Monodominance of Parashorea chinensis on fertile soils in a Chinese tropical rain forest

Abstract

Monodominance in the tropics is often seen as an unusual phenomenon due to the normally high diversity in tropical rain forests. Here we studied Parashorea chinensis H. Wang (Dipterocarpaceae) in a seasonal tropical forest in south-west China, to elucidate the mechanisms behind its monodominance. Twenty-eight 20 × 20-m plots were established in monodominant and mixed forest in Xishuangbanna, Yunnan province. All individuals 1 cm stem diameter and 16 soil variables were measured. Parashorea chinensis forest had a significantly higher mean tree dbh compared with mixed forest. Diversity did not differ significantly between the two forest types. However, within monodominant patches, all diversity indices decreased with an increase in P. chinensis dominance. Floristic composition of P. chinensis forest did differ significantly from the mixed forest. These differences were associated with more fertile soils (significantly higher pH, Mn, K and lower carbon pools and C :N ratio) in the P. chinensis forest than the mixed forest. In contrast to current paradigms, this monodominant species is not associated with infertile, but with fertile soils. Parashorea chinensis seems to be especially associated with high manganese concentrations which it can tolerate,
and with edaphic conditions (water, K) that allow this tall and exposed emergent species to maintain its water balance. This is in contrast with most previous studies on monodominance in the tropics that found either no effect of soil properties, or predict associations with nutrient-poor soils.

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Monodominance of Parashorea chinensis on fertile soils in a Chinese
tropical rain forest
Nic van der Velden, J. W. Ferry Slik, Yue-Hua Hu, Guoyu Lan, Luxian Lin, XiaoBao Deng and Lourens Poorter
Journal of Tropical Ecology / Volume 30 / Issue 04 / July 2014, pp 311 - 322
DOI: 10.1017/S0266467414000212, Published online: 23 June 2014
Link to this article: http://journals.cambridge.org/abstract_S0266467414000212
How to cite this article:
Nic van der Velden, J. W. Ferry Slik, Yue-Hua Hu, Guoyu Lan, Luxian Lin, XiaoBao Deng and Lourens Poorter (2014).
Monodominance of Parashorea chinensis on fertile soils in a Chinese tropical rain forest . Journal of Tropical Ecology, 30, pp
311-322 doi:10.1017/S0266467414000212
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Journal of Tropical Ecology (2014) 30:311–322. © Cambridge University Press 2014
doi:10.1017/S0266467414000212
Monodominance of Parashorea chinensis on fertile soils in a Chinese
tropical rain forest
Nic van der Velden∗,†, J. W. Ferry Slik∗,‡, Yue-Hua Hu§, Guoyu Lan§, Luxian Lin§, XiaoBao Deng§
and Lourens Poorter†,1
∗Center for Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Mengla, Yunnan 666303, China
†Forest Ecology and Forest Management Group, Wageningen University, P.O. Box 47, 6700 AA Wageningen, the Netherlands
‡Faculty of Science, Universiti Brunei Darussalam, Jln Tungku Link, Gadong, BE1410, Brunei Darussalam
§Keylab of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Mengla, Yunnan 666303, China
(Received 23 March 2013; revised 14 April 2014; accepted 17 April 2014)
Abstract: Monodominance in the tropics is often seen as an unusual phenomenon due to the normally high diversity
in tropical rain forests. Here we studied Parashorea chinensis H. Wang (Dipterocarpaceae) in a seasonal tropical
forest in south-west China, to elucidate the mechanisms behind its monodominance. Twenty-eight 20 ×20-m plots
were established in monodominant and mixed forest in Xishuangbanna, Yunnan province. All individuals ࣙ1cm
stem diameter and 16 soil variables were measured. Parashorea chinensis forest had a significantly higher mean tree
dbh compared with mixed forest. Diversity did not differ significantly between the two forest types. However, within
monodominant patches, all diversity indices decreased with an increase in P. chinensis dominance. Floristic composition
of P. chinensis forest did differ significantly from the mixed forest. These differences were associated with more fertile
soils (significantly higher pH, Mn, K and lower carbon pools and C : N ratio) in the P. chinensis forest than the mixed
forest. In contrast to current paradigms, this monodominant species is not associated with infertile, but with fertile
soils. Parashorea chinensis seems to be especially associated with high manganese concentrations which it can tolerate,
and with edaphic conditions (water, K) that allow this tall and exposed emergent species to maintain its water balance.
This is in contrast with most previous studies on monodominance in the tropics that found either no effect of soil
properties, or predict associations with nutrient-poor soils.
Key Words: diversity, manganese, monodominance, Parashorea chinensis, population structure, soil fertility, tropical
forest
INTRODUCTION
Tropical rain forests are well known for their immense
biodiversity, but paradoxically, monodominant, low-
diversity forests can also be found in the tropics where
the upper canopy layer is dominated by a single species
(Connell & Lowman 1989). Monodominant tropical
forests on well-drained soils can be found in all continents
(Degagne et al. 2009,Hartet al. 1989,Nascimento&
Proctor 1997, Whitmore 1984).
