The VIHsibilite Project is a community-based action-research initiative that examines newspaper coverage of HIV/AIDS issues in Quebec from 1988 to 2004. Using standard qualitative research methods, and in consultation with an advisory committee of people directly impacted by HIV/AIDS news coverage, the project discerns trends in reporting on HIV/AIDS and undertakes discursive content analysis of these, aiming to better understand in what normative ways seropositive people are represented in print media, and, ultimately, to reduce the stigma attendant upon HIV infection. Preliminary findings include indications that seropositive women tend to be represented markedly differently from men in the news.

Background: Black spruce (Picea mariana (Mill.) BSP)-forested peatlands are widespread ecosystems in boreal North America in which peat accumulation, known as the paludification process, has been shown to induce forest growth decline. However, the ecophysiological mechanisms that lead to growth reductions in black spruce remain unexplored. Trees growing in paludified forests have to deal with continuously evolving environmental conditions (e.g., water table rise, increasing peat thickness) that may require growth mechanism adjustments over time. In this study, we investigated tree ecophysiological mechanisms along a paludification gradient in a boreal forested peatland of eastern Canada by combining peat-based and tree-ring analyses. Carbon and oxygen stable isotopes in tree rings were used to document changes in carbon assimilation rates, stomatal conductance, and water use efficiency. In addition, paleohydrological analyses were performed to evaluate the dynamical ecophysiological adjustments of black spruce trees to site-specific water table variations.Results: Increasing peat accumulation considerably impacted forest growth, but no significant differences in tree water use efficiency (iWUE) were observed between the study sites. Tree-ring isotopic analysis indicates no iWUE decrease over the last 100 years, but rather an important increase at each site up to the 1980s, before iWUE stabilized. Surprisingly, inferred basal area increments did not reflect such trends. Our results suggest that the slower growth rates observed at the most paludified sites are attributable, at least partially, to both lower carbon assimilation rates and stomatal conductance. These findings show that iWUE variations do not necessarily reflect tree ecophysiological adjustments required by changes in growing conditions. Local water table variations induced no changes in ecophysiological mechanisms, but the synchronous shift in iWUE observed at all sites in the mid-1980s suggests a tree response to regional or global factors, such as increasing atmospheric CO2 concentration.Conclusions: Our study shows that paludification induces black spruce growth decline without, however, altering tree water use efficiency in boreal forested peatlands. This is the first attempt in exploring the complex interactions between stem growth, ecophysiological mechanisms, and environmental conditions in paludified sites. Additional research on carbon allocation strategies is of utmost importance to understand the carbon sink capacity of these widespread ecosystems and better predict their response to future climate change.

No abstract

No abstract

Background Paludification is widespread in the boreal biome, inducing tree growth decline in forested peatlands following the development of thick organic layers over the mineral soil. However, the ecophysiological processes involved remain poorly documented and little is known about the interactions between tree growth mechanisms and site conditions in these ecosystems. We investigated changes in stem growth and main ecophysiological processes in a black spruce forested peatland in eastern Canada by combining peat-based and tree-ring stable isotope analyses. These were conducted at three sampling sites located along a paludification gradient with different peat thicknesses.Results Organic layer thickening induces black spruce growth decline without altering tree ecophysiological mechanisms. A 40% increase in water use efficiency, or the ratio of carbon assimilated to water losses, was observed at the three sites from 1920 to the 1980s, but did not translate into enhanced tree growth. A clear shift in the 1980s revealed a decline in black spruce sensitivity to climate and rising atmospheric CO2 concentration, regardless of the organic layer thickness. Water table reconstructions revealed an important drawdown in the last few decades at the three sites, but we found no evidence of an influence of water table variations on stem growth.Conclusions This study shows that paludification induces black spruce growth decline without altering tree metabolism in boreal forested peatlands. This underlines that changes in water use efficiency are decoupled from changes in carbon allocation, which are constrained by site, or even tree-specific strategies to access water and nutrients from belowground. Our findings indicate that dynamic changes in edaphic conditions need to be considered in process models. Otherwise, failing to account for the degree of paludification can lead to misleading forest productivity predictions and result in considerable overestimations of aboveground carbon stocks from trees in the boreal regions.