Photosynthesis and biomass allocation of beech ... - Springer Link

J. For. Res. 5 : 1 0 3 - 1 0 7 (2000)

Short Communication

Photosynthesis and Biomass Allocation of Beech (Fagus crenata) and Dwarf-bamboo (Sasa kurilensis) in Response to Contrasting Light Regimes in a Japan Sea-type Beech Forest Tsuyoshi Kobayashi,*, 1,2 Hiroyuki Muraoka,**, 3 and Koji Shimano*** * Laboratory of Ecology, Department of Environmental Sciences, Faculty of Science, Ibaraki University, Mito 310-8512, Japan. ** Institute of Biological Sciences, University of Tsukuba, Tsukuba 305-8572, Japan. *** Department of Vegetation Ecotechnology, Institute of Environmental Science and Technology, Yokohama National University, Yokohama 240-8501, Japan. Regeneration of beech (Fagus crenata) forests depends on the formation of canopy gaps. However, in Japan Sea-type beech forests. a dwarf bamboo (Sasa kurilensis) conspicuously occupies sunny gaps. Therefore, F. crenata seedlings must escape the severe interference of S. kurilensis in the gaps and persist beneath a closed canopy of the beech forest. We hypothesized that the growth of F. crenata seedlings in the understory would be favored by their being more plastic than S. kurilensis in photosynthetic and morphological traits, which would support the matter production of F. crenata seedlings in a wide range of light availabilities. To examine this hypothesis, the photosynthetic-light response of individual leaves and the biomass allocation in aboveground parts (i.e., the culm/foliage ratio) were surveyed at sites with contrasting light availabilitiesin a Japan Sea-type beech forest in central Japan. In F. crenata, photosynthetic light utilization efficiency at relatively low light was greater, and the dark respiration rate was smaller in the leaves of seedlings ( 10 cm in height) beneath the closed canopy than in the leaves of saplings at the sunny forest edge. The culm/foliage (C/F) ratio of the F. crenata seedlings at the shady site was small, suggesting effective matter-productionbeneath the beech canopy. On the other hand. S. kurilensis both in the gap and beneath .the beech canopy showed low plasticity in photosynthesis and the culm/foliage ratio. Because the shoot density of S. kurilensis was smaller beneath the beech canopy than in the gap, the light availability at the bottom of the S. kurilensis layer was greater beneath the beech canopy. These results suggest that the photosynthetic productivity of the F. crenata seedlings would be enough for the seedlings to survive in the understory with a low density of S. kurilensis shoots beneath the closed beech canopy. Key words: canopy, C/F ratio, gap, plasticity, seedling

Japan Sea-type beech (Fagus crenata) forests are one of the typical climax deciduous forests in the cool temperate zone in Japan. The floors of such forests are usually covered by a dwarf bamboo, Sasa kurilensis, an evergreen clonal plant. Severe dominance of S. kurilensis, which is often observed in high light environments, inhibits the establishment of E crenata seedlings (Yanagiya et al., 1971) through the interception of light by its dense foliage and culms. In addition, most E crenata seedlings can occur only after a mast-seeding year, which comes every five to seven years (Hiroki and Matsubara, 1995). Therefore, E crenata seedlings need to persist in the shade environment of the forest floor for a long time until a stochastic opportunity, either the opening of a canopy gap or 'simultaneous death' in a dwarf bamboo community, is presented (Yoshioka 1939; Nakashizuka and Numata, 1982; Nakashizuka, 1988). Each of these events dramatically increases the light availability for seedlings in the understory. On the other hand, beneath the closed forest canopy, the light incidence at the bottom of the S. kulinensis layer is

i Corresponding author. 2 Present address: Japan Science and Technology Corporation, The Center for Forest Decline Studies, Hiroshima Technoplaza, 3-13-26 Kagamiyama. Higashi-Hiroshima 739-0046, Japan. 3 Present address: Institute for Basin Ecosystem Studies, Gifu University, Yanagido, Gifu 501-1193, Japan.

