筑波大農林技研 第 2 号：19－29，2014

Role of Environmental Conditions in the Habitat Segregation of
Two Abundant Vascular Epiphytes in a Warm-Temperate Forest
Akiko HIRATA1＊ Takashi KAMIJO1 and Satoshi SAITO2
1

Faculty of Life and Environmental Sciences, University of Tsukuba,
Tennodai 1-1-1, Tsukuba, Ibaraki, 305-8572, Japan

2

Forestry and Forest Products Research Institute,Matsunosato 1, Tsukuba, Ibaraki, 305-8687, Japan

Abstract
The relationship between vertical stratification of vascular epiphytes on host trees and epiphyte
ecophysiological strategy was examined. We compared the relative growth rate (RGR) of two epiphytic
ferns, Lemmaphyllum microphyllum and Lepisorus thunbergianus, which grow at different canopy positions
in warm-temperate forests. The experiment was conducted under two different light and waterconditions. In L. thunbergianus, the RGR of the leaves and roots were high under high-light conditions,while the mean RGR of the leaves was <0 under low-light conditions. In L. microphyllum, the RGRof the leaves was high under high-light conditions. Differences in the water supply did not havesignificant effects on epiphyte growth. However, L. microphyllum showed faster growth than that by
L. thunbergianus under increased water and light conditions. Different responses of the two epiphyte
species to light and water conditions corresponded approximately to their growing position on hosttrees. The positive influence of high-light conditions and negative influence of low-light conditions
on the growth of L. thunbergianus demonstrate the importance of light conditions for the growth andsurvival of the species, which inhabits a relatively bright zone (upper canopy). On the other hand,high growth rate of L. microphyllum, which is found at regions ranging from the bottom of the stems tothe basal part of the canopy, with increased light and water conditions indicates the importance of thetwo conditions for the growth and survival of the species.
Key words: Epiphytic fern, Growth rate, Light condition, Vertical distribution within canopy, Warm-temperate
forest, Water supply

Introduction
Epiphytic species frequently exhibit
different vertical distribution and partitioningof the available space on host tree species(Johansson 1974; Werneck and EspíritoSanto 2002). Different abilities of epiphyte

to acclimate to drought and varying light
conditions may allow them to coexist atdifferent positions within the same hosttrees. Habitat segregation among epiphyte
species is assumed to have implications on themaintenance of high diversity of these species
in forests; thus, the ecophysiology of epiphytes*Corresponding Author: Akiko HIRATA Faculty of Life and Environmental Sciences, University of Tsukuba
Tennodai 1-1-1, Tsukuba, Ibaraki, 305-8572, Japan
E－mail: a.hirata1845@gmail.com

