「森林総合研究所研究報告」（Bulletin of FFPRI）Vol.18-No.4（No.452）381-387 December 2019

論381

文（Original article）

Population responses of rodents to the mast seeding of dwarf bamboo
Sasamorpha borealis over the Chubu region of Japan
Takuya SHIMADA 1 *, Daisuke HOSHINO 2 , Tohru OKAMOTO 3 , Tomoyuki SAITOH 4 ,))Kazuyuki NOGUCHI 5 and Takeshi SAKAI 2
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Abstract
In 2017, the mass flowering of dwarf bamboo (suzutake, Sasamorpha borealis) occurred throughout the Chubu
region of Japan after a non-flowering interval of 120 years. Concern is growing that an abundance of seeds producedby the mass flowering could cause an outbreak of rodents and, thereby, damage to the forests. To investigate whether
the rodent population would increase from the mast seeding of suzutake, trapping surveys were conducted in the hinoki
cypress (Chamaecyparis obtusa) plantation forest in the Dando National Forest (Aichi Prefecture), located in the centerof the mass flowering. The estimated rodent density did not prominently increase in the fall after mast seeding. The next
spring, the density of voles (Microtus montebelli or Eothenomys smithii), which cause gnawing damage to trees,remained relatively low (3.3–23.3 individuals/ha), whereas the density of two wood mouse species (Apodemus
argenteus and A. speciosus) was greatly increased (53.3–80.0 individuals/ha). These results indicate that the possibilityof a widespread vole outbreak caused by mast seeding is low. However, further attention should be paid to population
fluctuations in voles because populations may increase in other areas suitable for vole growth and survival.
Key words: mass flowering, pulsed resource, suzutake, vole, wood mouse

1. Introduction

rodents. Accordingly, it is expected that the population of rodents

In 2017, the mass flowering of suzutake (Sasamorphawill increase after the mast seeding of dwarf bamboos. In fact,

borealis), a monocarpic species of dwarf bamboo, occurred inoutbreaks of rodents have been frequently observed after the

the Chubu region of Japan. The flowering area was estimatedmast seeding of bamboos or dwarf bamboos (Ito 1975 in Japan,

to extend over 200,000 km , from the southern part of Nagano

Gallardo and Mercado 1999 in Chile, Belmain et al. 2010 in

Prefecture through Aichi Prefecture to the eastern part of Mie

Bangladesh, Douangboupha et al. 2010 in Laos, Htwe et al. 2010

Prefecture (Kobayashi 2018, Okamoto et al. 2018). Reviewsin Myanmar). In most cases, the rodent outbreaks cause severeof ancient documents have revealed that this mass floweringdamage to trees and crops cultivated near forests (Belmain et al.

occurred after an interval of 120 years (Okamoto and Saitoh

2010, Douangboupha et al. 2010, Htwe et al. 2010). Therefore,2017), and it resulted in the production of an abundance of seeds,

studies undertaken to investigate the possibility of rodent

from late July to August, following the flowering months.

outbreaks caused by the mast seeding of suzutake are urgently

2

In recent years, the importance of evaluating the responses

required.

of rodents to pulsed resources has been recognized in an effort

Two types of rodents inhabit the forests of mainland Japan.

to predict and control the risk of rodent damage to agriculture

One is the wood mouse species, which includes the large

and forestry, as well as zoonotic infections (Schnurr et al. 2002,

Japanese wood mouse Apodemus speciosus and the small

Ostfeld et al. 2006). One of the typical examples of pulsed

Japanese wood mouse A. argenteus that mainly feed on seeds

resources is the mast seeding of dwarf bamboos, which isand small invertebrates (Ohdachi et al. 2015). The other is theaccompanied by mass flowering. The seeds of dwarf bamboos

vole species, which includes the Japanese field vole Microtus

are large and highly nutritious, consisting of carbohydrates asmontebelli, Smith’s red-backed vole Eothenomys smithii, andthe primary nutrient (Iwata and Nakajima 1942, Kiruba et al.

