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Dispersal traits determine passive restoration trajectory of a Nigerian montane forest



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Original article
Dispersal traits determine passive restoration trajectory of a Nigerian
montane forest
Andrew D. Barnes
, Hazel M. Chapman
School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
Systemic Conservation Biology, J.F. Blumenbach Institute of Zoology and Anthropology, University of Göttingen, Berliner Strasse 28,
37073 Göttingen, Germany
article info
Article history:
Received 7 February 2014
Accepted 25 February 2014
Available online
Community assembly
Fruit traits
Passive restoration
Seed dispersal
Passive restoration methods offer great promise for tropical regions where resources are limited but the
success of such efforts can be variable. Using trait-based theory, we investigated the likely trajectories of
passive restoration efforts in a degraded Nigerian montane forest system recently protected from
burning and cattle grazing. We quantied the density, species richness, and functional trait dispersion of
dispersed seeds and seedling communities at increasing distances from the forest edge. We then
determined which plant traits are responsible for colonisation by quantifying changes in functional-trait
dispersion and relative frequencies of dispersal-linked traits with increasing distance from the forest. We
found a rapid decrease in density and species richness, and signicant species turnover in both seeds and
seedlings just beyond the forest edge. This was mirrored by a signicant decline in functional-trait
dispersion and a shift in the relative frequencies of dispersal-linked traits. These ndings suggest that
the reassembly of plant communities adjacent to remnant forest is dependent on functional traits pre-
sent in these remnant source populations, providing support for the incorporation of trait-based theory
in restoration management.
Ó2014 Elsevier Masson SAS. All rights reserved.
1. Introduction
Throughout the tropics, anthropogenic pressures have led to
such severe forest loss and degradation (Asner et al., 2009; Geist
and Lambin, 2002) that there is now a global effort towards their
restoration (Chazdon, 2008; Holl, 2012) and the return of
ecosystem goods and services to local communities (Benayas et al.,
2009; Lamb et al., 2005). Activerestoration strategies, where
intervention techniques are used to re-establish forest, can be
costly and impractical in areas where community involvement is
essential but resources are very limited (Holl and Aide, 2011;
Parrotta et al., 1997). Alternatively, passiverestoration strategies,
which involve only the restriction or total prevention of land-use
practises from degraded land, are more easily employed and
require minimal resources (Holl and Aide, 2011; Morrison and
Lindell, 2011).
Although potentially useful, passive restoration can be very slow
and often ineffective depending on landscape and ecological con-
ditions (Duncan and Chapman, 1999; Laing et al., 2011; Myster,
2004). Factors such as insufcient seed rain (Cubiña and Aide,
2001; Duncan and Chapman, 1999; Martínez-Garza and Howe,
2003; Muñiz-Castro et al., 2006), seed bank composition
(Kalesnik et al., 2013), seed and seedling predation (Myster, 2004;
Nepstad et al., 1990), lack of suitable microsites for germination
(Eriksson and Ehrlén, 1992), and competition from grasses
(Chapman and Chapman, 1999; Duncan and Chapman, 1999) can
collectively hinder forest regeneration. Moreover, passive strategies
can lead to undesirable trajectories of ecosystem restoration
because they are highly dependent on the potential for natural seed
dispersal from nearby remnant habitat (Cole et al., 2011; del Castillo
and Ríos, 2008; Martínez-Garza and Howe, 2003). For example
(Kalesnik et al., 2013) showed that after 30 years of abandonment,
commercial forests of exotic willow and poplar in Argentina
remained mixed secondary forest with a high frequency of invasive
The likelihood of forest tree species dispersing into and estab-
lishing within adjacent degraded habitat is highly variable and
depends on a wide array of measurable factors including fruit and
*Corresponding author. Systemic Conservation Biology, J.F. Blumenbach Institute
of Zoology and Anthropology, University of Göttingen, Berliner Strasse 28, 37073
Göttingen, Germany. Tel.: þ49 551 395040.
E-mail address: (A.D. Barnes).
Contents lists available at ScienceDirect
Acta Oecologica
journal homepage:
1146-609X/Ó2014 Elsevier Masson SAS. All rights reserved.
Acta Oecologica 56 (2014) 32e40
seed traits (Cole, 2009; Dosch et al., 2007; Ingle, 2003; Muller-
Landau et al., 2008; Muñiz-Castro et al., 2006; Teegalapalli et al.,
2010). Seed traits have also been shown to be important for
determining the success of propagules from seed banks, which may
explain further variation in the reassembly of regenerating plant
communities (Pywell et al., 2003). However, despite the wealth of
evidence illustrating the importance of plant traits in mediating
community assembly (Cornwell and Ackerly, 2009; Shipley et al.,
2006), the role that fruit and seed traits play in determining
dispersal of propagules into adjacent regenerating habitats and
their germination potential at the early colonisation stage still re-
quires further investigation (Lebrija-Trejos et al., 2010). This is
especially necessary in African forests where, to our knowledge,
there have been no studies that have identied the trait de-
terminants of both seed dispersal distances and resulting seedling
establishment with increasing distance from remnant forest sys-
tems into adjacent grassland.
Here we go beyond differentiating between seed size, wind and
animal dispersal (Cubiña and Aide, 2001; Duncan and Chapman,
1999; Muñiz-Castro et al., 2006; Teegalapalli et al., 2010), and in
addition include dispersal traits such as fruit colour and fruit type,
which may affect frugivore choice (Gautier-Hion et al., 1985b) and
even secondary dispersal (Babaasa et al., 2004). To detect the role of
dispersal-linked traits in shaping assembly trajectories of forest
regeneration, we rst measured the potential for seed dispersal and
seedling establishment from nearby remnant-forest habitat into
grassland recently protected from cattle grazing and burning.
Secondly, we quantied the dependence of seed rain and seedling
species functional-trait composition on the distance from these
remnant forests. As such, this study aims to provide an indication of
the potential for using dispersal-linked traits in the prediction of
restoration trajectories for future passive-restoration attempts in
Afromontane forests.
2. Methods
2.1. Study site
The study was conducted at Ngel Nyaki Forest Reserve on the
Mambilla plateau in Taraba State, Nigeria. The plateau is part of the
Cameroonian Highlands Ecoregion (Olson et al., 2001). Ngel Nyaki
reserve covers a total area of 4600 ha and includes 750 ha of
continuous forest embedded within a savannah-grassland land-
scape (Beck and Chapman, 2008; Chapman and Chapman, 2001).
The forest is mid-altitude to sub-montane at 1400e1600 m asl
(Chapman and Chapman, 2001), the mean annual rainfall is
approximately 1800 mm (Nigerian Montane Forest Project [NMFP]
rainfall data) and the mean monthly maximum and minimum
temperatures for the wet and dry seasons are 26e13
C, and 23e
C, respectively (Matthesius et al., 2011).
