Evaluation and comparison of size-density relationships for pure even-aged stands of ash (Fraxinus excelsior L.), beech (Fagus silvatica L.), oak (Quercus petraea Liebl.), and sycamore maple (Acer pseudoplatanus L.)

Size-density relationships define the maximum number of stems that even-aged stands of a given species can hold in relation to the mean size of trees. They are used to derive stand density measures and are useful tools used to control tree mortality. Size-density relationships were already available in France for beech and oak. The objective of this study was to extend these relations to younger development stages and test if specific relations are needed to be established for a set of species of different shade tolerance, including beech, ash, sycamore maple, and oak. We relied on stands growing at maximum density and used selected data coming from the inventories of permanent control plots and specifically established temporary plots. A multiple comparison procedure was used to differentiate between the parameters of the relations. Two size-density relations were retained with a common slope and different intercepts for ash and beech on one hand, and for oak and sycamore maple on the other hand. Stands of shade-intolerant species like oak appeared able to hold less trees of a given mean size, but shade tolerance did not seem to influence the mortality rate which appeared to be the same.