Anderson’s red-backed vole E. andersoni that mainly feed on2007). Thus, they are considered an important resource forgrass, herbs, and tree bark and roots (Ohdachi et al. 2015). When

Received 23 July 2019, Accepted 12 September 20191) Department of Wildlife Biology, Forestry and Forest Products Research Institute (FFPRI)
2) Department of Forest Vegetation, FFPRI
3) Kansai Research Center, FFPRI
4) Tohoku Research Center, FFPRI
5) Aichi District Forest Office, Chubu Regional Forest Office* Department of Wildlife Biology, FFPRI, 1 Matsunosato, Tsukuba, Ibaraki, 305-8687 JAPAN; e-mail: tshmd@affrc.go.jp

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SHIMADA, T. et al.

the population density of these voles increases, they often cause

one animal was capture in the first survey, we decided to enlarge

severe damage to young planted trees and crops. According

the survey area not to miss the small changes of population

to a previous report, a large increase in population density influctuations in rodents. The information on the trapping survey

response to the mast seeding of dwarf bamboos occurs moreis shown in Table 1. Both plots were in the hinoki cypress

frequently in vole species than in wood mouse species (ItoChamaecyparis obtusa (about 50 years old) plantation forests

1975). This observation is likely related to their reproductive

and suzutake was dominant in the undergrowth.

characteristics. Voles can mate post-partum, and thus, if other
2.2 Trapping survey

conditions are suitable, many generations can accumulate in ashort period (Ando et al. 1988). In contrast, reproduction ofTrapping surveys were conducted three times, in August

the wood mouse species is highly regulated by the ambient2017, just after the dispersal of suzutake seeds; in October 2017;

temperature (Murakami 1974), which may prevent their prompt

and in April 2018. Twenty trap stations were constructed at

response to increased food availability as a result of mastintervals of about 5–10 m in a grid pattern within each plot andseeding. Therefore, particular attention must be paid to thetwo Sherman-type live traps were baited with oats and sunflower

population dynamics of voles.

seeds and placed at each station. Trapping was carried out forIn the present study, we conducted rodent trapping surveys

two or three consecutive days in the surveys of August 2017 andin the Dando National Forest, located in the center of the mass

those after October 2017, respectively. The species, sex, bodyflowering area, to investigate whether the rodent population

weight, distinction between adult or subadult, and reproductive

would increase with the mast seeding of suzutake and whether

status of the rodents were recorded upon capture. Reproductively

the rodents would damage trees in the area.

active females were defined as females with perforated vulvae
and/or developed mammillae, or in pregnancy or lactation,

2. Materials and methods

whereas reproductively active males were defined as males with

2.1 Study site

testis descent. A small portion of the fur of the buttock was cut

The field study was conducted in the Dando National Forest(the 96th compartment; 35°11ʹN, 137°46ʹE) in Shitara-cho, theeastern part of Aichi Prefecture. This area is located at the centerof the suzutake mass flowering. In this area, mass flowering
occurred from May to June 2017, and the culms began to
decline after flowering. Then, the mature seeds were dispersed
from late July to August 2017. A small non-flowering patch of
approximately 0.5 ha, in which no flowers were observed andthe culms were still alive, was found in this forest, surroundedby flowering patches. This patch could not be used as a control
for examining the effects of mast seeding on rodent population
dynamics because rodents could easily enter and leave the nonflowering patch. Instead, in order to investigate the habitat use

Fig. 1. Trapping plots for investigating rodent abundance inthe Dando National Forest.
Suzutake (Sasamorpha borealis) flowered throughout
this area in 2017 except for the non-flowering patch(shaded area). The flowering plot (grey area) in the firstsurvey (August 2017) was set adjacent to the nonflowering plot. In the subsequent surveys (October 2017
and April 2018), the flowering plot was newly established
about 100 m away from the non-flowering plot.

