Size-density data from pure even-aged stands of sycamore maple (Acer pseudoplatanus L.) growing at maximum density

For sycamore, data from unthinned long-term permanent plots were not available (Le Goff et al, 2011). The establishment of the maximum size–density relationship for sycamore relied only on temporary plots installed in spring 2006 in fully stocked stands with no sign of recent cleaning or thinning treatment and presenting natural mortality, in Lorraine and Alsace regions (NE France). In these plots live trees were generally inventoried at two dates for the purpose of this study, in years 2006 and 2007. Dead trees at plot installation were also inventoried by sorting them by “age” class (see Le Goff et al. 2011). In the sample plots, sycamore trees appeared often mixed with other tree species (most often ash and beech) and may be also over-topped by an upper layer of older trees reducing significantly the transmitted radiation. Selection criteria were then defined to ensure homogeneous growing conditions among selected plots: 1) stands relatively pure, sycamore trees representing more than 80% of the stand, in terms of number of trees and total basal area 2) minimum annual mortality rate of 1%, so that stands were close to maximum density 3) trees not completely covered by an upper layer. Moreover, the data from plot 5 of “Matstall” in 2007 were discarded, an over-topping tree being removed at the end of 2006. The selection criteria are notified for each plot in Table 2 of the related publication, but they also appear in the dataset. Inventories were extended for one or more years beyond the year 2007, depending on the plot (variable “Sel-data” = “extra” in the data set), allowing representing a part of the size-density trajectory of sycamore at maximum density, with an insight into the possible impacts of species mixture and upper layer cover on the trajectory. The following data appear for each inventoried plot in the sycamore dataset: “Plot” (name of plot location), “Dep” (department number), NoPlot (plot number), “Cover“ (upper layer cover: “none”, “half-covered gap”, “whole covered gap”), “Mixed” (other species present: “no”, “yes”), “Mixed-species” (species in mixture, if any), “Sel-data” (“yes”, if inventory year data were selected for maximum size-density line fitting in the related publication, “no” or “extra data” if not), “Year“ (year of inventory), “Age“ (stand age, in years), “Ntot” (total number of live trees per ha), “Nsyc%” (relative number of sycamore live trees, in %), “Gtot” (total basal area of live trees, m2 ha-1), “Gsyc%” (sycamore basal area, in %), “Cg” (quadratic mean girth at breast height of all live trees, cm), “Hg” (mean height of sycamore trees at the date of plot installation, m).