全 文 ：Received 12 Dec. 2003 Accepted 13 Jan. 2004
Supported by the Knowledge Innovation Program of The Chinese Academy of Sciences (KSCX2-SW-105, KSCX2-SW-103, KSCX1-07-
03) and the State Key Basic Research and Development Plan of China (G2000046802).
* Author for correspondence. E-mail: .
http://www.chineseplantscience.com
Acta Botanica Sinica
植 物 学 报 2004, 46 (7): 773-779
Seed Deposition Patterns of Oil Tea Camellia oleifera Influenced
by Seed-caching Rodents
WANG Yu-Shan, XIAO Zhi-Shu, ZHANG Zhi-Bin*
(State Key Laboratory of Integrated Management of Pest Insects and Rodents in Agriculture, Institute of Zoology,
The Chinese Academy of Sciences, Beijing 100080, China)
Abstract: The quality of seed deposition often involves habitat and microenvironment selection by
seed-dispersing agents (e.g. birds and small rodents) and deposition patterns (e.g. burial of seeds). However,
little is known where seeds and nuts are deposited by these animals after their shedding from parent trees.
In this study, seed deposition patterns of oil tea (Camellia oleifera Abel., Theaceae) influenced by seed-
caching rodents were studied by tracking individual oil tea seeds (labeled with small coded tin-tags) at two
stands (secondary stand and primary stand) in an experimental forest of Dujiangyan City, Sichuan Province,
China. We found that over 80% of the tagged seeds were well buried 0 – 60 mm deep in the soil and a small
part of them were deposited on the soil surface with some leaf litter covering at both stands. Small rodents
significantly preferred to select some specific microenvironments (e.g. shrub edge and under shrubs) to
cache and eat seeds at each stand. In these microenvironments, they may experience less predation risk
during the foraging process. We also found that the microenvironment distributions of caches changed
slightly with cache order: a higher proportion of the cached seeds was deposited under shrubs or at shrub
edge at higher order cache sites (i.e. secondary and tertiary caches) than at primary cache sites at both
stands. Our results indicate that burial of oil tea seeds by small rodents might be a greater benefit for seed
survival, seed germination and seedling establishment. Small rodents dispersed seeds from seed sources or
parent trees to different microenvironments, which may be beneficial to seed germination and seedling
establishment due to more seeds deposited in a favorable environment.
Key words: seed burial; microenvironment selection; scatter-hoarding; seed dispersal; seedling
recruitment; small rodents
In general, suitable “safe sites” for seed germination
and seedling establishment may greatly depend upon the
quality of microenvironments (e.g. soil, water, light gap,
leaf litter and vegetation) where a seed may be deposited
by seed-caching rodents and birds or other factors (Harper,
1977; Schupp, 1993). The quality of seed deposition often
involves habitat and microenvironment selection by seed-
dispersing agents (e.g. birds and small rodents) and depo-
sition patterns (e.g. burial of seeds) (Schupp, 1993). It has
been well known that seed-caching rodents and birds
harvest, transport and scatter-hoard many seeds and nuts
away from parent trees, which largely influences post-dis-
persal seed fates, subsequent seed shadows and seedling
recruitment (Howe and Smallwood, 1982; Smith and
Reichmen, 1984; Price and Jenkins, 1986; Forget, 1990; 1992;
Vander Wall, 1990; Jansen and Forget, 2001; Zhang and
Wang, 2001b). Therefore, potential suitable sites for seed-
ling recruitment may be greatly affected by habitat and
microenvironment selection by seed-caching animals
(Jordano and Schupp, 2000). However, little is known where
seeds and nuts are deposited by these animals after they
are shed from the parent trees (Vander Wall, 1993b; 1997;
Hoshizaki et al., 1999; Wenny, 1999).
Seed cache sites can be changed due to the reaching of
seeds and nuts by small rodents and birds (DeGange et al.,
1989; Vander Wall, 1995; Iida, 1996; Vander Wall and Joyner,
1998). But little is concerned whether the repeated changes
of cache sites for a given seed may ultimately affect seed
germination and seedling establishment (Vander Wall and
Joyner, 1998). The objective of this study was to examine
seed deposition patterns influenced by seed-caching ro-
dents by tracking individual seeds (with coded tin-tags) of
oil tea (Camellia oleifera, Theaceae) at two stands
(secondary stand and primary stand). We also discussed
the relative importance of seed caching and microenviron-
ment selection by small rodents.