by rodents, two study plots were established for rodent trapping,
one in the flowering patch and the other in the non-flowering
patch (Fig. 1). In the trapping survey performed in August 2017,
the flowering plot was set adjacent to the non-flowering plot but
in the surveys after October 2017, the flowering plot was newly
established about 100 m away from the non-flowering plot. Since
the original plots were relatively small (0.2 ha each) and only

Table 1. Summary of trapping surveys in the Dando National Forest.
PeriodTrapping days

Area (ha)No. of traps

Aug. 8–10, 2017

2

0.2

40

Oct. 16–19, 2017

3

0.3

40

Apr. 17–20, 2018

3

0.3

40

These settings were common both in the flowering and non-flowering plots.
森林総合研究所研究報告 第 18 巻 4 号, 2019

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Rodent response to dwarf bamboo masting

off to distinguish re-captured from newly captured individuals.

as analytical replicates. The seed coats were removed before

The population density was estimated using MNA (minimum

analyses and the crude protein, crude fat, crude ash, and moisture

number alive, Krebs 1999) and expressed as the number ofcompositions were determined. Nitrogen-free extract (NFE) was

individuals per hectare. The methods of animal handlingestimated as the remainder of the nutrients. Carbohydrate is a

conformed to the Guidelines for the Procedure of Obtaining

major component of NFE. Energy content (kJ/g) was calculated

Mammal Specimens as Approved by the Mammal Society ofusing the following formula: crude protein × 4 + crude fat ×

Japan. (http://www.mammalogy.jp/en/guideline.pdf, accessed

9 + NFE × 4. These analyses were performed by the Japan

2017–7–1). Our trapping surveys were permitted by the local

Functional Food Analysis and Research Center, Inc.

government (permission Nos. 29Shin6-1–4 and 29Shin12-1–4).
3. Results

Four species of rodents are known to be distributed throughout
this area, A. speciosus, A. argenteus, M. montebelli, and E.

In the whole study period, 47 A. argenteus, 43 A. speciosus,

smithii. The two Apodemus species were able to discriminatedand nine voles were captured. Two of five female voles wereby their appearance. Contrary to this, it is difficult to distinguish

identified as E. smithii from the mammae formula. In August

M. montebelli from E. smithii by appearance. We adopted the2017, just after dispersal of suzutake seeds, only one A.

mark-recapture method in this study and thereby did not sacrificeargenteus was captured in the flowering plot, which indicatedcaptured animals. Consequently, we could not examine the shape

the low density of any species of rodents (Table 2). In Octoberof the skull necessary for species identification. Only females

2017, A. argenteus showed an increasing tendency especially inwith developed mammillae of these two species can be identified

the non-flowering plot (over 20 individuals/ha), but the density

by appearance because characteristics of their mammae differ

of other species remained low (Table 2). However, in April

from each other (Ohdachi et al. 2015). For this reason, we treated2018, an increase of population density was observed in all

both species as voles in the present study. Both vole species arerodent species except for vole spp. in the flowering plot (Table

listed in the Red List of Aichi Prefecture as near-threatened2). The population of the two wood mouse species grew up to

species (Red List Aichi 2015, http://www.pref.aichi.jp/kankyo/

50–80 individuals in both trapping plots. In addition, most of

sizen-ka/shizen/yasei/redlist/, accessed 2017–7–1).

female mice were reproductively active in this period (Table
3). Contrary to this, the density of voles increased only in the

2.3 Nutritional analysis of seeds

non-flowering plot (Table 2), and the female reproductive ratio

To evaluate the potential of suzutake seeds as a food source forremained at 40% in total (Table 3).

rodents, the nutritional composition of the seeds was analyzed

In order to examine whether the rodent population structureusing samples collected in August 2017 in the Dando National

differed between the flowering and non-flowering plots, theForest. Two different samples of about 100 g (samples 1 andcharacteristics of captured in the different locations were

2) were collected at different locations in the forest to servecompared (Table 3). The data for all rodent species collected

Table 2. Changes in rodent density (ha−1) in the Dando National Forest.
The density is expressed in MNA (minimum number alive, Krebs 1999).
a) Flowering plot
Apodemus argenteus

