Plant invasions in treeless vegetation of the Australian Alps

Transcription

1 Perspectives in Plant Ecology, Evolution and Systematics 7 (2005) Perspectives in Plant Ecology, Evolution and Systematics Plant invasions in treeless vegetation of the Australian Alps Keith L. McDougall a,, John W. Morgan b, Neville G. Walsh c, Richard J. Williams d a Department of Environment and Conservation, PO Box 2115, Queanbeyan, NSW 2620, Australia b Department of Botany, La Trobe University, Bundoora, Victoria 3083, Australia c National Herbarium of Victoria, Birdwood Avenue, South Yarra, Victoria 3141, Australia d CSIRO Sustainable Ecosystems, PMB 44, Winnellie, Northern Territory, Australia Received 30 June 2005; accepted 10 September 2005 Abstract A total of 128 invasive plant species have been recorded in treeless vegetation in the Australian Alps. Most of these are forbs and most are uncommon. Cover of invasive species is generally minimal unless there has been gross disturbance to natural vegetation and soils. Although there is a significantly positive correlation between invasive and native species diversity, suggesting that conditions that allow numerous native species to co-exist also permit more plant invasions, altitude is the most important determinant of invasive species diversity. Only 22 of the 128 species have been recorded above 1800 m. Some plant communities (e.g. those with high ph or relatively nutrient-rich soils), however, seem to be vulnerable to invasions regardless of altitude. Most invasive species appear to have been introduced unintentionally (e.g. as seed attached to vehicles, animals and humans) but a few were introduced to assist with revegetation of disturbed soils and for amenity plantings in ski resorts, and have subsequently established in native vegetation. Treeless communities in the Australian Alps are likely to face increasing pressure from invasive species as a result of global warming and continued introduction of non-native plants to ski resort gardens. Whilst it may be difficult to prevent invasive species of low elevations migrating to higher elevations as temperatures rise, the risk of invasion from garden plants could be minimised through regulation. Non-native plants in ski resort gardens pose a far greater risk than most invasive species currently present in the Alps because they have been chosen for their capacity to survive at high altitudes. Crown Copyright r 2005 Published by Elsevier GmbH on behalf of Ru bel Foundation, ETH Zu rich. All rights reserved. Keywords: Alpine; Australian Alps; Garden escapes; Global warming; Invasive plants Introduction In reviewing environmental weeds in Australia, Humphries et al. (1991) rated alpine ecosystems, amongst others, Corresponding author. address: keith.mcdougall@environment.nsw.gov.au (K.L. McDougall). as being least vulnerable to invasion. This assessment is reiterated in recent texts on Australian alpine flora: in Tasmania (Kirkpatrick, 1997) and in Kosciuszko National Park (Costin et al., 2000). Only 14 non-native plant species are reported to be well established in the alpine zone of Kosciuszko National Park (Costin et al., 2000) and most of these are uncommon or restricted to highly modified environments such as roadsides and walking track edges /$ - see front matter Crown Copyright r 2005 Published by Elsevier GmbH on behalf of Ru bel Foundation, ETH Zürich. All rights reserved. doi: /j.ppees

2 160 K.L. McDougall et al. / Perspectives in Plant Ecology, Evolution and Systematics 7 (2005) Despite the apparent low vulnerability, there has been a steady increase in the number of non-native species recorded since the first botanical expeditions to the high country (Johnston and Pickering, 2001a). There was only one species recorded in the Kosciuszko area in 1899, six in 1954, and 48 in 1986 (Mallen, 1986). Although the intensity and extent of sampling differed between successive samples, the changes are probably real. The construction of the hydro-electricity scheme in the 1950s brought many people to the Alps. Attempts at that time to repair damage caused by past cattle and sheep grazing also introduced many new species to the alpine area. Much has changed since the evaluation of Humphries et al. (1991) and much continues to change. The effects of global increases in temperature in the Australian Alps are perhaps already being seen in the expansion of native shrubland and encroachment of trees into treeless vegetation (Wearne and Morgan, 2001; McDougall, 2003). In recent times there has been a steady increase in summer use of the alpine country, expansion of skiing development, several severe droughts, and the first major bushfire since There is also much more data available on the composition of the high mountain flora, including non-native species. In a recent review of the non-native flora of the Australian Alps, Johnston and Pickering (2001a) found records of 175 species. Many of these were recorded only in highly modified areas such as roadsides and ski resorts, making it difficult to evaluate the threat that individual species pose to natural vegetation. In this paper, we evaluate the current invasive flora of natural treeless vegetation in the Australian Alps and the potential for further invasions. We refer to species that do not grow naturally in the Australian Alps as nonnative. The sub-set of non-native species that have spread into natural treeless vegetation are referred to as invasive species. Characterisation of the Australian Alps The Australian Alps are a series of mountains and plateaux on and around the Great Dividing Range, a long ridge separating the inland river catchments from coastal catchments of mainland eastern Australia. They are the only part of the Range to receive regular, persistent snowfall in winter. The Alps extend roughly from Baw Baw National Park in Victoria ( S) to Namadgi National Park ( S) in the Australian Capital Territory, a distance of about 350 km (Fig. 1). Detailed descriptions of the ecology of Australian alpine environments can be found in McDougall (1982), Williams and Costin (1994), Kirkpatrick (1997), Costin et al. (2000) and Williams et al. (2003). Fig. 1. Location of the Alps in south-eastern Australia. Almost all of the Australian Alps is within National Parks (shaded area). The Alps are characterised by low annual minimum and mean temperatures. Sub-zero temperatures of the past have helped shape the landscape through localised glaciation and the fracturing of rock, and continue to influence the patterns of vegetation today (Williams and Ashton, 1987). On the mainland, glaciation in the last Ice Age was confined to a small area in the vicinity of Mt. Kosciuszko, although periglacial forces were responsible for many of the notable rock features elsewhere, such as block streams (Peterson, 1971). Glaciation was however, more extensive in the lower, but more southerly Tasmanian mountains. The Australian Alps are geologically diverse; most areas are underlain by granite or metamorphic material (gneiss and schist) but limestone, basalt, and various sedimentary rocks are locally exposed. Soils tend to be highly organic and acidic (Rowe, 1972). Unlike most of the coastal fringe of the Australian continent, which is dominated by one or more arborescent species of Eucalyptus (Myrtaceae), large parts of the Australian Alps are treeless. Low summer temperature and frequent frost limit the establishment of trees, creating alpine treelines on mountain tops. Generally, the elevation of alpine treelines increases with decreasing latitude, and so, for example, the alpine treeline at Mt. Howitt in Victoria (latitude S) is about 1600 m whilst the alpine treeline on Mt. Jagungal in NSW ( S) is at about 1900 m. The highest point in the Australian Alps is Mt. Kosciuszko (2229 m). Many subalpine valleys are also treeless. Cold air tends to accumulate in valleys at night producing frost and a large differential in air temperature between the valley bottom and ridge top (Williams and Costin, 1994). Native trees and many shrubs are incapable of recruiting past juvenile stages in such prolonged cold conditions.

