The UNSW CES’s Flow-MER vegetation team has begun monitoring lignum shrublands in the Macquarie River and Marshes catchment.

Native plants including lignum play crucial a role in waterways by filtering and cleaning water; reducing soil and water salinity; cycling nutrients; stabilising soil to prevent erosion; and providing habitat for flora and fauna.

Led by Dr Tanya Mason from the NSW Department of Climate Change, Energy, the Environment and Water (NSW DCCEEW), the team is using red, green and blue (RGB) and LiDAR (Light Detection and Ranging) drone imagery to estimate the extent and condition of lignum in the area.

RGB imagery will be used to classify lignum extent and condition. By capturing the red, green, and blue bands of the electromagnetic spectrum — those visible to the human eye — RGB data provides a rich source of visual information. When processed through advanced machine learning techniques, patterns in the RGB data can be identified and classified, enabling differentiation of lignum extent from other vegetation types and an assessment of its condition. LiDAR is also being trialled to measure changes in vegetation structure. It uses pulsed lasers to measure ranges (distances) to the Earth's surfaces. The light pulses generate three-dimensional information about surface characteristics. 

Drone surveys help overcome site access limitations of traditional on-ground surveys. Lignum shrubland is typically thick and difficult to access, particularly during wet periods. Remotely sensed data provides a repeatable and cost-effective method to monitor lignum health.

Results from the Macquarie monitoring program will feed into a Murray-Darling Basin-scale lignum study that will inform environmental water delivery to maintain healthy communities of this important native plant species.

Lignum (Duma florulenta) is a perennial shrub with long, thin, intertwined branches that form densely tangled thickets. Lignum thickets often appear leafless, especially during dry conditions. However, new leaves and shoots emerge in response to rainfall or flooding. This species is tolerant of saline conditions, and its root profile (at least 3 metres in deep) provides resilience during drought.

Lignum shrubland has important habitat value in the Murray Darling Basin (MDB). It provides protected breeding habitat for many species of group-nesting birds including Straw-necked ibis (Threskiornis spinicollis), Australian white ibis (Threskiornis moluccus), Glossy ibis (Plegadis falcinellus), Royal Spoonbills (Platalea regia) and Australasian Bitterns (Botaurus poiciloptilus).  

Lignum also contributes large amounts of carbon to floodplains, an essential nutrient for a healthy food chain. 

Straw-necked ibis nests in lignum, Macquarie Marshes 2022