Aug. 2017

Oct. 2017

Apr. 2018

5.0 (1)10.0 (3)66.7 (20)Apodemus speciosus

0.0 (0)0.0 (0)56.7 (17)†0.0 (0)3.3 (1)

3.3 (1)

Vole spp.

b) Non-flowering plot
Aug. 2017

Oct. 2017

Apr. 2018

Apodemus argenteus

0.0 (0)23.3 (7)53.3 (16)Apodemus speciosus

0.0 (0)6.7 (2)80.0 (24)†0.0 (0)0.0 (0)23.3 (7)Vole spp.

Numerals in parentheses represent the number of captured individuals.
†: Two vole species (Eothenomys smithii and Microtus montebelli),
which are difficult to distinguish by appearance, are included.

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SHIMADA, T. et al.

Table 3. Comparisons of rodent population characteristics between the flowering and non-flowering sites ofsuzutake (Sasamorpha borealis) in the Dando National Forest.
a) Apodemus argenteus in fall (Oct. 2017)
Number of captured individuals
Sex ratio (female / total)
Proportion of reproductively active femalesa)Flowering plot

Non-flowering plot

3

7

0.33 (1/3)

0.71 (5/7)

0.50

1.00

0.80

1.00

Statistics d)

Proportion of pregnant or lactating females

0.00

0.60

0.27

b)

1.00

1.00

1.00

0.33

0.00

0.30

19.3 ± 0.4

19.6 ± 1.9

t = 0.28, P = 0.79

Flowering plot

Non-flowering plot

Statistics d)20

160.50 (10/20)

0.50 (8/16)

1.00

Proportion of reproductively active males
Proportion of subadults
Average body weightc)b) Apodemus argenteus in spring (Apr. 2018)
Number of captured individuals
Sex ratio (female / total)

0.80

1.00

0.48

Proportion of pregnant or lactating females

0.30

0.63

0.17

b)

1.00

0.88

0.27

0.05

0.00

1.00

16.1 ± 2.3

17.5 ± 2.4

t = 1.75, P = 0.09

Flowering plot

Non-flowering plot

Statistics d)

17240.41 (7/17)

0.50 (12/24)

0.75

1.00

1.00

1.00

Proportion of pregnant or lactating females

0.17

0.33

0.47

b)

1.00

0.89

0.36

0.24

0.25

1.00

38.9 ± 3.9

37.6 ± 6.9

t = 0.61, P = 0.55

Flowering plot

Non-flowering plot

Statistics d)

Proportion of reproductively active females
Proportion of reproductively active malesa)Proportion of subadults
Average body weightc)c) Apodemus speciosus in spring (Apr. 2018)
Number of captured individuals
Sex ratio (female / total)
Proportion of reproductively active females
Proportion of reproductively active malesa)Proportion of subadults
Average body weightc)d) Vole spp. in spring (Apr. 2018)
Number of captured individuals

171.00 (1/1)

0.57 (4/7)

1.00

Proportion of reproductively active females a)

1.00

0.25

0.40

Proportion of pregnant or lactating females

0.00

0.00

1.00

–

0.00

–

Sex ratio (female / total)

Proportion of reproductively active malesb)

Proportion of subadults

0.00

0.00

1.00

Average body weight c)

32.5

29.7 ± 2.6

t = 1.00, P = 0.36

a): calculated without subadult individuals. Reproductively active females were defined as females with perforated
vulvae and/or developed mammillae, or in pregnancy or lactation.

