Directory UMM :Data Elmu:jurnal:A:Applied Soil Ecology:Vol13.Issue1.Sep1999:
Applied Soil Ecology 13 (1999) 57±68
Distribution patterns of the litter macrofauna in agroforestry
and monoculture plantations in central Amazonia as
affected by plant species and management
Katrin Vohlanda, GoÈtz Schrothb,*
b
a
Max-Planck-Institute for Limnology, Working Group Tropical Ecology, P.O. Box 165, PloÈn, Germany
Institute of Applied Botany, University of Hamburg, c/o Embrapa AmazoÃnia Ocidental, C.P. 319, 69011-970 Manaus-AM, Brazil
Received 3 June 1998; received in revised form 22 March 1999; accepted 22 March 1999
Abstract
Within heterogeneous land-use systems such as agroforestry or mixed tree crop plantations, the different morphological and
physiological characteristics of the plants, together with their species-speci®c management, lead to a mosaic of different living
conditions for the litter fauna. This may, in turn, in¯uence the processes of decomposition and nutrient cycling and, thus, the
growth-conditions of the plants. We studied the effect of different plant species on the litter macrofauna by collecting macroinvertebrates in the litter layer of an agroforestry system composed of four regionally important tree crop species in central
Amazonia: cupuac,u (Theobroma grandi¯orum), annatto (Bixa orellana), Brazil nut (Bertholletia excelsa) and peach palm
(Bactris gasipaes), with the leguminous cover crop Pueraria phaseoloides and spontaneous grasses as soil cover. The
agroforestry system was studied at two fertilisation levels and was compared with a peach palm monoculture. We found
invertebrates belonging to 18 orders and 44 families. The number of fauna individuals per unit area differed signi®cantly
between plant species within the agroforestry system. Both the number of individuals and the faunal biomass increased
linearly with litter dry matter per unit area. The Shannon±Wiener index of family diversity showed a non-linear increase with
increasing sampling area and litter mass in the samples, approaching saturation values between 2 and 2.5. The highest faunal
abundance and diversity was found in the litter of the peach palm monoculture, apparently due to the stable and protected
habitat provided by the ¯eshy offshoot remains from the palm harvests. The two fertiliser levels only differed with respect to
two invertebrate groups, snails and isopods. The results indicate that the creation of a litter and/or mulch layer of at least
3 Mg haÿ1, but preferably 6 Mg haÿ1 and the association of tree and cover crop species whose litter has a favourable effect on
the fauna with species whose litter has a less favourable effect are suitable management tools for the conservation of an
abundant and diverse litter fauna in plantations and agroforestry systems of the humid tropics. # 1999 Elsevier Science B.V.
All rights reserved.
Keywords: Agroforestry; Amazonia; Bactris; Bertholletia; Bixa; Faunal abundance; Faunal diversity; Litter; Perennial crops; Pueraria;
Theobroma
*Corresponding author. Tel.: +55-92-622-20-12; fax: +55-92-622-1100; e-mail: [email protected]
0929-1393/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 9 - 1 3 9 3 ( 9 9 ) 0 0 0 2 1 - 9
58
K. Vohland, G. Schroth / Applied Soil Ecology 13 (1999) 57±68
1. Introduction
Heterogeneous land-use systems such as agroforestry or mixed tree crop plantations are characterised
by a more or less regular spatial arrangement of the
plant species present. Alley cropping systems or
plantations of perennial crops with a monospeci®c
shade tree layer may contain only two principle plant
species in a regular pattern, whereas tropical homegardens may be highly diversi®ed species associations
with a forest-like structure (Nair and Muschler, 1993).
The different morphological and physiological characteristics of plant species such as their leaf mass,
turnover and decomposition rates, together with species-speci®c management practices including shoot
pruning, lead to distinct spatial patterns with respect to
the quantity and quality of the litter layer in heterogeneous land-use systems. Furthermore, crop species
in such systems differ in the amount of ground shading
which may in¯uence the activity of soil and litter
fauna (Kang et al., 1994), in the redistribution of rain
water passing through their canopy (Schroth et al.,
1999b) and in the required fertilisation rates. Together,
these factors create a mosaic of different living conditions for organisms dwelling in the litter layer.
