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Information on forest structure is fundamentally important to track successional vegetation dynamics for efficient forest management. This study reports on vegetation characteristics, dominance patterns and species height growth in a northern mistbelt forest type in South Africa. Common alpha-diversity indices (species richness and Shannon–Weiner diversity), structural vegetation parameters (tree density and basal area), and species importance value index were used. Size class distribution and height–diameter allometry were further examined for the overall stand and most important species. Stem densities (472.0 ± 43.5 and 605.3 ± 28.1 trees ha-1 for >5cm to <10 cm and > 10 cm dbh (diameter at breast height) classes, respectively) and basal area values (1.99 ± 0.19 and 48.07 ± 3.46 m2 ha-1, respectively) are comparable to other Afromontane forests in East Africa. The overall stand showed an inverted-J shaped distribution pattern which is a typical feature of stand size class distribution in most natural forests. Most ecologically important species also exhibited an inverted-J shaped distribution pattern, suggesting good regeneration and recruitment potential. There were significant differences in species on height, reflecting species-specific height growth patterns, possibly a result of intrinsic growth potential and competitive interactions. The present study suggests that conservation and management policies, including protection of surrounding land uses against fire, contribute to maintaining a successful recovery of these forests. However, it should be noted that these forests may be experiencing relatively slow dynamic flux as a result of the overmature state of some trees with several years under relatively strict protection.
Vegetation structure, dominance patterns and height growth
in an Afromontane forest, Southern Africa
Sylvanus Mensah
Anthony Egeru
Achille Ephrem Assogbadjo
Romain Gle
Received: 26 January 2018 / Accepted: 28 March 2018
Northeast Forestry University and Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract Information on forest structure is fundamentally
important to track successional vegetation dynamics for
efficient forest management. This study reports on vege-
tation characteristics, dominance patterns and species
height growth in a northern mistbelt forest type in South
Africa. Common alpha-diversity indices (species richness
and Shannon–Weiner diversity), structural vegetation
parameters (tree density and basal area), and species
importance value index were used. Size class distribution
and height–diameter allometry were further examined for
the overall stand and most important species. Stem densi-
ties (472.0 ±43.5 and 605.3 ±28.1 trees ha
for C5
cm to \10 cm and C10 cm dbh (diameter at breast
height) classes, respectively) and basal area values
(1.99 ±0.19 and 48.07 ±3.46 m
, respectively) are
comparable to other Afromontane forests in East Africa.
The overall stand showed an inverted-J shaped distribution
pattern which is a typical feature of stand size class dis-
tribution in most natural forests. Most ecologically
important species also exhibited an inverted-J shaped dis-
tribution pattern, suggesting good regeneration and
recruitment potential. There were significant differences in
species on height, reflecting species-specific height growth
patterns, possibly a result of intrinsic growth potential and
competitive interactions. The present study suggests that
conservation and management policies, including protec-
tion of surrounding land uses against fire, contribute to
maintaining a successful recovery of these forests. How-
ever, it should be noted that these forests may be experi-
encing relatively slow dynamic flux as a result of the over-
mature state of some trees with several years under rela-
tively strict protection.
Keywords Diversity Population structure Species
composition Size class distribution
Over the last century, tropical forests suffered severely
from natural disturbances (fires, winds, floods) and timber
harvesting. Logging and forest clearing for subsistence
agriculture increase loss of biodiversity, which affects
ecosystem integrity, functions and services (Foley et al.
2007). South Africa has not been immune to such impacts
(King 1941; Cooper 1985), as the country’s forests have
been exposed to fire and unregulated harvesting. Never-
theless, by 1939, illegal logging was prohibited, and this,
added to the efforts to control fire, has contributed to the
restoration of natural forest vegetation in many degraded
areas (Geldenhuys 2002).
Project funding: This work was supported by the African Forestry
Forum and the National Research Foundation of South Africa through
the ‘‘Catchman Letaba’’ project.
The online version is available at
Corresponding editor: Zhu Hong.
&Sylvanus Mensah
Laboratoire de Biomathe
´matiques et d’Estimations
`res, Faculte
´des Sciences Agronomiques, Universite
d’Abomey-Calavi, 04 BP 1525 Cotonou, Benin
Regional Universities Forum for Capacity Building in
Agriculture, Makerere University,
P.O Box 16811, Wandegeya, Kampala, Uganda
Laboratoire d’Ecologie Applique
´e, Faculte
´des Sciences
Agronomiques, Universite
03 BP 1974 Cotonou, Benin
J. For. Res.
Afromontane mistbelt forests are one of the few natural
forest ecosystems in South Africa which, due to the mod-
ification of the fire regime, have developed in areas that
were not previously covered in forests (Geldenhuys 2000;
Geldenhuys and Venter 2002). These forests persisted in a
fire-prone environment and then expanded into suitable ar-
eas with fire protection for timber plantations and intensive
agriculture. They consist of many small, fragmented and
widely distributed patches. Two mistbelt forests form part
of the eight natural forest groups in South Africa: the
northern mistbelt forests and the southern mistbelt forests
(Mucina and Rutherford 2006). One of the most striking
characteristics in the northern mistbelt forests is the tall
moist evergreen vegetation at altitudes up to 1800 m.
These forests serve as habitats for insect pollinators
(Mensah et al. 2017b), but also play important socio-eco-
nomic and ecological roles that support human well-being.
Among other benefits, they provide forage resources to
domestic animals and insect pollinators (contributing to
crop pollination in marginal agricultural areas), fuel wood,
food, medicinal resources, help to control biological inva-
sions, and alleviate the effects of climate change by storing
atmospheric carbon (Geldenhuys 2002; Rasethe et al. 2013;
Mensah et al. 2016a,2017a).
Information on current floristic composition and species
dominance are important to track successional dynamics of
the forest vegetation and its response to environmental
variations and human interventions. Most previous research
in the northern mistbelt forests assessed the potential for
regeneration and traditional plantation forestry of native
species (Geldenhuys and von dem Bussche 1997; Gelden-
huys 1997), growth and mortality of indigenous species
(Geldenhuys 2000), and biodiversity and floristic composi-
tion for management options (Geldenhuys and Venter 2002).
Most of these studies were conducted more than a decade ago
and although diversity and vegetation patterns are known to
be responsive to environmental conditions, species distri-
bution patterns, recovery and growth rates can also shift on a
temporal scale in response to the nature and intensity of
surrounding land uses, and to management practices (Ken-
nard 2002; Sampaio et al. 2007). Information on current
forest structure (horizontal and vertical) are crucial to char-
acterize the vegetation, and describe and interpret their
dynamics. This information is also relevant to appreciate the
effectiveness of management interventions in surrounding
land uses as well as conservation decisions.
In this study, recently collected inventory data from the
Woodbush–De Hoek natural forest in Limpopo province,
South Africa was used to explore patterns of species
diversity, vegetation structure and dominance. The specific
objective was to assess (i) overall vegetation patterns (in-
cluding dominance), focusing on taxonomic diversity
metrics (species richness and Shannon–Weiner diversity
index), and (ii) common vegetation structural parameters
such as regeneration density, tree density, basal area,
Importance Value Index, and size class distribution.
Materials and methods
Study area and data
The Woodbush–De Hoek natural forest is situated at
23500S and 29590E and is part of the northern mistbelt
forest group. The vegetation is dominated by tall evergreen
species at altitudes up to 1800 m (Geldenhuys 2002). The
area is surrounded by pine plantations managed by the
Komatiland Forests Company in Limpopo. The mean
annual rainfall is 1200 mm, with the highest peak during
summer. Additional information about the study area and
Woodbush–De Hoek natural forest are available in our
previous studies (Mensah et al. 2018a,b).
