Community structure of saplings of native woody species under forests dominated by an alien woody species, Casuarina
equisetifolia, on Chichijima Island
Kenji HATA
1*, Hidetoshi KATO
2and Naoki KACHI
11
Department of Biological Sciences, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-Osawa 1-1, Hachioji, Tokyo, 192-0397, JAPAN
2
Makino Herbarium, Tokyo Metropolitan University, Minami-Osawa 1-1, Hachioji, Tokyo, 192-0397, JAPAN
*
Author for correspondence (e-mail: [email protected])
ABSTRACT
On the Bonin (Ogasawara) Islands, thick litter accumulation of an alien woody species, Casuarina equisetifolia is observed under its dense canopy. This observation suggests that the thick litter accumulation could prevent establishment of seedlings of native woody species. To indentify the possible effects of litter accumulation on distribution of native woody species, we compared species composition of saplings, seed dispersal, and amounts of accumulated litter in forests dominated by C. equisetifolia with those in forests dominated by native species on Chichijima Island. Numbers of individuals of woody species smaller than 1.3 m in height (hereafter, “saplings”) were counted in thirty 5×5 m quadrats established at sites dominated by C. equisetifolia and 30 quadrats at sites dominated by native species in September 2007.
Numbers of dispersed seeds and amounts of accumulated litter in the quadrats were also measured. Density, frequency and species richness of saplings of woody species, especially of native species at the sites of C. equisetifolia were much lower than those at the sites of native species. More than 99% of dispersed seeds during the study period were those of a native woody species, Schima mertensiana and its numbers at the sites of C. equisetifolia were significantly smaller than those at the sites of native species. Dry weight and depth of accumulated litter at the sites of C. equisetifolia were significantly lager than those at the sites of native species. Our study suggested that saplings of native woody species should be prevented establishing in a forest dominated by C. equisetifolia caused by lack of seed dispersal and/or inhibition of their seedling establishment by thick litter accumulation of C.
equisetifolia.
Keywords: Bonin (Ogasawara) Islands, invasion, litter accumulation, Schima mertensiana,
species richness
INTRODUCTION
Invasion of an alien plant species often prevent native plants from subsequent establishment in the invaded communities (Gould and Gorchov 2000; Denslow 2006; EL-Keblawy and AL-Rawai 2005) due to shading (Weihe and Neely 1997), litter accumulation (Walker and Vitousek 1991) and allelopathy (Gentle and Duggin 1997). The lack of establishment of native plants has a potential to affect the structure and species composition of native plant communities. Quantifying possible effects of alien plants on native communities is crucial to determine based on scientific criteria whether an alien plant should be controlled or not (Parker et al. 1999; Pheloung et al. 1999).
An alien woody species, Casuarina equisetifolia Forst. (Casuarinaceae), has invaded in the Bonin (Ogasawara) Islands, Japan, oceanic islands in the north-western pacific (Shimizu 2003). This species is native to Australia and has been naturalized in tropical and subtropical areas (Weber 2003). This species was introduced to the Bonin Islands in the late 1800s and had been planted on several of the Bonin Islands (Toyoda 2003). Thereafter, plants of this species have been spread mainly surrounding a secondary forest and partly to a dry scrub (Shimizu 2003). High litter accumulation of C. equisetifolia is observed under its dense canopy, which suggested that it could prevent from establishment of native plants (Parrota 1995; Batish et al. 2001; Weber 2003). However, this has not been confirmed in the Bonin Islands because of lack of quantitative data on community structure and litter accumulation under forests where C. equisetifolia invaded. To indentify possible effects of litter accumulation of C. equisetifolia on the distribution of native woody species, we compared community structure of woody species, seed dispersal and amounts of accumulation of litter under forests dominated by C.
equisetifolia with those under forests dominated by native species on the largest island of the Bonin Islands, Chichijima.
STUDY SITES AND MEASUREMENTS
This study was conducted in forests at Suzaki in Chichijima Island (27°03’-27°04’N, 142°11’E) (Fig. 1). The mean annual temperature in the island is ca. 23 ºC and the mean annual amount of precipitation (1970-1999) is 1234.9 mm (Oka et al. 2000). Some sites in the forests had been plantations of C. equisetifolia and other sites had been cultivated areas in the early 1900s (Yamaguchi 1998). Currently, there are mainly two forest types in Suzaki: a forest dominated by C. equisetifolia and that dominated by native species mainly Schima mertensiana (Sieb. et Zucc.) Koidez. (Theaceae).
We selected 30 sites dominated by C. equisetifolia and 30 sites dominated by native
species in the forests (Fig. 1). At the 60 sites, plants of woody species larger than 1.3 m
in height (hereafter, the “trees”) of C. equisetifolia, Psidium cattleianum, Machilus kobu,
Pandanus boninensis, Pouteria obovata, Rhaphiolepis wrightiana and S. mertensiana were
observed in more than 30 sites (Appendix 1). Trees of C. equisetifolia were observed at sites
of C. equisetifolia more frequently than those of native species. There were no significant
differences in frequencies of trees of P. boninensis, P. obovata and R. wrightiana between
sites of C. equisetifolia and those of native species. Trees of P. cattleianum, M. kobu and S. mertensiana were observed at sites of native species more frequently than those of C.
equisetifolia.
The values of total basal area of all tress ranged from 27.5 m
2ha
-1to 75.5 m
2ha
-1at the sites of C. equisetifolia and from 25.7 m
2ha
-1to 71.4 m
2ha
-1at the sites of native species (Appendix 2). The values of total basal area of C. equisetifolia were highest at sites of C. equisetifolia (Fig.
2a). The percentages of the total basal areas of C. equisetifolia against those of all trees were lager than 40% at sites of C. equisetifolia. At sites of native species, S. mertensiana showed the highest value of the total basal areas of trees and percentages of the total basal areas of S.
mertensiana against those of all trees were lager than 30% (Fig. 2b).