Badejo et al. (1995) showed that different types of
tree mulch in¯uenced the microarthropod community
in maize plots, apparently through their different
chemical composition and their in¯uence on soil
temperature and moisture conditions. Perfecto and
Vandermeer (1996) reported changes in the diversity
of the ant community in coffee plantations due to
differences in shading and leaf litter. Accordingly, the
spatial heterogeneity of the litter layer in mixed tree
crop plantations should lead to small-scale differences
in the composition and activity of the litter-dwelling
faunal communities.
These litter-dwelling organisms are of crucial
importance for the growth conditions of the crop
plants and the sustainable functioning of agroecosystems through their role in litter decomposition and
concurrent nutrient release (Swift et al., 1979; Reddy,
1992; Henrot and Brussaard, 1997; Tian et al., 1997,
1998). An abundant and active litter fauna may thus
help to ensure rapid recycling of nutrients from dead
plant materials. This is particularly important under
low-input conditions and on infertile soils. Of course,
not all the fauna living in the litter layer is directly
involved in litter decomposition. Some groups are
predators whose feeding activity may be important
for regulating the abundance of other groups, including plant feeders and potential crop pests. So, the aim
of agroecosystem design and management could be to
increase the abundance of some groups (e.g., detritivores, fungivores) and to reduce the abundance of
other groups (e.g., pest species), eventually using
predators as biological control agents. This, however,
would require much more detailed information about
the ecological roles of the faunal groups involved and,
especially, their interactions under the speci®c conditions of the respective agroecosystem than what is
presently available, especially in the humid tropics.
So, for the time being, a good principle for the design
and management of tree crop plantations and other
land-use systems in the humid tropics may be to aim
for a high abundance and diversity of the litter-dwelling organisms, taking care that potential crop pests do
not become too numerous. This strategy seems to be
adequate both for reducing the probability of pest
outbreaks (Stamps and Linit, 1998) and for combating
species loss through agricultural intensi®cation (Perfecto and Vandermeer, 1996).
The aim of this study was to determine crop species
and management combinations which favour a high
abundance and diversity of the litter dwelling macrofauna in heterogeneous land-use systems in the humid
tropics. We collected and identi®ed the macro-invertebrates in the litter layer of an agroforestry system
composed of four locally important tree crop species
in central Amazonia, Brazil. Two fertilisation levels
and a monoculture of one of the species were included
in the study to assess the effects of management
intensity and composition of the plant communities
on the macrofauna. The study was part of a larger
project on the recovery of abandoned land through
site-adapted polyculture systems with perennial crops.
2. Methods
2.1. Study site
The study was conducted on the research station of
Embrapa AmazoÃnia Ocidental near Manaus, Brazil
(3880 S, 598520 W, 40±50 m asl). The climate is of the
KoÈppen Am type with an annual precipitation of
K. Vohland, G. Schroth / Applied Soil Ecology 13 (1999) 57±68
2622 mm, air temperature of 268C and atmospheric
humidity ca. 85% (mean values 1971±1993, O.M.R.
Cabral and C. Doza, unpublished). The driest months
are July to September, and the wettest months are
February to April. The soil is a Xanthic Ferralsol
according to the FAO/Unesco classi®cation (FAO/
Unesco, 1990) with a clay content of ca. 80% and a
pH in water of 4.5 at 0±10 cm depth. Detailed soil data
are given by Schroth et al. (1999a). The study site was
cleared from primary rainforest in 1980. In 1981, an
experiment with rubber trees (Hevea brasiliensis) was
established, which was abandoned in 1986. The developing secondary forest was manually cleared in 1992
and the vegetation was burnt on the site. The experimental plots were planted in the rainy season 1992/
1993.
The centerpiece of the study was an agroforestry
system with four locally important tree crop species:
Peach palm (Bactris gasipaes, Arecaceae) for the
production of heart of palm (palmito); cupuac,u (Theobroma grandi¯orum, Sterculiaceae), a small tree
related to cacao whose fruit pulp is widely used in
(and increasingly outside) the region for the preparation of juice, ice cream and sweets; the Brazil nut tree
(Bertholletia excelsa, Lecythidaceae) which, beside
the well-known nuts, produces excellent wood; and
annatto (Bixa orellana, Bixaceae) which is widely
cultivated in the tropics for its non-toxic red dye. Plot
size was 32 48 m. The trees were grown in rows
with 4 m spacing between the rows (Fig. 1). A row
with peach palm (at 2 m spacing within the row)
alternated with a mixed row of cupuac,u and Brazil
nut (at 6.7 m spacing between the trees within the
row), a row of annatto (at 4 m spacing within the row)
and again a mixed row of cupuac,u and Brazil nut, after
which the next row of peach palm followed. Between
the trees, Pueraria phaseoloides (tropical kudzu,
Fabaceae) was sown as a cover crop or developed
from residual seed from the former rubber plantation.
