by Audrey Verreault | 29 July 2020
Published in Annals of the Entomological Society of America 78: 14-19
ln laboratory studies larval development and total mortality of Agromyza frontella on hop medic, Medicago lupulina, were similar to previously reported values on alfalfa, M. sativa. However, pupal development was longer and both pupal weight and total fecundity were somewhat lower than for alfalfa-reared individuals. Nevertheless hop medic is a suitable alternate host and, given its widespread occurrence throughout northeastern North America, could play a role in the dynamics of established and expanding populations of A. frontella, particularly when alfalfa is unavailable.
by Audrey Verreault | 28 July 2020
Published in Canadian Journal of Forest Research 17: 840-845
Containerized jack pine (Pinus banksiana Lamb.) seedlings were grown in a peat moss – vermiculite substrate and inoculated at sowing with pure cultures of three ectomycorrhizal fungi. After 18 weeks of growth in the greenhouse, seedlings inoculated with Laccaria bicolor had 97% of their short roots mycorrhizal, while those inoculated with Hebeloma cylindrosporum had 36% of their rootlets mycorrhizal. No mycorrhizae were obtained with Rhizopogon sp. After both 12 and 18 weeks of growth with the fertilization schedule used, seedlings colonized with L. bicolor and H. cylindrosporum were significantly smaller than those inoculated with Rhizopogon sp. or control seedlings. After 18 weeks of growth, the available nitrogen (N) content of the substrate was considerably greater with L. bicolor inoculated seedlings than with control seedlings, whereas the available phosphorus (P) content of the substrate was the same for these two treatments. Also, after 18 weeks, seedlings mycorrhizal with L. bicolor had a greater concentration (%) of N and P in their tissues than control seedlings; however, they contained fewer milligrams of N and P than control seedlings. From our results on substrate fertility of mycorrhizal seedlings, we state that it is possible to induce mycorrhiza formation of jack pine seedlings with L. bicolor when substrate fertility in available N and P is less than or equal to 39 and 60 ppm, respectively, and that it is possible to maintain L. bicolor mycorrhizae when N and P fertility is less than or equal to 24 and 28 ppm, respectively. From analysis of tissue nutrient content in mycorrhizal seedlings, it appears that the appropriate N and P concentrations to maintain mycorrhiza formation of jack pine seedlings with L. bicolor are less than or equal to 1.6 and 0.2%, respectively.
by Marie-Claude Boileau | 28 July 2020
Published in Canadian Journal of Forest Research 18: 723-727
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.
by Marie-Claude Boileau | 28 July 2020
Published in Canadian Journal of Forest Research 19: 1564-1570
The anatomical characteristics of sapwood from the base of the live crown of trees from 11 jack pine stands (Pinus banksiana Lamb.) of different age and site quality were related to the patterns of change of longitudinal sapwood permeability (k) previously observed to occur among these stands. Tracheid length (Lt) increased rapidly from a minimum of 1.9 mm to a plateau of around 3.6 mm as stand age and site quality (productivity class) increased. Sapwood relative water content (Rs) measured before saturation ranged from 78 to 85% for the majority of trees. Samples taken from trees growing on poor sites, however, exhibited significantly lower values of Rs, which probably resulted in their remaining below saturation during the determination of sapwood permeability. The lower Rs values were assumed to be reflective of more adverse water balances during the growing season associated with rapidly drained and (or) shallow soils. Tracheid lumen diameter (Dl) was positively correlated with k within age-classes 15 and 35, but not thereafter. The initial relation between DI and k is thought to be associated with corresponding increases in the area of pit membranes, which determines the number of pores within a pit membrane. Values of k were never more than 60% of the values calculated by Poiseuille’s law for ideal capillaries (kc) and were generally less than 40%. Values of k tended to approach kc with increasing Lt, and decreasing Dl. Overall, Poiseuille’s law by itself could not explain the changes in the hydraulic properties of jack pine sapwood with stand development. However, Lt and Rs could together account for 72% of the variation in k. Young stands that had different k depending on site quality generally had corresponding differences in Lt, Rs, and (or) Dl. Mature stands that had reached maximum k on all quality sites no longer showed differences in Lt, Rs, or Dl.
by Marie-Claude Boileau | 28 July 2020
Published in Canadian Journal of Forest Research 19: 432-439
The saturated sapwood permeability (k) of jack pine (Pinus banksiana Lamb.) from stands of different ages and site qualities was measured using a constant water flow apparatus. Saturated sapwood permeability at the base of the live crown (BLC) increased with age and reached a plateau just beyond 4 x 10-12 m2. The rate at which this plateau was reached, however, was dependent on site quality. Such age-related increases in k can partially explain how trees can maintain similar daytime leaf water potentials at different stages of stand development. Within age-classes 15 and 35, k at BLC was greater on the better-quality sites and was strongly correlated with both diameter and height growth. For age-class 120, k at BLC was not significantly different among sites. Saturated sapwood permeability at BLC could be predicted from age and site quality, using a negative exponential function (R2 = 0.66). The ability to predict changes in k with stand development has potential for improving leaf area estimates derived from sapwood area – leaf area correlations. Sapwood conductance from ground level to the upper third of the crown decreased with age for good-quality sites and increased with age for poor-quality sites. It corresponded to the pattern of average annual height growth over the last 5 years (R2 = 0.61). The number of annual rings contributing to the sapwood at a given age was independent of site quality. This suggests that the historical reconstruction of a tree’s leaf area and growth efficiency is possible even after the formation of significant amounts of heartwood.