Floristic and structural data were collected by means
of forest inventories. Thirty circular plots of 500 m
were randomly laid out and thirty additional circul ar subplots
(250 m
) were laid out in each 500 m
plot. Inside the sub-
plots, diameter at breast height (dbh) was measured for all
stems C5cmto\10 cm while in the 500 m
plots, the
same measurements were taken for all trees with dbh C10
cm. Both dbh sizes were recorded to gain more insight into
regeneration and adult trees. Species names were recorded
using taxonomic keys of the revised and updated version of
the book, Trees of Southern Africa (Coates-Palgrave 2003).
Data analysis
Taxonomic diversity and floristic composition were anal-
ysed for all woody plants having dbh C5 cm. Taxonomic
diversity, species richness and Shannon–Weiner diversity
index were computed following Magurran (1988). Struc-
tural variables such as stem density (N, trees ha
) and
basal area (G,m
) were computed and combined to
provide relative species frequencies to determine the
importance value index (IVI; Curtis and McIntosh 1951)as
an indicator of a species relative ecological importance.
Tree density was calculated as the average number of trees
per hectare, and basal area as the sum of the cross-sectional
area 1.3 m above the ground using the following equation:
0:0001 d2
where Gis basal area; d
is diameter in cm of the i-th tree in
the plot and sthe unit area of the plot. IVI was calculated
by summing up the species relative frequency, relative
density and relative basal area as:
S. Mensah et al.
IVI ¼ni
where IVI is the importance value index; n
and c
respectively the density, frequency and basal area of the i-
th species. Size class distribution and height growth models
are important in understanding the dynamics of forest
stands. Stem diameter structures were established for the
overall stand and the ten most important species as
revealed by IVI. To better depict the size class distribution
patterns, we used the method of Condit et al. (1998). For
each species, we performed a least square linear regression
analysis using the number of individuals as dependent
variable and the midpoint of each size class as independent
variable. Each size class had 10 cm width, starting from
5 cm dbh. Because some size classes had no recording, the
number of individual species in each class was transformed
by ln (1 ?number of individuals), as suggested by Obiri
et al. (2002). The slope from each species-specific size
class regression was used as an indicator of the level of
recruitment and population structure (Lykke 1998). Nega-
tive slope values are indicative of a reverse-J SCD (size
class distribution) curve and of good recruitment, with
more individuals in smaller size classes and fewer in larger
classes (Obiri et al. 2002; Martins and Shackleton 2017).
Positive slope values indicate populations with a unimodal
SCD curve and limited recruitment, with more individuals
in larger size classes and fewer in smaller size classes.
For height growth, seven out of the ten most important
species were considered due to the limitation of height
data. The allometric relationship between tree diameter and
total height for these species were examined using the
linearized form of the power function (Mensah et al.
2016a,2017c). We tested whether height–diameter rela-
tionship varied among species by adding the species as a
categorical factor and performing an analysis of covari-
ance. Individual and interaction term effects were com-
puted from the fitted model:
ln hðÞ¼ln aðÞþbln dbh
ðÞþcspecies þe0ð3Þ
where, ln (a) is the intercept, bthe proportional height
growth rate induced by tree diameter, and c
the pro-
portional growth rate due to the species; ln (d
) is the
natural logarithm of tree diameter and e0the additive error.
Diversity, structures and dominance patterns
Fifty woody plant species belonging to 46 genera and 33
families were recorded. The overall Shannon–Wiener
diversity was 2.84. Species richness was slightly lower
for C5cmto\10 cm dbh class (35 species), compared
to the C10 cm dbh class (45 species). However, further
analyses showed that the number of species per plot was
significantly higher for smaller trees (\30 cm dbh) and
lowest for larger trees ([60 cm) (F = 115.19; P\0.001;
Fig. 1). The most diversified families were the Rutaceae
and Rubiaceae, with five and four species, respectively.
In terms of relative basal area, the most dominant
families were the Myrtaceae (12.7%) and Monimiaceae
(8.3%) (Table 1). These two families also had the highest
number of individuals, although both were represented by
only three species (Xymalos monospora (Harv.) Baill,
Syzygium gerrardii (Harv. ex Hook. f.) Burtt Davy and
Eugenia natalitia Sond.). Stem densities of the C5to\
10 cm and C10 cm dbh classes were 472.0 ±43.5 and
605.3 ±28.1 trees ha
, respectively. Xymalos mono-
spora,Syzygium gerrardii,Combretum kraussii Hochst.,
Cussonia sphaerocephala Strey, and Cassipourea mal-
osana (Baker) Alston were the most abundant species in
the C10 cm dbh class, with 139.3, 119.3, 43.3, 30.7 and
24.7 stems ha
, respectively. For the C5to\10 cm dbh
class, Cassipourea malosana (68.0 stems ha
), Kraussia
floribunda Harv. (56.0 stems ha
), Xymalos monospora
(50.7 stems ha
), Syzygium gerrardii (44.0 stems ha
Ochna arborea Burch. ex DC. (36.0 stems ha
) and Ri-
norea angustifolia (Thouars) Baill. (34.7 stems ha
) had
the highest densities, accounting for 61.3% of the density
in this class.
The basal areas for the C5to\10 cm and C10 cm
dbh classes were 1.99 ±0.19 and 48.07 ±3.46 m
respectively. Out of the 50 species, 42 had basal areas less
than 1.0 m
, contributing less than 20.0% of the stand
basal area; five species had basal areas between 1.0 and
3.0 m
(20.0% of the stand basal area). The greatest
contribution to stand basal area ([25%) was made only
the forest waterberry (Syzygium gerrardii (Fig. 2). The ten
Smalle r t rees Me d iu m tre es Larger t rees
Species richness
Fig. 1 Variation in plot species richness among larger, medium-sized
and smaller trees
Vegetation structure, dominance patterns and height growth in an Afromontane forest, Southern
most important species based on the Importance Value
Index were, in order of ecological importance: X. mono-
spora,S. gerrardii,C. sphaerocephala,C. kraussii,C.
malosana,Trichilia dregeana Sond., Nuxia congesta R. Br.
ex Fresen., Kraussia floribunda, Croton sylvaticus Hochst.,
and O. arborea (Table 2).
