Underground riparian wood: Reconstructing the processes influencing buried stem and coarse root structures of Black Poplar. (Populus nigra L.)

作者：Holloway James V; Rillig Matthias C; Gurnell Angela M

来源：Geomorphology, 2017, 279: 199-208.

DOI：10.1016/j.geomorph.2016.07.027

• Populus nigra
• Underground wood
• Riparian tree recruitment
• Flood disturbance
• Riparian vegetation dynamics
• Root system architecture

Following analysis of morphological (including dendrochronological and sedimentological) aspects of buried stem and coarse root structures of eight mature P. nigra individuals located within two sites along the middle to lower Tagliamento River, Italy (Holloway et al., in press), this paper introduces information on the historical processes of vegetation development and river flow and links this to the form of these eight trees.
Aerial images and flow time series are assembled to reconstruct the flood history, potential recruitment periods, and vegetation cover development in the vicinity of the studied trees. This information is combined with previous morphological evidence to reconstruct the development history of each tree via three-element summary diagrams showing (i) a time series of floods, aerial imagery dates, and potential recruitment periods, with colour coded bars indicating likely key stages in the development of the tree; (ii) colour-coded overlays on an SIM photogrammetric model of each tree; and (iii) colour-coded text boxes providing explanatory annotations.
The combined morphology-process analysis reveals complex three-dimensional underground structures, incorporating buried stems, shoots, and adventitious roots that are sometimes joined by grafting, linking the standing tree with the buried gravel surface on which it was recruited. Analysis of process data provides a firm basis for identifying and dating influential flow disturbance events and recruitment windows and shows that a relatively small number of flood events have significantly impacted the studied trees, which are mainly but not exclusively the largest floods in the record. Nevertheless, we stress that all suggested dates are best estimates in the light of the combined evidence. There is undoubted potential for building different interpretations of belowground woody structure development in light of such evidence, but we feel that the form and timing of the developmental trajectories we have proposed are reasonable and give balanced insights into the many possible ways in which this hidden component of riparian trees may develop.
Our results are relevant to river research and management issues concerning riparian woodland, fluvial wood dynamics, and wood budgets, as they indicate (i) a large hidden volume of wood that is often ignored; (ii) complex, deep, coarse anchorage structures that have relevance for rates of fluvial wood recruitment associated with lateral bank erosion/stability or wind throw; and (iii) a wood element that may significantly affect wood transport and retention within fluvial systems.

• 出版日期2017-2-15