Managing savanna riparian zones

Riparian vegetation in northern Australia is vulnerable to processes such as changes in water flows, fire, weed invasion and cattle grazing. Monitoring the condition of riparian vegetation is critical for effective adaptive management but can be challenging in northern Australia. Methods such as on-ground quadrats or transects have traditionally been used to survey vegetation but there is increasing interest in using remote-sensing techniques as these methods become more affordable, including drone-based photogrammetry and terrestrial laser scanning.

This component of the project compared two terrestrial laser scanning (TLS) sensors, drone photogrammetry and traditional vegetation transect methods to assess the structure of riparian vegetation in the lower Fitzroy River, Western Australia. The overview of the techniques focuses on the usability and application for management agencies, including associated costs and the level of knowledge, skills and experience required to process and analyse the data collected. Read more in the report for this component.

The Fitzroy River is in the Kimberley region of Western Australia.

Each of the tested methods has strengths and limitations in relation to scale (both detail/resolution and spatial coverage area), expertise, training and overall costs. Each method has potential to address specific questions in relation to the monitoring of riparian vegetation. TLS was found to be the most accurate and high-resolution method to investigate vegetation structure, but covers a smaller spatial area than drone photogrammetry. There are also a number of potential barriers to the application of TLS methods, including cost of equipment and software, advanced training expertise required, and field conditions. Drone photogrammetry provides TLS-like point-clouds, covers larger areas and has a lower cost to acquire data compared with TLS. However, drone photogrammetry provides less sub-canopy vegetation structure information and also requires high levels of expertise for processing and data extraction.

The TLS point cloud can be visualised at different angles. A side view (top) highlights the height of trees. A view from above (bottom) may better show the cover and distribution of vegetation.

Each of the tested methods produced different types of data, from highly detailed 3D point-clouds using TLS, to estimated vegetation health scores using rapid vegetation transect assessments. There were also differences in the spatial scale assessed by each method and the opportunities for sampling frequency.

Collection of data using a drone. Photo: Fiona Freestone.

While the technology to collect remotely sensed data is becoming increasingly user-friendly and affordable, processing the data remains a specialised skill. To derive metrics from TLS and drone photogrammetry requires access to appropriate computer processors, software and specialised knowledge, skills and experience. Therefore, the application of TLS or drone photogrammetry should align with the specific aims of the monitoring program and the budget and human resources available.

Completing surveys using the transects. Photo: Karen Dayman.

Stinking passionflower (Passiflora foetida) is a weed of significant environment concern along the banks of the Fitzroy River in Danggu (Geikie Gorge) National Park in Western Australia’s Kimberley region. Danggu is included in the West Kimberley National Heritage Place, and the listing specifically notes Danggu’s ‘lush riverine vegetation’. The area is of great significance to Traditional Owners and is a popular tourist location. Danggu also has high conservation values for several species, including the Australian freshwater crocodile (Crocodylus johnstoni).

This component of the project aimed to understand if and how the presence of stinking passionflower impacts on nesting success of freshwater crocodiles, and to develop prioritised weed management recommendations.

This research found no evidence that stinking passionflower currently limits the availability of crocodile nesting space at Danggu – seasonal flooding regularly removes weed biomass and opens up the riverbanks. However, this could change if river flows change in the future – for example, following multiple low-flow years or as a result of water extraction. There are other significant aesthetic, amenity and biodiversity reasons to manage stinking passionflower at Danggu, but this study was confined to the impacts of the weed on freshwater crocodile nesting.

A logical framework detailing timing and techniques of control of stinking passionflower was developed to optimise management. In the long term, a biological control solution is a feasible and effective way to reduce occurrence of the weed in the park and beyond, and Danggu represents a high-value landscape for biological control.

Read more in the report for this component.

Location of Danggu (Geikie Gorge) National Park.

Stinking passionflower covering the banks at Danggu. Photo: Ruchira Somaweera.

Framework for decision-making and intervention to control stinking passionflower at crocodile nesting sites at Danggu. PDF available here.

This project surveyed stinking passionflower at Danggu between 2016 and 2019 using field surveys, drones, and analysis of aerial and satellite imagery.

