Patterns of ecosystem development in jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana [Mill.] B.S.P.) plantations in northern Ontario, Canada

The goal of this research was to investigate ecosystem properties of jack pine (Pinus banksiana Lamb.) and black spruce ( Picea mariana [Mill.] B.S.P.) plantations in the Lake Nipigon area of northern Ontario. The study was designed to allow for comparisons among species (jack pine versus black spruce), site types (dry versus mesic), and ages, using a chronosequence approach combined with repeated sampling.; Ecosystem carbon and nutrient accumulations, including surface mineral soil, forest floor, understory vegetation, and aboveground tree biomass ranged from 40 to 130 t·ha−1 C, 900 to 2000 kg·ha −1 N, 400 to 1000 kg·ha−1 of P, 500 to 1300 kg·ha−1 of K, 1000 to 8000 kg·ha −1 Ca, and 150 to 1300 kg·ha−1 Mg. Coarse woody debris (CWD) biomass ranged from 0.5 to 11 t·ha −1. Aboveground NPP ranged from 1.8 t·ha−1 ·y−1 to 5.9 t·ha−1 ·y−1. Between 500 and 2000 kg·ha −1·y−1 of C, 7 and 28 kg·ha −1·y−1 of N, 1 and 3 kg·ha −1·y−1 of P, 2 and 6 kg·ha −1·y−1 of K, 2 and 25 kg·ha−1·y−1 of Ca, and 1 and 2.5 kg·ha−1·y−1 of Mg were returned to the forest floor via aboveground tree litterfall. The average mass remaining (percent of initial) of jack pine and black spruce foliar litter was 63% and 50%, respectively, after 2 years of in situ incubation. Decomposition was faster in 35-year-old stands compared to 12-year old stands, and in jack pine stands compared to black spruce stands at a given age.; Understory vegetation dynamics exhibited variation among stands in directions and rates of change in species composition over a 20-year period. From 1978 to 1998, species richness increased in young, dry pine stands, decreased in older, dry pine stands, and decreased in young spruce stands. The understory vegetation in stands on mesic sites was more diverse than that of dry, sandy sites in both 1978 and 1998. The rate of change in understory species composition slowed with time after disturbance, indicating an increasing stability in micro-environmental conditions as the influence of harvesting disturbance became weaker with time.; The results of this thesis suggest that altering the species composition and age distribution of forest stands in northern Ontario by converting natural forests to plantations will affect understory vegetation community dynamics, carbon and nutrient pools and fluxes, and net primary productivity over the boreal landscape.