WOODY BIOMASS AVAILABILITY IN A SEMI-ARID LANDSCAPE OF BURKINA FASO : THE POTENTIAL OF RAMIAL WOOD FOR SOIL AGGRADATION

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1 WOODY BIOMASS AVAILABILITY IN A SEMI-ARID LANDSCAPE OF BURKINA FASO : THE POTENTIAL OF RAMIAL WOOD FOR SOIL AGGRADATION March 2015 Colloquium Gaëlle Feur, MOA student. Supervision : G. Félix and J. Scholberg

2 Layout 2 I. Study context II. III. IV. Research questions-hypothesis Material and methods Results V. Discussion and limits Questions

3 I. Study context 3 Burkina Faso Sudano-Sahelian )

4 Agricultural landscapes Burkina Faso Forest Yilou (Photo: L. Cournac, 2014) Agricultural field with shrubs and Yilou (Photo: G. Félix, 2014) Homestead irrigated agricultural Kindi (Photo: G. Félix, 2013) Pasture Bankélédaga (Photo: G. Félix, 2014) Trend : Increasing threat of land degradation (Breman et al., 2001; Hessel et al., 2005; Roose et al., 1999; Scopel et al., 2012) Agricultural Bankélédaga (Photo: G. Félix, 2014) Agricultural Yilou (Photo: G. Félix, 2014)

5 Land degradation : a multi factors pattern 5 Increasing population Reduced fallow periods Cultivation of marginal land Extreme air and soil temperatures Unreliable rainfall

6 Land aggradation SWC : Soil and Water Conservation strategies 6 Agronomic Crop rotation Weeding Intercropping Mulching Physical Perennial grass strips Stone lines and bunds Living hedges Stalk and brick barriers Zai The competing uses of crop residues in the West Africa Semi Arid Tropics. Bationo et al,2007.

7 Recent emphasis : use of native evergreen woody shrubs (NWS) Traditional peasant practice Main species identified : Piliostigma reticulatum and Guiera senegalensis. On going trials in experimetal station (Kamboinsé) and farmers conditions (Yilou). Lahmar et al,2011 7

8 Knowledge gaps 8 Spatial distributions of standing woody biomass and its availability for mulching in Sudano-Sahelian farming systems Relations between availability and effective use of NWS are not well understood and thus need to be mapped and linked to local land use systems (Lahmar et al., 2012).

9 II. Research questions and hypothesis 9 What is the species composition at the landscape level in Yilou? Hyp 1:It is assumed that there are distinct vegetation types across the landscape in Yilou which are related to a diversity of soil classes What is the available standing woody biomass at the landscape level in Yilou? Hyp 2: It is assumed that vegetation composition and its corresponding biomass quantity are related to each other ( more diversity= more biomass) What is the potential standing woody biomass available for soil amendment? Hyp 3: It is assumed that woody biomass for soil amendment use concerns mostly shrub-shaped species and that the available biomass is distributed unevenly across the landscape

10 II. Research questions and hypothesis 10 What is the species composition at the landscape level in Yilou? Hyp 1:It is assumed that there are distinct vegetation types across the landscape in Yilou which are related to a diversity of soil classes What is the available standing woody biomass at the landscape level in Yilou? Hyp 2: It is assumed that vegetation composition and its corresponding biomass quantity are related to each other ( more diversity= more biomass) What is the potential standing woody biomass available for soil amendment? Hyp 3: It is assumed that woody biomass for soil amendment use concerns mostly shrub-shaped species and that the available biomass is distributed unevenly across the landscape

11 III. Material and Methods 11 Field site : Yilou 80 km North of Ouagadougou, municipality of Guibaré, province of Bam Annual rainfall : 700mm /year Rain season from May-October Soils : leached ferruginous soils, hydromorphic and sodic soils (low phophorus, nitrogen and organic matter content) dominance of sand. Main ethnic group : Mossi

12 Vegetation sampling 12 Systematic sampling of the whole village area 42 sampling quadrats

13 Vegetation sampling 13 Measured parameters : Species, diameter at breast height or basal circumference, height, canopy diameter, stem number and diameter

14 Biomass estimation 14 Use of allometric equations Statistical relationships between various characteristics of tree components Estimate the whole or partial (by components) biomass of a tree based on measurable tree parameters ( mainly trunk diameter and height) Y(Biomass) = a (DBH) + b Kangas and Maltamo, 2006 Main database : Globallometree.org, an international web platform for tree allometric equations to support volume, biomass and carbon stock assessment R 2 Calibration interval Sample size Predictive variable

15 Equation selection process 15 Species x Several specific equation One specific equation None specific equation available Select appropriate predictive variable : DBH/Cb (+ H) Check : 1 st Ecological zone 2 nd R2 value and sample size 3 rd Calibration range 4 th Tree components General models Output : General equations + specific equations = 3 Predictive models

