Jian R. Wang

Aboveground biomass and nutrient accumulation in an age sequence of paper birch (Betula papyrifera) in the Interior Cedar Hemlock zone, British Columbia

Abstract The aboveground biomass and nutrient content (N, P, K, Ca, Mg) of stands of Betula papyrifera Marsh, aged 2, 8, 15, 45, 60, 75 years were measured in the Thompson Moist Warm Interior Cedar Hemlock variant (ICHmw3) of the southern interior of British Columbia. For four of these ages (2, 8, 60 and 75 years) measurements were made on good, medium and poor sites. For the other two ages, only stands on good sites coulde be located. Allometric equations relating dry weights of stemwood, stembark, branches and leaves to tree diameter at breast height (DBH) were developed to estimate aboveground tree biomass. Equations were not significantly different among the three site qualities. Average total aboveground tree biomass for all sites increased with stand age from 1.4 t ha −1 in 2-year-old stands (varying from 0.45 to 2.1 t ha −1 on poor and good sites, respectively) to 202 t ha −1 in the 75-year-old stand (156 and 234 t ha −1 on poor and good sites, respectively). As stand age increased, an increasing proportion of annual biomass increment was allocated to stems, but nutrients were preferentially accumulated in the leaves. Nutrient content of aboveground tree biomass increased with stand age and was generally in the order of N > Ca > K > Mg > P. Average rates of nutrients accumulation in biomass were greatest in the early stages of stand development, and less marked as stands aged. The concentrations of nutrients in tissues decreased in the following order: leaf > branch > stembark > stemwood. Understory minor vegetation contributed little to the nutrient pool of these paper birch ecosystems. Mineral soil contained the largest amount of nutrients among the various ecosystem components.

Aboveground biomass and nutrient accumulation in an age sequence of aspen (Populus tremuloides) stands in the Boreal White and Black Spruce Zone, British Columbia

Abstract A chronosequence of Populus tremuloides Michx. stands ranging from 5 to 95 years of age was measured to document changes on aboveground biomass and nutrient (N, P, K, Ca, Mg) contents for three site classes (good, medium and poor) in the Boreal White and Black Spruce (BWBS) zone in northeastern British Columbia. Allometric equations relating dry weights of stemwood, branches and leaves to tree diameter at breast height were developed to estimate aboveground tree biomass. Total aboveground tree biomass increased with stand age from 34.8 t ha −1 in the 5-year-old stand to 359.7 t ha −1 in the 95-year-old stand on good sites, and from 8.3 t ha −1 to 267.7 t ha −1, respectively, on medium sites. On poor sites, the total aboveground tree biomass ranged from 33.9 t ha −1 in a 15-year-old stand to 245.4 t ha −1 in a 95-year-old stand. As stands aged, an increasing proportion of the aboveground biomass was allocated to stems. Nutrient accumulation in aboveground tree biomass increased with stand age and was in the order of N> Ca> K> Mg> P. Temporal patterns of nutrient accumulation followed the pattern of aboveground biomass accumulation. The nutrient concentrations in different tree tissues decreased in the order leaf> branch> stembark> stemwood, except for K. Understory vegetation contributed little to the nutrient pool of aspen ecosystems. Mineral soil contained the greatest proportion of nutrient capital of the various ecosystem components.

Physiological responses of paper birch to thinning in British Columbia

Abstract The influence of thinning on the net photosynthetic rate (A), specific leaf area (SLA), photosynthetically active radiation (PAR), water use efficiency (WUE) and nitrogen use efficiency (NUE) of 9 to 13-year-old paper birch (Betula papyrifera Marsh.) stands was studied during the 1992 and 1993 growing seasons. Study sites were located in the Interior Cedar Hemlock (ICH) zone within the moist, warm subzone (ICHmw) in the Kamloops Forest Region, British Columbia, Canada. The birch stands were thinned in June 1991, from initial densities which ranged between 11 000 and 31 000 stems ha−1, to control (unthinned), 400, 1000 and 3000 stems ha−1. Significant physiological responses to thinning were observed during the subsequent two growing seasons. Photosynthetic rate of trees in the thinned stands increased significantly compared with that in unthinned trees. Photosynthetic rates between 11:00 and 14:00 h on cloudless days in the second growing season were 2.2, 7.9, 10.6 and 16.4 μmol CO2 m−2 s−1 for unthinned, 3000, 1000 and 400 stems ha−1, respectively. This increase was attributed to increases in PAR and foliage nitrogen concentration and a decrease in SLA. Among the three thinning densities, the 400 stems ha−1 treatment had the best physiological responses to thinning. Thinning these stands to 1000 stems ha−1 appears more appropriate, however, when timber management objectives, such as improvement of stem quality, are considered.