Connell & Lowman (1989) proposed two contrasting
mechanisms through which species can attain
dominance: (1) through fast recruitment and growth
in unstable habitats with high disturbance, and (2)
through competitive exclusion in stable habitats with
low disturbance. Traits proposed to be involved in
1Corresponding author. Email: lourens.poorter@wur.nl
attaining monodominance in stable habitats include mast
fruiting, which may satiate predators and lead to massive
recruitment (Visser et al. 2011) and poor seed dispersal,
large seeds and shade tolerance that may result in a
dense seedling carpet on the forest floor (Peh et al. 2011a,
Torti et al. 2001, Zagt & Werger 1997). Architectural
traits such as the formation of a deep crown can cause
substantial shading which, in combination with shade-
tolerant juvenile stages and the production of tough, poor-
quality leaves may result in a thick litter layer on the forest
floor, thus blocking regeneration of other species (Torti
et al. 2001).
Many monodominant tropical species are ectomy-
corrhizal (Newbery et al. 1998, but see Torti & Coley
1999) which may enable them to acquire nutrients more
efficiently than their non-ectomycorrhizal competitors,
especially on poor soils. Early studies also suggest that
high soil toxicity, shallow soils or low nutrient levels can

312 NIC VAN DER VELDEN ET AL.
contribute to monodominance when a species is more
stress-tolerant than its competitors (Ashton 1971, Davis
&Richards1934). However, in contrast to these intuitive
observations,nosignificantdifferences have beenfoundin
soil-bound nutrients between monodominant forest and
adjacent mixed forest (Hart et al. 1989, Martijena 1998,
Nascimento et al. 1997,Pehet al. 2011b).
Clearly, monodominance on well-drained soils in the
tropics is complex and likely to be caused by a combination
of mechanisms (Peh et al. 2011a). So far, most of the
recent discussions of monodominance in tropical forests
have mainly focused on a few species in Africa and the
Neotropics (but see Hart et al. 1989 for older reports
from Asia). This study focuses on Parashorea chinensis,a
dipterocarp monodominant species in South-West China.
Parashorea chinensis dominates the canopy in patches
that are up to several hectares in size, surrounded by a
matrix of mixed forest. Historically shifting cultivation
was practised in the region leading to a mosaic of forests
in different successional stages. Here we evaluate the
potential causes for P. chinensis monodominance and
test the following hypotheses: (1) The understorey of
monodominant patches is floristically different from the
mixed forest, and P. chinensis dominance will result in
reduced species richness; (2) monodominant patches are
structurally different from mixed forest (because of the
large size of P. chinensis monodominant patches will
have higher basal area and mean stem diameter); (3) P.
chinensis distribution is driven by edaphic conditions, and
since it is mainly present in valleys and slopes, it is likely to
favour soils with a higher fertility; and (4) alternatively,
monodominant patches are remnants of primary forest
surrounded by secondary mixed forests that established
on former agricultural fields.
METHODS
Study site and species
Research was carried out in the tropical seasonal rain
forest of Xishuangbanna (21°3642N, 101°3426E) in
Yunnan Province, South-west China. This region has a
monsoonal climate with a mean annual precipitation of
1493 mm y−1of which about 80% falls between May
and October. The area is characterized by steep hills,
ranging between 500 and 2500 m asl, and contains for
the largest part laterite soils, developed from siliceous rock
that are typically red with a thin humus horizon and a pH
of 4.5–5.5 (Cao et al. 2006). The seasonal rain forest is
at the northern and altitudinal limits of tropical lowland
forest in Asia (Zhu et al. 2006) and it is dominated by
species from the Rubiaceae, Lauraceae, Euphorbiaceae,
Annonaceae and Moraceae (Zhu 2006). There are few
Dipterocarpaceae species, but they dominate the canopy
where they are present.
Parashorea chinensis H. Wang is an emergent tree that
can attain a height of 60 m and a maximum diameter of
1.5 m. It is generally restricted to mountain slopes, valleys
and hills, and dominates in patches ranging from 0.5 to
several hectares in size.
Floristic plots
To analyse differences in structure, species richness,
composition and edaphic conditions between monodom-
inant forest and mixed forest, 28 20 ×20-m plots were
established; 14 in monodominant patches and 14 in the
mixed forest adjacent to the patches. Twenty-two plots
were established in the 20-ha permanent forest dynamics
plot of the Centre for Tropical Forest Science (CTFS) in
Xishuangbanna, and six additional plots were established
just outside the CTFS plot. Since we had permission to
work in and around the CTFS plot, but not in the larger
forest reserve, we were able to include two independent
Parashorea chinensis patches only. The patches consisted
of several sub-patches due to the strong habitat preference
of Parashorea for lower slopes. We designed our plot
sampling in such a way that we covered as much of this
sub-structure as possible. The CTFS plot is divided into
subplots of 20 ×20 m. The scientific name, diameter at
breast height (dbh) and location of each woody plant ࣙ1
cm is known, as well as the slope and elevation of each
subplot. Monodominant patches in the CTFS plot were
identified by mapping all P. chinensis individuals >10 cm
dbh in ArcGIS and plots were selected where two or
more individuals were present. Mixed-forest patches were
selected adjacent to the monodominant plots, i.e. between
20 and 60 m from the monodominant plots, and when
possible at similar elevation. For the six additional plots
the dbh was measured for each tree and the species were
identified. Trees ࣙ5 cm dbh were measured in the whole
plot, whereas saplings (1–5 cm dbh) were measured in
a cross-sectional transect (2.6 m wide) running through
each subplot. A minimum of 25 saplings were measured
in each plot. Leaf samples were taken and species were
identified at the XTBG herbarium (HITBC).
