Twelfth Australian Weeds Conference MEXICAN FEATHER GRASS (NASSELLA TENUISSIMA) A POTENTIAL DISASTER FOR AUSTRALIA D.A. McLaren1, M. Whattam2, K. Blood1, V. Stajsic3 and R. Hore1 1 CRC for Weed Management Systems and Department of Natural Resources and Environment, Keith Turnbull Research Institute, PO Box 48, Frankston, Victoria 3199 2 Australian Quarantine and Inspection Service, Plant Quarantine Nursery, 621 Burwood Hwy, Knoxfield, Victoria 3180 3 National Herbarium of Victoria, Birdwood Avenue, South Yarra, Victoria 3141 Abstract Nassella tenuissima (Mexican feather grass) has led to the removal and destruction of these plants has been sold from nurseries in Victoria and NSW since from two Victorian nurseries and a review of AQIS 1998. This paper examines how such a potentially import regulations. weedy species could be legally brought into Australia Nassella tenuissima (Synonym - Stipa tenuissima) is and the pressures being applied by the nursery indus- native to Argentina, Chile, New Mexico and Texas try to continually introduce new exotic species. It also (Jacobs et al. 1998). N. tenuissima is commonly called examines actions by the Australian Quarantine and Mexican feather grass, Texas tussock, white tussock, Inspection Service (AQIS) to prevent such an incident ponytail grass and tussock grass. In Argentina, N. occurring again and explores the use of new technolo- tenuissima is regarded as an unpalatable grass (Moretto gies in both introducing and alerting authorities to the and Distel 1998) and has been classified as a non-pre- existence of emerging weeds. The potential distribu- ferred species that can become dominant under con- tion of N. tenuissima is assessed and compared to its tinual heavy grazing pressure with a low frequency of close relative, Nassella trichotoma (serrated tussock) high intensity fire (Distel and Boo 1995). Similarly, in Australia. it is regarded as a species that is rarely eaten by deer in INTRODUCTION Texas (Simons 1996). It has been estimated that weeds cost Australia in ex- In the 1990s, native grasses have become very popu- cess $3,300 million every year (National Weeds Strat- lar as ornamental plantings in Australia. In Melbourne, egy 1997) and they are also causing severe impacts on native grasses such as Poa tussock, Poa labillardierei the natural environment (Carr et al. 1992). Eleven ex- is being used extensively as a low maintenance, at- otic stipoid grass species have become naturalised in tractive groundcover along road and freeway verges. Australia this century (McLaren et al. 1998). One of The popularity of grasses in urban areas has resulted these species, serrated tussock, Nassella trichotoma in rare plant nurseries taking an increased interest in costs agriculture in New South Wales more than $40 importing new, attractive, hardy, easily grown spe- million annually (Jones and Vere 1998) and is also cies. The resemblance of these exotic stipoid species causing severe environmental impacts (McLaren et al. to indigenous Austrostipa species, has meant that they 1998). Another Nassella species almost identical to are easily overlooked as weeds, increasing the likeli- serrated tussock was found being sold at a Sydney hood that they will of successfully naturalise. nursery in 1996. It was being sold under the name One of the principal factors determining a plant’s dis- “Elegant Spear Grass”; (known to botanists as tribution is climate. Since the factors defining the suit- Austrostipa elegantissima (Labill.) which is an Aus- ability of a habitat to a particular plant may be un- tralian native grass (Dellow, pers. comm.)) but was known, computer models which create an empirical subsequently identified as Nassella tenuissima (Trin.) set of parameters based on current distribution can be Barkworth (Jacobs et al. 1998). Similarly, in 1998, a used to describe areas possibly suitable for a plants landscape gardener identified a plant resembling ser- survival. These parameters can then be used to predict rated tussock at a rare plant nursery at Mount Macedon the potential spread of weed species by analysing the (57 km north west of Melbourne) called Stipa climatic variables where the species is naturalised tenuissima. He alerted authorities via a computer email (Cousens and Pheloung 1996, McLaren et al. 1998). network called “Enviroweeds” that links people inter- A climate matching system called CLIMATE, devel- ested in environmental weed issues around Australia oped by Agriculture Western Australia has been de- and the world. This set in train an investigation that veloped from the concepts contained in the BIOCLIM 658 Twelfth Australian Weeds Conference (Busby 1991) and CLIMEX (Sutherst and Maywald and has almost certainly increased the rate of illegal 1985) prediction systems. The CLIMATE system gen- plant introductions coming into Australia. Table 1 lists erates a prediction of a species distribution based on a selection of some current sources offering N. the climate of its known distributions and is used par- tenuissima for sale or advertising its virtues