3 K.L. McDougall et al. / Perspectives in Plant Ecology, Evolution and Systematics 7 (2005) Many subalpine valleys in the Australian Alps thus have trees and tall shrubland on the upper slopes and ridges, and grasslands and low heaths in valley bottoms, the opposite of the pattern observed on the high peaks (Slatyer, 1989). Treeless vegetation of alpine and subalpine areas covers about 160,000 ha, of which about 20% is truly alpine (i.e. above the altitudinal limit of tree growth). Alpine and inverted treelines are often continuous (Fig. 2) and there is much overlap in flora and vegetation of alpine and subalpine areas (McDougall, 1982). The treeless vegetation of the Australian Alps is floristically diverse: 700 native taxa from 82 families have been recorded (K.L. McDougall and N.G. Walsh, unpubl. data). The best-represented families are Asteraceae (16.8% of the flora), Poaceae (10.6%), Cyperaceae (7.1%), Orchidaceae (4.5%), Fabaceae (4.0%), Apiaceae (3.6%), Ericaceae (3.4%) and Scrophulariaceae (3.3%). Of the native taxa recorded, about 45% are restricted to the treeless vegetation of the Australian Alps (although some extend for a short distance into the surrounding woodland vegetation and 15% of species also occur beyond the Australian mainland in the Tasmanian and New Zealand high country). The flora has strong affinities with the high mountain floras of Tasmania, New Zealand and South America (McDougall, 1982; Williams and Costin, 1994). Nomenclature of the Australian alpine flora follows Ross and Walsh (2003). Treeless portions of the Australian Alps have been intensively used by people, and negative effects on plants and vegetation from these uses are often obvious. Prior to European inhabitation in the 19th century, native peoples used the treeless areas to obtain food mainly the Bogong Moth (Agrotis infusa), which aestivates in the high country (Flood, 1980). In the mid-19th Century, cattle and sheep were brought from Fig. 2. The upper and lower treeline below Mt. Nelse, Bogong High Plains region, Victoria (altitude 1880 m). The treeless vegetation is continuous here (to left of photo) between the alpine and subalpine zones. lowland pastures to the high country over the snow-free months. In times of drought, grazing intensity was apparently great (Carr and Turner, 1959). Since the 1950s, grazing rights have gradually been withdrawn and, from summer 2005/2006, stock will be banned from the majority of treeless country. Tourism (downhill skiing, bushwalking and sightseeing) and hydro-electricity production have replaced grazing as the major land uses in recent times. The current invasive flora Between 1980 and 2005, about 1400 floristic quadrats have been sampled in surveys of treeless vegetation in the Australian Alps (McDougall, 1982; Walsh et al., 1984; Helman and Gilmour, 1985; Gilmour et al., 1987; Helman et al., 1988; Ecology Australia, 2003; K.L. McDougall and N.G. Walsh, unpubl. data). Quadrat size in these surveys ranged from 20 to 100 m 2 but all samples were taken in homogeneous vegetation. Based on these data, personal observations and specimens lodged in the National Herbarium of Victoria with adequate location and habitat information, 128 invasive taxa have been recorded in natural treeless vegetation in the Australian Alps (Appendix). Johnston and Pickering (2001a) list 175 taxa in a review of non-native plants in the Australian Alps. Although there is considerable overlap between that list and Appendix, the lists are not comparable because they have different geographic extents. The review of Johnston and Pickering (2001a) included invasive species of woodland and treeless vegetation above 1500 m and non-native species of roadsides and highly modified areas in ski resorts, but did not include invasive species of many of the lower subalpine treeless plains considered by us. Most invasive species are infrequent. Of the 56 species recorded in the surveys cited above, only six were observed in more than 5% of the quadrats (Acetosella vulgaris 43%, Hypochaeris radicata 27%, Trifolium repens 15%, Taraxacum officinale s.l. 9%, Cerastium glomeratum 8%, Cerastium vulgare 7%). The total cover of invasive species has rarely been greater than 5% in any community, except on limestone soils, and has generally been less than 1%. There is uncertainty about whether a few species are non-native or native. Three species (Kelleria laxa, Rytidosperma pumilum and Uncinia sinclairii) have been discovered in Australia recently, are known here from single populations and occur more commonly in the mountains of New Zealand. One of these, U. sinclairii, has been regarded as non-native (Hnatiuk, 1990). The other two are listed as threatened species under the Environment Protection and Biodiversity Act The New Zealand and Australian alpine areas share many

4 162 K.L. McDougall et al. / Perspectives in Plant Ecology, Evolution and Systematics 7 (2005) species (Costin et al., 2000) and, without evidence of a recent introduction, we can see no reason to treat any of these as non-natives. Alchemilla xanthochlora was recorded in the first botanical expedition to the Alps and is very close to, if not indistinguishable from the European species of the same name. It is very rare in alpine vegetation and may be an odd cosmopolitan species. Prunella vulgaris was similarly treated as a cosmopolitan species until recently. It is occasionally invasive in the Alps and is now regarded as an early introduction. Factors affecting plant invasions Godfree et al. (2004) found a positive correlation between species richness of natives and invasive species in plant communities at Long Plain, a subalpine treeless plain in Kosciuszko National Park, suggesting that invasion is a function of opportunities for plant establishment and survival for both native and invasive species. Using the available quadrat data for all treeless areas of the Australian Alps, there is also a significant, albeit weak, positive correlation (Po0:01) between native and invasive species richness (Fig. 3). Plant traits Almost half of all invasive taxa recorded in treeless vegetation are perennial herbs, 44% are annuals or biennials and 7% are woody (Table 1). Godfree et al. (2004) found that species that successfully invaded natural vegetation at Long Plain possessed the same traits as the majority of native plants (i.e. perennial herbs) and that those present in highly