F. Wayne Bell

Influence of microhabitat on bryophyte diversity in Ontario mixedwood boreal forest

As forest management intensifies, the conservation of forest biodiversity is a growing concern. Bryophytes are known to represent a considerable portion of plant diversity within northern forests. This is because bryophyte diversity is closely associated with microhabitat diversity. In this study, the influence of microhabitats on bryophyte diversity was investigated by comparing eight different boreal mixedwood microhabitats. The results indicate that bryophyte diversity (species richness, abundance, and evenness) is quite variable among microhabitats. The accumulation of species richness with microhabitat quantity within a forest stand also varies among microhabitats. β-diversity analyses indicate that the variety of microhabitats has considerable influence on community structure. Frequency analysis identified bryophytes that are restricted to or prefer particular microhabitats. Although all microhabitats are important to bryophyte diversity, decayed logs and rocks supported the greatest number of micro...

Growth response of Picea mariana seedlings to competition for radiation.

The growth response of 4-year-old black spruce seedlings (Picea mariana (Mill.) B.S.P.) to reduced radiation availability (DIFN) caused by herbaceous and woody competitors was investigated on a clay and on a loam site on a research plot in Ontario, Canada. Variability in black spruce growth was less explicable by reduced radiation availability caused by woody competitors than growth variability caused by herbaceous competitors. On the clay site, competition from fireweed (Epilobium angustifolium L.), Canada bluejoint grass (Calamagrostis canadensis (Michx.) Nutt.) and red raspberry (Rubus idaeus L. var. strigosus (Michx.) Maxim.) decreased black spruce diameter by more than 40% compared to seedlings without competition. Canada bluejoint grass and fireweed also distinctly reduced black spruce diameter performance on loam (>30%). These results are discussed in relation to the need of vegetation control.

Effects of silviculture intensity on plant diversity response patterns in young managed northern temperate and boreal forests.

Abstract : Throughout much of the northern temperate and boreal forests of Canada, intensifying silviculture to enhance fibre production is of increasing interest. However, some oppose the application of intensive silviculture, citing possible negative effects on biodiversity. Using fifth-year post-harvest data from the NEBIE Plot Network in Ontario, Canada, we studied the relationship between plant diversity, silviculture intensity, and contemporary climate. Neutral, linear (positive and negative), exponential (positive and negative), quadratic (concave up and concave down), cubic, and higher-order models were fit to the data. Here we discuss the potential influence of climate and silviculture on observed biodiversity patterns. As well, we address their effects on regional species pools, succession, hierarchical structure, invasibility by exotic species, and species resilience.

Climatic sensitivity, water-use efficiency, and growth decline in boreal jack pine (Pinus banksiana) forests in Northern Ontario

Rises in atmospheric carbon dioxide (atmCO2) levels are known to stimulate photosynthesis and increase intrinsic water-use efficiency (iWUE) in trees. Stand-level increases in iWUE depend on the physiological response of dominant species to increases in atmCO2. While tree-level response to increasing atmCO2 depends on the balance between the direct effects of atmCO2 on photosynthetic rate and the indirect effects of atmCO2 on drought conditions. The aim of this study was to characterize the response of boreal jack pine (Pinus banksiana) stands in Northern Ontario to changes in atmCO2 and associated climatic change over the past 100 years. The impact of changes in growing season length, temperature and precipitation, as well as atmCO2 on tree growth was determined using stable carbon isotopes and dendrochronological analysis. Jack pine stands in this study were shown to be in progressive decline. As expected, iWUE was found to increase in association with rising atmCO2. However, increases in iWUE were not directly coupled with atmCO2, suggesting that the degree of iWUE improvement is limited by alternative factors. Water-use efficiency was negatively associated with tree growth, suggesting that warming- and drought-induced stomatal closure has likely led to deviations from expected atmCO2 enhanced growth. This finding corroborates that boreal forest stands are likely to face continued stress under future climatic warming.