This study focuses on the evaluation of horizontal accuracy of smartphones for collecting and using spatial data in forests in comparison with other Global Navigation Satellite Systems (GNSS) devices. Accuracy evaluation was conducted at 74 points in a mixed deciduous-coniferous forest (during leaf-on and leaf-off season) and additionally at 17 points under open area conditions. Total station theodolite measurements served as a reference for all point positions. Positional accuracies of three smartphones (one with two differing OS versions), a tablet, a mapping- and a survey-grade receiver were compared. Root mean square errors of positional accuracies ranged from 4.96–11.45 m during leaf-on and 4.51–6.72 m during leaf-off season in the forest plots to 1.90–2.36 m under open area conditions. Differences in positional accuracy between leaf-on and leaf-off conditions were only significant in some cases, while differences between forest and open area were always significant. Differences between devices were only significant under leaf-on conditions except for the survey-grade receiver, which was significantly more accurate than all other devices in all tested cases. In a second experiment, two smartphones, a handheld receiver and satellite imagery were used to measure the area of wind damage in disturbed forests. The results obtained with the GNSS devices showed a significantly higher accuracy of area and timber volume assessment compared with visual estimation, particularly in larger disturbed areas. Generally, the results suggest that current smartphones can be successfully used for some tasks in forest management where precision of the spatial data is not of highest priority.