higher due to the lower shoot height and density of S. kulinensis under closed canopies than in sunny sites (Oshima, 1961; Kashimura, 1962; Oshima, 1962). Nakashizuka (1988) reported that E crenata seedling banks were maintained on the beech forest floor under a closed canopy with smaller S. kurilensis dominance, and Sawada et al. (1995) observed a smaller number of seedlings in a gap with dense S. kurilensis. The above results suggest that S. kurilensis is tess successful at exploiting shady micro-habitats, which increases the light resource there for E crenata seedlings and thereby enables the seedlings to persist beneath the forest canopy. However, there are few studies on the physiological and morphological traits of F. crenata and S. kurilensis regarding the interspecific shading of the two species. In the present study, to clarify the shading effects of 1) the beech canopy on dwarf bamboo in the understory and 2) the dwarf bamboo on beech seedlings at the bottom of the dwarf b a m b o o layer, we investigated the p h o t o s y n t h e t i c - l i g h t response and the biomass allocation in aboveground parts (i.e., the culm/foliage (C/F) ratio) of E crenata and S. kurilensis beneath a forest canopy and in a gap located in a Japan Seatype beech forest. We tested the following hypothesis: compared with S. kurilensis, F. crenata has higher plasticity of physiological and morphological traits for sites with different light availabilities, which enable the E crenata seedlings to persist beneath the beech canopy.

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J. For. Res. 5 (2) 2000:

Materials and Methods 1 Study site The study area was located in a beech forest on a fiat tableland of Buna-Daira (36°57'N, 139°20~E; 1,400 m a.s.l.), Hinoemata Village, Fukushima Prefecture, Japan. This forest is a typical Japan Sea-type beech forest with dwarf bamboo S. kurilensis in the understory and continually regenerating beech trees (Shimano and Okitsu, 1994). In this area, a 20 m × 50 m (1,000 m 2) plot was set up on August 12, 1998. This stand included two patches with contrasting overstory conditions: a closed canopy patch (225 m 2) and a gap patch (300 m2). In the closed canopy patch, most of the trees with a top height of more than 1.3 m were F. crenata. The other species included Prunus grayana and Acanthopanax sciadophylloides. The average top height and diameter at breast height ofF. crenata trees were 8.3 +__ 1.0 m and 10.5 _+ 1.5 cm (mean ___standard error, n = 26; Table 1). These values indicate that the ages of the trees are ca. 100 years (cf. Honma, 1995). Both the density and the top height of S. kurilensis shoots were significantly greater in the gap patch than in the closed canopy patch (p < 0.05, Mann-Whitney's U-test, n = 8-10). Conversely, the density of E crenata seedlings was significantly greater in the closed canopy patch than in the gap patch (p < 0.05). There were a few seedlings in the gap patch, and they grew in only particular areas, such as on sunny mounds. The top height of all E crenata seedlings was ca. 10 cm and their age was ca. 5 years. P h o t o s y n t h e t i c a l l y active photon flux density (PPFD, 400-700 nm) was measured with a quantum sensor (IKS-25, Koito, Japan) at the top and the bottom of the S. kurilensis layer (sub-canopy of understory) in the closed-canopy and gap patches. The PPFDs were recorded by a data logger (THERMODAC-E, Eto Denki, Japan) at 3-min intervals between 10:00 and 14:00 on a sunny day, August 15, 1998. The PPFD at the top of the S. kurilensis canopy layer (2 m above the

