Flooding occurring in mountainous rivers and stream channels, combined with the transport of rock material, cause erosive undercutting of slopes and damage to the exposed root systems of trees growing on banks. The consequence of high-energy events occurring in the stream channel is the generation of mechanical stress in the form of tension inside the tree trunks, resulting in a change in the cambium functioning pattern and deflection of the trunk heartwood. In the present work, the hypothesis that not only rapid landslide phenomena, but also the erosion activity of the stream can cause trees to be tilted from the vertical, which results in the eccentricity of current annual increments of trees growing in the vicinity of the stream channel was adopted. Thanks to this feature of trees, it is also possible to precisely determine the time of occurrence of high-intensity erosion phenomena in the past, as well as to indicate locations along the stream channel that are particularly vulnerable to these processes, which emphasizes the utilitarian aspect of the present work. The objective of this study is to assess the eccentricity of current annual increments in the trunks of spruce trees (Picea abies (L.) H. Karst) growing along the stream in a small forest mountainous catchment. The subject of the study is the width of the growth rings formed by spruces on both sides of the trunk as a form of response to the erosive activity of the stream. As a part of the fieldwork, incremental cores were made using the Pressler drill. The annual growth rings of spruce tree trunks were determined using the CooRecorder software, and the obtained results were additionally corrected in the CDendro application. The highest values of the eccentricity index of annual increments in the examined spruces were recorded in the 1960s and 1980s. The causes of stress inside the trunks of the studied trees include both natural erosion processes occurring on the slopes in the catchment area, and high-energy events occurring in the stream channel. Assessment of the eccentricity of annual increments, in combination with geomorphological and hydrological studies, may find its application in the works covering the problems of the dynamics of erosive processes occurring in forest mountainous catchments.