Changes in foliar nutrient content and resorption in Fraxinus excelsior L., Ulmus minor Mill. and Clematis vitalba L. after prevention of floods

This paper focuses on the impact of flood on tree mineral nutrition through measurement of resorption (i.e. transfer of nutrients from leaves to perennial organs). Nutrient (N, P, K, Mg, Ca) concentrations in leaves of three representative species, Fraxinus excelsior L., Ulmus minor Mill. and Clematis vitalba L. were measured before and after abscission on flooded and unflooded hardwood forests of the upper Rhine plain. The nutrient concentrations in the soils, which were measured in the top layer of the study sites, were higher in the flooded sites for P but slightly lower for N and K, and identical at both types of site for Ca and Mg. The summer foliage concentrations were higher for N and P in the flooded areas, and probably related to the flooding process, which contributes to regular nutrient inputs in the flooded forest, causes high fluctuations of water level and increases bioavailability of certain nutrients. Resorption occurred for all nutrients in the three species, and was higher for N, P and K (40-70 %) than for Ca and Mg (0-45 %), but not significantly different at the two sites. This paper stresses the variability of the test species response (nutrient content and resorption) to the soil and flood water nutrient sources, and tries to specify parameters which control resorption, i.e. soil fertility, tree species or flood stress. © 1999 Inra/Éditions scientifiques et médicales Elsevier SAS

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

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

Genetic polymorphism and phenotypic plasticity : two advantages for the dispersal of Japanese knotweeds

The Japanese Knotweed s.l. population of a riverine region of north-eastern France was examined for a variety of ecological and genetic parameters. The population was dominated by the hybrid Fallopia x bohemica, but the population was morphologically variable and unusual in its being comprised entirely of hermaphrodite 6x and 8x F. x bohemica plants, plus a single aneuploid adult. Chromosome counts are given, and these indicate that both aneuploid and euploid individuals are being produced and becoming established in the study area. It was also found that all plants examined had the F. japonica var japonica chloroplast haplotype. Based on differences in morphology and phenology, the clones were divided into four main categories (1 to 4). Category 1 was widely distributed (nearly 80 % of the area) with the other three having a much more restricted occurrence. Category 1 produced little seed and was not the tallest plant or the clone with the fastest growth. The other categories all produced seed and grew faster. From these results, we can conclude that from an ecological point of view, some clones are more aggressive than others with a similar chromosome composition. Aggressiveness can be linked to the absence of seed production and possession of large leaves, which might allow higher storage of nutrients and better volume of rhizome in the soilPlusieurs populations de renouées en Alsace ont été analysées du point de vue génétique et écologique. Elles sont dominées par l'hybride Fallopia x bohemica, mais celui-ci présente une grande variabilité génétique, et différents types de ploïdie : hexaploïde, octoploïde et aneuploïde. Toutes les plantes ont pour mère Fallopia japonica. Sur la base des différences morphologiques et phénologiques, les clones ont été divisés en 4 catégories. La catégorie 1 est largement distribuée (près de 80 % de l'aire d'étude). Elle produit peu de graines, mais c'est le clone le plus envahissant. D'un point de vue écologique, certains clones sont plus « agressifs » que d'autres de même composition chromosomique. L'agressivité serait liée à l'absence de production de graines et à la présence de grandes feuilles, ce qui permettrait un plus grand stockage des nutriments et un meilleur volume du rhizome dans le sol

Is there a future for wild grapevine (Vitis vinifera subsp. silvestris) in the Rhine Valley?

The wild grapevine, Vitis vinifera L. subsp. silvestris (Gmelin) Hegi, is considered to be an endangered taxon in Europe, mainly as a consequence of the introduction of pathogens from North America and of the destruction of its habitat. In the Rhine Valley, nearly all populations disappeared due to river management, the intensi.cation of forestry, and the introduction of phylloxera. After a growing awareness of the need to preserve endangered forest ecosystems, attempts to reintroduce wild grapevine in the Rhine Valley were performed, particularly in the French nature reserves Erstein and Offendorf since 1992. However, regular surveys of the plants indicate the rapid decline of the populations. In 2002, we proposed to summarise the knowledge accumulated after 10years of experiments. Results indicate that from the initial 91 individuals planted in 1992, only 14 survived in 2002 (2 in Erstein, 12 in Offendorf). The failure of the experiment may be explained by several factors: unsuitable sites (too shady, absence of support for the young plants), absence of monitoring, vandalism or predation. According to these results and recent knowledge of the ecology of the plant and of vines in general, new transplantation experiments are proposed in which the plants will be monitored during their establishment in the forests. The success of this second transplant (50 plants per reserve) will be enhanced by restoration projects of the Rhine River dynamics, with partial re-.ooding. Floods should help to avoid, or at least to reduce, pest and disease expansion on future adult plant

Quel système de référence pour la restauration des systèmes alluviaux rhénans ?

