Henriette Krebs



PDF im Hochschulschriften-Service der Universit├Ąt Wien

Comparison of herbivore communities on the native Field Maple Acer campestre (L.) and the neophyte Box Elder Acer negundo (L.)

Box elder, Acer negundo (L.), was introduced from North America to Europe more than 300 years ago as an ornamental and later became an invasive tree, mainly in riverine forests. The invertebrate fauna associated with A. negundo in its European range remains largely unknown. The aims of this study were to assess whether Acer negundo (1) may profit from a lower herbivore load; (2) has a different herbivore community structure, (3) which is dominated by generalist feeders; and (4) may be overall less damaged by herbivores than the co-occurring native A. campestre. I collected herbivore invertebrates from 42 trees of the invasive alien A. negundo and its native congeneric species A. campestre. Sampling occurred every two weeks by means of the beating method over four months (May to August 2011) in the Danube floodplain forest near the village Orth an der Donau. Furthermore different tree and habitat descriptors (e.g. tree height, diameter at breast height, distance to the nearest forest edge and water body) were measured. In total I recorded 4,342 herbivore invertebrates (100 species) and analyzed them to describe the herbivore load, species richness, diversity, host specificity and composition of the herbivore communities on each tree species. I also recorded the leaf area loss on 630 leaves (15 leaves per tree individual) over the whole vegetation period by means of digital photographs to quantify the magnitude of herbivore damage. In spite of its lower herbivore numbers Acer negundo showed a similar proportional leaf damage as the native A. campestre. The proportion of specialized herbivores was six times higher on the native tree (19 species, 281 individuals) than on the invasive one (7 species, 40 individuals). Insect assemblages on A. negundo were dominated by generalist feeders. Herbivore species composition on the two tree species responded differentially to habitat descriptors. For specialized species the most influencing factor was the maple species. For polyphagous species tree species rather unimportant but tree and site characters affected species composition (i.e. likelihood of flooding events, forest structure). This study suggests that the integration into the food web of the invasive alien Acer negundo in the Danube floodplain forest is not yet complete.