Suzanne Wetzel

Understorey environment and vegetation response after partial cutting and site preparation in Pinus strobus L. stands

Understorey vegetation response to thinning, site preparation and underplanting was investigated in three natural, 110-year-old eastern white pine (Pinus strobus L.) stands. The study was arranged in a split plot, randomized block design with four replicates, and included three thinning and four site preparation treatments. Early competition response, natural and planted white pine seedling growth and nutrient uptake were monitored. Light (PAR), soil moisture and temperature were assessed during the first two growing seasons. Environmental conditions varied with treatment. With increased thinning, overall the diversity of tree species decreased and shrub species increased, although this will change with time. PAR was the most crucial for successful seedling growth. At 50% PAR, seedling biomass of both natural and planted seedlings no longer appeared limited directly by light, and site preparation and brush control treatments resulted in further increased growth and improved seedling nutrition.

Nutrient availability and regeneration response after partial cutting and site preparation in eastern white pine.

A 27-ha field experiment was set-up to study the effects of thinning, site preparation and underplanting in three 110-year-old natural eastern white pine (Pinus strobus L.) stands using a four replicate, randomized block design. Three thinning and four site preparation treatments were applied. White pine seedlings were underplanted in sub-plots. Three years after treatment, a sample of natural and planted white pine seedlings was harvested to characterize growth and nutrient uptake. Ion exchange resin bags were used to assess soil nutrient availability. Light (PAR), soil moisture and soil temperature were assessed throughout the growing season. Nutrient availability was lower in the third as compared to the second growing season after treatment. Generally, environmental conditions improved and nutrient uptake and seedling growth increased after the silvicultural treatments were applied. Early white pine seedling growth was greatest following thinning of the overstory to a two-crown spacing, together with scarification and brush control.

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.

Heterogeneity of Forest Harvest Residue from Eastern Ontario Biomass Harvests

Abstract The environmental and economic problems associated with the use of fossil-based fuels have encouraged a shift to abundant renewable resources, such as forest residues. However, before fore...

Storage compounds in Populus cuttings in response to two different nitrogen regimes

Green cuttings of two Populus clones (DN 17 and DN 74) were rooted in peat/vermiculite in growth chambers and nitrogen supplied using a relative addition rate (RA) of either 4% or 8%. Growth chamber conditions were modified to induce active growth followed by dormancy and, finally, another cycle of active growth. During each of these three phases, total biomass and nitrogen, and protein, starch and triglyceride concentrations of leaf, shoot and root tissues were measured.

Bioenergy for the urban environment

Abstract: At the present time the use of bioenergy within larger municipalities in North America is limited, but a variety of technologies do exist to generate heat, electricity and transportation fuels from biomass, which can provide for the energy requirements of cities. One of the most efficient bioenergy options for cities is combined heat and power, which generates both electricity and heat simultaneously. Planning for bioenergy in a city requires consideration of a number of important variables. The first step is an assessment of available biomass resources within an area. Biomass extraction must be evaluated against socio-economic, logistical and environmental criteria, as well as greenhouse gas balances and appropriate technology. These criteria allow decision makers to select the most suitable biomass resources and energy conversion technologies. Numerous examples of successful bioenergy applications already exist in cities, suggesting that bioenergy can be a part of sustainable urban energy supply.