DOI: 10.5281/zenodo.16736963
title: Ring widths of Douglas fir (Pseudotsuga menziesii) growing under European temperate climate in Southern Belgium

description: Douglas -fir (Pseudotsuga menziesii (Mirb.) Franco) has been widely introduced in Europe due to its high productivity. Although it is considered as a relatively drought-tolerant species, its ability to cope with climate change remains uncertain. To investigate its growth response to climate and drought at its current climatic optimum in Europe, 720 cores were taken from 360 trees in 24 adult mature Douglas fir stands in southern Belgium (Wallonia). The stands spanned a range of annual climatic water balance, estimated maximal soil extractable water reserve, and stand basal area.
description: Sampling

At each study site, 15 dominant or co-dominant trees were selected for sampling from May to November 2021. These trees were dominant in diameter (greater than the minimum diameter of the six largest trees measured in each sample plot) and were spaced at least 10 meters apart with independent crowns. Heavily defoliated trees (>20% defoliation) and trees at the edge of the stand were avoided. Two cores were taken from each selected tree at 1.3 m height with a 5 mm Pressler borer, from both the eastern and northern sides of the trees, resulting in a total of 720 cores. The height and circumference of each sampled tree were also measured.

Preparation and measurement of wood cores

The wood cores were cut with a microtome along the transverse plane, then air-dried, and finally scanned at 2400 dpi. Ring widths were then measured using CooRecorder (Maxwell & Larsson, 2021). The last ring measured was the 2020 ring, as the 2021 ring had not yet fully formed at the time of sampling. The chronologies were visually cross-dated and then statistically verified using the COFECHA program (Holmes 1983). Individual tree-ring series were obtained by averaging the ring widths of the two cores of each tree.







Description of the study sites

All 24 sites are located on plateau, at elevations between 340 and 600 m. The sites are on well drained stony loam soils (Cambisols in the World Reference Base classification system). Two groups of soil Maximal Extractable Water (MEW) were defined based on soil depth and stoniness, as derived from the Belgian soil map and visually confirmed in the field using a soil auger. The average climate of the study sites was described using daily gridded climatic data with a 5 km resolution from the period 1961-2020, obtained from Royal Meteorological Institute of Belgium (RMI). Dendrometric characteristics of the stands (stand density, mean diameter, and dominant height) were obtained from measurements in four circular plots per stand, performed at the time of sampling.
description: The database contains the following files :



RW_douglas_fir.csv: contains tree ring width chronologies for each tree

 tree_info.csv: circumference, height, bark thickness, and sampling date for each tree measured

sites_info.csv: location, climate, and dendrometric characteristics of the sampled stands


+ associated README.txt files containing descriptions of all variables used in these three files