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Numerous studies demonstrated the potential of interferometric coherence for forest stem volume estimation in boreal forests. Coherence derived from winter images acquired at frozen conditions proved being favourable against unfrozen conditions. This also applies to PALSAR coherence, although featuring relatively large temporal baseline of at least 46 days. However, when using data acquired at unfrozen conditions, a large spread of coherence was observed at all stem volume levels. This scatter negatively effects the correlation of stem volume and coherence, and thus prevents using summer coherence for stem volume estimation. Besides environmental conditions, the different tree geometries can be assumed having an impact on the magnitude of decorrelation. So far, this impact has rarely been investigated in boreal forests. This paper presents the results of a study investigating the impact of tree species on PALSAR coherence. The results show increased scatter of coherence in summer. They also show that the coherence of dense forest is larger in summer than in winter. Eventually, a slight impact of the tree species on coherence was observed. This impact is larger in summer.