disturbed areas had a range of traits but included many annual herbs. The authors suggest that this indicates that invasion is most likely when the invaders possess the same traits as the native occupants. As Godfree et al. (2004) found for a single site, the majority (five out of six) of the common invasive species recorded in natural treeless vegetation throughout the Alps are perennial herbs. The greater diversity of perennial invasive species may be partly a function of the high frequency of frost and shortened growing season in mountain treeless areas that receive regular winter snow cover. Native annual herb and woody plant diversity is also low in such areas. Significant invasion by woody species at high altitude does occur, however, as major incursions of Salix cinerea in wetlands after the 2003 wildfire have shown. Origins of invasive species When propagules of non-native species are dispersed into natural vegetation, it is reasonable to expect that the species will be most successful when the environment of their origin is similar. Invasive species of mountain areas might be expected to have come from mountain areas elsewhere. Of the 128 invasive species recorded in natural treeless vegetation of the Australian Alps, 115 species (90%) are native to Europe (Appendix). Polunin (1969) describes the European habitat of 73 of these species; 71% are listed as occurring on waste ground, waste places and pasture, suggesting that many invasive species of the Australian Alps are also invasive in their places of origin. Only three species are listed by Polunin (1969) as occurring naturally in mountains: Aquilegia vulgaris, Hieracium aurantiacum and Mentha spicata. It is perhaps notable then that Aquilegia vulgaris and Hieracium aurantiacum are two of few species that have warranted active control of infestations (see below). The range of invasive species currently in the Alps is largely a reflection of the pool of species already present at lower elevations. For instance, all but one of the 20 most common invasive species recorded in surveys of treeless vegetation in Kosciuszko National Park have been recorded in surrounding vegetation at lower elevation (Table 2). Twenty-three of the 128 invasive species, however, were deliberately introduced into the Alps for revegetation of areas damaged by grazing, ski resort development or hydro-electricity works, and for amenity plantings in gardens of ski resorts. These species have been selected for their capacity to establish and survive in the cold, snowy conditions of the Alps. Abiotic correlates Fig. 3. Correlation between mean number of invasive species and mean number of native species per quadrat for 55 plant communities in the Australian Alps (r ¼ 0:35, Po0:01). Keith L. McDougall and N.G. Walsh (unpubl. data) identified 55 plant communities in the treeless vegetation of the Australian Alps in a floristic classification of 1229 quadrats. Of four variables measured for the communities (mean altitude, proportion of quadrats on limestone or basalt, mean estimated duration of snow cover,

5 K.L. McDougall et al. / Perspectives in Plant Ecology, Evolution and Systematics 7 (2005) Table 1. Invasive species of treeless vegetation in the Australian Alps by life form and most likely path of introduction to the Australian Alps Trees Shrubs Annual or biennial herb Perennial herb Totals Garden escape (11%) Revegetation (7%) Opportunist or unknown (82%) Totals 3 (2%) 6 (5%) 57 (44%) 62 (48%) 128 Table 2. Frequency of invasive species occurring in X1% of quadrat in treeless vegetation in Kosciuszko National Park (41200 m) and their frequency in quadrats in adjoining areas ( m) Species Frequency (%) in treeless vegetation (41200 m; K.L. McDougall and N.G. Walsh, unpubl. data), n ¼ 359 Frequency (%) in lower areas ( m; Thomas et al., 2000), n ¼ 859 Acetosella vulgaris Hypochaeris radicata Trifolium repens 15 8 Cerastium sp Taraxacum officinale s.l Anthoxanthum odoratum 7 4 Cirsium vulgare 5 12 Crepis capillaris 5 3 Tragopogon dubius 5 1 Vulpia bromoides 4 8 Holcus lanatus 3 9 Agrostis capillaris 2 1 Poa pratensis 2 1 Trifolium dubium 2 7 Aira caryophyllea 1 5 Festuca nigrescens 1 1 Myosotis laxa ssp. 1 1 caespitosa Myosotis discolor 1 2 Rosa rubiginosa 1 10 Sedum acre 1 0 Fig. 4. For 55 treeless plant communities in the Australian Alps, the correlation (a) between mean number of invasive species per quadrat and mean altitude (r ¼ 0:55, Po0:01), and (b) between mean number of invasive species per quadrat and proportion of quadrats within each community that were on basalt or limestone derived soils (r ¼ 0:58, Po0:01). mean estimated months with free water), only mean altitude and proportion of quadrats on limestone or basalt are significantly correlated with the mean number of invasive species per quadrat in a community. There is a significant negative correlation between invasive species diversity and elevation (Po0:01; Fig. 4a), and all of the communities with a mean elevation above 1800 m have less than one invasive species per quadrat. This relationship is probably representative of the inability of many invasive species to establish at very low temperature and with a long duration of snow cover in the alpine zone (Mallen-Cooper, 1990) rather than a difference in the vectors of introduction between low and high elevations within the Australian Alps. Communities occurring on basalt or limestone soils tend to have more invasive species per quadrat than communities on other rock types (Fig. 4b). The community with the highest mean number of invasive species per quadrat (Cave Creek grassland) occurs entirely on limestone soils. In limestone and basalt areas, high soil ph and