Floodplain ecosystems consist of a mosaic of shifting interactive habitats (forests, river channels and alluvial aquifers). Flood pulse, hydrological connectivity and geomorphological dynamics are key factors for high species diversity and productivity, complexity in successional trajectories and importance of ecotones between terrestrial and aquatic ecosystems. Most rivers in Europe have been drastically altered by dams and reservoirs, canalisation, reduction of the welland area, eutrophication and various other land-use developments. After a very long period of destruction of ftoodplain integrity, the need for protecting and restoring alluvial ecosystems slowly emerged over the last three decades. Restoration needs to define reference conditions, present conditions and restoration objective states, according to the principle of naturalness. This principle includes hydrological functionality (taking into account the flood pulse), the spatio-temporal diversity of habitat types and species, such as alluvial forest succession and connection of lateral arms to the active channel. We take examples in the upper Rhine valley to support the naturalness concept and to propose sorne principles on this basis for a restoration programme. The preservation of the hydrological functioning (i.e. flooding) ensures an efficient purifying capacity of the soil root system, with regard to phosphate and nitrate. As a consequence, groundwater nitrate and phosphate concentrations are very low under alluvial forests. Moreover the ftooding regime maintains a certain heterogeneity of aquatic and terrestrial habitats. The hydrological network, i.e. the former lateral arms, is supplied by different types of water (ground and/or surface water) and water quality differs according to their degree of conneclion to the active channel. The connected arms, is eutrophie whereas the disconnected arms evolve towards an oligotrophic state. The aquatic macrophytes communities reftect the change in water quality. The spatio- temporal variability of habitats is higher in the ftooded sectors than in the unftooded ones. As a consequence the ftooded sectors include more aquatic macrophytes communities (3 to 5 according to the hydrological year vs 2) and each community has greater species richness. A similar relationship exists for terrestrial habitats and forest communities. Hard wood forests tend to dominate the unftooded sectors whereas the flooded areas present a very rich spatio-tempoal mosaïc of forests units including all steps of the alluvial succession. The comparison of forest architecture between ftooded and unftooded sites shows that disconnection results in an increase of the ligneous density, a decrease of the tree height, the absence of treefall and a decrease of lianas (for example ivy).The Rhinau island, a still flooded sector in the Rhine floodplain can be used as a basis for the naturalness concept, due to the preservation of a certain functionnality, even if flooding duration is lower than before the Rhine canalisation (2 days versus 15 days). The two other sites, with differing durations of isolation (30 and 130 years), show different levels of change in floristic composition and structure of forests, and aquatic macrophyte communities . Accordingly, the restoration programme needs to engage more direct interventions. A key factor to emphasize should be the restoration of natural hydrological functioning. On the basis of the concept of naturalness, we therefore propose a four- step restoration programme : 1) restoration of free flow of water in the former lateral arms by connecting them to the river, 2) restoration of natural floods based on Rhine discharges, 3) development of a specific programme for the by-passed sections, 4) finally, development of the inter-connection of the restored areas along the riverLes zones alluviales, traversées par des flux d'eau et d'énergie fournis par un cours d'eau, sont organisées en ensembles fonctionnels interactifs associant des systèmes terrestres forestiers et/ou prairiaux et des systèmes aquatiques. Le fonctionnement par pulsations (« flood pulse »), la connectivité hydrologique et la dynamique géomorphologique sont les facteurs-clés de la diversité et de la productivité biologiques. Les aménagements hydrauliques des grands fleuves ont fortement réduit la surface du lit majeur et perturbé, voire supprimé, les fonctions d'écrêtement des crues, de recharge de la nappe, d'épuration des eaux et de diversité du complexe alluvial. Il est proposé de restaurer des zones inondables et de recréer ainsi des conditions favorables à la restitution de leurs fonctions. La restauration et la gestion de ces zones passent par la détermination de différents états, état de référence (celui du fleuve « sauvage » ), état actuel et état objectif sur la base du principe de naturalité. Ce principe inclut la fonctionnalité hydrologique (maintien d'un fonctionnement par pulsations), la diversité spatio-temporelle des habitats (conservation de la succession alluviale forestière, connexion des bras latéraux au fleuve) et des espèces. Au travers des exemples pris parmi les sites rhénans, présentant des degrés variables de naturalité, nous définissons les grands principes de mise en place d'un programme de restauration du Rhin supérieu

