Density and age of invasive Robinia pseudoacacia modulate its impact on floodplain forests
2014
Staska, Bernadette | Essl, Franz | Samimi, Cyrus
The invasion of black locust (Robinia pseudoacacia L.) into nutrient-poor and dry habitats strongly alters resident species composition, species diversity and nutrient availability. However, less is known if its occurrence in more nutrient-rich habitats and dense forests causes similar effects, and if so, how the gradient of stand density and tree age affect soil properties and vegetation composition.We chose riparian forests of the Donau-Auen National Park in Eastern Austria and selected 28 plots which differed in R. pseudoacacia stand density and tree age. Vegetation composition, physical and chemical soil parameters were analyzed. Data analysis was performed using descriptive and bivariate statistics.We found that the content of soil nitrogen, NO3 and carbon increased with black locust density and stand age, respectively, while total C/N ratio appeared to be less affected. While plant diversity (Simpson index) did not show a significant variation neither among Robinia age classes nor along density gradients, some nitrophilous species gained abundance with increased density and some other species with increased age of R. pseudoacacia stands. Only one species (Anemone ranunculoides) became less abundant with Robinia stem density. We argue that these changes in species abundance are primarily due to altered mineral nitrogen availability, but increased radiation intensity under the open canopy of R. pseudoacacia and allelopathic qualities of the tree might also play a role. However, we found evidence that these effects imply certain thresholds and are not linearly scaled.
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