Numbers of all tress ranged from 43 to 197 at the sites of C. equisetifolia and from 50 to 234 at the sites of native species (Appendix 3). Numbers of trees of C. equisetifolia, R.
wrightiana and S. mertensiana were highest at the sites of C. equisetifolia (Fig. 3a). At the sites of native species, R. wrightiana and S. mertensiana showed the highest values (Fig. 3b).
We established a 5×5 m quadrat at each site. All measurements were conducted between September 2007 and February 2008. Numbers of plants of all woody species smaller than 1.3 m in height (hereafter, “saplings”) in the quadrats were counted. To measure amounts of accumulated litter, we collected litter at one randomly-chosen 0.2×0.2 m within each quadrat after measurement of its litter depth at the sampling point. The litter was sorted by following five categories: leaves of C. equisetifolia, leaves of other species, reproductive parts (seeds, seedpods and flowers) of C. equisetifolia, reproductive parts of other species, branches including C. equisetifolia and other species and undistinguished parts. The litter was dried 70
Fig. 1 Locations of the 60 study sites at Suzaki in Chichijima Island. The solid triangles indicate the sites dominated by Casuarina equisetifolia, and opened sequares indicate the sites dominated by native species.
1 km
50
50 50
Chichijima Island Suzaki
200 m N
▲
▲▲▲▲ ▲ ▲
▲
▲
▲
▲ ▲
▲
▲
▲
▲
▲ ▲
▲ ▲
▲
▲
▲ ▲
▲ ▲
▲ ▲
▲ ▲
ºC for 72 h for weighing. A seed trap with 0.8 m in diameter and 0.8 m in depth was placed in each quadrat and numbers of seeds fallen into the traps between September 2007 and February 2008 were counted.
All statistical analyses were carried out with the software, R 2.6.2 (R Development Core Team 2007). Fisher’s exact probability tests were conducted to evaluate whether saplings of all woody species frequently presented at sites dominated by C. equisetifolia or sites dominated
Fig. 2 Total basal area of trees (>1.3 m in height) of dominant woody species (a) at the sites dominated by Casuarina equisetifolia and (b) at the sites dominated by native species.
Mean values and standard error were shown. Cas means C. equisetifolia, Poo means Pouteria obovata, Mak means Machilus kobu, Rhw means Rhaphiolepis wrightiana, Pab means Pandanus boninensis and Scm means Schima mertensiana. The values of the basal area were based on a data set of diameter at breast heights of trees within a 15×15 m quadrat surrounding a 5×5 m quadrat at each site in September 2007.
20 40
(a)
0 Cas Poo M ak Rhw Pab Scm
N um be r o f t re es (2 25 m
-2)
Species (b)
Cas Poo M ak Rhw Pab Scm 10
20 30 40
(a)
0 Cas Poo M ak Rhw Pab Scm
Total b as al a re a (m
2h a
-1)
Species (b)
Cas Poo M ak Rhw Pab Scm
Fig. 3 Numbers of trees (>1.3 m in height) of dominant woody species (a) at the sites
dominated by Casuarina equisetifolia and (b) at the sites dominated by native species. Mean
values and standard error were shown. Cas means C. equisetifolia, Poo means Pouteria
obovata, Mak means Machilus kobu, Rhw means Rhaphiolepis wrightiana, Pab means
Pandanus boninensis and Scm means Schima mertensiana. The values of the basal area
were based on a data set of diameter at breast heights of trees within a 15×15 m quadrat
surrounding a 5×5 m quadrat at each site in September 2007.
by native species. Numbers of saplings and its species richness in the quadrats at the sites of C. equisetifolia were compared with those in the quadrats at the sites of native species by generalized linear models (GLMs) with the Poisson error distribution. Same analysis was also conducted for the comparison of numbers of dispersed seeds in the seed traps between the two sites. Dry weight and depth of accumulated litter were compared between the sites by t-test.
Relationships between dry weight and depth of accumulated litter were also analyzed by analysis of covariance (ANCOVA). In the analysis, a dependent variable was the dry weight of accumulated litter, an independent variable was the two types of forests, and a covariate was depth of litter.
RESULTS
Saplings of M. kobu, P. obovata, R. wrightiana and S. mertensiana were observed in more than twenty 5×5 m quadrats (Table 1). Saplings of P. obovata, M. kobu and S. mertensiana were observed at the sites dominated by native species more frequently than those dominated
Species Total Cas. Native p value
Alien species Bischofia javanica 9 1 8 0.03
Caryota urens 5 0 5 0.05
Casuarina equisetifolia 3 3 0
Dypsis lutescens 1 1 0
Leucaena lucocephala 12 9 3 0.1
Morus australis 14 6 8 0.76
Psidium cattleianum 9 1 8 0.03
Native species Ardisia sieboldii 1 0 1
Celtis boninensis 2 0 2
Elaeocarpus photiniifolius 1 0 1
Ficus boninsimae 1 1 0
Hedyotis grayi 6 0 6 0.02
Ligustrum micranthum 7 0 7 0.01
Machilus kobu 21 0 21 < 0.001
Neolitsea aurata 2 0 2
Ochraosia nakaiana 4 0 4
Osmanthus insularis 6 1 5 0.19
Padanus boninensis 1 0 1
Pouteria obovata 47 17 30 < 0.001
Rhaphiolepis wrightiana 43 18 25 0.08
Schima mertensiana 23 0 23 < 0.001
Syzygium cleyeraefolium 4 0 4
Tarrenna subsessilis 16 2 14 < 0.001
Trema orientalis 4 2 2
Wikstroemia pseudoretusa 7 1 6 0.1
Table 1 Frequency of saplings (< 1.3 m in height) of woody species in 60 quadrats (5×5 m).
“Cas.” and “Native” indicate quadrats at the sites of Casuarina equisetifolia and those at the
sites of native species respectively. p values show Fisher’s exact probability test for woody
species that were present in more than 5 of the 60 quadrats.
by C .equisetifolia and those of R. wrightiana trend to be observed at the sites of native species frequently with marginal statistical significance. Few saplings of C. equisetifolia occurred at both sites.