Soil samples
Top soil layers are often strongly affected by the vegetation
growing on top of them, potentially leading to correlation
between soil measurements and species composition
(Duivenvoorden 1995). To reduce this risk we sampled
below the top soil layer in the mineral soil at a depth of
25–40 cm using a soil auger. Five samples were taken in
the centre and the four corners of each subplot, and then

Parashorea chinensis monodominance 313
bulked to one sample. Chemical and physical analyses
were done at the Chinese Academy of Sciences. Particle
size was measured using the pipette method (LY/T 1225–
1999) and then classified into clay (<0.002 mm), silt
(>0.002 to <0.02 mm) and sand (>0.02 mm). Soil
pH was determined by potentiometry with a soil : water
solution (1 : 2.5). Concentrations of total Ca, Al, Mg,
S, Fe, Mn and Na were determined using a digestion
with HClO4–HF. Total N and C were measured with a
Macro Elemental Analyzer. Available P was extracted by
0.03 mol L−1NH4F–0.025molL
−1HCl and determined
by colorimetry. Available K was extracted with 1 mol L−1
CH3COONH4(pH =7.0). Finally, presence or absence
of charcoal in the samples was recorded to determine
presence or absence of past human land use which
involved the use of fire for forest clearance.
Data analysis
To describe differences in forest structure between
the monodominant and mixed patches, a size class
distribution was made for each patch type using 10 dbh
classes of 10 cm width (ࣙ5cmto<15 cm, ࣙ15 cm
to <25 cm, etc., with the last class being ࣙ95 cm).
Subsequently a t-test was applied to each size class to
evaluate whether monodominant and mixed patches had
a different tree density per size class. To evaluate whether
P. chinensis dominance negatively affected species
richness, diversity and species evenness, Shannon–
Weaver’s, Simpson’s and Fisher’s alpha indices were
calculated for each plot. These indices were calculated
using the formulas provided in the package VEGAN 2.0
in R 2.13.1 (CRAN core-development team).
Differences in species composition between monodom-
inant and mixed patches were analysed using the relative
importance value (RIV) (Cottam & Curtis 1956). RIV is
defined as the sum of the Relative Dominance (Rdom),
Relative Density (Rden) and Relative Frequency (Rfreq)
(Appendix 1) and was calculated per species for each forest
type for the tree layer (ࣙ5 cm dbh) and the sapling layer
(1–5 cm dbh). The maximum RIV is 300. Correlation
between plot RIV scores of P. chinensis and soil variables
were made to examine whether P. chinensis dominance
was related to edaphic and environmental conditions.
The floristic composition of the plots was analysed
with a detrended correspondence analysis (DCA) using
CANOCO for Windows 4.5. The analysis was based on
the abundance of the species and was done separately
for trees and saplings. Environmental variables and
edaphic variables were added later to the DCA, to
explore the relationships between floristic composition
and the abiotic environment. Student’s t-tests were
done on the plot scores of the first two axes, to
evaluate whether the monodominant and mixed patches
differed significantly in species composition. Additionally
a constrained Canonical Correspondence Analysis with
a forward selection procedure with permutation tests
was done, to evaluate which soil variables significantly
explain variation in species composition. Differences
in structure, species richness, species composition and
edaphic conditions between monodominant and mixed
patches were analysed using t-tests. All statistical
analyses were performed using SPSS 17.0 (SPSS Inc.,
Chicago, IL).
RESULTS
Floristics
On average the monodominant plots had a similar
number of species per plot (23.1) as the mixed plots
(24.8) for the tree layer, but significantly more species
(14.9 versus 12.2) per plot in the sapling layer
(Table 1). Diversity (Fisher’s alpha, Shannon–Weaver
and Simpson’s index) was similar for the two forest
types, but correlated negatively with a continuous
measure (RIV) of P. chinensis dominance, when only
the monodominant patches were considered (Figure 1;
Pearson’s r Shannon–Weaver =−0.65, P =0.01; r Fisher’s alpha
=−0.60, P =0.02; r Simpson’s index =−0.59, P =0.03,
n=14 in all cases).
Structure
Stem density varied strongly ranging from 37 to 78
stems per plot. However, tree and sapling density did
not differ significantly between forest types (Table 1).
Both forest types showed a negative exponential diameter
distribution (Figure 2a). There were significantly fewer
trees present in the first diameter class (5–15 cm dbh) of
the monodominant forest (t =2.47, P =0.02) whereas
tree density in the second to sixth classes was statistically
similar. Mean dbh was significantly higher and basal
area tended to be higher in monodominant compared
with mixed patches (Table 1). Diameter distribution of P.
chinensis in the monodominant patches also showed a
negative exponential distribution (r2=0.83, P <0.001,
n=10 diameter classes), with the exception of the second
diameter class (15–25 cm), which contained more trees
than expected (Figure 2b).
