International Research Journal of Plant Science (ISSN: 2141-5447) Vol. 2(9) pp. 288-293, September, 2011
Available online http://www.interesjournals.org/IRJPS
Copyright © 2011 International Research Journals
Full length Research Paper
Evaluation of high-value indigenous trees for the
rehabilitation of deforested areas in Mayombe Rain
Forest, Southern Congo
Valentin Serge Pangou1, Jean-Pierre Kampé2, Catherine Lenoir3, Albertine Yulu Milandu1
1
Groupe d’Etude et de Recherche sur la Diversité Biologique, Brazzaville-Congo.
Centre Régional de Recherche Agronomique et Forestière d’Oyo, Oyo, Congo.
2
Faculté des Sciences, Université Henri Poincaré Nancy I, Nancy-France.
3
UR de Phytogénétique, GERDIB, Brazzaville, Congo.
2
Accepted 06 September, 2011
Evaluation on the growth of five indigenous timber species was performed nine years after planting.
The selected species were of Aucoumea Klaineana, Baillonella toxisperma, Carapa procera,
Pterocarpus soyauxii and Terminalia superba. Seedlings of these tree species were planted under open
area planting technique on secondary forest area at Les Saras in the Mayombe Rainforest, Southern
Congo. An experimental design of Randomized Complete Block Design (RCBD) was adapted. The
assessment involving measurements of diameter at breast height (DBH), height of the species and the
survival rate were carried out. The result shows that the higher growth increments for the DBH were
-1
-1
found at P. soyauxii (1.06 cm year ) and the lowest at B. toxisperma (0.97 cm year ). For the height
-1
increment, P. soyauxii was 1.38 m year which was the highest and the lowest was the C. procera (0.77
m year-1). However, the survival rate was found higher at P. soyauxii (76.3%) and the lowest was at the
C. procera (20.7%). These indicate that some indigenous species can be adapted to rehabilitate
secondary forest area.
Keywords: Degraded area, growth, indigenous trees species survival, forest enrichment.
INTRODUCTION
Forest area has been in demand for agricultural land,
timber and housing development, which has accelerated
deforestation in Congo. Deforestation is a worldwide
environmental issue (Sayer et al., 2004). In the tropics,
deforestation often leads to land degradation under
tropical climatic conditions (Eden and Parry, 1996).
Logging has a major impact on the structural and
compositional development of forests.
The extraction of large trees usually damages
neighboring trees and influences the development of the
under storey vegetation (Langenberger et al., 2005).
*Corresponding author email: serge_pangou@yahoo.fr
Bischoff et al. (2005) defined that secondary forest mean
forests, which are recovering from logging and not those
recovering from large natural disturbances. After forest
conversion to agriculture or pastureland, forest recovery
may occur through secondary succession. However,
when the probability of recreating initial conditions is low
or recovery time to long, human intervention may be
required to ameliorate land degradation (Pedraza and
Williams-Linera, 2003). The establishment of plantations
has been proposed as a tool for forest restoration of
degraded lands through their effects on vegetation
structure, microclimate and soils (Maitre, 1986; Pedraza
and Williams-Linera, 2003).
In such degraded areas, the native plant species is
prone to fail in surviving because the degraded soil
Pangou et al. 289
conditions are different from the original conditions
(Kanowski et al., 2005). Hence, there is the need for
continual exploration, evaluation and domestication of
tree species for reforestation, especially on degraded
lands, where not all introduced species perform well and
yet there is urgent need to restore productivity and
ecosystem services (Calvo-Alvarado et al., 2007). To
rectify the situation, fast growing indigenous tree species
were introduced extensively for plantation establishment
(Andrew et al., 2004). Furthermore, their wood is
generally more valuable and useful than that of fast
growing trees (Sakai et al., 2009).
Indigenous trees have some important biological
advantages, such as adaptation to the local environment,
resistance to pests and disease and the conservation of
local fauna and flora (Evans, 1992). However,
rehabilitation using indigenous timber species on a larger
scale usually encountered the following obstacles;
irregular supply and recalcitrance of seeds and high
variability in growth of seedlings of as yet unknown
genetic potential, as seedlings are raised from stumps or
wildings (Appanah and Weinland, 1993). The growth of
tropical secondary forest vegetation responds quickly to
changes in environmental conditions (Romell et al.,
2007). Therefore, the objective of this study was to
investigate the best species through growth parameters
for plantation and rehabilitation among selected wood
species.
