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The results are presented of an investigation into the use of MillPebs, grinding media ranging from 5 to 12 mm in size and produced by water granulation of molten steel, for processing iron oxide concentrate with 80% smaller than 0.6 mm. MillPebs were added to a 5.2 m diameter, 10.4 m long grinding mill charged with 25 mm balls. A six-month test demonstrated that the addition of MillPebs promoted the production of fine particles. However, a reduction in the quantity of 25 mm balls associated with the charging of MillPebs reduced the rate of breakage of coarse particles., The results are presented of an investigation into the use of MillPebs, grinding media ranging from 5 to 12 mm in size and produced by water granulation of molten steel, for processing iron oxide concentrate with 80% smaller than 0.6 mm. MillPebs were added to a 5.2 m diameter, 10.4 m long grinding mill charged with 25 mm balls. A six-month test demonstrated that the addition of MillPebs promoted the production of fine particles. However, a reduction in the quantity of 25 mm balls associated with the charging of MillPebs reduced the rate of breakage of coarse particles.

Case studies of Brunswick mine concentrator's Cu/Pb circuit and LaRonde mine's Zn circuit are used to show that froth characteristics such as texture, loading and stability may be used as indicators for diagnosis and control. The influence of manipulated variables on measured froth features is shown as well as the relationship between froth characteristics, mineral recovery and flotation selectivity., Case studies of Brunswick mine concentrator's Cu/Pb circuit and LaRonde mine's Zn circuit are used to show that froth characteristics such as texture, loading and stability may be used as indicators for diagnosis and control. The influence of manipulated variables on measured froth features is shown as well as the relationship between froth characteristics, mineral recovery and flotation selectivity.

The effects of recurrent spruce budworm (Choristoneura fumiferana (Clem.)) outbreaks on balsam fir (Abies balsamea (L.) Mill.) mortality have been extensively studied in Canada. Most studies report substantial seedling recruitment of balsam fir during outbreaks when reproductive trees are dying. According to previous research, this contradiction could be due to inaccuracies in the conventional aging method. Counting the maximum number of growth rings found at the tree base would significantly underestimate tree age. Counting terminal bud scars found on the entire trunk, including buried stem, would give a more accurate tree age. In this study, we compare recruitment dynamics obtained for aging seedlings in two balsam fir populations (about 500 km apart) using (i) the conventional method and (ii) bud scar counts. For both populations, the conventional method shows substantial recruitment during adult mortality, while the second aging technique reveals reduced recruitment during the epidemic phase of the spruce budworm outbreak.

The age structure of balsam fir (Abies balsamea (L.) Mill.) regeneration is frequently used to investigate boreal forest dynamics of North America. Tree ages are usually estimated by counting annual growth rings at the shoot-root interface located above or close to the root system. Inaccurately locating the shoot-root interface could lead to imprecise age determination. In this study, balsam fir seedlings (<2 m height) were harvested in whole from closed forest stands located in the province of Quebec, Canada. Seedling age was determined by (i) counting the number of annual growth rings at the presumed shoot-root interface, and (ii) counting all terminal bud scars from the apex to the base of the hypocotyl (true collar). For all seedlings with adventitious roots, the number of terminal bud scars on the entire trunk was higher than the number of growth rings at the shoot-root interface. The formation of adventitious roots on the belowground trunk was accompanied by a reverse taper phenomenon, i.e., the number of annual growth rings decreased from the presumed shoot-root interface to the true collar. Counting annual growth rings at any level on the trunk of balsam fir seedlings that form adventitious root systems would not be reliable, underestimation's exceeding 20 years are possible and the resulting age structures could lead to erroneous interpretations of regeneration dynamics.

Underplanting white pine (Pinus strobus L.) is a promising method to reduce competition and protect against white pine weevil (Pissodes strobi (Peck)) damage. However, shading caused by over-story trees can reduce growth, vigor and survival of white pine. The objective of this study was to determine tile effects of a light gradient on the growth and overall crown morphology of white pine saplings planted in 3-meter strips within a hardwood forest some six years earlier. In 1994, we measured total height and diameter, leader length (in 1994) and numerous crown morphological variables. We then estimated the light environment above the crown of 63 young white pine saplings representing six families of close provenance. White pine grew well (i.e., >20 cm in height/year) for the first six years when planted at light levels between 10 and 66% of full sunlight. Total height and diameter after six years tended to decline more sharply below 30% full sunlight, confirming earlier experiments made in controlled conditions. No significant changes in crown morphology were evident along the light gradient. This lack of crown morphological plasticity presumably contributes to limiting the ability of while pine to grow and compete in a very low light environment. Various silvicultural options are discussed in light of the results obtained in this study.

