Open Journal of Forestry
2014. Vol.4, No.1, 49-57
Published Online January 2014 in SciRes (http://www.scirp.org/journal/ojf) http://dx.doi.org/10.4236/ojf.2014.41009
Natural Regeneration Dynamics of Tree Seedlings on Skid Trails
and Tree Gaps Following Selective Logging in a Tropical Moist
Semi-Deciduous Forest in Ghana
Akwasi Duah -Gyamfi1*, Boateng Kyereh2, Kwame A. Ad am3,
Victor K. Agy eman1, Michael D. Swaine4
1Forestry Research Institute of Ghana, Council for Scientific and Industrial Research, Kumasi, Ghana
2Faculty of Renewable Natural Resources, Kwame Nkrumah
University of Science and Technology, Kumasi, Ghana
3Ghana Timber Millers Organization, Kumasi, Ghana
4Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, UK
Email: *firstname.lastname@example.org, email@example.com
Received October 19th, 2013; revised November 21st, 2013; accepted December 23rd, 2013
Copyright © 2014 Akwasi Duah-Gyamfi et al. This is an open access article distributed under the Creative
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provided the original work is properly cited. In accordance of the Creative Commons Attribution License all
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All Copyright © 2014 are guarde d by law and by SCIRP as a guardian.
One of the main threats to the sustainability of timber production in naturally managed forests in Ghana is
insufficient regeneration of timber tree species. This study assessed regeneration success of a logged for-
est by comparing the species composition, diversity, density, recruitment, mortality, and growth of natu-
rally established seedlings in 160 seedling plot samples of 50 m2 located randomly on main skid trails,
secondary skid trails, felled tree gaps and unlogged parts of the same forest. The study was done within a
134-ha compartment in a selectively logged moist semi-deciduous forest in Ghana over a period of 33
months involving four enumerations. Seedlings population was initially dominated by pioneers, but after
33 months, population in all sites was dominated by non-pioneers. Seedling densities showed an increase
initially in all the sites after logging, but declined after 10 months. The high seedling densities were
driven by four (Albizia zygia, Ceiba pentandra, Celtis mildbraedii and Turreanthus africanus) out of the
37 species that regenerated. All four species exhibited a period of exceptionally high new seedling re-
cruitment in the first 10 months. Diversity differed significantly among disturbance types initially, but af-
ter 33 months diversity was lower in the unlogged areas though not significant. Seedling mortality was
initially greater in unlogged areas of the forest and growth rates higher in the logged areas. These results
show that disturbed areas appear to be suitable sites for the regeneration of timber species following log-
ging, although the long-term fate of trees growing on these areas remains uncertain as growth rates de-
clined with time.
Keywords: Disturbance; Forest Succes si on; Ghana; Logging; Regeneration; Tropical Moist
In most tropical countries including Ghana, selective logging
with or without silvicultural treatment is the most widely
adopted system for the extraction of timber from natural forests.
It involves periodic entries into a given area of forest to remove
selected commercial timber trees using heavy extraction ma-
chines. In some tropical areas (e.g. South-East Asia), about
eight or more trees are removed per hectare at 30 - 40-year
intervals (Sist et al., 2003). In Ghana, the system involves the
removal of 2 - 3 trees per hectare at 40-year interval and has a
relatively high minimum diameter (50 - 110 cm) for felling
most species. This low intensity logging is supposed to result in
less damage to the residual forest and ensure sufficient regene-
ration after logging. However, the current system as currently
practiced lacks any standard post-logged silvicultural practices
to enhance regeneration and has often been cited as a cause for
the sparse regeneration in Ghana’s forests (Swaine et al., 1997).