Size class distribution
The overall size class distribution showed an inverted-J
shaped curve with several gaps in diameter classes beyond
100 cm dbh (Fig. 3). Overall, most trees were in the lower
diameter classes (\20 cm), and shows a drastic decline in
density in the higher classes. Diameter class structures
were further established for the ten most important species
Table 1 Number of species,
individuals and basal area per
taxonomic family
Family Number of species family Number of individuals Basal area (m
Rutaceae 5 23 0.5552
Rubiaceae 4 100 0.7278
Stilbaceae 3 63 3.6875
Celastraceae 3 38 0.3959
Myrtaceae 2 220 12.718
Lauraceae 2 28 1.5664
Achariaceae 2 25 0.8746
Ochnaceae 2 64 0.6915
Podocarpaceae 2 16 0.6155
Oleaceae 2 3 0.0175
Monimiaceae 1 247 8.3173
Araliaceae 1 47 6.0547
Meliaceae 1 31 3.7079
Combretaceae 1 82 2.7897
Euphorbiaceae 1 14 2.0073
Asteraceae 1 9 0.9156
Rosaceae 1 7 0.8973
Rhizophoraceae 1 88 0.8889
Curtisiaceae 1 12 0.6821
Moraceae 1 9 0.4275
Aphloiaceae 1 18 0.3847
Violaceae 1 49 0.3602
Putranjivaceae 1 23 0.2630
Thymelaeaceae 1 22 0.1180
Myrsinaceae 1 2 0.0854
Sapotaceae 1 2 0.0742
Cannabaceae 1 1 0.0634
Aquifoliaceae 1 2 0.0600
Malvaceae 1 4 0.0334
Melianthaceae 1 4 0.0293
Salicaceae 1 4 0.0269
Ebenaceae 1 2 0.0158
Fabaceae 1 3 0.0153
The top five most dominant families are bold
< 1 1–3 3–5 5–7 7–9 > 9
Contribution to basal area (%)
Number of species
Basal area (m2ha-1)
Fig. 2 Variation in number of species (solid line) according to their
contribution to the stand basal area
S. Mensah et al.
Table 2 Species names and importance value index (IVI)
Species RF RD RG IVI
Xymalos monospora (Harv.) Baill. 9.62 20.83 17.41 47.87
Syzygium gerrardii (Harv.) ex Hook. f.) Burtt Davy 7.45 15.85 23.75 47.06
Cussonia sphaerocephala Strey 5.62 3.61 9.68 18.91
Combretum kraussii Hochst. 4.17 6.10 5.97 16.25
Cassipourea malosana (Baker) Alston 5.08 6.32 1.41 12.82
Trichilia dregeana Sond. 2.56 3.15 6.97 12.69
Nuxia congesta R. Br. ex Fresen. 3.03 2.38 3.95 9.36
Kraussia floribunda Harv. 4.85 3.83 0.49 9.17
Croton sylvaticus Hochst. 2.35 1.78 5.02 9.16
Ochna arborea Burch. ex DC. 4.62 3.50 0.95 9.07
Cryptocarya transvaalensis Burtt Davy 3.29 1.79 3.20 8.28
Nuxia floribunda Benth. 1.97 2.05 3.40 7.43
Rinorea angustifolia (Thouars) Baill. 1.66 3.73 1.07 6.46
Oxyanthus speciosus DC 3.14 2.70 0.56 6.39
Aphloia theiformis (Vahl) Benn. 2.06 1.32 1.29 4.66
Curtisia dentata (Burm. f.) C.A. Sm. 1.87 1.08 1.67 4.62
Ochna holstii Engl. 2.60 1.60 0.39 4.60
Kiggelaria africana L. 1.76 1.09 1.69 4.54
Oricia bachmannii (Engl.) I. Verd. 2.71 1.26 0.39 4.35
Drypetes gerrardii Hutch. 1.63 1.81 0.85 4.30
Brachylaena transvaalensis Phill. & Schweick. p.p. 1.12 0.65 2.46 4.24
Peddiea africana Hook. 2.35 1.59 0.20 4.15
Podocarpus latifolius (Thunb.) R. Br. ex Mirb. 2.49 0.71 0.82 4.02
Rothmania capensis Thunb. 2.43 1.26 0.27 3.96
Prunus africana (Hook. f.) Kalkman 1.56 0.60 1.65 3.81
Ficus craterostoma Warb. ex Mildbr. & Burret 2.01 0.85 0.89 3.75
Pterocelastrus rostratus Walp. 2.02 1.34 0.18 3.54
Maytenus spp 1.09 1.58 0.63 3.30
Rawsonia lucida Harv. & Sond. 1.15 1.00 0.32 2.48
Ocotea kenyensis Robyns & R. Wilczek 1.05 0.34 0.33 1.73
Trimeria grandifolia (Hochst.) Warb. 1.28 0.35 0.07 1.71
Afrocarpus falcatus (Thunb.) R. Br. ex Mirb. 1.00 0.40 0.21 1.60
Bersama tysoniana Oliv. 1.09 0.29 0.06 1.45
Eugenia natalitia Sond. 0.74 0.52 0.11 1.38
Calpurnia aurea Baker 0.67 0.53 0.05 1.24
Calodendrum capense Thunb. 0.56 0.19 0.38 1.13
Ilex mitis (L.) Radlk. 0.70 0.18 0.11 1.00
Dombeya burgessiae Gerrard ex Harv. & Sond. 0.42 0.26 0.18 0.86
Mimusops obovata Pierre ex Engl. 0.33 0.15 0.34 0.82
Halleria lucida L. 0.56 0.17 0.09 0.81
Zanthoxylum davyi (I. Verd.) P.G. Waterman 0.44 0.16 0.18 0.78
Rapanea melanophloeos (L.) Mez 0.49 0.15 0.04 0.68
Celtis africana Burm. f. 0.42 0.09 0.15 0.65
Olea capensis L. 0.28 0.18 0.03 0.48
Diospyros whyteana (Hiern) F. White 0.28 0.16 0.03 0.46
Zanthoxylum capense (Thunb.) Harv. 0.33 0.11 0.01 0.46
Clausena anisata (Willd.) Hook. f. ex Benth. 0.28 0.16 0.02 0.46
Pavetta galpinii Bremek. 0.33 0.10 0.02 0.45
Pleurostylia capensis Oliv. 0.28 0.09 0.03 0.39
Chionanthus peglerae (C.H. Wright) Stearn 0.19 0.06 0.01 0.25
The top ten most important species are bold
RF relative frequency, RD relative density, RG relative dominance. Species order based on decreasing IVI
Vegetation structure, dominance patterns and height growth in an Afromontane forest, Southern
(Fig. 4). All species exhibited a tendency to the inverted
J-shape distribution, indicating higher frequency in the
lowest diameter classes and a gradual decrease from lower
to higher size classes. The J-shape distribution was more
pronounced for X. monospora,S. gerrardii,C. kraussii,C.
malosana, O. arborea and K. floribunda.C. sphaero-
cephala, T. dregeana,N. congesta and C. sylvaticus
showed a size class distribution with several gaps in
intermediate size classes. From the results of regression
analyses of SCD curves, these species had negative and
steeper slopes (from -0.09 to -0.04; Table 3), as com-
pared to N. congesta (slope = -0.03), T. dregeana
(slope = -0.01), C. sphaerocephala (slope = -0.01) and
C. sylvaticus (slope = -0.009). Size class distribution
slopes for both O. arborea and K. floribunda were not
significant due to the low number of size classes (Table 3).
These slope values suggest that species such as X.
Diameter class (cm)
0 50 100 150 200 250
0 100 200 300 400 500
Fig. 3 Size class distribution for the overall stand
Fig. 4 Size class distribution
for the ten most important
S. Mensah et al.
monospora, S. gerrardii,C. kraussii,C. malosana had a
higher number of individuals in smaller size classes.
Meanwhile, species such as C. sphaerocephala,S. ger-
rardii and C. kraussii were still present in the higher
diameter classes ([80 cm).
Dominant species height–diameter allometry
The results of the analysis of covariance show significant
effects of diameter and species on height growth (Table 4).
There was also significant interaction between diameter
and species (F statistic = 4.34; p\0.001; Table 4), indi-
cating that height growth varied among dominant species.
