Removal of invasive <I>Trachycarpus fortunei</I> at Nishinomiya Shrine, Hyogo Prefecture, Japan

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  • 兵庫県, 西宮神社における侵入種シュロの伐倒除去
  • ヒョウゴケン ニシノミヤ ジンジャ ニ オケル シンニュウシュ シュロ ノ バツトウ ジョキョ シャソウリン ノ セッキョクテキ ショクセイ カンリ ト ヒヨウ タイ コウカ
  • Cost effectiveness of active vegetation management in a shrine forest
  • 社叢林の積極的植生管理と費用対効果

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Various invasive species and escaped ornamentals have been reported to thrive in urban forest fragments. We found Trachycarpus fortunei Wendl. thriving in the shrine forest at Nishinomiya Shrine in southeastern Hyogo Prefecture. In this paper, we report on the complete removal of this species from the forest, the extent of the invasion, and the effect of the removal on the understory light environment. In addition, we assessed the cost of removal in relation to the amount of T. fortunei removed. T. fortunei density in the forest was 649 individuals per hectare, contributing 23% of the total number of trees taller than 1.3 m. Total basal area of T. fortunei was 1.7m2 ha-1, contributing only 3.4% of the total basal area, whereas in high-concentration areas leaf area index of T. fortunei was as high as 2.49-4.60. T. fortunei was especially concentrated in the northern edge of the forest facing a road and in the southwestern edge facing a parking lot. Reproductive individuals were also concentrated near the forest edge. In high-concentration areas, canopy openness in the understory was as low as 6-11%. After removal of T. fortunei, canopy openness increased by 2.2% on average (maximum 5.5%). The total cost of the removal of T. fortunei was 1, 390, 000 yen of which 72.0% was labor costs indicating that the cost of removal increases with the extent of the invasion. Shrine forests have traditionally been left unmanaged. However, this study showed that, active management is necessary to control invasive species if the objective is to sustain near-natural forest conditions. In fragmented urban forests, lack of management does not necessarily result in natural conditions. As such, human intervention may be needed to realize the management objectives of the land owner.

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