Presentation during ICRAF Science Forum meeting 6-8 September 2010, Nairobi, Kenya. 1p.

1. Variation in fuel value index of five tree species in Mali:
Variation in fuel value index of five tree species in Mali
relationships with rainfall gradients
Carmen Sotelo Montes1, John C. Weber1 , Dimas Agostinho da Silva2, Clarice Andrade2,
Rosilei A. Garcia3, Graciela Inês Bolzón de Muñiz2, Antoine Kalinganire1
1World Agroforestry Centre (Bamako, Mali), 2Universidade Federal do Paraná (Curitiba, Brazil),
3Universidade Federal Rural do Rio de Janeiro (Rio de Janeiro, Brazil)
Introduction
Rural communities in the West African Sahel depend on many native tree species for
fuelwood. Tree growth and wood properties such as density, moisture and ash content have
an effect on the fuel’s value. Rainfall varies with latitude and longitude in the region, so one
would expect that tree growth and wood properties of trees in natural populations would
also vary with latitude and longitude. Understanding variation among natural populations is
important for tree domestication and conservation programmes, but there has been very
little research in the West African Sahel. ICRAF initiated a project to investigate geographic
variation in growth and wood properties of native tree species in the Sahel. In this poster,
we present preliminary results of a study of variation in the fuel value index of five native
B. aegyptiaca
tree species in Mali. The major objective was to determine if the fuel value index of the P. reticulatum
wood varied with rainfall gradients. Five species were studied: Balanites aegyptiaca (L.)
Delile, Combretum glutinosum Perr.ex DC., Guiera senegalensis J.F. Gmel., Piliostigma
reticulatum (DC.) Hochst. and Ziziphus mauritiana Lam. All five species are used for
firewood, produce abundant natural regeneration if protected from animal browsing and
resprout vigorously after coppicing. Therefore, there is potential to manage natural
regeneration of the species for fuelwood production in rural communities.
C. glutinosum
Materials and Methods
Trees were sampled in natural populations (i.e. parkland agroforests and woodlands) in five
regions in Mali (Figure 1). In general, sampling was done along a latitudinal transect in each
Z. mauritiana
region: 15‐16 trees per species per region. Trees were selected if the stem diameter was 4‐
12 cm at 30 cm above ground, was not d
b d damaged and was not a resprout. A sample of the
d d l f h
wood was obtained from the stem (30‐40 cm above ground) for determination of wood
properties. For each tree, latitude, longitude and elevation were recorded with a GPS Figure 1. Geographic location of five tree species sampled in five regions in
receiver, and estimated mean annual rainfall was obtained from the WorldClim database. G. senegalensis Mali, and mean annual rainfall isohyets (mm) in the sample region.
Based on Pearson correlation coefficients between geographical coordinates and estimated
Table 1. Mean values of wood properties of five tree species sampled in Table 2. Regression equations predicting fuel value index of four tree species from
mean annual rainfall at the location of sampled trees, mean annual rainfall decreases with Mali. geographical coordinates and mean annual rainfall.
latitude and elevation and increases with longitude (r = ‐0.67, ‐0.12 and 0.41, respectively; Species FVI BDen (kg NetCV (MJ AshC MoistC
Species Equation R2 P SE
P<0.001 for latitude and longitude and 0.016 for elevation, N=395). m‐3) kg‐1) (%) (%)
B. aegyptiaca 1208.85709 – 4.57474(Lon2) 0.238 <0.001 0.93417
B. aegyptiaca 881 615 17.7 1.2 11.3 C. glutinosum 859.28441 + 0.00002108(Lat2Elev2) 0.119 0.002 0.00000655
The fuel value index (FVI) = [(BDen)*(NetCV)]/[(AshC)(MoistC)] where BDen = basic density C. glutinosum 1191 666 17.7 1.1 10.8 G. senegalensis 1841.45073 + 0.00199(ElevRain) 0.057 0.034 0.00091861
(kg m‐3), NetCV = net calorific value (MJ kg‐1), AshC = ash content (%) and MoistC = moisture G. senegalensis 2312 674 18.6 0.5 11.0
P. reticulatum 728.21833 – 2.28136(LatLon) 0.157 <0.001 0.60291
content (%) of the wood. BDen was measured on a disk (2 cm thick, sampled at 30 cm above P. reticulatum 472 531 17.7 1.9 11.7
Independent variables: Lat and Lat2 = linear and quadratic latitude (°N), Lon and Lon2 =
ground) using the water‐displacement method. NetCV, AshC and MoistC were measured on Z. mauritiana 907 582 18.1 1.2 10.9 linear and quadratic longitude (°W), Elev and Elev2 = linear and quadratic elevation (m),
sawdust (sampled 32‐40 cm above ground). NetCV is the energy available from an air‐dry FVI = fuel value index BDen = basic density NetCV = net calorific value
index, density, value,
Rain = estimated mean annual rainfall (mm). R2 = coefficient of determination of model.
