Bielak, K., M. Dudzińska, and H. Pretzsch. “Mixed Stands of Scots Pine (Pinus Sylvestris L.) and Norway Spruce [Picea Abies (L.) Karst] Can Be More Productive Than Monocultures. Evidence from over 100 Years of Observation of Long-Term Experiments”. Forest Systems, Vol. 23, no. 3, Dec. 2014, pp. 573-89, doi:10.5424/fs/2014233-06195.