Contrasting resistance and resilience to extreme drought and late spring frost in five major European tree species

International audienceExtreme climate events (ECEs) such as severe droughts, heat waves, and late spring frosts are rare but exert a paramount role in shaping tree species distributions. The frequency of such ECEs is expected to increase with climate warming, threatening the sustainability of temperate forests. Here, we analysed 2,844 tree‐ring width series of five dominant European tree species from 104 Swiss sites ranging from 400 to 2,200 m a.s.l. for the period 1930–2016. We found that (a) the broadleaved oak and beech are sensitive to late frosts that strongly reduce current year growth; however, tree growth is highly resilient and fully recovers within 2 years; (b) radial growth of the conifers larch and spruce is strongly and enduringly reduced by spring droughts—these species are the least resistant and resilient to droughts; (c) oak, silver fir, and to a lower extent beech, show higher resistance and resilience to spring droughts and seem therefore better adapted to the future climate. Our results allow a robust comparison of the tree growth responses to drought and spring frost across large climatic gradients and provide striking evidence that the growth of some of the most abundant and economically important European tree species will be increasingly limited by climate warming. These results could serve for supporting species selection to maintain the sustainability of forest ecosystem services under the expected increase in ECEs

Do alpine plants facilitate each other’s pollination? Experiments at a small spatial scale

Short growing seasons, low temperatures, and frequent strong wind classify high mountains as adverse environments, in which pollinator abundance and activity are reduced. In such environments, plants growing in dense stands comprising several species and thus exhibiting larger and more diverse flower displays may profit by attracting more visits from scarce alpine pollinators than do plants that grow alone or in patches only composed of conspecifics. To study whether aggregation of plants increases (facilitation) or decreases (competition) the attraction of pollinators, we measured the rate and numbers with which insects entered experimental plots in the Swiss Alps, and their behaviour at flowers in plots that they entered. The plots contained individuals of the blue-flowering cushion plant Eritrichium nanum, either alone or mixed with white- to yellowish-flowering Saxifraga species. Pollinators were generally rare: in 55% of 236 observation periods, no pollinators were observed. Over 95% of the pollinators were Diptera. The average probability of observing any insect at all was higher in plots that contained some Saxifraga flowers, including mixed plots, than in those containing only E. nanum flowers. However, although insects tended to choose Saxifraga as the first flower visited in mixed plots, in all other regards their visitation of Saxifraga and E. nanum flowers in such plots was statistically indistinguishable.We also detected no effect of floral neighbourhood on the frequencies of potentially geitonogamous visits or of transitions among individual plants of the same or different species. Thus, our study suggests that the presence of Saxifraga may facilitate visitation to E. nanum at larger spatial scales, but gives no evidence for either competition or facilitation at small scales within floral neighbourhoods

Action Research’s Potential to Foster Institutional Change for Urban Water Management

The paper discusses the potential of action research to meet the challenges entailed in institutional design for urban water management. Our overall aim is to briefly present action research and discuss its methodological merits with regard to the challenges posed by the different conceptual bases for extrapolating the effects of institutional design on institutional change. Thus, our aim is to explore how Action Research meets the challenge of scoping the field in an open fashion for determining the appropriate mechanisms of institutional change and supporting the emerging of new water institutions. To accomplish this aim, we select the Water Framework Directive (WFD) as an illustrative driving force requiring changes in water management practices and implying the need for the emergence of new institutions. We employ a case of urban water management in the Volos Metropolitan Area, part of the Thessaly region in Greece, where a Pilot River Basin Plan was implemented. By applying action research and being involved in a long process of interaction between stakeholders, we examine the emergence of new institutions dealing with urban water management under the general principles of the major driving force for change: the WFD