Since the 1950s, when cattle grazing pressure became severe on
the Mambilla Plateau (Bawden and Tuley, 1966), areas of over-
grazed grassland dominated by Sporobolus pyramidalis and Hyper-
rhenia rufa have been created within Ngel Nyaki forest by the
annual res lit by Fulani pastoralists to clear forest and stimulate
grass growth in the grasslands around the forest perimeter. Fires
run down grassy spurs leading into the forest and penetrate the
forest edge so that, over time, forest gaps comprising overgrazed
grassland have been created. These grassland areas are predomi-
nantly grassland with a scattering of tall herbs including Dissotis
species (Melastomaceae), Ocimum gratisimum and O. basilicum
(Lamaceae) and Guizotia species (Asteraceae). Small shrubs of
Maesa lanceolata and Psorospermun febrifugum were occasionally
present in all sites. As part of an initiative to promote forest
regeneration, in 2006 we established fences and re breaks across
the opening of these grassland areas where the pasture penetrates
into the forest to prevent further livestock and re encroachment.
The grassland sites described in this study had therefore all been
free of grazing and burning for four years. The sites were at least
1000 m apart, located around the perimeter of Ngel Nyaki forest.
2.2. Quantication of seed rain and seedling establishment
Sampling was carried out within four grassland areas that
ranged in size from ca 4400 m
to ca 8800 m
, dispersed
throughout Ngel Nyaki forest. Within each of the four areas, ve
sampling transects were established, spaced 10 m apart, at least
10 m from the fence-line and at least 30 m from the forest edge at
the end of the grassland area undergoing restoration (Fig. 1). Each
transect consisted of eight seed traps, spaced equidistantly at 5 m
intervals, from 5 m within the forest edge to 30 m out from the edge
in the adjacent grassland (Fig. 1). The edge (0 m) was dened as the
drip line of the outermost canopy trees at the forest perimeter. Seed
traps consisted of a 0.5 0.5 m piece of mesh netting held 0.3 m
above the ground with a wooden frame in order to prevent the
surrounding vegetation from interfering with seeds falling into the
traps and were protected by chicken wire to prevent the removal of
seeds by seed predators.
All seed traps were visited weekly over a ve year period from
January 2006 to December 2010, upon which all seeds found within
the traps were counted and identied to the species level. In the
most recent year of sampling (2010), we sampled seedling estab-
lishment across all trap locations whereby all trees and
shrubs 1 m tall and present within 2 m in any direction from a
seed trap (an area of approximately 12.5 m
) were counted and
Fig. 1. Layout of the four sampling-point transects in the regenerating grassland sites.
Values marked on the transects indicate the distance from the forest edge with
negative values used to denote sampling points within the forest and 0to denote the
forest edge.
A.D. Barnes, H.M. Chapman / Acta Oecologica 56 (2014) 32e40 33
identied to species. We then calculated the number of seeds and
seedlings m
to obtain a standardised measure of density.
2.3. Measurement of traits and functional dispersion
Traits that may contribute to the dispersal and recruitment
success of a species were obtained from the Nigerian Montane
Forest Project fruit database. Seed size was approximated by seed
diameter in mm and fruit traits included three categorical traits
that characterised the fruit: dispersal mode, colour, and type
(Table A.1). For dispersal mode, we specied whether the fruit is
ballistic, wind dispersed, gravity dispersed, and small (<10 mm
diameter) or large (>10 mm diameter) endozoochorous. Classi-
cation of fruit into small and large zoochorous was aimed at dis-
tinguishing between seeds that were dispersed by small and large
animal dispersers (Wheelwright, 1985); specically, we assumed
that the large fruit could only be taken by primates and hornbills,
whereas the small zoochorous fruit could be taken by all bird dis-
persers and also primates. Fruit colour was assessed by observation
to give a potential indication of both the attractiveness of fruits to
animal dispersers and the type of animal disperser likely to be
attracted (Gautier-Hion et al., 1985a; Willson and Whelan, 1990).
Fruit type provided a proximate morphological description by
indicating whether the fruit is a capsule, pod, winged, drupe, or
berry (Table A.1).
To determine if there was a community-wide shift in the
dispersion of seed and fruit traits between the forest and adjacent
regenerating grassland, we calculated a distance-based metric of
trait dispersion FDis(Functional Dispersion)using the FDpackage
(Laliberte and Legendre, 2010) in R 3.0.1 (R Development Core Team,
2013). The FDis metric takes into account multiple traits of species
within a community and measures the distance of each species to
the trait-mean centroid of the whole community. It is a multivariate
adaptation of weighted-mean absolute deviation where the
weighting is given by the relative abundance of species (Laliberte
and Legendre, 2010). Therefore, FDis is a weighted measure of trait
variation among species ina given community. As such, this measure
provided an indication of the potential for trait-based ltering in
seed rain and seedling establishment into the adjacent grassland.
2.4. Statistical analysis
We analysed density, species richness, and functional dispersion
in seed rain and seedling communities as non-linear functions of
distance from the forest edge into the adjacent grassland using
Generalised Additive Mixed Models (Wood, 2011) using the mgcv
package in R 3.0.1 (R Development Core Team, 2013). Seed-trap
observations were nested within site (n¼4) as random effects in
order to take into account the hierarchical layout of the sampling
design and avoid pseudoreplication (Zuur, 2009). To account for
non-normality and heterogeneity of variance, we modelled re-
sponses of seed and seedling densities and species richness on a
Negative Binomial distribution, which also accounts for over-
dispersion in the data (Zuur, 2009). We optimised smoothing pa-
rameters by selecting models based on the generalised cross-
validation (GCV) criterion, whereby a lower GCV indicates lower
prediction error (Wood, 2011). As the GCV criterion has a tendency
to over-tting, we applied a penalty on each degree of freedom,
whereby each effective degree of freedom (edf) was forced to be
counted as 1.4 degrees of freedom in the GCV criterion (Kim and Gu,
To test for spatial turnover in species relative abundances for
dispersed seeds and seedling communities, we rst calculated the
dissimilarity of species composition between sampling points using
a log-base ten Modied-Gower distance metric (Anderson et al.,
2011) with the veganpackage in R 3.0.1 (R Development Core
Team, 2013). Modied-Gower dissimilarity considers an order-of-
magnitude change in abundance (e.g., from 0.01 to 0.1) equal to a
change in composition (i.e. from 0 to 1 species), which therefore
accounts for changes in relative abundance of species in addition to
changes in the community composition per se (Anderson et al.,
2006). Compositional dissimilarity between the forest and adja-
cent grassland was visualised using non-metric multidimensional
scaling (NMDS) ordination. We then tested to see if the composi-
tional dissimilarity between samples could be explained by the
distance of the sampling point from the forest using a permuta-
tional distance MANOVA. Distance to the forest edgewas included
as a continuous predictor, with site(n¼4) specied as the strata
within which to constrain permutations, thus avoiding pseudor-
eplication resulting from the nested sampling design.
