Saltmarsh conservation through inventory, biogeographic analysis and predictions of change: Case of Tasmania, south‐eastern Australia

Abstract

Abstract Effective conservation of saltmarshes involves detailed and accurate mapping of their range, area of occupancy and plant community composition as part of region‐wide inventories. There is also a need to identify the major mesoscale influences on the distributions of types of saltmarsh, obligate saltmarsh plants and salt pans, and evaluate possible responses to macroclimatic changes. Tidal saltmarshes of Tasmania and its offshore islands (coastline of 4,882 km, spanning latitudes 39°40′ to 43°40′S), off south‐eastern Australia, were mapped at a high spatial resolution of 1 : 500–1 : 3,000. The distributions of types of saltmarsh, obligate plant taxa and salt pans were related to climatic, geomorphic and land‐use variation. The future distribution of climatically controlled species and communities was determined for two climate change scenarios. There was 58.6 km2 of tidal saltmarsh in Tasmania in 61 mesoscale complexes. The complexes were classified into three broad saltmarsh groups, which together offer a more ecologically relevant planning unit for saltmarsh conservation than macroscale bioregions. The small median patch size of 0.2 ha demonstrates the effectiveness of the manual interpretation and mapping with extensive field checking. Mapping of these smaller saltmarshes provides them recognition within the land use planning and approvals process. Climatic, but not geomorphic and land‐use, factors have strong effects on the distribution of saltmarsh plant communities, species and salt pans in Tasmania. Mean annual rainfall was most significant in predicting saltmarsh extent, range, plant community composition, salt pans and the three saltmarsh groups. Mean annual daily minimum temperature and saltmarsh area best predicted obligate plant distributions. Projected wetter and drier climatic change by 2100 is not expected to substantially alter macroscale plant community patterns but may reduce the range of the rare herb Wilsonia humilis R.Br. However, stochastic disturbances may continue to play an important role at local scales.