as an or- ticularly where detailed biological data on a species is namental plant. lacking. It does not take into consideration soil type, N. tenuissima has also been introduced into New Zea- day length or biotic factors and as such may produce land via the internet and the nursery industry. A con- overestimates of a plant’s potential distribution. tribution from the Stipa tenuissima – Imagine this web This paper presents data on some of the pathways by site (Table 1) stated: which these plants are entering Australia and outlines “I too fell in love with Stipa tenuissima at first sight. I some strategies that need to be put in place to ensure propagated heaps of it, only to find out that it could that such introductions are minimised. become a threat to our pastures in New Zealand, so I MATERIALS AND METHODS had to destroy them all. Our climate is very accommo- dating, i.e. they self-seed like mad. Do be warned Overseas distributions of N. tenuissima were obtained though, that the very fine seeds can get caught in pets from overseas herbaria and plant taxonomic descrip- coats and eyes and they are very difficult to detect. tions. A climate analysis was undertaken to determine However I am envious that you are allowed to grow the potential distribution of N. tenuissima and was then them and I loved your photo. In New Zealand it has compared to potential distribution of N. trichotoma. been mistakenly sold by garden outlets in recent years Overseas distributions were assessed using the CLI- and there is now a danger that it will invade the pas- MATE (Pheloung 1996) program which collected cli- toral land of Whitford.” mate data from the closest weather station to the N. tenuissima infestation. This climate data was then Climate Matching N. tenuissima is native to New compared to Australian climates using the BIOCLIM Mexico, Texas, Mexico, Argentina and Chile (Jacobs program (Nix 1986) using the CLIMATE system to et al. 1998). By using recorded native distributions, predict areas in Australia that possess similar climate its potential distributions were predicted using the profiles. CLIMATE program. For Mexico, its known distribu- tion’s were limited to presence or absence within states. Viability of N. tenuissima seed collected from a nurs- Whole Mexico states were therefore included for the ery in Mount Macedon, Victoria was tested by placing purpose of the climate analysis. An area from west- 100 seeds onto dampened seed germination paper in ern, central and southern Queensland to northern petri dishes within a constant temperature cabinet at NSW, northern Victoria, southern South Australia and 23°C under 16 hr daylength. central-east WA are predicted to be at risk of invasion RESULTS AND DISCUSSION (Figure 1). In total the potential distribution of N. tenuissima is predicted to be 14.1 million ha (best fit The Nursery Industry and the use of the internet only). In contrast, the potential distribution of ser- for introducing new plant species into Australia. rated tussock, Nassella trichotoma based on South Plant hunters have been roaming the planet for centu- American distributions is predicted to be 2.4 million ries, transporting plants for ornamental and commer- ha (best predictions only) primarily along the south cial uses to new countries. This practice continues and south-east coast of Australia (Figure 2). But based today and plant hunters are constantly bringing in new on current Australian distributions, the potential dis- material to Australia. Fads and fashion drive the nurs- tribution of N. trichotoma is estimated to be 32 mil- ery trade with customers constantly demanding new lion ha with substantial areas of New South Wales, and exciting plants resulting in a great deal of pressure Victoria and Tasmania at risk of invasion (McLaren et on nurseries and garden centres to seasonally provide al. 1998). The broader climatic profile of N. tenuissima new lines of plants. Novel plants are usually fist ob- enabling it to potentially invade nearly six times as tained legally but sometimes plant collectors, garden- much land as N. trichotoma in Australia, emphasises ers and some smaller nursery operators have brought the threat this species poses to the Australian environ- in material without approval from AQIS. The increased ment. N. tenuissima’s similarity in taxonomy, growth use of the internet for global trading has made plants and ecology to N. trichotoma means that it is very im- more accessible to a much wider range of customers portant to prevent it becoming naturalised in Australia. 659 Twelfth Australian Weeds Conference mel Figure 1. Potential distribution of Nassella tenuissima Figure 2. Potential distribution of Nassella trichotoma predicted from a climate profile of distributions in its predicted from a climate profile of distributions in its countries of origin countries of origin Best prediction (10% of mean) (20% of mean) Seed germination It was found that 20% of N. Worst prediction (30% of mean) tenuissima seeds germinated when exposed to constant 23°C and 16 hr daylengths.