Logging alters the forest environment by creating a hetero-
geneous canopy with a range of different microenvironments,
such as loading bays, skid trails, logging gaps and logging
roads, which differ primarily in light intensity and soil distur-
bance (Fredericksen & Mostacedo, 2000; Van Rheenen et al.,
2004). These changes imposed by the logging operations can
lead to a change in the species composition of the disturbed
forest (Brokaw & Scheiner, 1989) following shifts in tree spe-
cies composition during the progress of the post-harvest suc-
cession. In most tropical forests, this sequential species re-
placement is primarily due to major shifts in species relative
OPEN ACCESS 49
A. DUAH-GYAMFI ET AL.
abundance over time, where pioneer tree species characterized
by rapid dispersal and fast growth are favored initially, colonize
open areas, experience higher rates of mortality, and are re-
placed by non-pioneer species in the later stages of succession
(Swaine & Hall, 1988). Besides influencing the establishment
of tree seedlings, logging may also trigger the growth of weeds
and other competing vegetation that repress regeneration of
timber trees and thereby arrest the post-harvest succession in
gaps and skid trails (Fredericksen & Mostacedo, 2000; Frede-
ricksen & Pariona, 2002; Dupuy & Chazdon, 2006). In Ghana,
the herbaceous weed Chromolaena odorata and more recently
the invasive exotic woody plant Broussonetia papyrifera grow
profusely in open areas including log landings, gaps, skid trails
in logged forests, and are considered as major threats to natural
regeneration and succession in the natural forests of Ghana
(Agyeman, 2000; Honu & Dang, 2000). This poses a challenge
to the successful establishment of seedlings of timber trees
especially when there are no post-logging silvicultural treat-
ments as it exists in Ghana. Therefore, assessing the effects of
logging gaps and associated skid trails on tree seedling recruit-
ment, growth and mortality in logged forests, may provide in-
sights into seedling regeneration dynamics, and can also help
inform sustainable management of natural forests in Ghana.
Logging gaps and skid trails constitute about 10% of the a rea
of a logged compartment in Ghana (Hawthorne, 1993), are
disturbed heavily during logging and often show poor regenera-
tion due to loss of topsoil. It has been suggested that logging
gaps and skid trails should be a primary focus for improved
regeneration in tropical forests (Heinrich, 1978; FAO, 1983).
Despite their importance, natural regeneration processes in
these post-logged areas have not been adequately studied in
Ghana. Although earlier studies in Ghana by Hawthorne (1993),
Abebrese and Kyereh (2005), and Swaine and Agyeman (2008)
showed improved regeneration on skid trails and other dis-
turbed areas few months after logging, further knowledge of
the dynamics of tree species regeneration would be highly val-
uable. It is not known how post-logging disturbance types with
different degrees of logging disturbance differ in terms of re-
cruitment, mortality, and growth of naturally established tree
seedlings, and how these variables change with time as the
earlier studies did not monitor regeneration dynamics over a
period of time. In this paper, we describe the dynamics of natu-
rally regenerating seedlings over a period of 33 months involv-
ing four enumerations of permanent plots in a selectively
logged tropical moist semi-deciduous forest in Ghana. In par-
ticular, our aim was to evaluate the effects of logging on
changes in ecological species guild abundance, diversity, den-
sity, recruitment, mortality and growth rates of naturally rege-
nerating tree seedlings in post-logged disturbed and unlogged
areas of the same forest.
Materials and Methods
The study was conducted in the Pra-Anum Forest Reserve
(6˚15'N, 1˚12W) which falls within the moist semi-deciduous
forest sub type in the High Forest Zone of Ghana (Figure 1).
The forest has a total area of 12,332 ha, and is mostly of gentle
topography with an average height of about 140 m above sea
level. The mean annual rainfall is between 1500 and 1750 mm,
characterized by two peak rainy seasons (May -June, and Octo-
ber) and a mild harmattan (November to March). Mean annual
Map of southern Ghana showing distribution of forest types in the High
Forest Zone. The location of Pra-Anum Forest Reserve is indicated by
the small black rectangle. Source: Hall and Swaine (1976).
temperature is 26.5˚C (Hall & Swaine, 1981). Soils of Pra-
Anum are derived from thoroughly weathered parent materials
and are primarily classified as forest oxysol-ochrosol inter-
grades (Brammer, 1962). The forest structure is characterized
by very tall trees of about 50 m in a mixture of deciduous and
evergreen species of varying proportions (Hall & Swaine,
1981). The most common species in the reserve are Celtis
mildbraedii, Cylicodiscus gabunensis, Triplochiton scleroxylon
and Turreanthus africanus. The reserve has served as a timber
production area and silvicultural research station since 1954.
The specific experimental area was a 134 ha compartment
(Compartment 4 in the Research Working Circle) of Pra-Anum
Forest Reserve that was selectively logged by Swiss Lumber
Company in July and August 2000, using chainsaw felling and
extraction of logs with rubber-tired skidders. Selective logging
was limited to commercial tree species currently exploited in
Ghana using minimum felling diameter (MFD) limits of 50 -
110 cm dbh, depending on species and removing 2 - 3 trees per
hectare. For trees ≥ 70 cm dbh, the five most abundant species
in the research compartment are Triplochiton scleroxylon
(Sterculiaceae), 226 trees; Celtis mildbraedii (Ulmaceae), 197
trees; Cylicodiscus gabunensis (Fabaceae), 109 trees; Turrean-
thus africanus (Meliaceae), 86 trees and Ceiba pentandra
(Bombacaceae), 79 trees.
