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Part II: Symposium
DEMOGRAPHIC STUDY ON NON-TIMBER SPECIES FOR
SUSTAINABLE USE AND MANAGEMENT OF FOREST RESOURCES:
THE CASE OF GARCINIA LUCIDA VESQUE
N.M. Guedje1 and B.A. Nkongmeneck2
SUMMARY
Garcinia lucida Vesque. (Guttiferae) is a highly valued Non-Timber Forest Product for
domestic consumption and commercial purposes in the South-Cameroon region. The bark is
used as an additive in palm wine, while bark and nuts are also exploited for medicinal purposes.
To assess the sustainability of harvesting the fruits and the bark of this gregarious and small
sub-canopy tree of undisturbed forests, a detailed demographic study was carried out in
permanent plots established in low and high exploited areas in two locations. Preliminary data
concerning size-class distribution, phenology, germination and reproduction rates, from an
ongoing monitoring of a sample of marked trees are examined in the present paper. Analysing
this information on growth, mortality and reproduction may provide elements of transition
matrices that will serve as a tool to simulate population dynamics and to evaluate the impact of
the actual local extraction practices. These models will also serve to investigate or to predict
changes in population age/size structure when subjected to different harvesting or management
regimes, and to define the sustainable level of resource extraction. The plant demographic
survey was combined with an experimental approach to test different local harvesting
techniques and intensities, and a participatory monitoring and evaluation system. This
combination is expected to provide tools and applicable guidelines to develop an efficient,
socially appropriate and sustainable exploitation and management system of this resource, as
well as recommendations for the incorporation in forest management planning.
Keywords: non-timber forest products, Garcinia lucida, autecology, tropical rain forest,
Cameroon.
1. INTRODUCTION
Pressure on forest resources is increasingly notable in most Central African countries, as a result
of the economic crisis combined with the devaluation of the regional currency FCFA.
Processing of Non-Timber Forest Products (NTFPs) to generate sources of income or food for
subsistence has become more attractive for several unemployed people in these countries. In
Cameroonian humid forest area, Ndoye et al. (1997) recorded for Irvingia spp. kernel, Cola
acumita nuts, Garcinia kola and G. lucida nuts and bark, a total of 138 tons and 85 tons sold in
1995 and in 1996 for a total value of 84 072 000 and 76 424 700 FCFA. In the Southwest
Province of Cameroon, the market value of the Prunus africana bark is estimated at USD
150 000 000 per year and represents an average of 1923 metric tons of bark processed between
1986 and 1991 (Cunningham and Mbenkum, 1993). The kernel of Irvingia gabonensis is
exported from Cameroon to Nigeria and Gabon while the bark of Garcinia lucida and G. kola is
exported to Gabon and Guinea Equatorial. According to AEERD (1993), cited by Ndoye et al.
(1998), 428 tons of Gnetum africanum leaves were exported from Cameroon to Nigeria in 1992.
Unfortunately, in most cases, increased processing of these NTFPs has been directly linked to
resource depletion in natural forests. An average of 35 000 trees of Prunus africana is debarked
per year (Cunningham and Mbenkum, 1993) and this extraction threatens to eliminate the
1
2
Tropenbos-Cameroon Programme, P.O.B. 219, Kribi, Cameroon.
Department of Plant Biology and Physiology, University of Yaoundé I, Yaoundé, Cameroon.
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species. In the same area, Gnetum africanum is depleted by an intensive commercial extraction
of leaves. There are many other examples of resource depletion as a result of overexploitation:
Recent data show decreases in rattan yield in Cameroon (Bene, 1994). In the Bipindi-Akom II
region more than 50% of tree mortality has been recorded in some natural extractive areas of G.
lucida bark as a result of intensive extraction (Guedje, 1996).
This species is highly valued in the region for domestic consumption and commercial purposes.
It is a gregarious species of the family of Guttiferae and a small sub-canopy tree of undisturbed
or mature forest at more than 500 m altitude. It grows in restricted areas. The bark is used as an
additive in palm wine production, while bark and nuts are also exploited for medicinal purposes
as anti-poison and to cure stomach pains. The extraction of the bark is often done by stripping
the stem all around, resulting in the death of the tree.
