KOPPENAAL, R. S., TSCHAPLINSKI, T. J., and COLOMBO, S. J. 1991. Carbohydrate accumulation and turgor maintenance in seedling shoots and roots of two boreal conifers subjected to water stress. Can. J. Bot. 69: 2522-2528. Water potential components and organic solutes werc examined in shoots and roots of potted jack pine (Pittiis batlksiat~n Lamb.) and white spruce (Picea glouca (Moench) Voss) seedlings after exposure to 7 days of water stress. The osmotic potential at the turgor loss point ( $ , . , , , ) decreased in shoots and roots of water-stressed seedlings of both species, resulting in the maintenance of positive turgor at lower xylem water potentials ($, ) compared with nonstressed seedlings. Following water stress, ~JJ, . , , of shoots and roots declined by 0.28 MPa and 0.14 MPa, respectively, in jack pine, and 0.19 MPa and 0.28 MPa, respectively, in white spruce. The osmotic potential at saturation ($,,,,,J was significantly lower after water stress only in jack pine roots. Active osmotic adjustment during water stress was confirmed by higher concentrations of organic solutes in white spruce shoots (1.4 x increase relative to nonstressed plants) and roots (1.7 x ) and in the roots (2.2 x ) but not the shoots of jack pine. Carbohydrates, particularly fructose and glucose, were the primary organic solutes accumulating in both species. Tissue elasticity was greater in the roots than the shoots of both jack pine and white spruce regardless of treatment. Consequently, the relative water content at the turgor loss point was 22% and 18% lower in the roots than in the shoots of jack pine and white spruce, respectively. Osmotic adjustment in the roots and shoots of these two boreal conifers suggests that preconditioning planting stock by exposure to water stress may increase carbohydrate concentrations and enhance seedling drought tolerance. Key ,vords: carbohydrate accumulation, drought tolerance, organic solutes, osmotic adjustment, Picea glrrrrco, Pittr1.s barksiorra, water potential components. KOPPENAAL, R. S., TSCHAPLINSKI. T. J., et COLOMBO, S. J. 1991. Carbohydrate accumulation and turgor maintenance in seedling shoots and roots of two boreal conifers subjected to water stress. Can. J . Bot. 69 : 2522-2528. Les composantes du potentiel hydrique et les solutes organiques ont kt6 examines dans des tiges et des racines de pins gris (Pinrrs barlksinrlu Lamb.) et d'epinette blanche (Picerr glcrrrco (Moench) Voss) cultivCs en pot, apres 7 jours d'expositionii un stress hydrique. Le potentiel osrnotique au point de perte de turgescence ($,.,L.l) dirninue dans les tiges et les racines des plantules sournises au stress hydrique chez les deux especes, ce qui conduit au rnaintient.d'une turgescence positive au potentiel hydrique du xylkme le plus faible ($, ) comparativement aux plantules non-stressees. A la suite d'un stress hydrique, la valeur (t),,.,.,,) des tiges et des racines diminue ii environ 0,28 MPa et 0,14 MPa, respectivement, chez le pin gris, et 0,19 MPa et 0,28 MPa, respectivement chez I'epin...

The MASS (Montane Alternative Silvicultural Systems) trial was established in the coastal mountains of British Columbia to compare clearcut, patch cut, green tree and shelterwood systems. A number of studies were carried out at the MASS trial to determine the extent to which these variable levels of stand retention retained old-growth attributes of N cycling and associated ecological processes. Harvesting led to increases in N mineralization in the forest floor (2ϫ) and mineral soil (10ϫ), and fluxes of N through the upper 25 cm of mineral soil (2ϫ to 3ϫ). However, fluxes of N were not large (< 0.35 kg ha -1 per growing season). Nitrogen mineralized was predominantly ammonium and not nitrate in the forest floor (> 95% in all but clearcut, > 75% in clearcut) and upper mineral soil horizon (42-86%). The nitrate component came from heterotrophic decomposition of organic matter, not conversion of ammonium to nitrate by autotrophs, and nitrate increases resulted from decreased gross nitrate consumption with harvesting, rather than increased nitrate production. The increases in soil N availability resulting from harvesting were reflected in only slight increases in seedling foliar N concentrations for two to four years after logging (peak of~ 2% for western hemlock and ~ 1.6% for amabilis fir) before decreasing to below deficiency thresholds for both species. Overall, estimated losses of N from the rooting zone after harvesting (1 kg ha -1 yr -1 ) were minimal in comparison to estimated N inputs (4 kg ha -1 yr -1 ), N exports in logs at harvesting (250 kg ha -1 ) and soil reserves (11 400 kg ha -1 ). Although unlikely to affect future site productivity, losses of N could be reduced somewhat through the use of shelterwood harvesting.