In order to quantify the trait determinants of community as-
sembly with increasing distance from the forest, we adopted a
multivariate approach for categorical variables whereby individuals
were coded by their relative functional trait values as opposed to
their taxonomic classication. With these data, we calculated
resemblance matrices derived from the Gower dissimilarity metric
as this measure can deal with categorical variable types and is not
affected by missing values (Laliberte and Legendre, 2010). From
these resemblance matrices, we performed a permutational
MANOVA for each categorical trait (i.e. fruit type, dispersal mode,
and fruit colour), with distance to the forest edgeas a continuous
predictor and siteas a blocking factor, totest the effect of distance
from the forest edge on both seed rain and seedling community
trait-based compositional dissimilarity. For seed diameter, a
continuous variable, we used Generalised Additive Mixed Effects
Models to test for the effect of distance from the forest edge on
community-weighted mean seed diameter with seed-trap obser-
vationsnested within siteas random effects.
3. Results
3.1. Rapid decline in seed and seedling density across the forest edge
From ve years of seed trapdata we recorded a total of 6332seeds
comprising 31 species of trees and shrubs. We recorded a total of
2010 seedlings from 30 species across all sampling transects
(Table 1). 71% of these seedling species were also present in the seed
trap data. There was a signicant decline in seed-rain density from
the remnant forest into the grassland (edf ¼5.701; P<0.001), with a
98% average decrease in seeds per m
from the forest edge to 30 m
into the grassland (Fig. 2a). This considerable decline in seed density
with increasing distance into the grassland was mirrored by a 96%
decrease in seedling densities (edf ¼6.177; P<0.001; Fig. 2b). These
observed declines were only evident up to 10 m into the grassland,
reaching asymptote beyond this point. Likewise, our results showed
that the number of species from the seed rain data also declined
strongly with increasing distance from the forest (a 92% decrease;
edf ¼1.4 2 2; P<0.001; Fig. 2c) and the same trend was followed by
the number of seedling species (an 83% decrease; edf ¼1; P<0.001;
Fig. 2d). In contrastto the density responses, species richnessshowed
a more continuous decline with increasing distance from the edge,
without reaching any clear asymptote within the 30 m range
sampled. This was especially evident in seedling species richness,
which showed no departure from a linear relationship (edf ¼1).
3.2. Distance from source populations drives species composition
and a decline in functional dispersion
The NMDS visualisation indicated that the decrease in seed and
colonising plant densities with increasing distance from the forest
A.D. Barnes, H.M. Chapman / Acta Oecologica 56 (2014) 32e4034
was not equally distributed among species. This was suggested by
the gradient of increasing compositional dissimilarity from the
forest to adjacent grassland (Fig. B.1), indicating an overall shift in
speciesrelative abundances for seed rain and seedling commu-
nities. Furthermore, the permutational multivariate ANOVA
revealed a highly signicant effect of distance from the forest edge
on the dissimilarity of seed species composition (F¼6.574,
P<0.001) and the same was found for seedling communities
(F¼12.390, P<0.001). Interestingly, we found that distance from
the forest explained considerably more variation in seedling
composition (R
¼0.127) compared to seed rain composition
With the signicant decline in seed rain and seedling estab-
lishment away from the forest, we also found a decline in the range
of trait composition. In particular, there was a signicant decline in
functional trait dispersion (FDis) from the forest to the adjacent
grassland (edf ¼4.182; P<0.001; Fig. 3a). While this was also the
case for seedling communities (edf ¼1; P<0.001; Fig. 3b), the
degree of change in the functional trait dispersion of communities
was greater for seed rain composition than for establishing plant
communities (86% compared to only 75% decline for seed rain and
seedlings, respectively), with the greatest rate of change in FDis
within 10 m of the forest edge for the seed rain.
3.3. Trait-based ltering of propagules determines composition of
colonising plant communities
Community-weighted mean seed diameter did not signicantly
respond to the distance from forest edge for either seed rain
(edf ¼1; P¼0.749) or seedling communities (edf ¼1.507;
P¼0.331) and appeared to vary idiosyncratically with increasing
distance from the edge (Fig. B.2a and b). However, for all three
categorical traits (i.e. fruit type, dispersal mode, and colour) there
were clear changes in the relative proportion of traits with
increasing distance from the forest edge. In particular, fruit
dispersal mode in the seed rain data signicantly responded to
distance from the forest (F¼7.420, R
¼0.078, P<0.001) with
wind, small zoochorous and large zoochorous fruited species such
as Combretum molle, Bridelia speciosa, and Landolphia landolphioides
respectively, having the highest dispersal potential beyond w20 m
(Fig. 4c, Table 1). Furthermore, there was a signicant effect of
distance on seed rain community dissimilarity based on fruit type
(F¼9.132, R
¼0.094, P<0.001) and colour (F¼5.306, R
P<0.001), whereby seed from drupes and capsules were most
likely to reach distances up to 30 m, with red and blue fruits
having the highest frequency of dispersal to greater distances
(Fig. 3e and g).
Table 1
List of all species and associated families found in samples with the total number of individuals recorded from seed traps and seedling plots for distance categories: 5to0m,
5e15 m, and 20e30 m from the forest edge.
Family Species Seeds Seedlings
5 to 0 m 5 to 15 m 20 to 30 m 5 to 0 m 5 to 15 m 20 to 30 m
Mimosaceae Albizia gummifera 4541
Caesalpiniaceae Anthonotha noldeae 48 9 43 23 13
Euphorbiaceae Bridelia speciosa 2474 126 355 153 48 20
Meliaceae Carapa oreophylla 51 1
Cannabaceae Celtis gomphophylla 1
Oleaceae Chionanthus africanus 1
Rutaceae Clausena anisata 100 1 9 241 3
Combretaceae Combretum molle 66 31 4 1 2
Euphorbiaceae Croton macrostachyus 1
Sapindaceae Deinbollia pinnata 10 60
Ebenaceae Diospyros sp.127 595 5
Malvaceae Dombeya ledermannii 53 45 1
Meliaceae Entandrophragma angolense 22 1 96
Mimosaceae Entada abyssinica 25 3 1
Myrtaceae Eugenia gilgii 23 4
Clusiaceae Garcinia smeathmanii 7
Annonaceae Isolona deightonii 95 7
Apocynaceae Landolphia landolphioides 270 22 3
Leeaceae Leea guineensis 137 8 150 16 1
Myrsinaceae Maesa lanceolata 274 4
Mimosaceae Newtonia buchananii 61 35 123 13
Buddlejaceae Nuxia congesta 111 9 4 10 2
Rubiaceae Oxyanthus recemosus 15
Mimosaceae Parkia licoidea 1
Sapindaceae Paullinia pinnata 40 13
Araliaceae Polyscias fulva 127 2 10 2
Sapotaceae Pouteria altissima 129
Clusiaceae Psorospermun febrifugum 60533885018
Rubiaceae Psychotria sp.435 28 4
Rubiaceae Psychotria succulenta 413 5 107 48 6 146
Apocynaceae Rauvola vomitoria 7
Malvaceae Sterculia setigera 16
Olacaceae Strombosia scheferi 16
Clusiaceae Symphonia globulifera 7
Sapotaceae Synsepalum sp.3
Myrtaceae Syzygium guineense
sub sp. guineense
276 8 3 24 8 1
Ulmaceae Trema orientalis 103 96
Moraceae Trilepesium madagascariense 22
Rutaceae Zanthoxylum leprieurii 1
A.D. Barnes, H.M. Chapman / Acta Oecologica 56 (2014) 32e40 35
In contrast to the seed rain data we found that along with small-
zoochorous and wind-dispersed propagules, ballistic propagules
(mainly from the species Anthonotha noldeae and Dombeya leder-
mannii) also made it to larger distances and successfully germi-
nated (Fig. 3d, Table 1) with an overall signicant effect of distance
from the forest on relative abundances of fruit dispersal modes
(F¼15.354, R
¼0.153, P<0.001). We also found highly signicant
effects of the distance from the forest edge on trait-based compo-
sitional dissimilarity for fruit type (F¼12.702, R
P<0.001) and colour (F¼11.067, R
¼0.115, P<0.001) in seedling
communities. Whilst dispersed seedlings from drupes were still the
most frequent across all distances, we found that seedlings from
species such as A. noldeae and C. molle with pods and winged
propagules were also present at greater distances, albeit in low
Fig. 3. Generalised additive mixed models demonstrating the relationships between distance from the forest edge and functional trait dispersion (FDis) for seed-rain (a) and
seedling communities (b). Smoothed lines are tted values and shaded area is the 95% condence interval. R
is the proportion of explained deviance. Negative and positive x-axis
values denote forest and matrix, respectively, with 0 to denote the edge.
