Recommendations concerning inventory of timber, fuelwood, and nontimber products and charcoal species regeneration

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There may a lack of definite information to make an informed decision on the cutting cycle, but there are opportunities to gather information on growth from cuts of known ages.

Permanent plot remeasurement

PROGEDE established a series of permanent plots that in 2004. (See Figure 6.) They are scheduled to be re-measured in 2007. The number of plots in any ecogeographical zone is not large, and should be augmented, but the data should be available this year if PROGEDE follows through were their plan.

Re-visiting previously cut areas

There are areas in Tamba and Kolda where cutting occurred in known years. These should be re-visited for two reasons: quick information and the potential for tree-ring data.

In areas where the year of cutting is known, re-measuring plots can be a quick way to gather information on the re-growth of the charcoal producing species. Ideally, the cut areas would be areas of known age spanning up to 10 years. During this trip, we were only able to visit an area that was cut two years ago, but we were told that areas up to 10 years are known to exist. While these cutting areas are ‘opportunistic’, meaning that they probably are not distributed according to a well thought out plan, they would give the Wula Nafaa project some indication as to whether to continue or alter their current cutting strategy.

Counting tree rings

Re-cutting and then examining stumps in a previously-cut area could verify that counting tree rings is accurate for aging trees for charcoal species in the Tamba-Kolda regions. The Mémento Forestier (Centre Technique Forestier Tropical, France 1990 p. 92) states that growth rings are visible on some species of trees in the tropics. Alegria (1988) found that Combretums in Niger could be aged using tree rings by comparing the number of growth rings with the ages of known stems. Samples cut in Tamba are indicative (Figure 9).
f counting tree rings is found to be an accurate means of aging stems, then the project could cut stems of unknown age and reconstruct diameter growth curves. A standard method is to cut disks along the main stem at a set height interval above the ground, and count the annual rings. Using the diameter of the rings at the base disk, and the number of annual rings along the stem, the past diameter and height of the stem can be reconstructed. A sample of these stems by diameter class and species at each of a number of plots randomly scattered across the ecogeographical area of interest. The plotted diameter and height data would be the basis for estimating the number of years until stems achieve a desired diameter.

Analysis of growth data

Once plots are re-visited and data from re-measured sites are available, the following can be applied.

A simplistic model of growth is:

∆G = S + I – M – R

where ∆G is the change in growth over a unit of time

S is survivor growth. This is growth on a stem that was present and measured at the beginning of the time period and also measured at the end of the time period

I is ingrowth. These stems were too small at the beginning of the time period to be measured but grew across the threshold during the time period and measured.

M is mortality. These stems were live in at the beginning of the time period and measured but died some time before the end of the time period

R is removals or ‘cut’. These stems were present, live and measured in the beginning of the time period but were cut before the end of the time period.

There are other minor components not listed such as stems that were live but too small to be measured in the beginning of the time period, grew across the threshold but died before the end of the time period and a similar component for removals.

  • Using data from re-measured cut plots of known age will give you ∆G: the first time period would be age zero and the end of the time period would be the age of the stand, but you will not be able to tease out the other components.

  • Using data from tree rings only will give you survivor growth and ingrowth.

  • Permanent plots will give you all of the components in the formula, but it will take years to fill in all the variables.

Other unanswered questions

There are additional complications and concerns when determining the growth rates of these species even if the annual rings can be discerned. Some of these are:

  • Do single stem trees grow at the same rate at coppice stems?

  • Do the coppice stems grow at the same rate if all of the stems in the tree are cut as compared to coppice stems within a tree that has uncut stems?

There is also the possibility that the stems that were cut versus the stems that were left may not represent the same population, i.e. the stems left (or cut) were somehow different. Only a long-term study using permanent plots would be able to confirm or allay fears of these types of confounding effects.

These questions could be addressed in a carefully constructed study as soon as time and money are available. As before, it may be possible to locating existing cut sites of known ages to look into these issues, but the down side is that it may be difficult to find combinations of single stem trees, trees with all coppice stems, and trees with only some stems cut in the same general vicinity.


