title: Exotic Plants in the Australian Alps Including a Case Study of the Ecology of Achillea Millefolium, in Kosciuszko National Park
Creators: name: Johnston, Frances Mary
Publisher: name: Griffith University
Year: 2006
Subjects: subject: Achillea millefolium
subject: Kosciuszko National Park
subject: alpine ecology (Australia)
subject: Australian alpine vegetation

description: Exotic plants are a threat to natural areas world wide including the Australian Alps, one of the largest relatively undisturbed natural areas remaining in Australia. This thesis examines the diversity, abundance and distribution of exotic plants in the Australian Alps, including Kosciuszko National Park and then focuses on Achillea millefolium (L.) (Asteraceae) as a case study of the biology and ecology of an important environmental weed. To determine the diversity and abundance of exotics in the Australian Alps published records of exotic species were reviewed. A total of 175 exotic taxa were recorded in the alpine and subalpine areas representing 41 families and 122 genera. The distribution of exotics was associated with human activities with 80% of exotic taxa found along roads and tracks and nearly 60% around ski resorts. Just over 20% of exotic species were naturalised with some species presenting an environmental threat to the region. To examine the relationship between human disturbance and exotics, vegetation was surveyed and soil analysed on road verges, in runoff areas and in adjacent vegetation along a gravel road in the subalpine zone of Kosciuszko National Park. The road verge was dominated by exotics, the area 10 m from the road verge was dominated by natives and the road drainage areas were dominated by the exotic, A. millefolium. There were also clear differences in the soils, with coarse nutrient poor soils on the road verge, highly organic fine soils in the areas 10 m from the road, and soils with high nutrients and water content in the road drainage areas. The potential for exotics to colonise areas adjacent to roads after disturbance was examined in an experiment conducted along a subalpine road. The composition of plants colonising small gaps created in the existing vegetation (50 cm x 100 cm) was dependant on the distance from the road. In general, gaps one metre from the road verge were recolonised by exotic species while gaps five or ten metres from the road verge were predominantly recolonised by native early succession species. However the exotics A. millefolium and Acetosella vulgaris were present in many sites prior to disturbance, and were the major exotics to recolonise gaps five and ten metres from the road. Therefore disturbance of natural areas where there are exotic propagules present may not necessarily result in a native climax community, but in a community with an even higher cover of exotics than prior to disturbance. These initial studies highlighted the importance of A. millefolium as an environmental weed in the Australian Alps. Therefore further research was carried out on this species. A review of literature highlighted the capacity of this species to colonise and invade both disturbed and natural habitats. Based on current weed risk assessment methodologies this species presents a serious threat to both agricultural and natural environments in Australia. Data on the distribution of A. millefolium was used to develop a CLIMEX® model of its distribution worldwide and in Australia under current and changing climatic conditions. The models indicate that cool, temperate and Mediterranean climates are suitable for this species, while deserts and tropics are unsuitable. Under climate warming scenarios, there would be an overall reduction in the area suitable for A. millefolium, including within Australia, but an increase in suitable sites at higher altitudes. Field and glasshouse experiments were conducted examining the distribution, phenology, resource allocation, seed ecology and competitive abilities of A. millefolium, including any variation in these characteristics associated with increasing altitude. Field surveys and published records of A. millefolium indicate that A. millefolium populations are primarily associated with disturbance, with some limited spread into native vegetation. It occurs along more than 100 km of walking tracks, roads and trails within the Park. Achillea millefolium populations were observed growing between 800 m and 2100 m a.s.l., with the majority of populations occurring in areas above 1200 m a.s.l. The vegetative and flowering phenology studies of A. millefolium confirm that it is able to grow and flower from the tableland to high subalpine with flowering commencing earlier and lasting longer at lower altitude sites. However, even at sites 1760 m altitude, flowering occurred for approximately 80 days with large numbers of inflorescences (19 per m2) at the peak of flowering in early March. The effect of altitude on the allocation of biomass in A. millefolium between above ground, below ground and reproductive structures indicates that with increasing altitude there was a decrease in the relative and absolute allocation of biomass to reproductive structures (average 2.7 kg/m2), although the total number of flower heads was not affected (average 129 flowering heads/inflorescence). There was no effect of altitude on the absolute allocation to below ground (average 3.1 kg/m2) and above ground vegetative structures (average 0.7 kg/m2). The seed ecology of A. millefolium was examined including estimating the potential maximum seed production (51400 seeds/m2), seed rain, and seed viability. There was 60% viability of seed remaining after three years dry storage and 16% viability of seed remaining after three years of burial in the field. All these seed characteristics were highly variable among sites, with either no, or limited effect of increasing altitude. In a glasshouse competition experiment between A. millefolium and the dominant native snowgrass Poa fawcettiae, the weed produced four times as much biomass as the native grass at the end of the 12 week experiment. As a result, when grown together, A. millefolium significantly decreased the root and shoot biomass of P. fawcettiae while P. fawcettiae had no effect on the biomass of A. millefolium. Root interaction from the weed on the grass appeared to be the primary source of competition. Population dynamics modelling using data from this research and from the literature indicated that without human induced control this species has the potential to continue to spread from current populations in subalpine and alpine areas. Therefore a strategy to effectively control this species must include the removal of flowers to decrease the input of seed into the seed bank, limiting the establishment of seedlings and removal of the underground rhizome system. This study has shown that the high altitude areas of the Australian Alps are susceptible to exotic plant invasions. The results also highlight the importance of human induced disturbance in the introduction and distribution of exotics, including the case study species A. millefolium. Increasing severity of conditions with increasing altitude does not appear to be limiting the establishment, growth and reproduction of A. millefolium, even though altitude did affect some components of the ecology of this species in Kosciuszko National Park.