Relative importance
Parashorea chinensis was present in 14 plots with a total of
160 individuals making it the second-most commonly
observed species (Figure 3). Relative importance value

314 NIC VAN DER VELDEN ET AL.
Table 1. Summary of stand characteristics, tree species richness and diversity indices of
monodominant and mixed forest plots (20 ×20 m) in a tropical seasonal rain forest of
Xishuangbanna, China. Values are given separately for trees (ࣙ5 cm dbh) and saplings (dbh
1–4.9 cm). Values are mean ±SE, n =14 for both forest types. For N trees and species richness
the total number of trees and species is indicated in parentheses. Differences between the forest
types where tested using a student’s t-test (P <0.05).
Forest type
Monodominant Mixed t P
Trees
N trees 58.1 ±2.9 (816) 64.4 ±2.6 (902) −1.6 0.13
Diameter at breast height (cm) 14.8. ±0.5 13.1 ±0.4 3.1 0.002
Basal area (m2) 1.89 ±0.2 1.43 ±0.1 1.9 0.07
Species richness 23 ±1.7 (120) 24.6 ±2.1 (137) −0.6 0.56
Fisher’s alpha 14.9 ±1.7 17.5 ±3.7 −0.6 0.54
Shannon–Weaver 2.6 ±2.3 2.6 ±0.1 0.2 0.83
Simpson’s index 0.9 ±0.1 0.9 ±0.3 1.1 0.3
Saplings
N saplings 152.9 ±8.1 (350) 137.6 ±9.8 (350) 1.2 0.24
Species richness 14.9 ±0.7 (89) 12.2 ±0.9 (88) 2.3 0.03
Fisher’s alpha 17.7 ±2.2 11.8 ±2.3 1.8 0.08
Shannon–Weaver 2.4 ±0.1 2.1 ±0.1 1.8 0.07
Simpson’s index 0.9 ±0.01 0.8 ±0.03 1.7 0.1
(RIV) demonstrated differences in the composition of the
most dominant species between the forest types. Of the
10 species that were most dominant in each forest type,
only three species (Pittosporopsis kerrii Craib, Baccaurea
ramiflora Lour. and Garcinia cowa Roxb. ex Choisy)
were common to both monodominant and mixed forest
(Figure 3, Appendix 2). In the monodominant patches, P.
chinensis clearly had the highest RIV (70), whereas the
other species were much less dominant (RIV <22). In the
mixed forest the most dominant species was Castanopsis
echinocarpa Miq. (RIV =35) and the RIV scores of the
species were much more evenly distributed, indicating the
absence of a clear dominant species. Pittosporopsis kerrii
dominated the sapling layer in both forest types (RIV is
55 in monodominant vs. 72 in mixed forest), with P.
chinensis being the second-most dominant species in the
monodominant patches. Surprisingly, the sapling layer
of the mixed patches was strikingly more monodominant
than the sapling layer of the monodominant patches, and
also contained P. chinensis as the third-most dominant
species (Figure 3).
Species composition
The floristic composition of plots was described with
a Detrended Correspondence Analysis (DCA) for trees
(Figure 4) and for saplings (Appendix 3). The first axis
of the analysis based on trees explained 13.7% of the
variation in species composition, and the second axis
5.5%. The first axis was positively associated with C : N
ratio (Pearson’s r =0.68) and negatively associated
with Mn (r =−0.69) and the second axis was positively
associated with slope (r =0.35) and negatively associated
with Mn (r =−0.39). The monodominant forest plots had
significantly lower scores on the first axis (t =4.89, n =
28, P <0.001) and the second axis (t =2.14, n =28, P =
0.04) (Figure 4). A Canonical Correspondence Analysis
with forward regression procedure confirmed that species
composition of the trees was significantly explained by
C : N ratio (F =13, P =0.002), followed by Mn (F =1.54,
P=0.006) and slope (F =1.35, P =0.05). These three
factors alone explained 17.6% of the variation in species
composition.
The DCA for the saplings generated similar results to the
DCA for trees (Appendix 3). The two forest types differed
significantly in their scores on the first axis (t =−3.5, n
=28, P =0.002) and the second axis (t =−2.1, n =28,
P=0.04). The first axis was positively associated with Mn
(Pearson’s r =0.68) and negatively associated with C : N
ratio (r =−0.70), and the second axis was negatively
associated with slope (r =−0.41) and clay (r =−0.31).
The ordination plot scores of the trees and the saplings
were significantly correlated (first axis, r =−0.80, P ࣘ
0.01, second axis; r =−0.38, P ࣘ0.044), indicating that
speciescompositionofthe tree andsaplinglayer resembled
each other, and that floristic differences between the forest
types will persist in future when saplings recruit into the
tree layer.
Edaphic conditions
Soil texture consisted mostly of sand (49%) with smaller
proportions of silt (18%) and clay (30%). The two forest
types did not differ significantly in soil texture (Table 2).

Parashorea chinensis monodominance 315
R² = 0.42
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
020406080100120
Shannon-Weaver
R² = 0.37
0
5
10
15
20
25
30
0 20 40 60 80 100 120
Fisher's alpha
R² = 0.34
0.0
0.2
0.4
0.6
0.8
1.0
1.2
020406080100120
Simpson's index
RIV Parashore a (%)
a)
b
)
c
)
*
*
*
Figure 1. Relationships between diversity indices and the relative
importance values (RIV) of Parashorea chinensis in a tropical
seasonal rain forest of Xishuangbanna. Regression line, coefficient of
determination, and significance are shown for Shannon–Weaver vs RIV
(a), Fisher’s alpha vs RIV (b) and Simpson’s index vs RIV (c). Filled dots
indicate the monodominant forest plots (n =14) and open dots indicate
the mixed forest plots (n =14). For Fisher’s alpha one mixed-forest plot
with an extreme value (62) is not shown.
