The current database is part of the FEM growth and yield database, a collection of growth and yield data from even-aged monocultures (douglas fir, common oak, poplar, Japanese Larch, Norway spruce, Scots pine, Corsican pine, Austrian pine, red oak and several other species with only a few plots, even-aged mixed species forest plots, uneven-aged natural forest, uneven-aged selection forest and roadside plantations of poplar. The FEM growth and yield data base is currently supervised by Jan den Ouden and Frits Mohren. In the FEM growth and yield data collection for even-aged monocultures in general the data of four main studies and if available some additional studies are assembled: 1. Thinning research Wageningen University initiated by Becking1 1947 – 2005. For poplar there are no recordings after 1992. In total 58 monoculture plots were selected with ini-tial number of trees varying from 86 till 2207. Different varieties and a few aspen plots were selected. The treatments consisted of without thinning (28 plots), systematic thin-ning (35 plot) and thinning from below (2 plots). Over more than four decades, this study was supervised by A. van Laar, P.G. de Vries, J.H. Hildebrand, J.J. Jansen and H.H. Bartel-ink; 2. Growth and production study by research institute Dorschkamp/IBN 1923 – 1995. The aim of this research was the construction of yield tables. See Van Soest2 for the experi-mental design. There are 188 poplar plots in this study, but only the plots with 3 or more recordings were selected, in total 77 plots with known age but unknown recording date. But beside this plots there are also 5 aspen plots of which 4 with only 2 recordings with known age and recording date; 3. Spacing trials by research institute IBN 1960 – 1995; 6 plots with known age but un-known recording date; 4. HOSP3 1984 – 2000. A collection of about 3000 permanent sample point from the Dutch National Forest Inventory. In total 42 monocultures with poplar species or varieties were selected; 5. (only for douglas fir); 6. (only for douglas fir); 7. (only for Norway spruce); 8. Nelder Spacing trial by research institute IBN 1976-19954, containing 5 experimental Nelder fields of which 3 with poplar varieties with 6 to 9 series with equal spacing per tree. One series within the Nelder field is seen as a plot, resulting in 21 plots, but hence these plots are not all mutually independent