A Rapid Method for Assessing the Condition of Riparian Zones in the Wet/Dry Tropics of Northern Australia. Ian H. Dixon1, Michael M. Douglas1, John L. Dowe2, Damien W. Burrows2 and Simon A. Townsend3 1 Tropical Wetland Program, Charles Darwin University, Darwin NT, 0909, email@example.com, firstname.lastname@example.org 2 Australian Centre for Tropical Freshwater Research, James Cook University, Townsville, Qld, 4811, email@example.com, firstname.lastname@example.org 3 NT Department of Infrastructure, Planning and Environment, PO Box 30, Palmerston NT, 0831, email@example.com Abstract The health of riparian habitats across northern Australia is becoming increasingly important to its diverse land management community. Assessing, protecting and improving the condition of riparian habitats has been and will continue to be a major activity focus of regional planing in northern Australia. However, a lack of information on assessing the health of savanna riparian zones has resulted in little evaluation of the effectiveness of existing programs or the prioritisation of works for future programs. Many methods already exist to assess riparian health, but their application is often limited to specific areas or projects and purposes. Consideration of the vast river lengths present in northern Australia, often in remote areas, led us to develop a rapid appraisal method suitable for trained non-specialists to assess savanna riparian health. The method is being applied across northern Queensland and the Northern Territory and is comprised of attributes of vegetation cover, woody debris, weediness, native plant regeneration and evidence of disturbance. It is based on methods developed by Werren and Arthington (2002) and Jansen et al. (2004) and has been modified for the different conditions of northern Australia. It provides a consistent approach across large geographic areas and should help to assess and improve management of savanna riparian zones in pastoral, mixed use and conservation managed lands across northern Australia. Keywords Rapid appraisal, riparian habitat, vegetation condition, savannas. Introduction Riparian zones are vital elements of the landscape in the savannas of northern Australia. Their contribution to biodiversity, cultural values and the economy is disproportionately large considering the small area that they occupy (Finlayson 2001, MacLeod 2001). Savanna riparian zones are vulnerable to disturbances such as weed invasion, feral animals, fire, overgrazing and erosion (Burrows 2001, Choquenot et al. 2001, Douglas and Pouliot 1997, Grice 2001). Maintaining and improving the condition of riparian zones is likely to be identified as a high priority in most of the natural resource management plans that cover Australia’s tropical savannas. From many points of view, it is desirable and widely recognised that a method for rapidly assessing the health of numerous riparian locations across large geographic areas is required for a wide variety of management goals, including the need to demonstrate the positive effects of natural resource management activities undertaken through Landcare, Natural Heritage Trust (NHT II) and related programs. Savanna riparian zones are spread out across a vast area (approximately 25% Australia), much of which is remote from major population centres and is characterised by a low population density. A rapid appraisal approach to assessing riparian condition may be best, as too few technical experts are likely to be available to cover such a large area. Rapid appraisal methods can be undertaken by trained non-specialists to assess and monitor environmental conditions and they can be completed relatively quickly, simply, and inexpensively (Ward et al. 2003). A rapid appraisal typically requires the operator to score simple indicators of health using visual estimates to derive an index of condition (Innis 2000, Werren and Arthington 2002). When used by a trained operator, results obtained from a rapid appraisal are easily interpreted and highlight areas of ecological concern, and when repeated over time they can be used to monitor changes in condition. They may also be used to prioritise areas that require more detailed investigations. Many such methods already exist (eg, Table 1), with most only being used for specific studies in limited locations. There is currently no rapid appraisal method which has been developed and tested for use across northern Australia. The need for a standardised approach to assess riparian health that would be adopted across a broad range of user groups, from scientists to on-ground land managers, was recognised and a program set out to achieve this goal. The Tropical Savannas Cooperative Research Centre (Charles Darwin University, Australian Centre for Tropical Freshwater Research, NT and Qld Governments and CSIRO) and Land & Water Australia are currently developing the Tropical Rapid Appraisal of Riparian Condition (TRARC) which is being tested and applied in Queensland and the Northern Territory. This paper outlines the process used to develop the method and the choice of indicators. Developing the TRARC The program began with a review of existing