RESEARCH PAPER

Input, retention, and invertebrate colonization of allochthonouslitter in streams bordered by deciduous broadleaved forest,a conifer plantation, and a clear-cut site in southwestern Japan

Mikio Inoue • Sei-ichi Shinotou • Yusuke Maruo •

Yo Miyake

Received: 28 February 2011 / Accepted: 20 November 2011 / Published online: 13 December 2011

� The Japanese Society of Limnology 2011

Abstract In headwater streams, conifer plantation for-

estry may affect stream communities through the quantity

and quality of basal resources (allochthonous litter). We

compared (1) the seasonal patterns of litter input from the

riparian canopy, (2) those for the abundance of benthic and

drifting litter in streams, and (3) the density of litter-

associated invertebrates among streams bordered by

deciduous broadleaved forest, a plantation of Japanese

cedar (Cryptomeria japonica), and a clear-cut site, to

extract the characteristics of conifer-plantation streams in

terms of litter dynamics and benthic invertebrates. The

results illustrate differences in litter input and in-stream

processes between the broadleaved and plantation sites,

although the total annual inputs from canopy were similar.

In the broadleaved site, high litter storage was limited to

winter, probably because pulsed inputs of litter in autumn

were retained on the streambed but rapidly processed. In

contrast, litter input was more constant at the plantation

site, and litter was stored throughout the year. Although the

litter-patch-specific density of total invertebrates was sim-

ilar between the broadleaved and plantation sites, estimates

of the reach-scale, habitat-weighted density considering

differences in the coverage area of litter patches revealed

considerable differences. Although the habitat-weighted

density of total invertebrates was lower at the plantation

site than at the broadleaved site in winter, it was noticeably

higher at the plantation site in summer, owing to the sea-

sonal stability of benthic litter abundance. Our results

emphasized the importance of considering the spatiotem-

poral availability of benthic litter when assessing the

effects of conifer plantations on stream ecosystems.

Keywords Coarse particulate organic matter �Cryptomeria japonica � Forestry � Needle litter � Shredder

Introduction

Allochthonous litter input from the riparian canopy is a

major energy source for aquatic communities in headwater

streams (Cummins et al. 1989; Wallace et al. 1999). Fallen

litter retained on the streambed is colonized by microor-

ganisms, fed on by macroinvertebrates, and then broken

down and converted into fine particulate organic matter,

which is transported downstream (Wallace et al. 1982; Gomi

et al. 2002). The seasonal timing of litter inputs, their

retention in streams, and the rates at which they break down,

all of which are important factors determining spatiotem-

poral patterns in detrital resource availability, are largely

dependent on riparian vegetation types and plant species.

Therefore, changes in riparian vegetation can alter stream

communities and ecosystem processes (e.g., Bilby and Bis-

son 1992; Lecerf et al. 2005; Clapcott and Barmuta 2010).

In many regions of the world, plantation forestry is a

major cause of extensive changes in forest vegetation (Fri-

berg 1997; Kerr 1999; Giller and O’Halloran 2004; Hicks

et al. 2004; Nagaike et al. 2006). Conifers are often used for

commercial forestry, and such conifer plantations are

characterized as monotonic, even-aged stands. Most regions

Handling Editor: Misako Urabe.

M. Inoue (&) � S. Shinotou � Y. Miyake

Graduate School of Science and Engineering,

Ehime University, Bunkyo-cho 2-5,

Matsuyama 790-8577, Japan

e-mail: inom@sci.ehime-u.ac.jp

Y. Maruo

Faculty of Science, Ehime University,

Bunkyo-cho 2-5, Matsuyama 790-8577, Japan

123

Limnology (2012) 13:207–219

DOI 10.1007/s10201-011-0369-x

where conifer plantations dominate are located in biomes of

deciduous or evergreen broadleaved forests (e.g., northern

Europe: Friberg 1997; Kerr 1999; Giller and O’Halloran

2004; New Zealand: Hicks et al. 2004; Japan: Inoue and

Nakamura 2004). The conversion of broadleaved forests to

conifer plantations has raised concerns about their impacts

on stream ecosystems (e.g., Friberg 1997; Riipinen et al.

2010). In general, conifer needles have a higher C/N ratio

and decay much more slowly than deciduous leaves (Sedell

et al. 1975; Webster and Benfield 1986; Maloney and

Lamberti 1995; Hisabae et al. 2011), suggesting that conifer

litter provides poor-quality food for invertebrate detriti-

vores. Therefore, conifer plantations can have negative

effects on detritus-associated invertebrates. However, the

nutritive quality of litter is no more than one aspect; there are

several other aspects that are important for consumers, such

as retention and persistence in streams. For example, slow-

decaying litter may be poor-quality food, but it may be more

consistently available as food for detritivores owing to its

longer persistence in streams due to its low decomposition

rates. In addition, fallen litter needs to be retained on the

streambed before being processed by invertebrates. The

retention of litter is affected by its morphological properties,

such as its size and shape (Kobayashi and Kagaya 2008),

and conifer needles differ appreciably from broadleaves in

these properties. Therefore, the temporal availability of lit-

ter as well as its nutritive quality differ between conifer and

broadleaf litter, and this should be considered when the

effects of conifer plantations are examined.

In northern Europe, the effects of conifer plantations

have been examined from several aspects, such as litter

abundance (Murphy and Giller 2000a, b), retention (Pretty

and Dobson 2004) and breakdown (Murphy and Giller

2001; Collen et al. 2004; Riipinen et al. 2010), and inver-

tebrate communities (Ormerod et al. 1993; Friberg 1997;

Clenaghan et al. 1998; Murphy and Giller 2000a; Riipinen

et al. 2010). Although knowledge of the ecological effects

of conifer plantations has been gained from these studies,

the effects of plantations on stream ecosystems can vary

regionally, depending on the region-specific environmental

conditions (e.g., climate, geology). In particular, study

streams in northern Europe often suffer from stream acidi-

fication (Ormerod et al. 1993; Friberg 1997; Friberg et al.

1998; Murphy and Giller 2000a; Riipinen et al. 2010),

probably due to atmospheric pollution and the low acid-

buffering capacity of the surface soils of the study areas.

Because such acidification can be induced by establishing a

conifer plantation (Ormerod et al. 1993; Friberg et al. 1998),

it is often difficult to separate the effects of the presence of a

conifer forest per se from those mediated by acidification in

those European streams (see Giller and O’Halloran 2004;

Riipinen et al. 2010). Therefore, information from other

geographical regions is necessary to gain a general

understanding of conifer-plantation effects, given the global

growth in plantation forestry (Winjum and Schroeder

1997). However, investigations in regions other than

northern Europe are relatively rare.

