Effect of nitrogen availability on forest understorey cover and its consequences for tree regeneration in the Austrian limestone Alps |
| |
Authors: | Katharina Diwold Stefan Dullinger Thomas Dirnböck |
| |
Institution: | 1.Department of Conservation Biology, Vegetation Ecology and Landscape Ecology,University of Vienna,Vienna,Austria;2.VINCA-Vienna Institute for Nature Conservation and Analyses,Vienna,Austria;3.Department for Ecosystem Research and Monitoring,Federal Environment Agency Austria,Vienna,Austria |
| |
Abstract: | 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. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|