Vegetation Science
Online ISSN : 2189-4809
Print ISSN : 1342-2448
ISSN-L : 1342-2448
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Original articles
  • Nozomi NAKAOKA, Erika FUKUGAWA, Motoki HIGA, Shingo ISHIKAWA
    2020 Volume 37 Issue 1 Pages 1-12
    Published: 2020
    Released: July 07, 2020
    JOURNALS FREE ACCESS

    Invasion by alien plants that were introduced intentionally or unintentionally is a major issue facing ecosystem conservation around the world. In Kochi and Aki Cities in Kochi Prefecture, Japan, Bischofia polycarpa (Phyllanthaceae) has been planted along streets and in parks, although this species was misidentified as B. javanica for many years. If the ecological traits of B. polycarpa are similar to those of B. javanica, which is known to be an invasive alien tree, it is likely that escaped regenerated trees will expand into the surrounding vegetation. In this study, we assessed the expansion potential of B. polycarpa based on field and experimental surveys of planted and escaped tree distributions, seed productive traits, seed germination traits, and growth traits of current-year seedlings. In Ushioe, Kochi City, 38 planted or escaped B. polycarpa trees were found at nine sites in parks, school gardens, and roadsides. Most of these seedlings and saplings were found around planted trees;however, some were found under trees used by birds as perches far from any bearing trees of B. polycarpa. This species produces many fruits (3-19 fruits per infructescence) and seeds (0-6 seeds per fruit) with a high viable seed rate (>88%). In this study, B. polycarpa seeds showed light requirement for germination, but seed dormancy was broken under a short period of moist chilling treatment;thus, the rate of seed germination was high (>85%). Current-year seedlings showed a high shoot growth rate and high above- and belowground biomass under shaded conditions. These results suggest that most seeds will be dispersed near planted trees, but some will be dispersed farther away, depending on the spatial distributions of trees used by birds as perches. Most of these dispersed seeds will germinate the following spring. The seedlings of this species have high shade tolerance, and some might be able to survive on forest floors. If saplings also have a high shade tolerance and are able to survive under unstable conditions, this species is expected to expand into secondary forests and river floodplains in urban areas. To prevent unintentional expansion of B. polycarpa, it is essential to monitor the invasion status around planted trees and to prune trees before fruit maturation.

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  • Taiki MASUI, Minaco ADACHI, Hiroko FUJITA, Kazuo OBATA, Satoshi TSUDA
    2020 Volume 37 Issue 1 Pages 13-25
    Published: 2020
    Released: July 07, 2020
    JOURNALS FREE ACCESS

    In humid temperate regions such as Japan, prescribed burning has been proposed to conserve semi-natural grassland ecosystems and endangered species. The effect of prescribed burning on vegetation has been evaluated through comparing the vegetation of “burning site” and “control site”. Most of these studies focus only on vegetation. However, this kind of method makes it difficult to clarify what kind of environmental change is caused by burning semi-natural grassland vegetation. Therefore, in this study, we measured long-term fluctuations of soil temperature, and clarified the effect of fire in four sites with both burning and control treatments (un-burned) across semi-natural grasslands in eastern Japan. The maximum daily soil temperatures were overall higher in burned sites than in control sites, with some burned sites reaching over 40°C. By contrast, daily minimum soil temperatures did not differ between burned and control sites. As a result, the difference between the highest and the lowest soil temperatures (range of daily soil temperature fluctuations) increased at burned sites. We can conclude that the soil temperature increases after prescribed burnings because the fire removes litter, thus allowing direct sunlight to shine down on the soil surface. Contrastingly, at the control site, where no burning occurred, soil temperatures did not rise given that litter shielded the soil from sunlight. The differences in the range of daily soil temperatures between the burned and control sites disappeared in summer. This may be due to vegetation regrowth after the burning, which allowed vegetation to restore to its original state, and afterwards block sunlight from reaching the soils surface. In conclusion, the present study has demonstrated that the use of burning application methods in semi-natural grassland management in Japan dramatically alters soil temperatures. This may directly affect plant germination and growth, which are critical for maintenance of plant communities in semi-natural environments.