Simulation of Mixedwood Management of Aspen and White Spruce in Northeastern British Columbia

FORECAST, an ecosystem simulation model, was calibrated for aspen (Populus tremuloides Michx) and white spruce (Picea glauca (Moench) Voss) stands using data collected in the Boreal White and Black Spruce biogeoclimatic zone in northeastern British Columbia and published data. Simulations were undertaken to examine the effects of initial density of aspen on yield of white spruce in an aspen and spruce mixedwood stand, and to compare the predicted stemwood biomass yields of aspen, white spruce and mixedwood stands. Results of the simulations suggest that mixedwood management regimes on the same medium quality site should have higher stemwood yield compared to pure white spruce stand. Simulated stemwood biomass yield of pure aspen stands over 240 years on medium site varied from 682.5 Mg ha−1 to 239.1 Mg ha−1 for different rotation lengths (30 to 120 years). Repeated rotations of monoculture white spruce produced much less stemwood biomass, simulated yields over 240 years ranging from 877.3 Mg ha−1to 248.4 Mg ha−1 for rotation lengths of 60 to 240 years. Simulated aspen and white spruce mixedwood stands produced higher stemwood biomass yields than the pure white spruce stands, but less than the pure aspen stands; from 217.4 Mg ha−1 to 292.8 Mg ha−1 over 240 years. Variations in initial densities of aspen did not affect spruce stemwood biomass yield over the simulation period. This model shows potential for comparing the relative effects of different management strategies on harvestable volume and variety of other ecosystem variables. A calibrated version of the model should be useful as both a management simulator and a research tool. However, shortcomings in the representation of the canopy architecture of mixed species stands suggested the need to develop an individual tree version of this ecosystem management model for application to mixed species stands.

Competitive interactions in Ginkgo and crop species mixed agroforestry systems in Jiangsu, China

Intercropping Ginkgo and crop species in southern China is receiving increasing attention because it offers potential advantages for resource utilization, higher economic income to farmers and increased sustainability in crop production, We carried out a 2-year field intercropping system composed of Ginkgo with wheat, broad bean, and rapeseed, respectively, to determine the competitive interactions between the different species, and productivity and the economic yield of each intercropping system. The density of Ginkgo and crop species was varied systematically in a two-way density matrix composed of three monoculture densities and nine intercropping of all possible pairwise combinations of monoculture densities. Intercropping systems were assessed on the basis of several intercropping indices such as land equivalent ratio, relative crowding coefficient, relative competition intensity and vector competition analysis. The results showed that the combined biomass production of the component crop species was significantly greater in the Ginkgo/crop mixtures than in monocultures crops (Ginkgo, broad bean, wheat, and rapeseed). Ginkgo: rapeseed ratio 24:12, Ginkgo: bread bean ratio 24:5, and Ginkgo: wheat ratio 24:200 had the best total biomass production. Ginkgo: rapeseed (and broad bean) ratio 24:5 and Ginkgo: wheat ratio 24:200 in respective Ginkgo/crop mixtures had the maximum economic yield. Vector competition analysis showed that Ginkgo/rapeseed mixture exhibited an antagonistic interaction type and therefore is not suitable for intercropping. Ginkgo/broad bean mixture demonstrated the most beneficial effects among the three intercropping systems.

Post-harvest regeneration of lowland black spruce forests in northeastern Ontario

Success of natural regeneration has been a concern since the introduction of heavy machinery in harvesting. The objective was to compare the effect of three operational harvest methods careful logging around advanced growth (CLAAG), group seed tree (GST), and group seed tree followed by shearblading site preparation (SHE) on natural regeneration in the Clay Belt region of Ontario. A total of 30 stands, 562 cluster sample plots, were surveyed. Total density of black spruce regeneration did not differ, but height structure of black spruce regeneration did among harvest methods. The CLAAG method resulted in highest total regeneration density of other conifers. Decreasing density of other conifers from the CLAAG to GST to SHE sites indicated that the CLAAG method protected advance regeneration as expected and the SHE method removed advance regeneration in the path of the shearing blade. Both black spruce and other conifer regeneration densities increased with increasing time since harvest. Stocking of black spruce, all conifers, or all tree species did not differ significantly among harvest methods, nor did it change with time since harvest. Stocking was nonlinearly related to regeneration density. Models developed in this study predict that full stocking (i.e., 60%) can be reached based on regeneration density of 5000 stems per ha regardless of crop species choice preference. However, the existing stocking criterion for assessing black spruce regeneration may be problematic.

