No abstract

Assisted migration has been proposed as one tool to reduce some of the negative ecological consequences of climate change. The idea is to move species to locations that could better suit them climatically in the future. Although humanmediated movements are not a recent phenomenon, assisted migration has lately been the source of debate, in particular within conservation biology circles. In this paper, we outline the major perspectives that help define differing views on assisted migration and shed some light on the ethical roots of the debate in the context of Canadian forests. We emphasize that there are many different forms of assisted migration, each responding to different (often unstated) objectives and involving unique risks and benefits, thus making the debate more nuanced than often portrayed. We point out certain seeming contradictions whereby the same argument may be used to both support and oppose assisted migration. The current debate on assisted migration primarily focuses on ecological risks and benefits; however, numerous uncertainties reduce our capacity to quantitatively assess these outcomes. In fact, much of the debate can be traced back to fundamental perspectives on nature, particularly to the ethical question of whether to deliberately manage natural systems or allow them to adapt on their own. To facilitate discussion, we suggest that the focus should move towards a clearer identification of values and objectives for assisted migration.Keywords: assisted colonization, climate change, environmental ethics, species conservation, forest management RÉSUMÉ La migration assistée a récemment été suggérée comme outil permettant de réduire les conséquences écologiques néga-tives des changements climatiques. L'idée est de déplacer des espèces vers des sites qui leur conviendraient mieux dans le futur. Le déplacement d' espèces par l'homme n' est pas un phénomène nouveau. Cependant, la migration assistée a soulevé des débats récemment, particulièrement dans la sphère de la biologie de la conservation. Cet article a pour objectif de souligner les racines éthiques du débat en clarifiant les principales perspectives et visions sur la migration assistée au Canada. Le terme migration assistée s'applique à plusieurs types d'intervention, chacune correspondant à des objectifs différents (souvent non mentionnés) et impliquant des risques et bénéfices qui lui sont propres. Le débat serait en fait beaucoup plus nuancé que souvent décrit. Nous soulignons certaines contradictions où un même argument est utilisé pour supporter ou s' opposer à la migration assistée. Le débat actuel sur la migration assistée se concentre principalement sur la détermination scientifique des risques et bénéfices écologiques. Cependant, de nombreuses incertitudes réduisent notre capacité à évaluer de façon quantitative les résultats de ces interventions. Une grande partie du débat est en fait liée à notre perspective fondamentale sur la nature, particulièrement à la question éthique de la prise en charge des processus naturels...

Microbes such as fungi and bacteria play fundamental roles in litter-decay and nutrient-cycling; however, their communities may respond differently than plants to climate change. The structure (diversity, richness, and evenness) and composition of microbial communities in climate transects of mature Douglas-fir stands of coastal British Columbia rainshadow forests was analyzed, in order to assess in situ variability due to different temperature and moisture regimes. We compared denaturing gradient gel electrophoresis profiles of fungi (18S-FF390/FR1), nitrogen-fixing bacteria (NifH-universal) and ammonia-oxidizing bacteria (AmoA) polymerase chain reaction amplicons in forest floor and mineral soil samples from three transects located at different latitudes, each transect spanning the Coastal Western Hemlock and Douglas-fir biogeoclimatic zones. Composition of microbial communities in both soil layers was related to degree days above 0°C (2725–3489), while pH (3.8–5.5) best explained shifts in community structure. At this spatial scale, climatic conditions were likely to directly or indirectly select for different microbial species while local site heterogeneity influenced community structure. Significant changes in microbial community composition and structure were related to differences as small as 2.47% and 2.55°C in mean annual moisture and temperature variables, respectively. The climatic variables best describing microbial composition changed from one functional group to the next; in general they did not alter community structure. Spatial distance, especially associated with latitude, was also important in accounting for community variability (4–23%); but to a lesser extent than the combined influence of climate and soil characteristics (14–25%). Results suggest that in situ climate can independently account for some patterns of microbial biogeography in coastal Douglas-fir forests. The distribution of up to 43% of nutrient-cycling microorganisms detected in forest soils responded to smaller abiotic gradients than host trees.