riparian assessment methods (Table 1). Most of these methods use a similar set of attributes to assess riparian vegetation condition. Several include riparian vegetation as a sub-index of a broader assessment of stream condition (eg, Bjorkland et al. 2001, Chessman 2002, Ladson et al. 1999), although with varying degrees of consideration given to vegetation indicators. Table 1. Examples of Australian and north American methods of riparian vegetation assessment considered for testing in tropical savannas. Method Region Source (Jansen et al. 2004, Werren and Multi-metric rapid assessment of riparian habitat Qld, NSW Arthington 2002) Multi-metric bioassessment of streams with 4-7 NSW, Vic, (Chessman 2002, DEWA 2003, components—including riparian zone WA Ladson et al. 1999) Detailed survey of stream bed, banks, aquatic and (Anderson 1993, Faulks 1998, Qld, NT riparian habitats Faulks 2001) Bioassessment and predictive modelling of streams Australia (Lloyd and Cook 2002) with 6 components—including riparian zone Multi-metric rapid assessments of streams with 9-15 (Barbour et al. 1999, Bjorkland et USA components—including riparian vegetation al. 2001, Ward et al. 2003) The two methods considered most suitable (Jansen et al. 2004, Werren and Arthington 2002) were both developed specifically as rapid appraisals and have a strong focus on riparian vegetation condition. The method of Werren and Arthington (2002) was designed for the wet tropical coasts of NE Queensland whereas the method of Jansen et al. (2004), the Rapid Appraisal of Riparian Condition or RARC, has been used extensively in SE Australia (eg, Jansen and Robertson 2001). Both methods were tested in pilot trials in the Darwin region and in Kakadu National Park, Northern Territory, where researchers and land managers considered whether the methods would be: (1) user-friendly to the diverse land management community of northern Australia; (2) robust in a distinctly wet/dry seasonal environment; and (3) responsive to significant land development issues across the savannas. Following the trials, it was felt that these methods needed some modification to ensure that they would be reliable given the following features of the region: pronounced effects of seasonality on the vegetation; frequent fire events; regular, recurrent wet season flood events; lower diversity in land use patterns (generally dominated by cattle grazing); and, lower occurrence of exogenous impacts. A workshop was held at James Cook University, Townsville, in October 2003 where riparian ecologists agreed on a framework for developing the Tropical Rapid Appraisal of Riparian Condition (TRARC). The workshop participants determined which habitat indicators would be important to measure in savanna riparian zones and how best to measure them. Methods were formulated to provide a balance of accuracy, time, cost and ease-of-use (Dixon et al. 2004). Despite these alterations, the approach developed in this workshop is very similar to the RARC method of Jansen et al. (2004), thus giving it considerable comparability to the methods currently being developed for south-eastern Australia. The TRARC method developed from that workshop was trialled in the Northern Territory and Queensland—Darwin Region (Dixon and Douglas 2004), Douglas-Daly Region, Kakadu National Park, Victoria River District and the Burdekin River catchment (Dowe et al. 2004). These tests identified the need to make further refinements to improve accuracy and ease-of-use, and to cater for seasonal variation of vegetation growth. The program to develop the TRARC is currently in its second of three years. Once the developmental phase is completed, application of the methods across northern Australia will commence as phase two. The following section outlines our current progress. The TRARC framework to date The TRARC is a tool which gauges how well the riparian zone performs specific functions. It requires the operator to visually assess 21 indicators of riparian condition (Table 2) which were chosen to reflect the various functions of a riparian zone, such as those described by (Naiman and Decamps 1997): • Wood and leaves falling into the stream from riparian plants slows the stream down while the roots of riparian plants bind the soil. This helps to stabilise the stream banks. • Leaves, fruit, flowers, and seeds that fall into streams provide food for aquatic animals. • Wood, leaves, fruit, flowers, and seeds from riparian plants provide important habitats for aquatic plants and animals. • Shade provided by riparian plants regulates the temperature and the amount of light reaching the stream water. This can affect the stream’s productivity, the growth of aquatic plants, and the animal species that survive. • The riparian zone helps to maintain good stream water quality. Water from the catchment passes through the riparian zone before reaching the stream. The riparian vegetation slows its passage, allowing sediments, nutrients and pollutants to be trapped and filtered. Indicators are grouped into five sub-indices: cover, debris, natives, regeneration and disturbance. Each indicator is given a score, from 0-4, based on pre-defined condition