─ 19 ─

筑波大農林技研 第 2 号 2014

has received much attention.
Many studies on epiphyte ecophysiology
have focused on tropical rainforest species
and have shown that vertical stratificationof epiphytes within the canopy is correlated
to gradients in humidity, available moisture,and light conditions (Hietz and Briones 1998;
Zotz and Hietz 2001). Epiphytic species withhigh desiccation tolerance were found on
highly exposed branches, and species without
evident adaptations to drought were foundin the most humid and shaded conditions(Hietz and Briones 1998); water supply
exerted the strongest influence on epiphyte
growth (Laube and Zotz 2003). A few studies
have also examined the relationship between
vertical stratification of epiphytes and their
physiology in tropical dry forests. Graham andAndrade (2004) found that contrary to their
hypothesis, epiphytic bromeliads occurringin more exposed canopy locations had lesser
drought tolerance than that by other species.
Canopies in dry forests tended to be more open
than those in tropical rainforests (Zimmerman
and Olmsted 1992), and their humidity
gradient and exposure are not high (Graham
and Andrade 2004). Instead, receiving more
rainfall in the exposed locations and rainfall
interception in the lower canopy caused byoverhead tree branches and leaves (Graham
and Andrade 2004) may result in unexpected
outcomes in tropical dry forests. The resultsof previous studies suggest that verticalsegregation mechanisms in epiphytes differ
according to the surrounding environmentand canopy structure. However, the current
understanding of epiphyte ecophysiology
is highly biased regionally (Werneck andEspírito-Santo 2002), taxonomically, ande c o l o g i c a l l y ( Z o t z a n d H i e t z 2 0 0 1 ) . To
understand the manner in which abiotic
factors limit epiphyte growth, survival, andcoexistence, studies that include a much wider
range of regions, taxa, and growing positions
are needed (Zotz and Hietz 2001).
Limited information is available on therelationships between vertical stratificationof epiphytes and their physiological traits intemperate forests. Because the distribution ofvascular epiphytes is tightly associated withmoisture availability, their species diversity
and abundance is lower in temperate forests
than in tropical rain forests (Zotz 2005).
Although most tree species have the ability
to support epiphytic plants at suitably humidsites (Werneck and Espírito-Santo 2002),
with few such sites in temperate forests, only
trees with sufficient water-retention capacity
support epiphytes (Freiberg 1996). Therefore,
vertical segregation of epiphytes on limited
suitable host trees in temperate forests isimportant for the coexistence of epiphyte
species. However, only limited information isavailable on the specific ecophysiological traits
that enable epiphyte segregation in temperate
forests.
To examine the relationship between
vertical stratification and ecophysiologicaltrait of epiphytes in the warm-temperate
forests of Japan, we compared the growth of
two epiphyte species found in different canopy
positions under different light and waterconditions. On the basis of our experimental
results, we discuss the role of verticalenvironmental gradients in the segregation of
the two epiphyte species.
Materials and methods
1. Study site and plant distribution
Field measurements were performed at
the Kyushu Chuo Sanchi Semi-National Park,
southwestern Japan. The study area is in an
old-growth evergreen broad-leaved forest.
Between 1999 and 2009, the mean annual
rainfall was 2472.3 mm, and the mean annual
temperature was 17.2°C at the Saito Weather
Station. In 1989, a permanent 4-ha plot (200 m
× 200 m) was set up on a north to northwestfacing slope on Mt. Omori (1109 m asl; 32°
04’ N, 131°09’ E) at an elevation of 380-520
m (Sato et al. 1999). This plot has been used
for long-term ecological research, and species
name, diameter at breast height (DBH; 1.3m), and location of all trees with DBH greaterthan 5 cm have been recorded for this site─ 20 ─

Role of Environmental Conditions in the Habitat Segregation of Two Abundant Vascular Epiphytes in a Warm-Temperate Forest(Sato et al. 1999). In 2007, we established an
80 × 120 m plot within the permanent 4-haplot. We recorded the species and the growing
positions of all adult epiphytes on 283 trees
with DBH greater than 20 cm. On the basisof the revised zonation scheme described by
Johansson (1974), epiphyte growing position
was classified into five types: basal part of
the trunk (0-2 m); trunk from 2 m to the firstramification; basal part of the canopy (basal
third of the total branch length); middle partof the canopy (middle third of total branch
length); and outer part of the canopy (outer
third of total branch length). The distribution
pattern and composition of vascular epiphytes
in this forest have been described previously(Hirata et al. 2009). Excluding the accidental
epiphyte species, 8 orchids, 13 pteridophytes,
and 2 mistletoes were recorded.
We selected two of the most common
epiphytic ferns, Lemmaphyllum microphyllum andLepisorus thunbergianus, and compared theirdistributions in the canopy. L. microphyllum isa creeping fern, whereas L. thunbergianus is anerect fern. Although long-term climate data arelacking for all growing positions, instantaneous
photosynthetic photon flux density (PPFD)
values (measured using photometric sensors[Quantum Light Sensor 3668I, Spectrum
Technologies, Inc., Plainfield, IL] connected
to data loggers [WatchDog 200; Spectrum
Technologies, Inc., Plainfield, IL]) in our studysite indicate that light supply increased fromthe stem bottom to the canopy branching point.
The mean relative PPFD (RPPFD) during thedaytime was 0.1% at the stem bottom and3.7% at the branching point. The maximum
RPPFD value was 0.9% at the stem bottom
and 16.7% at the branching point. Humidity
was measured using a miniature hygrometer(Hygrochron, KN Laboratories, Inc., Osaka,
Japan) in August 2009 for growing positions 2,
3, and 4 because many epiphyte species occur
at these growing positions (Hirata et al. 2009).
Throughout the observation period, humidity
was higher at the stem bottom than at thebranching point (Fig. 1).

