CHARCOAL QUESTIONS

VALIDATION OF THE LENGTH OF CUTTING CYCLE; REGENERATION TIME FOR CHARCOAL SPECIES

(Adapted from Alegria and Polansky 2007: RECOMMENDATIONS CONCERNING INVENTORY OF TIMBER, FUELWOOD, AND NONTIMBER PRODUCTS AND CHARCOAL SPECIES REGENERATION for Areas of Wula Nafaa Intervention in Eastern and Southern Senegal)

Cutting protocols in use

An example of a cutting protocol in practice in Senegal allows for cutting stems that are between 10-25 cm in diameter. Stems less than 10 or greater than 25 are left standing. Also, for the sake of cutting conservatively and because of a lack of research on regeneration time and quality, producers have instructions to cut only one-half of the stems within this diameter range, and some species of trees are not to be cut regardless of their diameter. So if there are single-stemmed trees, the cutters are to cut one and leave the other. In multiple-stemmed trees with more than one stem between 10-25cm in diameter, the cutter will cut one and leave the other if the tree has two stems; cut two and leave one if the tree has three stems; etc.. The parcel is then left to regenerate for the next 8 years without cutting.

If the protocol is followed, the percent of the basal area or volume removed depends on the diameter distribution of the stand. Clearly, in stands with relatively few stems in the 10-25 cm range, the cutting acts as a light thinning. As the distribution shifts towards the larger stems, the proportion of wood removed will increase, but only to a point; then it will decrease as a significant amount of wood is left in large stems greater than 25 cm.

This protocol does not lend itself to the term ‘rotation age’. The key question is the rate of growth of the charcoal species and what are the criteria in determining when cutting should begin. Since the cutting prescription is light, the criteria should be based on economics. How long does it take for the amount of harvestable stems to reach a point where it is economically feasible to thin again? At the moment the criterion is size (10-25 cm) and the interval is every 8 years. The eight years is based on one study done in 1988, which simply stated that the maximum regrowth occurred within 8 years after cutting a stand in this rainfall zone.

We found one study on the density or energy value of wood that grows back from stumps: the proportion of bark to commercial wood increases in younger stems, so the shorter rotation would produce less dense wood with less energy value, although it is volume rather than weight which determines forest taxes. (See table of references.)

We don’t know how the charcoal diameter range used in the forestry rules was defined. Surely there is a minimum diameter below which woodcutters would find it not cost-effective to cut.

A proposal to adjust the cutting protocol

It is not clear if a protocol such as this would be or even should be applied in stands with significant amounts of wood in the 25 plus cm range. After eight years, the same protocol will be applied again, so that not only will there be even more wood tied up in large stems, but some of the stems left after the first round of cutting may have grown past the 25 cm mark and will be left until they die from other causes. Thus in a stand of many larger-diameter stems, this protocol will change the composition of the forest by favoring protected trees and increasing the amount of wood left standing even in the species allowed to be cut. Every piece of land has a maximum biological capacity in terms of biomass; thus as the stems that are off-limits to cutting increases, the amount available to cut will decrease.

To prevent an eventual shortage of legally-available stems in forests with a diameter distribution favoring stems 25cm and greater, the cutting rules could allow cutting stems over 25cm. First the diameter distribution should be evaluated by eye in the field, or by graphing existing inventory data. Divide the entire range of diameters into very few, maybe only two sub-ranges to apply rules specific to each one. For example, for every stem cut greater than 25 cm leave one. Continue to apply the current rule for trees between 10-25 cm in diameter. There could be a different prescription applied for each diameter range.