sample: it was measured using an adiabatic bomb calorimeter. AshC and MoistC were AshC = ash content, MoistC = moisture content. Sample size: 79 for all
P = probability of F ratio. SE = standard error of regression coefficient. Sample size: 79 for
all species.
measured using an incinerator. Tree age was estimated from the number of rings on the disk species.
(at 30 cm above ground): estimated mean age of all trees was 5.9 years. Trees varied in age
so the effect of age on the wood variables was investigated using analysis of covariance Balanites aegyptica Combretum glutinosum
1600
(ANCOVA) within each region. If the effect was significant (P<0.05), the variable was 1200
1400
adjusted using the covariate parameter from the ANCOVA (yadj = y – βregion(tree age – mean
1000
age across regions). After adjusting the variables, geographic variation was investigated 1200
using multiple regression analysis. Regression models were determined using the stepwise 800 1000
procedure: independent variables included linear, quadratic and interaction terms for the 800
FVI
600
trees’ latitude, longitude, elevation and estimated rainfall.
FVI
600
400
400
150 m
Results and Discussion 200 200
350 m
Mean FVI was highest for G. senegalensis and lowest for P. reticulatum (Table 1) due to the 0 0
large differences in BDen NetCV and AshC between these species Due to rounding error
BDen, species. error, 0 2 4 6 8 10 12 14 11.5
11 5 12 12.5
12 5 13 13.5
13 5 14 14.5
14 5
mean FVI in the table does not equal the product of BDen, NetCV, AshC and MoistC. Longitude (°W) Latitude (°N)
Piliostigma reticulatum
FVI of trees was significantly related to latitude, longitude, elevation and/or mean annual Guiera senegalensis 700
rainfall for four of the five species (Table 2). Judging from the R2, the strongest relationship 3000
600
was for B. aegyptiaca while the weakest relationship was for G. senegalensis. Plots of the 2500
regression equations (Figure 2) indicate that FVI did not vary in a consistent manner with 500
geographical coordinates and rainfall in all four species. The FVI of B. aegyptiaca and C. 2000
400
FVI
glutinosum was greater in the drier parts of the sample region (i.e. in the east and north):
FVI
1500
300
FVI of B. aegyptiaca increased from west to east, and FVI of C. glutinosum increased from
south to north especially at higher elevations. The FVI of P. reticulatum also increased from 1000 600 mm 200
5°W
west to east, but decreased slightly from south to north. In contrast, the FVI of G. 1000 mm 12°W
500 100
senegalensis was slightly greater in areas of higher rainfall, but the regression equation 0
explained very little variation among trees (Table 2). Moreover, there was no significant 0
0 50 100 150 200 250 300 350 400 450 11.5 12 12.5 13 13.5 14 14.5
relationship f Z mauritiana.
l ti hi for Z. iti Elevation (m) Latitude (°N)
Figure 2. Fuel value index (FVI) of four tree species predicted by geographical coordinates and mean annual rainfall in Mali
Conclusion (regression equations in Table 2).
We cannot make a general statement about the relationship between FVI of trees of these
species and rainfall gradients in Mali. Relationships depend on the specific species and the
variation in wood properties that affect FVI in that species. The species with higher FVI are
of course exploited more for charcoal and firewood production. Therefore, researchers
should work with rural communities to develop participatory domestication/conservation
strategies tailored for each species and sustainable fuelwood production systems for species
Research funded by a post‐doctoral research grant from the World Agroforestry Centre,
with higher FVI. the International Fund for Agricultural Development, UFPR and UFRRJ. Contact
c.sotelo@cgiar.org for further details.