In Japan, 67% of the total land area is covered by for-

ests, most of which have been affected by human activities

(Inoue and Nakamura 2004). Although plantation forestry

was established in Japan by the nineteenth century (Totman

1998), it was not until the 1960s that intensive conversion

from natural broadleaved forests (including coppices) to

conifer plantations became widely prevalent. At present,

40% of the total forest area is occupied by conifer plan-

tations (typically containing Japanese cedar Cryptomeria

japonica, or Japanese cypress Chamaecyparis obtusa),

many of which have now reached harvesting age (Inoue

and Nakamura 2004; Nagaike et al. 2006). Therefore, the

forest landscape, especially in southwestern Japan, is typ-

ically composed of planted stands of evergreen conifers,

clear-cut areas (for timber harvesting), and natural sec-

ondary broadleaved forests. The extensive and drastic

changes in the forest vegetation caused by the establish-

ment of conifer plantations over the past several decades

may have greatly altered stream communities and ecolog-

ical processes. On the other hand, there is little evidence of

surface water acidification in Japan, due to the dominance

of acid-tolerant catchments (Ohte et al. 2001; Nakahara

et al. 2010 and references therein). Such properties of

Japanese landscapes and environments can contribute to a

better understanding of conifer-plantation effects on stream

ecosystems. Nevertheless, the effects of conifer plantations

on stream communities and ecological processes have

rarely been examined (e.g., Yoshimura 2007), although

hydrological, erosional and geochemical effects of forestry

management on streams have been well documented (e.g.,

Komatsu et al. 2008; Shibata et al. 2009).

In this study, we compared (1) the seasonal patterns of

litter input from the riparian canopy, (2) those of the

abundance of benthic and suspended litter in streams, and

(3) the density of litter-associated invertebrates among

three streams with contrasting riparian vegetation (natural

broadleaved forest, a conifer plantation of Japanese cedar,

and a clear-cut site), to extract the characteristics of coni-

fer-plantation streams in terms of litter dynamics and

benthic invertebrates. We hypothesized that the temporal

variability in litter abundance in the conifer plantation

stream would be lower than that in the stream with

broadleaved forest, because accumulations of conifer litter

would persist in streams for longer periods due to their

lower breakdown rates (Hisabae et al. 2011). We also

expected that the among-stream differences in the abun-

dance of litter-associated invertebrates would reflect those

in seasonal stability of benthic litter abundance, as well as

those in litter quality.

208 Limnology (2012) 13:207–219

123

Methods

Study site

The study was conducted in headwater streams of the Ishite

River (33�550N, 132�540E; near the Forest Research Center

of Ehime University), a tributary of the Shigenobu River in

Shikoku, southwestern Japan (Ehime Prefecture). The cli-

mate of this region is warm-temperate, and its potential

vegetation is evergreen (elevation \700 m) or deciduous

([700 m) broadleaved forests. Annual precipitation is ca.

1800 mm, with the wet season occurring in summer,

especially mid-June to mid-July (the rainy season in

Japan). Headwater catchments of the Ishite River are

covered by forest vegetation, which is broadly categorized

as natural broadleaved forest, a plantation of evergreen

conifers (Japanese cedar or Japanese cypress), or a har-

vested stand (clear-cut site). Natural broadleaved forests

and clear-cut sites are patchily distributed within the matrix

of conifer plantation stands, which are the dominant veg-

etation type. The natural broadleaved forests are secondary

forests of deciduous-dominated stands, many of which

have been formerly used for coppice forestry intended for

charcoal production. Stream waters are circumneutral and

differ little between streams bordered by broadleaved for-

ests and those bordered by conifer plantations (pH 7.0–7.8;

based on data from five paired sites of broadleaved and

conifer reaches, M. Inoue and Y. Maeda, unpublished).

We selected three second-order streams for study sites

representing the three vegetation types (one site per type:

Table 1). These streams are commonly characterized by

high-gradient, boulder-dominated channels, although sand

and gravel are relatively abundant owing to the weathered

granite underlying the catchments. The riparian forest of the

broadleaved site was dominated by deciduous species such

as fusa-zakura (Euptelea polyandra), yama-guwa (Morus

australis), maples (Acer spp.), and an oak (Quercus serrata),

with some evergreen broadleaved species (e.g., Camellia

japonica, Lauraceae species) mixed in the lower layer,

whereas the riparian forest of the plantation site consisted

entirely of planted Japanese cedar (ca. 45 years old during

our investigation). This plantation site and the ‘‘conifer site’’

in our previous study (Hisabae et al. 2011) are the same

place. The clear-cut site was located at an area harvested

(formerly conifer plantation) more than eight years before

our investigation. This area stretched ca. 200 m along the

stream, with riparian stands of plantation (Japanese cedar)

upstream of the harvested area. Although seedlings of Jap-

anese cedar had been re-planted in the harvested area, the

stream channel of the clear-cut site was not yet covered by

canopy, with streamside vegetation being dominated by

shrubs (e.g., Deutzia spp., Rhus javanica) and herbs.

Because stream channels of the broadleaved and plantation

sites were shaded by canopies, canopy openness differed

among the three sites (Table 1). However, water tempera-

ture was similar among the three sites (around 9 and 20�C at

winter and summer maxima, respectively). The clear-cut site

had a larger channel with a lower gradient than the broad-

leaved and plantation sites, whereas the broadleaved site was

located at a higher elevation than the other two sites.

Litter sampling

At each study site, litterfall from the riparian canopy, the

litter patch area on the streambed, and the drifting litter in

streams were quantified seasonally to capture litter dynam-

ics. Litterfall was sampled using litter traps with a 0.2 m2

opening (hoop 0.5 m in diameter; 1 mm mesh net) from

October 2006 to 2007. Eight litter traps were placed along

the banks of each site, with the opening being positioned

approximately 0.6 m above the ground. Trapped litter was

sampled biweekly, sorted into (1) leaves, (2) needles, (3)

fruits and cones, (4) woody material, and (5) others (e.g.,

flowers), and subsequently dried at 60�C for 48 h before

being weighed. Litter of Japanese cedar falls as foliage litter

(shoots with needles) rather than as fragmented needles

(Katsuno and Hozumi 1987; Kaneko et al. 1997), and the

category ‘‘needle’’ in this study includes such foliage litter.

A study reach (60–70 m in length) was established at

each site to survey the litter patch area on the streambed.