MATERIALS AND METHODS
Plants materials
Five indigenous species were selected for the study
comprising Aucoumea Klaineana Pierre (Burseraceae),
Baillonella toxisperma Pierre (Sapotaceae), Carapa
procera DC. (Meliaceae), Pterocarpus soyauxii Taubert
(Fabaceae) and Terminalia superba Engler and Diels
(Combretaceae). They are typical large canopy trees
most common in Mayombe rainforest where they are
among the first timber tree species or of high-value
indigenous multi-purpose (CTFT, 1989).
These species are locally abundant and usually found
in dense patches or in deciduous forests. Typically 3-5
trees over 30 cm DBH (Diameter at Breast Height) are
recorded per hectare for these species in regional prelogging inventories in Mayombe rainforest (Pangou et al.,
2006). In this study, these species were selected
because of their important role in providing some
valuable timber and non-timber products and mainly
because of their relatively easy propagation and fast
growth (Maitre, 1986).
Study area
The study area was located in the vicinity of Dimonika
Research station, at Les Saras (latitude 12°26’10’’ to
12°27’04’’E, longitude 4°12’26’’ to 4°13’09’’S, at 250-400
m altitude), in the Mayombe rainforest (Southern Congo).
The area includes primary, secondary and logged-over
forests.
The climate is humid, and annual rainfall ranges from
1600 to 1800 mm. Mean annual temperatures are between
23 and 27°C (Vennetier, 1977). The soils on the plateaus
are primarily ferric oxisols, and the valleys mostly
hydromorphic ferric oxisols (Devigne, 1956).
The floristic community is composed of mixed forest type
with dominance of leguminous trees species where there is
Gilbertiodendron dewevrei (De Wild.) J. Leonard in soils with
high sand content and some edaphic moisture, being
substituted by Pterocarpus soyauxii and Terminalia superba
in ferralitic oxisols (Pangou et al., 2006).
The experimental plot chosen (42 ha) was a degraded
logged-over forest established in October 2001. The
mean annual rainfall for a ten years period (2000-2010)
was 1233.83 mm and the area experiences rainy season
in November, October and April. The mean daily
temperature was 20.3-30.7°C. The mean monthly relative
humidity of the area was about 80% (Pangou et al.,
2007).
Experimental design
Randomized Complete Block Design (RCBD) was used
to analyze the data obtained from three replications of
30x150 m block. Each block has 30 subplots with 5x10 m
each. In each subplot, a total of 15 seedlings were lineplanted at a spacing of 2x2 m. The total number of
potted-seedlings planted was 1,350. Open planting
technique had been used.
Measured variables
The growth parameters measured were as the diameter
at breast height, total height and the survival rate of the
planted wood species DBH taken at 1.3 m from root
collar by using Digmatic Diameter Caliper. The height of
the plants was measured from the root collar to the base
of the top bud by using Height poll and Haga. Three plots
(45 trees) from each block were counted for survival rate.
Measurement of the data was recorded to two decimal
points. The survival percentage of each species was also
noted.
Statistical analyses
Data were subjected to the Analysis of Variance and
Duncan’s Multiple Range test. An Analysis of Variance
290 Int. Res. J. Plant Sci.
Figure 1. Survival rate (%) after 9 years of planting. Mean for total DBH, are
significantly different (p ≤ 0.05). Column with the same letter are not significant
(ns = significant)
was used to evaluate the growth capacity of the species
(SAS, 2006).
there were not significant different (p>0.05) in increments
of DBH (Figure 2).
RESULTS
DISCUSSION
Rate of survival
Figure 1 shows the rate of survival of the different tree
species studied. Statistical analysis showed that there
were significant (p<0.05) differences in survival rate of
the species. The highest survival rate was P. soyauxii
(76.35), followed by T. superba (74.1%), A. klaineana
(48.2%), B. toxisperma (24.4%) and the lowest was C.
procera (20.7%).
Height and stem diameter (DBH) growth
Figures 2 and 3 show the mean total diameter and total
height attained by the different tree species at nine years
old. Based on both the height and stem diameter results,
T. superba, P. soyauxii and A. klaineana have proven to
be the fastest growing tree species out of the five
considered in this study, while B. toxisperma and C.
