translate English to French: Five-year-old walnut trees were pruned for 3 consecutive years to remove branches from 0, 20, 40, 60, or 80% of the total length of the main stem.
Des noyers noirs âgés de 5 ans furent élagués 3 années consécutives pour enlever les branches sur, 0, 20, 40, 60 et 80% de la longueur totale de la tige principale.