Numbers of all saplings in the quadrats ranged from 0 to 60 at the sites of C. equisetifolia and from 12 to 102 at the sites of native species (Appendix 4). The numbers of saplings at the sites of C. equisetifolia were significantly smaller than those in the quadrats at the sites of native species (Fig 4a). The similar trend was found in numbers of saplings of native species. There were no significant differences in numbers of saplings of alien species between the two types of forests. Numbers of saplings of M. kobu, P. obovata, R. wrightiana and S.
mertensiana at the sites of C. equisetifolia were significantly smaller than those at the sites of native species (Fig. 4b).
Species richness of saplings of all woody species and that of saplings of native species at the sites of C. equisetifolia were smaller than those at the sites of native species (Fig. 5). No significant differences in species richness of saplings of alien species were detected between the two types of forests. A mean value of Shannon-Weiner index, H’ in the quadrats at the sites of C. equisetifolia was 0.52 (± 0.08 s.e.) and that at the sites of native species was 1.31 (±
0.06 s.e.).
There was a significant difference in amounts of litter accumulation between the two types of forests. Dry weights and depths of accumulated litter at the sites of C. equisetifolia were larger than those at the sites of native species (Fig. 6). Significant positive relationships between the dry weight and depth were detected at both sites (Fig. 7). According to results of ANCOVA, dry weights of accumulated litter per unit depth at the site of C. equisetifolia were significantly larger than those at the site of native species (Fig. 7). At the sites of C.
Fig. 4 Numbers of saplings (<1.3 m in height)of (a) total, native and alien woody species and (b) four dominant native species in the quadrats (5×5 m). Closed and open areas indicate the number of saplings in the quadrats at the sites of Casuarina equisetifolia and those at the sites of native species respectively. Mean values and standard error were shown. Poo means Pouteria obovata, Mak means Machilus kobu, Rhw means Rhaphiolepis wrightiana and Scm means Schima mertensiana. ***: p < 0.001, n.s.: not significant by GLM. p values were based on likelihood ratio tests which were compared the GLM including two sites as an independent variable with the null model from which excludes the independent variable from the GLM.
0 20 40 60
total native alien
***
n.s.
***
(a)
0 10 20
Poo M ak Rhw Scm
N um be r o f s ap lin gs (2 5 m
-2)
Species
***
***
***
***
(b)
0 2 4 6 8
total native alien Sp ec ie s ric hn es s o f s ap lin gs (2 5 m
-2)
Species
***
n.s.
***
Fig. 5 Species richness of saplings of total, native and alien woody species in the quadrats (5×5 m).
Closed and open areas indicate the number of saplings in the quadrats at the sites of Casuarina equisetifolia and those at the sites of native species respectively. Mean values and standard error were shown. ***: p < 0.001, n.s.: not significant by GLM.
p values were based on likelihood ratio tests which were compared the GLM including two sites as an independent variable with the null model from which excludes the independent variable from the GLM.
Fig. 6 (a) Dry weight and (b) depth of accumulated litter at the sites dominated by Casuarina equisetifolia and the site dominated by native species. Mean values and standard error were showed. “Cas.” and “Native” indicate quadrats at the sites of C. equisetifolia and those at the sites of native species respectively.
0 50 100
D ry w ei gh t ( g 0. 04 m
-2) t-test, p < 0 .001 (a)
0 4 8
Cas. Native
D ep th (c m )
t -test, p < 0 .001
(b)
Cas. Native
Forest Type
Fig. 7 Relationships between dry weight of accmulated litter and its depth. The solid triangles indicate the sites of Casuarina equisetifolia (linear regression; dry weight=50.0+9.1×depth, r
2=0.75, p<0.001) and opened sequares indicate the sites of native species (dry weight=20.3+9.3×depth, r
2=0.41, p<0.001). Results of ANCOVA showed that significant differences in slope between the two regression models were not detected and that there were no interactions between the two types of forests (independent variable) and depth of litter (covariate).
0 50 100 150 200
0 5 10 15
D ry w ei gh t ( g 0. 04 m
-2)
Depth (cm)
equisetifolia, More than 40% of total amounts of accumulated litter were dead leaves of C.
equisetifolia (Table 2).
More than 99% of dispersed seeds of native species during the study period were those of
S. mertensiana. A significant difference in the numbers of S. mertensiana seeds between the C.
equisetifolia sites and the native sites was detected. The mean value of the numbers of the S.
mertensiana seeds at the sites of C. equisetifolia were 11.0 (± 3.3 s.e.) seeds trap
-1and that at the sites of native species was 345.0 (± 35.9 s.e.).
DISCUSSION
Lower density and lower frequency of saplings of native species at the sites of C. equisetifolia indicated that there would be lack of establishment of native species under forests dominated by C. equisetifolia. These findings are consistent with those of previous studies in other regions (Parrota 1995; Batish et al. 2001; Weber 2003). The lack of establishment of native species means that it is unlikely that native species would replace C. equisetifolia in the forests in the future. In some islands of the Bonin Islands, C. equisetifolia has been invaded and formed dense thickets (Kanto Regional Forest Office 2007), which could be a serious problem for conservation of native forests of the Bonin Islands.
The lack of saplings of native species in the forests of C. equisetifolia has at least possible two explanations: lack of dispersal of seeds and lack of subsequent establishment of seedlings.
First, dispersal of seeds of native species would infrequently occur in the C. equisetifolia forests because of lack of their seed sources in the forests. Our study period is too short to investigate phenology of seed dispersal of all native tree species. There may be infrequent seed dispersal from outside of the forests. However, at least, smaller numbers of dispersed seeds of S. mertensiana in the forests of C. equisetifolia could partly explain the lack of its saplings in the forests. Second, saplings of native species were absent in the forests of C.
equisetifolia because of lack of establishment of their dispersed seeds, which are likely to be related to litter accumulation of C. equisetifolia. Thicker and more dense accumulation of C.
equisetifolia litter in the forests of C. equisetifolia could inhibit germination of seeds of native species and survival of their seedlings by way of a mechanical barrier, which is observed in other plant species (e.g. Rotundo and Aguiar 2005; Navarro-Cano 2008). Allelopathic effects of C. equisetifolia may also play a role to prevent plants of native species from subsequent establishment (e.g. Bosy and Reader, 1995; Yirdaw and Leinonen, 2002; Raniello et al., 2007).