The agroforestry system was studied at two fertilisation levels, full fertilisation according to local
experiences, and 30% of this fertilisation level
(`low input plots'). The low input plots received no
N fertiliser since May 1996, about one year before the
study. For comparison, a peach palm monoculture was
included in the study, which was planted at 2 2 m
spacing and fertilised at the same rate per tree as the
peach palm in the agroforestry plots with full fertilisa-
59
Fig. 1. Layout of an agroforestry plot with Brazil nut (B), cupuac,u
(C), annatto (A) and peach palm (P) in central Amazonia. The soil
between the trees is covered by Pueraria phaseoloides and
spontaneous grasses.
tion. In November/December 1996, three months
before the study, the fully fertilised plots and the
monoculture, but not the low input plots, were limed
with 2.1 Mg haÿ1 of dolomitic lime. The plots were
arranged in a randomised complete block design with
three replications.
The Brazil nut trees were the largest of the four tree
species with a height of ca. 6±8 m. The cupuac,u trees
had a height of ca. 3 m and a shrubby growth habit.
Both species have relatively scleromorphic leaves.
Annatto was cut back annually at 1.5 m height and
had approximately the same size as the cupuac,u trees.
Its litter consisted not only of the soft leaves, but also
of branches and many fruit shells. From the peach
palms, the palmito was harvested by cutting the offshoots three times per year when they reached 8 cm
diameter at 1 m height. The palmito was extracted
directly in the ®eld, and the remains consisting of the
older and outer parts of the offshoots were left on the
soil where they formed most of the litter layer of this
species. The last palmito harvest before the litter
sampling had been in October 1996 (412 months before
the sampling).
2.2. Sampling
Litter samples were collected from 28 February to
11 March 1997, during the second half of the rainy
season. In each plot, we collected one litter sample
from each of the tree species present, i.e. peach palm,
60
K. Vohland, G. Schroth / Applied Soil Ecology 13 (1999) 57±68
cupuac,u, Brazil nut and annatto in the six agroforestry
plots, and peach palm in the three monoculture plots.
In the agroforestry plots, we also collected one litter
sample per plot from an area covered by Pueraria at
2±3 m distance from the neighboring trees, and one
sample from a similar area covered by spontaneous
grass growth. In the monoculture plots, there was little
ground vegetation because of the shade and presumably the root competition from the palms.
To obtain a representative sample for the litter of a
given tree, we sampled a triangular area under the tree
with the trunk at one corner and the other two corners
at 50 cm distance from the trunk and at 50 cm distance
from each other. Sampling area was 0.11 m2 per tree.
For the peach palm, this sampling scheme seemed less
appropriate because of the close spacing of the palms
within the rows (2 m). So, we collected here a rectangle of 100 cm length in the direction of the palm
row by 50 cm width, with the respective palm at one
corner. The sampling area was 0.5 m2 per tree. The
larger sampling area was used in this case because of
the much more heterogeneous distribution of the
coarse palm litter in comparison with the litter of
the dicot trees. Similar sampling areas were used
for the cover crop and the grass which also had a
heterogeneous litter because of the variable growth of
the soil cover species themselves and some in¯uence
from the litter of surrounding trees.
The sampling areas were marked and the borders
cut with a knife. The whole litter was rapidly put into a
bowl to avoid losses of mobile fauna, and the macrofauna was sorted out by hand and stored in ethanol.
Wet weight and humidity (by drying at 808C for 48 h)
of the litter were determined and the dry weight
calculated. The fauna was identi®ed to the family
level. Then, it was dried at 608C and weighed. Ants
and spiders were not quanti®ed in the samples,
because we considered them too mobile and too spotty
in their distribution to be assessed with this sampling
method. However, there were very few individuals of
both groups in the samples.