The surveys found that stinking passionflower has a variable but persistent presence in the park, with significant coverage in some years. This variation is likely the result of the intensity and frequency of seasonal flooding, rather than a result of management activities.

There were always suitable areas available for freshwater crocodile nesting throughout the survey period, but nesting site availability could change if several consecutive low-flow years reduced flooding and allowed the weed to proliferate.

Read more in the report for this component.

Stinking passionflower at Danggu National Park between 2016 and 2019 separated into areas where the vine was consistently present (dark green), occasional (light green) or consistently absent (unshaded).

This project also produced an eco-hydrological model to assess and quantify habitat for stinking passionflower and freshwater crocodiles at Danggu. This prototype approach is a combination of an environmental model – simulating hydrodynamics, soil moisture and temperature – and a habitat suitability model for the two species based on a literature review, results from experimental and field research, and expert judgement.

Suitable habitat for both species was successfully estimated using the model, indicating its potential usefulness in assessing scenarios linked to the management of stinking passionflower, and also scenarios associated with flow changes brough about by any water allocation in the catchment.

The model also identified the river interface as the habitat where these two species are most likely to interact.

Read more in the report for this component.

For this component of the project, researchers from The University of Western Australia (UWA) worked with the Yawuru Country Managers and the Yawuru Environmental Services team to develop a bilarra (wetland) monitoring program for the Yawuru Indigenous Protected Area (IPA) in the Kimberley region of north-western Western Australia. The monitoring program was developed to support the Country Managers to assess the sustainable cattle grazing operations on the IPA, and whether they are achieving their IPA objectives for protecting wetlands.

The 4-year project involved a Multiple Evidence Based approach, which sees different knowledge systems, such as Indigenous (Yawuru) and university-based science, as all validly contributing to understanding the natural environment – in this case, bilarra. A key part of the project was ongoing knowledge-sharing between Yawuru staff and project researchers, and a commitment to collaboratively adapt and refine a wetland monitoring protocol (designed in northern Australia for implementation by Indigenous groups) to the Yawuru context and management requirements. Importantly, the monitoring protocol was adapted to meet the information needs of the Country Managers and was also shaped by Yawuru knowledge of bilarra ecology and values.

The monitoring program focuses on riparian zones around bilarra that are vulnerable to many of the issues and disturbances common across the Kimberley (and northern Australia) including weeds, groundwater use, feral animals, uncontrolled fire, overgrazing and erosion. Management activities by Country Managers are also focused on reducing site disturbance at these culturally important places. The assessment of riparian zones also captures the condition of plants recognised as important to Yawuru people, with the plants along the edge of a wetland, for example, providing food and shelter to important animals.

Country Managers are using the adapted monitoring protocol to record information at 6 culturally and ecologically important bilarra that are under different management scenarios, including levels of cattle grazing. Although the monitoring protocol has only recently been finalised, the Country Managers are already using it to inform management of these bilarra, including refining their sustainable grazing operations. The approach and monitoring tools developed are being used to inform a broader Kimberley wetland project in partnership with Environs Kimberley and 5 additional Indigenous ranger groups across the Kimberley.

The Country Managers and Environmental Services team have co-authored a report with project researchers which provides more detail about the project how the monitoring protocol was developed and some of these management outcomes.

The Yawuru Indigenous Protected Area covers land and sea country near Broome in Western Australia. Image: Resilient Landscapes Hub.

Country Managers recording changes resulting from cattle management including recruitment of rirrwal (white dragon tree; Sesbania formosa) around springs. Photo: Rebecca Dobbs.

Monitoring vegetation transects around a recently fenced spring. Photo: Michelle Pyke.

Fenced spring on Roebuck Plains showing plant recovery following removal of cattle. Photo: Rebecca Dobbs.

Monitoring transects set up at sites. Photo: Michelle Pyke.

Yawuru Country Manager recording changes on the FULCRUM app. Photo: Rebecca Dobbs.

Summary poster for Tharndoo-Ngunjal developed to assist with individual site monitoring and management.

Summary poster for Mimiyagaman developed to assist with individual site monitoring and management.