ground) was greater in the gap patch than in the closed canopy patch (220-640 ~tmol m - 2 s - l vs. 25-65 ~tmol m 2 s - l). Conversely, at the bottom of the S. kurilensis canopy layer (10 cm above the ground), the PPFD in the gap patch was lower than that in the closed canopy patch (2.5-18 I.tmol m - 2 s I vs. 1 4 - 4 4 I.tmol m - 2 s - 1). The average PPFD at the top of the S. kurilensis canopy layer in the closed canopy patch relative to the PPFD just above the S. kurilensis canopy layer at the gap patch during 11:30 to 12:30 was 12.0% (Table 1). The PPFD at the bottom of the S. kurilensis canopy layer was 2.9% in the gap patch and 7.3% in the closed canopy patch when compared with PPFD at the top of the S. kurilensis canopy layer in the gap patch. 2 Light response curves of photosynthesis Measurements of photosynthetic light response curves in the leaves of F. crenata and S. kurilensis were carried out with a portable open gas exchange system (LI-6400, Li-Cor, USA) at the study site on August 12-15, 1998. Four plants or shoots grown in contrasting light regimes were selected for each species. For E crenata, we selected 1) saplings of ca. 5 m in height at the forest edge adjacent to the study area that were exposed to direct sunlight, and 2) seedlings shaded at the bottom of the S. kurilensis layer in the canopy patch. For S. kurilensis, we selected 1) sunlit shoots in the gap patch and 2) shaded shoots in the canopy patch (the seedlings could be found at the microsites with relatively low S. kurilensis shoot density). The leaves chosen for the measurements were the second leaves from the branch tip for the deciduous F. crenata, as the effects of mutual shading were small in these leaves. The third leaf (a l-year-old leaf) was chosen for the evergreen S. kurilensis, since the photosynthetic activity of the currentyear constructing leaves of S. kurilensis has been suggested to be less vigorous (Koike et al., 1997). Blue and red LEDs (LI-6400-02B) were used as a light source for the measurements. The PPFD level was decreased

Table 1 Attributes of vegetation of the present study site located in a Japan Seatype beech forest at Buna-Daira, Fukushima, Japan. Top height F. crenata trees (m) S. kurilensis shoots (cm) Tree or shoot density F. crenata trees (ha - l) F. crenata seedlings (m - 2) S. kurilensis culms (m - 2) Relative PPFD (%) Top ofS. kurilensis Bottom of S. kurilensis

Closed canopy

Gap

p*

8.3 + 1.0"* 127 _+ 11.7

0 169.7 + 6.5

< 0.05

1155.6"* 2.0 - 0.5 8.4 _+ 0.9

0 0.4 + 0.2 23.9 --- 1.6

< 0.05 < 0.001

100.0 -+- 16.3 2.9 --+0.4

< 0.001 < 0.001

12.0 --+ 1.1 7.3 -+ 1.2

There were two patches (closed forest canopy and forest gap) in the study area (20 m × 50 m). The densities and top heights of dwarf bamboo (Sasa kurilensis) and beech (Fagus crenata) seedlings were determined in 1 m × 1 m plots (n = 8-10). Photosynthetically active photon flux density (PPFD) was recorded at midday on 15 August, 1998. The PPFDs relative to the PPFD at the top of the S. kurilensis layer (sub-canopy of understory) in the gap patch were calculated from the values measured at 3-min intervals from 11:30 to 12:30 (n = 20). Mean + standard errors. *Mann-Whitney's U-test except for the height and density of F. crenata trees (canopy vs. gap). **n = 26 (Total number of F. crenata trees in the canopy patch).

Kobayashi et al.

