A trade-off in conservation: Weed management decreases the abundance of common reptile and frog species while restoring an invaded floodplain

Responsible conservation decisions are made when managers consider the benefits provided by an action in relation to the potential negative effects incurred. Some introduced grasses can be managed using fire and grazing, but experiments, replicated in time and space, are required to determine the relative costs and benefits of this action on native biodiversity. We aimed to experimentally determine the effect on reptile and amphibian assemblages of repeated burning and grazing of the invasive weed para grass (Urochloa mutica) over three years in a north Queensland conservation reserve in Australia. We measured the diversity and abundance of reptiles and amphibians, and quantified temperature and humidity during an experiment that repeatedly grazed, burnt, or burnt and grazed para grass in a replicated series of experimental plots. All burnt plots were drier and sites that were both burnt and grazed were hotter. The frog and reptile community was dominated by a few common species. Richness changed seasonally and was strongly related to the distance from the nearest woodland and free water, but it was unaffected by the management treatments. Abundance of the skink (Lampropholis delicata) and frog (Limnodynastes convexiusculus) decreased with burning and grazing, while a closely related frog (Limnodynastes tasmaniensis) remained unaffected. There was a clear trade-off between decreasing the abundance of a few common species to increase the overall suitability of habitat for a diversity of native species. We suggest that, in this case, it is reasonable to make the value judgement that this trade-off is acceptable.