Abstract
This research aimed to determine the temporal and spatial response patterns in amphipod density following seasonal fires in native grasslands, and explore possible implications for ecosystem functioning. The study was carried out in tussock grassland at 700m a.s.l. at Deep Stream, Otago, in the South Island of New Zealand.
To assess the temporal effects of burning, annual quantitative sampling was used to assess amphipod density in tussock and inter-tussock microhabitats in both summer and spring burn treatment and control plots that remained unburnt. Amphipod density was measured over a 14 year period which included 3 years pre-burn and 12 years post-burn. Further quantitative sampling was carried out to determine micro-habitat changes resulting from the fire that might affect recovery of amphipods. Plant composition and micro-habitat physical data were collected to investigate relationships between amphipod density and vegetation characteristics. Amphipods were identified to species, to examine species-related, spatial distribution within the habitat and between treatments. Litter bag experiments were used to determine the effect amphipods have on the rate of decomposition in tussock grasslands. Annual amphipod abundance varied considerably within control plots suggesting that populations are responding to the natural variation of biotic and abiotic factors within the ecosystem. Amphipod density in inter-tussock vegetation in both spring burn and summer burn treatments had been substantially reduced immediately post-burn and had failed to recover to pre-burn densities 12 years after treatment. Populations in tussock samples recovered more quickly, taking between 6 and 8 years to return to pre-burn densities. Litter depth in tussock samples was found to be a factor influencing the abundance of amphipods, likely reflecting the importance of this resource as food and shelter. Plant species composition showed some evidence to explain variation in amphipod abundance for inter-tussock samples. The effect of amphipods on the rate of litter decomposition in tussock grasslands was not able to be determined due to complete mortality of amphipods within litter bags during experimentation. Such a protracted period of recovery for an important member of the detritivore community was considered likely to have negative impacts on the recycling of nutrients, and therefore primary production in grasslands systems. Further research is needed to fully inform land managers of the impacts of burning in tussock grasslands.