In August 2000, immediately following harvesting, three
disturbance categories created from the logging activities in the
compartment namely, main skid trail (MST), secondary skid
trail (SST) and felled tree gap (FG), and unlogged areas of the
forest unaffected by the recent logging activities (UNL) were
mapped, using a tape and compass. Subsequently, 40 random-
ly-located sample plots were laid in each of MST, SST, FG and
UNL, giving a total of 160 permanent sample plots within the
entire compartment. In order that the sampled plots were repre-
sentative of the disturbance categories, main skid trail and sec-
ondary skid trail plots were located linearly along the trails and
were 10 m × 5 m; felled tree plots were laid in the direction of
tree fall with the stump as the base and measured 25 m × 2 m.
Samples in the unlogged areas of the forest were also 25 m × 2 m.
A. DUAH-GYAMFI ET AL.
Characte r i zation of Disturbance Types
The disturbance categories were characterized in terms of
light availability, measured indirectly as canopy openness, and
soil disturbance condition. Hemispherical photos were taken in
August 2000 and re-taken December 2012 using a Nikon F2
digital ca mera with a sigma 8 mm he mispherical le ns, mounted
on a tripod, to determine canopy openness. Photos were taken
with an overcast sky and at a height of 1 m in the center of each
plot. The photographs were analyzed with imaging software:
Winphot 5.0 (Ter Steege, 1996) to determine canopy openness.
Soil condition was assessed visually in each plot and assigned
to one of four categories: 1 (topsoil undisturbed), 2 (topsoil
slightly removed or displaced), 3 (topsoil largely removed,
rutted, no puddles) and 4 (topsoil removed, deeply rutted and
Following plot establishment (August 2000), post-logging
seedling recruits were enumerated on four occasions at ap-
proximately 0.5, 4.2, 10 and 33 months (mo) after logging
ceased in the compartment. At each enumeration, each tree
seedling was identified to seedling level and tagged, mapped
within the sample plot and its vertical height from the ground to
the apical bud measured with a meter tape or telescopic rod
where necessary. In subsequent re-enumerations, surviving
seedlings were re-measured for height, dead or missing seedl-
ings recorded, and new seedlings identified, tagged, mapped
and their heights measured. Species nomenclature and shade
tolerance guild follow Hawthorne (1995) classification: Pio-
neers (P) establish and survive only in high light conditions,
have very fast growth rates but higher mortality than other
groups; Non-Pioneer light demanders (NPLD) establish in
shade, however, further growth requires higher light; Non-
Pioneer shade bearers (NPSH) establish and grow in shade,
often with high densities, and lower mortality in shade. Because
most species in some plots were represented by only a few
individuals, seedlings were grouped for some analyses into the
ecological species guilds in accordance with Swaine et al.
In each disturbance category, the number of seedlings and
species within each 50 m2 plot at each census was counted and
recorded. These data were used to describe several attributes of
the seedling community of disturbance categories and unlogged
areas of the forest, including species richness, density and rela-
tive density of species. Chi-squared tests of independence were
used to determine if the distribution of seedlings among eco-
logical species guild changed within sites over the 33-month
study period. Sampl e-based rarefaction (Gotelli & Colwell,
2001), was used to compare species richness among site s at the
beginning and end of the study period, by constructing species
accumulation curves after 200 randomizations of sample order
with the program EstimateS (version 8, Colwell, 2006). Differ-
ences in diversity among disturbance categories were evaluated
by analyzing the Shannon-Wiener index (H') provided by Esti-
To establish the importance of mortality and recruitment in
explaining changes through time in the relative abundance of
ecological species guilds, we determined the mortality and
recruitment rates between successive census periods. Mortality
rates, m, were calculated using Equation (1) derived by (Sheil
et al., 1995),
where Nt is the number of seedlings alive at the end of the
measurement interval, t, and N0 is the number of seedlings at
the beginning of the interval. Recruitment rates, r, were calcu-
lated i n a si milar way ( S h eil et al., 2000) as,
where nr is the number of recruits during the period, and Nt
and t are as above. The height data was used to estimate relative
height growth rate (RHGR) as height growth per unit plant
height in cm∙cm−1∙mo−1. Differences in canopy openness, den-
sity and, growth, recruitment and mortality rates among distur-
bance categories were analyzed using analysis of variance
(ANOVA) after data had been screened for conformity to the
assumptions of normality and homogeneity of variance. When
these assumptions were not valid, even after data transforma-
tion, the Kruskal-Wallis test was used. Where the tests indi-
cated significant differences among land use types, means were
contrasted with post hoc Tukey HSD tests and for non-para-
metric data, Mann-Whitney tests was used to compare medians.
Detrended correspondence analysis (DCA) was used to ex-
plore the variation of floristic composition across sites. Abun-
dance of seedlings in the four censuses for each site was en-
tere d i n t he D CA which was executed in PC-ORD for Windows
(McCune & Mefford, 1997). Statistical analysis was carried out
using MINITAB (version 14).