Height growth and competitive relationship between paper birch and Douglas-fir in coast and interior of British Columbia

We examined height growth patterns of paper birch and Douglas-fir in two different biogeoclimatic zones (the Coast Western Hemlock and the Interior Cedar and Hemlock) in British Columbia. Stem analysis data from 20 paper birch and 20 Douglas-fir showed that height of Douglas-fir exceeded height of paper birch at about 50 years after stand establishment at the interior site. In comparison, Douglas-fir exceeded paper birch in height at about 25 years at the coastal site. Difference in height growth patterns of the two species at the two sites contributed to the explanation of differences in the distribution and persistence of paper birch between these two biogeoclimatic zones. This means that the interspecies competitive relationships are different in the two biogeoclimatic zones. However, other differences between the two different biogeoclimatic zones, such as differences in growing degree day, length of growing season, frequencies of natural fire, insect outbreak and forest diseases, may also be important in determining why paper birch is more abundant in the Interior Cedar-Hemlock zone but not in the Coastal Western Hemlock zone.

Stand age structural dynamics of North American boreal forests and implications for forest management

SUMMARY The age structure of a stand provides an understanding of important ecological processes taking place during stand development. The age of trees has been estimated by historical records, estimation from tree size, ring counting at breast height and ground level, pith node counting, and dendrochronological cross dating. Each of these methods has inherent advantages and limitations. In the fire-driven boreal forest, stand age structure has been found to shift from a relatively even-aged structure, where all trees establish immediately after fire with a similar height and diameter, to one that is uneven-aged, where trees vary in height and diameter as time since fire increases. The age structure dynamics differ with stand species composition and influenced by non-stand replacing disturbances. Traditional forest management can shift the age structure at both the stand and landscape level, but silvicultural systems and forest management planning techniques are available to mimic natural age structural patterns.

Foliar Responses of Understorey Abies lasiocarpa to Different Degrees of Release Cutting in a Betula papyrifera and Conifer Mixed Species Stand

Foliar responses of subalpine fir [Abies lasiocarpa (Hook.) Nutt.] to thinning were studied in a 35-yr-old mixed stand of paper birch (Betula papyrifera Marsh.) and conifers. The stand regenerated naturally after a wildfire with a canopy dominated by paper birch (average height 9.8 m) and an understorey dominated by subalpine fir (average height 1.6 m). The stand was thinned to four densities of birch: 0, 600 and 1200 stems ha-1 and control (unthinned at 2300-6400 stems ha-1) in the autumn of 1995. The understorey conifers, mainly subalpine fir, were thinned to 1200 stems ha-1. The study used a completely randomized split-plot design. Three sample trees were systematically selected from each treatment replicate and each tree stratum (upper, intermediate and lower understorey). One-year-old and older age class needles were collected from one south-facing branch within the fifth whorl from the tree top. Thinning of paper birch significantly (p <0.001) increased leaf area and dry weight per 100 needles for intermediate and short trees except in the 0 birch treatment. Understorey subalpine fir trees in 600 stems ha1 birch (T3) had the largest leaf area and leaf dry weight per 100 1-yr-old needles. Specific leaf area (SLA) decreased from unthinned (T1) to 0 birch (T4). Lower understorey trees had the largest SLA. One-year-old needles had significantly higher N, P and K concentrations in all the thinning treatments. These responses are consistent with the shade tolerance of subalpine fir. The results suggest that when managing a paper birch-conifers mixed-wood forest it may be of benefit to understorey conifers to leave a birch canopy as a nursing crop.

Relative competitive abilities and productivity in Ginkgo and broad bean and wheat mixtures in southern China

Ginkgo (Ginkgo biloba L.) is a multi-value deciduous tree species grown for the production of nuts, timber and foliage for medicinal products. Understanding the ecological and biological basis for Ginkgo agroforestry systems is essential for the design of optimum Ginkgo-crop species combinations. We established two greenhouse replacement series to examine interactions between Ginkgo and wheat (Triticum aestivum L.); and Ginkgo and broad bean (Vicia faba L.). The results showed that crop species were more competitive than Ginkgo at low Ginkgo density, but less competitive than Ginkgo at high Ginkgo density. Ginkgo: wheat ratio 5:1 and Ginkgo: broad bean ratio 5:1 had relative yield total (RYT) and relative land output (RLO) values of more than one and the largest total land output (TLO) values in respective mixtures. Therefore, these two ratios might be considered optimum Ginkgo: crop ratio for enhancing the combined biomass of the Ginkgo and crop in respective mixtures. Broad bean and wheat were more competitive than Ginkgo, which was less affected by wheat than by broad bean. However, there were compensatory interactions between Ginkgo and wheat, and Ginkgo and broad bean. There was significant belowground competition for soil N between Ginkgo and the two crop species in the Ginkgo/crop mixtures. The two mixtures outperformed monocultures of the individual species when comparing the mixtures with the crop monoculture system.