Monodominant patches had significantly higher pH
(4% higher), Mn concentration (100% higher) and K
concentration (29% higher) compared with the mixed
forest. Mn concentrations in the monodominant patches
were twice (0.34 g kg−1vs. 0.17 g kg−1) those of the mixed
forest. Monodominant patches also had a significantly
Figure 2. Tree diameter distributions in a tropical seasonal rain forest in
Xishuangbanna. Tree density-size distributions of monodominant forest
(dark bars) and mixed forest (hatched bars) (a). Size classes are in 10-cm
dbh intervals starting at 5 cm dbh, i.e. 10 indicates the diameter class
5–15 cm. Note that the y-axis has a log10-scale. Diameter distribution of
Parashorea chinensis in the monodominant patches (b). The regression
line indicates a negative exponential distribution (R2=0.83, P <0.001,
n=10 diameter classes).
lower organic carbon concentration (15% lower), and
therefore also a lower C : N ratio (12% lower). The other
nutrients did not differ significantly between the two forest
types. Charcoal was found twice as often (85% vs. 43% of
the plots) in mixed compared with monodominant plots,
but this was not significantly different (χ2=2.29, P =
0.13). A quick visual analysis of the soil pits showed, in
both forest types, a high variation of the depth where
charcoal was located. The local dominance (RIV) of P.
chinensis was positively correlated to Mn (Pearson r =
0.62, n =28, P <0.001) and K (r =0.42, P =0.028,
n=28) but not related to any of the other soil variables
or geographic variables (elevation and slope).

316 NIC VAN DER VELDEN ET AL.
Figure 3. Relativeimportance value (RIV) of the 10 most important tree species in a tropical seasonal rain forest of Xishuangbanna. RIV is calculated
for trees (ࣙ5 cm dbh) and saplings (1–4.9 cm dbh) in monodominant (a, c) and mixed forest (b, d). To calculate the RIV all 14 plots per patch type
were pooled.
DISCUSSION
The aim of this study was to evaluate to what
degree P. chinensis patches differ from the surrounding
forests, and to investigate the underlying mechanisms
explaining these differences. The monodominant patches
were indeed structurally and floristically different from
the surrounding mixed forest. Parashorea chinensis
dominance led to reduced species diversity and
monodominant patches were, surprisingly, associated
with more fertile soils, in contrast to current paradigms
about monodominance in the tropics.
Are Parashorea chinensis patches structurally different?
We hypothesized that monodominant patches would be
structurally different from the mixed forest, because of the
large size of P. chinensis. We indeed found that P. chinensis
patches had a larger average stem diameter, and tended to
have a larger basal area. Parashorea chinensis patches had,
compared with the mixed forest, relatively many large
trees and a paucity of trees in the smallest size class. Field
observations also suggest that P. chinensis patches were
taller and had a more heterogeneous canopy structure.
Possibly, shading by these large overstorey trees may
have led to less light and reduced tree regeneration in
the understorey. Similarly, more large trees were present
in the monodominant Gilbertiodendron dewevrei (De Wild.)
J. Leonard forest in central Africa (Hart et al. 1989)and
the Peltogyne gracipiles Ducke forest in Brazil (Nascimento
et al. 1997), compared with neighbouring mixed forest. It
is possible that tall tree species that can attain the same
maximum height as P. chinensis are absent from the mixed
forest, or only found in low densities (Zhu 1992), perhaps
because our study area is at the northern limit of the
tropical rain-forest zone. Large-tree species that dominate
the mixed forest, such as Elaeocarpus varunua Buch.-Ham.
ex Mast., Castanopsis hystrix Hook. f. & Thomson ex
DC., Pometia pinnata J.R. Forst. & G. Forst., Mezzetiopsis

Parashorea chinensis monodominance 317
Figure 4. DetrendedCorrespondence Analysis of the floristic composition of trees (ࣙ5 cm dbh) in monodominant patches (triangles) and mixed-forest
patches (crosses) in a tropical seasonal rain forest of Xishuangbanna. Arrows show the axis loadings of geographic variables (elevation, slope), soil
texture (sand, silt, clay) and edaphic conditions (pH, C, P, K, N, Al, Fe, Mg, Mn, Na and C : N ratio). The presence of charcoal is indicated with a box.
Outer boundaries of the two forest types are indicated with lines and show the overlap between the two forest types.
creaghii Ridl. and Cinnamomum tenuipile Kosterm. reach
maximum heights of up to 45 m which is substantially
lower than the maximum height of P. chinensis that can
grow up to 60 m.
Both the monodominant patches and mixed forest
showed a negative exponential size distribution. We used
stem diameter as an indicator of tree age as thicker
trees tend to be older on average, although there is a
wide scatter around this relationship (Brienen & Zuidema
2006, Condit et al.1998). The size distribution may
therefore give a first indication of the regeneration
behaviour of the species, but this should be confirmed by
dynamic data. In general, the negative exponential size
distribution indicates that both forest types have a healthy
population structure with continuous recruitment (cf.
