Annik Schnitzler

Impact of river management history on the community structure, species composition and nutrient status in the Rhine alluvial hardwood forest

The present-day Rhine alluvial hardwood forest (Querco-Ulmetum minoris, Issler 24) in the upper Rhine valley (France/Germany) is comprised of three vegetation units, one still flooded by calm waters (F) and the two others unflooded, one for 30 years (UF30) (after the river canalisation) and the other for about 130 years (UF130) (after river straightening and embankment work in the middle nineteenth century). In the three stands, species composition, structure and diversity of vegetation and nutrient content of mature leaf, leaf litter and soil have been studied. Fungi (Macromycetae) were only studied in two stands (F and UF130). The intensity of nutrient recycling was exemplified by comparing the chemical composition of rainwater, flood, throughfall, mature leaf, leaf litter, soil and groundwater in two of these stands (F and UF30).The elimination of floods has caused a change in floristic composition, tree density and plant diversity. Tree density was higher in the two unflooded stands and was related to a large increase in sapling (< 6 cm dbh) density more than to a change of stem (> 6 cm dbh) density. Sapling density increased 2 times and three times in the UF30 and the UF130 respectively, whereas the stem density increased only 12% in the first stand and decreased 29% in the second one. The saprophytic macromycete communities have been supplemented with mycorrhizal species. Leaf litter production was slightly greater in the flooded (4.44 T ha-1 yr-1) than in the two unflooded stands (≤ 3.72 T ha-1 yr-1). Foliar N level is twice as high in the flooded stands in spite of an opposite soil status. P level decreased in soil and leaves with the duration of isolation and was at the same level in the groundwater in two stands (F and UF30). K, Mg and Ca contents of green leaf and leaf litter were high due to the geochemistry of the Rhine substrate (calcareous gravels and pebbles) and similar in all the stands studied, even though there are large inputs of these three elements by floods. Moreover we showed that the groundwater chemistry reflected the variations of nutrient inputs and thus could be a good indicator of the functioning of an alluvial ecosystem and of its change as a result of human activities. The restoration of floods in hardwood forest contributes to the preservation of alluvial vegetational structure and composition, the stimulation of biological processes and a better plant mineral nutrition and water supply.

European alluvial hardwood forests of large flood plains

Alluvial hardwood forests (Querco-Ulmetum) are found on flooded but well-drained and fertile soils of big European floodplains. High disturbance regime of the river combined with a relatively warm and moist local climate of the floodplain valley are the main factors responsible for the original features of this community (dendroflora richness, structural and successional complexity, high productivity). This paper summarizes available information from this forest community in Europe with emphasis with the QuercoUlmetum of the Rhine valley (Alsace, France). The results obtained in this study area from twenty years of team work demonstrate that the floristic composition varies within sectors of a single stream with changes in channel slope. Floristic and structural features of hardwoods change too in the ditferent parts of the upper Rhine according to a flood-risk gradient

River dynamics as a forest process: Interaction between fluvial systems and alluvial forests in large European river plains

This paper corresponds to an overview of the impacts of the inundations on gallery forest processes, with examples of the upper Rhine valley, France. The geomorphic pattern of big river plains, the particularities of the nutrient cycle, the adaptations of the flora, the specificities of the sylvigenetic cycles are detailed, with examples of the upper Rhine valley.RésuméCet article se propose de passer en revue les impacts majeurs des rivières sur les forêts riveraines, en s’appuyant sur les écosystèmes alluviaux de la vallée du Rhin, en France. Les adaptations de la flore et les spécificités des cycles sylvigénétiques sont mis en relation avec les particularités géomorphologiques et celles des cycles biogéochimiques particuliers au milieu alluvial tempéré.

Evolution of major pattern models and processes of alluvial forest of the Rhine in the rift valley (France/Germany)

In the rift valley (North-East of France/South-West of Germany), the Rhine runs freely for 300 km from South to North. The absence of natural obstacles allows the development of a very regular profile of the river. We have therefore an opportunity to study very gradual modifications of the alluvial forest communities of the fluvial corridor from upstream to downstream, according to the gradual evolution of the ecological factors, related to slope decrease and hydrological modifications. We describe, from Basel to Mainz: 1) modification of dynamic processes in the forest communities such as successional sequences or sylvigenetic mosaïcs of the terminal stages. 2) modification of species richness. 3) reduction of species diversity. 4) simplification of the forest stratification. 5) modification of efficiency of the biogeochemical cycling. 6) ecological vicariances. 7) modification in species behaviour. modification of dynamic processes in the forest communities such as successional sequences or sylvigenetic mosaïcs of the terminal stages. modification of species richness. reduction of species diversity. simplification of the forest stratification. modification of efficiency of the biogeochemical cycling. ecological vicariances. modification in species behaviour.