2.3. Data analysis
For every sample, the water content of the fresh
litter and the litter dry weight were determined and the
number of fauna individuals per m2 and per g of dry
litter was calculated. The data were checked for
normality of distribution, homogeneity of variances
and independence of means and variances, and the
fauna data were log-transformed because of positive
correlations between means and variances (Little and
Hills, 1978). To analyse the spatial structures of litter
and litter fauna within the agroforestry plots, an
analysis of variance was conducted for a randomised
complete block/split plot design with the fertilisation
level as main plot treatment and the plant species as
subplot treatment for the different sampling positions
within the agroforestry systems, without considering
the monoculture treatment (Little and Hills, 1978). To
investigate if the system context of a plant species had
an in¯uence on the litter and litter fauna, the sampling
positions in the peach palm monoculture plots were
then compared with the peach palm positions from the
agroforestry plots at high and low fertilisation by
ANOVA for a randomised complete block design.
In case of signi®cance of the F-test at p < 0.05, the
means were compared by least signi®cant difference
tests at the same level of signi®cance. From the
families present in each sample, the Shannon±Wiener
index of diversity H was calculated (`family diversity'
in Fig. 4).
3. Results and discussion
3.1. Litter quantity and humidity
The amount of litter per m2 did not vary signi®cantly between the plant species within the agroforestry system, although on the average, Brazil nut had
the highest and grass had the lowest litter mass
(Table 1). The peach palm in the monoculture had a
much higher litter mass than in the agroforestry plots,
obviously because of the higher number of palms per
unit area. The difference was signi®cant at p < 0.06
(Table 2).
Within the agroforestry plots, the litter of the cover
crop, Pueraria and grass, had a signi®cantly higher
water content than the litter of the four tree species,
which did not differ signi®cantly between each other
(Table 1). This was in agreement with lower potential
evaporation directly above the litter of the soil cover
species than above that of the trees (F.W. Correia,
personal communication). The cupuac,u litter was at
the dry end of the observed range, followed by Brazil
61
K. Vohland, G. Schroth / Applied Soil Ecology 13 (1999) 57±68
Table 1
Comparison of litter and fauna under tree and ground cover species in an agroforestry system in central Amazonia (means of high and low
fertilisation levels)
Litter mass
(g mÿ2)
Peach palm
Annatto
Brazil nut
Cupuac,u
Pueraria
Grass
F
p
314
400
427
306
382
262
Litter humidity
(% of DM)
170b
208b
131b
117b
326a
351a
0.50
0.773
7.35
Distribution patterns of the litter macrofauna in agroforestry
and monoculture plantations in central Amazonia as
affected by plant species and management
Katrin Vohlanda, GoÈtz Schrothb,*
b
a
Max-Planck-Institute for Limnology, Working Group Tropical Ecology, P.O. Box 165, PloÈn, Germany
Institute of Applied Botany, University of Hamburg, c/o Embrapa AmazoÃnia Ocidental, C.P. 319, 69011-970 Manaus-AM, Brazil
Received 3 June 1998; received in revised form 22 March 1999; accepted 22 March 1999
Abstract
Within heterogeneous land-use systems such as agroforestry or mixed tree crop plantations, the different morphological and
physiological characteristics of the plants, together with their species-speci®c management, lead to a mosaic of different living
conditions for the litter fauna. This may, in turn, in¯uence the processes of decomposition and nutrient cycling and, thus, the
growth-conditions of the plants. We studied the effect of different plant species on the litter macrofauna by collecting macroinvertebrates in the litter layer of an agroforestry system composed of four regionally important tree crop species in central
Amazonia: cupuac,u (Theobroma grandi¯orum), annatto (Bixa orellana), Brazil nut (Bertholletia excelsa) and peach palm
(Bactris gasipaes), with the leguminous cover crop Pueraria phaseoloides and spontaneous grasses as soil cover. The
agroforestry system was studied at two fertilisation levels and was compared with a peach palm monoculture. We found
invertebrates belonging to 18 orders and 44 families. The number of fauna individuals per unit area differed signi®cantly
between plant species within the agroforestry system. Both the number of individuals and the faunal biomass increased
linearly with litter dry matter per unit area. The Shannon±Wiener index of family diversity showed a non-linear increase with
increasing sampling area and litter mass in the samples, approaching saturation values between 2 and 2.5. The highest faunal
abundance and diversity was found in the litter of the peach palm monoculture, apparently due to the stable and protected
habitat provided by the ¯eshy offshoot remains from the palm harvests. The two fertiliser levels only differed with respect to
two invertebrate groups, snails and isopods. The results indicate that the creation of a litter and/or mulch layer of at least
3 Mg haÿ1, but preferably 6 Mg haÿ1 and the association of tree and cover crop species whose litter has a favourable effect on
the fauna with species whose litter has a less favourable effect are suitable management tools for the conservation of an
abundant and diverse litter fauna in plantations and agroforestry systems of the humid tropics. # 1999 Elsevier Science B.V.