Relevance of the architectural model for analysing forest biodiversity. Application to nature reserve management in the Rhine area

Une illustration de l'intérêt du modèle architectural est proposée par l'analyse d'un profil architectural, effectué dans la réserve rhénane à bois durs de Rhinau (Alsace). Ce profil, choisi pour sa richesse en espèces ligneuses (14) et son architecture spontanée, montre le côtoiement de nombreuses éco-unités de petites dimensions, à différentes phases de développement. Les espèces les plus fréquentes sont le Frêne, qui se trouve surtout dans les éco-unités en phase de croissance. Les éco-unités matures sont dominées par de grands chênes en début de sénescence. Les densités élevées des petits arbres et des buissons, et la canopée ouverte expliquent l'architecture très étagée du profil (3 niveaux de stratification sont reconnus), la grande variabilité des indices foliaires (de 2,1 à 5,3) et du bilan radiatif (de 0,44 à 10,2 moles par mètre carré et par jour). Cette architecture étagée montre une certaine stabilité vis-à-vis des perturbations (inondations, vents). La stabilité de la forêt se manifeste également par la résistance à l'invasion par les plantes exotiques. L'absence du Chêne dans les éco-unités jeunes, notée également par d'autres approches méthodologiques, signe une évolution sylvigénétique vers la frênaie

Towards a new European wilderness: Embracing unmanaged forest growth and the decolonisation of nature

International audienceIn Europe today, relatively pristine forest areas are very rare, with only 1.4% of the landscape identified as untouched forest and another 3.3% as having minimal intervention. In response to the small, isolated nature of these forests, ideas have emerged around the re-creation of a "new European wilderness" as a nature conservation strategy. Indeed, since the end of the 19th century, traditional land use practices have been in steady decline throughout many of Europe's rural landscapes, particularly in mountainous regions and areas with poor soils and harsh climates. These very recent ecosystems have been identified as "emerging," "novel" or "feral," but given enough time these areas could grow into mature forests. A conservation strategy based upon letting ecosystems evolve out of human control is, as one might expect, a controversial one for Europeans. Indeed, many people enjoy the diverse and small-scale structured landscape shaped by milennia of sustainable practices by farmers, and their loss is usually seen negatively. In this essay I argue the necessity for such a re-wilding strategy and provide examples in unmanaged forests and natural successions of the Mediterranean basin, temperate Europe and floodplains with regard to the ecological benefits that they may bring to in terms of wildlife and social values. Advocating such a perspective may have broader value in diminishing the self-centred tendencies of modern societies in how they manage ecosystems. (c) 2014 Published by Elsevier By

Cent ans de dynamique forestière spontanée en plein petit âge glaciaire dans le Pays de Bitche, Lorraine

National audienceThis study is an analysis of a historical document dating back to 1758, entitled Atlas topographique du comté de Bitche (north-eastern France). This document was signed by a French engineer. It was drafted during the small ice age, following a period when forestry practices were stopped for 100 years or so because of severe political unrest. The document describes beech-oak forests (age, dimensions, sanitary state, regeneration) of the Pays de Bitche, in order to evaluate their richness. By converting the qualitative data of the atlas into semi-quantitative data, we managed to recreate landscapes at that time. The age-diameter matching proposed by the atlas was re-evaluated by coring present-day trees. The results showed the presence of a mature beech forest dominated by beech, very rich in large and very large trees, including a substantial number of oaks that died following competition with beech and repeated climate stress. The better resistance of beech to climate stress is discussed.Cette étude analyse un document historique datant de 1758, dénommé l’Atlas topographique du comté de Bitche, situé au nord-est de la France. Ce document signé d’un ingénieur français a été élaboré au cours du petit âge glaciaire, après une période d’abandon des usages d’environ 100 ans en raison de graves troubles politiques. Il y décrit les hêtraies-chênaies (âge, dimensions, état sanitaire, régénération) du Pays de Bitche, afin d’en évaluer les richesses forestières. Par conversion des données qualitatives de l’atlas en données semi-quantitatives, il a été possible de reconstituer les paysages de l’époque. Les correspondances âges et diamètres proposés par l’atlas ont été réévaluées par carottages d’arbres actuels. Les résultats indiquent une hêtraie mature dominée par le Hêtre, très riche en gros bois et très gros bois incluant aussi une grande quantité de chênes morts par compétition avec le hêtre et stress climatiques répétés. La meilleure résistance du hêtre aux stress climatiques est discutée