Indeed, phytotoxic chemicals included mainly in tree bark or root bark of C. equisetifolia prevents seeds of lettuce and radish from radial growth and root elongation (Nakahira and
Cas. Native
Leaves C. equisetifolia 43.5 ± 2.8 1.5 ± 0.3
Other species 1.7 ± 0.4 37.3 ± 1.8
Reproductive parts C. equisetifolia 8.2 ± 1.3 1.3 ± 0.4
Other species 0.3 ± 0.3 6.2 ± 0.6
Branches 18.2 ± 1.7 23.8 ± 2.1
Undistinguished parts 29.1 ± 2.3 29.9 ± 1.9
Table 2 Percentages of dry weight of accumulated litter at the sites at the sites dominated by Casuarina equisetifolia and the site dominated by native species. “Cas.” and
“Native” indicate quadrats at the sites of C. equisetifolia and those at the sites of
native species respectively.
Ohira 2005).
Our study demonstrated quantitively that saplings of woody species, especially of native species were absent in forests dominated by C. equisetifolia, and that the absence of native saplings of native species would be correlated with lack of seed dispersal of native species and/or inhibition of their establishment possibly by litter accumulation of C. equisetifolia. The quantified data can provide necessary information to determine whether the alien trees should be eradicated and controlled in the Bonin Islands. However, causal factors to cause the lack of native saplings are still not known from this study. To clarify the causal factors, it is necessary to clarify effects of litter of C. equisetifolia on seed germination and/or seedling performance of native woody species by experimental approaches.
ACKNOWLEDGMENTS
The Environmental Agency and the Department of National Forests in the Ogasawara Islands allowed us to conduct this study at the Chichijima island. This study was financially supported in part by a Grand-in-Aid for Scientific Research of Japan Society for Science Promotion and the Fund for the Global Environmental Research Program of the Ministry of the Environment of Japan (Grand No. F-51). We thank the Department of National Forests in the Ogasawara Islands and the Ogasawara Subtropical Agriculture Center for providing locations for this study.
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Species Total Cas. Native p value
Alien species Bischofia javanica 10 1 9 0.01
Caryota urens 5 1 4 0.35
Casuarina equisetifolia 47 30 17 < 0.001
Derris elliptica 1 0 1
Dypsis lutescens 1 0 1
Ficus wrightiana 1 0 1
Leucaena lucocephala 16 11 5 < 0.001
Morus australis 26 8 18 0.02
Pinus luchuensis 28 20 8 0.004
Psidium cattleianum 30 5 25 < 0.001
Native species Ardisia sieboldii 5 1 4 0.35
Callicarpa subpubescens 2 0 2
Drypetes integerrima 1 0 1
Elaeagnus rotundata 2 1 1
Elaeocarpus photiniifolius 8 1 7 0.05
Fagara boninsimae 1 0 1
Ficus boninsimae 4 2 2
Hedyotis grayi 13 3 10 0.06
Hibiscus glaber 4 2 2
Ilex mertensii 3 1 2
Ligustrum micranthum 24 5 19 < 0.001
Livistona chinensis 13 4 9 0.21
Machilus kobu 39 11 28 < 0.001
Neolitsea aurata 7 0 7 0.01
Ochraosia nakaiana 23 4 19 < 0.001
Osmanthus insularis 20 5 15 0.07
Osteomeles boninensis 1 1 0
Padanus boninensis 41 21 20 1
Photinia wrightiana 1 0 1
Pittosporum boninense 1 0 1
Pouteria obovata 42 20 22 0.79
Rhaphiolepis wrightiana 57 30 27 0.24
Schima mertensiana 49 19 30 < 0.001
Syzygium cleyeraefolium 12 2 10 0.02
Tarrenna subsessilis 18 1 17 < 0.001
Terminalia catappa 5 0 5 0.05
Trema orientalis 5 3 2 1
Wikstroemia pseudoretusa 26 6 20 < 0.001
Appendix 1 Frequency of trees (>1.3 m in height) of woody species at the 60 sites. “Cas.”
and “Native” indicate the sites of Casuarina equisetifolia and those of native species
respectively. P values show Fisher’s exact probability test for woody species that were
present in more than 5 of the 60 sites. The values of the frequency were based on a data set
of presence of trees within a 15×15 m quadrat surrounding a 5×5 m quadrat at each site in
September 2007.