: calculated without subadult individuals. Reproductively active males were defined as males with testis descent.

b): expressed as mean ± SD; calculated without subadult individuals.

c): Fisher's exact probability test except for t-test in body weight comparisons.

d)

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Rodent response to dwarf bamboo masting

Table 4. Nutritional composition and energy content ofsuzutake (Sasamorpha borealis) seeds

in 17 areas after the mast seeding of dwarf bamboos (Sasa

Constituentsand Chugoku regions in 1967–70. Of those 17 study areas, we

Sample 1

Sample 2

Crude protein (%)

9.1

9.3

Crude fat (%)

1.7

1.2

Crude ash (%)

0.9

0.9

Nitrogen-free extracts (%)

76.3

76.9

Moisture (%)

12.0

11.7

Energy (kJ / g)

14.9

14.9

Constituents are expressed as wet weight basis.

kurilensis and Sasa kurokawana) which occurred in the Kansai
reviewed data from five areas where the number of trapped
individuals was represented by each species. In four areas, M.
montebelli started to increase the fall after the mast seeding(40–240 individuals/ha) and a high density of this species (20–120 individuals/ha) was maintained until the next spring in twoareas. An increase in A. speciosus the following autumn was
also recognized in two areas (40–80 individuals/ha), whereas
no noticeable increases were observed in A. argenteus and E.
smithii populations. Similarly, another qualitative observationin April 2018, as well as the data for A. argenteus in Octoberhas reported large increases in vole numbers in the fall after the

2017, were analyzed because sufficient numbers of captures had

mast seeding of dwarf bamboos (Inukai 1955).

been obtained. The ratio of sexes, proportion of reproductively

Compared to those observations, the population fluctuation

active males or females, proportion of pregnant or lactatingof rodents observed in this study was quite different. First, no

females, proportion of subadults, and average body weight were

noticeable increase in the vole population was detected in ourcompared but there were no differences between the two plots.

study. Although there was a moderate increase in the number of

The nutritional composition of suzutake seeds is shown involes in the non-flowering plot in the spring, the population density

Table 4. As predicted, the main nutrient was NFE (carbohydrates),

did not seem to increase over a wide range. The observation thatcomprising an average of 76.6% of the seed content. The content

majority of voles were reproductively inactive also supports thisof crude protein was relatively high for plant materials. The twoidea. Both vole species, E. smithii and M. montebelli, are rare in

seed samples showed nearly identical results.

this region, so the source population that would respond to mast
seeding may have already been diminished. Accordingly, no

4. Discussion

noticeable increase in the vole population occurred. Voles were

The population density of rodents did not show a significant

more abundant in the non-flowering plot than in the flowering

increase in the fall after the mast seeding of suzutake, however,plot. This is probably because they preferred habitat with a densea large increase was seen in the density of two Apodemus species

understory of dwarf bamboos. Forests with dense understories

the next spring. In contrast, the vole density over the entire study

are, in general, a preferred habitat for rodents (Tanaka et al.

area remained low even in the spring and increased moderately

2006), because the vegetation can provide both food and refuge

only in the non-flowering plot. Ishida et al. (2018) also conductedfrom predators.

trapping surveys in 2017 in the same region, the eastern part ofOn the other hand, the two Apodemus species markedly

Aichi Prefecture, and found results similar to ours. They foundincreased their density the next spring. Was this phenomenon

an increased density in Apodemus species in the fall (10–30

related to the mast seeding of suzutake? Since there are no

individuals/ha) but no increase in voles. The two results suggest

data regarding rodent density in this study site in normal (non-that an outbreak of voles after the mast seeding did not occur, at

dwarf bamboo flowering) years, it is difficult to discriminate theleast not in the study area.

effects of the mast seeding from commonly observed, seasonal

Suzutake seeds were found to be nutritious. The nutritional

population fluctuations.

composition was very similar to that of brown rice (crude protein

The present study suggested that the possibility of a vole

6.8%, crude fat 2.7%, NFE 74.3%, crude ash 1.2%, moistureoutbreak over a wide range caused by the mast seeding of

14.9%, and energy 14.8 kJ/g) according to the 2015 Japansuzutake was low. However, attention should be paid to theStandard Tables of Food Composition (Seventh Revised Version,

population fluctuation of voles because vole outbreaks may still

http://www.mext.go.jp/a_menu/syokuhinseibun/1365297.

