Spatially Diffuse Tree Mortality during an Episodic Mortality Event

Episodic tree mortality events, such as those caused by insect outbreaks, are often characterized by aggregated tree mortality, resulting in patches of dead trees. However, simultaneously with mortality within these aggregates, individual tree mortality in the surrounding forest matrix can also be considerable. Consequences of this diffuse mortality for stand structure and further development differ from that of aggregated mortality. Here, we used change detection in LANDSAT-images and a stand-level field inventory in a naturally dynamic forest landscape in Arkhangelsk province in Russia, to examine the role of spatially diffuse mortality during an episodic tree mortality event, caused by drought and bark beetles. We show that even if patches of dead trees are a prominent and visible feature within the study landscape, diffuse mortality outside of these distinct patches was responsible for a large proportion of tree deaths. The findings demonstrate the potential importance of spatially diffuse tree mortality and the consequent finer scale forest dynamics even during episodic events.