categories (Table 2). Condition categories are based on the percentage cover, abundance or extent of the indicator. Scores for each sub- index are converted to a relative score out of 100, where higher scores indicate better riparian habitat condition. A summary of overall riparian condition is derived by summing all indicator scores, with a maximum score of 100. A detailed procedure for data analysis is under development and will be finalised in a future workshop. Table 2. An abbreviated framework of the TRARC. Twenty one indicators are grouped into five sub- indices. Each indicator is given a score between 0-4. Indicators marked with (*) have their score doubled. Final summary score is the sum of all indicators (maximum score = 100). SCORE * scores double weighted 0 1 2 3 4 COVER (maximum score = 28) • Riparian width (amount cleared)* major major/mod mod/minor minor uncleared • Canopy continuity <30% 30-55% 55-75% 75-90% 90-100% • Overstorey cover absent 1-30% 30-60% 60-85% 85-100% • Ground cover absent 1-30% 30-60% 60-85% 85-100% • Grass cover absent 1-30% 30-60% 60-85% 85-100% • Bare ground 100-75% 75-50% 50-25% 25-5% <5% DEBRIS (maximum score = 16) • Fine woody absent 1-30% 30-60% 60-85% 85-100% 1 tree OR 1 tree & • Coarse woody * absent 1-2 logs 3-5 logs >5 logs >5 logs • Standing dead >25% x 25-5% x <5% NATIVES (maximum score = 16) • Overstorey absent 1-30% 30-60% 60-85% 85-100% • Ground cover absent 1-30% 30-60% 60-85% 85-100% • Grass absent 1-30% 30-60% 60-85% 85-100% • Deleterious weeds (from list) 4 species 3 species 2 species 1 species 0 species REGENERATION (maximum score = 20) • Dominant canopy juveniles * absent 1 2-5 6-20 >20 • Sub-dominant juveniles * absent 1 2-5 6-20 >20 no little some large • Community structure trees absent variation variation variation variation DISTURBANCE (maximum score = 20) • Slumping erosion 100-50% 50-25% 25-5% 5-1% absent • Gully erosion 100-50% 50-25% 25-5% 5-1% absent • Fire impact abundant frequent occasional rare absent • Animal impact abundant frequent occasional rare absent • Other impact abundant frequent occasional rare absent Future development of the TRARC Development of the TRARC will continue over the next two years to ensure the methodology is accurate, repeatable and user-friendly, and that the data analysis produces final scores that are truly representative of the riparian condition. Further trials will be undertaken to specifically address the following questions: (1) how many sites are needed to give a fair representation of a particular reach?; (2) how sensitive is the method to inter-operator variability?; (3) how do potential end users respond to applying the method?; and (4) do results from the TRARC reflect those derived from other indicators of riparian and stream condition? The collaborative development of this method by a range of savanna researchers and stakeholders across northern Australia will ensure that a unified approach is taken to evaluate riparian condition. However, we recognise that the method may well need to be modified for use in different bioregions or for specific projects. The TRARC is likely to be adopted by a diverse range of users including government agencies, park rangers, indigenous land managers, pastoral land managers, private consultancies and Landcare groups. Each of these groups may have different reasons for assessing their riparian condition and different values of riparian health. Therefore, the initial outcome of the project will be to develop a standard ‘template’ that can be modified and calibrated for different purposes. This ‘template’ is currently being used by two research/monitoring groups in markedly different biogeographical regions in northern Australia: the Australian Centre for Tropical Freshwater Research in a catchment-wide assessment of the Burdekin catchment, Qld; and, the NT Department of Infrastructure, Planning and Environment – Water Monitoring Branch in their monitoring of streams flowing into Darwin Harbour and in the Douglas-Daly catchment, NT. Results from these programs have supported the envisaged need for regional calibration of the TRARC if it is to be comparable across northern Australia. Future workshops will address this need. Conclusion The TRARC provides a simple tool for obtaining an assessment of riparian condition. This will help those involved with land management to document improvements in riparian condition due to conservation and restoration programs and highlight areas of ecological concern that need priority for future programs. The use of rapid appraisal methods hold several benefits for riparian management. Developing a method that non-specialists can use that provides easily interpretable results will act as an educational tool, thus increasing understanding of ecological interactions in riparian zones. Land managers who gain knowledge of the riparian zone and actively participate in its assessment, maintenance and monitoring may be more likely to encourage others to do so. The greater the network of land managers who adopt the methods, the greater the potential for sustainable land use across the savannas. 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