Fig. 2. Generalised additive mixed models demonstrating the relationships between distance from the forest edge and density (abundance m
) of seeds (a) and seedlings (b), and
the number of species recorded from the seed-rain (c) and seedling data (d). Smoothed lines are tted values and shaded area is the 95% condence interval. R
is the proportion of
explained deviance. Negative and positive x-axis values denote forest and matrix, respectively, with 0 to denote the edge.
A.D. Barnes, H.M. Chapman / Acta Oecologica 56 (2014) 32e4036
frequencies (Fig. 3f, Table 1). However, seedlings from red and blue
fruits remained the most frequent across all distances from the
forest edge.
4. Discussion
4.1. What is the likelihood of success for passive restoration
attempts in Afromontane forests?
Our study demonstrates that dispersal-linked traits mediate the
reassembly trajectory of regenerating plant communities under-
going passive restoration following severe human-induced land-
scape degradation. Through a combination of ecological lters such
as dispersal limitation and factors inhibiting germination, our re-
sults suggest that simply protecting cleared areas of West African
montane forest from burning and cattle grazing will not lead
directly to the rapid reassembly of forest communities, but instead
to communities dominated by tree and shrub species characterised
by small, eshy, red or blue drupes mainly dispersed by birds and
primates. However, mostly within this functional group we found
much more potential for forest regeneration in seed rain and early
seedling establishment than has been recorded elsewhere in Africa
(Duncan and Chapman, 1999). We found seedlings in the grassland
up to 30 m away from the forest edge of grassland trees and shrubs
such as D. ledermannii and Psorospermun febrifugum, forest-edge
tree species including Eugenia gilgii and Nuxia congesta and the
large, leguminous forest tree species Albizia gummifera and
Anthonotha noldeae.
Of those seed species recovered from the traps, only 71% were
present as seedlings, and of those seedlings found beyond ve m
Seed rain
Type (proportion)
−5 0 5 10 15 20 25 30
Distance from edge (m)
Color (proportion)
−5 0 5 10 15 20 25 30
Distance from edge (m)
(a) (b)
(c) (d)
(e) (f)
Fig. 4. Relative proportions of dispersal mode categories for seed rain (a) and seedlings (b), frequencies of fruit type categories for seed rain (c) and seedlings (d), and frequencies of
fruit colours for seed rain (e) and seedling communities (f). Legend abbreviations for dispersal categories are: ballistic (B), gravity (G), large zoochorous (LZ), small zoochorous (SZ),
and wind (W). Fruit types are: berry (B), capsule (C), drupe (D), pod (P), and winged (W). Proportion areas for fruit colour are indicated by their actual colour. X-axis values of 5 and
0 denote 5 m within the forest and the forest edge, respectively.
A.D. Barnes, H.M. Chapman / Acta Oecologica 56 (2014) 32e40 37
from the forest edge, over 90% germinated from small, eshy
drupes. The 29% of seed species found in traps but never as seed-
lings comprised a wide range of seed types and their apparent lack
of regeneration is presumably explained by a combination of post
dispersal factors such as unsuitable microsites and seed predators
(Chapman and Chapman, 1999), competition from grasses such as
the introduced Sporobilis sp. and Hyperrhenia sp.(Chapman and
Chapman, 2001) and drought during the six month dry season
(NMFP rainfall records). Additionally, while there may be sufcient
seed dispersal and even germination of forest plant species, there
are likely to be other barriers limiting their recruitment, such as the
requirement of larger established trees for colonizing vine species
like Landolphia landolphioides (Table 1).
Seed rain density declined dramatically only just beyond the
forest edge, indicating that the matrix is important for mediating
rates of dispersal across the forestegrassland interface (Barnes
et al., 2014; Holl, 2012). Relatively high numbers of dispersed
seed were still found 5 m out from the forest edge, but beyond this
point seed densities dropped to only 2% of the densities found
under the forest canopy within 5 m of the forest edge. While
densities of animal dispersed seeds appeared to remain relatively
constant beyond 5 m out from the forest edge, even at the
maximum distance measured of 30 m, this was not the case for
wind dispersed seed which had dropped off dramatically ten m into
the grassland. Such a rapid decrease in density of wind dispersed
seed is to be expected and has been recorded in previous studies
from the Neotropics (Cubiña and Aide, 2001; Holl, 1999) and dry
forest in India (Teegalapalli et al., 2010). In regard to animal
dispersed seed our ndings suggests that in these regenerating
grasslands, which are often no wider than 60 m, regardless of the
distance from the forest edge we can expect equal densities of seed
rain from the adjacent forest.
In addition to the decline in seed and seedling densities, we
found that there was signicant turnover in species composition
with increasing distance from the forest edge, despite the relatively
ne-scale gradient of 5 m incremental changes in distance. For
example, seedlings of pioneer species with small, eshy fruit such
as Bridelia speciosa and Psychotria succulenta became relatively
more common with distance from the forest edge relative to forest
species such as Pouteria altissima and Deinbollia pinnata, which
have larger, green fruit. While it is possible that recruitment is
strongly limited after seedlings germinate due to factors such as
those described above (Duncan and Chapman, 1999; Holl, 1999;
Nepstad et al., 1990) our ndings suggest that in naturally regen-
erating West African montane systems, dispersal limitation may be
playing an important role in the early stages of community reas-
sembly, even across small spatial scales.
4.2. Can fruit and seed traits predict restoration outcomes?
From these ndings, the question arises as to which factors are
determining the varying levels of dispersal limitation. The answer
may be pivotal to understanding how forest communities are likely
to reassemble during passive restoration efforts. We found that
from the four selected dispersal-linked trait measures used, in
almost all instances they changed in relative frequency with
increasing distance away from the parent populations. Most
obvious was the nding that seed from fruits that were small-
zoochorous red drupes were dispersed relatively more often and
in greater quantities across most distances and were found at least
up to distances of 30 m more frequently than any other propagules.
