Ignea Gh., Ghaffaryian M.R., Borz, S.A., 2017. Impact of operational factors on fossil energy inputs in motor-manual tree felling and processing: results of two case studies. Ann. For. Res. 60(1): 161-172.Abstract. In many cases tree felling and processing operations are carried out motor-manually and knowledge about fossil fuel consumption and direct energy inputs when using such equipment is required for different purposes starting with operational costing and ending with environmental assessment of forest operations. In this study, fuel mixture, chain oil and direct fossil energy inputs were evaluated for two chainsaws which were used to fell and process trees in two silvicultural systems. The results of this study suggest that there is a strong dependence relation between selected tree size variables such as the diameter at breast height and tree volume on one hand and the fuel mixture, chain oil and direct fossil energy inputs when felling and processing broadleaved hardwood and resinous softwood trees on the other hand. For the broadleaved trees (mean tree volume of 1.50 m 3 tree -1 , DBH of 45.5 cm and tree height of 21.84 m) the mean direct fossil energy input was of 3.86 MJ m -3 while for resinous trees (mean tree volume of 1.77 m 3 tree -1 , DBH of 39.28 cm and tree height of 32.49 m) it was of 3.93 MJ m -3 . Other variables, including but not limited to the technology used, work experience and procedural pattern, may influence the mentioned figures and extensive studies are required to clarify their effects.