Acta Botanica Sinica 植物学报 Vol.46 No.7 2004774
1 Materials and Methods
This study was performed in an experimental forest
(altitude, 700-1 000 m) of Dujiangyan City (31º 4 N, 103º 43
E), Sichuan Province, China. The basic vegetation belt of
the study site belongs to subtropical broad-leaved ever-
green forest (altitude 700-1 500 m) (Chen, 2000).
Because of variation in stand age and vegetation
structure, we conducted our experiments in two stands:
primary stand (80-90 yrs, 2 hm2) and secondary stand (<
50 yrs, 2.5 hm2). In the primary stand (slope, 35-70º; aspect,
northwest), dominant canopy trees are Castanopsis fargesii
(Fagaceae), Quercus variabilis (Fagaceae), Pinus
massoniana (Pinaceae), and Acer catalpifolium
(Aceraceae), with a small population of other tree species
Quercus serrata (Fagaceae), Lithocarpus harlandii
(Fagaceae) , Phoebe zhenman (Lauraceae) and
Cyclobalanopsis glauca (Fagaceae). Dominant shrubs are
C. oleifera (Theaceae), Symplocos stellaris (Symplocaceae)
and S. laurina (Symplocaceae), and Pittosporum
daphniphylloides (Pittosporaceae). The ground flora is
poorly developed, consisting of small patches of
Dicranopteris pedata. In secondary stand (slope, 30-60º;
aspect, southeast), Q. variabilis, Q. serrata, and C. fargesii
are dominant canopy trees. The understory layer is mainly
composed of S. stellaris, S. laurina, Ilex purpurea, and Myrsine
africana. The ground flora is dominated by D. pedata.
In the study site, oil tea (Camellia oleifera Abel.) popu-
lation exists mainly in primary stand, but rare in secondary
stand. The flowering period of oil tea is from late September
to November, and the fruit-ripening period is in late Sep-
tember of the following year. After ripening, oil tea fruits
can naturally dehisce and the seeds inside fall on the ground
under or near the parent trees. Sometimes oil tea fruits as a
whole fall on the ground. The previous experiments have
shown that small rodents (e.g. Edward’s long-tailed rats)
prefer to consume and cache oil tea seeds (Xiao et al.,
2003; Xiao and Zhang, 2004).
At least 10 small nocturnal rodent species coexist in the
study site: Edward’s long-tailed rats (Leopoldamys
edwardsi), Bower’s rats (Berylmys bowersi), Norway rats
(Rattus norvegicus), Himalayan rats (R. nitidus), chestnut
rats (Niviventer fulvescens), Chinese white-bellied rats (N.
confucianus), Sichuan field mice (Apodemus latronum),
Chevrier’s field mice (A. chevrieri), Chinese field mice (A.
draco), and harvest mice (Micromys minutus), among which
Edward’s long-tailed rats, Bower’s rats, chestnut rats and
Chinese white-bellied rats were dominant species (Xiao et
al., 2002). All these rodent species consume seeds of Q.
variabilis, Q. serrata, C. fargesii, and C. oleifera in the
Dujiangyan forest (Xiao and Zhang, 2004). In the Dujiangyan
forest, there are other potential seed predators (e.g. Masked
palm civet (Paradoxurus larvata)) (Xiao et al., 2004) and
seed dispersers (e.g. Eurasian jays G. glandarius). Eur-
asian jays may be less important for short-distance seed
dispersal than rodents because of the small population
numbers of these bird species, but they are very important
for long-distance seed dispersal or predation.
A plot (200-250 m×50-60 m) was selected for seed
release at each stand. Twenty successive sites (at second-
ary stand) and 18 sites (at primary stand) were distributed
along each plot as experimental seed stations, and spaced
10 m apart. We prepared 800 oil tea seeds in 2000 and 720
ones in 2001 to label with a small, light tin-tag (4 cm×1 cm,
< 0. 1 g), each tag numbered using a sharpened metal-pen
to make each seed identifiable (Zhang and Wang, 2001b).
On November 23, 2000 (the end of seedrain of oil tea and
other nut-bearing trees) and October 14, 2001 (the peak of
seedrain of oil tea, but before the peak of other nut-bearing
trees), we placed 40 tagged seeds at each seed station.