6 164 K.L. McDougall et al. / Perspectives in Plant Ecology, Evolution and Systematics 7 (2005) relatively higher fertility (Rowe, 1972) possibly enable a greater diversity of invasive species to establish. After extensive bushfires in 2003, which burnt tens of thousands of hectares of mainland Australian alpine and subalpine landscapes, the cover of invasive species in some areas increased greatly. For example, at Yarrangobilly Caves, a limestone area with small treeless patches on rocky outcrops, some slopes became dominated by species such as Potentilla recta and Tragopogon dubius after the fire. A similarly dramatic expansion of the previously uncommon Salix cinerea occurred after this fire event in Sphagnum-dominated peatlands across the Bogong High Plains and on the Mt. Buffalo plateau. The diversity of invasive species in 60 quadrats in peatland communities increased significantly from species per quadrat before the fire to species per quadrat 1 year after the fire (Walsh and McDougall, 2004). Thirteen invasive species appeared in the quadrats after the fire that had not been recorded before. Biotic factors The grazing of cattle and sheep in the Australian Alps has probably influenced the current invasive flora. Cattle have been found to bring seed of non-native species and lowland native species to the Alps from lowland pastures in early summer and deposit them in their faeces (van Rees, 1984). They perhaps influence invasive species abundance more than diversity by maintaining a greater than natural area of bare ground (Wahren et al., 1994), which favours many invasive species that also commonly grow on roadsides and highly modified sites. Cattle also appear to be the main vector of Cytisus scoparius spread in the Australian Alps (Wearne and Morgan, 2004). Other animals that create bare ground (e.g. feral horses, deer, pigs and rabbits) may locally influence invasive species abundance. Patches of tussock grass killed by native moth larvae are often colonised initially by Acetosella vulgaris. Management of plant invasions There have been few plant invasions in treeless areas for which eradication has been attempted. The most common invasive species (Acetosella vulgaris, Hypochaeris radicata and Trifolium repens) are now so widespread in natural vegetation that control is impracticable. The approach of land managers has been to tackle species that pose a distinct threat and for which eradication might be possible. Small, high altitude infestations of Achillea millefolium are being controlled using herbicides (Sanecki et al., 2003). This daisy, although present in the high country for many decades, is regarded as a future threat in the alpine zone (Johnston and Pickering, 2001b). The rush Juncus effusus has been targeted for control with herbicides in bogs and fens with varying success. Two species of Hieracium (H. aurantiacum and H. praealtum) have been found in the last decade and have caused great concern amongst land managers (Morgan, 2000). Hieracium species are serious invaders of high mountain plant communities in New Zealand (e.g. Hunter, 1992; Rose et al., 1998; Wardle and Fahey, 2002) and parts of the North American continent (Heutte and Bella, 2003). Hieracium aurantiacum has now been found in several disjunct locations in the Australian Alps and, despite occurring in small isolated loci, has resisted attempts at control and continued to spread to new locations. Infestations of Cytisus scoparius just below the treeline in the Victorian high country, which have been the subject of control trials and research for the past decade (Robertson et al., 1999; Wearne and Morgan, 2004), have proven difficult to eradicate. So far, there have been few examples of Cytisus scoparius plants establishing above the treeline. Aquilegia vulgaris has established in several places in the Victorian high country, mostly in tall forest. It appears to have been eradicated from Falls Creek ski village, where it has occasionally been grown as an ornamental. It has also apparently been eradicated from the high alpine zone near Mt. Kosciuszko (at an elevation of 2050 m). Future plant invasion threats Superficially, the assessment of Humphries et al. (1991) that alpine areas in Australia are at least risk from plant invasions does not appear to have been illfounded. Almost 200 years of multifarious and, in places, intensive land-use have produced few abundant invasive species and only a handful of infestations warranting treatment. Being at least risk, of course, does not mean that the treeless plains and peaks are at no risk, nor that the assessment will be valid in the future. What factors will influence the invasive flora in the future? Global warming Based on current climate models, the projected change in mean annual temperature in Australian alpine areas to 2050 will be between +0.6 and C (Hennessey et al., 2003). The projected change in precipitation is between +2.3 and 24.0%. With these changes there is likely to be a contraction in the area receiving persistent snow and a reduction in the duration of snow cover. There is already an indication that trees are beginning to encroach on subalpine

7 K.L. McDougall et al. / Perspectives in Plant Ecology, Evolution and Systematics 7 (2005) Fig. 5. The number of invasive species recorded in surveys having their upper limit in five altitudinal divisions in the Australian Alps. treeless plains (Wearne and Morgan, 2001; McDougall, 2003). The predicted increase in mean temperature and reduction in snow cover are likely to increase chances of new plant invasions in the alpine zone. Currently, only 17% of invasive species recorded in surveys of treeless vegetation in the Australian Alps occur in the high alpine zone (between 1800 and 2229 m; Fig. 5). However, a further 32% of species have their maximum recorded elevation in the high subalpine zone (between 1600 and 1800 m) so there may not have to be a great change in climate to facilitate a large increase in the invasive flora at high altitude. The greater number of non-native species recorded by Johnston and Pickering (2001a) in the Australian Alps (175 in all vegetation above 1500 m including woodland and highly modified areas compared with 128 in natural vegetation recorded in this paper) also suggests that there are many potential invaders in close proximity to treeless vegetation. Invasions of new species in the alpine zone may have a major impact on biodiversity because many alpine communities are extremely localised and many species endemic to the alpine zone are present in very low numbers (Costin et al., 2000). Opportunist species New opportunist species are likely to reach the Alps. Mallen-Cooper (1990) found that, of non-native species that germinated in a glasshouse from soil collected in a ski resort car park, 27 species could not be found as plants in the surrounding area. Twenty of these species had not previously been recorded in the subalpine or alpine area. The seed had presumably arrived in mud on cars. Seed of non-native plants may also enter on shoes and clothing of visitors and in faeces of animals that come from outside