All rights reserved.
Keywords: Agroforestry; Amazonia; Bactris; Bertholletia; Bixa; Faunal abundance; Faunal diversity; Litter; Perennial crops; Pueraria;
Theobroma
*Corresponding author. Tel.: +55-92-622-20-12; fax: +55-92-622-1100; e-mail: [email protected]
0929-1393/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 9 - 1 3 9 3 ( 9 9 ) 0 0 0 2 1 - 9
58
K. Vohland, G. Schroth / Applied Soil Ecology 13 (1999) 57±68
1. Introduction
Heterogeneous land-use systems such as agroforestry or mixed tree crop plantations are characterised
by a more or less regular spatial arrangement of the
plant species present. Alley cropping systems or
plantations of perennial crops with a monospeci®c
shade tree layer may contain only two principle plant
species in a regular pattern, whereas tropical homegardens may be highly diversi®ed species associations
with a forest-like structure (Nair and Muschler, 1993).
The different morphological and physiological characteristics of plant species such as their leaf mass,
turnover and decomposition rates, together with species-speci®c management practices including shoot
pruning, lead to distinct spatial patterns with respect to
the quantity and quality of the litter layer in heterogeneous land-use systems. Furthermore, crop species
in such systems differ in the amount of ground shading
which may in¯uence the activity of soil and litter
fauna (Kang et al., 1994), in the redistribution of rain
water passing through their canopy (Schroth et al.,
1999b) and in the required fertilisation rates. Together,
these factors create a mosaic of different living conditions for organisms dwelling in the litter layer.
Badejo et al. (1995) showed that different types of
tree mulch in¯uenced the microarthropod community
in maize plots, apparently through their different
chemical composition and their in¯uence on soil
temperature and moisture conditions. Perfecto and
Vandermeer (1996) reported changes in the diversity
of the ant community in coffee plantations due to
differences in shading and leaf litter. Accordingly, the
spatial heterogeneity of the litter layer in mixed tree
crop plantations should lead to small-scale differences
in the composition and activity of the litter-dwelling
faunal communities.
These litter-dwelling organisms are of crucial
importance for the growth conditions of the crop
plants and the sustainable functioning of agroecosystems through their role in litter decomposition and
concurrent nutrient release (Swift et al., 1979; Reddy,
1992; Henrot and Brussaard, 1997; Tian et al., 1997,
1998). An abundant and active litter fauna may thus
help to ensure rapid recycling of nutrients from dead
plant materials. This is particularly important under
low-input conditions and on infertile soils. Of course,
not all the fauna living in the litter layer is directly
involved in litter decomposition. Some groups are
predators whose feeding activity may be important
for regulating the abundance of other groups, including plant feeders and potential crop pests. So, the aim
of agroecosystem design and management could be to
increase the abundance of some groups (e.g., detritivores, fungivores) and to reduce the abundance of
other groups (e.g., pest species), eventually using
predators as biological control agents. This, however,
would require much more detailed information about
the ecological roles of the faunal groups involved and,
especially, their interactions under the speci®c conditions of the respective agroecosystem than what is
presently available, especially in the humid tropics.
So, for the time being, a good principle for the design
and management of tree crop plantations and other
land-use systems in the humid tropics may be to aim
for a high abundance and diversity of the litter-dwelling organisms, taking care that potential crop pests do
not become too numerous. This strategy seems to be
adequate both for reducing the probability of pest
outbreaks (Stamps and Linit, 1998) and for combating
species loss through agricultural intensi®cation (Perfecto and Vandermeer, 1996).
The aim of this study was to determine crop species
and management combinations which favour a high
abundance and diversity of the litter dwelling macrofauna in heterogeneous land-use systems in the humid
tropics. We collected and identi®ed the macro-invertebrates in the litter layer of an agroforestry system
composed of four locally important tree crop species
in central Amazonia, Brazil. Two fertilisation levels
and a monoculture of one of the species were included
in the study to assess the effects of management
intensity and composition of the plant communities
on the macrofauna. The study was part of a larger
project on the recovery of abandoned land through
site-adapted polyculture systems with perennial crops.