Characteristics of annual rings are reliable indicators of growth and wood quality in trees. The main objective of our study was to model the variation in annual ring attributes due to intensive silviculture and inherent regional differences in climate and site across a wide geographic range of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Ring specific gravity and ring width of Douglas-fir were examined at five long-term Levels-Of-Growing-Stock (LOGS) installations, three in the US and two in Canada, covering a latitudinal gradient between 43°N and 50°N. At each location, increment cores were collected from replicated plots with three levels of stocking: control (unthinned), lightly thinned (70% basal area retention), and heavily thinned (30% basal area retention). X-ray densitometry analysis provided ring specific gravity and width profiles for 5676 rings from 134 trees. The reduction of stand density through repeated entries resulted in decreased ring specific gravity and increased ring width. A four-parameter mixed-effects logistic model was used to predict ring specific gravity using cambial age, stand density (as number of stems per hectare), and two climatic variables: average temperature from March to May and total precipitation from April to August. A three-parameter mixed-effects logistic model was used to predict ring width using cambial age, stand density (as stand density index), and total climatic moisture deficit of June and July. Both models indicated significant site differences that were included in the models through indicator variables. Ring specific gravity increased slightly with increasing average temperature from March to May and decreasing total precipitation from April to August. Predictions of ring specific gravity of Douglas-fir appear to be more sensitive to changes in temperature compared with changes in precipitation. Résumé :Les caractéristiques des cernes annuels sont des indices fiables de la croissance et de la qualité du bois chez les arbres. Le principal objectif de notre étude consistait à modéliser la variation des attributs des cernes annuels attribuable à la sylviculture intensive et aux différences régionales inhérentes au climat et aux stations sur une vaste étendue géographique occupée par le douglas de Menzies (Pseudotsuga menziesii (Mirb.) Franco). La densité et la largeur des cernes du douglas de Menzies ont été étudiées dans cinq endroits, trois aux États-Unis et deux au Canada, établis pour observer l'effet à long terme de la densité des tiges sur pied et couvrant un gradient latitudinal allant de 43°N à 50°N. À chaque endroit, des carottes ont été prélevées dans des placettes répliquées correspondant à trois niveaux de densité relative : témoin (pas d'éclaircie), éclaircie légère (rétention de 70 % de la surface terrière) et éclaircie forte (rétention de 30 % de la surface terrière). L'analyse par densitométrie aux rayons X a permis d'obtenir les profils de largeur et de densité de 5676 cernes provenant de 134 arbres. La réduction de la densité relative des ...

Late-rotation fertilization of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) 5 to 10 years before harvesting is a common management practice in British Columbia and the US Pacific Northwest. Despite widespread operational application, knowledge on the impact of late-rotation fertilization on forests, especially fibre properties, is lacking. In this study, we evaluate the growth response and fibre properties following nitrogen fertilization in a productive second-growth coastal Douglas-fir site at age 57 years. Destructive sampling of dominant and co-dominant trees in fertilized and control plots 5 years after fertilization indicated significant gain in stem volume (30%–40%) that was uniformly distributed along the stem. There were no discernible effects on wood quality at the log level in terms of resonance acoustic velocity. However, fibre properties within breast height tree rings indicated significant reductions of ring wood density (by 8%), earlywood density (17%), latewood percentage (10%), and modulus of elasticity (8%). Tracheid dimensions declined in earlywood (reduction of wall thickness by 15%), latewood (radial diameter by 8%), and fibre length (by 6%). Results indicate that late-rotation nitrogen fertilization of Douglas-fir may lead to a significant growth response with only minimal reduction of fibre properties. It is possible that the negative impact on fibre properties could become more significant for repeated applications or higher rates of nitrogen fertilization.