Appendix 2 Total basal area (m
2ha
-1) of trees (>1.3 m in height) of all woody species at sites of Casuarina equisetifolia (C01-C30) and those of n at iv e sp ec ie s (N 01 -N 30 ). Th e va lu es o f th e ba sa l a re a w er e ba se d on a d at a se t o f di am et er a t b re as t h ei gh ts o f tre es w ith in a 1 5× 15 m quadrat surrounding a 5×5 m quadrat at each site in Septem ber 2007. Sp ec ie s C 01 C 02 C 03 C 0 4 C 05 C 06 C 07 C 08 C 09 C 10 C 11 C 12 C 13 C 1 4 C 15 C 16 C 17 C 18 C 19 C 20 C 21 C 22 C 23 C 2 4 C 25 C 26 C 27 C 28 C 29 C 30 A lie n s pe ci es Bi sc ho fia j av an ic a 0.3 Caryota urens 0.2 C as ua ri na e qu is et ifo lia 27.6 26.1 51.2 49.6 37.2 46.4 35.3 33.7 39.6 47.0 30.8 44.7 26.1 64.9 38.5 33.0 48.9 60.0 60.0 26.8 67.2 24.3 31.0 43.9 27.8 22.1 42.7 38.1 26.3 34.6 D er ri s e lli pt ic a
Dypsis lutescens Ficus wrightiana Le uc ae na l uc oc ep ha la 0.1 0.4 0.9 0.9 < 0.1 0.1 < 0.1 0.3 2.8 1.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 0.4 < 0.1 0.5 0.1 M or us a us tr al is Pi nu s l uc hu en si s 0.1 < 0.1 0.3 0.2 1.1 3.6 2.5 0.5 8.4 0.2 0.6 6.5 8.9 0.8 < 0.1 2.6 5.3 1.8 3.4 0.3 Ps id iu m c at tle ia nu m < 0.1 < 0.1 < 0.1 < 0.1 0.1 Native species Ardisia sieboldi i 0.1 C al lic ar pa s ub pu be sc en s
Drypetes integerrima El ae ag nu s r ot un da ta < 0.1 El ae oc ar pu s p ho tin iif ol iu s < 0.1 Fa ga ra b on in si m ae Ficus boninsima e < 0.1 < 0.1 Hedyotis grayi < 0.1 0.1 < 0.1 H ib is cu s g la be r 0.1 0.1 0.6 Ile x m er te ns ii Ligustrum micranthum 0.2 < 0.1 < 0.1 0.1 < 0.1 Li vi st on a c hi ne ns is 0.9 0.9 1.1 2.8 M ac hi lu s k ob u < 0.1 0.1 0.2 0.9 0.3 0.6 0.6 0.3 < 0.1 < 0.1 0.2 < 0.1 N eo lit se a a ur at a Ochraosia nakaiana 2.4 0.3 < 0.1 < 0.1 O sm an th us i ns ul ar is < 0.1 0.1 < 0.1 0.2 < 0.1 O st eo m el es b on in en si s < 0.1 2.5 1.7 1.1 0.4 3.7 3.3 4.5 3.4 1.7 1.3 0.8 4.2 0.6 6.9 1.5 0.5 2.6 2.8 3.5 3.8 6.6 Pa da nu s b on in en sis Ph ot in ia w ri gh tia na Pi tto sp or um b on in en se Pouteria obovat a 0.2 0.3 < 0.1 < 0.1 < 0.1 < 0.1 0.7 < 0.1 < 0.1 0.1 0.9 < 0.1 < 0.1 < 0.1 0.6 0.3 < 0.1 < 0.1 0.3 < 0.1 Rh ap hi ol ep is w ri gh tia na 1.6 1.1 0.1 1.5 < 0.1 0.3 0.7 < 0.1 0.2 0.4 0.2 1.0 < 0.1 1.9 0.3 3.4 2.2 1.6 0.6 0.3 < 0.1 4.5 1.1 0.1 0.6 0.4 2.4 2.6 0.5 0.1 Schima mertensiana 4.6 5.5 2.1 5.3 14.7 5.4 0.1 10.7 17.8 1.2 0.1 21.8 6.3 0.8 13.3 14.8 14.1 7.2 20.4 Sy zy gi um c le ye ra ef ol iu m < 0.1 < 0.1 Ta rr en na s ub se ss ili s < 0.1 Te rm in al ia c at ap pa Tr em a o ri en ta lis 0.3 0.2 < 0.1 W ik st ro em ia p se ud or et us a < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 To ta l 34.2 34.0 60.0 53.9 38.5 48.2 48.8 51.1 49.5 48.8 54.6 67.0 27.5 68.7 41.1 40.2 51.6 64.8 68.2 63.3 75.5 39.5 36.9 60.5 51.2 41.1 48.9 48.2 40.8 55.2
Appendix 2 Continued. Sp ec ie s N 01 N 02 N 03 N 0 4 N 05 N 06 N 07 N 08 N 09 N 10 N 11 N 12 N 13 N 1 4 N 15 N 16 N 17 N 18 N 19 N 20 N 21 N 22 N 23 N 2 4 N 25 N 26 N 27 N 28 N 29 N 30 A lie n sp ec ie s Bi sc ho fia ja va ni ca < 0. 1 0.1 0. 3 0.3 0. 1 0.5 0. 2 1.2 0. 2 Caryota uren s 1. 1 0 .4 0. 9 0.8 C as ua ri na e qu is et ifo lia 4. 8 0.7 0.2 10. 8 < 0.1 2. 5 0.8 2. 2 < 0.1 < 0. 1 < 0.1 < 0. 1 < 0.1 0.4 10. 9 0.9 < 0. 1 6.0 3. 4 D er ri s e lli pt ic a < 0. 1 Dypsis lutescens 0. 6 Ficus wrightiana < 0. 1 Le uc ae na lu co ce ph al a 0. 8 4 .6 1. 2 1.5 0. 4 M or us a us tr al is 0. 2 < 0.1 < 0. 1 0.1 0. 1 0 .4 0. 2 1.0 0. 2 < 0.1 0. 2 0.6 0. 1 0.1 0. 1 0 .4 0. 2 < 0.1 Pi nu s l uc hu en si s 5. 6 2.6 0. 4 < 0.1 2. 3 2.1 < 0. 1 2 .4 Ps id iu m c at tle ia nu m < 0. 1 < 0.1 < 0. 1 0.1 0. 1 < 0.1 0. 2 < 0.1 0. 3 0 .4 0. 2 < 0.1 < 0. 1 0.2 < 0. 1 < 0.1 < 0. 1 < 0.1 < 0. 1 < 0.1 0. 1 0.1 < 0. 1 0.1 0. 1 Native species Ardisia sieboldi i < 0. 1 0.6 < 0. 1 0.3 C al lic ar pa su bp ub es ce ns 0. 1 < 0.1 Drypetes integerrima < 0. 1 El ae ag nu s r ot un da ta < 0. 