procera had the lowest value. Mean for DBH, total height
and increment height are significantly different (p ≤ 0.05)
by Duncan’s New multiple range test. On the other hand,
The present study indicated in the degraded forest area
showed that shade-tolerant species like B. toxisperma
and C. procera had poor survival rate. Most earlier
studies involving planting B. toxisperma in logged and
degraded forests have reported substantially higher
mortality rates (Fargeot and Pangou, 2000). For example,
Teillier (1994) reported seedling mortality rates of 39% for
Klainedoxa gabonensis and 22% for Irvingia gabonensis
over the first 6 months in degraded land in Ngoua 2,
Congo. Ilengo et al. (2001) registered survival rates
between 40 and 85% for Coula edulis, B. toxisperma and
C. procera, 2 years after planting. However, Fargeot and
Pangou (2000) found that Nauclea diderrichii is a useful
sivicultural species with high survival (>70%) in both
shaded and open sites if the regular maintenance like
weed cutting is carried out. As a result, B. toxisperma and
C. procera are considered as a shade-tolerant species
and need shading at early stage of planting (Dupuy and
Mile, 1991). Some of the reasons for the high mortality
rate in these tree species included high insect (pest)
infestation e.g., white woolly aphids on C. procera, and
unidentified fungal and viral diseases noted in B.
toxisperma.
Pangou et al. 291
Figure 2. Mean for total diameter at breast height (cm) and increment diameter
after 9 years of planting. Mean for total DBH, are significantly different (p ≤ 0.05)
by Duncan’s New multiple range test. Column with the same letter are no
significantly different (ns = significant).
Figure 3. Mean for total height (cm) and increment height after 9 years of
planting. Mean total height and increment height (by column) are significantly
different (p ≤ 0.05) by Duncan’s New multiple range. Column with the same letter
are no significantly different (ns = significant).
However, for light-tolerant species such as T. superba
and P. soyauxii showed high survival rate. Similar study
done by Teillier (1994) mentioned that T. superba had the
highest rate of survival. In another study, Fargeot and
Pangou (2000) reported that P. soyauxii exhibited the
highest survival rate in gap planting with 83.5%. The
survival of T. superba in the present study also coincided
with that of Nassi (2006) and Fuhr et al., (1998), who
noted that the survival rate of Aucoumea klaineana
provenances at the age of 58 months ranged between
75-95%. Another earlier study, non-shade tolerant
species was reported by Dupuy and Mille (1991) that the
survival of P. soyauxii trees at Dimonika in Mayombe,
Congo was greater than that of P. soyauxii. The high
survival rate could be due to the adaptability of the
species with site conditions like water stress and soil poor
nutrient. In degraded forests and in open areas, a
combination of increased run-off and higher light levels
may lead to increase water stress on planted seedlings
(Malmer, 1992). Unapplied treatment in this experiment
292 Int. Res. J. Plant Sci.
significantly affected the mortality rates, and
environmental conditions other than those manipulated in
the experiment must have a large impact on survival.
Environment factors like weather condition, pest attack
and animal distribution, weed competition and poor soil
condition are the factors possibly leading to variation in
survival rate and growth performance (Evans, 1992).
Furthermore, growing space also contributes to the
growth performance (Mohd Zaki et al., 2003).
The growth capacity of P. soyauxii was likely the same
as that studied by Teillier (1994), that the highest mean
-1
was basal diameter increment (3.49 mm year ) and
-1
height increment (46.44 cm year ) was at 36 months old
tree. According to Fargeot and Pangou (2000), the 25
year old A. klaineana has an average annual diameter
increment of 1.2 cm year-1. Maitre (1986) found that
individual trees in their early years grow at a rate of
-1
between 0.8 and 1.6 cm year in diameter. B
toxisperma is a slow growing species with annual
diameter increment of 0.6 cm year-1 only which is lower
as in comparison to the present study (Dupuy and Mille,
1991; Fargeot and Pangou 2000). However, Pangou et
al. (2006) stated that mean annual increment of height for
-1
B toxisperma and A. klaineana were 0.8 and 1.0 m year ,
respectively.
Better height and diameter growth of the species could
be because they adapt well to the locality or species-site
matching and have the ability to tolerate water stress and
other unfavorable site conditions. Azani et al. (2003) also
supported that the variation in growth of planted species
could be due to specific reaction of the species to
environmental conditions. As a result of experiences in
Indonesia and Malaysia, growth in terms of height and
diameter increments is influenced by the large growing
space (Mohd Zaki et al., 2003). However, this would be
most likely to promote weed or climbers to grow and
invade the site.
In conclusion, overall performance of indigenous tree
species indicates that P. soyauxii and T. superba have
good performance both in survival rate and growth in the
open planting technique. Slashing, sivicultural treatment
and monitoring have the potential to improve the survival
under secondary forest area.
ACKNOWLEDGEMENTS
This work was jointly supported by Ministère de la
Recherche Scientifique of Congo, the World Agroforestry
Centre (ICRAF). Also thanks to Pr. A Massanga and Dr.
P. Wilson for technical help and discussion, the
anonymous reviewers for theirs valuable comments and
remarks on the paper.
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