As expected, height increased with increasing diameter for
the seven dominant species (Table 5). For a given dbh, C.
malosana and C. sylvaticus had slopes that were respec-
tively 0.27 ±0.10 and 0.13 ±0.06 significantly higher
than the ones for K. floribunda, S. gerrardii,T. dregeana,
X. monospora and C. kraussii, which was used here as a
reference. These results indicate that, for the same dbh, C.
malosana and C. sylvaticus had significantly higher aver-
age heights at tree level, as compared to K. floribunda, C.
kraussii, S. gerrardii, X. monospora and T. dregeana
(Fig. 5).
When compared with Afromontane forests in Ethiopia
(Kebede et al. 2013; Tadele et al. 2014), our results show,
despite the limited spatial coverage, that the northern
mistbelt forest harbours considerable floristic diversity in
terms of both tree species and taxonomic families. More
species were expected to be found in the regeneration class,
as general floristic patterns in multispecies natural forests.
Out of the 50 species enumerated, 35 were in the C5
to \10 cm dbh class and 45 in C10 cm dbh class. The
slightly lower species richness in the 5-0 cm class could be
due to the 5-cm threshold considered, which excludes
additional species \5 cm. Our results further reveal that
Table 3 Slope of species-specific size class distribution
Species Slope SE R square pvalue
X. monospora -0.06 0.009 0.89 \0.001
S. gerrardii -0.05 0.008 0.83 \0.001
C. sphaerocephala -0.01 0.002 0.63 \0.001
C. kraussii -0.04 0.004 0.93 \0.001
C. malosana -0.09 0.02 0.75 0.037
T. dregeana -0.01 0.004 0.48 0.004
N. congesta -0.03 0.006 0.61 0.005
C. sylvaticus -0.009 0.006 0.11 0.183
O. arborea -0.13 0.01 0.99 0.053
K. floribunda ––– –
SE standard error; pvalue indicates the level of significance for each
slope value; these values were not calculated for K. floribunda due to
a limited number of size classes
Table 4 Results of the analysis of covariance on the effects of spe-
cies and diameter on height
Source of variation Df Sum Sq Mean Sq Fvalue Pr([F)
Log (dbh) 1 49.20 49.20 2544.00 \0.001
Species 6 3.57 0.60 30.80 \0.001
Log (dbh): species 6 0.50 0.08 4.34 \0.001
Residuals 263 5.09 0.02
dbh is diameter at breast height, Df is degrees of freedom, Sum Sq is
sum of squares, Mean Sq is mean square
Table 5 Results of the linear
models of individual and
interaction effects of species
and diameter on height
Terms Independent variable Estimate SE t value Pr([|t|)
Individual terms (Intercept) 0.96 0.09 10.96 \0.001
Log (dbh) 0.53 0.03 18.67 \0.001
C. malosana -0.49 0.22 -2.20 0.029
C. sylvaticus -0.27 0.18 -1.49 0.137
K. floribunda 0.08 0.22 0.35 0.729
S. gerrardii 0.18 0.11 1.69 0.093
T. dregeana 0.13 0.14 0.87 0.384
X. monospora 0.05 0.12 0.40 0.690
Interaction terms Log (dbh): C. malosana 0.27 0.10 2.85 0.005
Log (dbh): C. sylvaticus 0.13 0.06 2.25 0.026
Log (dbh): K. floribunda -0.15 0.11 -1.41 0.159
Log (dbh): S. gerrardii -0.04 0.03 -1.29 0.198
Log (dbh): T. dregeana 0.01 0.05 0.14 0.891
Log (dbh): X. monospora -0.06 0.04 -1.59 0.112
dbh is diameter at breast height
Vegetation structure, dominance patterns and height growth in an Afromontane forest, Southern
species richness decreased with increasing size class
(Fig. 1). Other studies have also demonstrated that species
richness declines from lower to upper diameter classes
(Lulekal et al. 2008; Kebede et al. 2013). Our findings are
also in agreement with Guilherme et al. (2004) who
reported higher floristic richness and diversity in lower/
intermediate layers than in upper layers of tropical forests.
The diversity patterns observed in regards to diameter
classes may be the results of species interactions (espe-
cially competition for light), which also determines the
maximum height.
Tree density and basal area were respectively,
472.0 ±43.5 stems/ha and 1.99 ±0.19 m
for the
C5to\10 cm dbh class, and 605.3 ±28.1 stems/ha and
48.07 ±3.46 m
/ha for the C10 cm class, suggesting that
these forests have great timber potential, comparable to
other Afromontane forests in East Africa (Lulekal et al.
2008; Fisaha et al. 2013; Kebede et al. 2013). For example,
with 75 (20 m 920 m) quadrats recording diameters and
heights greater than 2 cm and 2 m, respectively, Kebede
et al. (2013) reported lower values of tree density (379.3
stems/ha) and basal area (31.4 m
) in a remnant moist
Afromontane forest of Wondo Genet in south central
Ethiopia. Yirdaw et al. (2015) reported similar density
values (537.0–622.0 stems ha
) and relatively lower basal
area (29.4–36.2 m
/ha) in Afromontane cloud forests in the
Bale Mountains of southeast Ethiopia. Knowing that these
structural features are key indicators of forest biomass
potential, our results partly confirm the remarkable biomass
and carbon potential of these mistbelt forests (Mensah et al.
2016a). Over past decades, wild fires and forest fragmen-
tation took significant toll on these indigenous forests, now
confined to small, scattered patches. Given the historical
disturbances, it is important to note that conservation
policies and recent management interventions, including
the protection of surrounding land uses against fire, have
contributed to successful development of these forests. X.
monospora and S. gerrardii were the most abundant and
dominant species in the inventoried forest area. These two
species contributed more than 40% of the stand basal area.
Past studies in the Limpopo mistbelt forests also showed
similar dominance patterns (Geldenhuys 2002; Geldenhuys
and Venter 2002).
The overall size class distribution was an inverted
J-shape with a sharp decline in tree density towards the
higher classes, a typical feature of diameter class distri-
butions in most Southern Africa’s forests (Geldenhuys
1993,1996; Mujuru and Kundhlande 2007; Kebede et al.
2013). Few individual trees were over 80 cm, as also
shown in previous reports by Geldenhuys (2000) and
Geldenhuys and Venter (2002). The overall distribution is
characteristic of multi-species forest stands with sufficient
regeneration. An inverted J-shape without gaps is also
indicative of a species successful reproduction and suc-
cession in diameter classes. Inverted J-shape trends were
observed for X. monospora,S. gerrardii,C. kraussii,C.
malosana,O. arborea, and K. floribunda, indicating that
their regeneration pool would be sufficient for maintaining
their populations. However, given the 5-cm diameter
threshold considered in this study, more in-depth analyses
on stability across diameter classes for these species would
provide insights into their ecological status and dynamic
patterns. Species such as C. sphaerocephala, T. dregeana,
N. congesta and C. sylvaticus exhibited several gaps in
lower and intermediate size classes, which may be partially
due to natural events such as tree fall. For instance, the
gaps in C. sphaerocephala diameter class distribution is
possibly the result of frequent wind throw on steep slopes
and/or trees dying. Gaps in lower and intermediate size
classes may also be attributed to irregular and sporadic
seedling establishment as a result of competition for
nutrients and light (Geldenhuys 1993; Syampungani et al.
2015). When examining the relationship of species to
height, it was interesting to see that species with relatively
lower wood density such as C. sylvaticus (Mensah et al.
2016b), tend to have taller individuals. This is partially
attributable to the fact that species with lower wood density
grow faster than those with higher wood density (Mensah
et al. 2016a,b). The variation in height growth between
dominant species is also indicative of species-specific
performance resulting from differential resource acquisi-
tion, competition and biomass production.
