Levels of Leaf Damage by Phyllophages in Invasive Acer negundo and Native Betula pendula and Salix caprea

Abstract

The validity of some concepts underlying the enemy release hypothesis was tested using the example of Acer negundo, an invasive tree species in Eurasia. For this purpose, the frequency of leaf damage and the proportion of leaf area removed by phyllophagous invertebrates were compared between A. negundo and two native species, Betula pendula and Salix caprea. The leaves of these trees were collected in the city of Miass, the Southern Urals, where three rounds of sampling were carried out in the same habitats during the same growing season. A total of 10 000 leaves were examined to record damage by leaf chewers, miners, or gall makers, other kinds of damage, and the proportion of removed leaf area. By the end of the growing season, the proportion of damaged leaves in A. negundo was estimated at 37%, compared to 66% in B. pendula and 78% in S. caprea, with damage by specialized endophagous species (leaf miners and gall makers) in the first species being very low or absent; the proportion of removed leaf area (relative to the total) in A. negundo was less than 1%, compared to 5.8% in B. pendula and 7.5% in S. caprea. Thus, the level of leaf damage by phyllophagous invertebrates in A. negundo growing in the Southern Urals proved to be lower than in tree species native to this region. Therefore, the absence or low activity of natural enemies for A. negundo may be one of the factors accounting for the success of its invasion in Eurasia.