リュウキュウマツ一斉枯死後にアカギが侵入した父島の二次林における31年間の動態

To quantify dynamics of a secondary forest that was invaded by Bischofia javanica, after death of a dominant tree, Pinus luchuensis, we represented long-term monitoring data of a 20 x 20 m plot in the Fukiagedani Valley in Chichijima Island for 31 years (1984-2015). With the death of P. luchuensis, basal area of trees of all woody species reduced to less than half before the death, and thereafter increased. The numbers of trees and saplings decreased during the period. This suggested that individual trees grew after death of P. luchuensis but recruitments of seedlings did not occur, which could be related to closure of forest canopy with the growth of individual trees. All data of the study was published on the web site of the Ogasawara Research Committee of Tokyo Metropolitan University ([email protected]).リュウキュウマツの一斉枯死後にアカギが侵入した森林の長期的な動態を父島の二次林における31 年間のデータから明らかにした。マツ枯れ直後、森林のBA は50%以下に減少した。その後31年間で全体のBAは増加し、マツ枯れ以前の約70%程度まで回復したと考えられる。樹木の個体数は、1990年まで増加し、その後減少した。これは、マツ枯れ後、樹木が成長し、現存量が増加する一方で、競争によって小径木の枯死と新規加入個体の減少を示唆する。この研究で使用したデータを公開する。利用を希望する場合の問い合わせ先は、以下のアドレス（[email protected]）である

Soil phosphorous is the primary factor determining species-specific plant growth depending on soil acidity in island ecosystems with severe erosion

Abstract Disturbances caused by invasive ungulates alter soil environments markedly and can prevent ecosystem recovery even after eradication of the ungulates. On oceanic islands, overgrazing and trampling by feral goats has caused vegetation degradation and soil erosion, which can alter soil chemistry. To understand the effects of the changes on plant performance, we conducted a laboratory experiment to assess herbaceous species growth under various soil conditions with phosphorous, nutrients, and acidity. Subsoil was collected from Nakodo-jima in the northwest Pacific. Six herbaceous species dominating the island were grown in soils with three levels of added CaCO3 and P2O5 and two levels of added KNO3. After 4 weeks of growth, the total dry plant weight was significantly lower with no added P2O5, regardless of the addition of KNO3. Three species weighed more under P2O5 and KNO3 addition in high-pH soil, whereas the remaining three weighed less. Our results indicated that herbaceous species growth is limited primarily by phosphorous availability; the limitation is dependent on soil pH, and the trend of dependency differs among species. This implies that ecosystems with extreme disturbances cannot recover without improving the soil chemistry