Regeneration time and cutting protocols found in the literature

These are some estimates of the productivity of the sahelian zone found in the literature:

Charcoal variables and conversions used in Senegal and the Sahel

CONVERSION FACTORS

Weights and volumes	Source
Dry stems conversion to m3 on basis of 0.67Mg/m3 or 670kg/m3 (DRY MASS TO FRESH VOLUME RATIO) Trunk dry mass to fresh volume ratio = species weighted basic density = 0.68 Mg/m3. Trunk + branch + stemlets = each 1/3 total Dry Mass Trunk + its bark = 32-44% of Dry mass Basic density of Anogeissus, Combretum glutinosum, and C. nigricans = 0.72-0.80 Mg/m3	1 Burkina Faso 620 to 785 mm rainfall
1 stère = 215 to 600 kg (twisted branches versus straight wood from thinning)	3
1 stère = 0.5 m3 = 130 kg green wood 1 m3 = 2 stères = 260 kg green 1 quintaux = 100 kg DRY = 2 big sacks of charcoal 1 tonne dry wood: = 4 m3 = 8 stères = 10 quintaux = 20 sacks 1 truckload = 150-170 quintaux = 300-350 sacks = 40-50 stères 1 stère = 0.65 m3 = 2.5 sacks 1 m3 = 2.5 quintaux 9 tas = 300 sacks = 1 meule	Visites de terrain Kaolack 2005 Missirah 2006 Tamba 2007
Coefficient d’empilage south of 900mm rainfall (natural forest): stère/m3 = 3.5 (bois 3-6cm) stère/m3 = 2.2 (bois 7-12cm) stère/m3 = 1.7 (bois 13cm+) Tonnes/stère = 0.27 Density of wood T/m3 = 0.8 Density of charcoal = Density of kerosene = 0.79 Sack of charcoal = “45kg” Sack of charcoal = .045T Quintaux = “100kg” = “2 sacks” Quintaux/Tonne = 11	7
Coefficient of empilage: 0.45 to 0.8 m3 per stère (if all wood is round and of same diameter: = pi/4 = 0.785)	9
Yield of charcoal per kg of wood
16% (Outchoun 1983) to 30% of weight of raw material (drier wood yield = higher); low avg = 20% (See other examples in doc)	3
Productivity per meule
20m diameter kiln pile = 400 sacks (Casamance) 6m radius kiln = 100 quintaux 13m diameter kiln pile = 200 sacks 1 stère = 80 to 130 kg of charcoal 1 four (meule) of 300 stères green = 290 000 kg = 29 tonnes green, or 2.7 tonnes dry (divide by 11) 1 truckload = 150 quintaux = 300 sacks = 40-50 stères 1 meule = 1 camion = 300 sacks loaded in front of Service Forestier = 9 “tas”	Visites de terrain Kaolack 2005 Missirah 2006 Tamba 2007
Energy yields: Traditional meule = “18%” Casamance kiln = “30%” 3-stone cooker = “20%”	7 (these references are all sourced)