After seed removal from seed stations by small rodents, we
randomly searched the area around each seed station
(radius, ≥ 20 m) with equal efforts for the tagged seeds
and their fragments dispersed from each seed station by
rodents. The checking frequencies were Day 1, 2, 3, 4, 6, 8,
12, 16 and 156 at secondary stand, and Day 1, 2, 3, 4, 6, 8, 10,
14, 18, 22, 32, 42, 62 and 186 at primary stand. We used
bamboo sticks (10 cm from the cache sites) coded with the
number of the relocated seeds to mark cache locations. If a
marked cache was removed, the area around the cache
(radius, ≤10 m) was randomly searched. On April 29, 2001
(at secondary stand) and on April 20, 2002 (at primary stand),
we surveyed all previously found cache sites and newly
found cache sites to determine which site had surviving
seeds.
The relevant information of the relocated nuts was re-
corded by referring to Li and Zhang (2003), such as seed
fates (burial in the soil (burial), deposited on the soil sur-
face with some leaf litter covering (surface), eaten leaving
only tin-tags and seed fragments (eaten) and missing with
their true fates unknown (missing)), seed number per cache
(i.e. cache size), the distances of the tagged nuts or their
fragments to their original seed stations, and microenvi-
ronment characters of seed deposition.
The microenvironments around the tagged seeds or their
fragments were recorded within circle with the diameter 0.5
m. We sorted the microenvironments into five categories
(Li and Zhang, 2003): in the grass, on naked ground (fewer
WANG Yu-Shan et al.: Seed Deposition of Oil Tea Camellia oleifera Influenced by Seed-caching Rodents 775
grasses or shrub growing), at shrub edge, under shrubs,
and in rock caves (or near the rocks). We also measured the
height and cover of grass and shrub if a seed was depos-
ited in the grass, at shrub edge or under shrubs. In order to
see whether or not the microenvironment, where small ro-
dents deposited a seed, was randomly distributed, we esti-
mated the natural proportion of the former four types of
microenvironments (but rock caves) by dropping a dart (Li
and Zhang, 2003). The dart was randomly dropped in all
directions along the plot at each stand, and the falling sites
were located and their microenvironments were recorded.
In each stand, 500 drops were performed, and the frequency
was used to estimate natural distribution of four microenvi-
ronment types. The results showed that, among 500 ran-
dom drops at each stand, the frequency distribution of four
types of microenvironments was 30.8% in the grass, 29.4%
on naked ground, 19.0% at shrub edge, and 20.8% under
shrubs at secondary stand, and 6.2% in the grass, 31.2%
on naked ground, 25.8% at shrub edge, and 36.8% under
shrubs at primary stand.
2 Results
2.1 Burial of seeds by small rodents
After seed release, small rodents harvested most
(91.6% at secondary stand and 95.1% at primary stand) of
the tagged seeds from seed stations. And then, 0.5% of the
cached seeds at secondary stand and 4.2% at primary stand,
were moved from primary caches to higher order caches
(i.e. secondary caches and tertiary caches). We relocated
37.4% (274/733) of the tagged seeds at secondary stand
and 61.2% (419/685) at primary stand. At both stands, over
80% of the cached seeds located in different order caches
(i.e. primary, secondary and tertiary caches) were well bur-
ied 0 – 60 mm in the soil and a small part of them were
deposited on the soil surface with some leaf litter covering
(Table 1). The proportion of the tagged seeds (including
primary, secondary and tertiary caches) buried in the soil
versus sowed on the soil surface differed very significantly
at either stand (Chi-square test, df = 1, P < 0.001). In the
following spring (April), no cached seeds (including pri-
mary and secondary caches) survived to germinate at sec-
ondary stand, but 24 well-buried seeds (primary caches, n
= 23; secondary cache, n = 1) still survived to germinate or
remain viable at primary stand.
2.2 Microenvironment selection by small rodents
Compared with the natural distributions of microenvi-
ronments (not including rock cave) by dropping a dart,
small rodents significantly preferred to cache or eat seeds
at shrub edge or under shrub at both stands (Chi-square
test, primary stand, c2 = 199.663, df = 3, P < 0.001, second-
ary stand, c2 = 141.691, df = 3, P < 0.001; pooled the data of
all dispersal stages). Over 80% of the cached seeds, includ-
ing primary, secondary and tertiary caches, were deposited
under shrubs or at shrub edge at both stands, and over
90% seeds were eaten under shrubs or in rock caves (Figs.
