ALBERT

Description: Differences in N, P, and K status and N efficiency of some North American willow species and their clones were observed and evaluated. Salixeriocephala Michx., S. lucida Mühl., and S. exigua Nutt., represented by five clones each, were raised from cuttings in potted loamy sand for 113 days. Plants were subjected to three levels of fertilization (equivalent to 125, 250, or 500 kg N/ha) applied at exponential rates of addition (0.06, 0.071, and 0.082, respectively), using complete nutrient solutions and were compared with control plants (no fertilizer added). The experiment showed that nutrient concentration and nutrient uptake in the plants depended not only on treatments but also on species and clones. Thus, species and clones that removed smaller amounts of nutrients per unit of biomass could be selected. Species had a larger effect than clones on nutrient concentration and content. Total nutrient content, at the same treatment level, depended primarily on biomass production. Significant variation existed among species and clones in the ratio of biomass/total N. Salixeriocephala (the best species) produced 35.1% more than the other species, and the best experimental clones within species produced 27.8–41.6% more stem per unit of N than the poorest clones.

Description: The acetylene reduction assay was used to estimate amounts of nitrogen fixed by Lupinusarcticus Wats. (1.97 kg•ha−1•year−1) and Shepherdiacanadensis (L.) Nutt. (0.78 kg•ha−1•year−1) in a regenerating lodgepole pine (Pinuscontorta Dougl.) stand in southern British Columbia. These amounts appear to be significant, as lodgepole pine ecosystems are generally highly deficient in nitrogen. Thinning of excessively dense pine stands may provide an added growth benefit by increasing nitrogen fixation activity of understory vegetation.

Description: Total aboveground biomass and nutrient contents were measured in a mixed conifer and hardwood stand in Ontario. Removal of woody stems 〉 9 cm dbh (conventional harvest) yielded 138 000 kg/ha; removal of essentially all aboveground woody material (whole-tree harvest) yielded an additional 52 000 kg/ha, a 38% increase. Whole-tree harvest increased N removal by 191 kg/ha (132%). Logging slash on the conventional harvest plot added 163 kg N/ha to the forest floor. Nutrients within various biomass components of seven tree species were compared. Pinusresinosa Ait., the dominant conifer, produced the greatest amount of biomass per unit mass of nutrient, combining low nutrient concentrations with a high proportion of biomass in stem wood. Populustremuloides Michx., the dominant hardwood, had high proportions of cation-rich bark but had a lower whole-tree N concentration than most other species. High nutrient contents in Abiesbalsamea (L.) (Mill.) and Piceaglauca (Moench) Voss were related to large amounts of fine branches and foliage. Compared with the dominants, shade-tolerant species had less differences in nutrient concentrations between small and large diameter portions of stems and branches, suggesting a limited capacity for retranslocation. Abiesbalsamea was particularly poor at conserving K. A conventional harvest often leaves small diameter stems of species (Abiesbalsamea, Acerrubrum L.) that accumulate large amounts of nutrients and that may be poorly adapted to low throughfall cation inputs and high light intensities following overstory removal. Replacement of stands of Pinus spp. by Populus spp. represents a less efficient use of site nutrient capital in that the latter species produce less biomass per unit nutrient retained in permanent aboveground tissues. Whole-tree harvesting on nutrient-poor sites in the Great Lakes – St. Lawrence forest may lead to establishment of aspen stands of low productivity.

Description: In many northern forests, low nutrient availability constrains growth of young trees. We tested the efficacy of exponential nutrient application to load western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedlings with nutrients to enhance field performance. Seedlings were grown with conventional, constant-rate fertilization (100 mg N·L1) or with exponentially increasing fertilization at rates of 2% and 3% per day in a greenhouse. Growth and nutrient allocation were characterized. Seedlings from the three greenhouse treatments were then planted in an outdoor nursery experiment for 2 years with NPK fertilizer applied at 10, 25, or 100 mg N·L1, and in a 3-year field experiment with and without slow-release fertilizer. Seedling height, biomass, and nutrient concentration did not differ greatly among exponential or constant-rate fertilization treatments in the greenhouse. The influence of postplanting fertility, both in the nursery and in the field, outweighed the effect of greenhouse exponential nutrient application. In the outdoor nursery, seedlings from all greenhouse treatments showed increased growth with higher rates of fertilization. In the field, there were no differences in growth among seedlings from the three greenhouse treatments, but fertilization at planting increased growth. The capacity for nutrient loading in container-grown western hemlock was likely exceeded because large quantities of N were applied in all treatments.

Description: Soil and water chemistry and soil-respiration activity were studied in a mature, mixed conifer and hardwood forest and in adjacent whole-tree harvest (WTH) and conventional harvest (CH) areas dominated by hardwood sprouts. Compared with the uncut mature forest, forest floor contents of N and K were lower in the WTH area 3 years after harvest; Ca and Mg were higher in the CH area, probably owing to inputs in logging slash. Mineral soil Ca and pH were higher in the harvested areas than in the uncut area. During the 2nd year after harvest, cation concentrations in forest floor leachate varied in the order WTH 〉 CH 〉 uncut area, but differences largely disappeared the next year. Soil water NO3 concentrations were slightly elevated in the CH area, but only 1.6 kg N•ha−1•year−1 leached below the rooting zone. Bulk precipitation K and Mg concentrations were lower in the WTH area than in the CH area owing to the loss of canopy leaching from the residual stand. Slightly higher amounts of cations were found in the snowpack under the mature forest canopy. Midwinter rains caused movement of NO3 and H within the snowpack. Despite the higher soil-respiration rates in the harvested areas, no differences in soil organic matter pools were observed relative to the uncut area; harvest-related inputs of slash, decaying roots, and stumps may have offset respiratory carbon losses. Current high nutrient demands of rapidly growing sprouts in the WTH area greatly exceed nutrient inputs in bulk precipitation; this may lead to future growth declines.