2. Methods
2.1. Study site
The study was conducted on the research station of
Embrapa AmazoÃnia Ocidental near Manaus, Brazil
(3880 S, 598520 W, 40±50 m asl). The climate is of the
KoÈppen Am type with an annual precipitation of
K. Vohland, G. Schroth / Applied Soil Ecology 13 (1999) 57±68
2622 mm, air temperature of 268C and atmospheric
humidity ca. 85% (mean values 1971±1993, O.M.R.
Cabral and C. Doza, unpublished). The driest months
are July to September, and the wettest months are
February to April. The soil is a Xanthic Ferralsol
according to the FAO/Unesco classi®cation (FAO/
Unesco, 1990) with a clay content of ca. 80% and a
pH in water of 4.5 at 0±10 cm depth. Detailed soil data
are given by Schroth et al. (1999a). The study site was
cleared from primary rainforest in 1980. In 1981, an
experiment with rubber trees (Hevea brasiliensis) was
established, which was abandoned in 1986. The developing secondary forest was manually cleared in 1992
and the vegetation was burnt on the site. The experimental plots were planted in the rainy season 1992/
1993.
The centerpiece of the study was an agroforestry
system with four locally important tree crop species:
Peach palm (Bactris gasipaes, Arecaceae) for the
production of heart of palm (palmito); cupuac,u (Theobroma grandi¯orum, Sterculiaceae), a small tree
related to cacao whose fruit pulp is widely used in
(and increasingly outside) the region for the preparation of juice, ice cream and sweets; the Brazil nut tree
(Bertholletia excelsa, Lecythidaceae) which, beside
the well-known nuts, produces excellent wood; and
annatto (Bixa orellana, Bixaceae) which is widely
cultivated in the tropics for its non-toxic red dye. Plot
size was 32 48 m. The trees were grown in rows
with 4 m spacing between the rows (Fig. 1). A row
with peach palm (at 2 m spacing within the row)
alternated with a mixed row of cupuac,u and Brazil
nut (at 6.7 m spacing between the trees within the
row), a row of annatto (at 4 m spacing within the row)
and again a mixed row of cupuac,u and Brazil nut, after
which the next row of peach palm followed. Between
the trees, Pueraria phaseoloides (tropical kudzu,
Fabaceae) was sown as a cover crop or developed
from residual seed from the former rubber plantation.
The agroforestry system was studied at two fertilisation levels, full fertilisation according to local
experiences, and 30% of this fertilisation level
(`low input plots'). The low input plots received no
N fertiliser since May 1996, about one year before the
study. For comparison, a peach palm monoculture was
included in the study, which was planted at 2 2 m
spacing and fertilised at the same rate per tree as the
peach palm in the agroforestry plots with full fertilisa-
59
Fig. 1. Layout of an agroforestry plot with Brazil nut (B), cupuac,u
(C), annatto (A) and peach palm (P) in central Amazonia. The soil
between the trees is covered by Pueraria phaseoloides and
spontaneous grasses.
tion. In November/December 1996, three months
before the study, the fully fertilised plots and the
monoculture, but not the low input plots, were limed
with 2.1 Mg haÿ1 of dolomitic lime. The plots were
arranged in a randomised complete block design with
three replications.
The Brazil nut trees were the largest of the four tree
species with a height of ca. 6±8 m. The cupuac,u trees
had a height of ca. 3 m and a shrubby growth habit.
Both species have relatively scleromorphic leaves.
Annatto was cut back annually at 1.5 m height and
had approximately the same size as the cupuac,u trees.
Its litter consisted not only of the soft leaves, but also
of branches and many fruit shells. From the peach
palms, the palmito was harvested by cutting the offshoots three times per year when they reached 8 cm
diameter at 1 m height. The palmito was extracted
directly in the ®eld, and the remains consisting of the
older and outer parts of the offshoots were left on the
soil where they formed most of the litter layer of this
species. The last palmito harvest before the litter
sampling had been in October 1996 (412 months before
the sampling).
2.2. Sampling
Litter samples were collected from 28 February to
11 March 1997, during the second half of the rainy
season. In each plot, we collected one litter sample
from each of the tree species present, i.e. peach palm,
60
K. Vohland, G. Schroth / Applied Soil Ecology 13 (1999) 57±68
cupuac,u, Brazil nut and annatto in the six agroforestry
plots, and peach palm in the three monoculture plots.