105

in a stepwise manner from 1,500 to 0 Bmol m - 2 s - 1. Lightphotosynthesis curves were obtained at a constant leaf temperature of 23.2 ± 0.6 °C, which is close to the optimum temperature of photosynthesis in F. crenata leaves (Koike and Maruyama, 1998). CO2 concentration of the air entering the chamber was kept at 350 ± 0,1 p,mol mol - i. The leaf-toair water vapor deficit during the measurements was 0.78 ± 0.2 kPa. The flow rate of the air was 500 ± 0.1 Bmol s - i. The area and dry mass (70 °C, 48h) of leaves were determined after the above measurements to obtain a leaf mass area ratio (LMA). The near light-saturated photosynthetic rate (Amax) and the dark respiration rate (Ra) were calculated as the mean values of the net photosynthetic rate on a leaf area basis at PPFDs of 1,000-1,500 and at 0 Bmol m - 2 s 1, respectively. Photosynthetic light utilization efficiency at relatively low light (~3 was estimated from the slope of a linear regression between the net photosynthetic rate and the PPFD (0-250 gmol photons m - 2 s - I for the E crenata leaves at the forest edge, 0-35 Bmol photons m - 2 s i for the leaves of F. crenata seedlings, and 0-125 Bmol photons m - 2 s - 1 for the S. k u r i l e n s i s leaves). These ranges of PPFD were selected to obtain the highest coefficient of determination for the regression line. The fitting of the light-photosynthesis curve was determined from the procedure of Kachi et al. (1987; basically according to Thornley, 1976): A = [ Q " ~ ' + Aasym - {(¢"Q + Aasym)2 - 4t~"Aasym" 0}0"5]/20 - Rd

aboveground parts of 5-year-old seedlings shaded at the bottom of the S. k u r i l e n s i s layer in the closed canopy patch were sampled. For S. k u r i l e n s i s , five whole shoots were obtained from the gap and closed canopy patches. The shoots were separated into leaf, culm or stem and oven-dried (70 °C, 48 h) immediately after the harvest, and weighed.

Results and Discussion 1 Facultative response to light regimes in F. c r e n a t a The photosynthetic traits of E crenata leaves were remarkably different between the contrasting light regimes (Table 2, Fig. 1). The Amax, Rd, and L M A of E crenata were significantly greater in the leaves at the forest edge than in those in the closed canopy patch (p < 0.05, Mann-Whitney's U-test), and this trend was also shown in LCP, though it was not statistically significant (p = 0.15). The large Amax of sunlit F. crenata leaves at the forest edge (10.7 Bmol CO2 m 2 s - 1) is probably partly due to the greater L M A of these leaves (85.8 g m - 2). The greater L M A mainly represents the development of an area-based photosynthetic apparatus, such as the development of mesophyll layers that occurs when plants are exposed to increased light intensity (Givnish, 1988). Conversely, ~' was significantly greater in the leaves of F. Fagus

.,

.

.

.

.

crenata . . .

Sasa a.,

,

,

,

kurilensis , ,

,

,

.

(1)

where A is the net photosynthetic rate, Q is the incident PPFD, ~0' is the initial slope, Aasym is the asymptote value of Amax, 0 is the convexity of the curve and Ra is the dark respiration rate. The light compensation point (LCP) was taken as the PPFD when the value of the net photosynthetic rate was zero, using the above linear regressions.

3 Biomass allocation of aboveground parts The b i o m a s s allocation of the aboveground parts was indexed by the culm/foliage (C/F) ratio (the ratio of the biomass of non-assimilative organs to the assimilative organs; g g - J). Samples of the aerial shoots were harvested on August 18, 1998. For E crenata, five sunlit twigs (5-year-old shoots ca. 45 cm in length) of saplings at the forest edge and five

off ~o 2;° ,~0 ~'o 8;° ,o'oo,'oo,'o0 ' ~'o ,;0 °% 8~oJo............. Photosynthetically active photon flux density (pmol m 2 s-l)

Fig. 1 Light-photosynthesis curves for Japanese beech (Fagus crenata) and dwarf bamboo (Sasa kurilensis). Open circles show net photosynthesis in the sunlit leaves of F. crenata saplings at the forest edge, and S. kurilensis shoots in the forest gap. Closed circles show net photosynthesis in the shaded leaves of F. crenata seedlings and S. kurilensis shoots beneath the closed forest canopy. Bars represent standard errors (n = 4). Leaf temperature was 23 °C and CO,~ concentration of the air entering the leaf chamber was 350 ~tmol mol - i