Wise utilisation and management of this non-timber resource is needed to ensure its long-term
availability. To achieve this, it is essential to identify the conditions for sustainable exploitation,
which can help to assess the potential of forests. In general, quantitative analysis of the impact
of extraction on population structure and dynamics are lacking. Furthermore, there are few
available data on the establishment, growth, and reproductive ecology for most of these nontimber forest resources in Central Africa.
As the nature and the importance of NTFPs are closely related to the ecological, economic and
socio-cultural conditions of local population, the emphasis of the study presented here is to
combine demographic survey, experimental and participatory approaches. This study is part of
the Tropenbos-Cameroon Programme, which aims to develop methods and strategies for natural
forest management, directed at sustainable production of timber, non-timber forest products and
other services. As it is an ongoing study, most observations are incomplete. However, some sets
of data, particularly concerning size-class distribution; phenology, germination rates, and effects
of the traditional harvesting practices at plant level, lend themselves to a preliminary analysis
and are presented in this paper. The demographic survey, the test of harvesting practices and the
participatory monitoring and evaluation together may provide tools for developing efficient,
socially appropriate and sustainable exploitation and management system of Garcinia lucida
and its integration in forest management planning.
2. METHODOLOGY
2.1. Study site
The Tropenbos-Cameroon study site covers an area of approximately 170 000 ha in the South
Province (Bipindi, Akimbo II and Ebolowa districts), some 50 km east of the coast. The area is
flat in the west (40-280 m) and mountainous in the east (over 1000 m). According to Letouzey
(1985), the vegetation changes gradually from low altitude evergreen forest of Lophira alata to
mid altitude evergreen forest rich in Caesalpiniaceae. Biodiversity in this part of Cameroon
ranks among the highest in Africa. The climate is tropical with a yearly rainfall between 2000
and 2500 mm, with two rainy and two drier seasons. The forest cover is still largely present, but
due to human influence, is alternated with a mosaic of fields, fallow lands, secondary forests
and logged-over forests. Population density is low with Bantu and Bagyeli as the main
population groups. People live from hunting, fishing, gathering and practising shifting
cultivation. In addition to food crops, they grow cocoa and palm wine trees as cash crops. Offfarm employment is restricted to logging.
2.2. Data collection and analysis
The methodology was based on plant inventory and demographic surveys on NTFP species
described by Peters (1996), Hall and Bawa (1993) and Dallmeier et al. (1992). The sampling
design was determined on the basis of observations and data from previous surveys (Guedje,
1996). Based on an inventory of the entire G. lucida populations at two locations, demographic
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Part II: Symposium
data were collected in a series of eight plots of 100 x 40 m on growth, reproduction and
population dynamics. At each location, four plots were chosen, of which two in barely exploited
and two in heavily exploited sites (high and low rate of tree mortality after decorticating). In
each plot, all G. lucida individuals from the largest diameter classes (> 15 cm) were tagged,
mapped and diameter measured. Individuals from the lower size-classes were inventoried in
each plot on a random sample of five 4 x 5 m quadrates for seedlings, five 10 x10 m sub-subplot
for saplings and juveniles and five 20 x 20 m sub-plots for small adults (between 5 and 15 cm
dbh).
Phenology (presence of flowers, fruits and new shoots) of a sample of 135 adult trees (dhb ≥ 5
cm) were monitored once a month during 16 months.
After two periods with seed fall, the rate of germination as well as predation of dropped seeds
was monitored twice a week, during 12 months in a series of ten 5 x 4 m quadrates.
An experimental test of the traditional harvesting techniques and levels was carried out and
several treatments applied:
•
•
•
•
Knocking the bark with a stick and harvesting the bark over 1/3 and 2/3 of the diameter;
Peeling the bark with a machete and harvesting over 1/3 of the diameter;
Knocking or peeling the bark with a stick or a machete and harvesting all around;
Felling the tree at 1 m height.