16 17 Vegetation ecology related to soil classification Classification of J.Weigel 1994 (Agroforesterie pratique). 6 soil classification : good farming soil /low land soil / backwater soil degraded farming soil / poor forest soil / laterite soil Plot Plot Species Low land Good farming soil Soil classification Degraded Poor farming soil forest soil Laterite soil A1 Acacia seyal X X A1 Combretum micranthum X X X A1 Combretum micranthum X X X A1 Combretum micranthum X X X A1 Combretum micranthum X X X A1 Combretum micranthum X X X A1 Combretum micranthum X X X A1 Combretum micranthum X X X A1 Combretum micranthum X X X A1 Guiera senegalensis X X TOTAL Dominant soil Poor forest soil Poor forest soil : Natural vegetation : clear forest or woody savannah, trees of small size, plants indicators of soil tiredness. Cultivated vegetation : cultivation is not profitable anymore, presence of fallows and eventually peanut and millet. Soil : aspect plain and smooth, presence of dispersed lateritic

17 Individuals number IV. Results 18 General results 4612 individuals assessed (landscape level) Median per plot : 83 individuals ( Max = 307, Min= 0) A1 A2 A3 A4 A5 A6 A7 B1 B2 B3 B4 B5 B6 B7 C1 C2 C3 C4 C5 C6 C7 D1 D2 D3 D4 D5 D6 D7 E1 E2 E3 E4 E5 E6 E7 F1 F2 F3 F4 F5 F6 F7 plots A4. B1.

18 19 Frequency of species (%) identified during the inventory Aca. Macr Aca.nil Aca.sen Aca.sey Aca. Sie Ada.dig Ano.leiocarpa Aza. Ind Bal.aeg Cal.pro Cas.sie Com.acu Com.glu Com. Mic Dic.cin Dio.mes Eup.bal Fai.alb Fic.all Gard.sok Gui.sen Lan.aci Lan.mic Mit. Ine Pil.ret Pil.tho Sab.sen Scl.alb Scl.bir Tam.ind Ter.mac Unknown Vit.par Ziz.mau species identified 1 st : Guiera.senegalensis 2 nd : Piliostigma. reticulatum 3 rd : Conbretum.micranthum 73%

19 20 Species ecology : indicator for soil classification Good farming soil Low land soil Backwater soil Degraded farming soil Poor forest soil Laterite soil 1 plot 1 plot none 25 plots 25 plots 3 plots Dominant soil : humus greatly depleted, difficult to distinguish the first layer of the soil profile. Appearance flat and smooth, presence of dispersed lateritic concretion, deep compacted layer. J.Weigel, 1994

20 biomass in kg Standing biomass estimation 21 Use of species specific equations and general equations 3 predictive models A1 A2 A3 A4 A5 A6 A7 B1 B2 B3 B4 B5 B6 B7 C1 C2 C3 C4 C5 C6 C7 D1 D2 D3 D4 D5 D6 D7 E1 E2 E3 E4 E5 E6 E7 F1 F2 F3 F4 F5 F6 F7 Plots Predictive model 1 Precitive model 2 Predictive model 3 Predictive model 1 Predictive model 2 Predictive model 3 Median biomass per ha (kg DM) ( Model 3- Model 1)= 3792 kg DM/ha

21 Biomass per plot (kg DM) 22 Species diversity and its relation to biomass Number of species per plot related to total biomass y = x R² = Number of species per plot

22 23 F6 F4 F2 E7 E5 E3 E1 D5 D3 C7 C5 C3 C1 B6 B4 B2 A7 A5 A3 A1 Standing biomass estimation potentially available for wood amendment Biomass potentially available for soil amendment (Kg DM) Biomass per plot ( Kg DM) Median : 187 kg per plot = 748 kg/ha Average : 469 kg per plot = 1876 kg/ha Distribution of species in relation to soil amendment biomass 50% 11% 38% 1% Piliostigma.r Cassia.s Guiera.s Combretum.m

23 Discussion and limits 24 What is the species composition at the landscape level in Yilou? Hyp 1: It is assumed that there are distinct vegetation types across the landscape in Yilou which relates to a diversity of soil classes Results : Rather homogeneous. Mainly bush shaped. Dominance of the species Combretum micranthum, Guiera senegalensis and Piliostigma reticulatum ( more than 75% of the identified individuals). Species ecology show a dominance of poor forest/ degraded farming soil 37 plots out of 42

24 25 Poor forest soil Degraded farming soil Both

25 26 What is the available standing woody biomass at the landscape level in Yilou? Hyp 2: It is assumed that vegetation composition and its corresponding biomass quantity are related to each other ( more diversity = more biomass). No clear link between species diversity and biomass quantity ( R 2 =0.02) Important differences between the predictive models : 3792 kg DM/ha

26 27 What is the potential standing woody biomass available for soil amendment? Hyp 3: It is assumed that woody biomass for soil amendment use concerns mostly shrub-shaped species and that the available biomass is distributed unevenly across the landscape Indeed tree species are rather scarce. Biomass is heterogeneously distributed. Median : 758kg/ha. M.Ouedraogo (2014) suggested 2T/ha for significant improvements of crop yields and soil fertility maintenance To be checked : close or far from households?

27 28 Questions/ remarks?