Fig. 5 Height–diameter allometries for important species. Scatter
plots are based on 277 trees from seven dominant species
S. Mensah et al.
Limitations and conclusion
We assessed the patterns of species diversity, vegetation
structures and dominance in a northern mistbelt forest type
in South Africa. Vegetation observational studies often
benefit from larger sample and plot size. The sample size
used in this study was slightly lower than what Yirdaw
et al. (2015) (n = 36; 400 m
) used in studying floristic
diversity and structure in Afromontane cloud forests in
Ethiopia. Thus, our sampling design might have not cap-
tured the overall variation in these forests composition.
Despite the limited spatial coverage of our data, the results
in terms of flora and structure were comparable to previous
reports in other Afromontane forests. The overall stand
showed an inverted-J shaped diameter distribution pattern,
a typical feature of size class distribution in natural forests;
and similar diameter structures were observed for most
dominant species. We also found significant effects of
species on tree height, suggesting differential height
growth among dominant species, probably as result of
different wood density and competitive interactions.
Overall, this study suggests that the long period of rel-
atively strict conservation and the management policies,
including protection of surrounding agricultural and for-
estry land uses against fire, have contributed to maintain a
successful recovery of the forests. Considering adverse
climate and land use change effects, our results indicate
that diversity and structure in the study area will generally
benefit current from legal protection. However, these for-
ests might be experiencing a relatively slow dynamic flux
as a result of minimal anthropogenic disturbance and the
over-mature state of larger trees. Institutional and man-
agerial policies permitting few extractive human uses
would contribute to preserve a healthy ecosystem, which is
in line with the intermediate disturbance hypothesis and the
general idea that anthropogenic disturbance cannot be
abandoned as a regulatory force in species structuring
(Huston 2014).
Acknowledgements The data used in this study were collected
during the first author’s doctoral research field work, co-financed by
the African Forestry Forum and the National Research Foundation of
South Africa through the ‘‘Catchman Letaba’’ project. The authors are
grateful to the anonymous reviewers for the comments on the first
version of this paper.
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... Species that are commonly found in Northern Afrotemperate forests include many that were found in this study including, Celtis, Afrocarpus, Halleria and Scolopia; those missing were Olinia, Pittosporum and Rothmania. When extrapolated, the species area relationship of roughly 70 woody species in the forest patch as a whole is consistent with other Afromontane forest patches of similar size (50-110 species) (Gemeda, Lemenih & Gole 2018;Giliba et al. 2011;Mensah et al. 2020). These Northern Afrotemperate forest patches are generally dominated by late successional, canopy forming Podocarpus but due to relatively recent disturbance events common genera such as Combretum and Celtis have taken their place (Asrat et al. 2020) resulting in different types of forest. ...
... Regeneration potential using stand density in the Pongola Bush forest fragment is similar to some other studies in Southern African Afromontane patches, but these studies show highly variable results based on a range of biotic and abiotic factors. The Pongola Bush shows a high recruitment of small stems to a decrease in larger stems in a 'reverse J' distribution, as demonstrated in other studies (Adie et al. 2013;Asrat et al. 2020;Eriksson, Teketay & Granström 2003;Mensah et al. 2020). Smaller-stemmed plants such as S. mossambicensis and many smaller individuals of potentially large trees, such as A. falcatus dominate the forest. ...
... Smaller-stemmed plants such as S. mossambicensis and many smaller individuals of potentially large trees, such as A. falcatus dominate the forest. Populations of C. kraussii have few small stems which contrasts with previous stem diameter studies of forests in the region (Mensah et al. 2020). The limited small stem recruits could potentially affect the future composition of the forest as C. kraussii is a significant contributor to AGB and stem density. ...
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The Pongola Bush Nature Reserve lies in a narrow band along the escarpment between Mpumalanga and KwaZulu-Natal (KZN). Although referred to as ‘bush’, this vegetation type may be considered to fit into the intersection of two types of scarp forest: the Northern Afrotemperate Forest and the Southern Mistbelt Forest. The area was heavily logged in the early 1900s with the need for timber for the emerging gold mining industry in Barberton. The forest fragment is now protected but lacks formal tree diversity assessments, and this study sets out to establish its community composition and richness using a range of standard techniques. Distributed throughout the forest, 127 circular plots (each 80 m2) were surveyed. In these, 1152 stems were measured for species, height, and diameter at breast height (DBH). Four species contributed roughly 70% of the 70 Mg ha−1 above ground woody biomass. Stem size class distributions showed a high recruitment rate of small stemmed individuals and few large individuals. This pattern is consistent with the disturbance history of the site, with limited recruitment of certain species, mainly limited to early successional species. The Pongola Bush forest is particularly diverse in terms of tree species: 41 species were recorded, and it is estimated from the species area curve that there may be 70 tree species present. Conservation implications: This survey is the first formal tree diversity survey conducted on the Pongola Bush which may assist future research and conservation strategies.
... The plant canopy height is an essential parameter that specifies the ecosystem structure, functional diversity, species regeneration and recruitment, natural and anthropogenic disturbances and management activities [1,2]. The canopy height is measured through field harvesting, wherein the satellite light detection and ranging (LiDAR) data can be supplemented and minimize the ground data collection efforts. ...
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Forest canopy height estimates, at a regional scale, help understand the forest carbon storage, ecosystem processes, the development of forest management and the restoration policies to mitigate global climate change, etc. The recent availability of the NASA’s Global Ecosystem Dynamics Investigation (GEDI) LiDAR data has opened up new avenues to assess the plant canopy height at a footprint level. Here, we present a novel approach using the random forest (RF) for the wall-to-wall canopy height estimation over India’s forests (i.e., evergreen forest, deciduous forest, mixed forest, plantation, and shrubland) by employing the high-resolution top-of-the-atmosphere (TOA) reflectance and vegetation indices, the synthetic aperture radar (SAR) backscatters, the topography and tree canopy density, as the proxy variables. The variable importance plot indicated that the SAR backscatters, tree canopy density and the topography are the most influential height predictors. 33.15% of India’s forest cover demonstrated the canopy height <10 m, while 44.51% accounted for 10–20 m and 22.34% of forests demonstrated a higher canopy height (>20 m). This study advocates the importance and use of GEDI data for estimating the canopy height, preferably in data-deficit mountainous regions, where most of India’s natural forest vegetation exists.
... In addition to anthropogenic pressures, several other environmental factors such as competition with adult heterospecific and conspecific individuals as well as topography, soil texture and slope determine population structure and species dynamics Zhang et al., 2016;Mensah et al., 2020a). For instance, topography can induce heterogeneity in various abiotic variables such as soil moisture and underground nutrients, which are important for tree growth (Daws et al., 2002). ...