For each treatment, 20 trees were selected, equally distributed in two size-classes (> 17 and < 17
cm dbh). Health parameters are measured by monitoring two branches of each tree on a monthly
basis. Production parameters such as re-growth of bark and development of (stilt)roots were
monitored on a three-monthly basis. Especially the regeneration of the bark was monitored
using transparent paper on which the surface covered with regenerated bark was marked.
The data collected will be analysed with the help of matrix models in which the population
dynamics of the actual harvesting regime as well as the impact of the different harvesting or
management regimes will be simulated to estimate the sustainable level of resource extraction.
3. RESULTS
3.1. Population structure
Figure 1 gives the size distribution of healthy trees in two locations of Garcinia lucida in the
Bipindi – Akom II area. The curve displayed by these populations does not show a constant
reduction in numbers from the smallest to the largest classes. These G. lucida populations lack
individuals in the intermediate (large saplings) and the biggest (large adults) size classes.
However, the percentage of individuals in the smallest classes (seedlings and small saplings)
suggests a good recruitment.
In spite of the good recruitment in the smallest classes, it could be expected that the elimination
of large trees by decorticating has serious consequences for the continual regeneration of the
species. This structure shows the selective exploitation of the largest trees.
3.2 Phenology
Phenology is the timing of recurring biological processes within populations, such as flowering,
fruiting and leaf set. Observations in the field permit to notice that this small diocious species
has flowers and fruits during each month of the year. Although two flowering peaks can be
distinguished between March and June for the first peak and between September and December
for the second one, only one fruiting peak occurs between July and December, during the main
rainy season.
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Sustainable management of African rain forest
Individuals (%)
40
35
30
25
20
15
10
5
0
0 - 100 100 - 200 200 - 400 2.5 - 5
Height in cm
5 - 10
10 - 15
15 - 20
> 20
Dbh in cm
Figure 1. Size class distribution of Garcinia lucida in some sites in the Bipindi - Akom II region (n = 1726).
3.2. Seed predation and germination
After maturation, the medium-size seeds drop on the ground beneath the parent tree. The
percentage germination is high, around 70% (Figure 2) and the dormancy period of the seeds is
very short. The rate of predation of seedlings by rodents is high, around 30%. These rodents
may be also the dispersal agents of Garcinia seeds. However, the role of these animals seems to
be more that-of predators than of dispersers. Field observations indicate that other seed
destroyers are the larvae of insects.
The results indicate that predation by rodents and insects is the most common fate of G. lucida
seeds in the absence of human interference. Taking into account this high predation rate and the
extraction of seeds by the local population, one could expect a very low recruitment rate.
Number of
seeds (%)
80
70
60
50
40
30
20
10
0
0
2
4
6
8
10
Time (weeks)
Figure 2. Germination curve of Garcinia lucida seeds (n = 106)
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3.3. Impact of the traditional harvesting practices
The natural stands of G. lucida are under the regime of open-access for the exploitation of the
bark and seeds. The traditional harvesting techniques of G. lucida bark are peeling with a
machete or stripping with a stick (Guedje, 1996). In case of commercial use, the peeling or the
stripping involves an almost complete harvesting of the tree. Trees that are stripped all around
the stem die after few weeks or months. Mostly adult trees are exploited. Another technique,
although less frequently used, consists of felling the tree at approximately 1 m height before
decorticating (Guedje, 1996). The criteria used to select a tree for harvesting are mostly the
thickness of the bark, the facility of the bark to detach easily from the wood and the diameter of
the tree. These traditional harvesting techniques and levels of bark extraction have been tested
and the effects on plant health and vitality monitored. Preliminary results clearly established that
the practise of stripping the tree all around the stem is the most destructive (T4), with more than
60% tree mortality (Figure 3). The least damaging levels and techniques are stripping only 1/3
of the total bark surface with a stick or a machete (T2 and T1).