In the agroforestry plots, we also collected one litter
sample per plot from an area covered by Pueraria at
2±3 m distance from the neighboring trees, and one
sample from a similar area covered by spontaneous
grass growth. In the monoculture plots, there was little
ground vegetation because of the shade and presumably the root competition from the palms.
To obtain a representative sample for the litter of a
given tree, we sampled a triangular area under the tree
with the trunk at one corner and the other two corners
at 50 cm distance from the trunk and at 50 cm distance
from each other. Sampling area was 0.11 m2 per tree.
For the peach palm, this sampling scheme seemed less
appropriate because of the close spacing of the palms
within the rows (2 m). So, we collected here a rectangle of 100 cm length in the direction of the palm
row by 50 cm width, with the respective palm at one
corner. The sampling area was 0.5 m2 per tree. The
larger sampling area was used in this case because of
the much more heterogeneous distribution of the
coarse palm litter in comparison with the litter of
the dicot trees. Similar sampling areas were used
for the cover crop and the grass which also had a
heterogeneous litter because of the variable growth of
the soil cover species themselves and some in¯uence
from the litter of surrounding trees.
The sampling areas were marked and the borders
cut with a knife. The whole litter was rapidly put into a
bowl to avoid losses of mobile fauna, and the macrofauna was sorted out by hand and stored in ethanol.
Wet weight and humidity (by drying at 808C for 48 h)
of the litter were determined and the dry weight
calculated. The fauna was identi®ed to the family
level. Then, it was dried at 608C and weighed. Ants
and spiders were not quanti®ed in the samples,
because we considered them too mobile and too spotty
in their distribution to be assessed with this sampling
method. However, there were very few individuals of
both groups in the samples.
2.3. Data analysis
For every sample, the water content of the fresh
litter and the litter dry weight were determined and the
number of fauna individuals per m2 and per g of dry
litter was calculated. The data were checked for
normality of distribution, homogeneity of variances
and independence of means and variances, and the
fauna data were log-transformed because of positive
correlations between means and variances (Little and
Hills, 1978). To analyse the spatial structures of litter
and litter fauna within the agroforestry plots, an
analysis of variance was conducted for a randomised
complete block/split plot design with the fertilisation
level as main plot treatment and the plant species as
subplot treatment for the different sampling positions
within the agroforestry systems, without considering
the monoculture treatment (Little and Hills, 1978). To
investigate if the system context of a plant species had
an in¯uence on the litter and litter fauna, the sampling
positions in the peach palm monoculture plots were
then compared with the peach palm positions from the
agroforestry plots at high and low fertilisation by
ANOVA for a randomised complete block design.
In case of signi®cance of the F-test at p < 0.05, the
means were compared by least signi®cant difference
tests at the same level of signi®cance. From the
families present in each sample, the Shannon±Wiener
index of diversity H was calculated (`family diversity'
in Fig. 4).
3. Results and discussion
3.1. Litter quantity and humidity
The amount of litter per m2 did not vary signi®cantly between the plant species within the agroforestry system, although on the average, Brazil nut had
the highest and grass had the lowest litter mass
(Table 1). The peach palm in the monoculture had a
much higher litter mass than in the agroforestry plots,
obviously because of the higher number of palms per
unit area. The difference was signi®cant at p < 0.06
(Table 2).
Within the agroforestry plots, the litter of the cover
crop, Pueraria and grass, had a signi®cantly higher
water content than the litter of the four tree species,
which did not differ signi®cantly between each other
(Table 1). This was in agreement with lower potential
evaporation directly above the litter of the soil cover
species than above that of the trees (F.W. Correia,
personal communication). The cupuac,u litter was at
the dry end of the observed range, followed by Brazil
61
K. Vohland, G. Schroth / Applied Soil Ecology 13 (1999) 57±68
Table 1
Comparison of litter and fauna under tree and ground cover species in an agroforestry system in central Amazonia (means of high and low
fertilisation levels)
Litter mass
(g mÿ2)
Peach palm
Annatto
Brazil nut
Cupuac,u
Pueraria
Grass
F
p
314
400
427
306
382
262
Litter humidity
(% of DM)
170b
208b
131b
117b
326a
351a
0.50
0.773
7.35