ALBERT

Description: Management of boreal mixedwood forests in Canada has traditionally relied almost exclusively on the clear-cut silvicultural system. In recent years, greater utilization of the hardwood component of boreal mixedwoods and increased societal concerns over maintenance of the integrity and sustainability of these ecosystems has provided impetus for forest managers to consider alternative silvicultural practices in boreal mixedwood forests. Little is currently known, however, concerning the response of soils and vegetation to forest harvesting systems in the mixedwood forests of the Liard River valley, Northwest Territories (NWT). Therefore, the objective of this study was to quantify the effects of patch clear-cut, strip clear-cut, and clear-cut harvesting systems on soil properties and understory vegetation composition and structure. Treatment sites with 3 or 4 years of recovery since harvesting and adjacent uncut forest sites were sampled using transect methodology. Soil samples were collected and understory vegetation community species composition and percent crown cover were assessed in 1-m2 quadrats. Compared with the range of conditions present in the uncut forest, increases in mineral soil bulk density (2%), exchangeable calcium (7%), LFH horizon thickness (13%), pH (0.2 units), and total organic carbon (5%) and decreases in LFH horizon total nitrogen (6%) and exchangeable potassium (22%) were observed following harvesting. Harvesting resulted in the reduction in crown cover of feathermoss species and increased abundance of shrub and herb species and minimal changes to species composition. Multivariate analysis of the data indicated that the method of harvesting did not result in significant differences in species composition and structure of the understory vegetation community. Overall, winter harvesting of these boreal mixedwood sites did not have a major impact on the majority of soil properties evaluated or on the species composition of the understory vegetation community.

Description: Relatively little is known about belowground competition for nitrogen (N) between boreal forest species. The objective of this study was to compare the relative competitiveness of three early successional boreal forest species, trembling aspen (Populus tremuloides Michx.), fireweed (Epilobium angustifolium L.), and calamagrostis (Calamagrostis canadensis (Michx.) Beauv.), on 15N uptake and the growth response by containerized white spruce (Picea glauca (Moench) Voss) and jack pine (Pinus banksiana Lamb.) seedlings. Three densities (0, 2, and 6 plants/pot) of each competitor species were interplanted with individual seedlings in pots with 15N-labelled fertilizer and grown for 3 months. The conifer seedlings had the greatest fertilizer 15N uptake (129.5 and 82.3 µg/m2 root for white spruce and jack pine, respectively) when grown in monoculture and the lowest uptake when interplanted with six competitor plants (9.2 and 8.6 µg/m2 root for white spruce and jack pine, respectively). Whether grown in monoculture or with conifer seedlings, calamagrostis took up the greatest amount of fertilizer 15N. Vegetation management practices that reduce the establishment of this grass species in the field should benefit N uptake and growth of outplanted white spruce and jack pine seedlings.

Description: Moisture availability is the factor that most commonly influences the discrimination against 13C fixation (Δ) by C3 plants. Therefore, by changing the availability of moisture by way of controlling competing vegetation, Δ in white spruce (Picea glauca (Moench) Voss) seedlings should be affected. The objective of this study was to determine the influence of manual brushing on Δ in white spruce seedlings planted in disc-trenched and control (i.e., no site preparation) microsites. The effects of site preparation and vegetation management on soil moisture, photosynthetically active radiation (PAR), and Δ in white spruce seedlings were evaluated over three growing seasons. Vegetation management increased the amount of PAR reaching seedlings in the control and disc-trenched treatments by removing the shading by native vegetation around each seedling. It appears that the increase in PAR reaching seedlings decreased Δ by increasing the photosynthetic consumption of CO2. Differences in soil available moisture (up to 22%) between control and disc-trenched treatments were not reflected in Δ values, contrary to our initial hypothesis. This may indicate that the site was not moisture limiting. Also, these results underline the complexity and difficulty of determining the controlling mechanisms by which Δ is affected.

Description: The ability of noncrop plants to compete with white spruce (Picea glauca (Moench) Voss) seedlings for applied fertilizer N is not well understood. Therefore, the objective of this study was to examine the efficacy of fertilizer N uptake using 15N by planted white spruce seedlings and understory vegetation. Double 15N-labeled NH4NO3 was broadcast in 1-m2plots for control, disc-trenched, and disc-trenched + manual brushing treatments. The fate of applied 15N in white spruce and noncrop plants was determined at the end of the first two growing seasons. The major competitors for fertilizer 15N were Populus tremuloides Michx. and grasses during the first growing season, and Populus tremuloides, Epilobium angustifolium L., and Achillea millefolium L. during the second growing season. Disc-trenching plus manual brushing significantly increased the fertilizer use efficiency of white spruce seedlings by limiting competition; however,

Description: Greater utilization of hardwood species and societal concerns over maintenance of ecological integrity have provided impetus for forest managers to consider alternative silvicultural practices in boreal mixedwood forests. The objective of this study was to quantify the effects of five mechanical site preparation (MSP) treatments on soil properties and understory vegetation of mixedwood stands in the Northwest Territories (NWT). Soil and understory vegetation conditions in treatments (3 years post-MSP treatment) and adjacent uncut forest controls were sampled. Significant Shearblade Grizz R-ex and Shearblade treatment soil property effects were consistently found. Increases in bulk density (307%) and decreases for total organic carbon (92%); total nitrogen (86%); cation exchange capacity (74%); and exchangeable calcium (72%), magnesium (67%), and potassium (75%) in the soil surface (012.8 cm) were observed. Increases in mineral soil pH (1.0 units), total organic carbon (94%), cation exchange capacity (20%), and exchangeable calcium (35%) and magnesium (56%) were also found. Dissimilarity of the understory community with that of the uncut forest increased as follows: uncut forest 〈 harvested only 〈 MeriCrusher = Grizz R-ex 〈 Shearblade Meri-Crusher 〈 Shearblade Grizz R-ex 〈 Shearblade. This research suggests that winter shearblading should be utilized only where it is necessary to achieve specific management objectives.

Description: Little is known about the N uptake abilities of competitor species and planted seedlings in the boreal forest. The objective of this study was to determine the MichaelisMenten kinetic parameters of NH4+ and NO3 for white spruce (Picea glauca (Moench) Voss) and jack pine (Pinus banksiana Lamb.) seedlings, and three competitive common boreal forest early successional species: aspen (Populus tremuloides Michx.), fireweed (Epilobium angustifolium L.), and cala magrostis (Calamagrostis canadensis (Michx.) Beauv.). Uptake kinetics were measured in hydroponic cultures and expressed as maximum uptake (Imax) and ion affinity (Km). The ranking of Imax values (pmol·cm-2·s1) for NH4+ uptake was calamagrostis (84.6), fireweed (58.1), white spruce (20.7), aspen (12.5), and jack pine (10.9), and for NO3 uptake was calamagrostis (17.7), fireweed (12.5), aspen (5.8), white spruce (4.5), and jack pine (2.1). The ranking of Km values (µM) for NH4+ uptake was calamagrostis (125.9), fireweed (163.8), aspen (205.7), white spruce (217.1), and jack pine (270.5), and for NO3 uptake was calamagrostis (229.9), fireweed (274.6), aspen (336.5), white spruce (344.5), and jack pine (350.5). Calamagrostis exhibited the greatest uptake rates and affinity for NH4+ and NO3, suggesting that silviculture practices that specifically reduce establishment of this grass should benefit the growth of planted seedlings.