科学家较近利用Hiphen公司开发的Airphen多光谱表型成像系统发表了题为How far does the tree affect the crop in agroforestry? New spatial analysis methods in a Faidherbia parkland的文章（A six-band multispectral camera (Airphen®, Hiphen, Avignon, France) capturing light at 450, 530, 675, 730 and 850nm wavelengths, was flown over the six survey paddocks on 1 Oct 2018 using a manned, fixed wing aircraft. The imagery was acquired at approximately 9000 feet above ground level (AGL) in order to capture each paddock entirely），揭示了该系统其做为一种新分析方法在植物领域的应用。

How far does the tree affect the crop in agroforestry? New spatial analysis methods in a Faidherbia parkland

Abstract

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 (r2 = 0.41; RRMSE = 48 %) and litter production (r2 = 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.

Keywords

Geostatistics

Unmanned Aerial Vehicle (UAV)

Land Equivalent Ratio (LER)

Spectral indices

Distance of influence