the Australian Alps (van Rees, 1984; Whinam and Comfort, 1996; Whinam et al., 2005). The threat from most opportunist species is probably low, although there are significant exceptions (e.g. infestations of Cytisus scoparius have had a negative impact on native plant diversity; Wearne and Morgan, 2004). The most significant threat of such species is perhaps from visitors who have recently been to alpine areas beyond the Australian mainland. The infestation of Hieracium aurantiacum in Kosciuszko National Park is remote but near the track head of a popular walk. It may have established from seed attached to the walking boots or pack of someone who had recently visited alpine areas in New Zealand, where this invasive species is locally abundant. Revegetation species Soil in the high country is highly erodible when not adequately covered by native vegetation (Gibbons and Rowan, 1993). Stock grazing in the alpine zone of Kosciuszko National Park in New South Wales and the Alpine National Park in Victoria caused much exposure of bare ground and soil erosion (Costin et al., 2000; Williams et al., 2003). Engineering works associated with the hydro-electricity scheme in the 1950s and slope modification in ski resorts in more recent decades also created many bare surfaces. Research into stabilisation of alpine soils commenced in the 1950s with several nonnative species tested for their ability to grow and protect soils from further erosion. A mix of cultivars of Agrostis capillaris, Festuca rubra s.l., Lolium perenne, Phleum pratense and Trifolium repens was finally selected and used widely in the Australian Alps (Clothier and Condon, 1968). These non-native plants were effective at stabilising alpine soils, and two of the species, Agrostis capillaris and Trifolium repens, have since become common in natural vegetation throughout the Australian Alps. Colonisation by native species of areas sown with the non-native seed mix has been slow (McDougall, 2001), and many places are still dominated by Agrostis capillaris more than 40 years after the seed was sown. Native species are now widely used in revegetation but Festuca rubra s.l. is still often used because of its availability and rapid establishment. Whilst this species has not been especially invasive of native vegetation near ski resorts, which are at m in elevation, it is highly invasive in a few low subalpine plains. An increase in mean annual temperature associated with global warming could allow this species to be much more invasive in ski resort areas and beyond. Garden escapes Some of the ski resorts in the Australian Alps, in addition to their winter patronage, have sought to

8 166 K.L. McDougall et al. / Perspectives in Plant Ecology, Evolution and Systematics 7 (2005) attract visitors in summer. The use of the villages in summer led some lodge owners to establish gardens. The choice of plants for these gardens has probably been influenced by their likely survival in the cold and snowy conditions that prevail there. Their capacity to grow and survive in the gardens of ski resorts and their proximity to native vegetation suggest that some will be future threats. Of the 103 non-native species found in a survey of Victorian ski villages (McDougall and Appleby, 2000), 25 are likely to have escaped from gardens. In a recent survey of Thredbo ski village, 77 non-native species were identified in gardens and nine of these had established beyond the gardens (Pickering et al., 2002). Whilst few of the garden escapes have established in native vegetation, the gardens are mostly young and the potential invasiveness of species is perhaps yet to be realised. In some cases, there is a considerable lag between planting and reproductive maturity. For example, a selection of Pinus species planted above Falls Creek ski village in the 1950s remained stunted and sterile until the 1990s when seedlings of Pinus contorta began to appear beside the plantations and at some distance beyond. One of the species found growing in a garden at Thredbo was Calluna vulgaris. This dwarfshrub is one of only 28 species on the Australian Alert List for Environmental Weeds and is considered a future threat to Australia s alpine country, as it already is in New Zealand (CRC for Australian Weed Management, 2003). The threat from garden plantings may further increase as lodge owners search for better-adapted species. Many species from high mountain regions around the world can be purchased in local nurseries. For example, 81 largely European species featured in a handbook of alpine flowers of the world (Moggi, 1985) are listed by Hibbert (1997) as available in a range of nurseries in south-eastern Australia. Few of these species appear to have been grown yet in ski resort gardens. Future plant invaders of alpine ecosystems may also come from within other Australasian alpine ecosystems. For instance, 16 Tasmanian endemic species, which have been recorded for the Tasmanian high country by Kirkpatrick (1997), are listed by Hibbert (1997) as available in local nurseries. Native plants from lower elevations may also be a future threat. The native species Ammobium alatum was recorded for the first time in Kosciuszko National Park in Its natural extent is uncertain but it is probably not native to the Alps area. This species, although mostly found on disturbed roadsides, has many of the properties of a future threat: it can survive in cold and snowy environments (e.g. Thredbo ski village) and has proven to be most invasive in places without tree cover (McDougall, 2004). Planting of non-native species is now banned in New South Wales ski resorts and an assessment is proposed of the invasiveness of existing plantings (Department of Environment and Conservation, 2004). However, there are apparently no restrictions on plant selection in Victorian ski resorts, although only two resorts currently have gardens containing planted non-native species. Future management of invasive species Adequate management of future incursions of new non-native species in the Australian Alps will require exceptional vigilance by land managers because, as the recent discovery of Hieracium aurantiacum in Kosciuszko National Park has shown, invasive species may appear in remote places. Most of the Australian high country is well removed from roads and infrastructure but there are numerous walking tracks throughout the area and many vectors