Litter patches were categorized into two types—trapped

and deposited patches—on the basis of their retention

mechanisms. Trapped patches are formed at the upstream

faces of obstacles (e.g., boulders, woody debris) that trap

passing litter. Deposited patches are formed in eddies or

slow-current areas where litter can settle through passive

sinking, without mediation by trapping obstacles. Trapped

and deposited patches in our study correspond to the riffle

patches and middle patches defined by Kobayashi and

Kagaya (2002, 2004), respectively; the edge and alcove

Table 1 General descriptions of the three study sites in headwater

tributaries of the Ishite River

Broadleaved Plantation Clear-cut

Elevation (m) 620 530 520

Channel gradient (%) 8.0 8.2 4.7

Mean wetted width (m) 1.7 2.3 3.3

Water temperature (min–max, �C)

Summer (August 2006) 16.0–20.0 15.5–19.5 16.0–20.5

Winter (February 2007) 5.5–8.5 3.0–8.5 2.5–9.0

Canopy openness (%)a

Summer (August 2007) 4.6 5.9 36.7

Winter (March 2007) 16.2 8.0 41.9

a Canopy openness was calculated using the program CanopOn 2 (see

Sugiura et al. 2009) on the basis of photographs taken by fisheye lens

Limnology (2012) 13:207–219 209

123

patches defined by Kobayashi and Kagaya (2004) may be

categorized as trapped and deposited patches, respectively,

in our study. In each study reach, every litter patch with an

area of [0.02 m2 within the wetted channel was catego-

rized as a trapped or deposited patch, and its long axis and

several widths were measured to estimate its coverage area.

Wetted width was measured at 5 m intervals along the

stream to estimate the wetted surface area of each reach by

multiplying reach length by mean wetted width. This patch

area survey was conducted monthly from August 2006 to

August 2007. In addition, three litter samples per patch

type were taken in summer (August 2006), autumn

(November 2006), winter (February 2007), and early

summer (May 2007) to obtain litter category composition.

Litter was collected by hand from about 0.02–0.03 m2 of

litter patches using a hand net (0.3 mm mesh) placed

immediately downstream. Litter samples were sifted

through 5 and 1 mm mesh sieves. Coarse particulate

organic matter (CPOM) [5 mm was sorted into the above

five categories (the same as litterfall samples), dried at

60�C for 48 h, and weighed. Coarse particulate organic

matter of size 1–5 mm, as a single category, was also

weighed in the same manner.

Drifting litter was sampled in late summer (September

2006: before leaf fall season), early winter (December 2006:

immediately after leaf fall season), midwinter (February

2007), and early summer (May 2007). A drift net

(0.25 9 0.25 m opening, 0.3 mm mesh) was placed in a

riffle at each site for 30–50 min; sampling was conducted on

five different days in each season (n = 5 per site for each

season, but one sample for December 2006 was lost by an

accident). To estimate the volume of water sieved, the cur-

rent velocity was measured at the center of the net opening

using a current meter (model CR-11, Cosmo Riken Inc.,

Kashihara, Japan). Litter in drift samples was classified and

weighed in the same manner as benthic litter patch samples.

Invertebrate sampling

Litter-associated invertebrates were sampled in midwinter

(February 2007) and midsummer (August 2008). To stan-

dardize the quantity of litter to be sampled, we used wire

mesh trays (0.02 m2 area; 0.2 9 0.1 9 0.03 m, 6 mm

mesh) for sampling. In each site, eight litter patches were

selected for each patch type (trapped: 5–15 cm in water

depth, 10–30 cm s-1 in current velocity; deposited:

10–40 cm in water depth, 0–10 cm s-1 in current velocity),

and a mesh tray filled with in situ litter (directly from the in-

stream litter patch) was embedded in each litter patch by

tying it to a metal stake hammered into the streambed. The

mesh trays were sampled after two weeks (21 February

2007, 12 August 2008) using a hand net (0.3 mm mesh)

placed immediately downstream, and preserved in 10%

formalin. Two weeks are sufficient for disturbed (or newly

created) habitats to be colonized by substantial numbers of

invertebrates (e.g., Townsend and Hildrew 1976; Maloney

and Lamberti 1995; Matthaei et al. 1996; Kobayashi and

Kagaya 2009). In summer, this invertebrate sampling could

not be conducted at the clear-cut site due to a lack of litter

patches. The mesh-tray samples were sifted through 5 and

1 mm mesh sieves, and invertebrates were sorted from the

material [1 mm, preserved in 70% ethanol, and identified

to genus or family. Coarse particulate organic matter was

treated in the same manner as benthic litter patch samples.

Although the mesh trays had initially been filled with

similar volumes of litter (i.e., the volume of the mesh tray)

to standardize the litter quantity by volume, the weight of

CPOM during the sampling varied substantially among the

mesh trays (mean ± SD: 25.9 ± 16.7 g dry weight),

depending on the amounts of both the trapped CPOM

transported from upstream and the loss from the mesh trays

during the two weeks. The variation in the CPOM weight

was also attributable to differences in litter composition,

which was distinctly different among the sites and patch

types (see Fig. 3). During the two weeks, some trays were

turned over by increased flow, and such disturbed samples

were not used (winter: two, one, and one sample for plan-

tation-deposited, clear-cut-trapped, and clear-cut-deposited,

respectively; summer: one, one, and two samples for

broadleaved-trapped, broadleaved-deposited, and planta-

tion-deposited, respectively).

Data treatment and analyses

Biweekly litterfall data were expressed as the dry weight

per m2 per day to express seasonal variations in litterfall,

and annual litterfall (g m-2 year-1) was also calculated.

Although we did not quantify lateral inputs, which may

correspond to 10–35% of litterfall on an annual basis (Pozo

et al. 1997; Kishi et al. 1999; Abe et al. 2006), we think

that seasonal patterns in total litter input can be represented

by litterfall (direct input). The area covered by benthic

litter patches was expressed as the patch area (m2) per

100 m2 wetted-channel area as an index of benthic litter

abundance. Drifting CPOM concentration was expressed as

the dry weight per volume of sieved water (m3). To

examine whether drifting CPOM abundance differed

among the three sites, two-way analysis of variance

(ANOVA) with site and sampling month as factors was

used. When the site and/or interaction effects were sig-

nificant, Tukey’s HSD multiple comparison tests were

performed to determine which site had greater values.