Bongers et al. 1988). Parashorea chinensis itself also
followed a negative exponential population structure,
which indicates that it is a shade-tolerant species (Wright
et al.2003). Interestingly, the second diameter class
contained more individuals than expected; perhaps
reflecting a recent regeneration wave, as P. chinensis
is a mast-fruiting species. Chien et al.(2008) found a
similar negative exponential distribution for P. chinensis
in Vietnam and showed with matrix models that it had
a stable population. It can therefore be assumed that
the local dominance of P. chinensis in Vietnam and
South-West China is persistent. Seeds of P. chinensis will
germinate and are able to persist under the canopy of the
monodominant patches and the mixed forest. Juvenile
traits such as relatively large seeds, shade tolerance
and ectomycorrhizal associations give it a better chance
of survival under nutrient-limited or shaded conditions
(Connell & Lowman 1989). Parashorea chinensis is able
to establish in both the monodominant and the mixed
forest. However, in the mixed forest it seems not to be able
to grow beyond the sapling stage, as larger individuals are
almost completely absent from the mixed forest. This may
be attributed to the lower soil fertility and drier conditions
in the mixed forest. Alternatively, P. chinensis patches may
have only recently started expanding in the mixed forest.
Do Parashorea chinensis patches differ in species
composition and diversity?
Boundaries of the P. chinensis patches are abrupt
and particularly visible when the emergent trees are
flowering. This degree of dominance was also reflected
in the importance value of P. chinensis in the patches
with RIV scores of P. chinensis far exceeding values of
other species. We hypothesized that monodominance
would lead to a reduced species diversity, simply because
the monodominant species makes up most of the
community biomass. Monodominant wet tropical forest
often shows significant lower species richness compared
with the adjacent mixed forest (Connell & Lowman
1989,Hartet al. 1989,Henkel2003, Martijena &
Bullock 1994,Newberyet al. 1998). Surprisingly, in
our study there was no significant difference in average
species richness and diversity between the two forest

318 NIC VAN DER VELDEN ET AL.
Table 2. Comparisons of soil texture and edaphic conditions of the
monodominant and mixed forest plots in a tropical seasonal rain forest
of Xishuangbanna. Values are mean ±SE, n =14 for both forest types.
The results of a t-test, the t value, and significance (P) are shown. df =
26 except for K (df =21.4 based on a t-test with unequal variances).
Forest type
Variable Monodominant Mixed t P
Sand (%) 50.1 ±1.9 48.3 ±1.9 0.66 0.513
Silt (%) 19.9 ±0.8 18.8 ±1.1 0.81 0.422
Clay (%) 28.4 ±1.6 31.6 ±1.4 −1.50 0.144
pH 4.9 ±0.06 4.7 ±0.04 2.26 0.032
Al (g kg−1) 41.3 ±1.8 41.9 ±1.5 0.24 0.810
Ca (g kg−1) 0.25 ±0.01 0.21 ±0.02 1.65 0.112
C(gkg
−1) 7.9 ±0.5 9.3 ±0.4 2.22 0.035
C:N ratio 8.5 ±0.3 9.7 ±0.4 2.44 0.022
Fe (g kg−1) 23.1 ±0.9 24.1 ±0.8 0.82 0.418
K (mg kg−1) 120 ±10.3 93.4 ±6.2 2.26 0.034
Mg (g kg−1) 4.9 ±0.3 4.7 ±0.3 0.33 0.741
Mn (g kg−1) 0.34 ±0.03 0.17 ±0.03 3.52 0.002
N(gkg
−1) 0.91 ±0.03 0.95 ±0.03 0.86 0.396
Na (g kg−1) 0.6 ±0.01 0.58 ±0.02 0.96 0.344
P (mg kg−1) 1.3 ±0.2 1.3 ±0.2 0.08 0.937
S(gkg
−1) 0.05 ±0.004 0.04 ±0.005 0.97 0.342
types, however, all diversity indices were significantly
negatively correlated with P. chinensis dominance (RIV)
within the monodominant patches. Parashorea chinensis
patches also had a different species composition compared
with the mixed forest, both for the tree and sapling
layers and the two forest types had few dominant species
in common. This difference is likely associated with
differences in edaphic conditions between P. chinensis
patches and mixed forest.
Is monodominance associated with soil fertility?
Since P. chinensis is mainly present in valleys and slopes
(Cao et al. 2008) we hypothesized that monodominance is
favoured by soils with a higher fertility and/or wetter soil
conditions. Monodominant patches had indeed slightly
higher pH in combination with a substantially higher Mn,
K and modestly lower C and C : N ratio compared with the
mixed forest. A high pH and low C : N ratio is often an
indicator of a higher overall soil fertility.
Parashorea chinensis responded strongly to manganese.
Manganese is an essential micronutrient that is involved
in the light reaction of photosynthesis, and acts as a
cofactor in 35 enzymes (Marschner & Marschner 2012).