UTILISATION AND ECOLOGY

Dakar market
100 000 tonnes/yr (1980)	3
300 000 tonnes of charcoal per year = 3 million quintaux	Visites terrain Kaolack 2005
(approx 10 quintaux per tonne) Thies at 70km from Dakar was a main exploitation zone from 1950 to 1966, producing up to 2/3 of the total for Senegal. Closed for charcoal making from 1983. St-Louis, 200+ km from Dakar, was prominent from 1970 to 1982 because of natural populations of Acacia nilotica killed off by drought. Kaolack (200+km from Dakar) was prominent from 1959 to 1987, with stands on each side of the railroad. (Senegal population 1976 = 5 million) Tambacounda, at 400-500 km from Dakar, took over in 1985, with a harvest on the order of one million quintaux per year. (Senegal population 1988 = 6.9 million) Kolda at 700km from Dakar from 1990 to 1999 has gone from 4% to 67% of the total charcoal production. (Senegal Population 1990 = 7.3 million, 2000 = 9.5 million) Quota proposed for 2000 was 60 000 tonnes plus 20,000 tonnes of reserves. 1994: Dakar ville charcoal consumption = 114,300 T, gaz = 40,300 T	7
Heat value
(An estimation of 70% of standing stock as being acceptable for fuelwood other species for fruit and other uses, or not dense enough) -- “Results of this study indicate that the share of commercial fuelwood in young successional forest could be much lower when taking into consideration the multiple uses of these forests.” “Nevertheless, the concept of commercial fuelwood depends on supply and demand and, with increased scarcity, less suitable fuelwood species will be used.” Barkless wood preferred in Niger. On an area-based volume, excluding branches, stemlets, bark, and non-optimal species results in a use-able 25% of volume.	1 Burkina Faso (620-785 mm rainfall)
Dry wood: 4500 to 4770 Kcal/kg; Green wood: 3500 Kcal/kg X 0.08 = 280 Kcal/kg wood (thermal E yield=8% or 5% on 3-stone stove) Charcoal: 7500 Kcal/kg X 0.2 char yield X 0.28 = 420 Kcal/kg wood (Thermal E=28%) Petrol product: 10 000 Kcal/litre	3
tep = 42 Gjoules kWh = 3.6 Mjoules Pci of kerosene = 43.5 Mjoules/kg Pci of butane = 45.7 Mjoules/kg Pci of charcoal = 29 Mjoules/kg Pci of wood = 17 Mjoules	7
Productivity per area
“If protected for 5 yrs after clearcutting, 0.6 to 3 m3/ha/yr” Devineau (1997) used repeated meas. to estimate increment at 0.7 m3/ha/yr (mature savanna) and 0.3 m3/ha/yr (12-yr fallow) Cameroun Regrowth @ 800mm rainfall = 0.5 m3/ha/yr, 3 yrs after clearcut. Botswana regrowth @ <1000mm rainfall on sandy soil = 0.9 Mg/ha/yr Burkina regrowth @ 1000mm rainfall = 0.7 m3/ha/yr in mature savanna Guinea regrowth @ 1300mm rainfall = 1.3 m3/ha/yr in savane arbust; 2.3 m3 in savane boisée	1
“Exploitable” =15 stères/ha green + 3st/ha dead (Dosso) (Combretum micranthum, C. nigricans, Guiera senegalensis)- Maradi and Dosso	2 Niger
11.3 m3/ha/year all species mixed = 2640 kg/ha/yr = 290 kg charcoal/ha/yr = 3 quintaux/ha/yr	Visites terrain Kaolack 2005 Missirah 2006 Tamba 2007
6 years of cultivation leads to 50% density loss and 14 years leads up to 80% loss.	6
Total production of 1 million quintaux in 1994, and of 1 500 000 Qtx in 1988 and 1993.	7
Productivity in Mg/ha/yr = .051 + 1.082(pluviom)^2thus 600-800mm yields 0.4-0.7 m3/ha/yr. Protection: increase by 25%; Degradation: decrease by 25%	8, cited in 9
Regen info; rotation age
“Short” (<20-yrs) coppice cut rotation recommended in Abbot and Lowore, 1999; Bellefontaine/Gaston/Petrucci 1997; Jensen 1995; Catinot 1994. Short rotation means a different proportion of bark and branchwood than older trees. This affects density although volume is the variable that is taxed and that is predicted in equations. Thus dry mass=more appropriate for evaluation of growth and fuelwood value. “If Burkina Faso Forest Service applied the same cutting criteria for firewood trees as was used in 1982, a rotation period of more than 30 years would be required for regrowth to the same volume.” (Based on 29 to 70 m3/ha that were removed during clearcutting in 1982) -- i.e. woody Dry Mass in mature stand would be less than reported in other studies in same rainfall conditions. Coefficients of Variation compared between current study 2004 and the CV for harvested wood in 1982 are comparable (11 to 29% range for both). “Longer rotation periods may produce a larger proportion of commercial fuelwood and this option should therefore be investigated.” (pg 84)	1 Burkina Faso (620-785 mm rainfall)
Annual cut allows 69% to 80% of the annual growth Allowable = >6m diam at 20cm ht, “taillis fureté” or selective removal of sprouts (Combretum micranthum, C. nigricans, Guiera senegalensis)- Maradi and Dosso	2 Niger
Wound the roots at moment of high nutrient reserves for Combretums and many other sahelian spp= drageonnage	4
Combretum/ Anogeissus forests as “pseudo-climax” remain in spite of decreasing rainfall and degradation because of ability of stumps to regenerate since 1950s (pg. 25)	5
Note: Cutting permits do not have an expiration date, so once they are granted, the wood can be cut any time. The quota system directs woodcutters to specific Regions by limiting quotas from each.	7

