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Göttingen, Germany

Vockenhuber E.A.,University of Gottingen | Scherber C.,University of Gottingen | Langenbruch C.,University of Gottingen | Meissner M.,University of Gottingen | And 3 more authors.
Perspectives in Plant Ecology, Evolution and Systematics | Year: 2011

In temperate deciduous forests, the herb layer contributes most to total vascular plant species richness. The diversity of the tree layer can influence herb layer diversity by modifying resource availability and environmental conditions relevant to herb layer plants. Here, we explore the relationship between tree layer diversity and herb layer species richness and cover. Also, we address the question how different environmental factors that are potentially modified by the tree layer influence herb layer characteristics. Our study area is located in the Hainich National Park, one of the largest continuous stretches of broad-leaved deciduous forest in Central Europe. We recorded herb and tree layer composition on 79 plots selected along a tree diversity gradient ranging from two to nine tree species. In addition, canopy cover, soil pH, mass of the humus layer, soil C:N ratio, soil moisture and distance to the forest edge were determined. We used generalized least square models to analyse effects of tree diversity, environmental variables, and spatial plot positions on herb layer species richness and cover. Species richness and cover of the herb layer increased with increasing tree diversity. In addition, both species richness and cover showed a negative response to increasing canopy cover and mass of the humus layer. Herb layer species richness was also positively related to increasing soil pH and the distance to the forest edge. The proportion of forbs increased with increasing tree diversity, whereas the proportion of tree saplings decreased and the proportion of graminoids was not affected. The proportion of true forest species increased with increasing canopy cover. We conclude that forest stands with a high tree diversity feature a more diverse herb layer and a higher herb cover. Furthermore, the environmental variables humus layer mass, light availability and pH also strongly affect herb layer species richness and cover. © 2011 Perspectives in Plant Ecology, Evolution and Systematics. Source

Gregorova A.,University of Graz | Hrabalova M.,University of Natural Resources and Life Sciences, Vienna | Kovalcik R.,Lindner Mobilier | Wimmer R.,Burckhardt Institute
Polymer Engineering and Science | Year: 2011

Poly (lactic acid) (PLA), a biodegradable aliphatic semicrystalline polyester was filled with 40 wt% spruce wood flour (WF), to produce composite materials. Hydrothermal treatment, as well as maleic anhydride, vinyltrimethoxysilane, and stearic acid surface treatments were applied. The influence of surface modifications for WF was tested in terms of thermal, mechanical, and viscoelastic properties. The recorded results show that in both, the untreated and treated PLA/WF composites, the rigid amorphous phase content has been enhanced. The presence of WF causes a stiffness increase of the PLA/WF composites, while damping factor was decreased. The effect of wood surface modifications on interfacial compatibility with PLA was estimated by dynamic fragility parameter m calculated according the Williams-Landel-Ferry equation. The incorporation of untreated WF increased dynamic fragility of PLA/WF composites markedly, whereas used silane, maleic anhydride and hydrothermal treatments lead to lower values of parameter m. © 2010 Society of Plastics Engineers. Source

The strict forest reserve "Königsbuche" was established in 1972. In 1997, parts of the old beech stand were destroyed by a local summer storm, which created a disturbance gradient ranging from unaffected areas to smaller and extensively large gaps. After a first inventory during the years 1998 to 2001, flora and vegetation were recorded again on permanent plots in 2010 in order to understand plant succession and regeneration in unmanaged windthrown beech forests (Galio odorati-Fagetum) according to the initial disturbance intensity. 13 years after windthrow plant species diversity was higher compared to the year 1998 and was positively correlated with the disturbance gradient unthrown stand - gap - extensively thrown stand. Contrasting the three disturbance categories, light emerged as the most important environmental factor explaining differences in species richness. In comparison to the initial situation after windthrow changes in microclimate (temperature, water supply) seemed also to be important for plant species composition. Furthermore, the decomposition of high amounts of dead wood (mainly from twigs and brushwood), particularly on the extensively thrown plots, favored plant species indicating a higher nutrient supply of these originally mesotrophic soils. Therefore, an Urtica-Rubus-stage has been established on these plots for a short period, which was as well characterised by a high proportion of plant species of both forests and open sites. On the contrary, in unthrown stands and gaps species of closed forests dominated together with young beech indicating a fast and secure natural regeneration of the beech forest community after small-scale disturbance. However, the current vegetation survey showed that also in the extensively thrown stands beech is the dominant regenerating tree species overcrowding most parts of the Urtica-Rubus-stage now. Pioneer tree species (Betula pendula, Salix caprea) - well-known from managed windthrown areas on acidic soils - established rarely in the strict forest reserve "Königsbuche". With increasing initial disturbance intensity, however, shrub species (Crataegus monogyna, Sambucus nigra, S. racemosa) as well as some other deciduous tree species (Acer pseudoplatanus, Carpinus betulus, Prunus avium) became more important. Nevertheless, these species can only survive on extensively thrown stands with a sufficient light supply and under low roe deer browsing pressure as shown by comparing fenced and unfenced plots. Source

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