Table 2 Net photosynthetic rate at near light-saturating irradiance (Amax),dark respiration rate (Rd), light compensation point (LCP), photosynthetic light utilization efficiency at relatively low light level (initial slope, ~%, and leaf dry mass per leaf area (LMA) for F. crenata leaves at the forest edge and beneath the closed forest canopy, and S. kurilensis leaves in the forest gap and beneath the closed forest canopy. Am~,x Rd (t.tmolCO2m-2s-l) (btmolCO2m-es

LCP

~'

1) (Bmolphotonsm es-~) (I.tmolCO2Bmol lphotons)

LMA (gin -2)

Fagus crenata

at forest edge beneath canopy p*

10.70 ± 0.41 3.34 ± 0.39 < 0.05

1.57 ± 0_17 0.47 ± 0.14 < 0.05

30.34 _ 13.57 3.43 -- 0.83 = 0.15

0.022 ± 0.003 0.040 ± 0.010 < 0.05

85.80 _+_5.51 23.81 ± 0.78 < 0.05

12.26 ± 1.03 8.27 ± 0.75 < 0.05

0.33 --- 0.08 0.36 ± 0.03 = 0.77

4.78 ± 2.55 3.16 ± 0.93 = 0.77

0.036 -+ 0.005 0.031 ± 0.002 = 0.25

75.46 -4- 3.85 53.23 ± 1.99 < 0.05

Sasa kurilensis

in gap beneath canopy p*

Mean + standard error (n = 4). *p-values were determined by Mann-Whitney's U-test (forest edge vs. forest floor, or gap vs. beneath a canopy).

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J. For. Res. 5 (2) 2000:

crenata seedlings in the closed canopy patch than in those of saplings at the forest edge (p < 0.05). In addition, the C/F ratio of E crenata seedlings (1.6 +__0.1; Fig. 2) tended to be small-

er than the reported values of 2.0-2.7 in severer shade environments (7% of full sunlight; Hashizume and Noguchi, 1977; Hashizume, 1982). The small C/F ratio found in this study is an indication of effective matter-production under shady conditions (Monsi et al., 1962; Kuroiwa et al., 1964). Thus, a greater ¢' and smaller values of Rd, L C E and the CIF ratio would help the E crenata seedlings to grow in the shade at the bottom of the S. kurilensis layer in the canopy patch. On the other hand, the Arnax of sunlit leaves of E crenata was three times that of the shaded leaves (Table 2, Fig. 1). This implies that E crenata seedlings beneath the canopy could grow vigorously if the light conditions were improved by a canopy gap opening and/or a simultaneous death of dwarf bamboo. 2 Small changes in the photosynthesis and C/F ratio of S. kurilensis Amax and L M A of S. kurilensis were significantly lower in the leaves beneath the beech canopy than in the leaves in the gap (p ~ 0.05) (Table 2, Fig. 1). However, the reductions of Amax and L M A of S. kurilensis due to shading by the beech canopy (33% and 29% reductions, respectively) were less than half of the reductions in E crenata (69% and 72%). In addition, Amax of shaded S. kurilensis leaves (8.3 gmol CO2 m 2 s - ~) tended to be greater than Amax of leaves in other Sasa species grown in shady conditions (Agata and Kubota, 1985; Yuruki et al., 1987; Lei and Koike, 1998). The C/F ratio of S. kurilensis beneath the closed canopy was only 16% lower than it was in the gap (Fig. 2), which was not a significant difference. Thus, the ability of the C / F ratio to

10

Fagus crenata

Sasa kurilensis

O

respond to changes in light availability appears to be small in S. kurilensis shoots. However, the aboveground structure of the S. kulinensis shoots, i.e., the presence of leaves on the upper part of the culm (Oshima, 1961), would enable the leaves to capture light effectively since the light availability increases with height, even in the understory vegetation (see Table. 1). In agreement with this, Koyama and Ogawa (1993) and Hori et al. (1998) have also suggested that dwarf-bamboos in the understory of deciduous forest that have a high C/F ratio, i.e., relatively long shoots, can position their leaves to receive light efficiently even in shady conditions.