Canopy openness immediately after harvesting ranged from
4.9% in the unlogged forest to 14.7% in the felled tree gap
(Table 1). There were no significant differences between skid
trails and felled tree gaps immediately after logging, but the
openness of these disturbed areas was significantly (P < 0.05)
higher than the unlogged forest.
The distribution of soil disturbance categories amongst the
forest types is shown in Figure 2. All the samples in unlogged
parts of the forest had relatively undisturbed topsoil, whilst the
majority of felling gaps and secondary skid trails were only
slightly disturbed. The main skid trail samples, used several
times for the transport of logs, were mostly heavily disturbed
with deeply rutted and puddled soil.
Shift in Ecological Guild Distribution, Species
Composition and Diversity
Across all sites the distribution of seedling abundance by
ecological species guild changed significantly throughout the
study period (Table 2). In general, relative abundance of
non-pioneers increased significantly over the period from 0.5%
to 59%, at the expense of the relative abundance of pioneers,
which decreased in the same period from 98% to 2%. Pioneers
were much more abundant initially on skid trails and tree-fall
gaps and after 33 months pioneer population had significantly
OPEN ACCESS 51
A. DUAH-GYAMFI ET AL.
Soil conditions (cond.) in disturbance categories.
Mean canopy openn ess (±SE) in four disturbance categories in a moist
semi-deciduous forest in Ghana.
Disturbance category Canopy openness (%)
2000 (n = 40) 2012 (n = 10)
Felling gap 14.7 (0.86)a 13.9 (0.51)a
Main skid trail 14.5 (0.90)a 13.6 (0.44)a
Secondary s kid trail 14. 1 (1.07)a 9.5 (1.43)b
Unlogged for est 4.9 (0. 44)b 4.3 (0.41)c
Note: Within each year, values followed by a different letter are significantly.
different (P < 0.05).
declined with the lowest abundance (2%) in the unlogged forest.
With the decline in pioneers, the non-pioneers became more
numerous on all sites 33 months after logging with highest
relative abundances of 59% and 53% recorded for NPSH on
main skid trail and the unlogged areas respectively. Contin-
gency table evaluations using chi-squared test of independence
found significant differences in frequency distribution of seedl-
ings of the various guilds in all sites over the period (P < 0.001,
in all cases).
Species composition of the initial pioneer community was
predominantly C. pentandra and R. heudelotti. The two species
represented more than 90% and 80% of the initial seedling
population on skid trails and tree-fall gaps respectively, but less
than 30% in the closed canopy forest. A small-stature pioneer C.
patens was common and particularly numerous in the first
measurement. Among the non-pioneers, C. mildbraedii was
common in all sites during the final census. Other common
non-pioneers included the shade-bearers T. africanus, N. papa-
verifera and the non-pioneer light-demander A. zygia. These
species attained high numbers at different periods indicating
differences in recruitment patterns. Other species had few or
poor regeneration: T. scleroxylon, a common species in the
compartment was not recorded until at t he third enumeration; C.
gabunensis, also had poor regeneration.
DCA showed that the seedling composition of the sites, in-
itially dominated by pioneers, was distinct from that at the end
of the study, and was depicted by the wide separation of these
seedling communities on the first axis of the DCA (Figure 3).
The first axis of the DCA, which explained 46.3% of the total
variation in species data, appeared to be associated with suc-
cessional development and separated sites by census period
with the initial pioneer dominated census at one end while later
censuses dominated by non-pioneers grouping together.
Species accumulation curves followed an asymptotic pattern
in all sites, and showed that species richness was higher in the
unlogged area at the initiation of the study (Figure 4). By the
Detrended correspond ence an alysis o f 30 tree species that h ad
a minimum of eight seedlings in at least one of the censuses
in the disturbance categ o ries. Each species is represen ted b y a
small ci rcle, and the position of each disturbance category in
ordination space is shown with a cross. The eigenvalue for
axis 1 was 0.406 and for axis 2 was 0.100.
Species accumulation curves (x ± 1 SD) for tree seedlings
present in unlogged forest area, tree gap, secondary skid trail
and main skid trail at (a) the beginning and (b) completion of
study in a moist semi-deciduous forest in Ghana.
MST 2MST 3
FG 1FG 2FG 3
A. DUAH-GYAMFI ET AL.
Relative densities of seedlings of tree species in disturbance categories at 0.5, 10 and 33 mo following selective logging in a moist forest in Ghana.
