Forest ecosystem research in Hainich National Park (Thuringia) : first results on flora and vegetation in stands with contrasting tree species diversity

A floristic description is presented of the study sites of the Research Training Group “The role of biodi-versity for biogeochemical cycles and biotic interactions in temperate deciduous forests”. To investi-gate different aspects of plant biodiversity in Hainich National Park (Thuringia), deciduous forest stands with low, medium and high canopy tree species diversity were compared. The results of species richness and forest communities show that the research sites are characterised by a typical central European forest flora. Greater vascular plant species richness occurs with higher diversity of tree species. Six of altogether twelve research sites are assigned to the beech forest alliance (Galioodorati-Fagion), the second half belongs to the oak-hornbeam forest alliance (Carpinionbetuli). Suballiances within the Galioodorati-Fagion in the study area include the Galio-Fagetum and the Hordelymo-Fagetum. All Carpinionbetuli relevées are assigned to the suballiance Stellario-Carpinetum

High functional diversity is related to high nitrogen availability in a deciduous forest - evidence from a functional trait approach

The current study tested the assumption that floristic and functional diversity patterns are negatively related to soil nitrogen content. We analyzed 20 plots with soil N-contents ranging from 0.63% to 1.06% in a deciduous forest near Munich (Germany). To describe species adaptation strategies to different nitrogen availabilities, we used a plant functional type (PFT) approach. Each identified PFT represents one realized adaptation strategy to the current environment. These were correlated, next to plant species richness and evenness, to soil nitrogen contents. We found that N-efficient species were typical for low soil nitrogen contents, while N-requiring species occur at high N-contents. In contrast to our initial hypotheses, floristic and functional diversity measures (number of PFTs) were positively related to nitrogen content in the soil. Every functional group has its own adaptation to the prevailing environmental conditions; in consequence, these functional groups can co-exist but do not out-compete one another. The increased number of functional groups at high N-contents leads to increased species richness. Hence, for explaining diversity patterns we need to consider species groups representing different adaptations to the current environmental conditions. Such co-existing ecological strategies may even overcome the importance of competition in their effect on biodiversity

The estimation of aboveground biomass and nutrient pools of understorey plants in closed Norway spruce forests and on clearcuts

The estimation model PhytoCalc allows a non-destructive quantification of dry weight and nutrient pools of understorey plants in forests by using the relationship between species biomass, cover and mean shoot length. The model has been validated with independent samples in several German forest types and can be a useful tool in forest monitoring. However, in open areas within forests (e.g. clearcuts), the current model version underestimates biomass and produces unreliable nutrient pool estimations. Thus, tissue density, as approximated by leaf dry matter content (LDMC), is systematically higher under high light compared to low light conditions. We demonstrate that the ratio of LDMC under clearcut conditions to LDMC under forest conditions can be used to adjust the PhytoCalc model to clearcut conditions. We investigated the LDMC ratio of five exemplary species commonly occurring on clearcuts. Integrating the square of the ratio as a correction factor improved estimates of biomass to more than 70% fit between observations and predictions. Results also suggest this ratio can be used to correct nutrient concentrations modelled in PhytoCalc, which tend to be overestimated in clearcuts. As morphological groups of plant species exhibit significantly different ratios, we advise using group-specific correction factors for clearcut adjustments in the future

Are Ellenberg indicator values useful to predict the risk of nitrate leaching in forests?