Manganese (Mn2+) becomes available when Mn reserves
in the soil (MnO2) or unavailable forms of Manganese
(Mn3+) are reduced (Hue et al.2001). This occurs
especially in acid soils (pH <6) and poorly drained,
anaerobic soils. Under these conditions Mn may become
toxic, leading to leaf chlorosis and necrosis, and a reduced
uptake of Ca and Mg (Barker & Pilbeam 2007,Hueet al.
2001). Species may vary tremendously in their tolerance
to manganese (Marschner & Marschner 2012). Given the
fact that P. chinensis is dominant in acid, waterlogged
patches with high Mn concentrations, it may be that P.
chinensis can attain dominance because it is tolerant to
Mn, whereas the other species are not.
Potassium is involved in fine-tuning the stomatal
aperture, and hence, in reducing water loss from leaves
(Benlloch-Gonz´
alez et al. 2008). This may especially be
important for an emergent tree species like P. chinensis,
which has its exposed crown above the canopy, where it
faces dry conditions due to high wind speed, high vapour
pressure deficits, and a long water transport pathway
from the soil to the leaves. The higher water requirement
that comes along with being an emergent tree, may also
explain why P. chinensis is associated with valleys and
slopes which typically have higher soil water potentials
(Markesteijn et al. 2010).
With plant-soil associations it is always difficult to
disentangle cause and effect. Trees do not only respond
to soil, but they can also modify soil nutrient composition
to their own benefit (Wardle et al. 2004). For example,
three monodominant ectomycorrhizal species in Korup,
Cameroon, enhanced soil phosphorus concentrations
through their litter input (Newbery et al.1997). We feel
that our results reflect tree responses to soil conditions as
soil nutrients were not determined near the soil surface
(where trees would have the largest modifying impact),
but at deeper soil layers (25–40 cm depth). However,
only (reciprocal transplanting) experiments (Ashton et al.
2006, Baltzer et al.2005) can definitely show how trees
respond to soil conditions. An experimental study in a

Parashorea chinensis monodominance 319
Panamanian rain forest confirms that K may indeed play
an important role; 8 y after NPK fertilization in the forest
understorey, seedling growth is strongly increased by K
addition, whereas N and P have only an effect when
applied together (Santiago et al.2012).
In combination, our results suggest that despite its
ectomycorrhizal status, P. chinensis prefers fertile soils,
either because of higher water and nutrient requirements,
because it tolerates higher levels of Mn, or because it
will be outcompeted by other species under drier and/or
infertile soil conditions. This contradicts the popular
theory that monodominant species occur mostly on
infertile soils where they can outcompete other species.
In Ituri, monodominant forest had lower levels of soil
nitrogen concentrations (Torti et al. 2001) and deep-soil
K(Hartet al. 1989) compared with the neighbouring
mixed forest. But overall, most studies do not find
conclusive evidence that specific soil conditions lead to
monodominance (Martijena 1998, Nascimento & Proctor
1997,Pehet al. 2011a, Torti et al. 2001), with the
exception of a study in Africa, which showed that three
co-dominant Caesalpinoids were found on P-richer soils.
Are Parashorea chinensis patches remnants of old-growth
forest?
Many hypotheses regarding monodominance focus on
disturbance as an explanatory factor. Monodominance
of shade-tolerant climax species can arise because of a
prolonged absence of exogenous disturbance (Hart et al.
1989), whereas monodominance of light-demanding
pioneer species can arise because of recent large-scale
disturbances (Wyatt-Smith 1954). We hypothesized that
disturbances can shape monodominant P. chinensis
patches by affecting the surrounding forest, but not
the patches themselves, i.e. P. chinensis patches could
be the remnants of old-growth forest in a matrix of
disturbed (shifting-cultivation) forest. The high number
of large trees and the tendency of a higher basal area in
the monodominant patches favour this hypothesis. One
way to assess past human disturbance is by measuring
charcoal in the soil (Van Gemerden et al. 2003). Charcoal
was indeed more frequently found in mixed forest,
but this difference with monodominant forest was not
significant. Therefore, it remains uncertain whether the
monodominant patches are the result of anthropogenic
disturbance in the surrounding matrix. Finally, it should
be said that, although this old-growth forest remnant
hypothesis may explain the size and position of the
patches, and why they contrast with the surrounding
forest matrix, it does not explain why P. chinensis is
monodominant.
In sum, P. chinensis patches are both floristically and
structurally different from the surrounding mixed forest.
In contrast to current paradigms, this monodominant
species is not associated with infertile, but with fertile soils.
Parashorea chinensis seems to be especially associated with
manganese, and with edaphic conditions (water, K) that
allow this tall and exposed emergent species to maintain
its water balance, something that is of critical importance
for an emergent species in a strongly seasonal forest at the
northern edge of the tropical biome.
ACKNOWLEDGEMENTS
This research could not have been completed without the
help and efforts of the people at the Plant geography lab
at XTBG (Chinese Academy of Sciences), Kingsly Beng,
Liu JiaJia, Yu Fei and Lu Yun, and logistic support of the
Xishuangbanna Ecological Field Station. We thank two
anonymous reviewers for their helpful comments on the
manuscript.
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Parashorea chinensis monodominance 321
Appendix 1. Method of calculating the relative importance value (RIV) of a species importance
in a tropical seasonal rain forest of Xishuangbanna. The RIV is calculated as the sum of the
relative dominance (Rdom), relative density (Rden) and the relative frequency (Rfreq).