These results point to the importance of traits that are linked to
avian dispersal as these would be among the most attractive fruit to
such dispersers (Duncan and Chapman, 1999; Willson and Whelan,
1990). However, birds are known to be extremely habitat selective
and have been found not to contribute usefully to seed rain in forest
regeneration elsewhere in Africa (Duncan and Chapman, 1999).
While investigation of the role of birds in dispersing seeds into
these grasslands is currently underway at Ngel Nyaki, the fact that
such fruits are also dispersed by several primate species including
tantalus monkeys (Chlotocebus tantalus), which regularly enter and
feed in grassland (Agmen et al., 2010), may explain the pattern of
seed rain we observed. Moreover, our nding that seed diameter
appeared to be of little importance for the dispersal potential of
seeds and germination of seedlings with increasing distance from
the forest edge is also most likely explained by primate dispersal as
the wider gape of primates relative to passerine birds allow them to
swallow larger seed (Jordano et al., 2007). While such ndings are
also in contrast to previous Neotropical studies (Cubiña and Aide,
2001; Holl, 1999) they are similar to those of Teegalapalli et al.
(2010) who investigated the dispersal of large seed from Indian
dry forest into pasture related to grazing patterns of large
mammalian frugivores.
A particularly interesting nding was the relatively high density
of seedlings from ballistic-dispersed seeds across larger distances
from the forest, despite relatively lower numbers within the forest
sampling points. For example the very large, nutritious seeds of
Anthonotha noldeae were rarely found in seed traps beyond 5 m into
the grassland, yet seedlings were found up to 30 m away from the
forest edge. Such a pattern is indicative of dispersal by secondary
seed dispersers such as scatter-hoarding rodents (Nyiramana et al.,
2011). While not included in this study, we have observed a similar
phenomenon in Carapa oreophylla whose seedlings establish many
metres from the forest edge (personal observation). Wind was also
found to be a successful mode of dispersal for trees to colonise
these grasslands as both seed and/or germinating seedlings from
wind/winged classed species, such as Albizia gummifera,Com-
bretum molle and Entandrophragma angolense, were found at low
but relatively consistent numbers across all distances.
4.3. Applications for trait-based theory in habitat restoration
By quantifying patterns in functional trait dispersion and
changes in community trait composition of seeds and seedlings
across the interface of remnant forest and passively regenerating
grassland, this study shows that regenerating plant communities
undergo trait-based ltering, which appears to increase in intensity
with increasing distance from the forest. Despite the strong
ltering of species dispersing into these adjacent grasslands, the
somewhat high density and diversity of germinating seedlings in-
dicates that there is still promise for passive restoration efforts in
Afromontane forest landscapes. It must be noted, however, that this
study has only taken into account a relatively short time-scale of
regeneration time (over just 5 years) and therefore provides insight
into the initial recolonisation process. It is likely that over a much
greater time-scale there may be rare, chance dispersal events that
result in the dispersal of important pioneer species into these
regenerating communities which may in fact catalyse the restora-
tion process (Rodrigues et al., 2004). Furthermore, there is evidence
in the Afrotropics that regeneration can be arrested due to dispersal
limitation and/or the competitive dominance of other non-forest
species (Babaasa et al., 2004; Duncan and Chapman, 1999). Still,
our study provides a characterisation of the early recolonisation
processes that are likely to take place in passive restoration at-
tempts, which is important for identifying the mechanisms that can
potentially lead to undesirable restoration trajectories.
While previous studies have shown that plant traits play an
important role in later phases of community assembly within
passively restored habitats (Muñiz-Castro et al., 2006; Pywell et al.,
2003) we still lack an understanding of how these traits determine
A.D. Barnes, H.M. Chapman / Acta Oecologica 56 (2014) 32e4038
community reassembly at the initial stages of habitat regeneration.
This study highlights the value of quantifying these trait de-
terminants so that they can be utilised to gain a priori knowledge of
the potential for success and likely trajectory of passive restoration
efforts, depending on the functional-trait composition of nearby
parent populations. Therefore, we recommend that future attempts
to passively restore tropical forests should rst quantify the po-
tential for species to colonise target-restoration areas from nearby
remnant forests by utilising the libraryof functional traits found
within these communities.
We thank the Taraba State Forest Service for inviting us to work
in Ngel Nyaki Forest, Usman Abubakar for assistance in the eld,
and the other Nigerian Montane Forest Project staff for logistical
support at the NMFP eld station. Kristy Udy, Laura Young, and the
Chapman lab group provided invaluable comments on earlier drafts
of the manuscript. We also thank two anonymous reviewers for
providing comments and suggestions that substantially improved
this paper. The study was funded by the North of England
Zoological Society (Chester zoo), Nexen Inc. and the A. G. Leventis
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
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... Natural regeneration through dispersal of fruits and seeds plays a vital role in the restoration of threatened forest landscapes. Studies have shown that Afro-tropical montane forests are one of the most threatened landscapes due to their uniqueness and rarity (Geist and Lambin, 2002; Barnes and Chapman, 2014). ...
... Seed dispersal by animals provides a wide range of benefits to the tree whose seeds they disperse. A plant may benefit from dispersal in one or more ways (Barnes and Chapman, 2014). Un-dispersed seeds typically fall beneath the parent and for many species the probability of survival beneath the parent is low due to density and distance dependent mortality (Chapman and Chapman 1999;Barnes and Chapman, 2014;Aliyu et al., 2014). ...
... A plant may benefit from dispersal in one or more ways (Barnes and Chapman, 2014). Un-dispersed seeds typically fall beneath the parent and for many species the probability of survival beneath the parent is low due to density and distance dependent mortality (Chapman and Chapman 1999;Barnes and Chapman, 2014;Aliyu et al., 2014). Seed dispersal may benefit whole plant communities by promoting species diversity and the formation of diverse local seedling assemblages, which may reduce competition, increase seedling survival through diversity dependent effects (Aliyu et al., 2014;Barnes and Chapman, 2014). ...
Full-text available
Montane habitats are generally rare and disproportionately distributed around the world; and are rich in biodiversity with a high concentration of endemic species of conservative interest. These rare forests are highly threatened and their remnants are often surrounded by deforested landscapes typically dominated by high human population. These high concentrations of humans within and around these unique landscapes often exert undue pressures on the fragile ecosystem leading to habitat degradation and species loss. Restoration through dispersal actions by some vertebrates is therefore crucial to the survival of these threatened landscapes. Individuals each of Agelanthus brunneus and Globimetula braunii were monitored on different host tree species at both forest edge and fragments to record various avian dispersers. A total of 13 bird species, from 11 genera and 10 families were recorded, with only four species (African thrush, African green pigeon, Yellow rumped tinker bird, and Western green tinker bird) identified as mistletoe dispersers. Yellow rumped tinker bird was the most dominant disperser and moved the highest number (70) of seeds. Avian species abundance in concert with host-mistletoe pair combinations partially predicted species' relative contributions to fruit dispersal of the two mistletoe species.