1, 2). Table 2 shows the cover and height of grass and
shrubs surrounding the tagged seeds and their fragments
at each stand. At primary stand, The proportion of the
cached seeds in different microenvironments (except rock
caves) was 11.0% in the grass, 10.7% on naked ground,
25.8% at shrub edge, and 52.5% under shrubs, while the
proportion of the cached seeds surviving in the following
spring was 20.8% in the grass, 4.2% on naked ground,
16.7% at shrub edge, and 58.3% under shrubs. There was
no significant difference of seed cache proportion and seed
Table 1 Number and proportion of the tagged seeds sowed by
small rodents: burial in the soil (burial) and deposited on the soil
surface (surface) in different order caches (i.e. primary, second-
ary and tertiary caches) at both stands
Burial (n/%) Surface (n/%)
Secondary stand
Primary cache 122/92.4 10/7.6
Secondary cache 4/100 0/0
Primary stand
Primary cache 259/81.7 58/18.3
Secondary cache 22/68.8 10/31.2
Tertiary cache 2/100 0
Fig.1. Frequency distributions of the tagged seeds or their
fragments (i.e. Burial, Surface and Eaten) scattered in different
microenvironments (i.e. in the grass, on naked ground, at shrub
edge, under shrubs and in rock caves) by small rodents in different
dispersal stages: Dispersal Ⅰ, Dispersal Ⅱ +Ⅲ after seed re-
lease at seed stations at secondary stand.
Acta Botanica Sinica 植物学报 Vol.46 No.7 2004776
survival proportion between under shrubs and at shrub
edge (Chi-square test, c2 = 0.092, df = 1, P = 0.762).
The microenvironment distribution of cache sites
changed slightly with dispersal stages (from DispersalⅠ
to DispersalⅡ +Ⅲ) at each stand during the experiment
(Figs.1, 2). In DispersalⅠ, the tagged seeds and their frag-
ments were deposited in all types of microenvironments,
but mainly under shrubs and near shrub edge, while they
were deposited more (nearly 100%) under shrubs and rock
caves in Dispersal Ⅱ and Ⅲ, especially at primary stand
(Figs.1, 2).
3 Discussion
Our results indicated that, small rodents tend to bury
more seeds (over 80%) in surface soil (ca. 0 – 60 mm deep)
at both stands, though they deposit a tiny part of seeds on
the soil surface with some leaf litter covering. Burial of seeds
and nuts by hoarding animals may be beneficial for seed
survival, seed germination and seedling establishment
(Vander Wall, 1990; 1993). First, burial reduces the preda-
tion risk of seeds and nuts after they fall on the ground
under or near parent trees. Predation rates of seeds and
nuts on the soil surface are near 100% but decrease as
depth of seeds in soil increases (Cahalane, 1942; Kikuzawa,
1988; Borchert et al., 1989). Second, seed burial in surface
soil or under leaf litter can help maintain seed viability in a
favorable condition (e.g. temperature and moist) (Griffin,
1971; Borchert et al., 1989). For example, the availability of
water for buried seed is more stable, preventing from rot-
ting during moist periods and desiccation during periods
of drought (Forget, 1990; Kollmann and Schill, 1996). Third,
buried seeds and nuts often have a higher probability to
germinate and emerge (Shaw, 1968; Griffin, 1971; Vander
Wall, 1990; 1993; Forget, 1990; 1997; Zhang, 2001; Zhang
and Wang, 2001a). Borchert et al. (1989) also demonstrated
that the recruitment rates for buried acorns of blue oak
(Quercus douglasii) were twice those for surface-sown
acorns due to improved germination and reduced predation.
We found that small rodents significantly preferred some
specific microenvironments (e.g. at shrub edge and under
shrubs) to scatter-hoard and eat oil tea seeds at both stand.
