Alison D. Munson

Soil Microbial Community Response to Silvicultural Intervention in Coniferous Plantation Ecosystems

Five years after planting and initial treatment, we examined the response of a microbial community to three intensive silvicultural practices: soil surface modification (scarification), fertilization, and control of competing vegetation by herbicide. We correlated microbial response with changes in environmental conditions following treatment, including soil temperature and moisture, total and available nutrients in soil, and light intensity in the tree canopy. The microbial biomass C (2.1-5.3 mg/g in the F/H horizon and 0.14-0.62 mg/g in the surface mineral soil) as determined by the fumigation-extraction method was reduced by vegetation control and fertilization. The ratio of microbial to total organic carbon (Cmic /Corg ) was also reduced by vegetation control, and tended to increase in the new organic horizon developed during the 5 yr after soil surface scarification. Microbial biomass N (0.15-0.40 mg/g in the F/H horizon and 0.014 to 0.057 mg/g in the mineral soil) was not affected by the treatments. The microbial community structure (relative volumes of bacteria and fungi) was evaluated on glass slides placed in the litter bags of pine and aspen litter. The treatment effects on the relative volumes of microorganisms on slides were similar to effects noted for microbial biomass C in the soil. Five years of vegetation succession resulted in conservative N cycling and N limitation of the plant community in control plots. In response to silvicultural treatments this state may either remain relatively unchanged after fertilization, the N limitation may be increased (scarification), or apparent C limitation induced (vegetation control). Reducing the nutrient pool by scarification caused an apparent nutrient limitation, and the microbial community tended to widen the C/N ratio. Increasing the nutrient pool by fertilization or vegetation control tended to narrow the C/N ratio of microbial biomass.

Response of northeastern North American forests to climate change: Will soil conditions constrain tree species migration?

Plant species distribution and plant community composition vary along environmental gradients. At the continental scale, climate plays a major role in determining plant distribution, while at the local and regional scales vegetation patterns are more strongly related to edaphic and topographic factors. The projected global warming and alteration of the precipitation regime will influence tree physiology and phenology, and is likely to promote northward migration of tree species. However the influence of soil characteristics on tree species migration is not as well understood. Considering the broad tolerance of most tree species to variations in soil factors, soils should not represent a major constraint for the northward shift of tree species. However, locally or regionally, soil properties may constrain species migration. Thus, while climate change has the potential to induce a northward migration of tree species, local or regional soil properties may hinder their migratory response. These antagonistic f...

Soil nitrogen dynamics and nutrition of pine following silvicultural treatments in boreal and Great Lakes-St. Lawrence plantations

Abstract Six years after establishment of a boreal forest plantation (Ontario, Canada), the impact of intensive silvicultural treatments on soil nitrogen (N) reserves, N availability and nutrition of jack pine ( Pinus banksiana Lamb.) was examined. Treatments of scarification (blade removal of entire forest floor), fertilizer application (annually) and vegetation control (annually for 4 years) were applied in a factorial design, and the site was subsequently planted to native conifer species. In the sixth season after transplanting, no significant impacts of treatments on total N reserves in the humus or surface mineral soil were noted. Scarification markedly reduced both soil ammonium (NH 4 N) and nitrate (NO 3 N) availability, especially early in the growing season. The positive effect of vegetation control on NH 4 N and NO 3 N availability was also significantly reduced by scarification. Vegetation control significantly increased NH 4 N and NO 3 N availability in the mid to late growing season, and highest levels of NO 3 N (ten times greater than control) were noted with combined fertilization and vegetation control. We compared the nutritional and growth response of jack pine on the boreal site with white pine ( Pinus strobus L.) response to the same treatments on a more southern Great Lakes-St. Lawrence forest site. Response to treatments was interpreted by vector analysis, using crown biomass estimates, rather than needle biomass, to integrate longer term response to treatment. For both species, treatments including vegetation control by herbicide resulted in greater crown biomass and N accumulation; the greatest response was observed following the three treatments combined: scarification, fertilization and vegetation control. White pine had a stronger relative response to treatments than the boreal species, jack pine, supporting the hypothesis that the boreal species does not show as great an acclimation response to changing resource availability.

