Fig. 1

Illustration of the different variables measured with the histologic approach. Delimitation of the different areas of interest on the processed image with ImageJ: the area of cell wall proportion measurement (red polygon), and the radial increment measurements on three radial files (blue lines) on the image. With P, phloem; C, Cambium, PR, ring of the previous year. The image represents the sample for Tree no 2 sampled on 9th of June 2015 with the original image a and the same image after gray-scale and thresholding processing b