Invertebrate density was expressed as the number per

CPOM dry weight (g) because of the among-sample vari-

ation in litter quantity. Densities of total invertebrates and

numerically dominant taxa ([3% at either site in either

210 Limnology (2012) 13:207–219

123

season) were compared by site and patch type (trapped/

deposited) using two-way ANOVA. This ANOVA was

performed separately by season (winter/summer) because

of the lack of clear-cut site data in summer. When site and/

or interaction effects were detected in the ANOVA on

winter data, Tukey’s HSD multiple comparisons among the

three sites were performed separately for each patch type;

site effects were interpreted on the basis of multiple com-

parison results for the patch type with higher density. The

dominant taxa examined were two mayflies (Baetis, Par-

aleptophlebia), non-predatory midges (non-tanypodinae

chironomids: i.e., Chironominae and Orthocladiinae com-

bined), a caddisfly (Lepidostoma), two stoneflies (Nemoura,

Amphinemura), and a gammarid amphipod (Gammarus);

the three taxa of the mayflies and midges were categorized

as collector-gatherers, whereas the four taxa of the caddis-

fly, stoneflies, and amphipod were typical shredders.

We also calculated the habitat-weighted density of total

invertebrates (number per 1 m2 wetted area) to assess

among-site differences in litter-associated invertebrates at

the stream reach scale by considering differences in the

abundance of benthic litter patches. Habitat-weighted

density was calculated using the mean invertebrate number

per mesh tray (0.02 m2 area) for each patch type and the

area of each patch type in each site in February and August

obtained via the monthly patch area survey. This habitat-

weighted density is a rough estimation that does not con-

sider the amount of litter per patch area (thickness of the

litter patch). Litter patches were generally thicker in the

plantation site than in the broadleaved and clear-cut sites,

especially in summer. Therefore, in summer, the habitat-

weighted density in the plantation site is likely an under-

estimate relative to that in the broadleaved site.

All statistical analyses were performed using SPSS

(v.13.0J; SPSS Inc., Chicago, IL, USA). In the ANOVAs,

drifting CPOM concentrations and invertebrate densities

were log10 transformed prior to analysis.

Results

Litter

The total amounts of annual litterfall (direct input) were

similar between the broadleaved and the plantation sites,

although that at the clear-cut site was considerably lower

than those at the two sites (less than 10% of the amounts at

the two sites; Table 2). Litterfall at the broadleaved and

clear-cut sites was dominated by leaves, whereas that at the

plantation site was dominated by needles (Table 2).

Although the total amounts of litterfall were similar

between the broadleaved and plantation sites, its seasonal

variation differed (Fig. 1). At the broadleaved site, litterfall

peaked in November, sharply declined in December,

remained near to zero during the defoliation period (Jan-

uary–March), and gradually increased with sprouting (from

April). Such clear seasonality was not found at the plan-

tation site. At the plantation site, although an autumnal

peak like that seen in the broadleaved site occurred in

November, litterfall values similar to or higher than that in

November were also found in midwinter (February), spring

(March), and early summer (May).

Among-site differences in abundance and seasonal

variations of benthic litter were similar to those in litterfall

in that the clear-cut site had lower values throughout the

year and the broadleaved site exhibited strong seasonality

(Fig. 2). At the broadleaved site, the litter patch area peaked

in December to January, following the peak of litterfall, and

declined through spring (February–April) to below 3 m2

(per 100 m2 reach) in summer (July–September). On the

Table 2 Annual litterfall and the compositions of litter categories

Broadleaved Plantation Clear-cut

Total litterfall (g m-2 year-1) 360 376 29

% in each litter category

Leaves 71.0 0.5 59.9

Needles 3.8 75.5 5.7

Fruits and cones 4.8 6.8 1.9

Woody material 12.3 3.0 14.2

Others 8.0 14.1 18.3

Deciduous broadleaved

Conifer plantation

Clear-cut

Litte

rfal

l dry

wei

ght (

g m

-2da

y-1 )

10

4

21

0

10

4

21

0

1

0Oct Dec Feb Apr Jun Aug Oct

2006 2007

Fig. 1 Seasonal variations in litterfall from the riparian canopy

(mean and SD) at the broadleaved, plantation and clear-cut sites. The

vertical axes are on a logarithmic scale

Limnology (2012) 13:207–219 211

123

other hand, at the plantation site, it seems that the litter

patch area gradually increased from summer (August 2006)

to the peak in the next early summer (June 2007), and

subsequently declined sharply (after the rainy season of

mid-June to mid-July). As expected, temporal variability in

the litter patch area at the plantation site was lower than that

at the broadleaved site (coefficient of variation: broad-

leaved, 110.9%; plantation, 43.5%; clear-cut, 81.6%; see

Fig. 2). As a result, although the litter patch area was larger

in the broadleaved site than in the plantation site in winter

(November to February), it reversed from spring to autumn

(April–October).

Trapped patches were generally more abundant than

deposited patches in the broadleaved and plantation sites

(Fig. 2). At the plantation site, trapped patches occupied

more than 70% of the total coverage area throughout the

year. At the broadleaved site, although the contribution of

trapped patches exceeded 80% from September to the next

June, it declined in summer (July to August; 50–70%). At

the clear-cut site, the relative abundance of trapped patches

was substantially lower than that at the other two sites from

spring to autumn, except for July. In particular, deposited

patches dominated from August to October. Litter category

composition differed among the three sites and between the

two patch types (Fig. 3). The among-site differences were

reflected in trapped patches rather than deposited patches.

Trapped patches in the broadleaved and plantation sites

were dominated by leaves and needles, respectively; those

in the clear-cut sites were dominated by leaves in the leaf

fall season (November) but by needles in the other seasons

(August, February, and May). Trapped patches were

dominated by leaves or needles as above, whereas depos-

ited patches were dominated by small fragmented CPOM

(\5 mm) and woody material.

Drifting CPOM in the three sites was commonly domi-

nated by small fragments (CPOM \ 5 mm) (Table 3). At

the broadleaved site, leaves were dominant among the

categories of larger CPOM ([5 mm). At the plantation site,

however, the percentage of needles was very low (less than

3%), despite a large percentage of needles in the direct input

from the canopy ([75%, Table 2). A two-way ANOVA on

the concentration of total CPOM indicated that the site

effect was significant without interaction (site: F2,47 =

32.27, P \ 0.001; month: F3,47 = 6.55, P = 0.001; inter-

action: F6,47 = 0.42, P = 0.863), with a higher concentra-

tion in the broadleaved site than in the other two sites

(Tukey’s HSD test, P \ 0.001). The scatter plot for the

relationship between CPOM concentration and litterfall

showed that the lower CPOM concentrations in the clear-

cut site corresponded to the lower input of litterfall, but that

Litte

r pa

tch

area

(m2

2pe

r 10

0-m

wet

ted-

chan

nel a

rea)

0

5

10

15

20

25

Deciduous broadleaved

Conifer plantation

Clear-cut

Aug Oct Dec Feb Apr Jun AugRel

ativ

e ab

unda

nce

of

trap

ped

patc

h (%

)