Conclusions In this study, we found that 1) the number of F. crenata seedlings was greater beneath the closed forest canopy where S. kulinensis density was lower than in the gap patch, and 2) the photosynthetic and shoot structural traits of F. cret~ta were more plastic with respect to light availability than are those of S. kulinensis. Beneath the overstory, this response in S. kurilensis would have favored the survival of F. crenata seedlings by increasing the light incidence at the bottom of the S. kurilensis layer (see Table 1). In addition, the improvements of leaf photosynthetic traits and biomass allocation in F. crenata in response to changes in light availability would make efficient use of the increased light incidence as a result of the low S. kurilensis shoot density. These results suggest that safe sites for the establishment of E crenata seedlings are created by the overstory of developed F. crenata trees via their negative effects on the density of S. kurilensis shoots. F. crenata seedlings beneath the closed canopy would have a role as a seedling bank between mast years. We wish to thank Profs. Dr. Y. Yamamura, Dr. M. Shiyomi and Dr. Y. Hori of Ibaraki University for their helpful support and valuable suggestions in the course of this study, and Mr. K. Teraoka of Yokohama National University for his assistance in the field work. We are also grateful to Dr. O. Kitade and Mr. R. Yonekura of Ibaraki University for their advice on the statistical analysis, and to Mr. M. Hori of Tokyo University for providing useful references. Many thanks are extended to two anonymous reviewers for their critical advice.

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Literature cited

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0.1

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Fig. 2 CtF ratio (the ratio of non-assimilative organs to assimilative organs) of sunlit twigs of F. crenata saplings at the forest edge and S. kurilensis shoots in the forest gap (white bars), and shaded shoots of F. crenata seedlings and S. kurilensis beneath the closed forest canopy (black bars). Different letters at the upper right of each bar indicate the existence of significant differences (p < 0.05, Scheffe's test based on the significance of the Kruskal-Wallis test using log-transformed data). Bars represent standard errors (n = 5).

Agata, W. and Kubota, F. (1985) Ecological characteristics and dry matter production of some native grasses in Japan. IV. Influence of light intensity on the growth of Sam nipponia and Sasa borealis in deciduous broad-leaved forest. J. Jpn. Grassl. Sci. 31 : 272-279. Givnish, T. J. (1988) Adaptation to sun and shade: A whole-plant perspective. Aust. J. Plant Physiol. 15: 63-92. Hashizume, H. (1982) The effect of light intensity on the growth and development of Fagus crenata seedlings. Bull. Fac. Agric., Tonori Univ. 34: 82-88. (in Japanese with English summary) Hashizume, H. and Noguchi, K. (1977) Studies on the process of formation of beech forest. III. Regeneration and growth of natural seedlings in beech forest. Bull. Tottori Univ. For. 10: 31-50. (in Japanese with English summary) Hiroki, S. and Matsubara, T. (1995) Fluctuation of nut production and seedling appearance of a Japanese beech (Fagus crenata Blume). Ecol. Res. 10: 161-169. Honma, S. (1995) Analysis of structures and regeneration processes of Japanese beech (Fagus crenata Blume) forest. Ph.D. thesis. 77pp. Dept. Biol., Fac. Sci., Tokyo Metro. Univ. Hori, Y.. Kawarasaki, S., and Kobayashi, T. (1998) Plasticity of C/F ratio

