Wetland vegetation regeneration in response to tidal reinstatement on an abandoned sugar cane farm

Abstract

Supratidal wetlands are threatened by agricultural production and are highly vulnerable to climate change, particularly through sea level rise (SLR). While vegetation structure and composition of supratidal wetlands will likely change under projected SLR with run‐on effects for ecosystem service provision, these changes can provide opportunities for restoration of adjacent agricultural land. Here, we investigated the natural regenerative potential of supratidal wetlands on abandoned agricultural land in Southeast Queensland, Australia, specifically, responses of wetland vegetation communities to simulated SLR, through tidal reinstatement. In 15 years since crop abandonment, distinct communities of typical supratidal wetland vegetation have naturally reestablished, in predominately freshwater conditions, with minimal management intervention. Reinstating tidal floodwater increased the flooded extent and permanence of brackish water. Four repeat surveys of vegetation composition, structure, and condition were conducted in permanent plots established in Casuarina swamp, Melaleuca swamp, herbaceous marsh, and riparian zone vegetation communities, to observe change over time. Species richness decreased in all regenerating communities (Herbaceous marsh, Casuarina, and Melaleuca) post flood gate removal. Understory vegetation cover also decreased in Melaleuca and Casuarina plots, but increased in herbaceous marsh plots, with increased cover of salt‐tolerant species throughout. Changes in woody vegetation community and structure were not observed during this short study (2.5 years), although the regenerative capacity of woody and herbaceous species was reduced. Supratidal wetland vegetation communities can naturally reestablish in areas of abandoned agricultural land, however, increased saltwater flooding (likely with SLR) will put these communities at risk of transition to salt‐tolerant vegetation.