Die Definition der N-Sättigung von Wäldern wurde bisher überwiegend an N-Haushaltsgrößen geknüpft (ÅGREN & BOSATTA 1988, ABER et al. 1989, KÖLLING 1991, BML 2000). Aber auch mit vegetationskundlichen Methoden ist es möglich, Veränderungen des N-Status zu erkennen (ROST-SIEBERT & JAHN 1988, DIEKMANN & DUPRE 1997, BRUNET et al. 1998, DIEKMANN et al. 1999, FISCHER 1999, LAMEIRE et al. 2000, HOFMEISTER et al. 2002, BERNHARDT 2005). Dies geschieht oftmals mit Hilfe der Stickstoff- und Reaktions-Zeigerwerte nach Ellenberg (ELLENBERG et al. 2001). Sie können damit zur Indikation des Standortzustands von Wäldern und seiner Änderungen herangezogen werden. Im vorliegenden Aufsatz wurde untersucht, welchen Beitrag die Zeigerwerte der Bodenvegetation zur Vorhersage erhöhter Nitratkonzentration unter Wäldern leisten können. Die Nitratinventur Bayern (MELLERT et al. 2005a, 2005b), bei der auch die Bodenvegetation aufgenommen wurde, bot die Möglichkeit, das Indikatorpotential der Bodenvegetation als Zeiger für Nitratausträge zu prüfen. Die Analyse bietet überdies Ansatzpunkte, zwischen einem durch das Standortpotential bedingten Risiko und dem durch N-Depositionen als anthropogene Ursache für Nitratausträge zu unterscheiden. Zudem wurde geprüft, ob das zur Regionalisierung eingesetzte logistische Regressionsmodell (MELLERT et al. 2005c) durch die Hinzunahme der N-Zeigerwerte verbessert werden kann. Wegen der zu erwartenden Korrelation der Zeigerwerte mit den im Modell verwendeten Standortsindikatoren erhob sich insbesondere die Frage, ob der Zeigerwert die im Modell benutzten Prädiktoren lediglich (z.T.) ersetzt oder ob er die Prognosemöglichkeiten verbessert. Eine wirkliche Verbesserung der Vorhersage ist dann gegeben, wenn der N-Zeigerwert als zusätzlicher Prädiktor ins Modell aufgenommen werden kann und sich die unerklärte Varianz hierdurch signifikant verringert. Von praktischer Bedeutung könnten auch Korrelationen innerhalb der durch die Haupteffekte (Faktoren Wald- und Substrattyp) festgelegten Straten sein.The data of the nitrate inventory in Bavaria allowed to examine whether nitrate leaching of forest soils can be predicted by Ellenberg indicator values. Significant correlation between nitrate concentrations in the top- and the subsoil stressed the indicator potential of the ground vegetation. Significant relationships with modelled ammonium deposition and other deposition indicators reveal the causes of eutrophication of forests in the perspective of the ground vegetation. These relationships point once more to the agriculture as the most important source of nitrogen deposition in forests. Despite, the demonstrated indicator potential the explanation of the analysed regionalisation model could not be improved much by the inclusion of indicator value for nitrogen. Moreover, the limited basis of appropriate geodata hinders the use of ground vegetation within spatial modelling. Nevertheless, the observation of ground vegetation within the biogeochemical monitoring of forests is an important complementary tool. Comprehensive analyses of such approaches should be intensified. This would help to improve the understanding of consequences and dynamics within the process of nitrogen saturation

Impact de l'utilisation des terres sur les densités juvéniles de plantes ligneuses dans une savane d'Afrique de l'Ouest

