Predicting the occurrence of riparian tree species to inform environmental water planning

Riparian zones are some of the most threatened ecosystems on earth. Globally, flow alteration has changed riparian plant assemblages, often with detrimental impacts on ecological and cultural values. Environmental water planning aims to quantify the risk of change to these values, including riparian vegetation, as a result of altered flows. Determining appropriate, or minimum, flows needed to meet environmental water objectives requires an understanding of the relationship between vegetation and flows. However, this knowledge is either not available or limited for many riparian systems around the world, particularly in remote tropical regions.

The primary objective of this study was to understand how reduced surface water flows might affect the spatial distribution of riparian tree species in the lower Fitzroy River floodplain, in the Kimberley region of Western Australia, to inform water management. We investigated the mechanisms that drive the distribution of riparian trees, hypothesising that it is primarily determined by hydrological variables, in particular duration of inundation. Results were linked to a predictive model with spatially-explicit flow scenarios. This information was used to create maps and assess changes in the distribution of environmentally and culturally important riparian trees with reduced duration of inundation. By linking the distribution of riparian trees to available hydrological data preliminary predictions were made about the relative risk to riparian trees under different water reduction scenarios. Our approach was informed by a specific management problem, identified through consultation with State Government water managers, and our collaboration ensures uptake of our recommendations by managers.