Many studies have estimated approximately ranges of thresholds of low soil temperature in the growth and ecophysi-ological traits of trees, but difficultly determined the exact values. To resolve the problem, black sp...Many studies have estimated approximately ranges of thresholds of low soil temperature in the growth and ecophysi-ological traits of trees, but difficultly determined the exact values. To resolve the problem, black spruce （Picea mariana） and jack pine （Pinus banksiana） seedlings were exposed to 5, 10, 15, 20, 25, 30 and 35℃ soil temperature in greenhouses. After 90 days of the treatment, net photosynthetic rate （A）, stomatal conductance （gs）, transpiration rate （E）, water use efficiency （WUE） and specific leaf area （SLA） were measured. This study showed that all the traits had an asymmetrical peak relationship with changing soil temperature, the relationship was well simulated using a cubic curvilinear model, and the exact thresholds could be derived from the second derivative of the model. The results revealed that the thresholds varied among ecophysiological traits and between tree species. In black spruce, the thresholds were 14.1, 14.7, 10.7, 14.4 and 16.2℃ forA, gs, E, WUE and SLA; 15.4, 10.4, 14.7, 16.9 and 10.5℃ for the corresponding traits in jack pine. The lowest thresholds of E in black spruce and gs in jack pine were an indicator representing the minimum requirement of soil temperature for the regular processes of ecophysiology. The highest thresholds of SLA in black spruce and WUE in jack pine suggest they are the most sensitive to decreasing soil temperature and may play an important role in the acclimation. The averaged thresholds were at 14.0 and 13.6℃ for black spruce and jack pine, suggesting that the sensitivity of both species to low soil temperature was quite close.展开更多
It is of considerable importance to investigate the influence of weathering on the degradation processes of heat-treated wood. Kiln-dried （untreated）jack pine （Pinus banksiana） and jack pine heat-treated at three ...It is of considerable importance to investigate the influence of weathering on the degradation processes of heat-treated wood. Kiln-dried （untreated）jack pine （Pinus banksiana） and jack pine heat-treated at three different temperatures （190 ℃, 200 ℃, and 210 ℃） were exposed to artificial weathering for different periods in order to understand the degradation processes due to weathering. Before and after exposure, their color and wettability by water were determined. Structural changes and chemical modifications at exposed surfaces were also investigated using SEM （scanning electron spectroscopy）, FTIR （Fourier transforms infrared spectroscopy）, and XPS （X-ray photoelectron spectroscopy）. The results revealed that the photo-degradation of lignin and the presence of extractives play important roles in color change and wetting behavior of heat-treated wood surfaces during weathering. The structural changes also influence the wettability. The effects of weathering for woods heat-treated under different conditions were similar, but different from those for untreated wood.展开更多
Insects respond to changes in microhabitat caused by canopy disturbance, and thus can be used to examine the ecological impacts of harvesting. Single-tree selection harvesting is the most common silvicultural system u...Insects respond to changes in microhabitat caused by canopy disturbance, and thus can be used to examine the ecological impacts of harvesting. Single-tree selection harvesting is the most common silvicultural system used to emulate local small-scale natural disturbance and maintain uneven-aged forest structure in temperate forests. Here, we test for differences in richness, abundance, and composition of hymenopteran and saproxylic insect assemblages at four different taxon levels （selected insect orders; and all hymenopteran families, and braconid subfamilies and morphospecies） between the canopy and understory of unharvested and single-tree selection harvested sites in a northern temperate forest from central Canada. Harvesting had no effect on insect assemblage richness, composition or abundance at the three highest taxon levels （order, family and subfamily）. Similarly, richness and abundance at the lowest-taxon level （braconid morphospecies） were similar, although composition differed slightly between unharvested and harvested stands. Insect assemblages were vertically stratified, with generally higher abundance （for Diptera, Hymenoptera, some hymenopteran families and braconid subfamilies） and richness （for braconid morphospecies） in the understory than the canopy. In particular, composition of the braconid morphospecies assemblage showed relatively low similarity between the understory and canopy. Single-tree selection harvesting appears to influence wood-associated insect taxa only subtly through small changes in community composition at the lowest taxon level, and thus is recommended as a conservative approach for managing these northern temperate forests.展开更多
We studied late-entry commercial thinning effects on growth, yield, and regeneration in a 48-year-old jack pine(Pinus banksiana Lamb.) stand. Applied thinning intensities were 27, 32, and 47% of merchantable basal are...We studied late-entry commercial thinning effects on growth, yield, and regeneration in a 48-year-old jack pine(Pinus banksiana Lamb.) stand. Applied thinning intensities were 27, 32, and 47% of merchantable basal area(BA) excluding skidding trails. After 15 years, mean diameter at breast height of surviving trees in the 47% BA removal increased by 4.9 cm(25%) compared to the unthinned control. The 47% BA removal also increased gross merchantable volume(GMV) tree-1by 46% compared to the control. The 27% BA removal had twice as much GMV ha-1compared to the 47% BA removal after15 years. Moreover, cumulative GMV ha-1was much higher in the 27% BA removal than in the unthinned control. The highest thinning intensity produced larger trees on average, while the lowest thinning intensity maximized volume production per hectare. Maintenance of acceptable growing stock throughout the 15-year period in the 27% BA removal could provide other ecosystem functions such as biodiversity enhancement or wildlife habitat by delaying senescence. Regeneration data showed that a shift in species composition occurred in the understory. After 15 years, the understory was dominated by black spruce(Picea mariana(Mill.) B.S.P.), white birch(Betula papyrifera Marsh.), and trembling aspen(Populus tremuloides Michx.). If regenerating jack pine is an objective after final overstory removal, additional efforts will be needed to re-establish this species.展开更多
