Dating past geomorphic processes with tangential rows of traumatic resin ducts

Past activity of geomorphic processes can be reconstructed on tree-ring series using the presence of injuries, reaction wood or abrupt changes in the annual increment. The analysis of these features provides valuable data on years with process activity. In contrast, an intra-annual dating has so far normally only been possible through the analysis of injuries. In this technical note, it is shown that, in tree-ring studies realized with conifers, resin ducts may have the potential for providing information on the intra-seasonal timing of past geomorphic processes as well. However, because ducts may occur as a result of influences other than geomorphic, detailed field investigations and the identification of processes present at the study site imperatively need to precede dendrogeomorphological investigations. Data obtained from 1298 cross-sections indicate that the presence of resin ducts in Picea abies (L.) Karst. and Larix decidua Mill. can be considered to be the result of geomorphic activity if they form tangentially oriented rows with a compact and continuous arrangement of traumatic ducts. The presence of resin ducts may also help to improve the quality of reconstructions in studies using Abies alba Mill. as vertical resin ducts occur exclusively at or next to injuries. In contrast, resin ducts apparently cannot be used for dendrogeomorphological analyses of Pinus ssp.