Fig. 1 Humidity at Growing positions 2, 3 and 4 in August 2009. Growing position 2 is the trunk from 2 m up
to the first ramification; Growing position 3 is the basal part of the canopy (basal third of total branch
length); Growing position 4 is the middle part of the canopy (Site 4, middle third of total branch length).
─ 21 ─

筑波大農林技研 第 2 号 2014

2. Plant collection and treatment
We collected approximately 48 individualsof each species from the field site in June
2009. Individual plants were planted inplastic pots with pumice soil and kept in agreenhouse at the University of Tsukuba for
two months under neutral-density shade cloth
which provided approximately 50% ambient
PPFD. Water was supplied every three days.
It is difficult to distinguish an individual L.
microphyllum because of its creeping form.
Therefore, we defined an individual as a plantpart with rhizome meristems and more than 30
leaves. After two months, we measured the leaf
and root lengths of all plants.
3. Growth experiment and data analysis
The growth experiment was conductedfrom August 2009 to February 2010. We used
two different light and water conditions:high light (L+; approximately 75% of direct
sunlight) and low light (L-; approximately
10% of direct sunlight); and high watering(W+; watered once every three days) and
low watering (W-; watered once every fivedays). There were 10 replicates per treatment( n = 4 × 10 individuals per species) for eachspecies. Under the W+ condition, the soil
surface was rarely dry, whereas under the Wcondition, the soil surface was dry for morethan two days. All plants were provided withthe same amount of fertilizer every 15 days. At
the beginning of the experiment, no significant
difference was observed in plant size between
the treatments (P > 0.05, Kruskal-Wallis test).
After approximately six months, we measured
the length and width of leaves and the length ofroots. Leaf area of fresh leaves was determinedusing Lia32 image-analysis software (http://
www.agr.nagoya-u.ac.jp/%7Eshinkan/LIA32).
We also measured the dry weight of leaves androots separately for each species.
The response variable in the growthexperiment was relative growth rate (RGR)(g·g-1·d-1), which is defined as follows:
RGR = (lnDWୣ୬ୢ െ lnDW୧୬୧୲୧ୟ୪ )/οt ,where, DW is plant dry weight and Δt is theduration of the experiment in days (Evans

1972). Unhealthy and particularly small
individuals at the beginning of experimentwere removed from the growth analysis. We
evaluated RGR separately for the leaves androots by using formulas from a preliminary
experiment. The initial DW of the leaves androots was estimated from measured leaf length(Ll), leaf width (Lw), root length (Rl), and root
width (Rw) as follows:
For L. microphyllum,
DW୪ୣୟ୤ = 7.53eିହ × Aୣୱ୲ + 2.60eିଶ (R2 = 0.87,
P < 0.001),
DW୰୭୭୲ = 3.98eିସ × R ୪ + 4.63eିଷ (R 2 = 0.84,
P < 0.001),
Aୣୱ୲ = L୪ /2 × L୵ /2 × Ɏ .
The leaf shape of L. microphyllum differs
between sterile and fertile leaves, and theratio of leaf width to length for fertile leaves issmaller than that of sterile leaves. Therefore,
we used the leaf length and width to estimate
the DWleaf in L. microphyllum.
For L. thunbergianus,
DW୪ୣୟ୤ = 7.71eିସ × L୪ െ 6.82eିଶ (R 2 = 0.90,
P < 0.001),
DW୰୭୭୲ = 1.70eିଷ × R ୪ × R ୵ + 2.39eିଶ (R 2 =0.70, P < 0.001),
Because the thickness of L. thunbergianus roots
varied between individuals regardless of theroot length, DWroot correlated more strongly
with the formula that used both the root length
and width than that using only the root length(R2 = 0.53, P < 0.001). Therefore, we used theroot length and width to estimate DWroot in L.
thunbergianus.
A two-way ANOVA was performed to test
the effects of light and water conditions on
the growth of each species. We also tested theeffects of light and water conditions on changes
in the leaf mass per area (LMA g·g-1·d-1) for
each species by using a three-way ANOVA. All
statistical analyses were performed using R
2.15.2 (R Core Team 2012).
Results
L. microphyllum and L. thunbergianus were
distributed across different growing positionsin the canopy. L. microphyllum was generally─ 22 ─