Relative dens ity ( % ) Re lative dens ity ( % ) Re lati ve dens i ty ( % )
Census 1 (0. 5 mo) Cen sus 3 (10 mo) C ensus 4 (33 mo)
Species Fa mily Guild MST SST FG UNL MST SST FG UNL MST SST FG UNL
Ceiba penta ndra Bombacaceae P 75.67 69.05
28.92 15.13 22.6 37.33 3.29 4.22 6.31 11.47
Ricinoden dron heudelotii Euphorbiaceae
P 20.6 24.74
3.01 1.52 4.42 7.03 0.4 0.31 0.41 2.34 -
Distemonanthus benthamianus Fabaceae P 0.25 - - 0.6 - - - 0.07 0.62 0.27 0.33 0.67
Terminalia su pe rba Combretaceae P - - - 0.6 0.93 0.29 1.46 0.07 0.77 0.41 1 -
Cedrela odorata Meliaceae P - - - - 7.3 3.96 8.55 6.32 5.04 2.88 10.47
Cleistopholis patens Annonaceae P 1.24 3.31 4.12 - 0.93 1.9 3.8 0.86 0.67 1.23 3.34 0.27
Triplochiton scleroxylon Sterculiaceae P - - - - 1.19 0.11 0.32 0.2 1.75 0.27 0.78 0.13
Milicia excelsa Moraceae P 0.25 - - - 5.46 7.82 13.13 0.07 2 2.88 4.45 -
Alstonia boone i Apocynaceae P - - - - 1.58 1.96 1.04 - 1.34 3.02 0.67 -
Canarium scweinfurthii Burseraceae P 0.25 - 0.56 - - - 0.05 - - - 0.11 -
Nauclea dide rrichii Rubiaceae P - - - - 2.98 0.54 0.31 - 2.37 0.35 0.11 -
Petersianthus macroc arpus Lecythidaceae P - - - - - - 0.47 - - - 0.89 -
Bombax buonopozense Bombacaceae P - - - - 0.04 - - - 0.05 - - -
Daniellia ogea Fabaceae P - - - - - 0.03 - - - - - -
Mansonia altissima Sterculiaceae NPLD - 0.1 1.89 24.73 0.61 0.13 1.46 1.19 1.9 1.37 5.46 1.6
Antiaris toxicaria Moraceae NPLD - - 0.44 3.01 0.5 0.75 0.78 1.58 0.93 1.85 2.12 4.8
Piptadeniastrum africanum Fabaceae NPLD - 0.42 - 3.01 - 0.38 0.1 0.59 - 0.62 0.33 1.34
Albizia zygia Fabaceae NPLD 0.5 0.42 0.11 2.41 13.37 31.13 7.76 52.96
9.63 30.73 7.35 20.59
Sterculia rhinopetala Sterculiaceae NPLD - - 0.11 2.41 0.79 0.51 0.36 1.85 2.42 2.67 0.22 9.49
Blighia sapida Sapindaceae NPLD - - 0.11 1.2 0.4 0.11 0.1 0.13 0.93 0.48 0.45 0.67
Albizia ferruginea Fabaceae NPLD - - - 0.6 - - - 0.07 - - - -
Entandrop hragm a a ng ole nse Meliaceae NPLD - - - 0.6 - - 0.05 - 3.24 0.62 0.89 2.27
Pterygota m acrocarpa Sterculiaceae NPLD - - 0.11 0.6 - 0.08 0.32 0.07 1.39 0.48 1.45 1.07
Aningeria robusta Sapotaceae NPLD - - - - - 0.03 0.1 - - 1.03 1.56 1.07
Khaya spp. Meliaceae NPLD - - - - - 0.27 - - 0.15 0.14 0.11 1.07
Cola gigantean Sterculiaceae N PLD - - 0.11 - 0.18 - 0.05 - 0.62 - 0.33 0.4
Albizia adianthifolia Fabaceae NPLD - - 0.11 - 0.11 - - 0.07 0.05 - -
Sterculia oblonga Sterculiaceae NPLD - 0.1 - - 0.14 0.03 0.1 - 0.15 0.07 4.68 -
Pycnanthus angolensis Myristicaceae NPLD - - - - - - - - - 0.07 - -
Celtis mildbraedii Ulmaceae NPSH 0.74 1.14 1.67 15.66 14.16 6.88 8.65 5.5 14.26 18.24 22.16
Nesogordonia papaverifera Sterculiaceae NPSH 0.5 0.42 2.67 9.04 14.41 1.42 3.34 2.83 22.54 4.25 8.8 8.02
Strombosia glaucesc ens Olacaceae NPSH - 0.1 0.44 1.2 0.29 0.08 0.26 0.07 - 0.34 0.45 1.34
Turreanthus africanus Meliaceae NPSH - - 0.67 1.2 16.68 13.58 0.89 17.92
21.26 18.38 6.68 33.16
Hymenostegia afzeli i Fabaceae NPSH - - - 0.6 0.11 0.96 1.77 0.73 - 0.14 0.11 0.27
