Dendrochronologie et dynamique forestière au pays des kiwis

La Nouvelle-Zélande est un paradis pour les écologues intéressés à la vie des forêts vierges: elles couvrent d'immenses surfaces, et sont périodiquement affectées par différents types de perturbations, comme les tempêtes, les tremblements de terre, les insectes ravageurs ou les sécheresses. Une étude en dendrochronologie permet de mieux comprendre l'équilibre naturel entre deux espèces de Nothofagus

Entwicklung der Flora im Raum Osnabrück im Hinblick auf mögliche Klimaveränderungen : mit 6 Tabellen

Die Entwicklung der Flora im Lauf des Jahrhunderts im Raum Osnabrück wurde untersucht, um eine eventuelle Wirkung einer für diesen Raum recht geringen Klimaveränderung zu finden. Die Ergebnisse zeigen, daß ein solcher Einfluß auf keinen Fall nachgewiesen, aber für einige Arten auch nicht ausgeschlossen werden kann. Die menschlichen Aktivitäten sind fast für die ganzen Änderungen der Vegetation verantwortlich und überdecken andere Ursachen. Die Ab- oder Zunahme einiger Arten bleibt jedoch unerklärt und vollständigere Untersuchungen würden vielleicht erlauben, sie als Zeiger der Klimaveränderungen zu benützen.In order to detect possible climate induced changes, the development of the flora of the Osnabrück region was analysed. The result of this analysis shows that no decisive correlation could be established between flora changes and climate change, the latter being very small anyhow. The changes of some species, six alltogether, could be interpreted as climate induced. However, the directly imposed environmental changes by human activities can explain the majority of changes in the floral composition and cover mostly other possible causes. Only for a few species are the changes unexplained and these may be useful as climate change indicators. The result of this study warrants more extensive analyses for other floras possibly covering a wider geographical range

Seed dispersal distances: a typology based on dispersal modes and plant traits

The ability of plants to disperse seeds may be critical for their survival under the current constraints of landscape fragmentation and climate change. Seed dispersal distance would therefore be an important variable to include in species distribution models. Unfortunately, data on dispersal distances are scarce, and seed dispersion models only exist for some species with particular dispersal modes. To overcome this lack of knowledge, we propose a simple approach to estimate seed dispersal distances for a whole regional flora. We reviewed literature about seed dispersal in temperate regions and compiled data for dispersal distances together with information about the dispersal mode and plant traits. Based on this information, we identified seven "dispersal types" with similar dispersal distances. For each type, upper limits for the distance within which 50% and 99% of a species' seeds will disperse were estimated with the 80th percentile of the available values. These distances varied 5000-fold among the seven dispersal types, but generally less than 50-fold within the types. Thus, our dispersal types represented a large part of the variation in observed dispersal distances. The attribution of a dispersal type to a particular species only requires information that is already available in databases for most Central European species, i.e. dispersal vector (e.g. wind, animals), the precise mode of dispersal (e.g. dyszoochory, epizoochory), and species traits influencing the efficiency of dispersal (e.g. plant height, typical habitats). This typology could be extended to other regions and will make it possible to include seed dispersal in species distribution models

Saxifrage bouc et veaux: une histoire d'amour

Version vulgarisée avec compléments de l'article en anglais (Vittoz et al., 2006). Situation et répartition de l'espèce au niveau européen, sociologie de l'espèce dans les différents marais jurassiens, hydrologie et microtopographie, enracinement, sol, rôle du bétail dans la conservation de l'espèce, génétique et quelques pistes pour sa protection

Seed dispersal distances: a typology based on dispersal modes and plant traits

Vittoz P. and Engler R. 2007. Seed dispersal distances: a typology based on dispersal modes and plant traits. Bot. Helv. 117: 109-124. The ability of plants to disperse seeds may be critical for their survival under the current constraints of landscape fragmentation and climate change. Seed dispersal distance would therefore be an important variable to include in species distribution models. Unfortunately, data on dispersal distances are scarce, and seed dispersal models only exist for some species with particular dispersal modes. To overcome this lack of knowledge, we propose a simple approach to estimate seed dispersal distances for a whole regional flora. We reviewed literature about seed dispersal in temperate regions and compiled data for dispersal distances together with information about the dispersal mode and plant traits. Based on this information, we identified seven "dispersal types” with similar dispersal distances. For each type, upper limits for the distance within which 50% and 99% of a species' seeds will disperse were estimated with the 80th percentile of the available values. These distances varied 5000-fold among the seven dispersal types, but generally less than 50-fold within the types. Thus, our dispersal types represented a large part of the variation in observed dispersal distances. The attribution of a dispersal type to a particular species only requires information that is already available in databases for most Central European species, i.e. dispersal vector (e.g. wind, animals), the precise mode of dispersal (e.g. dyszoochory, epizoochory), and species traits influencing the efficiency of dispersal (e.g. plant height, typical habitats). This typology could be extended to other regions and will make it possible to include seed dispersal in species distribution model

Biomass production of the last remaining fen with Saxifraga hirculus in Switzerland is controlled by nitrogen availability

Olde Venterink H. and Vittoz P. 2008. Biomass production of the last remaining fen with Saxifraga hirculus in Switzerland is controlled by nitrogen availability. Bot. Helv. 118: 165 - 174. For conservation management of endangered plants it is important to know which nutrient(s) control growth of the vegetation, because maintenance of low nitrogen (N), phosphorus (P) or potassium (K) availability requires different management measures. The aim of this study was to determine the type of nutrient limitation for the vegetation in the last remaining site with Saxifraga hirculus in Switzerland, using nutrient ratios in the aboveground vegetation as an indicator. We made vegetation relevees, collected biomass of the vascular plants, and took soil samples in three plots at this site. The biomass was very low (152-231 g m -2), and all three plots were clearly N-limited with N:P ratios of 7- 8. Soil extractable N concentrations were generally low, and P and K concentrations were moderate to high, which was consistent with the indicated N limitation. Hence conservation management first of all needs to prevent N-enrichment, and needs to avoid increased mineralization rates through drainage, or the accumulation of N in the system from atmospheric deposition. Therefore N output seems required through for instance grazing or mowing. The current grazing management seems to function well, since total aboveground biomass is very low and S. hirculus has a high abundance in this last remnan

Biomass production of the last remaining fen with Saxifraga hirculus in Switzerland is controlled by nitrogen availability

For conservation management of endangered plants it is important to know which nutrient(s) control growth of the vegetation, because maintenance of low nitrogen (N), phosphorus (P) or potassium (K) availability requires different management measures. The aim of this study was to determine the type of nutrient limitation for the vegetation in the last remaining site with Saxifraga hirculus in Switzerland, using nutrient ratios in the aboveground vegetation as an indicator. We made vegetation relevees, collected biomass of the vascular plants, and took soil samples in three plots at this site. The biomass was very low (152-231 g m-2), and all three plots were clearly N-limited with N:P ratios of 7-8. Soil extractable N concentrations were generally low, and P and K concentrations were moderate to high, which was consistent with the indicated N limitation. Hence conservation management first of all needs to prevent N-enrichment, and needs to avoid increased mineralization rates through drainage, or the accumulation of N in the system from atmospheric deposition. Therefore N output seems required through for instance grazing or mowing. The current grazing management seems to function well, since total aboveground biomass is very low and S. hirculus has a high abundance in this last remnant