PRODUCTIVITY PER WORKER:

150 QUINTAUX PER CHARCOAL LABORER PER YEAR (Tambacounda estimate, 2007)

SOURCES

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. (c. 2003?) n.a. Résumé du Plan d’Aménagement forestier du massif de Baban Rafi Sud (Département de Madarounfa) 3 pages -- internet site

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 the value of charcoal with a 28% thermal energy equals the price of its transport by old truck at a distance of 1000 km.

4. Bellefontaine, R, E. Nicolini, S. Petit. 1999. Réduction de l’érosion par l’exploitation de l’aptitude à drageonner de certains ligneux des zones tropicales sèches. Bulletin Réseau Erosion (IRD-Montpellier et CTA-Wageningen), no. 19, p. 342-352

5. Ba, M., A. Toure, and A. Reenberg. Mapping land use dynamics in Senegal. Case studies from Kaffrine Departments. Working paper 45.2004 for Sahel-Sudan Environmental Research Initiative, Institute of Geography, Copenhagen. 33 pages

6. Faye, E., D. Masse, and M. Diatta. 2002. Dynamique de la régénération ligneuse durant la phase de culture dans un système de culture semi-permanente du Sud du Sénégal. In Savanes africaines: des espaces en mutation, des acteurs face à de nouveaux défis. Actes du colloque, mai 2002. Marouna, Cameroun. 30 pages.

7. 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”.

8. Clément, J. 1982. Estimation des volumes et de la productivité des formations mixtes forestières et graminéennes tropicales. B.F.T., No. 198, in CTFT Mémento Forestier page 507.

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

The above references point to typical growth of 0.4 to 0.7 m3 per hectare per year in sahelian rainfall zones. Clément’s (1982) study includes data from Senegal but used a conservative conversion of stères to m3 of 0.4. Re-applying the currently-used 0.65m3/stère, the data showed that the 600-700mm zone produced 0.4 to 0.6 stères per hectare in unprotected cut areas separated by 20 years. Using the value of 0.5m3/ha/yr, if a parcel is clearcut and yields 10 m3 per hectare (or 15 stères or 25 quintaux/ha), then it would take 20 years to grow back to the same volume.

If the parcel is only partially cut and yields 5 m3 per hectare (or 12 quintaux/ha), then it would take 10 years to regrow the removed volume. This illustrates why we should want to know how much wood or charcoal is coming off each hectare, and why we should compare that with what is written in a forest management plan.

RECOMMENDATIONS FOR DETERMINING GROWTH RATES

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

Many projects have established permanent plots in past years. These should be re-visited using the best re-location method possible. With the advent of more accurate GPS data since 2001, it may even be able to visit plots not originally designated as “permanent” to obtain re-measurement data.

Re-visiting previously cut areas

Where areas have been previously cut in known years, the sites should be re-visited for two reasons: quick information, and the potential for tree-ring data.

Where the year of a cut 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. While these cutting areas may be ‘opportunistic’, meaning that they probably are not distributed according to a well thought-out plan, they would give some indication as to whether to continue or alter a cutting strategy that is being implemented.

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. 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 Tambacounda, Senegal, are indicative that the practice could be used in other countries.

If counting tree rings is found to be an accurate means of aging stems, then one 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.