Role of Environmental Conditions in the Habitat Segregation of Two Abundant Vascular Epiphytes in a Warm-Temperate Forest

found on the lower parts of host trees, whereas
L. thunbergianus was found on the higher andexposed parts of host trees (Fig. 2).
The growth rates of both the species wereconsistently low. The highest RGR values were,respectively, 0.009 and 0.007 g·g -1·d -1 for L.
microphyllum leaf and root and 0.018 and 0.007
g·g-1·d-1 for L. thunbergianus leaf and root.
The RGR of the leaves of both the speciesgrown under high-light conditions was higher
than of those grown under low-light conditions(Fig. 3, Table 1). The RGR of L. thunbergianus
roots grown under high-light conditions washigher than that under low-light and highwater conditions. Differences in the watersupply did not have significant effects on
epiphyte growth; however, L. microphyllum had
higher leaf growth when grown under highwater and high-light conditions (Fig. 3). In L.
thunbergianus, the mean RGR of leaves was <0when grown under low-light conditions (Fig. 3).
Changes in the biomass allocation patterns
differed between the two species (Fig. 4). In L.
microphyllum, the leaf/root ratio was higher inplants grown under the high-light and highwater conditions than that under the low-lightand low-water conditions. In L. thunbergianus,
the leaf/root ratio was higher in plants grownunder the high-light and high-water conditions

Lemmaphyllum microphyllum

Table 1

FactorDF

F

P

Lemmaphyllum microphyllum (leaves)
L

1

14.97

< 0.001

W

1

0.52

0.48

L:W

1

3.30

0.08

Residuals

26

Lemmaphyllum microphyllum (roots)
L

1

2.27

0.14

W

1

0.61

0.44

L:W

1

1.01

0.32

Residuals

26

Lepisorus thunbergianus (leaves)
L

1

37.24

< 0.001

W

1

0.67

0.42

L:W

1

0.15

0.70

Residuals

34

Lepisorus thunbergianus (roots)
L

1

5.16

0.03

W

1

0.10

0.76

L:W

1

0.21

0.65

Residuals

34

Lepisorus thunbergianus
0.6Frequency (%)

0.6

Frequency (%)

Results of a two-way ANOVA of the effects
of light(L) and water(W) on relative
growth rate (RGR) after the growthexperiment.

0.4
0.2
0.0
1

2

3

4

0.4
0.2
0.0
1

5

Growing site

2

3

4

5

Growing site

Fig. 2 Distribution of two epiphytic ferns in host trees in a Japanese warm-temperate forest. Frequency
indicates occurrence frequency of each epiphyte species on each growing position of 283 host trees
in the study plot. Growing positions are: the basal part of the trunk (Growing position 1, 0-2 m); thetrunk from 2 m up to the first ramification (Growing position 2); the basal part of the canopy (Growing
position 3, basal third of total branch length); the middle part of the canopy (Growing position 4, middle
third of total branch length); and the outer part of the canopy (Growing position 5, outer third of total
branch length).
─ 23 ─

b/HDI
Lemmaphyllum microphyllum
b

a

ab

a

W-L-

W-L+

W+L-

W+L+

W-L-

Treatment
W-L+
W+L-

W+L+

a
a

0.004 0.004

ab

0.000 0.000/HDI

5RRWLemmaphyllum microphyllum
-1 -1
d(g•g
) -1d-1)
RGR (g•g
RGR

í0.004í0.004
0.000 0.000
0.004 0.004-1 -1
RGR (g•g
RGRd(g•g) -1d-1)

