Vegetation change and effects of cattle grazing in the transition mire "Burgmoos”

Mires are highly threatened ecosystems in the lowlands of Central Europe. Reduced water levels and eutrophication promote shrub encroachment and the expansion of tall species, such as common reed (Phragmites australis). In the "Burgmoos”, a Swiss mire of national importance, attempts have been made to reverse these developments through cattle grazing in parts of the mire area. To monitor overall vegetation change and to assess the influence of grazing (which started in 2004), the vegetation was surveyed in 1995, 2001 and 2007. Ecological indicator values of the vegetation changed considerably between 1995 and 2007: mean indicator values for nutrients and soil pH increased in 80 and 72% of the relevés, respectively, while mean indicator values for moisture, humus and light decreased in 81, 86 and 76% of the relevés, respectively. Plant species from bogs, transition mires and fens decreased, while trees, pasture species and P. australis increased. Grazing had a weak effect on P. australis and did not prevent an increase in abundance of this species. The abundance of transition mire species was maintained in the grazed area between 2001 and 2007, whereas it continued to decrease in the ungrazed areas. This positive effect of grazing was, however, compensated by several adverse effects: In the non-forested parts of the mire, grazing accelerated the increase of nutrient indicator values, the decrease of bog species and the increase of pasture species. We conclude that grazing has not been effective in preventing undesirable vegetation changes in the Burgmoo

Contribution of multi-source remote sensing data to predictive mapping of plant-indicator gradients within Swiss mire habitats

Remote-sensing plays an important role in wetland monitoring on the regional and global scale. In this study we assessed the potential of different optical sensors to map floristic indicator gradients across complex mire habitats at the stand level. We compared traditional CIR photographs from RC30 cameras with modern digital ADS40 data and SPOT5 satellite images as well as fine-scale topo-structure derived from LIDAR data. We derived about 70 spectral and 30 topo-structural variables and evaluated their ability to predict the mean ecological indicator values of the vegetation across a sample of 7 mire objects. The airborne images (RC30, ADS40) and the LIDAR data were found to have a high potential for use in vegetation mapping; they explained on average 50% of the variation in observed ecological indicator values. The RC30 data slightly outperformed the less optimally collected ADS40 data. The LIDAR topo-structural variables showed equal overall predictive power as the airborne images, but they performed clearly better in predicting soil moisture, soil dispersion and light. Combining both airborne images and topo-structural data improved the predictions of all indicator values considerably. The combined use of these data sources is therefore recommended for use in fine-scale monitoring of priority habitats in nature conservatio

Secondary succession in a Swiss mire after a bog burst

Severe natural disturbances can lead to the recovery of the original vegetation or the shift to new vegetation types. While post-disturbance succession is well documented for regularly disturbed ecosystems, little is known about the pathways and rapidity of vegetation dynamics after rare events such as peat mass movements in bogs. We monitored the floristic changes in a mire subject to a bog burst in 1987 for two decades through the repeated sampling of permanent plots. The mean species number per plot increased continuously, while the evenness increased only in the first decade and then slightly decreased. Declining species were mostly mire species, while colonist species were mostly wet meadow species. Species turnover was higher in the first decade after the disturbance, and was also higher in the area of peat erosion than in the area of peat accumulation. Changes in plant species composition indicate a succession towards tall-forb vegetation (Filipendulion), acidic fen vegetation (Caricion fuscae) and swamp willow forest (Salicion). We conclude that the effects of the disturbance are still ongoing, and that the mire's potential for recovery is therefore difficult to predic

Five-year changes in Swiss mire vegetation

To assess whether short-term changes in mire vegetation can be detected using the phytosociological approach, paired vegetation relevés from two surveys of 112 mire sites of Switzerland were assigned to phytosociological alliances through a numerical approach. About 30% of the plots were assigned to different alliances in the two surveys. These transitions were analysed based on species frequencies and interpreted ecologically using Landolt's indicator values. Transitions between different alliances were more frequently related to the appearance of new species rather than to the disappearance of species. Transitions from and to peat bog communities were frequent. Many plots with fen vegetation were transformed into other wetland types. Fen-grassland increased in abundance, mainly at the cost of small-sedge fens. To re-establish the function of the Swiss mires as peat producers, we recommend to raise the mean summer water table to a maximum depth of 10c