of spreading plant propagules. On-ground management staff will need to be trained in the identification of native plant species to enable the more rapid detection of non-native and perhaps invasive species. A key element of future management programs will be raising awareness of the threat from plant invasions and eliciting public support for invasive species management programs. Although the campaign to detect and eradicate Hieracium aurantiacum and Cytisus scoparius in Falls Creek ski village has been well supported by local managers and residents, many lodge owners still do not accept that non-native species in their gardens pose a threat to the alpine landscape. Conclusions Almost 200 years of European land use in treeless parts of the Australian Alps has resulted in the establishment of 128 invasive plant species, few of which are common across the landscape, and none of which is abundant unless vegetation is greatly disturbed. In the coming years, increasing temperatures associated with global warming may see the altitudinal limit of growth of existing invasive species increase. Changes in land use, from agricultural to tourism, are likely to test a new suite of non-native species in the natural alpine environment. The assessment of Humphries et al. (1991) that alpine ecosystems are at least risk from plant invasions may have been valid last century. However, in the current century there is a much greater likelihood that land managers will have to actively control invasive species to protect natural assets of the Alps. A first step in the battle, however, should be prevention. Limiting planting of non-native species in gardens in the Alps to species that are demonstrably

9 K.L. McDougall et al. / Perspectives in Plant Ecology, Evolution and Systematics 7 (2005) non-invasive and prohibiting sale in nurseries of alpine species and genera that have proven to be invasive elsewhere would be positive measures. Vigilance will be required to detect new plant invasions before they are impossible to control. The cold environment of the Alps is not a barrier to plant invasion. It is more a sieve with an ever-growing hole size. Acknowledgements We are grateful to Hansjo rg Dietz and two anonymous reviewers for their suggestions for improvement of the manuscript. We also acknowledge the many people who have helped gather quadrat data in the Australian Alps over the past 25 years. Appendix Invasive species recorded in treeless vegetation in the Australian Alps by life form and region of origin based on quadrat data (K.L. McDougall and N.G. Walsh, unpubl. data), personal observations, and specimens lodged in the National Herbarium of Victoria with adequate location and habitat information. Nomenclature follows Ross and Walsh (2003). Species Origin Abundance in natural vegetation Trees Malus domestica Europe, Asia Widespread but rarely persisting Pinus contorta North America Rare a Salix rubens Europe Rare Shrubs Cotoneaster horizontalis Asia Rare, at treeline Cytisus scoparius ssp. scoparius Europe Rare, locally abundant in subalpine woodland Rosa rubiginosa Europe, West Asia Common in a few locations near treeline Rubus anglocandicans Europe Rare Rubus leucostachys Europe Rare Salix cinerea Europe, North Africa, West Asia Rare until 2003 fires but now common in a few locations Annual (or biennial) forbs Anagallis arvensis Europe, Asia, North Africa Rare Aphanes arvensis Europe, West Asia Widespread but only abundant after disturbance (e.g. fire) Aphanes inexpectatus Europe Rare Arenaria leptoclados Europe, Middle East Rare Arenaria serpyllifolia Europe, Asia, North Africa Rare Barbarea verna Europe, West Asia Rare Capsella bursa-pastoris Europe Rare Centaurium erythraea Europe, West Asia, North Africa Rare Cerastium glomeratum Europe, Asia, North Africa Widespread and common Cirsium vulgare Europe, North Africa, Asia Widespread but only abundant after disturbance (e.g. fire) Crepis capillaris Europe, West Asia Widespread but rarely common Dianthus armeria Europe, South-west Asia Rare Downingia elegans North America Rare Echium vulgare Europe, Asia Rare Erophila verna ssp. verna Europe Rare Geranium molle Europe, Asia, North Africa Rare Gypsophila tubulosa South-west Asia Rare Hirschfeldia incana Europe, West Asia, North Africa Rare Hypochaeris glabra Europe, West Asia, North Africa Rare

10 168 K.L. McDougall et al. / Perspectives in Plant Ecology, Evolution and Systematics 7 (2005) Appendix (continued) Lactuca serriola Europe, West Asia North Africa Rare Lepidium campestre Europe, West Asia Rare Malva nicaeensis Europe, West Asia North Africa Rare Melilotus albus Europe, Asia, North Africa Rare Moenchia erecta Europe Rare Myosotis laxa ssp. caespitosa Europe, Asia Widespread and locally common in damp vegetation Myosotis discolor Europe, North-west Africa, West Asia Navarettia squarrosa North America Rare Parentucellia latifolia Europe, West Asia, North Africa Rare Petroragia nanteuillii Europe Rare Widespread but only abundant after disturbance (e.g. fire) Ranunculus muricatus Southern Europe, Asia, North Rare Africa Rorippa palustris Europe, North America, Asia Rare Sagina procumbens Europe, Asia Rare Sonchus asper Europe, Asia, North Africa Rare Sonchus oleraceus Europe, South-west Asia Rare Spergularia rubra Europe, Asia, North Africa Rare but one of few species at high elevation Tragopogon dubius Europe, West Asia Common in subalpine zone of northern part of Alps Tragopogon porrifolius Europe, West Asia, North Africa Rare Trifolium arvense Europe, North Africa, Middle East Rare Trifolium campestre Europe North Africa, Middle East Rare Trifolium dubium Europe, North Africa, Middle East Widespread but rarely common Urtica urens Europe, North Africa Rare Verbascum thapsus Europe, Asia Rare Verbascum virgatum Europe Rare Veronica arvensis Europe, West Asia, North Africa Rare Vicia sativa Europe, Asia, North Africa Rare Perennial forb Acetosella vulgaris Europe, Asia, North Africa Widespread and common Achillea millefolium Europe, Asia, North America Locally common but mainly on road verges Aquilegia vulgaris Europe, North Africa Rare Callitriche stagnalis Europe, Asia, North Africa Rare Cerastium vulgare Europe, Asia, North Africa Widespread and common Chenopodium album Europe Rare Chondrilla juncea Europe, West Asia, North-west Rare Africa Cirsium arvense Europe, North Africa, West Asia Rare Epilobium ciliatum North America, South America Common in a few locations in damp vegetation Fallopia japonica East Asia Rare Hieracium aurantiacum Europe Rare but apparently restricted to Australian Alps Hieracium praealtum Europe, Asia Rare but apparently restricted to Australian Alps Hypericum perforatum Europe, Asia, North Africa Rare Hypochaeris radicata Europe, Asia, North Africa Widespread and common Leucanthemum maximum Europe Rare Leucanthemum vulgare Europe, West Asia Rare

