レクリェーションを目的とした二次林の改良とその林床管理に関する生態学的研究

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Since suburban secondary woodlands such as red pine (Pinus) forests and deciduous oak (Quercus) forest, or coppice, ceased being utilized for fuel resources, those abandoned woodlands have developed closed canopy and thick floor vegetation (Photo. 1). Accordingly, when considering the development of recreational possibilities on these sites, it is very important to prepare suitable forest composition for such use. The purpose of this study is to ascertain the ecological response of floor vegetation under conditions of periodical weeding and changes in degree of light, in order to develop an effective management program for recreation forests. Experimental work was conducted over ten-year period in Pinus forests and Quercus forests in selected districts in the Kansai area, specifically, in Nose, Senboku and Nishigori in Osaka Prefecture, Kameoka in Kyoto Perfecture, Miki in Hyogo Prefecture, and Hashimoto in Wakayama Prefecture. In an atempt to obtain universal validity in the study, the existing recreation forests in selected areas of the Kanto area, Musashi in Saitama Prefecture, Tsukuba in Ibaragi Prefecture, etc., were investigated. The results of study suggest the following principles which can serve to guide the development of forest management programs for various recreational needs and functions (Fig. 25, Table 7). 1. The composition and succession stage of floor vegetation. (1) Composition of the floor vegetation before weeding Regardless of locality or forest type (Pinus or Quercus), such broad-leaved evergreen shrubs as Eurya japonica, Irex crenata and Irex pedunculosa dominated in the floor vegetation (Fig. 1-3). Furthermore, since seedlings of Quercus glauca, Neolitsea sericea, etc., as component species of potential natural vegetation, were found growing on the floor, these forest areas are considered to be in progress toward becoming broad-leaved evergreen forest. The light condition on the floor is so dark that not only herbaceous plants are scarce but also wild Rhododendron and other deciduous shrubs were found to be stunted. (2) The succession movements of the floor vegetation One year after weeding, the floor was covered with vegetation which was mainly generated from stumps of shrubs. This kind of vigorous growth hindered herbaceous plants from making normal development (Fig. 4, 5). Six years later, the shrubs had grown so thick that it was extremely difficult to walk through the floor (Photo. 2). At this time, species diversity was the highest since weeding. Three years later, diversity was reduced by half due to the shading of broad-leaved evergreen shrubs. Judging from the above mentioned results, it was concluded that floor vegetation should be weeded at six years rotations in order to maintain rich species diversity in the interests of providing food supply for wild birds and animals. At the very least, floor vegetation should be weeded at ten years rotations in order to avoid succession to broad-leaved evergreen forests. These long term rotations are suitable for floor management when we intend both effects as buffer forests and nursing forests. However, it is important to divide the forest into several zones and to conduct weeding on a staggered basis, that is, weeding one zone one year, another zone the second year, etc., in order to obtain appropriate growth-stages for continuous effect. 2. The results of different frequency and season of weeding on floor vegetation (1) Results in red pine forest in the Kansai area (Fig. 6-9) Regardless of whether weeding was done in winter or summer, the reproductive power of woody plants was not reduced by biennial and triennial weeding. Since visibility was interrupted in the case of triennial weeding (Photo. 3), it was considered that we should weed floor vegetation at least at two year rotations when we intend to keep visibility along the strolling trail, but not for walking on the floor (Photo. 4). On the other hand, annual summer weeding reduced floor vegetation to bareness, as was the case with semiannual summer and winter weeding, whereas deciduous shrubs and such high-stem herbage as Miscanthus sinensis and Pteridium aquilinum grew vigorously under annual winter weeding condition. Accordingly, in cases in which the floor is to be utilized resting and strolling, weeding should be done in the spring, but not in summer or winter. Otherwise, it is essential to seed or plant suitable herbaceous species which can endure under summer weeding conditions. (2) Results in Pleioblastus chino var. viridis in the Kansai area This plant often occurs in woodlands or grasslands on hills or mountainsides in the Kansai area, in similar to the case of P. chino in the Kanto area. Since the plant has tall stems and grows vigorously, experimental work was conducted in order to control their stem-height and to form desirable floor of Pleioblastus. Semiannual weeding prevented regrowth of Pleioblastus. Likewise, biennial and triennial weeding led to Pleioblastus being oppressed and shaded by high-growing shrubs, in the case of light condition (Fig. 11, 12). On the other hand, Pleioblastus regenerated well under annual winter weeding. However, the stem was too high for strolling. Furthermore, high-stem herbage also flourished in the case of light condition (Photo. 5). Annual late-spring weeding controlled the height of Pleioblastus to below 30cm, and the resulting thick regeneration hindered undesirable herbage from invading. Under annual summer weeding, on the other hand, Pleioblastus could not regenerate and high-stem naturalized herbage grew vigorously (Photo. 6). (3) Results in the recreation forests in the Kanto area In the Kanto Plains, in contrast with the Kansai area, not only the topography is flat or gentle, but also the soil is good. Based on a field survey, it became clear that Pleioblastus chino-type floor could be obtained from original abandoned forest floor covered with thick shrubs under annual summer weeding condition, at a stem-height below 25 to 30cm (photo. 9, Fig. 15). Under conditions of two or three weedings per year, the floor changed into herbage-type just after three years (photo. 10, Fig. 16). The above mentioned results suggest that such conditions as gentle topography and good soil effect the floor vegetation regeneration. Further, an important factor is that since the plain forests adjoin dry farms, various weed seeds can easily reach and germinate in the floor. In the Kansai area, on the other hand, because the majority of farms are paddy fields in which species composition of weeds is different, and slso because the land is more hilly, it is more difficult for weed seeds to reach and germinate in the floor. 3. Condition of flowering of wild Rhododendron Such wild Rhododendron as R.reticulatum, R. kaempferi and R. macrosepalum are frequently seen in abandoned secondary woodlands. However, since the thick forest canopy and shrubs intercept the sunlight, the Rhododendron produce few blooms due to the light shortage (Photo. 12). In order to ascertain desirable conditions for flowering, experimental work and field surveys were conducted (Photo. 13-16). The research results suggest that at least 30% relative light intenstity is necessary for satisfactory flowering of R. reticulatum (Fig. 19), 20% in the case of R. kaempferi (Photo. 18, Fig. 21), and even 40% is not adequate light for R. macrosepalum (Photo. 17, Table 4). The flower color becomes more pale under the darker condition, and the number of blooms decreases significantly with only 5～10% reduction in the specified light levels. An anatomical survey revealed that the beginning of flower formation occurs between July 1 and July 8 (Fig. 22). Therefore, it is necessary that at least by the beginning of June the appropriate tree stand density must be provided in order to open the canopy. Furthermore, floor shrubs should be removed, except for Rhododendron. This ecological study suggests that abandoned secondary woodlands can be changed into desirable recreation forests by appropriate management as shown in table 7. By utilizing secondary woodlands for recreationl use, we can also conserve important parts of our rural landscape in Japan.
大阪府立大学の論文
1988-03-31

著者

重松敏則
Laboratory Of Landscape Architecture College Of Agriculture

レクリェーションを目的とした二次林の改良とその林床管理に関する生態学的研究

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