Conservation of Threatened Plant Species Adonis Ramosa by Transplantation. — 14 Years Monitoring and Future Population Dy Mics —

27 Mar Conservation of Threatened Plant Species Adonis Ramosa by Transplantation. — 14 Years Monitoring and Future Population Dy Mics —

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Abstract

福島県阿武隈川水系大滝根川に建設された三春ダムでは, 貯水予定区域内にフクジュソウが自生しており, 冠水の影響を受けることが明らかであった. そのため, 冠水前に, 一部を自生地に残し, 残りを保全措置として冠水しない 4 地点に分けて移植した. 本研究では, 試験湛水前の 1996 年から 2009 年までの 14 年間, フクジュソウの個体群を追跡した. 自生地では試験湛水後, 個体数は増加傾向にあり, 開花個体 (F), 結実個体, 芽生え (S), 幼植物 (J1～J4) も存在していた. 移植地 4 地点のうち造成地は, 移植後, 大幅に個体数が増加し, 生育している面積も拡大傾向であった. 残り 3 地点のうち自生地と同様の落葉樹林下の 2 地点は, 移植後 14 年を経た 2009 年段階で, 開花個体 (F), 結実個体, 芽生え (S), 幼植物 (J1～J4) も生育していたが, 開花個体 (F) 数に着目すると減少傾向であった. 自生地とは立地環境が異なり, 生育に不適と考えられた 1 地点では, 個体数は減少し, 2006 年以降開花が見られない状態であった. 生活史ステージごとに収集したデータを元に, 50 年間のフクジュソウ個体群存続確率を予測した. その結果, 自生地および造成地は長期的に個体群が維持されると予測された. 自生地と同様の落葉樹林下の 2 地点は 15～17 年は維持され, 生育に不適な地点は約 6 年で消失すると算出された. 2009 年のフクジュソウ開花・結実個体数は, 移植時より多い個体数までに回復し, 生育している面積も湛水前の自生地より広くなっている. 今後も少なくとも 2 地点では長期にわたり存続が可能であり, 移植により個体群は維持できると考えられる.

English Abstract

Before the first infilling of Miharu Dam reservoir, a population of vulnerable species, Adonis ramosa, was found in 1996 on a shore slope that was supposed to be submerged by the initial impoundment. The main area of A. ramosa community was on a shore slope between the normal water level and surcharge water level of the reservoir. It was obvious that the initial impoundment would cause a devastating impact on the A. ramosa population. For the conservation purpose, we transplanted the most of A. ramosa individuals to another 4 places before the initial impoundment. In additon, for the exami tion purpose, we left a part of the community on the origi l habitat and monitored it. To examine the effect of transplant and influence of submersion, we monitored at 5 sites during 14 years since 1996, of which the first 2 years were taken as the pre-first filling and 12 years were done as the post-first filling. At all sites, A. ramosa individuals were observed after 12 years, though juveniles and blooming individuals were not observed at one transplant site. At the other 3 sites and the origi l habitat, juveniles and blooming individuals existed. It was suggested that re-production were continued at each site. Future prospect of the populations in the next 50 years were calculated using a Leslie matrix. It suggested that A. ramosa communities would be continued at site D and the origi l habitat, whereas they would be extinct at the other 3 sites. However, the conservation of A. ramosa population was succeeded since the total number of individuals and distribution in recent years were recovered and became larger than the previous time before the initial impoundment. The future populations will be sustai ble for a long time at least 2 sites.