A phytosociological classification of Swiss mire vegetation

The mapping and monitoring of Swiss mires has so far relied on a classification system based on expert judgement, which was not supported by a quantitative vegetation analysis and which did not include all wetland vegetation types described in the country. Based on a spatially representative sample of 17,608 relevés from 112 Swiss mires, we address the following questions: (1) How abundant are wetland vegetation types (phytosociological alliances) in Swiss mires? (2) How are they distributed across the country--is there a regional pattern? (3) How clearly are they separated from each other? (4) How clear and reliable is their ecological interpretation? Using published wetland vegetation relevés and lists of diagnostic species for phytosociological units (associations and alliances) established by experts, we developed a numerical method for assigning relevés to units through the calculation of similarity indices. We applied this method to our sample of 17,608 relevés and estimated the total area covered by each vegetation type in Switzerland. We found that vegetation types not included in previous mapping were either rare in Switzerland (partly due to mire drainage) or poorly distinguished from other vegetation units. In an ordination, the Swiss mire vegetation formed a triangular gradient system with the Sphagnion medii, the Caricion davallianae and the Phragmition australis as extreme types. Phytosociological alliances were clearly separated in a subset of 2,265 relevés, which had a strong similarity to one particular association, but poorly separated across all relevés, of which many could not be unequivocally assigned to one association. However, ecological gradients were reflected equally well by the vegetation types in either case. Overall, phytosociological alliances distinguished until now proved suitable schemes to describe and interpret vegetation gradients. Nevertheless, we see the urgent need to establish a data base of Swiss wetland relevés for a more reliable definition of some vegetation unit

Reaktion des Schweizer Waldes auf Nutzung und Klimawandel: Schlussbericht im Programm "Wald und Klimawandel"

Die Veränderung der Schweizer Waldvegetation wurde anhand von wiederholten Vegetationsaufnahmen untersucht, um die Bedeutung des Klimawandels im Verhältnis zu anderen Faktoren zu schätzen. Die beobachteten Änderungen der Anteile einzelner Baumarten am Bestand und die Änderungen der Höhenverteilungen konnten mit Einflüssen erklärt werden, die nicht vom Klima abhängen. Die Zeigerwertanalyse der Krautvegetation ergab jedoch eine Höhenverschiebung, welche nur teilweise unabhängig von einer Klimaerwärmung erklärt werden konnte. Die Höhenverschiebung der Vegetation war geringer als die von Klimaprojektionen vorausgesagte. Aufgrund dieser Resultate gehen wir davon aus, dass bei Eintreffen eines moderaten Klimaszenarios dem Schweizer Wald landesweit betrachtet genügend Zeit bleibt, um sich ohne grossflächige Schadensphänomene an die neuen Bedingungen anzupassen. Handlungsbedarf dürfte vor allem beim Schutz vor Naturgefahren entstehen. Nicht nur wegen des Klimawandels, aber dadurch verstärkt, drängen sich mittelfristig auch Anpassungen bei der Holzproduktion auf

Response of Swiss forests to management and climate change in the last 60 years

International audienceContext Forest vegetation is forecasted to shift upslope several hundred metres by 2100 due to climate warming. However, only a small number of detailed assessments in selected regions have confirmed a climate response on the part of forest vegetation.AimsThis study aimed to analyse the relative contributions of temperature and other factors to range shifts in forest vegetation by comparing old and revisited relevés in Swiss forests.MethodsIn order to investigate such range shifts, we revisited 451 relevé plots in forests in all parts of Switzerland. Collected data comprise two independent samples, one dating from the 1950s (age 60 sample) on 126 plots and the other dating from the 1990s (age 15 sample) on 325 plots. We defined an indicator value for elevation to estimate the upslope and downslope range shifts of forest species. The influence of different site factors on range shifts was assessed by variance partitioning using Landolt’s (2010) averaged species indicator values. Vegetation changes were analysed by balancing both increasing and decreasing frequencies of plant species.ResultsOur findings show significant differences between the two survey periods, where the averaged species indicator for elevation varied greatly in both the age-60 and the age-15 samples. In addition, a significant upslope shift in the herbaceous forest layer (herbs and tree regeneration) of about 10 m per decade since the mid-twentieth century is evident. Downslope shifts were detected in the shrub/tree layer at lower elevations, which may be explained by factors other than climate warming.ConclusionsTo date, the impact of global warming on tree species composition in Swiss forests has been weaker in comparison to the effects arising from forest management and land use change. Understorey vegetation, however, shows a strong signal of upslope shift that may be explained most adequately by a combination of climate change and other factors