... Our overall hypothesis in this study is that Afromontane forest tree species, being pre-adapted to change , will, in the presence of isolated grassland trees and protected from fire, disperse into grassland and establish relatively quickly. We add to the Barnes and Chapman (2014) study from montane Nigeria by investigating the role of isolated trees and identifying key frugivores in forest restoration. Specifically, we ask: a) How does seed rain and seedling establishment differ away from and under isolated grassland trees? ...
... The arrival of the Bantu farmers from Cameroon over a thousand years ago (Zeitlyn & Cambell, 2003), followed by the arrival of Fulani cattle herders around the 1930's (Hurault, 1998), has led to almost complete loss of forest and wide expanses of degraded grassland. Since 2006, areas of this grassland surrounding Ngel Nyaki forest have been fenced-off and protected from grazing and burning as part of the conservation effort led by the Nigerian Montane Forest Project (NMFP) (Barnes & Chapman, 2014). Within just a couple of years of protection from grazing and burning, Sporobolus grassland is replaced with a rich grassland flora including species of Hyparrhenia, Ludetia, Leptaspis, and Andropogon grasses and woody herbs of Dissotis, Vernonia, and Protea (Barnes & Chapman, 2014). ...
... Since 2006, areas of this grassland surrounding Ngel Nyaki forest have been fenced-off and protected from grazing and burning as part of the conservation effort led by the Nigerian Montane Forest Project (NMFP) (Barnes & Chapman, 2014). Within just a couple of years of protection from grazing and burning, Sporobolus grassland is replaced with a rich grassland flora including species of Hyparrhenia, Ludetia, Leptaspis, and Andropogon grasses and woody herbs of Dissotis, Vernonia, and Protea (Barnes & Chapman, 2014). Evidence of forest recovery is slower. ...
Restoration of Afromontane forests is critical because of their biodiversity richness and ecosystem service provision. With an evolutionary history of rapid forest migration into grassland in response to shifting climate, traits of Afromontane forests such as a high frequency of light tolerant, small fruited, and bird dispersed species may pre‐adapt them to relatively rapid recolonization of grassland protected from fire. Here, we test this hypothesis with a focus on the role of isolated grassland tree species in promoting forest regeneration. Through seed, seedling, and frugivore surveys, we found that seed rain below small, isolated grassland trees was almost 300 times that in open grassland, with 30 times more seedlings established under trees. However, these seedlings were mostly grassland or forest edge woody shrubs or small trees. Dispersal limitation was moderate to high and establishment limitation high for all other species. Ecological filtering of seed species favored some over others, which needs further exploration. Key tree traits attracting frugivore visits were distance from forest edge, height, and “leaflessness.” Across a year of sampling almost 90% of frugivore visits to isolated trees were by just two grassland / forest edge species, the common bulbul Pycnonotus barbatus (71%) and the speckled mouse bird Colius striatus (17%). Overall, our results suggest that while anthropogenic changes within Afromontane systems render any pre‐adaption Afromontane forests may have to rapid reestablishment of forest into grassland ineffectual, small, isolated grassland trees are nevertheless critical for the first stage of succession. We tested the hypothesis that Afromontane forests are pre‐adapted to rapidly regenerate into grasslands. On the contrary, we found extreme dispersal and establishment limitation of tree species in grassland. One species, the common bulbul (Pycnonotus barbatus) is responsible for vast majority of seeds dispersed.
... Outside of the plot, this grassland is heavily grazed by cattle and annually burnt by the Fulani pastoralists. Edge effects are consequently severe (Barnes & Chapman, 2014) and lianas such as Clerodendrum bucholzii, Thunbergia sp, Psydrax acutifolia, and Landolphia spp are common throughout the canopy (Chapman & Chapman, 2001). ...
... The answer for Ngel Nyaki forest remains to be determined. Tropical montane forest populations are recognized as being less fecund than lowland populations but given the large fruit crops of many species such as Anthonotha noldeae (Barnes & Chapman, 2014) and Pouteria altissima (Matthesius et al., 2011), as well as the mid-rather than high elevation location of this site, lack of sufficient seeds seems unlikely. To what extent lianas are depressing fruit production has been shown elsewhere (García León et al., 2018) but needs testing at this site. ...
Predicting how forest species composition may change in response to global change is essential for meaningful management. Which species are most likely to successfully recruit depends on a multitude of factors, but processes operating at the seed‐to‐seedling transition being especially important. Here, we explore how insufficient seed dispersal (dispersal limitation) and ecological filtering of seedlings (establishment limitation) influence species recruitment in an Afromontane Forest. We combined census data from seeds in seed traps and seed‐seedling transition plots in a Nigerian montane forest to measure dispersal and establishment limitation across species, life history strategies, and seed sizes. From 106 seed traps and 318 seedling plots, we recorded 11,278 seeds from 38 species and 2688 seedlings of 61 species. All species except for one liana showed strong dispersal limitation while 23 out of the 30 species showed establishment limitation. The two lianas sampled had significantly lower dispersal limitation compared to the trees investigated in the study. Our results suggest that both dispersal and establishment limitation are markedly high in this Afromontane forest than would be expected in a lowland counterpart. Which species are most likely to successfully recruit depends on a multitude of factors, but with processes operating at the seed‐to‐seedling transition being especially important. In this study, we explore how insufficient seed dispersal (dispersal limitation) and ecological filtering of seedlings (establishment limitation) influence species recruitment in an Afromontane Forest. Our results suggest that both dispersal and establishment limitation are markedly high in this Afromontane Forest than would be expected in a lowland counterpart.
... As part of this many studies specifically mentioned facilitation processes which ameliorate micro-environmental site conditions and often contributed to increased restoration success 54,104,174,175 . Facilitative interactions were deliberately employed in restoration studies, e.g. through applied nucleation tree island planting 11,172 , exotic plantations to recover native understories 129 , bracken ferns as facilitators for late succession tree seedlings 128 or planting to attract seed dispersers 120,140,141,172 . Moreover, site management variables related to removing disturbance, such as eradication of invasive species 84,176 , and protection of restoration sites 6,177 were mentioned as promoting success. ...
