Facilitation of management plan development via spatial classification of areas invaded by alien invasive plant

Propagule supply and habitat suitability strongly influence the success of invasive alien plants. Thus, an invaded area is likely to have an adequate propagule supply, a suitable habitat, or both for species persistence. Based on this idea, we classified invaded areas into four categories as follows but with establishment still occurring in some cases: Class 1, adequate propagule supply and habitat suitability; Class 2, adequate propagule supply but limited habitat suitability; Class 3, limited propagule supply and adequate habitat suitability; and Class 4, mid- to low-level propagule supply and habitat suitability. We propose a framework for the classification of invaded areas into these four classes and present a case study in which this framework was applied. Classifying target areas in this manner could facilitate more efficient and practical management planning, thereby saving time and resources. We selected the alien shrub Leucaena leucocephala L. (Fabaceae) as a model species, which has invaded the Nakodo-jima Island in the Ogasawara Archipelago of Japan. We developed a species distribution model by incorporating proxy variables for propagule supply and habitat suitability as well as submodels for propagule supply or habitat suitability. Using these submodels, we estimated the levels of propagule supply and habitat suitability in each, and classified the current distribution range appropriately. Using these classifications, land managers could set priorities to concentrate their efforts to efficiently control target species

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

Light reduction by regional haze and its effect on simulated leaf photosynthesis in a tropical forest of Malaysia

The general level of haze has increased rapidly in tropical regions over the last decades. To reveal the effects of haze on tropical forest ecosystem, photosynthetic photon flux density (PFD) at the top of and within a tropical forest canopy was measured on days with and without visible haze, in the Pasoh Forest Reserve, Peninsular Malaysia. Total daily PFD at 40 m aboveground on hazy days was only about 50% of that on the days without visible haze. The reduction of PFD on hazy days was much larger at 50 cm aboveground within the forest. During the period with haze, the forest understory received few PFD higher than 50 μ mol photons m−2 s−1. Photosynthetic carbon gain was estimated to examine the potential effect of PFD extinction by haze. Under hazy conditions, the simulated net carbon gain, which included photosynthetic carbon gain of daytime and respiratory carbon loss at night, decreased to about −6 mmol CO2 m−2 for an ‘average’ shade leaf of understory plants. This marked decrease of leaf carbon gain might have important impacts on the growth and survival of understory plants, and therefore on the regeneration of tree species in the tropical forest

Functional differences in seasonally absorbed nitrogen in a winter-green perennial herb

Nitrogen (N) uptake in response to its availability and effective N-use are important for determining plant fitness, as N is a major limiting resource and its availability changes both seasonally and annually. Storage organs such as bulbs are considered an adaptive trait with respect to plant N-use strategies. It is well known that N is remobilized from storage organs to satisfy the high demand for new growth that is not completely satisfied by external uptake alone. However, little is known about how this N absorbed during different seasons contributes to plant performance. By manipulating seasonal N availability in potted Lycoris radiata var. radiata (Amaryllidaceae), a winter-green perennial, we found that the N absorbed during different seasons had different effects on leaf growth and leaf N concentrations, effectively increasing the growth and survival of the plants. N absorbed during the summer (leafless period; N was thus stored in the bulb) enhanced plant growth by increasing leaf growth. Compared with the plants supplied with N during autumn (leaf flush period), the leafy plants also showed greater growth per unit leaf area despite the lower area-based photosynthetic capacity of the latter. By contrast, N absorbed during the autumn increased the leaf N concentration and thus the photosynthetic capacity, which was considered to enhance survival and growth of the plant during winter by reducing the potentially fatal risk caused by the absorption of photons under low temperature. Our findings have important implications for estimating plant responses to environmental changes. We predict that changes in seasonal N availability impact the performance of plants, even that of perennials that have large storage organs, via an altered relative investment of N into differen