The possible reason is that small rodents may experience
less predation risk at shrub edge, under shrubs or in rock
caves during the foraging process (Kotler et al., 1991;
Table 2 The surrounding microenvironmental characteristics (mean ± SD) of the tagged seeds and their fragments (including the seeds
in all dispersal stages, i.e. Dispersal Ⅰ, Ⅱ and Ⅲ) at both stands
Burial Surface Eaten
Secondary stand
Grass cover (%) 16.25 ± 14.58 21.54 ± 14.59 18.33 ± 12.91
Grass height (cm) 32.50 ± 13.89 31.48 ± 8.79 41.67 ± 4.08
Seed number 6 0 6
Shrub cover (%) 43.58 ± 22.63 38.89 ± 20.12 60.55 ± 23.52
Shrub height (cm) 127.79 ± 43.32 120.00 ± 47.96 140.70 ± 94.13
Seed number 101 9 131
Primary stand
Grass cover (%) 15.70 ± 16.19 34.46 ± 22.40 61.67 ± 35.47
Grass height (cm) 32.39 ± 11.06 40.77 ± 11.88 36.67 ± 5.77
Seed number 26 13 8
Shrub cover (%) 45.07 ± 20.20 39.84 ± 21.57 57.05 ± 21.76
Shrub height (cm) 181.71 ± 89.84 169.69 ± 81.73 157.61 ± 53.39
Seed number 235 40 135
Fig.2. Frequency distributions of the tagged seeds or their
fragments (i.e. Burial, Surface and Eaten) scattered in different
microenvironments (i.e. in the grass, on naked ground, at shrub
edge, under shrubs and in rock caves) by small rodents in different
dispersal stages: Dispersal Ⅰ, Dispersal Ⅱ +Ⅲ after seed re-
lease at seed stations at primary stand.
WANG Yu-Shan et al.: Seed Deposition of Oil Tea Camellia oleifera Influenced by Seed-caching Rodents 777
Morris and Davidson, 2000; Li and Zhang, 2003). Still, mi-
croenvironment selection by small rodents may largely af-
fect spatial distributions of seeds and seedlings, seed ger-
mination and seedling establishment (Schupp, 1993; Russell
and Schupp, 1998; Hoshizaki et al., 1999). Vander Wall and
Joyner (1998) also indicated that the seeds of Jeffrey pine
(Pinus jeffreyi) deposited in shrubby habitats by chipmunks
are more favorable to establish a seedling. In this study,
most of cached seeds were deposited under shrubs or at
shrub edge, where oil tea seeds are more likely to germinate
and emerge (because oil tea seeds can germinate and its
early seedlings grow well under shrubs or the closed
canopy, personal observation). At primary stand, we found
that some seeds from different order caches or different
seed stations were eaten in several rock caves (at least 1 m
deep, where we attempted to search for some evidence about
the missing seeds by using a long wooden stick) and dense
shrubs (cover > 80%) during the survey period. Therefore,
many seeds may have no chances to germinate and emerge
if transported into underground burrows, dense shrubs
(cover > 80%) and rock caves for larder-hoarding.
Our results also indicated that the initial microsite of the
cached seeds may not be the final microsite for seedling
establishment. In this study, a higher proportion of the
cached seeds was deposited under shrubs or near shrub
edge in higher order cache sites (e.g. secondary and ter-
tiary caches) than in primary cache sites at either stand
(Figs.1,2). Vander Wall and Joyner (1998) also observed the
same trend that the microenvironment distributions of
caches gradually changed with cache order: 48.2% of pri-
mary caches were under or at the edge of a shrub canopy,
whereas 64.6% of secondary through quaternary caches
were under or at the edge of a shrub canopy. If more cached
seeds, however, were transported into underground
burrows, dense shrubs (cover > 80%) and rock caves, the
recaching of seeds by small rodents would have a negative
effect on seedling recruitment.
In conclusion, seed deposition patterns influenced by
seed-caching rodents are very complicated. In the study
site, small rodents may have become an important selective
force to affect post-dispersal seed fates, spatio-temporal
patterns of seed shadows and subsequent seedling recruit-
ment of oil tea (C. oleifera). Burial of oil tea seeds by small
rodents may be a greater benefit for seed survival, seed
germination and seedling establishment. However, the mi-
croenvironments where small rodents deposit a given seed
are not simply suitable or unsuitable, and they may vary
continuously with respect to seed survival, germination,
and seedling growth and survival (Janzen, 1983). Further
experiments are needed to test the effects of different mi-
croenvironments selected by small rodents on seed germi-
nation and seedling establishment.
Acknowledgements: We are very grateful to the Subal-
pine Mountain Plant Garden of West-China, The Chinese
Academy of Sciences, and the Forest Bureau of Dujiangyan
City, Sichuan Province, for much support for our field
investigation. We thank Darrin-Londe of the American Mu-
seum of Natural History for correction the English of the
Manuscript.
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