筑波大農林技研 第 2 号 2014
Lemmaphyllum microphyllum
Lemmaphyllum microphyllum

5RRW

W-L-

W-L+

W+L-

W+L+

W-L-

Treatment
W-L+
W+L-

W+L+

Treatment

Treatment
Lepisorus thunbergianus

/HDI

b

b

a

a

í0.001í0.001
0.001 0.001
0.003 0.003
0.005 0.005b/HDI Lepisorus
thunbergianusb-1 -1
RGR (g•g
RGRd(g•g) -1d-1)

í0.005í0.005
0.000 0.000
0.005 0.005
0.010 0.010-1 -1
RGR (g•g
RGRd(g•g) -1d-1)

Lepisorus thunbergianus

a

a

W-L-

W-L+

W+L-

W+L+

W-L-

Treatment
W-L+
W+L-

W+L+

a
5RRW Lepisorus
thunbergianusaab5RRW

a

a
b

ab

b

W-L-

W-L+

W+L-

W+L+

W-L-

Treatment
W-L+
W+L-

W+L+

b
ab

ab

a
1.34
1.05

0.96
1.02

W-L-

W-L+

W+L-

W+L+

Treatment

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Lemmaphyllum microphyllum

Leaf/root ratio

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Leaf/root ratio

Fig. 3 Response of relative growth rate (RGR) to varying levels of water (W) and light (L) supply. Data are
Treatment
Treatment
means ± SD. The twolevels of resource supply are indicated as low (-)
and high (+). Different letters
indicate significant differences among treatments (Tukey post-hoc test, P < 0.05).
Lepisorus thunbergianus
b

a

ab

a

1.39
0.67

1.29

0.64

W-L-

W-L+

W+L-

W+L+

Treatment

Fig. 4 Leaf/root ratio under varying levels of water (W) and light (L) supply. The two levels of resource supply
are indicated as low (-) and high (+). Different letters indicate significant differences among treatments(Steel-Dwass multiple comparison test, P < 0.05). The numbers below the boxplots indicate the medianvalue.

than that under the low-light and low-water or
high-light and low-water conditions. Under the
low-light conditions, median leaf/root ratio of L.

thunbergianus was <1.
The effect of different light conditions on
LMA was statistically significant in both the─ 24 ─

140

160

Role of Environmental Conditions in the Habitat Segregation of Two Abundant Vascular Epiphytes in a Warm-Temperate Forest

120
100

䃂

䃂

60

80

LMA (g/m2)

䃂
䃂

WíLí

WíL+

W+Lí

W+L+

Fig. 5 Response of leaf mass area (LMA) to varying levels of water (W) ant light (L) supply. Gray dashed lines
and filled circles indicate results for Lepisorus thunbergianus and black lines and open circles indicate
results for Lemmaphyllum microphyllum. Data are means ± SD. The two levels of resource supply are
indicated as low (-) and high (+).

species (Fig. 5, Table 2). High-light conditions
increased LMA in both the species. The mean
LMAs in L. thunbergianus were larger thanthose in L. microphyllum for all the treatments,
although the difference in LMA between thetwo species was statistically significant under
the low-light and high-water conditions andhigh-light and high-water conditions (t-test, P <0.05).
Table 2

Results of a three-way ANOVA of theeffects of light (L), water (W) and epiphyte
species on LMA after the growing
experiment.
DF