11 Appendix (continued) K.L. McDougall et al. / Perspectives in Plant Ecology, Evolution and Systematics 7 (2005) Linaria arvensis Europe, Wouth-west Asia, Northwest Rare Africa Lotus angustissimus Europe, Asia, North Africa Rare Lotus corniculatus Europe, Asia, North Africa Widespread but uncommon Lotus uliginosus Europe, North Africa, West Asia Rare Lupinus polyphyllus North America Rare Mentha spicata Europe, West Asia, North Africa Rare Mimulus moschatus North America Common in a few locations in damp vegetation Plantago major Europe, Asia Rare Polygonum arenastrum Europe, Asia Rare Polygonum aviculare Europe, Asia Rare Potentilla recta Europe, Asia Rare except on limestone soils Prunella vulgaris Europe, Asia, North Africa, North Widespread but uncommon America Ranunculus repens Europe, Asia Rare Rumex conglomerates Europe, West Asia, North Africa Rare Rumex crispus Europe, Asia, North Africa Rare Rumex obtusifolius Europe, South-western Asia Rare Salvia verbenaca South-west Europe, North Africa, Rare West Asia Sedum acre Europe, Asia, North Africa Only apparently found on limestone soils where common Tanacetum parthenium Europe Rare Taraxacum officinale s.l. Europe, Asia Widespread and common Trifolium ambiguum Europe, West Asia Rare Trifolium hybridum Europe, Asia Rare Trifolium pratense Europe, North Africa, Asia Rare Trifolium repens Europe, North Africa, Asia Widespread and common Viola arvensis Europe, North Africa, Asia Widespread but uncommon Annual grasses Aira caryophyllea Europe, North Africa, West Asia Widespread but uncommon Aira elegantissima South Europe, West Asia, North Rare Africa Aira praecox Europe, West Asia Rare Apera interrupta Europe, West Asia Rare but apparently restricted to Australian Alps Bromus diandrus Europe, West Asia, North Africa Rare Bromus hordeaceus Europe, West Asia, North Africa Rare Bromus madritensis South Europe, Asia, North Africa Rare Bromus molliformis Europe, West Asia, North Africa Rare Hordeum glaucum South-west Europe, West Asia, Rare North Africa Poa annua Europe, Asia Rare Vulpia bromoides Europe, North Africa, West Asia Widespread but uncommon Vulpia myuros East Europe, Asia, North Africa Rare Perennial grasses, sedges, rushes Agrostis capillaris Europe, Asia, North Africa Widespread and locally common Agrostis stolonifera Europe, Asia, North Africa, North Rare America Alopecurus pratensis Europe, Asia Rare Anthoxanthum odoratum Europe, Asia, North Africa Widespread and common Arrhenatherum elatius var. bulbosum Asia Rare

12 170 K.L. McDougall et al. / Perspectives in Plant Ecology, Evolution and Systematics 7 (2005) Appendix (continued) Bromus catharticus South America Rare Carex buxbaumii Europe, Asia, North America Rare Carex ovalis Europe, Asia Rare Cynosurus cristatus Europe, West Asia Rare Dactylis glomerata Europe, North Africa, Asia Rare Festuca arundinacea Europe, Asia, North Africa Rare Festuca rubra s.l. Europe, Asia Widespread and locally common Holcus lanatus Europe, North Africa, Asia Widespread and locally common Juncus articulatus Europe, Asia, North Africa, North Rare America Juncus bulbosus Europe, North Africa Rare Juncus effuses Europe, Asia, Africa, North Widespread but uncommon America Juncus ensifolius North America, Asia Rare Juncus tenuis North America, South America Rare Lolium perenne Europe, Asia, North Africa Rare Phleum pratense Europe, Asia, North Africa Rare Poa pratensis Europe, Asia, North Africa Widespread and locally common a rare ¼ small populations in a few locations. References Carr, S.G.M., Turner, J.S., The ecology of the Bogong High Plains. I. The environmental factors and the grassland communities. Aust. J. Bot. 7, Clothier, D.P., Condon, R.W., Soil conservation in alpine catchments. J. Soil Cons. N.S.W. 24, Costin, A.B., Gray, M., Totterdell, C.J., Wimbush, D.J., Kosciuszko Alpine Flora. CSIRO Publishing, Collingwood. CRC for Australian Weed Management, Heather (Calluna vulgaris) Weed Management Guide. Co-operative Research Centre for Australian Weed Management, Adelaide. Department of Environment and Conservation, Draft Plan of Management. Kosciuszko National Park. New South Wales Department of Environment and Conservation, Sydney. Ecology Australia, Kosciuszko resorts vegetation assessment. Unpubl. Report to Planning NSW. Ecology Australia, Melbourne. Flood, J.M., The Moth Hunters. Aboriginal Prehistory of the Australian Alps. Australian Institute of Aboriginal Studies, Canberra. Gibbons, F., Rowan, R.K., Soils in relation to vegetation in Victoria. In: Foreman, D.B., Walsh, N.G. (Eds.), Flora of Victoria, vol. 1. Inkata Press, Melbourne, pp Gilmour, P.M., Helman, C.E., Osborne, W.S., An ecological study of the Mount Tennent Blue Gum Creek area, A.C.T. Unpubl. Report. Conservation Council of the Southeast Region and Canberra, Canberra. Godfree, R., Lepschi, B., Mallinson, D., Ecological filtering of exotic plants in an Australian sub-alpine environment. J. Veg. Sci. 15, Helman, C.E., Gilmour, P.M., Treeless vegetation above 1000 m altitude in the A.C.T. Unpubl. Report. Conservation Council of the Southeast Region and Canberra, Canberra. Helman, C.E., Gilmour, P.M., Osborne, W.S., Green, K., An ecological survey of the Upper Cotter Catchment Wilderness Area, Namadgi National Park, A.C.T. Unpubl. report. Conservation Council of the South-east Region and Canberra, Canberra. Hennessey, K., Whetton, P., Smith, I., Bathols, J., Hutchinson, M., Sharples, J., The impact of climate change on snow conditions in mainland Australia. A Report for the Victorian Department of Sustainability and Environment, Victorian Greenhouse Office, Parks Victoria, New South Wales National Parks and Wildlife Service, New South Wales Department of Infrastructure, Planning and Natural Resources, Australian Greenhouse Office and Australian Ski Areas Association. CSIRO Atmospheric Research, Melbourne. Heutte, T., Bella, E., Invasive Plants and Exotic Weeds of Southeast Alaska. USDA Forest Service, Anchorage. Hibbert, M., The Aussie Plant Finder 1997/8: South- Eastern Australia. Florilegium, Sydney. Hnatiuk, R.J., Census of Australian Vascular Plants. Australian Flora and Fauna Series No. 11. Australian Government Publishing Service, Canberra. Humphries, S.E., Groves, R.H., Mitchell, D.S., Plant invasions of Australian ecosystems: a status review and management directions. Kowari 2, Hunter, G.G., King devil hawkweed (Hieracium praealtum) in wet, alpine, tall tussock grassland, Hopkins Valley, South Canterbury. In: Hunter, G.G., Mason, C., Robertson, D.M. (Eds.), Vegetation Changes in Tussock Grasslands, with Emphasis on Hawkweeds: Record of a