1 El ae oc ar pu s p ho tin iif ol iu s 0. 3 < 0.1 < 0. 1 < 0.1 < 0. 1 0.5 < 0. 1 Fa ga ra b on in si m ae 0. 1 Fi cu s b on in si m ae 0. 1 < 0.1 Hedyotis grayi 0. 1 < 0.1 < 0. 1 < 0.1 < 0. 1 < 0.1 0. 4 < 0.1 < 0. 1 < 0.1 H ib is cu s g la be r 1. 1 0.1 Ile x m er te ns ii 0. 6 < 0.1 Li gu st ru m m ic ra nt hu m < 0. 1 < 0.1 < 0. 1 0.1 < 0. 1 0.2 0. 4 < 0.1 0. 1 < 0.1 0. 2 < 0.1 < 0. 1 < 0.1 < 0. 1 < 0.1 0. 2 0.1 0. 1 Li vi st on a ch in en si s 1. 3 1.3 1. 2 1.5 7. 5 9.9 6. 2 1.5 1. 1 M ac hi lu s k ob u 1. 2 1.7 4. 9 2.5 0. 5 2.8 0. 7 0.2 3. 6 3.8 0. 2 0.3 1. 1 0.2 1. 1 4 .8 1. 9 < 0.1 0. 2 < 0.1 1. 5 0.3 0. 4 0 .5 0. 4 0 .3 0. 1 0 .4 N eo lit se a au ra ta 0. 6 1.1 0. 1 0.2 0. 6 1.1 0. 0 Ochraosia nakaiana < 0. 1 < 0.1 0. 3 0.5 1. 5 7.6 6. 0 < 0.1 2. 9 0.1 0. 3 1.9 0. 1 4.4 0. 1 1.2 4. 3 0.6 3. 9 O sm an th us in su la ri s < 0. 1 < 0.1 < 0. 1 < 0.1 0. 1 < 0.1 < 0. 1 < 0.1 < 0. 1 < 0.1 < 0. 1 < 0.1 0. 2 < 0.1 < 0. 1 O st eo m el es b on in en si s Pa da nu s b on in en sis 0. 3 0.3 2. 7 0.3 1. 3 5.5 0. 7 1.6 1. 1 0.6 5. 7 0.2 5. 5 0.2 0. 4 1.4 0. 3 1 .4 1. 0 0.7 Ph ot in ia w ri gh tia na < 0. 1 Pi tto sp or um b on in en se < 0. 1 Pouteria obovat a 0. 1 < 0.1 7. 5 0.2 0. 7 0.2 0. 2 0.8 3. 2 1.5 0. 4 0 .3 < 0. 1 < 0.1 0. 2 0.1 0. 2 < 0.1 0. 1 < 0.1 0. 1 0 .4 Rh ap hi ol ep is w ri gh tia na < 0. 1 0 .4 0. 6 1.0 0. 2 0.1 10. 3 2.6 2.6 11. 7 6.0 12. 1 1.2 < 0. 1 1.6 0. 4 0.4 4. 9 4 .1 < 0. 1 1.7 1. 3 0 .4 1. 2 0.7 2. 3 1.0 Schima mertensiana 46.0 40.3 36.4 42.0 38.0 34.9 25.6 52.2 28.1 22. 6 1 .4 < 0. 1 30.9 27.3 22.4 34.1 47.1 33.0 53. 4 8 .2 27.7 49.5 33.9 50.8 42.8 55.6 47.4 63.1 57.9 38. 8 Sy zy gi um c le ye ra ef ol iu m < 0. 1 0.0 0. 1 < 0.1 < 0. 1 < 0.1 0. 2 < 0.1 < 0. 1 < 0.1 Ta rr en na su bs es si lis < 0. 1 < 0.1 < 0. 1 < 0.1 < 0. 1 < 0.1 < 0. 1 < 0.1 < 0. 1 < 0.1 < 0. 1 < 0.1 < 0. 1 < 0.1 < 0. 1 < 0.1 < 0. 1 Te rm in al ia c at ap pa 1. 1 5.7 5. 0 5.6 1. 0 Tr em a or ie nt al is 0. 1 < 0.1 W ik st ro em ia p se ud or et us a < 0. 1 0.1 0. 1 0.1 < 0. 1 < 0.1 < 0. 1 < 0.1 < 0. 1 0.1 0. 1 < 0.1 0. 2 0.1 < 0. 1 0.2 < 0. 1 0.1 < 0. 1 < 0.1 < 0. 1 To ta l 52.9 51.3 45.8 49.0 46.6 39.6 54.2 56.2 36.4 39.3 33.5 32.5 38.4 36.6 34.9 37.8 49.0 41.9 64.8 25.7 44.0 61.1 40.0 52.0 52.0 63.0 55.4 71.4 68.0 48. 0
Sp ec ie s C 01 C 02 C 03 C 0 4 C 05 C 06 C 07 C 08 C 09 C 10 C 11 C 12 C 13 C 1 4 C 15 C 16 C 17 C 18 C 19 C 20 C 21 C 22 C 23 C 2 4 C 25 C 26 C 27 C 28 C 29 C 30 A lie n s pe ci es Bi sc ho fia j av an ic a 17 Caryota urens 1 C as ua ri na e qu is et ifo lia 50 60 33 25 41 91 39 22 16 53 15 9 100 21 28 20 53 23 23 49 16 45 27 9 3 4 3 1 27 29 11 10 D er ri s e lli pt ic a
Dypsis lutescens Ficus wrightiana Le uc ae na l uc oc ep ha la 11 10 19 17 1 20 2 7 95 57 2 M or us a us tr al is 3 1 1 2 8 1 35 3 2 1 1 1 2 8 2 2 11 1 1 9 2 1 1 3 10 2 3 1 Pi nu s l uc hu en si s Ps id iu m c at tle ia nu m 1 1 1 1 2 Native species Ardisia sieboldi i 9 C al lic ar pa s ub pu be sc en s
Drypetes integerrima El ae ag nu s r ot un da ta 1 El ae oc ar pu s p ho tin iif ol iu s 1 Fa ga ra b on in si m ae 1 2 Ficus boninsima e Hedyotis grayi 1 1 1 H ib is cu s g la be r 3 2 Ile x m er te ns ii 2 8 1 1 7 1 Ligustrum micranthum Li vi st on a c hi ne ns is 1 1 1 2 M ac hi lu s k ob u 1 3 6 7 8 8 1 2 1 3 1 N eo lit se a a ur at a 4 1 1 1 Ochraosia nakaiana O sm an th us i ns ul ar is 1 2 1 1 1 O st eo m el es b on in en si s 3 Pa da nu s b on in en sis 8 4 4 1 11 10 13 9 4 8 3 14 1 2 3 4 2 9 11 10 12 21 Ph ot in ia w ri gh tia na Pi tto sp or um b on in en se Pouteria obovat a 18 7 4 5 4 3 1 7 4 9 16 3 14 7 1 7 3 2 1 5 1 Rh ap hi ol ep is w ri gh tia na 16 16 8 57 3 4 3 2 3 6 11 5 10 10 27 11 12 32 55 17 24 1 4 8 11 2 12 6 36 27 8 2 23 25 22 19 46 11 1 3 2 4 3 27 3 74 26 6 3 4 24 4 3 18 30 Schima mertensiana Sy zy gi um c le ye ra ef ol iu m 2 1 Ta rr en na s ub se ss ili s 1 Te rm in al ia c at ap pa 3 1 1 Tr em a o ri en ta lis W ik st ro em ia p se ud or et us a 3 3 2 3 2 5 To ta l 120 129 109 113 50 98 126 80 49 85 76 71 143 82 66 55 98 197 107 184 117 148 49 52 92 94 80 82 61 43
