Large wood load fluctuations in an Andean basin

• Published in: Earth surface processes and landforms Vol. 46; no. 2; pp. 371 - 384
• Main Authors: Picco, Lorenzo, Scalari, Cordelia, Iroumé, Andrés, Mazzorana, Bruno, Andreoli, Andrea
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.02.2021
• Subjects: Aggregation; Chile; Deposition; Diameters; Fluctuations; Fluxes; large wood; Load fluctuation; long‐term monitoring; Mountain environments; Rio Toro; Roughness; roughness index; Statistical models; Surveys; Wildfires; Wood; wood load
• ISSN: 0197-9337; 1096-9837
• DOI: 10.1002/esp.5030

The importance of monitoring and analysing wood fluxes in mountain environments is widely recognized. However, there is a lack of information related to the long‐term fluctuations in wood load and associated to the changes in large wood (LW) characteristics. The main aims of the research were to analyse (i) changes in wood characteristics, (ii) fluctuations in wood load, and (iii) the relationship between wood load and sub‐reach settings, proposing an ad hoc roughness index (RI). Repeated field surveys to measure wood load and LW characteristics during a 13‐year period were conducted within a 2.2 km‐long reach of the Rio Toro (Chile), which flows through the Malleco Forest National Reserve that was affected by wildfires in 2002 and 2015. Two spatial scales (i.e. study reach and sub‐reach) were considered. Irrespective of the adopted scale wood load fluctuated considerably, in both number and volume, with significant changes in LW characteristics (i.e. mean diameter and length). Moreover, a clear tendency to the aggregation in wood jams (WJs) was observed within the entire study reach. Based on our results, we conclude that 17 years after the first wildfire wood recruitment has started in the upper parts of the basin. Moreover, Generalized Linear Mixed Models (GLMM) analyses were carried out to investigate the relationship between RI and both number and volume of LW. Both models are characterized by high adjusted R2 of 74.9% and 72.8% for volume and number, respectively. This demonstrated that the RI can characterize the reaches in terms of tendency to deposition and trapping of wood. These results are promising, particularly in improving the knowledge related to potential deposition areas that can control wood load fluctuations, also permitting its management to be improved. © 2020 John Wiley & Sons, Ltd. In the last 13 years, huge fluctuations in wood load were detected from 2006 (592 logs), to 2009 (324 logs), and until 2019 (1329 logs). This fact demonstrated that after two subsequent wildfires (2002 and 2015) the recruitment is already going on, even if there are not so many surficial instabilities and mass movement directly connected to the channel network. Positive correlations were detected between the preferential sub‐reaches of deposition and both, mean slope and a newly introduced roughness index.