Full-text available
Many tropical mountain ecosystems (TME) are severely disturbed, requiring ecological restoration to recover biodiversity and ecosystem functions. However, the extent of restoration efforts across TMEs is not known due to the lack of syntheses on ecological restoration research. Here, based on a systematic review, we identify geographical and thematic research gaps, compare restoration interventions, and consolidate enabling factors and barriers of restoration success. We find that restoration research outside Latin-America, in non-forested ecosystems, and on socio-ecological questions is scarce. For most restoration interventions success is mixed and generally limited by dispersal and microhabitat conditions. Finally, we propose five directions for future research on tropical mountain restoration in the UN decade of restoration, ranging from scaling up restoration across mountain ranges, investigating restoration in mountain grasslands, to incorporating socioeconomic and technological dimensions. Tropical mountain ecosystems (TME) are hotspots of biodiversity 1,2 and endemism 3 and are located in tropical latitudes between 1000 and 4000 m asl, and the elevation gradients give rise to a variety of ecosystems including montane forests, montane cloud forests, forest-grassland treelines, mountain grasslands and azonal formations (Table 1). TME span across all continents in the tropical belt, and despite their small spatial extent of just over 4 million km 2 (Table 1) they provide numerous ecosystem services to people and society, including carbon sequestration, water regulation and supply, timber and food provision, erosion control, and cultural services 4. Notwithstanding their tremendous biological importance and complexity, TME are still relatively under-studied compared to temperate mountain systems 5. In recent decades, TME have been experiencing increasing pressure from multiple external drivers and stressors, such as anthropogenic pressures due to agricultural encroachment, pasture conversion and population growth 6 , exotic plantations 7,8 , invasion by exotic animals 9 and exotic plants 10-12 , as well as accelerating climate change impacts 13. These drivers lead to severe degradation in TME, impacting all levels of ecological organization, such as disruption of ecosystem services, losses in community diversity, changes in species interactions, reductions of population sizes and lowered genetic diversity 14. Degradation in TME is far-reaching and ubiquitous: Tovar et al. 15 projected that climate change will alter 3-7% of tropical Andean biomes, resulting in a 31.4% loss in extent of high-altitudinal Páramo grasslands due to replacement by montane forests by 2039. Further, Helmer et al. 16 indicate that in the next 25-45 years, reductions in cloud immersion are estimated to diminish 57-80% of Neotropical montane cloud forests. Hall et al. 17 estimate that the Tanzanian Eastern Arc mountains have lost 25% of forested areas since 1955, with deforestation rates of 57% in sub-montane forests (800-1200 m). At the same time, socioeconomic drivers have led to migrations of people from tropical mountains to urban areas, abandoning many previously cultivated and inhabited areas 24-26 and creating a large opportunity for ecosystem recovery and restoration across many TME. Restoration of biodiverse ecosystems, such as TME, has the potential to simultaneously recover lost biodiversity and ecosystem functioning and improve local livelihoods 27 , and has recently come to the fore of global conservation efforts 28. Restoration is defined as "the process of assisting the recovery of an ecosystem that has been degraded, damaged or destroyed" 29 and, as such, encompasses a broad suite of approaches ranging from passive restoration, to assisted recovery and active restoration. The urgency for global restorative actions culminated in global restoration pledges like the 2011 Bonn Challenge and the proclamation of the UN Decade of Ecosystem Restoration. Motivations to restore damaged ecosystems include conserving biodiversity (specific habitats or species), enhancing ecosystem processes (such as nutrient cycling), combatting climate change (through carbon OPEN
... As part of this many studies specifically mentioned facilitation processes which ameliorate micro-environmental site conditions and often contributed to increased restoration success 54,104,174,175 . Facilitative interactions were deliberately employed in restoration studies, e.g. through applied nucleation tree island planting 11,172 , exotic plantations to recover native understories 129 , bracken ferns as facilitators for late succession tree seedlings 128 or planting to attract seed dispersers 120,140,141,172 . Moreover, site management variables related to removing disturbance, such as eradication of invasive species 84,176 , and protection of restoration sites 6,177 were mentioned as promoting success. ...
Full-text available
Many tropical mountain ecosystems (TME) are severely disturbed, requiring ecological restoration to recover biodiversity and ecosystem functions. However, the extent of restoration efforts across TMEs is not known due to the lack of syntheses on ecological restoration research. Here, based on a systematic review, we identify geographical and thematic research gaps, compare restoration interventions, and consolidate enabling factors and barriers of restoration success. We find that restoration research outside Latin-America, in non-forested ecosystems, and on socio-ecological questions is scarce. For most restoration interventions success is mixed and generally limited by dispersal and microhabitat conditions. Finally, we propose five directions for future research on tropical mountain restoration in the UN decade of restoration, ranging from scaling up restoration across mountain ranges, investigating restoration in mountain grasslands, to incorporating socio-economic and technological dimensions.
... Studies of dispersal of seeds of about 40 Ngel Nyaki forest species up to 30 m into grassland from the forest edge using seed traps showed that Deinbollia was one of the small number of forest species that do not disperse seeds out of the forest, but that within forest, natural regeneration from seed does occur. The species has been classified as a shade-bearer and is not a pioneer (Barnes & Chapman, 2014). Deinbollia ''pinnata'' was one of three species of tree used to test the Janzen-Connell hypothesis at this site. ...
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We test the hypothesis that the tree species previously known as Deinbollia sp. 2 . is a new species for science. We formally characterise and name this species as Deinbollia onanae (Sapindaceae-Litchi clade) and we discuss it in the context of the assemblage of montane tree species in the Cameroon Highlands of West-Central Africa. The new species is a shade-bearing, non-pioneer understorey forest tree species reaching 15 m high and a trunk diameter that can attain over 40 cm at 1.3 m above the ground. Seed dispersal has been recorded by chimpanzees ( Pan troglodytes ellioti ) and by putty-nose monkeys ( Cercopithecus nictitans ) and the species is used by chimpanzees for nesting. Cameroon has the highest species-diversity and species endemism known in this African-Western Indian Ocean genus of 42, mainly lowland species. Deinbollia onanae is an infrequent tree species known from six locations in surviving islands of montane (sometimes also upper submontane) forest along the line of the Cameroon Highlands, including one at Ngel Nyaki in Mambilla, Nigeria. Deinbollia onanae is here assessed as Endangered according to the IUCN 2012 standard, threatened by severe fragmentation of its mountain forest habitat due to extensive and ongoing clearance for agriculture. The majority of the 28 tree species of montane forest (above 2000 m alt.) in the Cameroon Highlands are also widespread in East African mountains (i.e. are Afromontane wide). Deinbollia onanae is one of only seven species known to be endemic (globally restricted to) these highlands. It is postulated that this new species is morphologically closest to Deinbollia oreophila, a frequent species at a lower (submontane) altitudinal band of the same range. Detailed ecological data on Deinbollia onanae from the Nigerian location, Ngel Nyaki, where it has been known under the name Deinbollia “pinnata”, is reviewed.
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In the early 20th Century, Guibourtia copallifera Benn. was extensively exploited as a source of gum copal. Its geographic distribution in Sierra Leone is now restricted to a few square kilometers in a single badly degraded forest reserve. We conducted a series of seed rain experiments to quantify its seed dispersal potential. Transects of seed traps were laid out and a total of 1,164,880 seeds were collected over the two months when G. copallifera sheds its" seeds. Seeds from a further 85 species were collected. The majority of species were wind dispersed followed by terrestrial animals, bats and birds. Leguminosae-Caesalpiniaceae had the highest number of species, followed by Euphorbiaceae, Apocynaceae, Rubiaceae and Sterculiaceae. There is no statistically significant difference between the transects (p>0.05, df=79, F=0.023) or the types of traps (p>0.05, df=118, t=0.089). Median dispersal distances of G. copallifera seeds was 41.22 m from the forest edge. The reserve still possesses a high natural regeneration potential for G. copallifera but increasing human disturbance is opening the canopy allowing pioneering species to dominate and reducing the ability of G. copallifera seedlings to establish.