Dialium aubrevillei Fabaceae NPSH - 0.1 - 0.6 - 0.03 - - 0.1 0.35 - 0.13
Cylicodiscus gabunensis Fabaceae NPSH - 0.1 - - 1.19 - - 3.16 1.29 - 0.22 0.27
Guarea cedrata Meliaceae NPSH - - - - - - 0.42 - - 0.14 0.67 -
OPEN ACCESS 53
A. DUAH-GYAMFI ET AL.
end of the study, curves had reached their asymptotes and le-
velled off indicating that the area sampled was large enough to
estimate the total number of species in each site. Species rich-
ness increased most in the skid trails and tree gaps, and rose
slightly in the unlogged area. Species diversity estimated by the
Shannon-Wiener index increased in all four sites, rising most
on the skid trails and tree-fall gap because of substantial in-
creases in number of species recorded with time (Figure 4).
Initially, species diversity was significantly different among
sites (F = 4.3, d.f. = 3, P = 0.027) with the unlogged area being
the most diverse followed by the tree-fall gap, secondary skid
trail with the main skid trail being the least diverse. However,
after 33 months diversity indexes appeared slightly higher in all
the disturbed areas (compared to the unlogged area (Figure 4),
though not significant (F = 1.6, d.f. = 3, P = 0.240).
Mortali t y and Recruitment Patterns
For all ecological species guild, recruitment rate across dis-
turbance categories was higher than mortality rate for the first
and second measurement interval except for mortality rate of
pioneers in the unlogged area which was higher compared to
recruitment rate, the reason for the significantly lower (negative)
net gain rate recorded for only pioneers during that period
(Figure 5(b)). For recruitment and net gain rates there were
significant interactions between ecological species guild and
disturbance categories (recruitment: F = 5.58, d.f. = 2 and P <
0.001 and net gain rate: F = 2.61, d.f. = 6 and P < 0.05). Pio-
neers had a significantly higher recruitment rate (P < 0.05) than
the other two groups, and logged areas had significantly higher
recruitment rates (P < 0.05) than unlogged areas. Mortality
rates were significantly higher for pioneers than the other
groups across all disturbance types (Figure 5(a)). For the latter
censuses, recruitment rates were significantly higher (P < 0.05)
for the non-pioneers than pioneers across all sites with highest
rates in unlogged areas (Figure 5(c)). Net gain rates were sig-
nificantly higher (P < 0.05) and positive for non-pioneers
across all disturbance categories while pioneers had signifi-
cantly lower net gain rates across all sites (Figure 5(d)).
Across all sites seedling densities increased steadily and
peaked at 10 mo, thereafter declined till the termination of the
study ( Table 3). S e edling density was highest in secondary skid
trail for most part of the study period, and was much lower in
the unlogged forest. Among the logged sites, median densities
were lower in gaps compared to skid trails but were less vari a-
ble than those on skid trails. The period recorded for maximum
density attaine d by most species varied during the study. At 0.5
mo, density of the pioneer species, C. pentandra, was highest at
all sites, about 2.5 and 13 times higher than densities of other
common species for that period such as R. heudelotii and C.
mildbraedii, respectively, on secondary skid trails. For most
Mean mortality, recruitment and net gain rates for pioneer, non-pioneer light demander and non-pioneer shade bearer
across disturbance types between the measurement intervals 1 and 2 (a, b) and 3 and 4 (c, d). Mortality rates are
represented as negative values. The net gain rate is the sum of the recruitment and (negative) mortality rates.
A. DUAH-GYAMFI ET AL.
Seedling density at 0.5, 4.2, 10 and 33 mo after logging in a tropical forest in Ghana.
Months after logging
0.5 mo 4.2 mo 10 mo 33 mo
Main skid trail
Secondary s kid trail
Felled tree gap
Unlogged for est
0.13 (0 - 2.60)a
0.32 (0 - 2.75)b
0.28 (0.07 - 1.95)b
0.03 (0 - 0.47)c
0.34 (0.10 - 9.16)a
0.89 (0.10 - 7.94)b
0.49 (0.08 - 3.20)c
0.06 (0 - 0.70)d
0.96 (0.28 - 10.20)a
1.36 (0.25 - 19.86)b
0.81 (0 - 2.85)a
0.32 (0 - 6.97)c
0.62 (0.10 - 5.49)a
0.49 (0.04 - 7.68)a
0.28 (0.02 - 1.72)b
0.27 (0 - 0.90)b
species, densities peaked at 10 mo with A. zygia and C. pen-
tandra dominant on skid trails, and A. zygia in unlogged areas.
