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Australasian Plant Conservation

Originally published in Australasian Plant Conservation 18(3) December 2009 - February 2010, p 15-16

Aerial mapping of two riparian vine weeds in Tweed Shire, New South Wales

Sally Jacka1, Carla McKevitt2 and Tom Alletson1
1Tweed Shire Council, Murwillumbah. Email: sjacka@tweed.nsw.gov.au
2Ecosure Proprietary Limited, West Burleigh, Qld.


Madeira Vine (Anredera cordifolia) smothering a Casuarina cunninghamiana tree. Photo: Ecosure Pty Ltd.

Introduction

Tweed Shire covers an area of 1303 km2 encompassing the whole of the Tweed River Catchment. The catchment, consisting of three main waterways—the Oxley River, the Tweed River and the Rous River—is surrounded by the Mt Warning (Wollumbin) caldera, which is part of the World Heritage listed Gondwanan Rainforest. The Shire consists of various vegetation communities, including the Environment Protection and Biodiversity Conservation Act (EPBC Act) listed Littoral Rainforests and Coastal Vine Thickets of Eastern Australia Threatened Ecological Community. The Shire is home to 43 flora and 25 terrestrial fauna species listed under the EPBC Act.

Rainforests and Coastal Vine Thickets have been fragmented due to past sand-mining, urban expansion and clearing for agriculture. The riparian network provides important corridors for genetic exchange and movement of fauna, connecting component populations of rainforest and World Heritage areas.

The spread of introduced vine weeds in New South Wales is recognised as a key threat to the preservation of native flora and fauna. Cats Claw Creeper (Macfadyena unguis-cati) and Madeira Vine (Anredera cordifolia) are regarded as the most severe weed threat to the environmental quality of waterways and riparian habitat in the Tweed River Catchment and are a serious threat to the biological diversity of the Shire. Their proliferation there is severely degrading some of the highest conservation value forest by smothering canopy and understorey and killing mature trees.

Cats Claw Creeper and Madeira Vine are native to South America and were introduced to Australia as ornamental plants. Cats Claw Creeper is a tuberous, woody climber with tendrils ending in sharp, hooked claws. Madeira Vine is a semi-succulent perennial that successfully reproduces from both aerial and underground tubers and will regrow from axillary buds still attached to leaf petioles (Big Scrub Rainforest Landcare Group, 2008). Both species are characterised by prolific flowering, rapid growth and effective dispersal within the riparian environment. They infest the canopy of native vegetation and can rapidly smother and kill mature trees, ultimately toppling them and creating gaps in the riparian corridor which leads to additional weed infestation. As a consequence, riparian zones become dominated by non-native species.

In July 2008, the Tweed Shire Council, with New South Wales Environmental Trust funding, contracted Ecosure Pty Ltd to survey and map the extent of riparian vine weeds in approximately 730 km2 of the Tweed River catchment (see Ecosure, 2009).

The aims of this project were to identify and map the extent of Cats Claw Creeper and Madeira Vine infestations within the Oxley, Tweed and Rous rivers catchments. The primary purpose of mapping was to provide a framework to guide the preparation of a strategic plan for vine weed suppression at a strategic scale. It has enabled the identification and assessment of existing vine weed locations and set priorities for actions and resource allocation to effectively suppress these weeds.

Methods

Both Cats Claw Creeper and Madeira Vine are often interspersed within the canopy of native species and generally are difficult to discriminate from other vine species without close inspection. However, both species present distinguishing colour displays when flowering, and their in situ distribution can be estimated by mapping the extent of the flowers. Flowering periods vary between three and six weeks, but flowering may be asynchronous. Variations in flowering times are caused by elevation, aspect of habitat towards the sun, water and nutrient availability of each population of vine species. Flower retention may also vary with ambient conditions.

Observations from a helicopter were made when the vines were flowering and highly visible within the canopy of riparian vegetation. Most areas were surveyed at least twice during the flowering period to account for flowering variability. This method of mapping is the most effective means of covering large distances and negates the problems of passing through hard terrain, dense vegetation on the ground and gaining land owner permission to access private land. Helicopters also allow for a high level of speed and manoeuvrability that are ideal for surveying the terrain within the Shire.




Flowers of the Cats Claw Creeper (Macfadyena unguis-cati) (top) and Madeira Vine (Anredera cordifolia) (bottom). Photos: Eddy Roberts (top) and Ecosure Pty Ltd (bottom).

Eight hours of ground surveys were performed for each target weed species, to ensure that the species mapped from the air as Cats Claw Creeper and Madeira Vine were correctly identified. Randomly located sites were also surveyed to confirm that there were no target weeds in areas that were mapped as ‘no weed species being present’.

An ike 305 laser GPS (Global Positioning System) was used with an integrated 3.2 mega pixel camera, a 905 nm (invisible infrared) laser range finder (1000 m), a digital compass and an inclinometer (Survey Lab in New Zealand). This unit can capture positions remotely with offset positions calculated in real time. The unit was coupled with a Sokkia AXIS3 Differential unit that receives real time correction through the OmniSTAR Virtual Base Station system that allows for sub-metre precision.

The capture software used was an ike GPS version of GBM Mobile (MapInfo). It was customised as necessary to suit the project, allowing specific attributes of each weed to be captured in the field as meta data.

The patch size and relative density of each weed infestation was assessed and attributed to the location at the point of data capture. This delineation allowed the production of the maps, which illustrate the position, density and size of each weed patch. Different symbols were used to represent the size and density of weed patches within the catchment.

Results

During the aerial surveys, 521 ha and 172 isolated infestations of the target weeds were identified and mapped. Generally, both weeds occur on or near waterways with only a few patches found terrestrially as ornamental specimens in gardens.

Both of the target weeds are distributed throughout the three main waterways surveyed (the Oxley, Tweed and Rous rivers). The only waterways where the target weeds were not identified were tributaries to the Rous River. All other tributaries contain some level of infestation of the target weeds, although some only at the very downstream section where they join the main waterways.

Eight small patches of Madeira Vine and four small patches of Cats Claw Creeper were identified on the ground that were not seen from the air. These sites were not mature infestations, with the majority of the weed mass not having reached the canopy. This is a known limitation of aerial surveys where vines growing beneath the canopy may be shielded from aerial view.

Recommendations

The knowledge of the mature infestation locations gained through this survey will be an extremely useful tool that will aid the planning and management of future weed control programs. Key target properties will be identified for vine weed control with priority given to upper-most stream infestations of streams not heavily infested. Using this strategy, it may be possible to eradicate the vine weeds from small sub-catchments. When planning the strategic treatment of these weeds, consideration will also be given to the protection of areas of high conservation value.

References

Ecosure (2009). Aerial mapping of riparian weeds. Report to Tweed Shire Council, Ecosure, West Burleigh, Qld.

Big Scrub Rainforest Landcare Group (2008). Common weeds of subtropical rainforests of eastern Australia. Big Scrub Rainforest Landcare Group, Bangalow, NSW.

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