0

20

40

60

80

100

2006 2007

Fig. 2 Seasonal variations in the coverage area of litter patches on

the streambed and in the contribution of trapped patches to the total

patch area at the broadleaved, plantation, and clear-cut sites

Needle > 5 mm

Deciduous broadleaved

Conifer plantation

Clear-cut

CPOM < 5 mm

Leaf > 5 mm

Woody material > 5 mm

Trapped patch Deposited patch

Per

cent

age

Aug Nov Feb May Aug Nov Feb May

2006 2007 2006 2007

80

40

0

80

40

0

80

40

0

80

40

0

Fig. 3 The composition of litter categories (mean and SD in percent

for each category) in trapped (left panels) and deposited (right panels)

patches on the streambed at the broadleaved, plantation, and clear-cut

sites in each sampling month

212 Limnology (2012) 13:207–219

123

in the plantation site did not (Fig. 4). In December, Feb-

ruary, and May, litterfall in the plantation site was similar to

or higher than that in the broadleaved site. Nevertheless,

CPOM concentrations in the plantation site were consis-

tently lower than that in the broadleaved site.

Invertebrates

In winter, litter patch assemblages in the broadleaved sites

were dominated by non-predatory Chironomidae (45%)

and Nemoura (16%), whereas those in the plantation site

were dominated by Gammarus (34%) and Nemoura (25%)

(Fig. 5). In the clear-cut site, the dominant taxa were

Amphinemura (31%) and non-predatory Chironomidae

(17%). In summer, similar trends were found; non-preda-

tory chironomids (51%) and Gammarus (79%) were

dominant in the broadleaved and plantation sites, respec-

tively (Fig. 6).

A two-way ANOVA on winter data indicated that both

site and patch-type effects on the densities of total inver-

tebrates, Baetis, Chironomidae, Gammarus, Lepidostoma,

Nemoura, and Amphinemura were significant (Table 4). In

addition, site 9 patch-type interaction effects were detec-

ted on Baetis, Chironomidae, Gammarus, Nemoura, and

Amphinemura. The densities of total invertebrates, Baetis,

Chironomidae, Nemoura, and Amphinemura were higher in

trapped patches than in deposited, while those of Gamm-

arus and Lepidostoma were higher in deposited patches

(Fig. 5). Among-site comparisons indicated that total

density was higher in the clear-cut site than in the

Table 3 The composition of litter categories in drifting CPOM

Broadleaved Plantation Clear-cut

CPOM \ 5 mm 50.9 (26.2) 86.9 (24.0) 79.6 (22.2)

CPOM [ 5 mm

Leaves 28.6 (26.1) 0.1 (0.5) 9.0 (17.3)

Needles 1.0 (2.8) 2.3 (4.6) 3.2 (10.3)

Fruits and cones 0.0 (0.0) 3.5 (15.6) 0.0 (0.0)

Woody material 9.0 (16.6) 2.1 (9.1) 1.7 (6.0)

Others 10.5 (14.5) 5.1 (17.8) 6.6 (10.2)

Mean and SD (in parentheses) across the four sampling seasons

(September, December, February, and May) are shown

Deciduous broadleaved

Conifer plantation

Clear-cut

Litterfall (g m-2 day-1)

1

4

10

20

40

80

160

CP

OM

drif

t (m

g m

-3)

0 1.0 2.0 3.00.4

Feb

MaySep

Dec

Sep

Dec

Feb

May

Dec

May

Feb

Sep

Fig. 4 Concentrations of drifting CPOM (mean and SD) in relation

to mean litterfall in each sampling month (Sep September 2006, DecDecember 2006, Feb February 2007, May May 2007). CPOM data in

September 2006 is plotted against litterfall data in September 2007

because litterfall was not sampled in September 2006 (see Fig. 1).

Both axes are on a logarithmic scale

30

10

3

10

Total Gammarus

3

1

2

0

LepidostomaBaetis

10

4

21

0

Paraleptophlebia Nemoura

15

8

421

0

Chironomidae(non-tanypodinae) Amphinemura

T D

Broad-leaved

T D

Coniferplantation

T D

Clear-cut

T D

Broad-leaved

T D

Coniferplantation

T D

Clear-cut

(33.6)

(0.0) (0.0)

(1.0) (0.3)

(4.3)

(2.2)(3.4)

(11.0)

(12.1)(15.4) (18.1) (16.2)

(25.1)

(5.9)

(45.2)

(13.2) (16.9) (9.0)

(2.6)

(30.5)

Den

sity

(nu

mbe

r pe

r g

CP

OM

dry

wei

ght)

abb

a

a

b b

a

bb

a

b

b

a

abb

aa

b b

b

a

Winter

Fig. 5 Comparisons of densities (mean and SD) of litter-associated

invertebrates in winter by site and patch type (T trapped patch,

D deposited patch). The taxa on the left and right panels are collectors

and shredders, respectively. Relative abundance (%) of each taxon in

each site is indicated in parentheses. The vertical axes are on a

logarithmic scale. Data labeled with the same letter are not

significantly different (P [ 0.05) by Tukey’s HSD tests, which were

conducted for a patch type with higher densities than another type in

the case where a patch-type or interaction effect was detected by two-

way ANOVA (Table 4)

Limnology (2012) 13:207–219 213

123

plantation site, with the broadleaved site being intermedi-

ate. Baetis density was also highest in the clear-cut site, and

did not differ significantly between the broadleaved and

plantation sites. The same trend was detected for Lepi-

dostoma and Amphinemura. Chironomidae density was

higher in the broadleaved and clear-cut sites than in the

plantation site. In contrast, the density of Gammarus was

highest in the plantation site. Nemoura density in the

plantation site was also highest, followed by that in the

broadleaved site.

In summer, no significant effects on the total density

were detected by two-way ANOVA (Table 4). The site,

patch type, and their interaction effects on the densities of

Baetis and Paraleptophlebia were all significant. Both

Baetis and Paraleptophlebia densities tended to be higher

in the broadleaved site than in the plantation site, although

Baetis was higher in trapped patches while Paralepto-

phlebia was higher in deposited patches (Fig. 6). Only the

site effect on Chironomidae and Gammarus was signifi-

cant, with the former and latter being higher in the

broadleaved and plantation sites, respectively. For Nemo-

ura and Amphinemura, only patch-type effects were sig-

nificant, and the densities of both taxa were higher in

trapped than in deposited patches.

Estimation of reach-scale, habitat-weighted density

considering differences in the coverage area of litter pat-

ches revealed that invertebrate abundance in the broad-

leaved site was approximately two times higher than that in

the plantation sites in winter (Fig. 7); that in the clear-cut

site was about one-quarter lower than that in the plantation

site. In summer, although the total density was similar

between the broadleaved and plantation sites in terms of

density per CPOM weight (Fig. 6), habitat-weighted den-

sity was considerably higher in the plantation site than in

the broadleaved site, due to the summer paucity of benthic

litter in the broadleaved site.

