Estimation of fruit tree production by quantitative indicators: the case of lychee in Madagascar

Madagascar is the first exporter of lychee in the world. Within only a one-month period, the country yearly exports approximately 25,000 t to Europe to meet the seasonal consumption of lychee over the end of the year festivities. Lychee production is concentrated in the eastern part of Madagascar and mainly relies on smallholder farmers. Export management is challenging due to important climatic variations from season to season, and differences in agricultural practices. Thus, methods and techniques that allow an improved estimation of the lychee production is needed in order to better organize the lychee export. Thus, the objective of this study is to estimate a lychee tree production. Several tree traits (i.e., basal trunk diameter, the diameter at breast height or DBH, the canopy diameter, the canopy height, the number of bunches, the load rate) have been considered to estimate the number of fruits and fruit weight. A methodology of image analysis based on hue angle criteriawas also developed simultaneously to predict individual tree yield. The study was performed on 35 trees of various sizes over two year harvesting periods. Results indicated that the large variation in yield observed between trees, i.e., from 1 to 860 kg of fruit, were significantly related (R2>0.8) to the diameter breast height, the basal trunk diameter and the number of bunches. Nevertheless, an effective yield prediction was obtained by using the volume of the canopy and the fruit load rate as indicators (R2>0.8). Promising results were also obtained using the picture analysis methodology that was developed (RZ=O. 7 5). These results lead to a method which can easily be used to estimate the fruit production of a lychee tree just before harvest, from both the tree structural measurements and/or by using simple images of the two faces of the lychee tree at harvest