1. Department of Forestry and Management of the Environment and Natural Resources, Democritus University of Thrace, Pantazidou 193, 68200 Orestiada, Greece
2. National Agricultural Organization—‘‘DEMETER’’, Forest Research Institute, 57006 Thessaloniki, Greece
3. Department of Forestry and Natural Environment, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece