Forest dynamics following spruce budworm outbreaks in the northern and southern mixedwoods of central Quebec

The effects of 20th century spruce budworm (Choristoneura fumiferana (Clem.)) outbreaks on forest dynamics was examined in the southern and northern parts of the mixedwood forest zone in central Quebec, Canada. In each region, three study areas were placed in unmanaged stands that had not burned for more than 200 years. Disturbance impacts and forest succession were evaluated using aerial photographs and dendrochronology. Spruce budworm outbreaks occurred around 1910, 1950, and 1980 in both regions. The 1910 outbreak seemed to have limited impact in both regions, and the 1950 outbreak caused heavy mortality in conifer stands (mostly of balsam fir, Abies balsamea (L.) Mill.) in the southern region. The 1980 outbreak caused major mortality in the northern region, but had little impact in the southern region. Successive spruce budworm outbreaks led to a massive invasion by hardwood species in the last century in the southern region but not in the northern region. The reason for such contrasting dynamics between regions is unknown, but we hypothesize that differences in disturbance intensities, influenced by climate, played a major role. Results from this study emphasize that generalizations about the effect of spruce budworm outbreaks on forest dynamics cannot be derived from observations made during a single outbreak or at a single location

An accumulation of climatic stress events has led to years of reduced growth for sugar maple in southern Quebec, Canada

Understanding the influence of climatic variation on forest dynamics is of great ecological and economic interest, and is essential to prescribe silvicultural interventions that will facilitate ecosystem acclimation to global change. However, the retrospective identification of climatic events responsible for the inter-annual variation of tree growth is challenging, notably because both their duration and their subsequent effects can be highly variable in time. In this study, we aimed to (1) quantify empirically the effect of climatic stress events on the short- and long-term growth dynamics of sugar maple trees; (2) compare the effects of different types of climatic events, that is, drought and thaw–freeze; and (3) compare the effects of climatic stress events to those of traditional monthly level climate metrics. To achieve this, we paired cross-dated tree-ring series to monthly and daily-level climate metrics over more than 50 yr in two distinct regions of southern Quebec. While the analysis from monthly level metrics first suggested a weak and non-stationary relationship between climatic conditions and tree growth, the analysis from daily-level metrics showed that climatic stress events, and more particularly thaw–freeze events, were strongly related to the growth of sugar maple trees. Our results suggest that the synergic influence of cumulative climatic stress events, which was exacerbated by insect outbreaks during the early 1980s, induced an important shift in the growth dynamics of sugar maple and in its response to variation in climatic conditions. These results highlight the potential negative impact of global climate change on our capacity to predict stand productivity accurately, especially if climate-sensitive growth models are based on projections of future monthly metrics. Because adverse climatic events are expected to increase both in frequency and in severity over the next decades, a general decrease in the growth rate of sugar maple is apprehended in southern Quebec

Mathematik Didaktik (teaching-learning mathematics) : an overview of the development of a web-based European module

This paper outlines the development of the chapter (module) Mathematik Didaktik as a part of the electronic ‘text book’ Didaktik/Fachdidaktik developed by TNTEE Subnetwork E. The overall approach to the development of the module is based on a model of teaching-learning as an ‘integrative transformative science’ that pays due attention to the general aims of society as well as curricula, content and learning situations. As part of this perspective, teacher competence is broadly conceptualized in terms of "professional action structures" in contrast with the narrow emphasis on technical competence and on mechanistic conceptions of a ‘technology of teaching’ that currently prevail in some parts of Europe. The teaching-learning approach is based on problem-oriented, research-oriented and co-operative learning processes. Underpinning the development are particular ideas about the nature of mathematics itself. In particular the starting point for the development is around ‘big ideas’ in mathematics – in contrast to the fragmentation that is evident in the thinking of some policy makers at this time

Gap formation and dynamics after long-term steady state in an old-growth Picea abies stand in Norway: Above- and belowground interactions

Stand dynamics and the gap initiation prior to gap formation are not well- understood because of its long- term nature and the scarcity of late- successional stands. Reconstruction of such disturbance is normally based on historical records and den-droecological methods. We investigated gap initiation and formation at the fine- scale stand level in the old- growth reserve of Karlshaugen in Norway. Given its long- term conservation history, and thorough mapping in permanent marked plots with spatially referenced trees, it provides an opportunity to present stand development before, during, and after gap formation. Late- successional decline in biomass was recorded after more than 50 years of close to steady state. Gaps in the canopy were mainly cre-ated by large old trees that had been killed by spruce bark beetles. Snapping by wind was the main reason for treefall. Long- term dominance of Norway spruce excluded downy birch and Scots pine from the stand. Comparisons of the forest floor soil prop-erties between the gap and nongap area showed significantly higher concentrations of plant available Ca within the gap area. Plant root simulator (PRS™) probes showed significantly higher supply rates for Ca and Mg, but significantly lower K for the gap compared to the nongap area. Soil water from the gap area had significantly higher C:N ratios compared to the nongap area. Fine- scale variation with increasing distance to logs indicated that CWD is important for leaking of DOC and Ca. Our long- term study from Karlshaugen documents gap dynamics after more than 50 years of steady state and a multiscale disturbance regime in an old- growth forest. The observed dis-turbance dynamic caused higher aboveground and belowground heterogeneity in plots, coarse woody debris, and nutrients. Our study of the nutrient levels of the forest floor suggest that natural gaps of old- growth forest provide a long- lasting biogeo-chemical feedback system particularly with respect to Ca and probably also N. Norway spruce trees near the gap edge responded with high plasticity to reduced competition, showing the importance of the edge zone as hot spots for establishing heterogeneity, but also the potential for carbon sequestration in old- growth forest.Gap formation and dynamics after long-term steady state in an old-growth Picea abies stand in Norway: Above- and belowground interactionspublishedVersio