L

1

W
SP
L:W
L:SP
W:SP
L:W:SP
Residuals

1
1
1
1
1
1
98

F

P

51.74
0.09
13.43
0.43
0.09
0.80
0.19

< 0.001
0.76< 0.001
0.51
0.76
0.37
0.66

Discussion
The different responses of the two
epiphyte species to light and water conditions
corresponded approximately to their growing
position on the host trees. Increased light
supply stimulated growth in both the species.
However, this trend was more remarkable inL. thunbergianus, which was found in relatively
bright and dry locations in the upper canopy(Fig. 3, Table 1). The positive influence of highlight conditions and the negative influenceof low-light conditions on the growth of L.
thunbergianus demonstrate the importance oflight conditions in the growth and survival of
the species. On the other hand, variations in
the water supply did not affect growth of L.
thunbergianus (Fig. 3, Table 1). Increasing windspeed, radiation, temperature oscillation, andvapor-pressure deficit increase evaporationand transpiration from the stem base to theouter twigs (Parker 1995). Because of thesefactors, drought stress in epiphytes is more
severe in the upper canopy. L. thunbergianus,
a species typically found in the upper canopy,
may have higher drought tolerance. L.

─ 25 ─

筑波大農林技研 第 2 号 2014

thunbergianus had higher RGR under highlight condition regardless of water conditions.
Conversely, L. microphyllum had higher RGR
under high-light and high-water conditions.
Such growth responses to drought may
contribute to maintaining the high abundanceof L. thunbergianus in the upper canopy.
The growth rate of L. microphyllum was highunder high-light and high-water conditions(Fig. 3, Table1). The ability to utilize boththe high light and water conditions may be
important for the growth and survival of
L. microphyllum. L. microphyllum is generally
found at the bottom of the stems to thebasal part of the canopy on host trees. In the
canopy of host trees in our study site, lightand humidity showed opposite trends along
the vertical axis. Thus, it is reasonable thatat the intermediate position on host trees(upper part of the stems and basal part ofthe canopy), where L. microphyllum may be
exposed to moderate light and humidity, is theprimary location of L. microphyllum. However,
L. microphyllum was also found at the bottomof the tree stems, which are relatively shaded
environments. L. microphyllum may be highly
shade tolerant, although we did not directly
measure its photosynthetic abilities. We foundthat L. microphyllum had thinner leaves thanthat of L. thunbergianus, when grown underhigh water conditions. Generally, succulence(LMA) increases with light exposure (Hietz andBriones 1998), and plants that are adapted toshade tended to have thinner leaves to avoid
maintaining leaf tissue at light conditions
below the compensation point (Larcher 1995).
Thus, the thinner leaves of L. microphyllum
when grown under high water conditions
suggest that L. microphyllum was highly shadetolerant under high water condition. At thestem bottom, addition to the higher humidity
than upper canopy (Fig. 1), large volumes of
stemflow may be generated during rainfall
because of the funneling effect of the tree
crown (Herwitz 1987). For instance, Masukata
et al. (1990) reported that the stemflow of an
evergreen broadleaved tree species Lithocarpus
edulis was 64% of the rainwater that fell onto

its crown. This abundant water supply atthe bottom of the tree stems may allow L.
microphyllum to grown in relatively shaded
environments.
Changes in the leaf/root ratio of both
species to light and water conditions also
differed. L. thunbergianus allocated relatively
more biomass to the leaves than to the roots
under high-light conditions, whereas relatively
more biomass was allocated to the roots under
low-light conditions. Negative leaf growth of
L. thunbergianus under low-light conditions
may be because of the investment of biomass
to the roots, although root growth under lowlight and high-water conditions was also
lower than that under high-light and highwater conditions (Fig. 3). Morphologicaladjustments to shade suggest an increase inbiomass allocation to aboveground organs
and a decrease in biomass allocation to theroots (Poorter and Nagel 2000). However, theopposite response occurred in L. thunbergianus
allocation. In L. microphyllum, allocation toleaf biomass was high in plants grown underhigh-light and high-water conditions. Biomass
allocation was nearly constant in plants
grown under other conditions although thevariation was large in some treatments. This
may suggest that allocation plasticity differs
between the two species. L. thunbergianus, which
is an erect epiphyte, cannot occupy a large
area of the host tree by rooting unlike that by
L. microphyllum, which is a creeping epiphyte.
Plasticity in allocation may confer somecompetitive advantages because the plant can
immediately change its allocation strategy
according to changes in the environment (Rünk
and Zobel 2007).
Graham and Andrade (2004) reported thatin a tropical dry forest, drought tolerance
had a stronger influence on epiphyte verticalstratification than that by photoprotective
ability. They proposed that it was caused byhigh rainfall and dew at higher locations in
the canopy. In this study, the low sensitivityof the two epiphyte species to water supply
was an unexpected result, because the verticalhumidity gradient and rainwater are high in─ 26 ─

