EROSION POTENTIAL UNDER MICONIA CALVESCENS STANDS ON THE ISLAND OF HAWAI'I

This study provides evidence that Miconia calvescens has the potential to accelerate surface erosion in stands where it invades by (i) reducing under-canopy light levels, thereby reducing the establishment of ground cover vegetation, and (ii) producing highly erosive throughfall drops on large leaves in a single-layer canopy. The throughfall energy in a stand of invasive miconia on the Island of Hawaii (USA), assessed by measuring the drop size and drop velocity distributions with a laser disdrometer, was significantly higher than that in a stand of native hia (Metrosideros polymorpha) and ambient rainfall. Median throughfall drop size for miconia (383mm) was twice that of ambient rainfall (162mm). Highly erosive throughfall resulted from large drops forming on large miconia leaves and relatively high fall velocities associated with the single-story miconia canopy. In contrast, multi-storied natural hia had a larger median drop size; however, a lower fall height reduced throughfall effective kinetic energy. Furthermore, the effective kinetic energy for miconia was high because large drops (> 38mm) with high kinetic energy accounted for 60 per cent of the total energy (versus 30-40 per cent for other vegetation types). Consequently, unit kinetic energy of throughfall was 28Jm(-2)mm(-1) under miconia, compared with <24Jm(-2)mm(-1) for rainfall and <20Jm(-2)mm(-1) under hia. These data, combined with the observation of limited protective ground cover under miconia, show the potential for accelerated erosion occurring on forest floors in stands of invasive miconia. Copyright (c) 2013 John Wiley & Sons, Ltd.