Nitrogen and phosphorus release from humus and mineral soil under black spruce forests in central Quebec

In the black spruce (Picea mariana (Mill.) BSP) forests which span North America, low annual temperatures, high nitrogen and phosphorus absorption by feathermosses and small litter inputs contribute to reduced annual N and P transformation rates in soils of these ecosystems. In past studies of nutrient dynamics in these systems, concentrations of dissolved organic N (DON) and P (DOP) in soil extracts have equaled or exceeded those of mineral N and P; therefore, organic forms of N and P may be an important source of nutrition to plants growing in this region. Our objective was to determine if DON and DOP were important constituents in repeated extractions of laboratory incubated organic material and mineral soils taken from recently burned, recently harvested and fully stocked black spruce stands in central Quebec. Cumulative concentrations of DON ranged from 7 to 17% and 31 to 45% of total N extracted from the organic material and mineral soils, respectively. Cumulative concentrations of DOP ranged from 35 to 44% and 37 to 48% of total P extracted from the organic material and mineral soils, respectively. We detected a pulse of CO2-C release from the organic material after thawing, and weekly CO2-C release was related to NH4+-N release (R2=0.36, P=0.0001). These results suggest that increases in temperature after a winter freeze result in a pulse of microbial activity and NH4+-N mineralization in organic layers and that DON and DOP are an important part of N and P cycling in these boreal systems.

Silvicultural options to promote seedling establishment on Kalmia–Vaccinium-dominated sites

Seedling growth is often hampered on sites dominated by Kalmia angustifolia. In June 2000, a trial was established on a clear-cut site in Quebec, Canada, with a high cover of Kalmia and Vaccinium species. The objectives were to evaluate how soil scarification and fertilization at the time of planting influence early growth and establishment of black spruce [Picea mariana (Mill.) BSP] and jack pine (Pinus banksiana Lamb.) seedlings. During the first 2 years, scarification reduced Kalmia cover three-fold and doubled the distance from seedlings to the nearest Kalmia stem. Scarification did not increase soil-extractable NH4-N concentration, and reduced soil potassium, calcium and magnesium. Scarification had no effect on seedling water stress. Seedling growth improved and foliar nutrient concentrations were generally higher in scarified plots than in unscarified control plots. No differences were observed between single- and double-pass scarification for any variables except for ground-level stem diameter of seedlings, which was greater with double-pass scarification (12.1 vs 13.1 mm). Spot fertilization increased seedling growth and foliar nitrogen concentrations. Jack pine growth was greater than black spruce growth, an effect enhanced when seedlings were fertilized.

Three large fire years threaten resilience of closed crown black spruce forests in eastern Canada

An emerging paradigm regarding vegetation response to climate warming is that the interaction of weather extremes and disturbance will trigger abrupt changes in ecosystem types by overcoming resilience of dominant species. Black spruce (Picea mariana (Mill.)) ecosystems are widespread across the North American boreal forest, because of ecophysiological adaptations that allowed these communities to thrive in fire-prone areas. We investigated resilience of spruce-moss forests to weather-disturbance interaction after a 3-year period (2005 to 2007) of major fire activity caused by extreme fire weather in eastern Canada. Pre- and post-fire conifer densities and environmental parameters related to seed rain, post-fire seedbeds, microclimate, and post-fire weather were measured in 133 burned stands throughout the closed-crown forest of Quebec. Critically low black spruce (BS) regeneration was observed in almost all of the stands, leading to a decrease in stand density and a shift of species dominance from BS to jack pine (Pinus banksiana (Lamb.), JP). The studied sites were characterized by thick residual organic matter, resulting in a predominance of charred duff, a seedbed associated with low water retention and high variation in temperature. While high levels of JP seedling establishment were reported on this seedbed, it was unfavorable to BS germination and survival in the context of warm and dry weather that prevailed in post-fire summers. In these ecosystems, early vegetation establishment patterns are generally reliable predictors of future stand composition and the exclusion of BS will presumably be maintained through succession. During large fire years, high proportions of the landscape are subjected to the interaction of fire regime and weather that creates unsuitable conditions for BS regeneration. Hence, vegetation change is susceptible to happen at a broad scale. Therefore, the frequency of major fire years could have a decisive influence on the rate of vegetation response to climate change in this biome.