基金supported by the Lakehead University Graduate Fellowship, Nature Science and Engineer Research Council Scholarship of Canada (NSERC) PGS A,the National Natural Science Foundation of China (Grant No. 30872000)K. C. Wong Education Foundation of Hong Kong (2008) and the funding initiative of Institute of Mountain Hazards and Environment, Chinese Academy of Sciences to the author and NSERC research grant to Qing-Lai Dang
文摘Many studies have estimated approximately ranges of thresholds of low soil temperature in the growth and ecophysi-ological traits of trees, but difficultly determined the exact values. To resolve the problem, black spruce （Picea mariana） and jack pine （Pinus banksiana） seedlings were exposed to 5, 10, 15, 20, 25, 30 and 35℃ soil temperature in greenhouses. After 90 days of the treatment, net photosynthetic rate （A）, stomatal conductance （gs）, transpiration rate （E）, water use efficiency （WUE） and specific leaf area （SLA） were measured. This study showed that all the traits had an asymmetrical peak relationship with changing soil temperature, the relationship was well simulated using a cubic curvilinear model, and the exact thresholds could be derived from the second derivative of the model. The results revealed that the thresholds varied among ecophysiological traits and between tree species. In black spruce, the thresholds were 14.1, 14.7, 10.7, 14.4 and 16.2℃ forA, gs, E, WUE and SLA; 15.4, 10.4, 14.7, 16.9 and 10.5℃ for the corresponding traits in jack pine. The lowest thresholds of E in black spruce and gs in jack pine were an indicator representing the minimum requirement of soil temperature for the regular processes of ecophysiology. The highest thresholds of SLA in black spruce and WUE in jack pine suggest they are the most sensitive to decreasing soil temperature and may play an important role in the acclimation. The averaged thresholds were at 14.0 and 13.6℃ for black spruce and jack pine, suggesting that the sensitivity of both species to low soil temperature was quite close.
文摘It is of considerable importance to investigate the influence of weathering on the degradation processes of heat-treated wood. Kiln-dried （untreated）jack pine （Pinus banksiana） and jack pine heat-treated at three different temperatures （190 ℃, 200 ℃, and 210 ℃） were exposed to artificial weathering for different periods in order to understand the degradation processes due to weathering. Before and after exposure, their color and wettability by water were determined. Structural changes and chemical modifications at exposed surfaces were also investigated using SEM （scanning electron spectroscopy）, FTIR （Fourier transforms infrared spectroscopy）, and XPS （X-ray photoelectron spectroscopy）. The results revealed that the photo-degradation of lignin and the presence of extractives play important roles in color change and wetting behavior of heat-treated wood surfaces during weathering. The structural changes also influence the wettability. The effects of weathering for woods heat-treated under different conditions were similar, but different from those for untreated wood.
基金funded by the Richard Ivey Foundationthe Haliburton ForestWild Life Reserve
文摘Insects respond to changes in microhabitat caused by canopy disturbance, and thus can be used to examine the ecological impacts of harvesting. Single-tree selection harvesting is the most common silvicultural system used to emulate local small-scale natural disturbance and maintain uneven-aged forest structure in temperate forests. Here, we test for differences in richness, abundance, and composition of hymenopteran and saproxylic insect assemblages at four different taxon levels （selected insect orders; and all hymenopteran families, and braconid subfamilies and morphospecies） between the canopy and understory of unharvested and single-tree selection harvested sites in a northern temperate forest from central Canada. Harvesting had no effect on insect assemblage richness, composition or abundance at the three highest taxon levels （order, family and subfamily）. Similarly, richness and abundance at the lowest-taxon level （braconid morphospecies） were similar, although composition differed slightly between unharvested and harvested stands. Insect assemblages were vertically stratified, with generally higher abundance （for Diptera, Hymenoptera, some hymenopteran families and braconid subfamilies） and richness （for braconid morphospecies） in the understory than the canopy. In particular, composition of the braconid morphospecies assemblage showed relatively low similarity between the understory and canopy. Single-tree selection harvesting appears to influence wood-associated insect taxa only subtly through small changes in community composition at the lowest taxon level, and thus is recommended as a conservative approach for managing these northern temperate forests.
基金supported by the grant from Forest Research Branch of the Québec Ministry of Forests,Parks,and Wildlife(No.142332012)
文摘We studied late-entry commercial thinning effects on growth, yield, and regeneration in a 48-year-old jack pine(Pinus banksiana Lamb.) stand. Applied thinning intensities were 27, 32, and 47% of merchantable basal area(BA) excluding skidding trails. After 15 years, mean diameter at breast height of surviving trees in the 47% BA removal increased by 4.9 cm(25%) compared to the unthinned control. The 47% BA removal also increased gross merchantable volume(GMV) tree-1by 46% compared to the control. The 27% BA removal had twice as much GMV ha-1compared to the 47% BA removal after15 years. Moreover, cumulative GMV ha-1was much higher in the 27% BA removal than in the unthinned control. The highest thinning intensity produced larger trees on average, while the lowest thinning intensity maximized volume production per hectare. Maintenance of acceptable growing stock throughout the 15-year period in the 27% BA removal could provide other ecosystem functions such as biodiversity enhancement or wildlife habitat by delaying senescence. Regeneration data showed that a shift in species composition occurred in the understory. After 15 years, the understory was dominated by black spruce(Picea mariana(Mill.) B.S.P.), white birch(Betula papyrifera Marsh.), and trembling aspen(Populus tremuloides Michx.). If regenerating jack pine is an objective after final overstory removal, additional efforts will be needed to re-establish this species.