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Detarium microcarpum Guill & Perr. and Detarium senegalense J.F.Gmel. are two species of wild trees that contribute significantly to the livelihoods of local communities in sub-Saharan Africa. Exploration of the ecological patterns of their population structure is, therefore, necessary to ensure long-term management. The aims of this study were to: (i) determine the floristic composition of the habitats of D. microcarpum and D. senegalense, (ii) assess the population structure of both species, and (iii) assess the influence of biotic and abiotic drivers on the structural parameters of these species. A total of 177 plots were installed in eight sites in Benin. The data collected included the dbh1.30m, the crown diameter, the total height, and the type of regeneration (generative, sprout, and sucker). The topographical and soil parameters of the plots were also recorded. A generalized linear model (binomial negative regression) and ANOVA were used for the analysis of density and morphological features data, respectively. The floristic composition of D. microcarpum habitats was found to be relatively distinct (p = 0.001) from one zone to another. A significant difference (p = 0.001) in heterospecific individuals was also observed between the habitats of both species. The density of individuals of D. microcarpum decreased significantly from the Sudanian zone (4594 ± 207 stems/ha) to the Guinean zone (93.60 ± 11.90 stems/ha; p < 0.001). In the Sudano-Guinean zone where both species were found, the density of D. senegalense was very low (19.07 ± 7.64 stems/ha). The density of adult individuals of D. microcarpum was significantly high on gravelly soils. The regeneration of the species was negatively correlated with the slope, soil texture and basal area of heterospecific individuals. In D. senegalense, its regeneration was negatively correlated with elevation and positively with the density of its adult individuals. The height of both species of Detarium was positively associated with altitude. This study showed the effect of biotic and abiotic factors determining the population dynamics of Detarium spp. species and could be considered in the sustainable management of these species.
... Tree density was computed as the number of trees per hectare, and basal area as the sum of the cross-sectional area 1.3 m above. Further, Size Class Distribution is also important in understanding the dynamics of forest stand (Mensah et al., 2018). In that line, we established the overall size class for the two sites (CFM and Non-CFM). ...
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It is prominently claimed that including the local community in forest management by adopting Collaborative Forest Management (CFM) approach could help for sustainable forest management. Therefore, information on its effectiveness is still needed for better planning in forest conservation. This study assessed the effectiveness of CFM on both forest status conditions and local community livelihoods in Mabira Central Forest Reserve (MCFR) in Uganda. A floristic survey was conducted to collect data on the species composition in the sites under CFM and Non-CFM. Also, interviews and focus group discussions were used to collect data on the socioeconomic aspect of the adjacent local community. Forest species composition status was assessed using common alpha diversity indices (Species richness, Shannon Weiner index, and Simpson index), beta diversity (Jaccard Coefficient), structural vegetation parameters (tree density and basal area) and species Importance Value Index (IVI). Further, size class distribution was established for the two sites (CFM and Non-CFM). Regarding local community livelihood, descriptive and inferential statistics were used. Results revealed that the two sites have low similarity with the CFM site having low species diversity compared to Non-CFM site. The size class distribution of the site under CFM shows stable vegetation, suggesting good regeneration and recruitment potential. In contrary, the adjacent 124 Makerere University Journal of Agricultural and Environmental Sciences community livelihoods seemed to not be improved after the implementation of the CFM approach. Their income has considerably decreased because most of their activities were based on forest resources. We, therefore, argue that CFM approach should be updated and mixed with a top-down approach to improving forest status and local community livelihoods.
... Reverse-J SCD curves indicate good recruitment, with more individuals in smaller size classes and fewer in larger classes (Obiri et al., 2002;Martins and Shackleton, 2017). Unimodal SCD curves indicate populations with a limited recruitment, with more individuals in larger size classes and fewer in smaller size classes (Mensah et al., 2020). ...
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The Seychelles granitic islands have been small, mid-oceanic, equatorial, mountainous and moist islands for at least 50 million years, with an uninterrupted vegetation cover since their separation from Gondwana. Therefore, unlike hotspot oceanic islands that drastically vary in environmental heterogeneity according to their age, the Seychelles can provide observational data where evolutionary time is de-correlated from habitat heterogeneity. In this paper, we aim to describe for the first time its most widespread, least known, and most threatened ecosystem type: the lowland rain forest. Surprisingly, this had never been done before and the reason is simply that only 6.5 % of those forests have survived untouched by the 2.5 centuries of human presence on these islands. We set six permanent vegetation plots within the largest (ca. 50 ha) and best-preserved relict of this forest, plus four permanent plots in a nearby site (1 km away) that is ecologically homologous but has been intensively modified, abandoned for the last 40 years and which is now a structurally mature late secondary forest. Each plot covered 500 m² and all vascular plants were inventoried in a series of subplots corresponding to different strata. Within the 0.5 ha of surveyed forest, we observed 35 native species (17 canopy/under-canopy trees, 8 shrubs or small understorey trees, and 10 herbs), of which 11 are endemic (31 %). All plots within the natural forest site were floristically and structurally very similar. Their flora (within just 500 m²) represented about 87 to 92 % of the total flora of the Seychelles lowland mesic forests (defined as an ecological group). In addition, the three most dominant under-canopy trees corresponded to paleo-endemic species having the particularity to be both climax and pioneer trees, which is very unusual. Our study also shows that exotic species were hardly present in undisturbed natural forests but, in disturbed forests, on the other hand, native species were re-colonizing so-called novel ecosystems. Based on these results, we present a list of native species which are appropriate for restoration programs in the Seychelles lowland rain forests, including one that was previously considered as an exotic invasive but which could greatly improve restoration work. Finally, our study sets the basis for long term monitoring of natural ecosystem resilience to invasions on the one hand, and biotic novelty of novel ecosystems on the other.
... Aunque se usan comúnmente especies exóticas debido a su confiabilidad basada en resultados previos (Ruiz, 2002). Sin embargo, en Madre de Dios, otros estudios utilizaron exitosamente La estructura de la vegetación, luego de 20 años del establecimiento de la reforestación, presentó un patrón de tipo jota invertida, típico de los bosques naturales tropicales y que sugiere un buen potencial de reclutamiento de la regeneración natural en estas áreas luego del abandono (Astudillo-Sánchez et al., 2019;Mensah et al., 2020). Las especies espontáneas están dominando el estrato arbóreo en el sitio 2019-C M. poepigii (> 15 m altura) y en el sitio A Tachigali sp. 1 (< 15 m), además de otras especies como C. micrantha, Jacaranda glabra, Alchornea triplinervia y V. macrophylla. ...
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Madre de Dios es uno de los bosques naturales más diversos y mejor conservados de la Amazonía. Sin embargo, esta mega diversidad está amenazada por la minería ilegal de oro. El objetivo del presente estudio fue analizar la diversidad, estructura y biomasa aérea en 3 sitios reforestados hace 20 años en Huepetuhe, sureste de la Amazonía peruana. La reforestación se realizó para recuperar áreas abandonadas por minería, utilizando principalmente especies exóticas. Se utilizaron 3 parcelas de 20 m × 20 m por sitio, donde se inventariaron todos los individuos con un diámetro > 2.5 cm. Se registraron 25 especies arbóreas, solo 3 de estas se plantaron al inicio de la reforestación (Tachigali sp. 1, Senna reticulata y Acacia mangium). El estrato arbóreo está dominado por vegetación espontánea como Vismia baccifera, Cinchona micrantha y Miconia poepigii y una especie exótica (Tachigali sp. 1). Encontramos árboles de M. poepigii con más de 20 cm de diámetro y 18 m de altura. Las especies espontáneas representan más del 80% del total. El bosque almacenó entre 30-69% menos biomasa que bosques secundarios de edad similar. Los proyectos futuros deberían considerar estas especies nativas para la restauración ecológica de áreas degradadas por minería.
... Mistbelt forests in South Africa are often referred to as Afromontane forest due to the altitudinal belt and slope gradient covered by their woody floristic vegetation. They are tall moist evergreen forests occurring at altitudes up to 1800 m, and consisting of many small, fragmented and widely distributed patches (Mensah et al., 2018b). Rockfall is a natural event in such mountain areas, but forests, through their crowns, help prevent water from splashing directly and washing the stones, thereby preventing rockfall. ...
