抄録
2004年12月26日のスマトラ沖地震時の大津波がタイ国南部マレー半島部西岸(Krabi県〜Phuket県〜Pang-nga県〜Ra-nong県)の沿岸植生に及ぼした影響の緊急調査を2005年3月中旬に行った。海に面した砂地にモクマオウ(一部は約30年前から植栽),海や川に面した泥炭上にマングローブ林(大半は自然林),これらの背後にメラルーカ林やココヤシ園が分布していた。建築物や人命の被害が多かった場所は,アンダマン海に面した海岸リゾート地や漁村であった。これらの場所はいずれも共通して海抜高が低い。海岸林の津波被害軽減効果については,マングローブ特にRhizophora属樹種で林内約10mまでに多くの物体や生存者がトラップされ,その効果が高かった。マングローブの地上根密度の高さが貢献していると考えられた。モクマオウ,メラルーカなどの林やココヤシ園では,幹の密度が低く,顕著なトラップ効果は認められなかった。大形のモクマオウは根系の洗掘による根返り,小形のものは押し倒しによる枯死被害が認められた。生き残った個体でも異常落葉が認められた。林内の草本植生の多くは津波によって運ばれた海砂に埋もれ,灌木などの木本植生の大半は押し倒しなどによる枯死被害が目立った。マングローブ林では海砂の堆積が顕著であり,今後の根系呼吸への障害となることが懸念された。海水を被ったメラルーカなどの常緑林では塩害と思われる葉の褐変や異常落葉が認められた。海岸林の津波被害は,その発生時の物理的被害に止まらず,水ストレスや塩ストレスなどによる将来の衰退・枯死被害発生が予測される。
We surveyed the impact of Tsunami, which slaughtered the coastal zone surrounding Andaman Ocean in December 26th, 2004, on the coastal vegetation at west coast (Krabi, Phuket, Pang-nga, and Ranong) of Malay Peninsula in southern Thailand in middle of March, 2005. Casuarina forests including some plantation aged ca. 30 years old distributed on the sandy beach and natural mangroves developed on riverine and basin peaty habitat were the major forest types in this area. Some Melaleuca forests as well as Coconuts plantations were also observed at interior regions. Serious damages of buildings and/or on human were observed in the beach resorts and fishery villages facing to the Andaman Sea at where the elevation is low. We recognized that mangroves, especially Rhizophora forests could mitigate Tsunami damage by trapping many flown wreckages within the 10m from forest edge, which saved many lives at interior. It was thought that highly developed above ground stilt root system of mangrove contributed to the trapping effects. Remarkable trap effect was not observed in Melaleuca forests and Coconuts plantations with low tree density. Large Casuarina trees at water front were found to be uprooted by erosion and small Casuarina trees were all mown down by direct impact. Unusual defoliation of trees was also observed in many places. Herbs and shrubs grown under the Casuarina stands were also mown down and buried by sand from shallow water of west coast. This sand deposit may present the smooth respiration of mangrove roots and affects on their survival seriously in near future. At the beach forests e. g. Melaleuca forest covered by sea water began to show the chlorosis of leaves and unusual defoliation considered to be the damage by saline condition were observed. We predict that the Tsunami damage of coastal forest appears not only as the direct impact but also appears as the gradual, severe and long lasted deterioration of forest health.