By 33 mo, densities of pioneers had declined with the non-
pioneer shade bearers C. mildbraedii and N. papaverifera
common in all sites and T. africanus highest in unlogged areas.
There were significant differences (P < 0.001) among sites in
total seedling density over the entire period of the study; for the
beginning and end of the study period (KW χ2(3) = 56.40 and
22.97, respectively, P < 0.001 in both cases).
Thirty-three months after the start of the study, the tallest
seedlings of most species were located in the logged areas and
the smallest were situated in the unlogged area. At the begin-
ning of the study, there was little difference in seedling height
among the sites, and this difference became apparent after 1.5
mo for R. heudelotti, 1.6 mo for M. altissima, 1.8 mo for N.
papaverifera and 4.5 mo for C. mildbraedii.
The relative height growth rate for all species was signifi-
cantly (P < 0.05) higher in logged forest (secondary skid trail
and main skid trail at the beginning and end of the study re-
spectively) and lowest in unlogged area in all cases (Figure 6).
Across sites, pioneers grew faster than non-pioneers. Among
the common species that survived to the end of the study, the
pioneer species C. pentandra and R. heudelotti had the highest
RHGR. Over the period, estimated mean RHGR of C. pentan-
dra and R. heudelotti were 0.11 cm∙cm−1 mo−1 ± 0.003 and 0.10
cm∙cm−1∙mo−1 ± 0.005 in main and felled tree gap respectively.
The RHGR of common non-pioneers C. mildbraedii and N.
papaverifera 0.06 cm cm−1∙mo−1 ± 0.011 and 0.04
cm∙cm−1∙mo−1 ± 0.003 respectively in the tree gap. There was a
decrease in the mean RHGR of species i n all the sites.
Logging had a positive impact on the regeneration of seedl-
ings as the initial establishment and subsequent growth of
seedlings increased with increasing soil disturbance and canopy
openness. However, this initial increase was mostly due to pio-
neer species notably C. pent andra. This species is light-seeded,
shade-intolerant that would be expected to benefit from the soil
disturbance caused by logging machinery as well as the in-
creased light from canopy removal. The present result showed
that recruitment and density of seedlings, especially pioneers,
over the first 10 mo after logging was substantially higher in
skid trails and tree gaps than in unlogged areas of the forest.
Our results support the widely held view that disturbance fa-
vours pioneers as observed in tropical forests (Fredericksen &
Mostacedo, 2000; Fredericksen & Pariona, 2002; Sist and
Nguy e n -Thé, 2002; Van Rheenan et al., 2004; Gourlet-Fleury
et al., 2004; Swaine & Agyeman, 2008). Even though higher
Mean relative height growth rate of seed lings f rom (a) 0.5 to 4 .5 mo (b)
4.5 to 10 mo and (c) 10 to 33 mo in areas disturbed by logging and
unlogged areas in a tropical moist forest in Ghana. Treatments with
different letters are significantly different at P < 0.05.
OPEN ACCESS 55
A. DUAH-GYAMFI ET AL.
soil compaction can impede the establishment of seedlings
(Pinard et al., 2000), greater canopy openness, and soil distur-
bance (Denslow, 1995; Dickinson & Whigham, 1999), and the
intensity of logging (Cornell, 1978; Sheil & Burslem, 2003) can
favour tree seedling regeneration. For instance, least disturbed
areas with upturned soil from the churning action of skidder,
may facilitate establishment of small-seeded, light demanding
tree species (Putz, 1983). This is possible especially on the
secondary skid trails where the lesser degree of soil mechanical
disturbance from single passage of skidder could offer favoura-
ble substrate conditions for seedling establishment.
Changes in species guild composition during the course of
succession was an indication of shifts in the relative abundance
or dominance of the ecological species guilds of the seedling
community within the sites from pioneers at the beginning of
the study to non-pioneers at the end of the study. This shift in
dominance from the more light demanding pioneers to the
shade-tolerant non-pioneers may be a reflection of the intrinsic
responses of the guilds to changes in the microenvironment of
the sites with time, particularly light. Initially, the high amount
of light resulting from the logging operations may have favored
the regeneration of pioneers while at the latter stages the re-
duced irradiance and temperature may have favoured the
non-pioneers especially the shade bearers. A possible explana-
tion for this observation is that gaps created by logging in trop-
ical forests could be potentially occupied by both pioneer and
non-pioneer tree species; however, the species with inherently
long lifetimes will gradually replace the short-lived ones (Kuu-
sipalo et al., 1996). Similar changes in seedling composition
were observed in a Brazillian rain forest by Gomes et al., (2003)
who reported that in a forest undergoing successional change,
understory shade tolerant populations become more common as
the canopy recovers. Detrended correspondence analysis pro-
vided further evidence that composition of the seedling com-
munities became similar over time. This may have been ac-
counted for by the intact forest surrounding our sites providing
readily supply of seeds for the recruitment of seedlings over
time but declining environmental conditions within the sites,
especially reduction in light levels, may have influenced the
dominance of ecological species guilds with the passage of time.
