Measured and estimated tree dimensions of maritime pine (Pinus pinaster) and birch (Betula pendula) in the tree diversity experiment ORPHEE at the end of 2014

The ORPHEE experiment is located 40km south of Bordeaux (44°440 N, 00° 460 W) and belongs to the worldwide Tree Diversity Network (TreeDivNet). The experimental plantation was established in January 2008 on a clear cut of former maritime pine stands on a sandy podzol. Eight blocks were established, with 32 plots in every block. Each plot contained 10 rows of 10 trees planted 2 m apart, resulting in 100 trees within a plot of 400 m². The total initial stand density was therefore 2500 trees per hectare in each plot. Each plot was planted with one to five species. Only maritime pine (Pinus pinaster/Ppin) and silver birch (Betula pendula/Bpen) were considered in this data set. For this study, we have selected 14 plots per blocks. The present data set is composed by data collected in 2014 (7 years-old) on the target trees at the center of the plots in order to avoid edge effects (measured planting locations = 36). The total height was measured on living trees using a graduate pole. We also measured circumferences at 1.30m height on 7 randomly chosen pines and 7 randomly chosen birches per plot. We estimated missing tree heights and circumferences and tree volumes by: - Using height-circumference relationships to estimate the circumferences of trees that have not been measured in 2014 by mean of separate generalized additive models for each stand composition and tree density. - Using the generic model developed by Deleuze et al. (2014) to aboveground tree volumes. We assigned a minimum volume of 0.01m3/ha to the few trees below 1.30m in height (corresponding to the minimum volume found in the data set). - Eventually we estimated dimensions of dead trees by averaging diameter, height and volume of living trees in the plot.