Discussion

Litter dynamics

Our data on the litterfall from canopy, the litter patch area

on the streambed, and the drifting CPOM in the water

column illustrate differences in allochthonous litter

dynamics among the three study sites with contrasting

riparian vegetation. Litter dynamics in the clear-cut site

was characterized by a scarcity of benthic litter and low

export of drifting CPOM due to low input from the canopy.

In the broadleaved and plantation sites, although the total

annual inputs from the canopy were similar, the seasonal

patterns of input and in-stream processes differed between

the two sites. It is suggested that the pulsed inputs from the

deciduous canopy in the broadleaved site were retained on

the streambed but rapidly processed, and their high storage

was limited to winter. On the other hand, intermittent

inputs from the conifer canopy at the plantation site were

likely to be effectively trapped and stored on the streambed

for longer periods.

The seasonal variation in benthic litter abundance was

lower in the plantation site than in the broadleaved site,

resulting in a higher abundance in the former than the latter

except in winter. The litterfall and drift data suggest that this

difference in benthic litter abundance was related to the

input and retention processes, as well as breakdown. In the

30

10

3

1

0

4

2

1

0

0.6

0.3

0.1

0.0

10

4

21

0

Den

sity

(nu

mbe

r pe

r g

CP

OM

dry

wei

ght)

Total Gammarus

Chironomidae(non-tanypodinae)

Amphinemura

T D

Broad-leaved

T D

Coniferplantation

T D

Broad-leaved

T D

Coniferplantation

(0.6)

(78.8)

(11.8) (0.9)

(4.2) (2.8)

(1.9)

(0.1)

(0.7)

(1.1)

(50.6) (3.9)

(20.2)(6.9)

Summer

LepidostomaBaetis

Paraleptophlebia Nemoura

Fig. 6 Comparisons of the densities (mean and SD) of litter-

associated invertebrates in summer by site and patch type

(T trapped patch, D deposited patch). The taxa on the left and rightpanels are collectors and shredders, respectively. Relative abundance

(%) of each taxon in each site is indicated in parentheses. The verticalaxes are on a logarithmic scale. Sampling was not conducted in the

clear-cut site because litter patches were scarce

214 Limnology (2012) 13:207–219

123

plantation site, inputs of relatively high amounts of litter

continued intermittently from autumn to early next summer

(November 2006–May 2007), whereas litterfall in the

broadleaved site rapidly declined after the autumnal peak

and the direct supply from the canopy was cut off during the

defoliation period. In the plantation site, both the abundance

of the total drifting CPOM and the percentage of needles in

it were noticeably low relative to those of the litterfall

(Fig. 4; Tables 2, 3), indicating that most needle litter from

the conifer canopy was effectively retained within the study

site. Further, our previous study using litter bag experiments

indicated that the breakdown rate of Japanese cedar needles

is considerably lower than that of deciduous broadleaves

(E. polyandra) (Hisabae et al. 2011); 80–90% of the needle

litter remained throughout the 77-day experimental period

in winter (December–February), while the broadleaf litter

was reduced to\40%. These lines of evidence suggest that

the rate of litter input to the plantation stream exceeds the

disappearance rate due to export and processing under

lowflow conditions, resulting in a gradual increase of stored

benthic litter unless it is flushed by highflow events. This

view is consistent with the increasing trend of litter patch

area at the plantation site from summer (August 2006) to

just before the rainy season (June 2007), in which the

accumulated litter tends to be flushed out by spates. Our

results suggest that streams bordered by Japanese cedar

plantations are more retentive than those bordered by

deciduous broadleaved forests, due to the intermittent but

relatively continuous input, the high retentiveness, and the

lower breakdown rate of the litter in the former streams.

Although the lower breakdown rate of conifer needles

(Japanese cedar) in our streams (Hisabae et al. 2011) can

be regarded as a general trend for conifers (Sedell et al.

1975; Webster and Benfield 1986; Maloney and Lamberti

1995; Collen et al. 2004), the intermittent input from the

canopy and the high retentiveness of the litter found in our

conifer stream were not always similar to those reported

from other conifer streams. Pulsed autumnal inputs similar

to deciduous leaves have been reported for conifer needles

[western red cedar (Thuja plicata), western hemlock

(Tsuga heterophylla), Douglas fir (Pseudotsuga menziesii)]

in British Columbia, Canada (Richardson 1992), whereas

an unpulsed, relatively constant input of conifer needles of

Table 4 Results of ANOVAs

testing for the effects of site and

patch type on the densities of

litter-associated invertebrates.

Chironomidae includes only

non-predatory chironomids (i.e.,

Tanipodinae is excluded). Bold

characters indicate statistical

significance (\0.05)

Site Patch type Site 9 patch type

F P F P F P

Winter (df = 2, 38) (df = 1, 38) (df = 2, 38)

Total density 4.48 0.018 13.27 0.001 2.76 0.076

Baetis 14.81 <0.001 12.85 0.001 5.04 0.011

Paraleptophlebia 2.36 0.108 1.38 0.248 1.79 0.181

Chironomidae 22.73 <0.001 22.97 <0.001 4.10 0.025

Gammarus 28.00 <0.001 5.81 0.021 5.97 0.006

Lepidostoma 13.63 <0.001 25.85 <0.001 3.08 0.058

Nemoura 6.65 0.003 22.67 <0.001 4.43 0.019

Amphinemura 41.98 <0.001 91.37 <0.001 26.69 <0.001

Summer (df = 1, 24) (df = 1, 24) (df = 1, 24)

Total density 0.21 0.650 3.89 0.060 1.36 0.254

Baetis 62.34 <0.001 82.10 <0.001 35.34 <0.001

Paraleptophlebia 8.08 0.009 8.87 0.007 5.67 0.026

Chironomidae 65.10 <0.001 0.02 0.898 0.02 0.900

Gammarus 44.13 <0.001 0.02 0.884 0.00 0.993

Lepidostoma 0.95 0.340 1.87 0.184 0.82 0.374

Nemoura 2.66 0.116 17.11 <0.001 2.69 0.114

Amphinemura 15.77 0.001 77.18 <0.001 0.75 0.394

0

500

1000

1500

2000

2500

B P C B P

Winter (Feb.) Summer(Aug.)