Myrmecochory, the dispersal of seeds with lipid-rich appendages by ants, is a significant ant–plant interaction. Less well understood is the potential for ant dispersal of non-myrmecochorous seeds. Here we investigate ant–diaspore interactions in a West African montane habitat. We combine observation with depot experiments to determine ant species that move diaspores and distance moved across a forest-edge-grassland gradient. We recorded seed cleaning by ants using a bird/mammal dispersed Paullinia pinnata to determine whether seed cleaning improved plant fitness. We found that two out of a total of 17 ant species ( Pheidole sp. 1 and Myrmicaria opaciventris ) interacted with 10 species of non-myrmecochorous diaspores across nine plant families. Diaspores were from large canopy trees, understorey trees and vines. Both ant species interacted with small (≤0.24 g) and large (≥0.24 g) diaspores. Ants individually moved small diaspores up to 1.2 m and worked together to clean larger ones. Our experiments with P. pinnata showed that ants removed the pulp of 70% of fruit over 5 days. Cleaned seeds germinated significantly faster and produced seedlings with significantly longer shoot length and higher fresh weight than seedlings from intact seeds. Together our results suggest that ant dispersal may be less significant than seed cleaning in Afromontane forests. However, given the decline in vertebrate frugivores across Africa, a small dispersal advantage may become increasingly important to plant fitness.
Questions A leading hypothesis for species coexistence in species‐rich, lowland tropical forests is conspecific negative density dependence (CNDD), driven by host‐specific pests and pathogens and competition for available resources. The extent to which this applies to Afromontane forests with relatively low diversity, a high frequency of single‐species stands, relatively few pests and pathogens and larger edge:core ratios, is unknown. We hoped that the results of our investigation would either confirm the generality of CNDD across these different tropical forest types or offer novel insights into alternative mechanisms leading to the maintenance of Afromontane tree species diversity. Location Ngel Nyaki Forest Reserve, southeastern Nigeria. Methods We monitored the survival of 10,741 seedlings of 93 species over two years in a long‐term Forest Global Earth Observatory (ForestGEO) study plot in a montane forest in Nigeria. We assessed the effect of conspecific and heterospecific seedling and adult neighbours on the survival of every seedling and seedling guild (shade vs light‐demanding; canopy vs understorey; edge specialists vs generalists; small vs large seedlings). Results We found strong evidence for non‐species‐specific positive and negative density dependence. CNDD was stronger in canopy species and light‐demanding species than in the other growth form and shade tolerance guilds. Conclusions Our study offers some clear predictions about drivers of community coexistence in this environment, which will require further testing using field‐based experiments.
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Tropical montane forests (TMFs) are recognized for the provision of hydrological services and the protection of biodiversity, but their role in carbon storage is not well understood. We synthesized published observations (n = 94) of above-ground biomass (AGB) from forest inventory plots in TMFs (defined here as forests between 23.5° N and 23.5° S with elevations ≥ 1000 m a.s.l.). We found that mean (median) AGB in TMFs is 271 (254) t per hectare of land surface. We demonstrate that AGB declines moderately with both elevation and slope angle but that TMFs store substantial amounts of biomass, both at high elevations (up to 3500 m) and on steep slopes (slope angles of up to 40°). We combined remotely sensed data sets of forest cover with high resolution data of elevation to show that 75% of the global planimetric (horizontal) area of TMF are on steep slopes (slope angles greater than 27°). We used our remote sensed data sets to demonstrate that this prevalence of steep slopes results in the global land surface area of TMF (1.22 million km2) being 40% greater than the planimetric area that is the usual basis for reporting global land surface areas and remotely sensed data. Our study suggests that TMFs are likely to be a greater store of carbon than previously thought, highlighting the need for conservation of the remaining montane forests.
Summary. Recent work by Reiss and Ogden provides a theoretical basis for sometimes preferring restricted maximum likelihood (REML) to generalized cross-validation (GCV) for smoothing parameter selection in semiparametric regression. However, existing REML or marginal likelihood (ML) based methods for semiparametric generalized linear models (GLMs) use iterative REML or ML estimation of the smoothing parameters of working linear approximations to the GLM. Such indirect schemes need not converge and fail to do so in a non-negligible proportion of practical analyses. By contrast, very reliable prediction error criteria smoothing parameter selection methods are available, based on direct optimization of GCV, or related criteria, for the GLM itself. Since such methods directly optimize properly defined functions of the smoothing parameters, they have much more reliable convergence properties. The paper develops the first such method for REML or ML estimation of smoothing parameters. A Laplace approximation is used to obtain an approximate REML or ML for any GLM, which is suitable for efficient direct optimization. This REML or ML criterion requires that Newton–Raphson iteration, rather than Fisher scoring, be used for GLM fitting, and a computationally stable approach to this is proposed. The REML or ML criterion itself is optimized by a Newton method, with the derivatives required obtained by a mixture of implicit differentiation and direct methods. The method will cope with numerical rank deficiency in the fitted model and in fact provides a slight improvement in numerical robustness on the earlier method of Wood for prediction error criteria based smoothness selection. Simulation results suggest that the new REML and ML methods offer some improvement in mean-square error performance relative to GCV or Akaike's information criterion in most cases, without the small number of severe undersmoothing failures to which Akaike's information criterion and GCV are prone. This is achieved at the same computational cost as GCV or Akaike's information criterion. The new approach also eliminates the convergence failures of previous REML- or ML-based approaches for penalized GLMs and usually has lower computational cost than these alternatives. Example applications are presented in adaptive smoothing, scalar on function regression and generalized additive model selection.
In the Pacific region, tropical montane cloud forest (TMCF) typically occurs as small and isolated patches on the rugged upland ridges and peaks of high volcanic islands. In addition to copious amounts of orographic rainfall, these forests receive substantial “horizontal precipitation” through direct canopy interception of wind-driven cloud water. Pacific Island cloud forests are also known as mossy, dwarf, or elfin forests because of the plethora of herbaceous epiphytes that festoon the gnarled and stunted trunks and branches of the woody vegetation.
The enormous amount of research carried out on the sociology of nonhuman primates clearly demonstrates the interest in this group in which we find our roots and a rational explanation for the basis of human behavior. It would thus be logical that the prosimians whose anatomy and physiology conceals a large number of ancestral characteristics (Vallois, 1955; Piveteau, 1958; Le Gros Clark, 1961; Luckett, 1969; Charles-Dominique and Martin, 1970; Martin, 1975, 1979), would attract the attention of primatologists in so far as their study might bring clarity to the most remote origins of the social behavior of our ancestors. The social structures of prosimians have been studied since the 1960s’ demonstrating the importance of olfaction in communication and, in nocturnal species, a social organization based on territorial arrangements and the subtle exchange of chemical signals contained in their urinary markings (Sauer and Sauer, 1963; Charles-Dominique, 1972, 1977a, b; Martin, 1972; Niemitz, 1974, 1984; Doyle, 1975; Bearder and Martin, 1980; Schilling, 1979, 1980; Bearder, 1987). Research on species belonging to different orders of placental mammals reveals a great deal of similarity to nocturnal primates, which suggests a common base in mammalian social organization (Eisenberg and Gould, 1970; Eisenberg and Kleiman, 1972; Kleiman, 1974; Emmons, 1975, 1978; Charles-Dominique, 1978a, b; Feer, 1989).