Death individuals (%)
70
T0
60
T1
T2
T3
T4
50
40
30
20
10
0
1
3
6
9
12
Months after decortication
Figure 3: Mortality curves of different bark harvesting treatments for Garcinia lucida species
Notes: T0: control; T1: peeled with machete 1/3 of diameter; T2: knocked with stick 1/3 of diameter; T3: knocked
with stick 2/3 of diameter; T4: harvested all around; n = 120
4. DISCUSSION AND CONCLUSION
The goal of a detailed study of population dynamics is to understand its basic ecological
requirements. The size-class distribution of a healthy population, almost comparable to those
obtained by LaFrankie (1994) and Murali et al. (1995), shows good recruitment in smallest
classes and severe lack of individuals in medium and largest classes. The timing of flowering
and fruiting in terms of duration tends to be staggered over the year. However, two maxima in
flowering and one in fruiting have been recorded. The first maximum in flowering occurs
between the dry and the wet season, the second one during the dry season; the production of
Garcinia fruits occurs during the main rainy season as for many tropical trees (Mori and Prance,
1987). Garcinia lucida seeds produced by female trees exhibit a good and rapid germination
with a rate of approximately 70% two weeks after seedfall.
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Sustainable management of African rain forest
These data, in addition to growth and mortality rates will be used to construct transition
matrices. Matrix models record the number of individuals in age or size classes through
repeated cycles of growth, mortality and reproduction. These models, using average values of
growth, survival and fecundity for all individuals in the population, allow a detailed analysis of
life history properties. They will reveal, among others, potential rates of population increase,
predicted stable size-class structures, and sensitivity of the population to change in rates of
growth, survival and fecundity (Enright and Watson, 1991). The effects of changes in the rates
of fecundity, growth and survival can be simulated easily with these models, by changing one or
more coefficients of the initial matrix and calculating the dominant latent root for the new
matrix. There are many examples of the use of matrices to model the demography of tropical
trees, see Hartshorn, 1975; Enright and Ogden, 1979; Peters, 1991; Debroux, 1998.
With these models, the sustainability of the current bark extraction practices will be tested, as
well as the long-term consequence of different harvesting or management regimes. The model
constructed for Grias peruviana by Peters (1990) suggests that a natural population could
withstand harvesting of up to 80% of its seed crops without showing a decline in the population.
The use of matrix models for prediction purposes in the case of Garcinia lucida will be difficult
and is hindered by the fact that both the bark and seeds are harvested, from which the latter are
also eaten by rodents and almost the largest individuals are selected for exploitation.
The assessment of the traditional harvesting practices permits to determine their various effects
on plant health and viability. The effective use, by forest gatherers, of the least damaging
techniques and levels of bark removal resulting from the test could permit to reduce tree
mortality in natural stands. In consequence, the number of adults, especially individuals with
thickly bark, as well as the fruit production, the regeneration of the species will increase and the
"genetic quality" of trees will be preserved in natural populations. The unique way to achieve
this is through participatory approach, based on indigenous knowledge and practices, in which
forest gatherers will be actively involved in the process of evaluating the harvesting practices,
determining and selecting the least damaging, the most efficient and socially appropriate
techniques and levels of bark extraction.
The establishment of such appropriate systems could permit to improve the sustainable use and
management of this important NTFP resource in order to ensure the long-term availability of the
species and to increase incomes to local population.
Acknowledgements
This work received financial support from CARPE and the Tropenbos Foundation and logistic
support by the Tropenbos-Cameroon Programme. We thank the TCP staff and the local
population of the Bipindi – Akom II region for their assistance and participation.
REFERENCES
Bene, D. (1994). Etude de la filière de transformation du rotin dans la ville de Yaoundé.
Mémoire fin d’étude. University of Dschang, Dschang, Cameroon. 117 pp.
Cunningham, A.B. and Mbenkum, F.T. (1993). Sustainability of harvesting Prunus africana
bark in Cameroon: a medicinal plant in international trade. People and Plants Working
Paper 2. Division of Ecological Sciences, UNESCO, Paris, France.
Dallmeier, F., Kabel, M. and Rice, R. (1992). Methods for long-term biodiversity inventory
plots in protected tropical forest. In: Dallmeier, F. (ed.). Long-term monitoring of biological
diversity in tropical forest areas: methods for establishment and inventory of permanent
plots. MAB Digest 11. UNESCO, Paris, France.
