large wood, ephemeral stream, Mediterranean, Crete

Many scientific papers have acknowledged the importance of large wood (LW) in the geomorphic functions of rivers and streams and its unique benefits for aquatic biota (e.g., increased habitat heterogeneity, providing source of food, creation of refuges for aquatic organisms). Although LW has been intensively studied in forested basins of humid temperate climates, data on LW patterns coming from different fluvial environments are scarce. We investigated the dimensions, characteristics, longitudinal distribution, and dynamics of LW along a 4.05-km-long reach of an ephemeral channel typical of semi-arid European Mediterranean mountainous landscape (Sfakiano Gorge, Crete, Greece). We analysed a total of 795 LW pieces, and the mean observed abundance of LW was generally lower (14.3 m3 per hectare of active valley floor or 19.6 LW pieces per 100 m of stream length) than is usually documented for more humid environments. The number of LW pieces was primarily controlled by trees growing on the valley floor, whereas LW recruitment from steep adjacent hillslopes was less important. The valley floor width and the distance from the coastline (the moisture gradient) played crucial roles in the distribution of living trees as the main source of LW for the studied channel. These living trees acted as important LW supply agents (by tree throws or the supply of individual branches with sufficient LW dimensions) and flow obstructions during large flood events, causing storage of transported LW pieces in jams.