Relative Importance Value (RIV) RIV =Rdom +Rden +Rfreq
Rdom =Relative dominance Rdom =BA sp./ BA all sp. ×100%
Rden =Relative density Rden =N individuals of a sp. / tot. N individuals ×100%
Rfreq =Relative frequency Rfreq =freq. of a sp. / sum freq. all sp. ×100%
Appendix 2. Summary of the top ten most important species based on relative importance value of two forest types in a seasonal rain forest
of Xishuangbanna. Upper part: top ten of the most important species of trees ࣙ5 cm dbh of the two forest types. Lower part: top ten most
important species of saplings ࣙ1 cm–5 cm in dbh. Rdom =relative dominance, Rden =relative density, Rfreq =relative frequency, RIV =
relative importance value.
Trees Rdom Rden Rfreq RIV Trees Rdom Rden Rfreq RIV
1. Parashorea chinensis
H.Wang
46.70 19.4 4.35 70.4 1. Castanopsis echinocarpa Miq. 22.56 10.6 2.03 35.2
2. Pittosporopsis kerrii Craib 2.07 15.7 4.35 22.1 2. Pittosporopsis kerrii Craib 3.45 19.7 3.78 27.6
3. Baccaurea ramiflora Lour. 2.16 6.00 3.73 11.9 3. Garcinia cowa Roxb. ex
Choisy
3.57 8.65 3.78 16.0
4. Knema furfuracea (Hook. f.
& Thomson) Warb.
2.15 4.41 3.42 9.98 4. Castanopsis hystrix Hook. f.
& Thomson ex A. DC.
8.08 2.00 2.03 12.1
5. Garcinia cowa Roxb. ex
Choisy
1.75 3.19 3.73 8.66 5. Baccaurea ramiflora Lour. 1.33 3.55 2.33 7.21
6. Mezzettiopsis creaghii Ridl. 1.04 4.17 2.48 7.69 6. Phoebe sp. A 0.79 4.21 2.03 7.04
7. Castanopsis indica (Roxb. ex
Lindl.) A.DC.
4.03 1.10 1.86 7.00 7. Alseodaphne sp. A 4.82 0.55 1.16 6.53
8. Pometia pinnata J.R. Forst. &
G. Forst.
3.79 1.35 1.55 6.69 8. Cinnamomum bejolghota
(Buch.-Ham.) Sweet
1.88 2.00 2.62 6.49
9. Sloanea hainanensis Merr. &
Chun
2.90 1.59 1.55 6.04 9. Aporusa yunnanensis (Pax &
K.Hoffm.) F.P.Metcalf
1.32 2.00 2.33 5.64
10. Chisocheton siamensis
Craib
0.97 1.96 3.11 6.04 10. Sapium baccatum Roxb. 4.31 0.44 0.58 5.34
Saplings Saplings
1. Pittosporopsis kerrii Craib 24.95 23.7 6.70 55.4 1. Pittosporopsis kerrii Craib 36.03 28.9 7.56 72.4
2. Parashorea chinensis
H.Wang
11.55 12.0 6.22 29.8 2. Garcinia cowa Roxb. ex
Choisy
7.02 8.00 5.81 20.8
3. Saprosma ternatum (Wall.)
Hook.f.
5.19 6.00 5.26 16.5 3. Parashorea chinensis
H.Wang
2.75 6.29 3.49 12.5
4. Knema furfuracea (Hook.f. &
Thomson) Warb.
2.58 4.00 3.83 10.4 4. Baccaurea ramiflora Lour. 3.60 3.43 4.07 11.1
5. Mezzetiopsis creaghii Ridl. 3.44 2.86 3.35 9.65 5. Phoebe sp. A 3.18 2.57 3.49 9.24
6. Baccaurea ramiflora Lour. 2.27 2.86 3.35 8.48 6. Knema furfuracea (Hook.f. &
Thomson) Warb.
2.44 3.14 3.49 9.07
7. Nephelium sp. A 2.98 1.71 2.39 7.09 7. Dichapetalum gelonioides
(Roxb.)Engl.
2.95 2.29 2.91 8.14
8. Dichapetalum gelonioides
(Roxb.) Engl.
2.60 2.00 2.39 7.00 8. Phoebe minutiflora H.W.Li 1.82 1.71 2.91 6.44
9. Garcinia cowa Roxb. ex
Choisy
2.19 2.29 2.39 6.87 9. Saprosma ternatum (Wall.)
Hook.f.
1.79 1.71 2.91 6.42
10. Cryptocarya acutifolia
H.W.Li
2.41 1.43 1.91 5.75 10. Castanopsis echinocarpa
Miq.
2.02 1.71 1.16 4.90

322 NIC VAN DER VELDEN ET AL.
Appendix 3. Detrended Correspondence Analysis of the floristic composition of saplings (1–4.9 cm dbh) in monodominant patches (triangles) and
mixed forest patches (crosses). Arrows show the axis loadings of geographic variables (elevation, slope), soil texture (sand, silt, clay) and edaphic
conditions (pH, C, P, K, N, Al, Fe, Mg, Mn, Na and C :N ratio). The presence of charcoal is indicated with a box. Outer boundaries of the two forest
types are indicated with the lines and show the overlap between the two forest types.