Search

This study performs a meta-analysis of existing studies of European riparian forests to investigate which exotic species have successfully established in intact riparian forests and which characteristics of these forests correspond with successful establishment. We used analysis of covariance models to investigate the relationship between community species richness, percent exotic species, and several environmental variables. We found a total richness of 1380 species, of which 45 (3.3%) were exotic. Species-rich communities generally had the higher percentage of exotics, but were not significantly related to latitude or environmental variables. Exotics, in contrast, were at generally higher levels at lower latitudes and were more abundant in large river plains and communities with intermediate levels of disturbance. These results suggest that future climate change and human actions that mimic intermediate levels of disturbance may further enhance the spread of exotic species. [Copyright &y& Elsevier]

Abstract: Ivy (Hedera helix L.) favours moist nutrient-rich substrates of the floodplains of Western Europe. In this study we investigated ivy dynamics in two forest reserves of the upper Rhine. The aim was to determine the influence of flooding on ivy development following the cessation of cuttings at two forest sites of contrasting flooding regimes: the Rhinau Reserve is currently flooded while the Erstein site has not been flooded for 30 years. We also examined the impacts of severe storms in 1993 and 1999 and a long-lasting flood that occurred in 1999. Our results show that the population of Rhinau was smaller and younger because ivy is severely limited by long periods of anoxia, even though it is favoured by regular short-period floods. Indeed, juvenile growth was more rapid at Rhinau where nutrient and moist conditions are more favourable than in Erstein, but mortality was higher because of the long-lasting flood of 1999. At Erstein, the ivy showed a tendency to clump around several big trees, especially oaks and ashes, which may make the host tree vulnerable to windfall. Uprooted or broken ivies were found to survive better than the fallen host tree but could not climb to another trunk highlighting a strong dependence of ivy on its hosting tree. [Copyright &y& Elsevier]

Abstract: For many years, browsing wild ungulates have been considered the major cause for the decline of silver fir (Abies alba) in Europe. To better understand the dynamics of silver fir–beech forests hosting important deer populations, we studied forest renewal using a synchronistic approach, i.e. by comparing similar stands of different ages. Regeneration in a series of forests, where seedlings (<150cm) were submitted to an increasing browsing pressure, was examined initially. We then analysed young stands (>2m), which have grown in similar ecological conditions and also under increasing browsing. Published results on regeneration have identified three key factors as modulators of the effects of deer browsing on the composition of regeneration: understory abundance, stand composition and orientation to sun. This paper deals with the second part of the study. It examines the influence, over time, of the three environmental characteristics, identified at regeneration stage, by analysing the composition and the structure of young stands grown under comparable conditions. A total of 152 plots of 150m2 each were selected, spread over 30km2 of an ancient game reserve and core analysis was used to identify whether trees were under 150cm when browsing became noticeable. Our results confirmed the critical role of stand composition, orientation to sun and understory—the latter being far predominant. Indeed, previous stand composition (i.e. seed trees at the time of regeneration) and orientation to sun did not explain current young stand composition alone, but when a south-exposed slope was previously occupied by mature spruce, then young spruce trees were frequent. Understory clearly played a positive role in the conservation of fir, despite increased browsing by deer. In fact, fir was abundant in the young stands when understory above seedlings was important at the time of regeneration, but when understory was poor, spruce became the dominant species and fir was seldom observed. Overall, silver fir was often the dominant species among young stands, despite a progressive increase in spruce numbers. The dominance of fir may be explained by the particular sylvicultural history of the studied forests. However, in the future, the expansion of spruce, favoured by deer foraging on fir and by even-aged sylviculture, may lead to localized failure of fir regeneration. To promote silver fir–beech forest renewal, forestry practices should change towards a system more closely resembling natural forest dynamics. [Copyright &y& Elsevier]

Analyzes a concrete case in an intensively managed landscape of low altitude in eastern France. Regeneration, structure and natural cycles of small unmanaged forest stands; Level of naturalness in the landscape; Conversion of authentic biodiversity.