Role of Environmental Conditions in the Habitat Segregation of Two Abundant Vascular Epiphytes in a Warm-Temperate Forest

closed temperate forests. Our results may havebeen caused by small differences between the
two levels of water supply. In this study, we
employed low watering level once every fivedays, considering the change in substrate fromtree bark to pumice soil. Under this treatment,
the soil surface remained dry for about threedays during each watering period. However,water supply may be more limited under in situ
conditions. Thus, it was difficult to compare
the relative importance of water or light
conditions on epiphyte growth and verticalstratification in this study. On the other
hand, L. microphyllum showed more sensitive
response to water conditions than that by L.
thunbergianus. Therefore, we assume that waterconditions also affect the difference in vertical
distribution of the two species.
In this study, we used adult individuals
in the growth experiment. However, verticalsegregation will be determined at earlier
stages, such as at germination and during
the growth of young individuals. Previous
studies have shown size-dependent responses
to environmental conditions (Laube andZotz 2003; Zotz 2009). Differences in theenvironmental conditions may strongly affectthe establishment and survival of the epiphyte
species at early growth stages. Future studies
are necessary to examine the effects of lightand water conditions on smaller individuals.
Acknowledgements
We thank Y. Endo, M. Sato, Y. Hayashi, H.
Iijima, M. Miyamoto, N. Tani, and K. Suzuki
for their support and helpful suggestions
for our study. We also thank the Miyazaki
District Forestry Office for allowing the useof their facilities for our study. We also thanktwo anonymous reviewers for their valuablecomments. We used some data of Forest
Dynamics Data Base (FDDB) established by
FFPRI (Forestry and Forest Products ResearchInstitute) and JST (Japan Science andTechnology Agency).

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Role of Environmental Conditions in the Habitat Segregation of Two Abundant Vascular Epiphytes in a Warm-Temperate Forest

2 種の維管束着生植物のすみわけに対する環境要因の役割

平田晶子1＊・上條隆志1・齊藤
1

305－8572

哲2

筑波大学生命環境系
茨城県つくば市天王台1－1－1
2305－8687

森林総合研究所
茨城県つくば市松の里1

要旨

ホスト樹木内での着生部位が異なる 2 種の着生植物、マメヅタとノキシノブを対象に、 2 段階の光と水条件のもとで生育実験を行い、着生部位の違いと生理生態学的特性との関係を検討した。ノキシノブの葉と根茎の相対成長速度（RGR）は明るい光条件下で高くなり、低い光条件下では葉のRGR平均値は負の値をとった。マメヅタはより明るい光条件下で葉のRGRが高くなった。水条件の違いは 2 種の成長に有意な影響を与えていなかったが、マメヅタについては、光、水条件ともに良好な条件下でRGRが高くなる傾向があった。 2 種の着生植物の光と水条件に対する反応は、ホスト樹木内の着生部位の環境条件と概ね一致していた。比較的明るい環境である樹冠上部に生育するノキシノブの成長、生存には、光条件が重要な役割を果たしており、より湿度の高い樹幹部から樹冠中央部に分布が集中するマメヅタの成長には、光条件とともに水条件も重要である事が示唆された。
キーワード：樹木内の垂直分布、成長速度、暖温帯林、着生シダ、光条件、水供給＊連絡者：平田晶子 筑波大学生命環境系
305－8572 茨城県つくば市天王台1－1－1
E－mail：a.hirata1845@gmail.com

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