Inve

rteb

rate

den

sity

(Num

ber

m-2

wet

ted

area

)

Fig. 7 Reach-scale, habitat-weighted density of total litter-associated

invertebrates at the broadleaved (B), plantation (P), and clear-cut

(C) sites, considering among-site differences in litter patch area

(Fig. 2). Sampling was not conducted in the clear-cut site in summer

because litter patches were scarce

Limnology (2012) 13:207–219 215

123

similar species was found in Washington, USA (Bilby and

Bisson 1992). For retentiveness, although studies compar-

ing conifer needles and broadleaves are limited, conifer

needles are generally believed to be less retentive due to

their size and shape (e.g., Riipinen et al. 2010); Pretty and

Dobson (2004) actually demonstrated that conifer needles

[Scots pine (Pinus sylvestris)] were less retentive than

broadleaves, unlike in our case. The absence of strong

seasonality in litterfall and the high retentiveness in our

conifer plantation stream can be attributed to species-spe-

cific properties of Japanese cedar. Needles of Japanese

cedar die in autumn, but the dead needles remain attached

to foliage shoots and fall under the influence of external

forces (Kaneko et al. 1997). Therefore, litterfall of Japa-

nese cedar is induced by climatic events, such as wind-

storms and heavy snow, after the needles have died,

resulting in intermittent inputs from late autumn (Kaneko

et al. 1997; Abe et al. 2006). Further, the litter of Japanese

cedar falls as foliage litter (shoots with needles) 0.3–1.0 m

in length, rather than fragmented needles (Kaneko et al.

1997; see Katsuno and Hozumi 1987, 1988, 1990 for the

form of the forage shoot). Thus, the litter of Japanese cedar

shows high retentiveness due to its brush-like shape, and

further, it tends to trap other drifting CPOM, forming litter

accumulations. It should be noted that conifer plantations

of other species do not always have such characteristics in

their litter dynamics. For example, the scale-like leaves of

Japanese cypress, another major plantation species in

Japan, fall as small fragments, which probably have very

low retentiveness in streams.

Differences in litter category composition between the

two litter-patch types and their relative abundances

describe the mechanisms of litter retention. Trapped pat-

ches were dominated by leaves or needles, whereas the

dominant categories of deposited patches were woody

material and small fragmented CPOM (\5 mm). This

corroborates the characterization of litter-patch types by

Kobayashi and Kagaya (2002, 2004, 2008) (riffle patch and

middle, edge, and alcove patches in pools), who reported

that more leaves are retained on riffle and edge patches,

while more woody materials and small CPOM are retained

on middle patches. This consistent pattern in litter category

composition among patch types suggests that fallen leaves

were initially retained by trapping obstacles such as coarse

woody debris and boulders; they were then fragmented by

both physical and biological processes to smaller particles,

which were swept by the flow and deposited in eddies or

slow-current areas. In the plantation site, where large-sized

needle litter (foliage litter) was relatively abundant

throughout the year, trapped patches made up more than

70% (in coverage area) of the litter patches in every month.

On the other hand, in the broadleaved site, the relative

abundance of trapped patches declined in summer; that in

the clear-cut site was substantially lower than those in the

other two sites from spring to autumn. In the broadleaved

site, large-sized leaf litter was rare during summer due to

low inputs and high breakdown rates of deciduous broad-

leaves. Therefore, deposition in slow-current areas is more

important as a retention mechanism in summer than in

other seasons. The substantially lower contribution of

trapped patches in the clear-cut site probably reflects the

scarcity of large-sized litter due to the lack of a canopy,

which provides direct input. Kobayashi and Kagaya (2002,

2004, 2005a) revealed distinct differences in dominant

shredder taxa and litter breakdown rates among litter-patch

types, and emphasized that the composition of litter-patch

types is an important factor determining community

structure and ecological processes at the stream-reach

scale. Our results suggest that differences in streamside

vegetation can affect the composition of litter-patch types

through differences in retention mechanisms associated

with litter property (size, shape). Streams bordered by

Japanese cedar plantations can be characterized by higher

amounts of trapped patches throughout the year. According

to Kobayashi and Kagaya (2005a), litter breakdown rates

are lower in riffle patches (trapped patches) than in middle

patches (deposited patches). If this is a general trend, the

dominance of trapped patches in streams with Japanese

cedar plantations further contributes to lower breakdown

rates at the stream-reach scale.

Overall, the characteristics of our plantation stream can

be summarized as weak seasonality in the input and storage

of conifer litter and its higher persistence. The contrasts

between the broadleaved and plantation sites can be viewed

in terms of differences in the relative importance of abiotic

and biotic processes. Our results suggest that litter

dynamics in the conifer plantation stream is strongly

affected by abiotic processes such as climatic events that

induce both litterfall and downstream transport of accu-

mulated litter. On the other hand, litter dynamics in the

deciduous broadleaved stream is likely to be regulated

more by biotic processes, such as the phenology of riparian

plants and breakdown/decomposition by organisms. The

typical description of allochthonous energy flow in forested

headwater streams is that pulsed input of leaf litter

(CPOM) in autumn is converted to FPOM through bio-

logical processes, and the latter is continuously exported

downstream (e.g., Wallace et al. 1982; Gomi et al. 2002).

In conifer plantation streams, the conversion from CPOM

to FPOM is strongly retarded and CPOM tends to be

accumulated, resulting in the pulsed downstream export of

detritus as CPOM induced by highflow events, rather than

its continuous export as FPOM under baseflow conditions.

Our findings suggest that (1) resource availability (quan-

tity) in conifer plantation streams is relatively high and

seasonally stable for CPOM feeders but relatively low for

216 Limnology (2012) 13:207–219

123

FPOM feeders, and (2) downstream export of detritus from

conifer plantation streams is highly variable, which may

affect downstream communities and ecosystem processes.

Invertebrates

The two-way ANOVA showed taxon-specific responses to

site and patch-type effects. Although interaction effects of

site and patch type were frequently detected, the response of

each taxon to patch-type effect was broadly consistent

among sites and seasons. The densities of Baetis, Nemoura,

and Amphinemura tended to be higher in trapped than in

deposited patches in both winter and summer; such a trend

was found also for chironomids, although only in winter. On

the other hand, Paraleptophlebia, Gammarus, and Lepi-

dostoma exhibited higher densities in deposited than in

trapped patches in winter or summer. The trends in Baetis,

Nemoura, Paraleptophlebia, and Lepidostoma are consis-

tent with previous findings from central Japan by Kobayashi

and Kagaya (2002, 2005b), who reported differences in

invertebrate assemblages among litter patch types and fur-

ther showed their consistency among stream reaches with

different channel sizes and gradients. In particular, they

have attempted to explain the higher densities of stonefly

shredders (Nemoura, Protonemura) in riffle and edge pat-

ches (trapped patches) and those of caddisfly shredders

(Lepidostoma) in middle patches (deposited patches) from

several aspects, such as among-taxon differences in body

size and morphology and among-patch differences in cur-

rent velocity (oxygen supply), litter category composition

(food quality), and patch locations (accessibility during drift

dispersal) (Kobayashi and Kagaya 2002, 2004, 2005b,

2009). Our results corroborating Kobayashi and Kagaya’s

work suggest that interactions among litter properties (e.g.,

size, shape), retention mechanisms (e.g., trapped, depos-

ited), and hydraulic characteristics (water depth and current

velocity) generate certain consistent patterns in the forma-

tion of litter patches and their associated invertebrate

assemblages in headwater streams.