Debroux, L. (1998). L’aménagement des forêts tropicales fondé sur la gestion des populations
d’arbres : l’exemple du moabi (Baillonella toxisperma Pierre) dans la forêt du Dja,
130
Part II: Symposium
Cameroun. Thèse de doctorat. Fac. Université des Sciences Agronomiques de Gembloux,
Gembloux, Belgium.
Enright, N.J. and Ogden, J. (1979). Application of transition matrix models in forest dynamics:
Araucaria in Papua New Guinea and Nothofagus in New Zealand. Australian Journal of
Ecology 4: 3 – 23.
Enright, N.J. and Watson, A.D. (1991). Population dynamics of the nikau palm, Rhopalostylis
sapida (Wendl. et Drude), in a temperate forest remnant near Auckland, New Zealand. New
Zealand Journal of Botany 30: 29 - 43.
Guedje, N.M. (1996). Evaluation écologique de quelques Produits Forestiers Non-Ligneux
(PFNL) de la région de Bipindi – Akom II : abondance, distribution et impact des récoltes
sur les peuplements. Tropenbos-Cameroon Programme, Kribi, Cameroon. 37 pp.
Guedje, N.M. (1999). Ecologie et exploitation durable des Produits Forestiers Non-Ligneux : le
cas de Garcinia lucida Vesque dans la région de Bipindi – Akom II
University of Yaoundé I, Yaoundé and Tropenbos-Cameroon Programme, Kribi, Cameroon.
LaFrankie, J.V. (1994). Population dynamics of some tropical trees that yield non-timber forest
products. Economic Botany 48: 301 – 309.
Hall, P. and Bawa, K. (1993). Method to assess the impact of extraction of Non-Timber
Tropical Forest Products on plant populations. Economic Botany 47: 234 - 247.
Hartshorn, G. S. (1975). A matrix model of tree population dynamics. Pp. 41 – 52 in: Golley, F.
and Medina, E. (eds.). Tropical Ecological Systems. Springer, New York, USA.
Letouzey, R. (1985). Notice de la carte phytogéographique du Cameroun au 1 : 500 000.
Domaine de la forêt dense humide toujours verte. Institut de la Carte International de la
Végétation, Toulouse, France.
Mori, S.A. and Prance, G.T. (1987). Species diversity, phenology, plant-animal interrelations,
and their correlation with climate, as illustrated by the Brazil nut family (Lecythidaceae). Pp
69 – 89 in: Dickinson, R.E. (ed.). The geophysiology of Amazonia. John Wiley and Sons,
New York, USA.
Murali, K.S., Shankar, U., Shaanker, R.U., Ganeshaiah, K.N. and Bawa, K.S. (1996). Extraction
of Non-Timber Forest Products in the forest of Biligri Rangan Hills, India. 2. Impact of
NTFP extraction on regeneration, population structure and species composition. Economic
Botany 50: 252 – 269.
Ndoye, O., Ruiz Pérez, M. and Eyebe, A. (1997). Les marchés des produits forestiers non
ligneux dans la zone de forêt humide du Cameroun. Réseau foresterie pour le
Développement rural, Document du réseau 22 c. ODI, London, United Kingdom.
Peters, C.M. (1990). Population ecology and management of forest fruit trees in Peruvian
Amazon. Pp. 86 - 98 in: Anderson, A.B. (ed.). Alternatives to deforestation: Steps toward
sustainable use of Amazonian rain forest. Columbia University Press, New York, USA.
Peters, C.M. (1991). Plant demography and the management of tropical forest resources: a case
study of Brosimum alicastrum in Mexico. Pp. 265 - 272 in: Gomez-Pompa, A., Whitmore,
T.C. and Hadley, M. (eds.). Rain forest regeneration and management. Man and the
Biosphere Series 6. UNESCO, Paris, France.
Peters, C.M. (1996). The ecology and management of non-timber forest resources. World Bank
Technical Paper 322. World Bank, Washington DC, USA.
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