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Scheffknecht S.,University of Natural Resources and Life Sciences, Vienna | Winkler M.,University of Natural Resources and Life Sciences, Vienna | Hlber K.,VINCA Vienna Institute for Nature Conservation and Analyses | Rosas M.M.,Institute Ecologa | Hietz P.,University of Natural Resources and Life Sciences, Vienna
Journal of Tropical Ecology | Year: 2010

The distribution of epiphytes differs between branches within tree crowns as well as within habitats. Where the original forests have been lost, shade coffee plantations can be important refuges for epiphytes, but are not suitable for all species. To understand what affects habitat quality, we transplanted 1440 seedlings each of two orchids, one, Lycaste aromatica, restricted to forests, the other, Jacquiniella teretifolia, common on trees in coffee plantations and in forests. Seedling mortality and growth were compared between three forests, three young and three old coffee plantations to test for differences between habitats and to analyse which habitat features affect growth and mortality. In J. teretifolia there was no clear pattern of habitat effect on mortality (c. 0.08 mo 1), but the production of new shoots was higher in coffee plantations than in forests. In L. aromatica, growth rates as well as seedling mortality increased over time. During the last census growth rates in forests (1.8 mm mo 1) were significantly higher than in old (0.9 mm mo 1) and young (1.2 mm mo 1) coffee plantations, and seedling mortality was about four times higher in old (0.10 mo 1) and young (0.11 mo 1) coffee plantations than in forests (0.025 mo 1), which may explain the natural absence of L. aromatica from coffee plantations. Mortality in L. aromatica at individual sites was negatively correlated with bryophyte cover on branches (Pearson r = -0.75) and positively with lichen cover (r = 0.70) and canopy openness (r = 0.75). Branch cover with non-vascular epiphytes, whether directly responsible by improving the water supply to epiphytes or indicative of differences in microclimate, may be a useful indicator of suitable habitats for vascular epiphytes. Copyright © 2009 Cambridge University Press. Source


Diwold K.,University of Vienna | Dullinger S.,University of Vienna | Dullinger S.,VINCA Vienna Institute for Nature Conservation and Analyses | Dirnbock T.,Federal Environment Agency Austria
Plant Ecology | Year: 2010

The impact of airborne nitrogen on tree regeneration has attracted increasing interest as deposition loads are by far exceeding natural amounts. Eutrophication may have both direct and indirect effects on the regeneration of forest trees. Here, we focus on potential indirect effects, mediated by nitrogen-dependent patterns in forest understoreys. Using data from a long-term monitoring site in a montane forest ecosystem of the Northern Limestone Alps, we first evaluated correlations between understorey cover of herbs and graminoids and nitrogen availability, as indicated by soil C/N ratios. Then, recruitment and growth rates of the four major tree species of this system (Acer pseudplatanus, Fraxinus excelsior, Fagus sylvatica and Picea abies) were related to understorey cover by means of linear and generalized linear mixed models, taking covariates (soil pH value, radiation, microrelief properties) and spatially varied seed input into account. Nitrogen availability is positively related to graminoid and herb cover. Herb cover had a negative effect on A. pseudoplatanus recruitment, while graminoids had a positive effect on F. sylvatica. Browsing damage on juvenile trees was reduced when graminoid cover was higher We conclude that under specific abiotic and biotic conditions, like on steep, erosion prone slopes, or under high levels of herbivore pressure, understorey vegetation may facilitate tree seedlings rather than compete with them. This highlights the complexity of the factors controlling tree regeneration and the difficulty to predict the net effects of the excess deposition of airborne nitrogen. © 2010 Springer Science+Business Media B.V. Source


Hietz P.,University of Natural Resources and Life Sciences, Vienna | Winkler M.,University of Natural Resources and Life Sciences, Vienna | Scheffknecht S.,University of Natural Resources and Life Sciences, Vienna | Hulber K.,VINCA Vienna Institute for Nature Conservation and Analyses
Biotropica | Year: 2012

This study explores whether differences in germination ability shape habitat distributions among closely related epiphytic species, particularly in the context of the ability to colonize disturbed habitats. We compared the germination of three epiphytic bromeliad species differing in their ability to colonize secondary arboreal vegetation in natural forests, and in old and young coffee plantations. We asked if germination is related to their distribution within the canopy and between habitats, and the extent to which the substrate (branch) or microclimate affects germination success. Tillandsia viridiflora, a species that is largely restricted to closed forests, had highest germination success in natural forests, Tillandsia juncea, a pioneer species, germinated best in young coffee plantations, and Tillandsia heterophylla, an intermediate species, equally in forests and young plantations. Surprisingly germination rates of all three species were lowest in old plantations. Bryophyte cover on branches had a positive effect on germination of T. viridiflora and T. heterophylla, but T. juncea germination rates were largely independent of climate and substrate. These results show that germination can limit the ability of species to colonize disturbed habitats and also contributes to within-canopy distribution. © 2011 The Author(s). Journal compilation © 2011 by The Association for Tropical Biology and Conservation. Source


Noroozi J.,University of Vienna | Akhani H.,University of Tehran | Willner W.,VINCA Vienna Institute for Nature Conservation and Analyses
Phytocoenologia | Year: 2010

The present paper deals with the phytosociology and ecology of the high alpine zone of Tuchal Mts. (Central Alborz). On the basis of 185 phytosociological relevés, the vegetation of high alpine snow-beds, fellfields and xerophytic habitats of Tuchal Mts. is analysed. By means of phytosociological classification and ordination (Detrended Correspondence Analysis), the plant communities and environmental factors governing the variance in vegetation are described and discussed. The studied plant communities are arranged in two provisional orders, four alliances (Taraxaco brevirostris-Polygonion serpyllacei, Astragalion iodotropidis, Cousinion multilobae and Acantholimion demawendici) and 13 associations (Polygonetum serpyllacei, Ranunculetum crymophili, Trifolietum radicosi, Astragaletum iodotropidis, Galio decumbentis-Thymetum pubescentis, Vicietum ciceroideae, Rumicetum elbursensis, Bufonio kotschyanae-Cousinietum multilobae prov., Hordeo violacei-Cousinietum multilobae prov., Astragalo chrysanthi-Cousinietum multilobae prov., Oxytropido persicae-Cousinietum multilobae, Acantholimetum demawendici and Jurinelletum frigidae). The communities of these habitats strongly depend upon the duration of snowcover. Edaphic and hydrological quality of micro-sites is more important for the species composition and vegetation mosaic than the regional climatic gradient. About 90% of the species of the study area are Irano-Turanian elements. All syntaxa are further characterized by life form spectra. Flowering phenology of seven associations was studied according to the snowmelt gradient. © 2010 Gebrüder Borntraeger, 70176 Stuttgart, Germany. Source

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