Leaf level response of planted eastern white pine (Pinus strobus L.) seven years after intensive silvicultural treatments

The present study examines the impact of intensive silvicultural treatments on environmental conditions, leaf level morphology and physiology, and growth of planted eastern white pine (Pinus strobus L.) saplings and evaluates how silvicultural treatments and the presence of competing vegetation influence the relationships between leaf nitrogen, leaf morphology, and leaf level photosynthetic capacity of saplings. The six silvicultural treatments evaluated consisted of combinations of scarification (removal of entire humus layer), vegetation control (herbicide), and fertilization (slow release fertilizer). Competing vegetation (mainly Populus tremuloides Michx.) had negative impacts on shoot water potential (Ψx), leaf nitrogen, leaf mass per unit leaf area (LMA), height, and basal area of 7-year-old saplings. Net CO2 assimilation rate at light saturation (A; both on a mass and area basis) and stomatal conductance for water vapor (gwv) were not significantly influenced by the presence of competing vegetation. The only significant impact of competition on gas exchange variables was to decrease water-use efficiency (both instantaneous and long-term WUE as expressed by carbon isotope discrimination or Δ). Scarification significantly increased predawn Ψx, height, and basal area of suppressed saplings, and Aarea, gwv, and LMA of saplings subject to herbicide application. These positive impacts of scarification were attributed to enhanced root growth due to higher soil temperatures. No positive impact of fertilization was observed in either suppressed or open conditions. Leaf nitrogen and LMA were both driving variables for photosynthetic capacity of saplings across all conditions created by silvicultural treatments, but also within both suppressed and open conditions. This suggests that the dependency of the photosynthetic apparatus on leaf nitrogen and LMA occurs whether there is competing vegetation (and/or shade) or not. However, the gradient of light availability under suppressed conditions was accompanied by a gradient of soil temperature due to scarification. It would be pertinent to investigate more fully the interactions between light availability and soil temperature, both influencing root growth and leaf level morphology and physiology of young eastern white pine.

Radiation and soil temperature interactions on the growth and physiology of eastern white pine ( Pinus strobus L.) seedlings

A greenhouse experiment was set up during one growing season to test the hypothesis that soil temperature controls a significant part of the light response of eastern white pine (Pinus strobus L.) seedlings that is observed in the field. The experimental design was a three by three factorial split-plot design, with three levels of light availability: 10%, 40% and 80% of full light; and three levels of soil temperature: 16 °C, 21 °C, and 26 °C in the soil at midday. The results show significant interactions between light and soil temperature factors on several variables (gas exchange, root growth, leaf-mass ratio and leaf–mass per unit area), but not on shoot dry mass. These interactions indicate that, in the field, a significant proportion of the light response of young eastern white pine could result from changes in soil temperature, especially under conditions of limiting water availability. Our results suggest that soil temperature must be taken explicitly into account as a driving variable when relating the growth of young eastern white pine to photosynthetic radiation.

Optimum Nutrient Concentrations and CND Scores of Mature White Spruce Determined Using a Boundary-Line Approach and Spatial Variation of Tree Growth and Nutrition

ABSTRACT Standards of optimum nutrition are not readily available for mature trees of the Canadian boreal forest. The objective of this study was to determine foliar nutritional standards for white spruce for all major nutrients [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and manganese (Mn)] using critical values (CVA) and compositional nutrient diagnosis (CND). Trees were sampled at two locations in Ontario and Quebec to cover a gradient of soil fertility levels. A boundary-line approach was used in combination with quadratic regression models to estimate the relationship between growth and foliar-nutrient concentrations or CND scores when free of the effects of interacting environmental factors. White spruce optimum nutrition ranges were computed from significant relationships (P ≤ 0.10) for N, P, K, Ca, and Mn concentrations and for N, P, and K CND scores. Optimum concentrations for first-year needles were 12.3, 1.9, 7.3, 6.5, and 0.39 mg g−1 for N, P, K Ca, and Mn, respectively, whereas optimum CND scores were 0.17, −1.65, −0.40, and −0.30 for N, P, K, and Ca, respectively. Samples from a broader range of environmental conditions will be required in order to establish standards for all major nutrients and to ascertain toxicity levels of most nutrients.

Washing procedure for mixed‐bed ion exchange resin decontamination for in situ nutrient adsorption

Abstract Mixed‐bed cation + anion exchange resin bags are frequently used to assess in situ nutrient availability in forest soils, and have demonstrated their utility for comparing the impacts of different disturbances associated with treatments. They are generally installed in organic or mineral soil horizons for a certain time period, then recovered and extracted, to inform about nutrient availability during that period. For the method to be effective, the ion exchange sites of resins must be clear from any contaminants prior to installation in the soil. A washing procedure to be conducted before in situ burial of mixed‐bed resins was developed and is described. The IONAC NM‐60 H+/OH‐ resins are consecutively washed with 2 N NaCl, deionized water, and 0.1 N NaOH. Finally, resins are rinsed with deionized water and stored moist and cold until bag preparation and burial in the soil.