Accommodation space as a framework for assessing the response of mangroves to relative sea-level rise

Mangroves thrive in tidally influenced environments and will be central to any discussion regarding the implications of sea-level rise for coastal communities. Mangrove forests can respond to sea-level rise by adjusting their position within a tidal frame that is transitioning upwards, and this response is dependent upon a range of hydrological, sedimentological and ecological factors. The availability of accommodation space, defined as the lateral and vertical space in which mineral and organic sediments and organic material from in situ vegetation can accumulate, is increasingly proposed as a means of conceptualizing the response of shorelines to sea-level rise. Recent analyses demonstrated the significance accommodation space has on global carbon storage in coastal wetlands over the past few millennia, and likely influence on future carbon sequestration and coastal wetland resilience. Mangrove forest vulnerability is commonly indicated by comparing rates of substrate elevation change to rates of sea-level rise, but these comparisons may overemphasize mangrove forest vulnerability to sea-level rise as they do not adequately account for the resilience provided by mineral and organic sediments that previously filled accommodation space and increased substrate elevations beyond critical thresholds for submergence. This paper demonstrates that the geological concept of ‘accommodation space’ applied in a way that incorporates ecological processes and recognizes the full range of processes altering accommodation space may provide a unifying framework for integrating information between disciplines and increasing our understanding of the response of mangrove forests to sea-level rise. This paper also defines available accommodation space as the space available for sediment accumulation; realized accommodation space as the space that has converted from being available, primarily due to sediment accumulation; and the boundary conditions delimiting both available and realized accommodation space (See Appendix I for the full list of definitions). It is anticipated that this paper will serve as a challenge for researchers across disciplines to collaborate, share and integrate knowledge so that the past is interpreted appropriately and integrated into models, and the best information is available to inform coastal planning and management.