This study examines balsam fir (Abies balsamea (L.) Mill.) recruitment in old fir stands. Studying the regeneration of these stands is essential to understand the regeneration dynamic of the species in the absence of standdestroying disturbances. The objectives were (1) to obtain substrate-seedling associations for different age-classes and according to the presence or absence of adventitious roots; (2) to evaluate the contribution of the seed rain to seedling recruitment; (3) to re-examine age structures using the most appropriate method that minimizes estimation errors due to the presence of adventitious roots. A total of 90 quadrats (1 m2) were established along transects. In each quadrat, subtrates were characterized (type and topography) and their area was estimated. All balsam fir seedlings (<50 cm tall) present in the quadrats were located, harvested whole (root and shoot), and described (age, height, presence of adventitious roots, etc). Fir seedlings were strongly associated with woody mounds covered with thin mats of mixed mosses and Pleurozium shreberi (Bird.) Mitt. but negatively associated with flat topography particularly dominated by Hylocomium splendens (Hedw.) B.S.G. The presence of adventitious root is related to seedling age more than substrate type or topography. The age structure is in agreement with seed production and disturbance regime.

Numerous researchers have suggested a causal relationship between low leaf biomass in suppressed trees and the lack of radial growth at the base of the trunk. The objective of this study was to verify this relationship with suppressed balsam fir (Abies balsamea (L.) Mill.) saplings found growing in an old-growth fir stand. A total of 29 saplings varying in height from 67 to 183 cm were uprooted. All saplings had adventitious roots. All terminal bud scars (TBS) found between the apex of the terminal leader and the trunk base (first adventitious root) as well as those found below ground were localized, and rings were counted between TBS along the aboveground trunk. Various morphological traits and the ratio of photosynthetic tissue dry mass (P, needles) to non-photosynthetic tissue dry mass (nP, above-ground stem) were used as an indicator of tree vigour. Between 3 and 33 rings counted along the aboveground trunk were missing at the trunk base. The number of missing rings at the base of the trunk was correlated with total height (r = 0.41), height growth (r = -0.51), radial growth (r = -0.44), the P/nP ratio (r = -0.73), and the proportion of live crown (r = -0.62). Moreover, from 2 to 35 additional rings, missing at the trunk base, were found in the belowground section of trunk and these missing rings were associated with the adventitious roots phenomenon. In conclusion, suppressed firs had missing rings at the base of the trunk. When all of the missing rings were added to the number of rings counted at the base of the trunk, age estimates provided a different temporal pattern of recruitment compared with that obtained by solely counting rings at the base of the trunk. Stem analysis on the entire trunk is the best aging method for suppressed balsam fir saplings.

The percentage of above-canopy Photosynthetic Photon Flux Density (%PPFD) was measured at 0, 50 and 100 cm above the forest floor and above the main understory vegetation in stands of (1) pure Betula papyrifera (White birch), (2) pure Populus tremuloides (Trembling aspen), (3) mixed broad-leaf-conifer, (4) shade-tolerant conifer and (5) pure Pinus banksiana (Jack pine) occurring on both clay and till soil types. %PPFD was measured instantaneously under overcast sky conditions (nine locations within each of 29 stands) and continuously for a full day under clear sky conditions (five locations within each of eight stands). The percentage cover of the understory layer was estimated at the same locations as light measurements. Mean %PPFD varied from 2% at the forest floor under Populus forests to 15% above the understory vegetation cover under Betula forests. Percent PPFD above the understory vegetation cover was significantly higher under shade intolerant tree species such as Populus, Betula and Pinus than under shade tolerant conifers. No significant differences were found in %PPFD above the understory vegetation cover under similar tree species between clay and till soil types. The coefficient of variation in %PPFD measured in the nine locations within each stand was significantly lower under deciduous dominated forests (mean of 19%) than under coniferous dominated forests (mean of 40%). %PPFD measured at the forest floor was positively correlated with %PPFD measured above the understory vegetation and negatively correlated with cumulative total percent cover of the understory vegetation (R2 = 0.852). The proportion of sunflecks above 250 and 500 μmol m-2 s-1 was much lower and %PPFD in shade much higher under Populus and Betula forests than under the other forests. Differences in the mean, variability and nature of the light environment found among forest and soil types are discussed in relation to their possible influences on tree succession.