Responses of the densities to the site effect also varied

among taxa. In winter, the densities of Baetis, Lepidos-

toma, and Amphinemura were higher in the clear-cut site

than in the other two sites, whereas the densities of

Gammarus and Nemoura were higher in the plantation site.

The higher density of Baetis in the unshaded clear-cut site

is probably attributable to its higher autotrophic produc-

tion, because Baetis species are not obligate detritivores,

and their positive responses to deforestation due to

increased autotrophic production have often been reported

(e.g., Newbold et al. 1980; Gurtz and Wallace 1984;

Behmer and Hawkins 1986). However, the higher densities

of Lepidostoma and Amphinemura in the clear-cut site

cannot be explained by autotrophic production because

they are typical shredders. Their high densities may be

related to the scarcity of benthic litter in the clear-cut site

even in winter. Their populations may be concentrated in

the limited litter patches, resulting in higher densities than

the other two sites, which had more abundant litter.

Differences in invertebrate assemblages between the

broadleaved and plantation sites were largely associated

with the densities of non-predatory chironomids and

Gammarus. Chironomids were numerically dominant in the

broadleaved site, and their densities were significantly

higher in the broadleaved than in the plantation site in both

winter and summer. In contrast, Gammarus exhibited the

opposite trend. A similar trend of chironomids has been

reported by Murphy and Giller (2000a), who compared

litter-associated invertebrates between a conifer plantation

stream and a deciduous forest stream in Ireland. In addition,

the trend for chironomids is consistent with our previous

litter-bag experiment, which showed that chironomid den-

sity tended to be higher in deciduous leaves than in Japanese

cedar needles (Hisabae et al. 2011). However, the trend for

Gammarus in the present study contradicts the previous

experiment, which also revealed a preference of gammarids

for deciduous broadleaves rather than Japanese cedar nee-

dles (Hisabae et al. 2011). Further, the trend for Gammarus

in the present study also contrasts with a major trend in

northern Europe. Most studies in northern Europe have

suggested that shredder assemblages in conifer plantation

streams are characterized by the absence or low abundance

of gammarids (Friberg 1997; Friberg et al. 1998; Murphy

and Giller 2000a; Riipinen et al. 2010). The striking con-

trast in gammarid abundance between the previous studies

in northern Europe and ours may be due to differences in

water quality (acidity) and detritus quantity. In northern

Europe, the absence of gammarids in conifer plantation

streams was generally explained by lower pH (acidificat-

ion), a critical factor for gammarids (Peeters and Gardeniers

1998), and/or lower quality and quantity of detritus. How-

ever, our conifer stream had circumneutral water that

allowed inhabitation by gammarids. Further, as discussed

above, the availability of CPOM in our conifer plantation

stream was high and seasonally stable. In particular, a

higher seasonal stability of CPOM abundance is favorable

for gammarids, which spend all year round in streams, while

most aquatic insects spend only part of the year in streams.

In temperate forest streams, detritivores including gam-

marids often suffer from seasonal food limitation (Gee

1988; Richardson 1991). Although benthic CPOM in our

broadleaved site (i.e., leaf litter) may be a higher-quality

food for detritivores than that in the plantation site (i.e.,

needle litter) (Hisabae et al. 2011), our data showed that

benthic CPOM in the broadleaved site was severely limited

in summer (Fig. 2). The higher density of Gammarus in our

conifer plantation site than in the broadleaved site may be

Limnology (2012) 13:207–219 217

123

largely due to the higher seasonal stability of benthic

CPOM abundance in the plantation stream.

The comparisons of patch-specific density of total

invertebrates (Figs. 5, 6) may convey the impression that

the abundance of litter-associated invertebrates did not

differ greatly among the three sites (or the clear-cut site

had a higher abundance). However, the estimation of

habitat-weighted density showed considerable differences

at the stream-reach scale (Fig. 7). In winter, the clear-cut

site had the lowest density when assessed at the reach

scale. Further, although the abundance of litter-associated

invertebrates was lower in the plantation site than in the

broadleaved site in winter, it was noticeably higher in the

plantation site in summer, owing to the seasonal stability of

litter-patch abundance. Effects of riparian vegetation on

benthic invertebrates have often been assessed on the basis

of their habitat-specific abundance (e.g., Newbold et al.

1980; Behmer and Hawkins 1986; but see Gurtz and

Wallace 1984). In the case of litter-associated inverte-

brates, however, the distributions of their food and habitat

are extremely patchy within stream, and spatiotemporal

variations in quantity as well as quality of the resource

patch (i.e., litter patch) are strongly affected by riparian

vegetation. Therefore, assessments based only on patch-

specific abundance may be misleading. Our results suggest

that Japanese cedar stands may not cause drastic declines in

litter-associated invertebrates despite the lower nutritive

quality of conifer litter. Rather, Japanese cedar plantations

can contribute to the seasonal stability of benthic litter

abundance—a favorable aspect for CPOM feeders. How-

ever, because forestry activities inevitably include timber

harvesting, grown stands will be clear-cut, resulting in

drastic changes in basal resources in streams flowing there.

Plantation forestry of Japanese cedar produces two con-

trasting states in stream ecosystems at different places and

times, from a highly retentive, detritus-based system to a

detritus-poor, autotrophic-based system.

Acknowledgments We are grateful to Shogo Sakamoto, Shugo

Kikuchi, Yuhki Nakamoto, Yoshifumi Sumizaki, Yasutaka Hida,

Ryota Kawanishi, Tatsuya Sugihara, Shinji Fujii, Yuri Shoji, and

Shinsuke Futagami for help in the field or laboratory, and to Shigeo

Kuramoto for advice on interpreting the litterfall data. Comments

from two reviewers improved the manuscript. This research was

supported by Grants-in-Aid for Scientific Research from JSPS

(19580174 to M. Inoue) and a Special Fund for Education and

Research from the Japanese Ministry of Education, Culture, Sports

and Technology.

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