Studies on how biodiversity influences ecosystem multifunctionality (EMF) help elucidate ecological mechanisms (e.g. niche complementarity and selection) underlying provision of multiple ecosystem services. While it is acknowledged that biodiversity contributes to EMF, the relative importance of functional traits diversity (niche complementarity) and dominance (selection effects) for EMF needs further investigation. To address this gap, we analysed how tree species diversity influences EMF, using data on species functional traits (specific wood density, specific leaf area and maximum plant height) and four ecosystem functions (carbon storage, habitat quality, forage provision and rockfall protection) in an Afromontane forest in South Africa. We tested the hypotheses that (i) trait diversity rather than dominance would link species richness to EMF; and (ii) diversity rather than species richness effects would increase with the level of EMF. For all possible scenarios of EMF indices, functional trait diversity metrics, especially functional divergence and functional richness correlated positively with EMF. On the other hand, functional dominance also influenced EMF, but played limited role in mediating EMF response to species richness, when compared with functional diversity. Results further revealed that total diversity effects, not species richness effect, generally increased with the level of EMF. In summary, we show that species richness does not fully capture the functional contribution of different species. Compared to dominance, trait diversity had significant advantage in explaining biodiversity-EMF relationship, stressing a greater role of niche complementarity as mechanism underpinning delivery of multiple functions. We argue that functional dominance reflects more the competitive dominance of traits and species within a given community and therefore is more likely to have greater effects on single functions than on multifunctionality.
... In both periods of assessments, the overall diameter and height class distribution of woody species revealed that a positively skewed distribution was prevalent in which more individual species were found in the lower diameter and height classes. It is a general pattern of healthy population structure and good recruitment potential of vegetation (Zegeye et al., 2006;Lulekal et al., 2008;Goncalves et al., 2018;Mensah et al., 2018). ...
Conservation of forest ecosystems plays a great role to combat one of the major environmental problems of biodiversity loss. This study was conducted in Denkoro dry evergreen Afromontane forest, south Wollo zone of Amhara National Regional State, Ethiopia to evaluate the changes of woody species composition, structure and regeneration status over 16 years (2001–2017) of conservation effort. Thirty-eight permanent sample plots of 10 m × 50 m size were laid along 50 m altitudinal intervals via nine transect lines which were running parallel to each other for vegetation data collection. Subplots of 2 m × 10 m were laid at two opposite corners of main plots for seedling and sapling inventory. Fifty woody species that belong to 43 genera and 31 families and 59 woody species that belong to 49 genera and 32 families were recorded in 2001 and 2017, respectively. Seventeen new species were registered and eight species were lost in 2017. The density and total basal area of woody species increased from 986 to 1011 individuals ha ⁻¹ and 32.68 to 34.74 m ² ha ⁻¹ , respectively over 16 years. Olinia rochetiana, Olea europaea subsp. cuspidata and Apodytes dimidiata were the most frequent species in the forest in 2017. Myrsine melanophloes, Olea europaea subsp. cuspidata, Apodytes dimidiata and Olinia rochetiana were the most ecologically important woody species with higher important value index over the studied period (2001–2017). The overall population structure of woody species showed that the forest is under good recruitment potential in both assessments. The numbers of medium DBH class individuals increased in 2017. Poor recruitment and regeneration were also evident in certain woody species. Though woody species composition, structure and regeneration in Denkoro dry evergreen Afromontane forest improved, the forest needs more attention for further conservation and management efforts.
The forests of South Africa and the neighbouring countries, including Lesotho, eSwatini, Namibia, Botswana, Zimbabwe, and Mozambique (south of the Zambezi River), were mapped and classified according to the global system of biomes. The new four-tier hierarchical biome system suggested in this paper includes zonobiome, global biome, continental biome (all recognised earlier), and regional biome – a novel biome category. The existing spatial coverages of the forests were revised and considerably improved, both in terms of forest-patch coverage and mapping precision. Southern Africa is home to three zonal forest types, namely Subtropical Forests (Zonobiome I), Tropical Dry Forest (TDF; Zonobiome II) and Afrotemperate Forests (Zonobiome X). These three biomes are characterised by unique bioclimatic envelopes. Five, two, and eight regional biomes, respectively, have been recognised within these zonal biomes. Recognition of the Zonobiome I and the global biome Tropical Dry Forests in southern Africa is novel and expands our knowledge of the biome structure of African biotic communities. The system of the azonal regional biomes is also new and comprehensively covers the variability of the azonal helobiomes (riparian woodlands and swamp forests), mangroves, and azonal coastal forests. In total, 11 azonal regional biomes have been recognised in the study area. The forest biomes in southern Africa were captured in our electronic map in the form of more than 60 000 polygons, covering 42 416 km² (1.27% of the study area). No less than 83% of these forests occur in the territory of southern Mozambique. Abbreviations: for the abbreviation of the biome units, see Table 1; CE: centre of endemism; IOCB: Indian Ocean Coastal Belt; MBSA: the area of the Map of Biomes of Southern Africa; VegMap2006 and VegMap2018: Vegetation Map of South Africa, Lesotho and Swaziland (as released in respective years); for the meaning of the codes of the biome units see Table 1, and for the meaning of the abbreviations of climatic characteristics see Appendix S1
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Information on how abiotic and biotic factors affect species population structures and regeneration are critical for understanding plant growth in natural habitats. Here, we used data from three spatially distinct populations of Afzelia africana Sm. in the Pendjari Biosphere Reserve in Benin, to determine how the species population structures respond to abiotic and biotic factors. Afzelia africana population structures were studied using several parameters including basal area, tree height, density of successive diameter classes, and size class slope. We tested for individual effects of abiotic (mound density, soil type, terrain slope) and biotic (heterospecific tree density) factors on the species population structure. We also tested for similarity of species composition among studied A. africana population stands. Results revealed a tree density structure with mature individuals, and size class distribution indicating a recruitment bottleneck at the juvenile stage (10-20 cm diameter), possibly due to mammal browsing, natural and artificial fires. Heterospecific tree density was positively associated with A. africana adult density, but negatively related to the species growth parameters (mean diameter, basal area and tree height). These results indicate some degrees of niche overlap between A. africana and coexisting species, but also partly reflect A. africana tolerance and adaptation to limited resources environment. Soil type significantly influenced both basal area and regeneration density, greater values being observed on silt-sand-rocky soils. Basal area was higher on steeper slope, probably a result of species conservative strategies. These findings were discussed in line with management and restoration action needs in the Pendjari Biosphere Reserve.
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Forest stratification plays a crucial role in light interception and plant photosynthetic activities. However, despite the increased number of studies on biodiversity-ecosystem function, we still lack information on how stratification in tropical forests modulates biodiversity effects. Moreover, there is less investigation and argument on the role of species and functional traits in forest layers. Here, we analysed from a perspective of forest layer (sub-canopy, canopy and emergent species layers), the relationship between diversity and aboveground biomass (AGB), focusing on functional diversity and dominance, and underlying mechanisms such as niche complementarity and selection. The sub-canopy layer had the highest species richness and diversity, while the emergent layer had the highest AGB. Species richness–AGB relationship was positive for each forest layer, but stronger for sub-canopy layer than for canopy and emergent layers. Total AGB was strongly correlated with functional diversity, leaf and wood traits of species in the sub-canopy and canopy layers. This suggests that sub-canopy and canopy species are major drivers of stand diversity-AGB relationship, and that resource filtering by canopy or emergent trees may not reduce the strength of diversity–AGB relationship in the sub-canopy layer. We argue that complementary resource use by sub-canopy species that supports niche complementarity, is a key mechanism driving AGB in natural forests. Selection effects are most evident in emergent species and niche complementarity effects for sub-canopy and canopy species, supporting arguments that AGB is affected by sub-canopy species efficient use of limited resources despite competition from emergent species.
