%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Roupsard, O.
%A Audebert, A.
%A Ndour, A. P.
%A Clermont Dauphin, Cathy
%A Agbohessou, Y.
%A Sanou, J.
%A Koala, J.
%A Faye, E.
%A Sambakhe, D.
%A Jourdan, C.
%A le Maire, G.
%A Tall, L.
%A Sanogo, D.
%A Seghieri, Josiane
%A Cournac, Laurent
%A Leroux, L.
%T How far does the tree affect the crop in agroforestry ? New spatial analysis methods in a Faidherbia parkland
%D 2020
%L fdi:010078974
%G ENG
%J Agriculture Ecosystems and Environment
%@ 0167-8809
%K Geostatistics ; Unmanned Aerial Vehicle (UAV) ; Land Equivalent Ratio (LER) ; Spectral indices ; Distance of influence
%K SENEGAL ; NIAKHAR ; ZONE SEMIARIDE. ZONE SOUDANOSAHELIENNE
%M ISI:000527601600006
%P art. 106928 [14 ]
%R 10.1016/j.agee.2020.106928
%U https://www.documentation.ird.fr/hor/fdi:010078974
%> https://www.documentation.ird.fr/intranet/publi/2020/05/010078974.pdf
%V 296
%W Horizon (IRD)
%X The trees in agroforestry plots create spatial heterogeneity of high interest for adaptation, mitigation, and the provision of ecosystem services. But to what distance, exactly, from the tree? We tested a novel approach, based upon geostatistics and Unmanned Aerial Vehicle (UAV) sensing, to infer the distance at which a single agroforestry tree affects the surrounding under-crop, to map yield, litter (i.e. stover) and compute crop-partial Land Equivalent Ratio (LERcp) at the whole-plot level. In an agro-silvo-pastoral parkland of semi-arid western Africa dominated by the multi-purpose tree Faidherbia albida, we harvested the pearl-millet under-crop at the whole-plot scale (ca. 1 ha) and also in subplot transects, at three distances from the trunks. We observed that the yield was three times higher below the tree crown (135.6 g m(-2)) than at a distance of five tree-crown radii from the trunk (47.7 g m(-2)). Through geostatistical analysis of multi-spectral, centimetric-resolution images obtained from an UAV overflight of the entire plot, we determined that the 'Range' parameter of the semi-variogram (assumed to be the distance of influence of the trees on the Normalized difference vegetation index (NDVI)) was 17 m. We correlated the yield (r(2) = 0.41; RRMSE = 48 %) and litter production (r(2) = 0.46; RRMSE = 35 %) in subplots with NDVI, and generated yield and litter maps at the whole-plot scale. The measured whole-plot yield (0.73 t ha(-1)) differed from the one estimated via the UAV mapping by only 20 %, thereby validating the overall approach. The litter was estimated similarly at 1.05 tC ha(-1) yr(-1) and mapped. Using a geostatistical proxy for the sole crop, LERcp was estimated 1.16, despite the low tree density. This new method to handle heterogeneity in agroforestry systems is a first application. We also propose strategies for extension to the landscape level.
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