In den westafrikanischen Savannen beeinflusst die Landnutzung die Dichte der Gehölzkeimlinge und Jungpflanzen, indem sie physikalische, chemische und biologische Eigenschaften der Flächen verändert und zu unterschiedlichen Landnutzungstypen führt. Es wurde der Einfluss der Landnutzung auf die Individuendichte von Keimlingen und Jungpflanzen von 25 charakteristischen Savannengehölzarten auf nicht kultivierten Flächen, in Brachen und in einem Schutzgebiet (insgesamt 39 Parzellen) untersucht. Darüber hinaus haben wir den Einfluss der Landnutzung auf die Individuendichte mit 23 Umweltparameter in Beziehung gesetzt, die die Bodeneigenschaften und die Vegetationsstruktur beschreiben. Die Bodensäure, die Korngrößenzusammensetzung des Bodens und die Vegetationsstruktur unterscheiden sich zwischen den Landnutzungstypen. In Bezug auf den menschlichen Einfluss, ließen sich fünf Artengruppen unterscheiden, die jeweils ähnlich auf die Landnutzung reagieren. Obwohl wir signifikante Unterschiede in den Bodeneigenschaften festgestellt haben, sind ihre direkten Auswirkungen auf die Individuendichte der Gehölzkeimlinge und Jungpflanzen weniger ausgeprägt als ihre indirekten Effekte. Die Bodeneigenschaften verändern die Verfügbarkeit von Ressourcen und beeinflussen darüber die Höhe und Bedeckung der Pflanzen, die im Umfeld des Gehölzjungwuchses wachsen. Dadurch erhöht sich die Konkurrenz um Licht, Wasser und Nährstoffe für den Jungwuchs in seiner Etablierungs- und anfänglichen Wachstumsphase. Diese Effekte werden durch die Landnutzung verstärkt und variieren zwischen Landnutzungstypen.In West African savannas, human land use affects the density of woody species seedlings and saplings (juveniles) by altering the state of the physical, chemical, and biological characteristics of the land resulting in different land-cover types. We determined juvenile densities of 25 characteristic woody savanna species on non-arable sites, in fallows and in a protected area (in total 39 plots), and analyzed the influence of land use on juvenile densities. We further related the influence of land use on juvenile densities to 23 environmental parameters describing soil properties and vegetation structure. Soil acidity, particle size distribution of the soil, and vegetation structure differed between land-cover types. In terms of human impact, we detected five groups of species responding similarly to land use. Although we detected significant differences in soil properties, their direct effects on juvenile densities are less pronounced than their indirect effects. By altering the availability of resources, soil properties affect height and cover of all plants growing in the surrounding of a young woody plant, increasing the competition for light, water and nutrients during the establishment and initial growth. These effects are intensified by human land use and vary between land-cover types.Dans les savanes de l'Afrique de l'Ouest, l'occupation des sols affecte la densité des semis et des jeunes plants des espèces ligneuses par son influence sur les caractéristiques physiques, chimiques et biologiques des terres, ce qui entraîne de différents types de couvert végétal. Nous avons déterminé la densité juvénile de 25 espèces caractéristiques de savane ligneuse sur des sites non arables, en jachère et dans une aire protégée (au total 39 parcelles), et nous avons analysé l'influence de l'utilisation des terres sur les densités juvéniles. Nous avons également mis en rapport l'influence de l'utilisation des terres sur les densités juvéniles avec 23 paramètres environnementaux décrivant les propriétés du sol et la structure de la végétation. L'acidité du sol, la répartition granulométrique du sol et la structure de la végétation différaient selon les types de couvert végétal. En termes d'impact humain, nous avons détecté cinq groupes d'espèces répondant de manière similaire à l'utilisation des terres. Bien que nous ayons détecté des différences significatives dans les propriétés du sol, leurs effets directs sur les densités juvéniles sont moins prononcés que leurs effets indirects. En modifiant la disponibilité des ressources, les propriétés du sol affectent la hauteur et la couverture de toutes les plantes qui poussent à l'entour d'une jeune plante ligneuse, augmentant la concurrence pour la lumière, l'eau et les nutriments pendant l'établissement et la croissance initiale. Ces effets sont intensifiés par l'utilisation des sols et varient selon les types de couvert végétal

The impact of livestock grazing and canopy gaps on species pool and functional diversity of ground flora in the Caspian beech forests of Iran

Gefördert im Rahmen des Projekts DEAL; Alexander von Humboldt-Stiftun

Adaptation intraspécifique à l'habitat: Comment la capacité de germination des graines des plantes herbacées change-t-elle en function des conditions environnementales dans les savanes Ouest Africaines

Knowledge about the herbaceous layer in relation to environmental factors in West African savannas is still scarce. Early life-cycle events like germination of the herbaceous species are of special interest, as these stages can play critical roles in establishing of the plants and determine population and community dynamics. We aim to assess intraspecific differences in the germinability of herbaceous savanna species with respect to environmental conditions to reveal adaptations in this early life cycle stage. The study was conducted in the Sudanian savanna of Burkina Faso in West Africa. We collected seeds of two annual herbs (Chamaecrista mimosoides, Spermacoce stachydea) along a climatic gradient from different habitats and land use types and conducted germination experiments under equal conditions in climate chambers. For both species several environmental factors showed a significant impact on the germination rates. While higher precipitation caused an increase in the germination rate only for S. stachydea, habitat conditions had a significant influence for both species. Intermediate habitats with balanced soil moisture caused an enhancement of the germination success. Moreover shrub cover had a positive effect on the germinability of C. mimosoides, whereas the germinability of S. stachydea decreased due to an increasing herbaceous cover. The study showed that certain environmental factors are able to modify the intraspecific variability of the germinability trait, which might affect the establishment of the species populations.Les connaissances sur la strate herbacée en relation avec les facteurs environnementaux dans les savanes Ouest africaines sont encore rares. Les événements précoces du cycle biologique, comme la germination des espèces herbacées, présentent un intérêt particulier, car ces stades peuvent jouer un rôle crucial dans l'établissement des plantes et être déterminant dans la dynamique des populations et des communautés. Notre objectif est d'évaluer les différences intraspécifiques dans la capacité de germination des espèces herbacées de savane selon les conditions environnementales afin de révéler les adaptations à ce stade précoce du cycle biologique. L'étude a été menée dans la savane soudanienne du Burkina Faso en Afrique de l'Ouest. Nous avons collecté des graines de deux espèces herbacées annuelles (Chamaecrista mimosoides, Spermacoce stachydea) le long d'un gradient climatique en fonction de différents types d’habitats et d'utilisation du terres. Nous avons ensuite mené des expériences de germination dans des conditions identiques à celles des savanes en utilisant des chambres climatiques. Pour les deux espèces, plusieurs facteurs environnementaux ont eu un impact significatif sur les taux de germination. Alors que les fortes précipitations n'ont provoqué une augmentation du taux de germination que pour S. stachydea, les conditions d'habitat quant à eux, ont eu une influence significative sur les deux espèces. Les habitats intermédiaires avec une humidité du sol équilibrée ont permis d'améliorer le succès de la germination. De plus, le taux de recouvrement des arbustes a eu un effet positif sur la germination de C. mimosoides, tandis que la capacité de germination de S. stachydea diminue avec l’augmentation du taux de recouvrement des herbacées. L'étude a montré que certains facteurs environnementaux sont capables de modifier la variabilité intraspécifique du trait de germination, ce qui pourrait affecter l'établissement de la population des espèces