Appendix 3 Density (225 m
-2) of trees (>1.3 m in height) of all woody species at sites of Casuarina equisetifolia (C01-C30) and those of native species (N01-N30). The values of the density were based on a data set of numbers of trees within a 15×15 m quadrat surrounding a 5×5 m quadrat at each site in September 2007.
Appendix 3 Continued. Sp ec ie s N 01 N 02 N 03 N 0 4 N 05 N 06 N 07 N 08 N 09 N 10 N 11 N 12 N 13 N 1 4 N 15 N 16 N 17 N 18 N 19 N 20 N 21 N 22 N 23 N 2 4 N 25 N 26 N 27 N 28 N 29 N 30 A lie n s pe ci es Bi sc ho fia j av an ic a 1 4 2 1 4 7 20 17 23 4 Caryota urens 5 2 8 6 C as ua ri na e qu is et ifo lia 1 3 1 12 1 4 2 5 1 1 1 1 3 13 1 1 3 D er ri s e lli pt ic a 1 Dypsis lutescens 5 Ficus wrightiana 1 Le uc ae na l uc oc ep ha la 6 4 1 12 22 1 M or us a us tr al is 10 2 3 1 3 20 6 26 9 1 10 6 9 3 5 5 5 3 Pi nu s l uc hu en si s 2 1 2 1 1 1 1 1 Ps id iu m c at tle ia nu m 3 3 1 8 3 4 23 2 1 8 9 4 9 1 6 4 1 2 5 5 3 6 10 3 5 1 Native species Ardisia sieboldi i 1 5 1 3 C al lic ar pa s ub pu be sc en s 2 1 Drypetes integerrima 1 El ae ag nu s r ot un da ta 1 El ae oc ar pu s p ho tin iif ol iu s 1 1 3 1 1 2 1 Fa ga ra b on in si m ae 2 Ficus boninsima e 2 2 Hedyotis grayi 2 2 3 1 1 9 1 6 1 2 H ib is cu s g la be r 4 1 Ile x m er te ns ii 2 1 Ligustrum micranthum 1 5 1 5 1 4 7 4 3 3 7 10 1 7 1 2 4 7 5 Li vi st on a c hi ne ns is 1 1 1 1 3 8 2 1 1 M ac hi lu s k ob u 9 6 25 20 10 13 15 10 13 1 1 4 8 8 9 22 20 13 2 6 3 16 12 7 8 4 9 4 14 N eo lit se a a ur at a 2 8 4 1 8 11 2 Ochraosia nakaiana 1 1 7 2 7 6 13 6 4 3 1 3 2 17 1 12 20 11 5 O sm an th us i ns ul ar is 1 3 1 1 5 2 1 1 1 1 5 2 6 1 1 O st eo m el es b on in en si s Pa da nu s b on in en sis 1 1 6 1 2 1 4 2 5 3 1 8 1 1 5 1 1 4 1 3 2 2 Ph ot in ia w ri gh tia na 1 Pi tto sp or um b on in en se 1 Pouteria obovat a 26 8 4 2 1 4 16 4 3 3 4 3 9 5 2 7 2 1 11 1 1 5 4 2 Rh ap hi ol ep is w ri gh tia na 1 7 27 45 9 7 117 97 20 63 24 43 29 2 33 39 2 40 43 1 32 20 6 8 4 0 51 39 1 4 Schima mertensiana 86 86 62 45 49 47 32 71 86 41 2 1 61 45 70 68 67 17 30 32 49 81 76 23 58 91 57 68 79 54 Sy zy gi um c le ye ra ef ol iu m 4 1 1 1 3 1 4 2 2 1 Ta rr en na s ub se ss ili s 3 2 1 2 6 2 3 1 3 3 1 2 4 3 4 7 7 Te rm in al ia c at ap pa 1 3 6 2 2 Tr em a o ri en ta lis 1 1 W ik st ro em ia p se ud or et us a 2 11 18 21 15 1 3 2 3 2 2 1 17 6 1 14 2 5 5 1 To ta l 103 132 178 154 83 82 225 230 175 127 118 112 151 139 131 135 167 78 91 148 149 94 182 50 117 234 144 184 160 105
Sp ec ie s C 01 C 02 C 03 C 0 4 C 05 C 06 C 07 C 08 C 09 C 10 C 11 C 12 C 13 C 1 4 C 15 C 16 C 17 C 18 C 19 C 20 C 21 C 22 C 23 C 2 4 C 25 C 26 C 27 C 28 C 29 C 30 A lie n s pe ci es Bi sc ho fia j av an ic a 5
Caryota urens C as ua ri na e qu is et ifo lia 6 1 1 Dypsis lutescens 1 Le uc ae na l uc oc ep ha la 10 11 56 12 1 8 11 17 10 M or us a us tr al is 1 1 1 3 3 8 Ps id iu m c at tle ia nu m 1 Native species Ardisia sieboldi i C el tis b on in en si s El ae oc ar pu s p ho tin iif ol iu s Ficus boninsima e 3 H ed yo tis g ra yi
Ligustrum micranthum M ac hi lu s k ob u N eo lit se a a ur at a
Ochraosia nakaiana O sm an th us i ns ul ar is 1 Pa da nu s b on in en sis Pouteria obovata 1 4 1 3 5 4 3 8 5 2 2 1 1 2 4 3 1 Rh ap hi ol ep is w ri gh tia na 1 6 1 1 2 6 1 4 2 9 1 1 5 1 1 3 1 3
Schima mertensiana Sy zy gi um c le ye ra ef ol iu m Ta rr en na s ub se ss ili s 1 1 Tr em a o ri en ta lis 2 3 W ik st ro em ia p se ud or et us a 2 To ta l 11 13 60 28 1 2 2 5 5 10 5 12 9 19 3 5 5 17 10 9 17 2 7 1 3 0 3 7 5 4
Appendix 4 Density (25 m
-2) of saplings (>1.3 m in height) of all woody species in the quadrats (5×5 m) at sites of Casuarina equisetifolia (C01-C30) and those at the sites of native species (N01-N30) .