occur in areas where voles are not rare or in habitats preferredhtm, accessed 2018–6–1). The nutritious composition of dwarf

by voles, such as orchards, grasslands, and young plantations,bamboo seeds, together with the vast amount produced, may

or in cases where mass flowering lasts for more years, gradually

have facilitated the increases in rodent populations that havechanging the flowering areas.

been frequently observed after mast seeding (Ito 1975, Gallardo
and Mercado 1999, Belmain et al. 2010, Douangboupha et al.
2010, Htwe et al. 2010).
Ito (1975) investigated the population fluctuation of rodents
Bulletin of FFPRI, Vol.18, No.4, 2019

Acknowledgement
We are grateful to the staff of the Aichi District Forest Office,Chubu Regional Forest Office for providing support for the field

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SHIMADA, T. et al.

survey. We also appreciate two anonymous reviewers for theircomments. This study was funded by Research grant #201710 of
the Forestry and Forest Products Research Institute.

271, 39-92. (in Japanese with English summary)
Iwata, H. and Nakajima, M. (1942) On seeds of dwarf bamboo—
Nutritional research on emergency food (11)., J. Agri.
Chem. Soc. Jpn., 18, 1149-1152. (in Japanese)

References
Ando, A., Shiraishi, S. and Uchida, T. (1988) Reproduction
in a laboratory colony of the Smith’s red-backed vole,
Eothenomys smithii. J. Mammal. Soc. Jpn., 13, 11-20.
Belmain, S., Chakma, N., Sarker, N. J., Sarker, S. U., Sarker, S. K.
and Kamal, N. Q. (2010). The Chittagong story: Studies on

Kobayashi, M. (2018) Mass flowering of suzutake in MinamiShinshu in 2017. Bull. Botanical Soc. Nagano, 51, 35-45.
(in Japanese)
Kiruba, S., Jeeva, S., Das, S. S. M. and Kannan, D. (2007)
Bamboo seeds as a means to sustenance of the indigenous
community. Indian J. Trad. Know., 6, 199-203.

the ecology of rat floods and bamboo masting. In Singleton,

Krebs, C.J. (1999) Ecological Methodology (2nd edition).

G. R., Belmain, S. R., Brown, P. R. and Hardy, B. (eds.)

Addison-Welsey Educational Publishers, Inc., Menlo Park,“Rodent Outbreaks: Ecology and Impacts”. International
Rice Research Institute, Los Baños (Philippines), 49-64.

CA, 624pp.
Murakami, O. (1974) Growth and development of the Japanese

Douangboupha, B., Singleton, G. R., Brown, P. R. andwood mouse (Apodemus speciosus). I. The breeding season

Khamphoukeo, K. (2010) Rodent outbreaks in the uplandsin the field. Jap. J. Ecol., 24, 194-206. (in Japanese withof Lao PDR. In Singleton, G. R., Belmain, S. R., Brown, P.

English summary)

R. and Hardy, B. (eds.) “Rodent Outbreaks: Ecology andOhdachi, S., Ishibashi, Y., Iwasa, M., Fukui, D. and Saitoh,

Impacts”. International Rice Research Institute, Los Baños

T. (2015) The Wild Mammals in Japan (2nd edition),(Philippines), 99-111.

Shoukadoh, Kyoto, 538pp.

Gallardo, M. H. and Mercado, C. L. (1999) Mast seeding ofOkamoto, T. and Saitoh, T. (2017) Gregarious flowering cycles

bamboo shrubs and mouse outbreaks in southern Chile.

of sasa in and around the Kiso District. 128th Japanese

Mastozool. Neotrop., 6, 103-111.

Forest Society meeting, P2–072. (in Japanese)

Htwe, N. M., Singleton, G. R., Thwe, A. M. and Lwin, Y. Y.