Sacks of charcoal in a meule, in a truck, or on a hectare

In a management plan or PAF, there is an estimate of the cubic meters of wood available within a parcel. Wula Nafaa consultants and field facilitators work with the villagers to determine whether the villagers can cut the estimated amount, or whether they should contract part of the cutting to a third party.

The amount of wood that is actually made into charcoal in a season is based on a number of quintaux (100-kg units) allocated to a department by the central Senegalese Forest Service (as in the Schema Directeur depicted in Figure 8). To ensure the total allotted quintaux are produced, the Forest Service delegates the appropriate number of professional migrant charcoal producers (“Sourgas”) to the area. All the actors in the charcoal market chain use factors that convert cubic meters of wood to stères, to sacks of charcoal, or to quintaux; 300 is the number of charcoal sacks per truck.

The “Sourga” is assumed to produce 150 quintaux per year. Outside the community-based PAF areas, the Senegalese Forest Service plans its annual quota production around this factor and stations Sourgas in producing areas according to the volume available, according to our colleagues.

The table below gives an idea of the variability inherent in the constants being used. Double asterisk ** indicates definite discrepancies in conversion factors being used.


Dry wood conversion to m3

Weight of a stère

Stères in a cubic meter

Coefficient of empilage (m3/stère)

  • 670kg/m3 (1)

  • 680kg/m3 (1) species weighted basic density

  • Trunk + branch + stemlets =each 1/3 total Dry Mass (1)

  • Trunk + its bark = 32-44% of Dry mass (1)

  • Basic density of Anogeissus, Combretum glutinosum, and C. nigri-cans = 720-800kg/m3 (1)

  • 1 tonne dry wood = 4 m3 (2a)

  • 1 tonne dry wood = 20 sacks (2a)

  • 1 stère = 215 to 600 kg (twisted branches versus straight wood from thinning) (3)

  • 1 stère = 130 kg green wood (2a)

  • 2 stères = 260 kg green (2a)

  • 8 stères = 1tonne dry wood (2a)

  • Tonnes/stère = 0.27 (4)

  • 1 stère = 80 to 130 kg of charcoal (2c)

  • Sack of charcoal = “45kg” (4)

  • 1 m3 = 2 stères (2a)

  • 1 m3 = 260 kg green (2a)

    In 900mm rainfall natural forest:

  • stère/m3 = 3.5 (bois 3-6cm) (4)

  • stère/m3 = 2.2 (bois 7-12cm) (4)

  • stère/m3 = 1.7 (bois 13cm+) (4)

  • 1 stère = 0.5m3; 2 stères/m3 (Wula Nafaa)

  • (if all wood is round, straight, and of same diameter: = pi/4 = 0.785)

  • 0.45 to 0.8 (5)

  • .29 to .59 for wood ranging 3cm to 13cm diameter (4)

** 0.65 m3 = 2.5 sacks (2c)

Density of wood T/m3 = 0.8 (4)

Density of kerosene = 0.79 (4)

Volume in a “camion”:

Volume in a “meule”

    Yield of charcoal per kg of wood


1 camion = 150 quintaux (2c)

1 camion = 40-50 stères (2c)

1 camion = 1 meule (2c)

1 camion = 300 sacks loaded in front of Service Forestier (2c)

1 camion = 150-170 quintaux

= 300-350 sacks

= 1 “meule”

= 9 “tas” (2c)

  • 20m diameter kiln p = 400 sacks (Casamance) (2b)

  • 13m diameter kiln = 200 sacks (2c)

  • 6m radius kiln= 100 quintaux (2c)

  • 1 four (meule) of 300 stères green = 2.7 tonnes dry (divide by 11) (2a)

1 meule = 1 camion (2c)

1 meule = 9 “tas” (2c)