Kobayashi et al. of aerial parts and its ecological significance of a bamboo grass, Pleioblastus chino. J. Jpn. For. Soc. 80: 165-169. (in Japanese with English summary) Kachi, N., Kawai, S., and Furukawa, A. (1987) Acclimation of photosynthetic characteristics in Quercus myrsinaefolia saplings to light environment of forest understory. In Studies in acclimation and adaptation of matter-production and -reproduction of plants to temperature and light environment. Yokoi, Y. (ed.), 97pp, Report of Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (No. 60304003), 33-46. (in Japanese) Kashimura, T. (1962) On the times of the day-compensation of leaves over and under the Sasa layer in the beech forest. Ecol. Rev. 15: 177-183. Koike, T. and Maruyama, Y. (1998) Comparative ecophysiology of the leaf photosynthetic traits in Japanese beech grown in provenances facing the Pacific Ocean and the Sea of Japan. J. Phytogeogr. Taxon. 46: 23-28. (in Japanese with English summary) Koike, T., Homma, K., Lei, T. T., Matsui, K., and Makita, A. (1997) Characteristics of the light response of photosynthetic rate in Sasa kurilensis seedlings. Bamboo J. 14: 15-19. Koyama, N. and Ogawa, Y. (1993) Growth characteristics of Nezasa dwarf-bamboo (Pleioblastus variegatus Makino). 1. Photosynthesis and utilization of stored nitrogen. J. Jpn. Grassl. Sci. 39: 28-35. (in Japanese with English summary) Kuroiwa, S., Hiroi, T., Takada, K., and Monsi, M. (1964) Distribution ratio of net photosynthate to photostnthetic and non-photosynthetic systems in shaded plants. Bot. Mag. Tokyo 77: 3742. Lei, T. T. and Koike, T. (1998) Functional leaf phenotypes for shaded and open environments of a dominant dwarf bamboo (Sasa senanensis) in northern Japan. Int. J. Plant Sci. 159: 812-820. Monsi, M., Iwaki, H., Kuraishi, S., Saeki, T., and Nomoto, N. (1962) Physiological and ecological analysis of shade tolerance of plants. 2. Growth of dark-treated green-grams under varying light intensities.

107 Bot. Mag. Tokyo 75: 185-194. Nakashizuka, T. (1988) Regeneration of beech (Fagus crenata) after the simultaneous death of undergrowing dwarf bamboo (Sasa kurilensis). Ecol. Res. 3: 21-35. Nakashizuka, T. and Numata, M. (1982) Regeneration process of climax beech forests. I. Structure of a beech forest with the undergrowth of Sasa. Jpn. J. Ecol. 32: 57-67. Oshima, Y. (1961) Ecological studies of Sasa communities. I. Productive structure of some of Sasa communities in Japan. Bot. Mag. Tokyo 74: 199-210. Oshima, Y. (1962) Ecological studies of Sasa communities. V. Influence of light intensity, snow depth and temperature upon the development of Sasa kurilensis community. Bot. Mag. Tokyo 75: 4348. Sawada, S., Chiba, S., and Saito, M. (1995) The dynamics of seedling populations in a gap of beech (Fagus crenata) forest. Sci. Rep. Hirosaki Univ. 42: 29-39. (in Japanese with English summary) Shimano, K. and Okitsu~ S. (1994) Regeneration of natural Fagus crenata forests around the Kanto district. Jpn. J. Ecol. 44: 283-291. (in Japanese with English summary) Thornley, J. H. M. (1976) Mathematical models in plant physiology. 318pp, Academic Press, London. Yanagiya, S.-I., Kon, T., and Konishi, A. (I 971) On the characteristics of floor plants and regeneration of Buna (Fagus crenata) natural forest --Especially on Sasa plants--. J, Jpn. For. Soc. 53: 146-148. (in Japanese) Yoshioka, K. (1939) Montane forests on Mr. Hakkoda. I. On the forests of Fagus-Sasa climax zone. Ecol. Rev. 4: 27-38. (in Japanese with English summary) Yumld, T., Ohga, S., and Aragami, K. (1987) Ecological studies of S uzutake (Sasa borealis) IV. Individual growth and photosynthesis. Bull. Kyushu Univ. For. 57: 9-15. (Accepted February 29, 2000)