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  • Masahito INOUE, Yoshitaka TAKAHASHI
    2020 Volume 37 Issue 1 Pages 27-35
    Published: 2020
    Released: July 07, 2020
    JOURNALS FREE ACCESS

    The purpose of this study is to grasp the potential for the restoration of grassland plants from seed bank in the sites where the grassland management was given up. We selected three sampling sites that have different grassland managements. “Grassland-grassland site” has been maintained as grassland by grazing or mowing. “Grassland - forest site” was a pasture, but grassland management was ceased 30 years ago and changed to the forest. “Forest - forest site” has been forest longer than 70 years. We conducted germination tests for soil samples taken from three sites. The buried seed compositions were different in three sites. In the “grassland - grassland site”, nine grassland plants appeared from seed bank, although only a few appeared in “grassland - forest site” and “forest - forest site”. Furthermore species compositions are different between above ground vegetation and buried seed. For example in “grassland-grassland site”, more than 25 grassland plants lived in the above ground vegetation, but only nine grassland plants appeared from buried seed. The result of this study suggests that the resumption of grassland plants from seed bank seems to be difficult in the forest where the grassland management was ceased.

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Short communications
  • Hiroko FUJITA, Makoto KANNO
    2020 Volume 37 Issue 1 Pages 37-47
    Published: 2020
    Released: July 07, 2020
    JOURNALS FREE ACCESS

    Surveys of aquatic plants distribution and salinity were conducted using a canoe at Lake Tofutsu, Hichirippu Pond, Mochirippu Pond and Tosamuporo Pond. All four of them are brackish water lakes in the eastern part of Hokkaido Island. In Tosamupolo Pond, only Zostera marina was growing. In Hichirippu Pond and Mochirippu Pond, Z. marina and Z. japonica were distributed. In addition to these two species, eight aquatic plant species were found in Lake Tofutsu. In Lake Tofutsu, Z. marina and Z. japonica were distributed as far as 5 km away from the mouth of the lake, and they could not be found anywhere beyond. Both species appeared mainly in places where the salinity was 1% or more. The area far from the mouth of Lake Tofustu had salinity of 1% or less, and other species, except the two Zostera species, were present. However, growth of Z. japonica was also confirmed in area of low salinity. The salinity of Hichirippu Pond, Mochirippu Pond and Tosamuporo Pond were range from 2.61% to 3.15%, and it became clear that only the two Zostera species were able to grow. It was found that the distribution of aquatic plants in the brackish water lake is closely related to salinity. This suggests that brackish water lake with high biodiversity has a wide range of salinity within the lake. Japanese Ministry of the Environment listed 56 lakes as brackish water lakes in Japan, of which 23 lakes exist in Hokkaido. Although there are past survey data on 21 of the 23 lakes, there has been no survey in recent years. These facts show the necessities to conduct regular monitoring surveys on brackish water lakes in Hokkaido.

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  • Seiki TAKATSUKI
    2020 Volume 37 Issue 1 Pages 49-55
    Published: 2020
    Released: July 07, 2020
    JOURNALS FREE ACCESS
    Supplementary material

    Typhoon No. 24 in 2018 hit Tokyo at midnight of September 30th for several hours, which resulted in many trees along the Tamagawa-josui canal being felled. We recorded the number of such trees (> 20 cm in diameter) along the 30 km canal, and found 111 (3.7 tree/km). Felled trees occurred more in the eastern part than the western one. As many as 78.4% of the trees fell down to NW, N and NW directions, suggesting the wind blew from south to north. One third of the felled trees were relatively large cherry trees. The Koganei block in the central part of the Tamagawa-josui canal is famous for cherry trees from Edo Era where trees other than cherry are logged. In this block, wind damage was 7.1 times greater and more cherry trees were felled than in other blocks. Canopy opening caused by fallen stems and thinning by branch breakage has resulted in more light reaching the ground layer, which will likely cause vegetational changes.

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