Successional status of trees in gallery forest along the river Rhine.

. 20 alluvial forest stands of different ages along the river Rhine in central Alsace, France, are described. A natural complex landscape occurs which is formed by erosion activity of the river. Recent human impact (canal construction, cutting) has affected river hydrology: flooding is eliminated over large areas and the underground water levels are stabilized. The forest vegetation varies in species diversity and structure, from young pioneer to older, mid-successional forests. The forests were classified into four associations: Salici-Populetum nigrae, Ligustro-Populetum nigrae, Fraxino-Populetum albae and Querco-Ulmetum minoris. The first three communities are ‘softwood’ because of the dominance of Salix and Populus, the fourth, dominated by Quercus robur, Fraxinus excelsior and Ulmus minor, is ‘hardwood’. Differences in structure, species composition and diversity in 10 widely varying stands in 30-yr and 150-yr old forests are quantified and interpreted in relation to the processes and gradients (moisture and texture) involved. A model of forest succession is developed as follows: 1 Whatever the topographic level, Salix and Populus species are the most competitive in colonizing bare sediments. 2 Under natural conditions, pioneer softwoods are generally replaced by hardwoods in less than 100 yr. 3 Old Querco-Ulmetum is basically the terminal stage of the alluvial succession. 4 Old softwood forests result from an interruption of the natural course of succession. Softwoods may be an intermediate or late-successional phase depending on the interruption. 5 Successional processes change according to hydrological and edaphic gradients. 6 Allogenic processes of flooding are fundamental in the space-time species pattern. 7 Allogenic processes are responsible for the high species and community diversity.

Conservation of biodiversity in alluvial hardwood forests of the temperate zone. The example of the Rhine valley

Abstract Destruction of wetland temperate forests was particularly high during the past three decades throughout the world. Among the alluvial communities, the hardwood forest, which represents the highest level of organization in big river plains, is very vulnerable to environmental damage. The present hardwood forests are scarce in Europe after wide clearcuts, and have suffered great damage after elimination of the natural river dynamics. In Europe, the Rhine is probably the most damaged fluvial system. However, hardwood forests are still present along the river, even if mainly seminatural and unflooded. The purpose of this paper is to present an overview of the ecological features of the Rhine hardwoods before and after human alteration, and to propose a planning strategy for their conservation, following the island biogeography theory of Harris. The ideas developed here could be used for other damaged river forests in the temperate zone.

Biodiversity of floodplain forests in Europe and eastern North America: A comparative study of the Rhine and Mississippi Valleys

In this study, we investigate the mechanisms driving biodiversity in floodplain forests with a comparison of the composition and dynamics in the warm-temperate floodplain forests of the lower Mississippi Valley and the cool-temperate floodplain forests of the lower Wisconsin and Rhine River Valleys. We employ data from original research, as well as from the literature. We compare species, genus, and family diversity across regions with respect to species richness, numbers of species per family and genus, and a similarity index. We examine these results within a historical context, as well as with respect to river-floodplain dynamics. We also compare productivity data and successional stages for each region. We find a lower species, genus, and family richness in the cool-temperate forests of the Rhine compared to the cool-temperate forests of the Wisconsin, a probable result of the lack of available refugia for Rhine species in times of glacial expansion. We find the highest richness in the lower Mississippi Valley, likely a result of climatic factors and the availability of refugia in this region. In each of the regions, floodplain forests are more diverse than their upland counterparts, demonstrating the role of river-floodplain dynamics in maintaining species diversity. Each region maintains a high and relatively similar level of productivity in the floodplain forests. They also experience similar stages of succession, although succession becomes more complex in the warm-temperate forests of the Lower Mississippi.