16% (Outchoun 1983) to 30% of weight of raw material (drier wood yield = higher);

low avg = 20% (other examples in doc) (3)

Energy yields per meule (4) :

Traditional meule = “18%”

Casamance kiln = “30%”

3-stone cooker = “20%”

  • **Quintaux = “100kg” = “2 sacks” (4)

  • **Quintaux/Tonne = 11 (4)

  • 2.5 quintau/m3 (2c)

  • 150 quintaux/camion

  • 1 quintaux = 100 kg DRY (2a)

  • 10 quintaux =1 tonne dry wood = (2a)

  • 100 quintaux = 6m radius kiln (2c)

  • 150 quintaux=1camion (2c)


(1) Nygard, R., L. Sawadogo, and B. Elfving. 2004. Wood-fuel yields in short-rotation coppice growth in the north Sudan savanna in Burkina Faso. Forest Ecology and Management 189 77-85. Elsevier B.V.

(2) Visites de terrain a. Kaolack 2005 b. Missirah 2006 c. Tamba- Koulor -Nétéboulou 2007

(3) Keita, J.D. Undated. Article presenting a comparison of energy balance for fuelwood and for charcoal. 6 pages. See very interesting sections on economics of transport: it is shown that charcoal with a 28% thermal energy equals the price of its transport by old truck at a distance of 1000 km.

(4) FAO Documents 1 and 5 on Consommation en Charbon de Bois au Senegal: Dept des Forêts Rapport d’étude sur les Données du Bois-Energie au Sénégal”, and “Etude sur les Ressources Forestières et les plantations Forestières au Sénégal”.

(5) C.T.F.T. 1989. Mémento Forestier. Ministère de la Coopération et du Développement, Paris. (Out of print)

Example of conversion factors used with SIEF output and annual quota

The SIEF output gives cubic meters. The annual quota is in quintaux. Let’s say that according to the PAF written with the help of SIEF, a parcel has 1,000 cubic meters available.

___ Convert to quintaux: 1,000 m3 x 2.5 quintaux per m3 = 2,500 quintaux

___Convert to quintaux via stères:

(1,000 m3 x 2 stères/m3 x 130kg wood/stère) /(100kg/quintaux) = 2,600 quintaux

___Convert to quintaux via coefficient d’empilage and stères:

((1,000m3) / (.65m3/stère)) X ((130kg/stère)/ (100kg/quintaux)) = 2,000 quintaux

This example shows how the various coefficients used can allow the estimated cubic volume allocated as sustainable cut to turn into various possible true volumes coming out. Bearing in mind that a single quintaux can be worth 10,000 FCFA ($20) on the market, an estimate that is off by 500 quintaux can result in a windfall or a loss to someone of 5,000,000 CFA or $2,000.

Thus, in spite of all the careful measurements on the plots and all the computerized calculations of the inventory data, there is a broken link between the inventory data and the potential profit because the inventory data are converted at the last step.

Example of conversion factors used with PAF and area of production

Remember that the PAF volume tables are supposed to be half of what the SIEF software outputs. This is a manual conversion that has no means of verification because it is a step undescribed in the manual. Then, since half the stems are left to grow during the rotation time of 8 years, one can assume that the “rotation age” of cut stems is really more than 8 and less than 16, with a midpoint of 12 years.

The management plan gives cubic meters. Let’s say that according to the PAF, a parcel has 1,000 cubic meters available. How many meules should be built to reach this 1,000 cubic meters, and how many hectares will be required to make this 1,000 cubic meters into charcoal? Let’s take the 1,000m3 to be 2,500 quintaux from calculation above.

From the tables describing productivity per hectare, one finds that a typical estimation of productivity based on rainfall gives a value of 0.5 m3/ha/yr. If the ostensible rotation age is 12 years, then each hectare should be producing an allowable cut of (12 X 0.5 =) 6.0 m3 after 12 years.