A similar explanation could be offered for the increase in di-
versity of the logged areas to comparable but slightly higher
values than the unlogged areas by 33 mo. As expected, in the
first census richness was higher in the unlogged forest areas
than in both skid trails and gaps. Over time, skid trails and gaps
showed higher richness and diversity than in the unlogged for-
est because of the in-growth of new species, mostly pioneer
species that are uncommon in unlogged areas (Felton et al.
Seedling density rose sharply and declined over time in all
sites as previously found in other studies (Abebrese & Kyereh,
2005; Capers et al., 2005). Initial high seedling density ob-
served in skid trails and gaps suggests enhanced regeneration or
recruitment to these sites following logging, as evidenced by
the higher net gain rates. The higher recruitment of fast growth
pioneers, expressed by their high relative density at the initial
stages could have created an environment where competition
was much higher promoting higher mortality rates at the same
time. Decrease in seedling density during the latter part of the
study could have resulted at least in part from declining light
levels which appeared to be important in reducing the recruit-
ment and density of seedlings especially pioneers. Decline in
density of pioneers is a reflection of the imbalance between
recruitment and mortality-decreasing recruitment rate and in-
creasing mortality rate-during the study period. As a conse-
quence of higher mortality rates and lower recruitment, density
of pioneers decreased in the sites, inverting the tendency ob-
served during the first 10 mo when density increased across all
sites. This was explicitly reflected at 33 mo where only pio-
neers had a negative net gain rate. A similar trend was observed
in the non-pioneers, however, the effect of mortality rate over
recruitment was less than in pioneers. Consequently, after 33
mo density of non-pioneers was higher than pioneers, hence a
positive net gain rate at 33 mo. Similar effects for recruitment,
mortality, and plant density have been reported before in natu-
ral and artificial gaps (e.g. Dupuy & Chazdon, 2006; D’Oliveira
& Ribas, 2011).
Growth rates were significantly higher in skid trails and gaps
than unlogged areas throughout the study. However, by 33 mo
growth rates had reduced by over 90% and 40% of the initial
rates in the logged and unlogged areas respectively. It seems
that the initial soil disturbance in combination with high post-
logging light availability associated with the disturbed sites did
not negatively affect the initial growth of seedlings. Our obser-
vations concur with other studies in the tropics (e.g. Frederick-
sen & Mostacedo, 2000; Van Rheenen et al., 2004). The de-
crease in growth rate across the disturbance types suggests the
need of some silvicultural treatment to allow the maintenance
of high growth rates. Although the influence of competing ve-
getation on seedling regeneration was not determined in this
study, observations on the study plots and results from similar
studies in the tropics point out that, competing vegetation may
be one reason for the observed decrease in growth rate (Frede-
ricksen & Mostacedo, 2000; Honu & Dang, 2000). In Ghana,
the invasive C. odorata has been shown to repress regeneration
in gaps and in open fields (Honu & Dang, 2000). Low light
availability may also partially account for the decrease in
growth rate (Van Rheenen et al., 2004).
We conclude that the present study demonstrates some bene-
ficial effects of logging disturbance on natural regeneration at
least for the first three years. Logged forest areas differed from
unlogged areas in terms of seedling recruitment, density,
growth rate and mortality. The contrasts were due mostly to the
rapid recruitment and fast growth of pioneers in skid trails and
tree gaps. However, the sparse or lack of regeneration of other
species in the compartment regardless of soil disturbance or
light environment created by logging is worrying and indicates
the need for improvements or silvicultural interventions in the
harvesting operations currently practiced in Ghana. The decline
in relative height growth rate shows one of the effects which
can be achieved by silvicultural treatments (weeding, liberation
thinnings, etc.) as employed in the Malayan Uniform System,
or the Tropical Shelterwood System, which reduces mortality
rates and secures tree regeneration.
Financial support for the research was provided by the Uni-
versity of Aberdeen, the British Ecological Society, the Tro-
penbos International and the International Tropical Timber
Organization. We are grateful to Kwaku Asumadu, Peter
Amoako, Vincent Berko and Dominic Bosompem for tireless
A. DUAH-GYAMFI ET AL.
fieldwork. We also thank the Forestry Research Institute of
Ghana for logistic support.
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