13 K.L. McDougall et al. / Perspectives in Plant Ecology, Evolution and Systematics 7 (2005) Workshop of the New Zealand Ecological Society, Cass Field Station, Canterbury, 3 6 October New Zealand Ecological Society, Christchurch, pp Johnston, F.M., Pickering, C.M., 2001a. Alien plants in the Australian Alps. Mt. Res. Dev. 21, Johnston, F.M., Pickering, C.M., 2001b. Yarrow, Achillea millefolium L.: a weed threat to the flora of the Australian Alps. Victorian Nat. 188, Kirkpatrick, J.B., Alpine Tasmania. An Illustrated Guide to the Flora and Vegetation. Oxford University Press, Melbourne. Mallen, P.J., Introduced vascular plants in the high altitude and high latitude areas of Australia with particular reference to the Kosciuszko alpine area. In: Barlow, B.A. (Ed.), Flora and Fauna of Alpine Australasia: Ages and Origins. CSIRO, Australia, pp Mallen-Cooper, P.J., Introduced plants in the high altitude environment of Kosciusko National Park. Ph.D. Thesis, The Australian National University, Canberra. McDougall, K.L., The Alpine Vegetation of the Bogong High Plains. Environmental Studies Publication No. 357, Victorian Ministry for Conservation, Melbourne. McDougall, K.L., The colonisation by alpine native plants of a stabilised road verge on the Bogong High Plains. Victorian Ecol. Manag. Rest. 2, McDougall, K.L., Aerial photographic interpretation of vegetation changes on the Bogong High Plains, Victoria, between 1936 and Aust. J. Bot. 51, McDougall, K.L., Winged everlasting Ammobium alatum threatened species, weed or itinerant? Victorian Nat. 121, McDougall, K.L., Appleby, M.L., Plant invasions in the high mountains of north-eastern Victoria. Victorian Nat. 117, Moggi, G., The Macdonald Encyclopedia of Alpine Flowers. Macdonald and Co., London. Morgan, J.W., Orange Hawkweed Hieracium aurantiacum L.: a new naturalised species in alpine Australia. Victorian Nat. 117, Peterson, J.A., The equivocal extent of glaciation in the southeastern uplands of Australia. Proc. R. Soc. Victoria 84, Pickering, C.M., Appleby, M.L., Good, R.B., Hill, W., McDougall, K.L., Wimbush, D.J., Woods, D., Plant diversity in subalpine and alpine vegetation recorded in the Kosciuszko Biodiversity Blitz. In: Green, K. (Ed.), Biodiversity in the Snowy Mountains. Australian Institute of Alpine Studies, Jindabyne, pp Polunin, O., Flowers of Europe. A Field Guide. Oxford University Press, London. Robertson, D.C., Morgan, J.W., White, M., Use of prescribed fire to enhance control of English broom (Cytisus scoparius) invading a subalpine snow gum woodland in Victoria. Plant Protect. Q. 14, Rose, A.B., Basher, L.R., Wiser, S.K., Platt, K.H., Lynn, L.H., Factors predisposing short tussock grasslands to Hieracium invasion in Marlborough, New Zealand. N.Z. J. Ecol. 22, Ross, J.H., Walsh, N.G., Census of the Vascular Plants of Victoria. Royal Botanic Gardens, South Yarra. Rowe, K., A Study of the Land Catchment of the Kiewa River. Soil Conservation Authority of Victoria, Melbourne. Sanecki, G.M., Sanecki, K.L., Wright, G.T., Johnston, F.M., The response of yarrow (Achillea millefolium L.) to herbicide application in the Snowy Mountains, southeastern Australia. Weeds Res. 43, Slatyer, R.O., Alpine and valley bottom treelines. In: Good, R. (Ed.), Scientific Significance of the Australian Alps. Australian Alps National Parks Liaison Committee Australian Academy of Science, Canberra, pp Thomas, V., Gellie, N., Harrison, T., Forest Ecosystem Classification and Mapping for the Southern CRA Region. A Report Undertaken for the NSW CRA/RFA Steering Committee. NSW National Parks and Wildlife Service, Queanbeyan. van Rees, H., Behaviour and Diet of Free-Ranging Cattle on the Bogong High Plains, Victoria. Environmental Studies Publication No Victorian Department of Conservation, Forests and Lands, Melbourne. Wahren, C.-H.A., Papst, W.A., Williams, R.J., Longterm vegetation change in relation to cattle grazing in subalpine grassland and heathland on the Bogong High Plains: an analysis of vegetation records from 1945 to Aust. J. Bot. 42, Walsh, N.G., McDougall, K.L., Progress in the recovery of treeless subalpine vegetation in Kosciuszko National Park after the 2003 fires. Cunninghamia 8, Walsh, N.G., Barley, R.H., Gullan, P.K., The Alpine Vegetation of Victoria (Excluding the Bogong High Plains), Volume 1. Environmental Studies Publication No Victorian Department of Conservation, Forests and Lands, Melbourne. Wardle, K., Fahey, B., Monitoring vegetation changes at Treble Cone Ski Field, New Zealand. Science for Conservation 192. Department of Conservation, Wellington, New Zealand. Wearne, L.J., Morgan, J.W., Recent forest encroachment into subalpine grasslands near Mt. Hotham, Australia. Arct. Antarct. Alp. Res. 33, Wearne, L.J., Morgan, J.W., Community-level changes in Australian subalpine vegetation following invasion by the non-native shrub Cytisus scoparius. J. Veg. Sci. 15, Whinam, J., Comfort, M., The impact of commercial horse riding on sub-alpine environments at Cradle Mountain, Tasmania, Australia. J. Env. Manag. 47, Whinam, J., Comfort, M., Bergstrom, D.M., Subantarctic hitchhikers: expeditioners as vectors for the introduction of alien organisms. Biol. Cons. 121, Williams, R.J., Ashton, D.H., The composition, structure and distribution of heathland and grassland communities in the subalpine tract of the Bogong High Plains, Victoria. Aust. J. Ecol. 12, Williams, R.J., Costin, A.B., Alpine and subalpine vegetation. In: Groves, R.H. (Ed.), Australian Vegetation, second ed. Cambridge University Press, Melbourne, pp Williams, R.J., Mansergh, I.M., Wahren, C.-H.A., Rosengren, N.J., Papst, W.A., Alpine landscapes. In: Attiwill, P.M., Wilson, B. (Eds.), Ecology: An Australian Perspective. Oxford University Press, Oxford, pp