The effect of fire on terrestrial amphipods (Crustacea: Amphipoda) in a natural grassland community

Terrestrial amphipods are an important component of decomposer communities on southern hemisphere land masses where they underpin ecosystem services. Fire is known to cause severe and protracted reductions in some invertebrate communities. We aimed to determine the temporal and spatial response patterns in density of amphipods following seasonal fires in natural grasslands in southern South Island, New Zealand. Fires lit for management purposes in spring generally contrast in intensity with fires that occur in hot dry summer conditions. Spring fires are regarded as being cooler and less detrimental to the ecosystem. Annual quantitative sampling was used to measure amphipod density in tussock grassland communities for 3 years before, and 12 years after summer or spring experimental fires. In inter-tussock vegetation, amphipod populations failed to recover to pre-burn densities up to 12 years after treatment, whereas those sampled from tussock plants showed faster recovery, taking 6 to 8 years to return to pre-burn densities. Recovery to pre-burn densities was slowest in the spring-burnt plots. Eleven years post-burn, the spatial distribution of amphipods in relation to micro-habitat was also examined. Two amphipod species were present and they were distributed differently in tussock and inter-tussock vegetation, and responded differently to fire but not to fire season. Amphipods are prone to desiccation and litter removal through fire could therefore be expected to have a significant adverse impact on their populations. Such a protracted period of recovery for an important member of the detritivore community is likely to have negative impacts on nutrient cycling, and therefore primary production in grassland systems. Amphipods may be good environmental indicators since as detritivores they are key ecosystem service providers, vulnerable to habitat change, generally abundant and relatively easy to sample.