No.225 研究課題 / Project
多摩川河川敷におけるニセアカシアの分布拡大と生育環境に関する調査研究A Research of Robinia pseudoacacia and Its Living Sites Along the Riversides of Tama River.| 学術研究 Academic Research |
No.225 |
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| 代表研究者 Principal Investigator |
池谷 奉文 Hobun Ikeya |
| 所属（採択当時） Affiliation |
（財）日本生態系協会会長 Ecosystem Conservation Society.Japan |
| 研究内容要約 Research Summary |
①まず既存研究より、ニセアカシアの生態について文献調査を行った。 ②次に多摩川の河川敷におけるニセアカシア群落の分布の変遷を把握するために、 １９７９年、１９８５年、１９９５年に作成された既存の植生図を基にニセアカシア群落 の拡大傾向を解析した。 ③地形条件と植生との関係を把握するために、多摩川の中流域（河川河口部から ４０．２～５８．９ｋｍ）を対象に川に対して横断方向に調査ベルトを９箇所設定し、地 形、表層土砂および植生の調査を行った。樹林が成立しているところについては、毎 木調査も併せて実施した。 ④ニセアカシアの種子による繁殖の貢献度を検討するために、河川敷の踏査による 実生の分布調査、豆果および種子の攪拌実験、また濃硫酸処理を行った種子の発 芽実験を行った。 ⑤また、多摩川直轄河川区域の上流、多摩川河口部から５８．６ｋｍ付近（東京都青 梅市）を対象とし、植生の空間分布と地形条件との関係を把握するために、複数時期 に撮影された空中写真や赤外カラー空中写真、１９７９年、１９８４年、１９９５年に作製 されている既存の植生図、また１９７５年、１９８５年、１９９５年に作製されている河川 平面図からＧｌＳデータベースを整備し、これを用いた解析及び、現地調査による確認 を実施した。 ⑥同様の対象地域において、洪水流による物質輸送とそれによる高水敷土壌中の栄 養塩環境の形成に関する現地観測および数値計算を実施した。 ⑦併せて、移入種に関する取り組みについて、国際的な動向および国内での取り組 みについて調査を行った。 ⑧これらの調査結果に基づき、多摩川河川敷のニセアカシアの管理方法について提 言を行った。 In order to investigate how Robinia pseudoacacia is growing on different sites along the terrace of Tama River, vegetation, topography and sediments were surveyed in nine transverse sections of the river terrace. In the feasibility study of 1999, different forms of Robinia pseudoacacia stands were identified. On the riverside area with lower elevation from the water level, the stands of Robinia pseudoacacia were sparse in density (1.3/100㎡)and rather short in height (6-7m at max). The surface soil of these stands was composed of the mixture of gravy fraction and fine sands. On the relatively high elevation areas, the surface soil was composed only of fine sands. The Robinia pseudoacacia stands on these areas were rather tall (10-16m) but the density of them had a wider range (5-47/100㎡). On high elevation areas with the rather low possibility of suffering from flood, the stands height reached about 15m and the surface soils consists of organic matter. Late successional tree species were also found at the floor of these stands. In 2000 the number of the study sites was increased and the topographic survey was added. Every Robinia pseudoacacia stands found while this survey was on the area higher than 1m from the water label. The stands on the area with surface soil of gravy fraction were rather short in height (approx. 4m at max) and quite sparse in density (3/100㎡). The growth of the individuals and the stands were considered to be restricted in those sites. The height of the stands which were on the area with the surface soil of fine sands or the mixture of gravy fraction and fine sands, tended to increase with the elevation from the water level. The height and density of the Robinia pseudoacacia stands on the sands tended to decrease as the thickness of the sand's layer of the surface soil increased. Any Robinia pseudoacacia stands were not found where the thickness of the sands layer was more than 35cm. In order to investigate the contribution of the seed of Robinia pseudoacacia to the expansion of its stand, the riverside of Tama River was surveyed to find the individuals that were raised from seeds. The buoyancy of the legumes and the seeds, and the conditions that were necessary for the seeds to germinate were also tested. During the riverside survey only two plants of Robinia pseudoacacia found were estimated as those, which were raised from the seeds. The seeds did not float on the water, but the legumes floated. It was estimated that the seeds did not move a long distance in the water but the legumes could move. The germination rates of the seeds were increased by longer vitriol. In the field it was estimated that the seed coat would be hurt by rocks while running down the river, and the seed would become able to germinate. The germination of the seeds of Robinia pseudoacacia was found to be promoted by higher temperature. The seeds with this characteristic will germinate in late spring when the temperature becomes higher. The size of the seeds of Robinia pseudoacacia is rather large and not so good in water absorption, so it is estimated that the germination site for the seed of Robinia pseudoacacia is the place where fine sediments are rich and so the water conditions for absorptions. |
| 共同研究者 Collaborators |
池田駿介・倉本宣・戸田祐嗣・高橋俊守・熊谷雄介・川池芽美 |
| 研究全文 Full Text |
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