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Novel species-specific equations for the estimation of height and aboveground biomass were established for four dominant tree species (Syzygium gerrardii Burtt Davy, Combretum kraussii Hochst., Trichilia dregeana Sond. and Croton sylvaticus Hochst.), in the Northern Mistbelt Forests of South Africa. A non-destructive sampling methodology was applied, which was based on measuring standing trees, selecting smaller branches and taking core samples. The species-specific aboveground biomass equations were fitted using predictor variables such as diameter at breast height (DBH) and total height (H). The relative error of estimation was used to examine the accuracy of a pantropical biomass equation versus our established specific model. Biomass values were afterwards up-scaled from tree to stand level for each species, based on the selected models and the forest inventory data. As expected, the DBH–height relationship varied among studied species. The incorporation of both DBH and H in the biomass models significantly improved their precision. A model with DBH² × H as a single variable was suitable for three out of the four studied species, with more than 98% of explained variance. An existing pantropical biomass equation for moist forests showed larger relative error of estimation, especially in the upper range of tree diameter. The estimated aboveground biomass density varied significantly among studied species, with the highest values recorded for S. gerrardii (87.7 ± 15.4 Mg ha⁻¹), followed by T. dregeana (29.4 ± 14.7 Mg ha⁻¹), C. sylvaticus (24.3 ± 11.5 Mg ha⁻¹) and C. kraussii (20.1 ± 6.7 Mg ha⁻¹). It is also found that species-specific production of biomass at the tree level is not always sufficient to reflect the stand-level biomass density. The results from this study contribute to accurately predict aboveground biomass, thereby improving the reliability of the estimates of forest biomass and carbon balance.
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Biomass allocation is closely related to species traits, resources avail- ability and competitive abilities, and therefore it is often used to capture resource utilisation within plants. In this study, we searched for patterns in biomass alloca- tion between foliage and wood (stem plus branch), and how they changed with tree size (diameter), species identity and functional traits (leaf area and specific wood density). Using data on the aboveground biomass of 89 trees from six species in a Mistbelt forest (South Africa), we evaluated the leaf to wood mass ratio (LWR). The effects of tree size, species identity and specific traits on LWR were tested using Generalised Linear Models. Tree size (diameter) was the main driver of bio- mass allocation, with 44.43 % of variance explained. As expected, LWR declined significantly with increasing tree diameter. Leaf area (30.17% explained variance) and wood density (12.61% explained variance) also showed significant effects, after size effect was accounted for. Results also showed clear differences among species and between groups of species. Per unit of wood mass, more biomass is allocated to the foliage in the species with the larger leaf area. Inversely, less bio- mass is allocated to the foliage in species with higher wood density. Moreover, with increasing diameter, lower wood density species tended to allocate more biomass to foliage and less biomass to stems and branches. Overall, our results emphasise the influence of plant size and functional traits on biomass allocation, but showed that neither tree diameter and species identity nor leaf area and wood density are the only important variables.
In southern Mozambique, the sap and leaves of the palms Hyphaene coriacea and Phoenix reclinata are harvested by local people as sources of traditional beverages, weaving, roofing, fencing and furniture material. The harvesting of these palm products may affect palm population structure, dynamics and viability. This work evaluates the abundance, population structure and harvesting selection of these two heavily harvested palm species. Hyphaene coriacea was more abundant, with a mean density of 601.5 ± 455.9 stems ha⁻¹ against the 251.9 ± 527.3 stems ha⁻¹ of Phoenix reclinata. Both species exhibited steeper negative slopes in the regression analyses of the size class distribution, indicating the presence of more individuals in smaller size classes. Although there was a dominance of shorter over taller size classes, limited recruitment was observed through low densities of seedling and juvenile size classes compared to the size class 1–50 cm. The Simpson index of dominance, the permutation index, and the fluctuating quotients between the consecutive size classes showed a degree of instability in both populations. Hyphaene coriacea appears to be more resilient to tapping than Phoenix reclinata, evident in the higher rate of stem survival after tapping. Hyphaene coriacea is favored for tapping compared to Phoenix reclinata. Tappers exhibited positive selection for five out of the six Hyphaene coriacea size classes, against only one Phoenix reclinata size class. The most preferred size class to tap for both species was between 101 cm and 150 cm tall. The instability detected by the indices of population stability, the coincidence between the size classes with high numbers of dead stems and the most preferred and the low level of the sexual reproduction encountered in both population emphasizes the need for long-term monitoring as well as management measures that integrate the resource users, to ensure the long-term sustainability of these populations.
Honey bees play a vital role in the pollination of flowers in many agricultural systems, while providing honey through well managed beekeeping activities. Managed honey bees rely on the provision of pollen and nectar for their survival and productivity. Using data from field plot inventories in natural mistbelt forests, we (1) assessed the diversity and relative importance of honey bee plants, (2) explored the temporal availability of honey bee forage (nectar and pollen resources), and (3) elucidated how plant diversity (bee plant richness and overall plant richness) influenced the amount of forage available (production). A forage value index was defined on the basis of species-specific nectar and pollen values, and expected flowering period. Up to 50% of the overall woody plant richness were found to be honey bee plant species, with varying flowering period. As expected, bee plant richness increased with overall plant richness. Interestingly, bee plants’ flowering period was spread widely over a year, although the highest potential of forage supply was observed during the last quarter. We also found that only few honey bee plant species contributed 90 percent of the available forage. Surprisingly, overall plant richness did not significantly influence the bee forage value. Rather, bee plant species richness showed significant and greater effect. The results of this study suggest that mistbelt forests can contribute to increase the spatial and temporal availability of diverse floral resources for managed honey bees. Conservation efforts must be specifically oriented towards honey bee plant species in mistbelt forests to preserve and enhance their potential to help maintain honey bee colonies. The implications for forest management, beekeeping activities and pollination-based agriculture were discussed.
Ecosystem services (ESs) underpin human livelihoods around the world. Understanding how socio-environmental aspects influence stakeholders’ perceptions and use of ESs, is important for decision-making processes that target the social expectations. In this study, face-to-face interviews were conducted with eighty-six householders in four villages of Limpopo province (South Africa), to assess the importance and use of ESs. Descriptive rank analysis, ordered logistic regression and Poisson generalised linear mixed-effects models were used. Supporting and provisioning ESs were rated the most important, followed by regulating and cultural ESs. Among the provisioning ESs, timber, firewood and edible plants were the most important, the most cited and used. Age, gender, income and prior recreational experiences played important roles in householders’ perceptions. The frequency of collection of provisioning ESs declined with increasing distance to the forest and presence of foothills in landscape, which formed natural barriers. The results further revealed that employed householders benefited more from these services than unemployed householders. However, there was no significant effect of income variable on the use of the provisioning ESs, suggesting that the collection is more likely oriented towards a domestic usage. The implications of the results were discussed in a context of local development planning.