Okamoto, T., Saitoh, T. and Hoshino, D. (2018) Spatial pattern of(2010) Rodent population outbreaks associated withgregariously flowering in 2017 of Sasamorpha borealis inbamboo flowering in Chin State, Myanmar. In Singleton,

the Chubu Region. 129th Japanese Forest Society meeting,

G. R., Belmain, S. R., Brown, P. R. and Hardy, B. (eds.)“Rodent Outbreaks: Ecology and Impacts”. International

P2–174. (in Japanese)
Ostfeld, R. S., Canham, C. D., Oggenfuss, K., Winchcombe, R.

Rice Research Institute, Los Baños (Philippines), 79-98.

J. and Keesing, F. (2006) Climate, deer, rodents, and acorns

Inukai, T. (1955) A rare type of the vole damage on the forest due

as determinants of variation in Lyme-disease risk. PLoS

to the abundance of sasa bamboo seed at Atsuga in Hitaka,
Hokkaido. Memoirs Fac. Agri., Hokkaido Univ., 2, 92-96.
(in Japanese with English summary)
Ishida, A., Kurita. S. and Eguchi, N. (2018) Extensive flowering

Biol., 4, 1058-1068.
Schnurr, J., Ostfeld, R. and Canham, C. (2002) Direct andindirect effects of masting on rodent populations and tree
seed survival, Oikos, 96, 402-410.

and death of Sasa borealis and its effect for rats and voles

Tanaka, M., Saito, M., Ohi, K., Fukuda, H. and Shibata, E. (2006)

population in Aichi prefecture: States up to the second

Relationship between dwarf-bamboo growth and small

summer after first flowering. Chubu For. Res., 66, 43-44.

rodents on Mt. Ohdaigahara, central Japan, with special(in Japanese)reference to construction of deer-proof fences. J. Jpn. For.

Ito, T. (1975) Outbreaks of the field vole, Microtus montebelli,Soc., 88, 348-353. (in Japanese with English abstract)in Kansai and Chûgoku Districts. Bull. Gov. For. Exp. Sta.,

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中部地方で発生したスズタケ（Sasamorpha borealis）一斉結実に対する
野ネズミ個体群の反応島田 卓哉 1 *、星野 大介 2 、岡本 透 3 、齋藤 智之 4 、野口 和幸 5 、酒井 武 2
)

)

)

)

)

)

要旨
2017 年中部地方の広い範囲で、120 年振りにスズタケ（Sasamorpha borealis）の一斉開花が生じた。
スズタケの一斉開花、そしてその後の一斉結実にともなって、野ネズミの個体数が増加し、森林への被害が生じるのではないかという懸念が広まっていた。そこで、一斉結実による野ネズミの大発生が生じるかどうかを明らかにするため、愛知営林署管内段戸国有林ヒノキ人工林において、野ネズミの捕獲調査を実施した。野ネズミは、一斉結実直後の 2017 年秋には顕著な増加を示さなかった。2018
年春には、林木被害を引き起こすハタネズミ・ヤチネズミ類（Microtus montebelli または Eothenomys
smithii）の密度は比較的低いままであったが（3.3–23.3 個体/ha）、アカネズミ類（Apodemus argenteus
および A. speciosus）の密度は大幅に増加した（53.3–80.0 個体 /ha）。これらの結果は、スズタケ一斉結実に起因してハタネズミ・ヤチネズミ類が大発生し、森林被害が広範囲で発生する可能性は低いことを示している。しかし、よりハタネズミ・ヤチネズミ類の増加に適した地域において大発生が生じる可能性は残っているため、個体数変動には今後も注意を払う必要がある。
キーワード： 一斉開花、変動する資源、スズタケ、ハタネズミ・ヤチネズミ類、アカネズミ類

原稿受付：令和元年 7 月 23 日 原稿受理：令和元年 9 月 12 日
1）森林総合研究所 野生動物研究領域
2）森林総合研究所 森林植生研究領域
3）森林総合研究所 関西支所
4）森林総合研究所 東北支所
5）中部森林管理局 愛知森林管理事務所* 森林総合研究所 野生動物研究領域 〒 305-8687 茨城県つくば市松の里 1
Bulletin of FFPRI, Vol.18, No.3, 2019