influence of overstory composition on understory vegetation and resource environment in the boreal forests of canada
abstract
study areas : thunder bay region, northwestern ontario ; northeastern quebec. the forest canopy is a major determinant of microclimate within the forest
ecosystem, as it intercepts, absorbs and modifies light environment in the understory. the
availability of resources in the understory has implications on the growth and
establishment ofunderstory plants. the objectives ofthis thesis were to: (1) determine by
means of literature synthesis whether understory plant species diversity is driven by
resource quantity and/or resource heterogeneity, and (2) examine the influence of
overstory composition on understory vegetation, and on the understory light resource
environment in mature boreal forest stands of central and eastern canada.
a database of studies that investigated the effects of resources on understory plant
diversity was compiled and analyzed using log-linear models. whether resource quantity
or resource heterogeneity is the determinant of understory plant diversity in individual
studies was dependent on stand successional stage( s ), presence or absence of intermediate
disturbance, and forest biome within which the studies were conducted. resource
quantity was found to govern species diversity in both young and mature stands, whereas
resource heterogeneity dominated in old-growth stands. resource quantity remained the
important driver in both disturbed and undisturbed forests, but resource heterogeneity
played an important role in disturbed forests. the results suggested that neither resource
quantity nor heterogeneity alone structures species diversity in forest ecosystems, but
rather their influence on understory plant diversity vary with stand development and
disturbances in forest ecosystems.