Prioritizing tidal marsh restoration in grazing lands.

Globally, tidal marshes have been intensively grazed, leading to changes in ecosystem functioning, and consequently in the provision of ecosystem services. Fencing is a cost-effective animal exclusion measure to restore lost or damaged tidal marshes and protect upland areas for inland ecosystem migration due to sea level rise. However, limited funding and poor site selection hinder the implementation of restoration projects at meaningful scales. We applied the decision support tool Marxan to identify priority areas for 1) the restoration of collapsed tidal marshes within grazing land, and 2) the creation of new tidal marsh areas adapting to sea-level rise along the Victorian coastline in Australia. For both objectives we tested two scenarios: 1) recovering at least 30 % of multiple ecosystem services including carbon and nitrogen sequestration, enhancement of commercial and recreational fisheries, and coastal hazard mitigation, and 2) recovering at least 30 % of each individual ecosystem service at a time, while minimizing management costs for each management approach. The sensitivity of the spatial location of selected restoration sites was tested by varying the targets, including recovering 10 % and 20 % of multiple ecosystem services. The results show that fencing 26 % of collapsed tidal marsh area and fencing 22 % of future inundated areas to allow tidal marsh upland migration due to sea level rise could help recover nearly 30 % of the total supply of ecosystem services. High-priority restoration sites concentrated in two of the five Catchment Authority Management regions, West Gippsland (43 %) and Melbourne Water (36 %). Our results show the spatial distribution of restoration sites differed depending on the ecosystem services and target levels. Prioritizing restoration sites exclusively for coastal hazard mitigation delivered poor outcomes for other ecosystem services showing that there are trade-offs. High spatial variability of ecosystem services influenced spatial priorities rather than management costs, unlike many other spatial planning processes. Planners must clearly identify which ecosystem services are most important, given the spatial trade-offs between them. Due to these trade-offs, future studies should focus on refining the quantification of ecosystem services, particularly coastal hazard mitigation, and incorporate measures of site condition and opportunity costs.