the past. In this study, we report a method for reconstructing the development of the sapwood area of dominant and codominant balsam fir (Abies balsamea (L.) Mill.). The technique is based on establishing a species-specific relationship between the number of annual growth rings in the sapwood area and tree age. Because the number of annual growth rings in the sapwood of balsam fir at a given age was found to be independent of site quality and stand density, the number of rings in sapwood (NRS) can be predicted from the age of a tree thus: NRS = 14.818 (1 - e(-0.031 age)), unweighted R(2) = 0.80, and NRS = 2.490 (1 - e(-0.038 age)), unweighted R(2) = 0.64, for measurements at breast height and at the base of the live crown, respectively. These nonlinear asymptotic regression models based only on age, were not improved by adding other tree variables such as diameter at breast height, diameter at the base of the live crown, total tree height or percent live crown.
Cambial electrical resistance in 10 balsam fir (Abiesbalsamea (L.) Mill.) and 10 white spruce (Piceaglauca (Moench) Voss) trees in Québec was measured 42 times during July and August 1985. Simultaneous measurements of relative humidity and temperature were also taken so that water potential in air (ψa) could be determined. In both species, cambial electrical resistance, corrected to a constant temperature of 15 °C (CERCOR), was negatively correlated with ψa. On the other hand, 10 measurements on 14 balsam fir trees that had been severely defoliated by the spruce budworm (Choristoneurafumiferana (Clem.)) in 1983 and 1984, and 12 measurements on 14 protected trees showed that the correlation was stronger for sprayed trees than for those that had been defoliated. We propose that the correlation coefficient between cercor and ψa may be a useful index of tree vigor. However, in situations where plots can be visited only once during the season, cambial electrical resistance measurements should be made in the morning when the relative humidity is high.
In the spring of 1985, 125 young balsam fir trees (Abiesbalsamea (L.) Mill.) originating from advanced regeneration following a clear-cut in 1970 were pruned to live crown ratios of 0.6, 0.4, 0.2 and 0.0 as compared with control trees which had naturally developped a live crown ratio of 0.8. Subsequently, the cambial electrical resistance of these trees was measured at breast height 17 times between June and October. Ten days after pruning, there was a decrease in cambial electrical resistance. Relating these results to factors influencing the movement of water through the tree leads to a better understanding of the physiological significance of tree stem cambial electrical resistance.
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