Effects of Moderate Nitrate and Low Sulphate Depositions on the Status of Soil Base Cation Pools and Recent Mineral Soil Acidification at Forest Conversion Sites with European Beech (“Green Eyes”) Embedded in Norway Spruce and Scots Pine Stands

High N depositions of past decades brought changes to European forests including impacts on forest soil nutrition status. However, the ecosystem responses to declining atmospheric N inputs or moderate N depositions attracted only less attention so far. Our study investigated macronutrient (N, S, Ca2+, Mg2+, K+ ) pools and fluxes at forest conversion sites over 80 years old in Central Germany with European beech (so-called “Green Eyes” (GE)). The GE are embedded in large spruce and pine stands (coniferous stands: CS) and all investigated forest stands were exposed to moderate N deposition rates (6.8 ± 0.9 kg ha−1 yr−1 ) and acidic soil conditions (pHH2O 59%) and CS (>66%). The litter fall base cation return at GE (59 ± 6 kg ha−1 yr−1 ) is almost twice as large as the base cation deposition (30 ± 5 kg ha−1 yr−1 ) via throughfall and stemflow. At CS, base cation inputs to the topsoil via litter fall and depositions are at the same magnitude (24 ± 4 kg ha−1 yr−1 ). Macronutrient turnover is higher at GE and decomposition processes are hampered at CS maybe through higher N inputs. Due to its little biomass and only small coverage, the herbaceous layer at GE and CS do not exert a strong influence on macronutrient storage. Changes in soil base cation pools are tree species-, depth- and might be time-dependent, with recently growing forest floor stocks. An ongoing mineral soil acidification seems to be related to decreasing mineral soil base cation stocks (through NO3 − and especially SO4 2− leaching as well as through tree uptake)

Responses of competitive understorey species to spatial environmental gradients inaccurately explain temporal changes

Understorey plant communities play a key role in the functioning of forest ecosystems. Under favourable environmental conditions, competitive understorey species may develop high abundances and influence important ecosystem processes such as tree regeneration. Thus, understanding and predicting the response of competitive understorey species as a function of changing environmental conditions is important for forest managers. In the absence of sufficient temporal data to quantify actual vegetation changes, space-for-time (SFT) substitution is often used, i.e. studies that use environmental gradients across space to infer vegetation responses to environmental change over time. Here we assess the validity of such SFT approaches and analysed 36 resurvey studies from ancient forests with low levels of recent disturbances across temperate Europe to assess how six competitive understorey plant species respond to gradients of overstorey cover, soil conditions, atmospheric N deposition and climatic conditions over space and time. The combination of historical and contemporary surveys allows (i) to test if observed contemporary patterns across space are consistent at the time of the historical survey, and, crucially, (ii) to assess whether changes in abundance over time given recorded environmental change match expectations from patterns recorded along environmental gradients in space. We found consistent spatial relationships at the two periods: local variation in soil variables and overstorey cover were the best predictors of individual species’ cover while interregional variation in coarse-scale variables, i.e. N deposition and climate, was less important. However, we found that our SFT approach could not accurately explain the large variation in abundance changes over time. We thus recommend to be cautious when using SFT substitution to infer species responses to temporal changes.</p