Publications by J.W. Fyles

Interactions among Kalmia angustifolia, soil characteristics, and the growth and nutrition of black spruce seedlings in two boreal Newfoundland plantations of contrasting fertility

Fri, 10 Jan 2003

To determine the nature of the negative influence of Kalmia angustifolia L. on black spruce (Picea mariana (Mill.) BSP) seedling growth and foliar nutrient concentrations; the effect of proximity of Kalmia on spruce seedlings was studied on two Kalmia-dominated sites of contrasting soil characteristics in central Newfoundland. Spruce seedlings and the soil at the base of their stems were sampled, and spruce leader length and foliar N and P concentration, as well as various physicochemical soil characteristics, were determined. Path analysis was used to determine the strength of direct and indirect relationships among variables hypothesized to the causally linked. Path diagrams were generated based on current knowledge of nutrient cycling in boreal ecosystems and mechanisms previously hypothesized to account for the influence of Kalmia on black spruce. On the wetter and richer site, proximity to Kalmia was associated with reduced spruce growth and humus extractable NH4-N, suggesting nutrient competition. On the drier and poorer site, results were consistent with a direct negative effect of Kalmia on the N nutrition of spruce. On both sites, we also found evidence for a direct effect of Kalmia on spruce growth that is consistent with allelopathic effects on spruce function.

Impacts of clearcut harvesting and wildfire on soil nutrient status in the Quebec boreal forest

Wed, 20 Mar 2002

The importance of forest floor disturbance in the early regeneration patterns of the boreal forest of western and central Quebec

Fri, 09 Aug 2002

The nonvascular and vascular plant composition of the early regenerating vegetation present following wildfires and clear-cut logging has been compared separately in three areas of the black spruce (Picea mariana (Mill.) BSP) – feathermoss (Pleurozium schreberi (Brid.) Mitt.)) forest of western and central Quebec. In each area, a detrended correspondence analysis successfully differentiated the burned and logged stands along the first ordination axis. This separation mainly resulted from the greater abundance of pioneer species or lichens after fire and the greater abundance of residual species after clear-cutting. Spearman’s correlation coefficients were calculated to relate variables characterizing physical disturbance of the forest floor and general site conditions to the two first differentiating axes. Variables characterizing forest floor disturbance severity were strongly associated with the first ordination axis in two of the study areas but not in the third one. The interpretation of compositional differences in the light of plant reproductive strategies led to the identification of regeneration patterns that illustrated the influence of disturbance type and severity on post-disturbance vegetation composition. These results suggest that certain forestry practices such as careful logging with the protection of regeneration and soil, scarification, and prescribed burning may differ in their capability to address sustainable forest management issues.

Labile C, humus form and N cycling in forests: Concepts and methods

Sat, 26 Aug 2000

Respirometry techniques, as well as a new kinetic parameter that assesses the potential energy supply to soil microbes, are described. We discuss the potential and limitations of substrate-induced respirometry for deriving ecophysiological indices describing the energy and nutrient limitations of soil microbial communities. The salient points of recent investigations on the interactions between labile-C and humus forms in controlling microbial and nutrient dynamics are reviewed.

A bioassay study demonstrated that the rhizosphere of paper birch (Betula papyrifera Marsh.) seedlings increased available-C and microbial biomass in a mull soil but decreased microbial nutrient limitation. These results suggested an alternative conceptual model for microbial N acquisition termed co-metabolic N mineralization. In another study, the presence of birch and other seedlings lowered the N flux in a mor humus, probably as the result of changes in microbial community structure following the introduction of roots into microsites dominated by ligninolytic organisms. In a third study, humus from two sites colonized by the ericaceous shrub Kalmia angustifolia L. were treated with chronic small doses of glucose and the evolution of microbial biomass, basal respiration and metabolic quotient (qCO2) were compared to indices of N cycling and humus chemical quality. Results suggested that phenolic compounds in Kalmia humus could play a key role in sequestering N and restricting microbial activity, thereby overriding the effects of labile C additions on N cycling. In a fourth study involving the growth of black spruce (Picea mariana (Mill.) B.S.P.), paper birch, and Kalmia on three humus forms from central Newfoundland, it was found that complex soil x species interactions controlled the physiology of microorganisms and gross N process rates. Results were interpreted in terms of the growth strategy and competitive ability of each species.

Nitrogen acquisition and competitive ability of Kalmia angustifolia L., paper birch (Betula papyrifera Marsh.) and black spruce (Picea mariana (Mill.) B.S.P.) seedlings grown on different humus forms

Sat, 26 Aug 2000

Two species of boreal tree seedlings, paper birch (Betula papyrifera Marsh.) and black spruce (Picea mariana (Mill.) B.S.P.), and the ericaceous shrub Kalmia angustifolia L. were grown in pots with humus from a birch-dominated site and two spruce-Kalmia sites. Root systems interacted with humus form in controlling soil-N cycling as well as energy and nutritional deficiencies of soil microorganisms. In general, Kalmia seedlings affected microbial dynamics and N cycling differently than birch and spruce seedlings did. Birch and spruce seedlings reduced gross N mineralization and immobilization rates, soil mineral-N pools and the amounts of NH4+-N accreted on buried cation exchange resins in all three soils. Compared to birch and spruce seedlings, the growth of Kalmia resulted in significantly higher gross N mineralization rates, soil mineral-N pools and resin-NH4+- accretion in soil from the fertile birch site. Gross N immobilization rates in all soils were generally higher with Kalmia than with spruce or birch seedlings. All three species of seedlings acquired N from the birch site soil, whereas only Kalmia seedlings acquired N from the two spruce-Kalmia site soils. Relative to control treatments, the amount of N mineralized anaerobically increased in the birch-site soil and decreased in the poor spruce-Kalmia site soil with all three species of seedlings. All seedlings increased the microbial biomass in the birch-site soil. Kalmia humus and Kalmia root systems increased microbial energy-deficiency and decreased microbial nutritional deficiency compared to the other humus and seedlings used. Results are discussed in terms of each species' nutrient acquisition mechanism and its competitive ability during secondary succession.