Species composition and stand structure of the exotic tree Ailanthus altissima community established at deforested sites under severe feeding pressure by sika deer （Cervus nippon）
2014 Volume 31 Issue 2 Pages 165-178
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2014 Volume 31 Issue 2 Pages 165-178
Ailanthus altissima, a deciduous tree native to China, is known to invade open and disturbed sites and has been naturalized in many regions of Japan. I examined the species composition and stand structure of A. altissima community established at deforested sites under severe feeding pressure by sika deer （Cervus nippon） in the northern part of Hyogo Prefecture, Japan. These deforested sites were formed by clear-cutting secondary oak forests and artificial Japanese cedar forests. Many A. altissima individuals of ≥1.5 m in height were found at the deforested sites, but none was found at neighboring sites covered by secondary oak forests and artificial Japanese cedar forests. Many native plant species, but not A. altissima, were browsed on by sika deer, indicating that A. altissima is unpalatable to sika deer. Native pioneer tree species （e.g., Mallotus japonicus and Aralia elata） that are strong competitors of A. altissima showed very low dominance in the A. altissima community.
This was the case in the community with low dominance of A. altissima, established at the deforested sites.
These findings suggest that browsing on native plant species by deer greatly contributed to the establishment of the A. altissima community. The height class distribution of A. altissima individuals of ≥1 m in height was unimodal in the A. altissima community, indicating that the regeneration of this species is discontinuous. However, 2880 A. altissima individuals per hectare （<1 m in height） were found in the understory of the community, most of which were ramets that originated from roots. The establishment of such a ramet bank may contribute to the regeneration of the A. altissima community to some extent. The maximum height of A. altissima trees was 15 m; the relationship between height and stem diameter at breast height for A. altissima showed that the height of the species has still not peaked in the study area. Thus, the A. altissima community is likely to continue growing and existing for more than a century.