How many quintaux are in the 6m3? By straight conversion, (6/1000 =) .006 X 2500 quintaux per 1,000 m3 = 15 quintaux. This means that each and every hectare in the parcel is supposed to yield 15 quintaux. If a meule of about 15m in diameter contains 150 quintaux in it (from table above), then you would need to build 10 meules of this same size on the entire parcel.

  • Alternatively, you would need to count all the stères that are placed in the meules on the entire parcel, and make sure that they don’t go beyond 1,538 stères (=1,000m3 divided by 0.65 coefficient d’empilage).

  • Alternatively, you could measure volumes in all the meules constructed in a parcel, and stop when you reach the allowed 1,538 stères (as verified by measuring the cubic volumes measured as below).

Productivity of Casamance kiln versus traditional meule

The Senegalese Forest Service has a legal requirement that all charcoal production in community-managed areas be done in improved kilns or meules. The Casamance kiln is mentioned by name in arrêtés to this effect. In principle, the Casamance kiln when correctly used yields a higher percentage of the wood into charcoal, condenses toxic byproducts from pyrolization into usable liquids, and takes fewer days to produce the charcoal. More formal studies of these claims need to be carried out, since paying for, constructing, and hauling around the welded metal barrels that make up the chimney pose hardships for most subsistence producers, who would prefer to use traditional open-air kilns or meules. Some references that can assist in designing a study comparing the two types are given in the Annex at the end of this report.

Measurement of volume in a meule

The wood cutters that we visited were aware of the need to stack and measure the amount of wood removed in stères. In fact, they had a meter stick and demonstrated the proper procedure for measuring a stère, but admitted that they do not use the system in stères but rather in “tas” (piles): 9 tas make a meule. The specialists hired to build a meule and produce the charcoal rely on their own experience as to how much charcoal will be produced from a meule. A truck is assumed to carry 300 sacks of charcoal, but people acknowledge that additional sacks (up to 50 or more) are often stacked in the truck for a variety of reasons.

It is not known how careful the woodcutters are in keeping track of the number of stères that they cut. If they are diligent about their work, clearly it would be a significant amount of effort to cut the stems into 1 meter lengths, carefully stack them, and then keep accurate records of the number of stères cut.

It appears that the objective is to record the amount of removals from the land and to record the amount of charcoal in sacks or quintaux that the wood produces.

If the relationship between the number of stères and the sacks of charcoal can be established then there would be an option of measuring the number of stères, or just measuring the sacks of charcoal and converting the sacks of charcoal to stères or even back to cubic meters of wood. To test if this is feasible another approach is recommended that only involves measuring the volume of the meule. This method requires the use of a laser inclinometer. The steps are:

  1. Fasten a stick vertically to the air vent or chimney located at the very top of the meule (Figure 10).

  2. Use a tape from the vertical stick and measure out to a set distance on the ground. Slope distance is OK. Mark the same distance in each cardinal direction. Experiment on a distance that would be convenient. Set a tripod at one of these spots.

  3. Measure the distance to the meule at regular angles moving up the slope of the meule with the laser inclinometer. Record both the angle and the distance to the base of the meule as well as the distance to each point along the side of the meule (Figure 11).

  4. Repeat at each cardinal direction but be sure that the tripod is exactly the same distance from the center stick.

The more recordings, the finer the volume of the meule will be calculated. Any vertical distance can be extrapolated from the two closest measurements by using a straight line interpolation.

The meule can be sliced into disks which are actually truncated cones. The volume of each truncated cone can be calculated and summed. One thing to consider is whether the center vent does not have the same dimensions through the meule. If it actually is larger at the base and tapers to the top, then this volume needs to be estimated and deducted from the total volume. The necessary formulas and Excel spreadsheet for this research can be provided by USFS if WN decides to take it on.

This procedure will allow a relationship between stacked wood volume and sacks of charcoal to be determined. There will still be a need for establishing other links between meule volume and the forest area in hectares required to produce the meule and the resulting sacks of charcoal, for purposes of verifying compliance with the management plan and validating what the plan said was available to cut.

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