Hydrological response to wildfire, integrated logging and dry mixed species eucalypt forest regeneration: The Yambulla experiment

Abstract

Eucalypts are commonly planted hardwoods worldwide and 'Eucalyptus' dominated forests naturally grow in the headwaters of many Australian water supply catchments. The hydrological effects of disturbances have been extensively reported for one species, 'E. regnans' (Mountain Ash). The typical response to disturbance is unusual in that following an initial increase, with heavy seed dispersal and rapid regeneration, streamflow from these forests is greatly reduced. In New South Wales (NSW), native forests are dominated by different 'Eucalyptus' species that typically grow in mixed-species and mixed-age stands that regenerate less vigorously. In this study the long term streamflow records from the six Yambulla catchments in southeastern NSW were analysed to assess the relative effects of wildfires, integrated logging operations and subsequent mixed species eucalypt forest regeneration on catchment hydrology. In all five treated catchments an increase in total streamflow, baseflow and stormflow was detected following the 1979 wildfire and/or integrated logging activities that occurred at various intervals. A subsequent reduction of streamflow to below that of a mature stand was not detected in three of the catchments but was detected in the two that had been subjected to integrated logging followed by a wildfire, and a wildfire followed by salvage logging, respectively. The reduction, however, was minor and short-lived in each case meaning that overall there was a cumulative increase in streamflow in the post-disturbance period. These results contribute to a growing body of evidence indicating that catchment-scale hydrological responses to disturbance of mixed species eucalypt forests do not follow the unusual response often reported in wet Mountain Ash forests. This has important implications for the modelling and management of mixed species eucalypt hydrology.