Changes In Forest Species Composition Research Articles

Post fire indicators of fire intensity at indigenous forest margins in the southern Cape, South Africa

Synopsis The aim of this study was to identify post fire indicators of fire intensity at indigenous forest margins in the southern Cape. Three sites in the southern Cape were subjectively chosen in recently burnt areas to represent areas of varying fire intensity. Tree mortality outside the forest edge confirmed our subjective classification of the three sample sites into high, medium and low fire intensity sites. Fire intensity was correlated to Virgilia divaricata seedling density, species richness, the width of the Virgilia divaricata strip and the width of the burnt forest margin. These easy to measure parameters could in future be used as practical field indicators of post fire intensity. Fire intensity could then be correlated to changes in forest species composition and structure to further quantify the impacts of fires on the indigenous forest margin.

Contributions of coniferous and broad-leaved species to temperate forest carbon uptake: a bottom-up approach

Changes in forest species composition could influence ecosystem carbon uptake rates. To understand how species differed in their contributions to canopy photosynthesis, we investigated how the dominant coniferous (eastern hemlock, Tsuga canadensis (L.) Carr.) and broad-leaved (northern red oak, Quercus rubra L.; red maple, Acer rubrum L.) species in a central Massachusetts forest differed in canopy carbon uptake rates. We considered what factors influenced in situ leaf-level photosynthesis and then used a bottom-up summation approach to estimate species-specific total canopy carbon uptake rates. Variation in canopy light strongly influenced leaf-level photosynthetic rates: sunlit leaves had significantly higher rates than shaded leaves, and photosynthesis increased with canopy height. Species also differed in leaf-level photosynthetic rates, with the broad-leaved species having up to twofold higher rates than hemlock. Within hemlock, needles older than 2 years had lower photosynthesis than younger needles. Variation in leaf-level photosynthesis scaled up to influence canopy carbon uptake rates. Red oak consistently had the highest canopy photosynthetic rates, while through the season, hemlock's relative contribution to carbon flux increased and that of red maple decreased. Thus, in such mixed forests, future changes in species composition could have substantial impacts on forest carbon dynamics, particularly if red oak is the primary broad-leaved species to expand at the expense of hemlock.

Fire and Insects in Northern and Boreal Forest Ecosystems of North America

Fire and insects are natural disturbance agents in many forest ecosystems, often interacting to affect succession, nutrient cycling, and forest species composition. We review literature pertaining to effects of fire-insect interactions on ecological succession, use of prescribed fire for insect pest control, and effects of fire on insect diversity from northern and boreal forests in North America. Fire suppression policies implemented in the early 1900s have resulted in profound changes in forest species composition and structure. Associated with these changes was an increased vulnerability of forest stands to damage during outbreaks of defoliating insects. Information about the roles that both fire and insects play in many northern forests is needed to increase our understanding of the ecology of these systems and to develop sound management policies.