Predicting the Recruitment of Large Woody Debris throughout a Watershed

Information about the spatial distribution of riparian vegetation, and the ecosystem services it provides, is required to prioritise the protection and restoration of riparian zones within watersheds. Large woody debris performs a range of fluvial geomorphic and ecological functions within streams. This paper describes a new technique for estimating how much large woody debris is provided by riparian vegetation distributed throughout a semi-arid watershed in Queensland, Australia. The technique uses fieldwork combined with a vegetation classification derived from medium resolution satellite imagery to identify four different types of riparian vegetation (woodland, closed forest etc) throughout the watershed. The three attributes of each vegetation type: number of stems per hectare; mean tree height and mean diameter at breast height, are calculated using field data. These attributes are extrapolated beyond the sampling sites using a vegetation classification that was generated from satellite imagery. These attributes are then used to calculate the amount of large woody debris produced by the riparian vegetation. An independent set of field data is used to assess the accuracy of the vegetation classification and to assess the reliability of the attributes predicted by the classification. Results are presented for the whole watershed with discussion on reliability of index results and the potential to use this approach to prioritise the protection and restoration of riparian zones. KEY TERMS: large woody debris, aquatic ecology, watersheds, riparian zones, spatial extrapolation