Towards an ecological basis for the conservation of subalpine heath-grassland on the upper ridges of the Vosges

. The subalpine oligotrophic heath-grasslands, assigned to the Pulsatillo-Vaccinietum and Violo-Nardetum, occurring at the upper ridges in the Vosges at 1100 - 1300 m a.s.l. are of conservational interest because they form natural, mature and stable ecosystems. The Pulsatillo-Vaccinietum is particularly rich in endemic plant species and subspecies due to a local oceanic-subarctic climate and the continuous occurrence of the community throughout the Holocene period, when the association was not affected by changes in the prevailing environmental conditions. After a period of abandonment during and after World War II, agriculture was intensified through mineral fertilization and liming, sometimes mowing, and even ploughing and sowing. Seven pastures were selected to estimate the present plant biodiversity. Losses of biodiversity were assessed on the Kastelberg ridge by diachronic analysis of the vegetation composition and structure over the last 30 years. Species diversity changed in both associations through a decrease in the abundance of oligotrophic, acidophilic species, typical of the mountains of western Europe, and an extension of grassland types of the Violo-Nardetum trifolietosum. Strategies for a return to more natural conditions include the abandonment of fertilization and liming, except locally around farms. Regular mowing is needed in order to decrease the nutrient level of the sites.

Comparison of landscape diversity in forests of the upper Rhine and the middle Loire floodplains (France)

Traditional measures of biotic indices (α, β, δ) from phytosociological relevés are used to compare diversity at three scale-levels in the upper Rhine valley (Alsace, northeastern region) and the middle Loire (Bourgogne, central region), France. Both study areas included a tributary. The Ill, which is the Rhine tributary in this sector, has no forest communities in common with the main river because of opposite hydrological and edaphic characteristics. This is not the case in the Loire valley, in which the fluvial characteristics are close to those of its tributary, the Allier.Nearly all forest communities (12/14) were shown to be species-rich, due to the role of natural disturbances. Species richness peaks in late-successional forests of the Rhine valley (for example, up to 50 woody species in Querco-Ulmetum). Sixty per cent of the forest-communities are comon to the two floodplains, which explains why 85% of the families, 65% of the genera and 55% of the species are in common. Compared to the Loire valley, the Rhine valleys shows higher biotic diversity. This was related first to its geographical situation, and second to higher landscape heterogeneity. Human disturbance through river management is responsible for changes in species composition as shown by floristic comparison of flooded and unflooded sites. Insularity of natural forests among man-made landscapes is involved in species diversity. In order to preserve the natural diversity of such rich landscapes, floodable areas should be recreated and the attitudes of foresters should evolve accordingly.

Dynamics in natural mixed-beech forest of the Upper Vosges

Forest dynamics were analysed in the Upper Vosges mountains of north-eastern France in two reserve areas, Frankenthal-Missheimle (FM) and Grand Ventron (GV), located in the Ballons des Vosges Natural Regional Park (Parc Naturel Regional des Ballons des Vosges). Two plots of 3000 m2 each were established in mixed beech woodlands located just below sub-alpine beech forests for long-term monitoring. The main aim of the study was to interpret how the different species populations in mixed-beech woodlands in the Vosges grow and interact over the long term, and to determine the disturbance history. The study combined vegetation description, dendrological and structural data, architectural descriptions and drawings and light distribution and soil analysis. Historical information was also taken into consideration. Soils in the two plots showed available phosphate P values > 0.14 g kg−1, indicating good levels of phosphorus supply for plants, except for A1/C horizon (1Va soil) which corresponds to a medium-fertility soil. However, soils were found to be shallow because of the slope, a factor that may limit water availability for adult trees and seedlings. As the canopy (composed of existing trees) consists of shade trees, the growth rates for seedlings and saplings (potential trees) depends on the canopy architecture: when growing in sunlit gaps, saplings reach full daylight (canopy height) in less than 100 years. When developing in shade (suppressed state), saplings may need up to 150 years before reaching full daylight. Alternating periods of rapid and slow growth explain why some trees present a wide range of stem diameters and ages in the area leading up to the canopy (some trees are more than 300-years-old), in contrast with the relatively homogeneous height classes distribution, indicating suppression periods. Trees in the FM and GV plots were found to have different growth rates. Both study plots developed with similar past disturbance events, the two most important being at the beginning of the 18th century. In addition, the forests were regularly affected by smaller disturbances until present. Because of the spatial heterogeneity and large range of ages represented, the forest stands within the two natural reserve areas are presently considered to be the best-preserved sites in the upper Vosges, but their situation near the timber line prevents them from becoming models for forest management at lower altitudes.