Appendix 4 Continued. Sp ec ie s N 01 N 02 N 03 N 0 4 N 05 N 06 N 07 N 08 N 09 N 10 N 11 N 12 N 13 N 1 4 N 15 N 16 N 17 N 18 N 19 N 20 N 21 N 22 N 23 N 2 4 N 25 N 26 N 27 N 28 N 29 N 30 A lie n s pe ci es Bi sc ho fia j av an ic a 1 1 1 6 1 2 1 11 Caryota urens 2 1 1 1 1 C as ua ri na e qu is et ifo lia
Dypsis lutescens Le uc ae na l uc oc ep ha la 1 17 12 M or us a us tr al is 1 1 2 1 24 8 2 1 Ps id iu m c at tle ia nu m 2 1 1 1 1 2 2 1 Native species 1 Ardisia sieboldi i C el tis b on in en si s 1 1 El ae oc ar pu s p ho tin iif ol iu s 1 Ficus boninsima e 1 1 1 1 1 4 H ed yo tis g ra yi Ligustrum micranthum 4 1 1 2 1 1 1 M ac hi lu s k ob u 5 5 3 1 1 9 1 1 3 1 9 4 5 4 3 1 1 5 4 1 3 N eo lit se a a ur at a 3 3 1 2 1 1 Ochraosia nakaiana O sm an th us i ns ul ar is 1 1 1 1 1 Pa da nu s b on in en sis 1 Pouteria obovata 1 6 26 5 1 4 9 54 17 22 77 10 30 5 11 9 6 9 4 1 0 12 1 4 1 1 1 6 4 0 22 3 4 3 2 19 19 2 4 6 28 13 9 4 13 11 13 19 3 3 10 1 12 11 2 24 6 7 19 15 51 36 3 Rh ap hi ol ep is w ri gh tia na Schima mertensiana 1 3 14 3 11 20 1 4 4 15 1 2 3 6 8 3 8 10 1 6 16 13 8 11 Sy zy gi um c le ye ra ef ol iu m 1 1 1 1 Ta rr en na s ub se ss ili s 2 1 4 2 1 1 1 1 2 3 1 1 2 5 1 11 Tr em a o ri en ta lis W ik st ro em ia p se ud or et us a 3 1 1 6 1 1 To ta l 15 5 4 7 5 25 32 38 72 50 57 102 19 39 27 50 33 30 32 12 24 22 62 12 39 59 37 71 61 95 69 15
ABSTRACT IN JAPANESE
父島の外来木本種モクマオウが優占する森林の 林床における在来植物の群集構造
畑 憲治1・加藤英寿2・可知直毅1
1首都大学東京理工学研究科生命科学専攻
2首都大学東京牧野標本館
小笠原諸島において、外来木本種であるモクマオウが優占する林分の林床における 在来木本種の定着、リターの堆積、種子散布の現状を定量的な情報に基づいて把握 するために、モクマオウが優占する林分（以下モクマオウ林）と、モクマオウが優 占せず在来種が優占する林分（以下在来林）の間で、林床における在来木本種の種 構成、リターの堆積量、種子散布量について比較した。2007年
9
月に父島の洲崎の 二次林の中のモクマオウ林と在来林において、5×5 mの方形区を30
箇所ずつ設置し、出現した高さ
1.3 m
以下の木本個体（以下稚樹）の数をカウントした。また、各方形 区においてリターの厚さを測定後、0.2×0.2 mの範囲でリターを採取し、器官別に乾 燥重量を測定した。さらに、各方形区にシードトラップを設置し、2007年9
月から2008
年2
月までにトラップ内に落下した種子数をカウントした。モクマオウ林の林 床では、在来林の林床と比較して、在来木本種の稚樹の個体数、出現頻度、種多様 性は極めて小さかった。調査期間中にシードラップに落下した種子のほとんどがヒ メツバキの種子であり、モクマオウ林における種子数は、在来林におけるそれより も少なかった。また、モクマオウ林における堆積しているリターの厚さ、乾燥重量 および単位厚さあたりの乾燥重量は、在来林におけるそれよりも有意に大きかった。以上の結果は、モクマオウ林では在来木本種の定着が欠如しており、その要因とし て在来木本種の種子散布による加入の欠如やリターの堆積による在来木本種の種子 の発芽、実生の成長の阻害などが考えられる、ということを示唆する。
