K Bridle

ENVIRONMENT AND FLORISTICS OF TEN AUSTRALIAN ALPINE VEGETATION FORMATIONS

Data on floristics, structure and environment were collected from quadrats throughout the geographic range of alpine vegetation in Australia. These data were used to explore the floristic and environmental relationships of ten alpine vegetation formations: bolster heath, coniferous heath, heath, alpine sedgeland, fjaeldmark, tall alpine herbfield, short alpine herbfield, grassland, bog and fen. Alpine sedgeland and coniferous heath, and tall alpine herbfield and grassland, proved to be closely similar in their floristics. Grassland and coniferous heath were most separated in ordination space. The environmental variables with the largest numbers of significant differences between formations were extractable phosphorus, summer temperatures, winter temperatures and topography. However, many other edaphic, climatic, topographic and biotic variables were important in discriminating between formations. The results of the formation-environment analyses were largely consistent with the relationships suggested in the previous literature. However, some environmental differences between formations that were observed or posited from local studies did not prove to be exportable to the alpine zone as a whole. Edaphic and topographic variables appear to be more important in discriminating the environments of alpine formations than the environments of alpine floristic communities.

Perception of climate change and its impact by smallholders in pastoral/agropastoral systems of Borana, South Ethiopia

This study investigates the perception of historic changes in climate and associated impact on local agriculture among smallholders in pastoral/agropastoral systems of Borana in southern Ethiopia. We drew on empirical data obtained from farm household surveys conducted in 5 districts, 20 pastoral/agropastoral associations and 480 farm households. Using this data, this study analyses smallholders’ perception of climate change and its associated impact on local agriculture, and the effect of various household and farm attributes on perception. Results suggest that most participants perceived climatic change and its negative impact on agricultural and considered climate change as a salient risk to their future livelihoods and economic development. Different levels of perception were expressed in terms of climate change and the impact on traditional rain-fed agriculture. Age, education level, livestock holding, access to climate information and extension services significantly affected perception levels. Household size, production system, farm and non-farm incomes did not significantly affect perception levels of smallholders. Smallholders attributed climate change to a range of biophysical, deistic and anthropogenic causes. Increased access to agricultural support services, which improves the availability and the quality of relevant climate information will further enhance awareness of climate change within of the rural community and result in better management of climate-induced risks in these vulnerable agricultural systems.

Decades-scale vegetation change in burned and unburned alpine coniferous heath

Fire appears to be a rare event in alpine vegetation, suggesting that its effects might be more persistent than in most lowland vegetation types. However, it has been suggested that the Australian alpine biota is resilient to infrequent large fires. This paper describes decades-scale vegetation and soil change after fire in paired plots overfire boundaries in Tasmanian alpine coniferous heath. The effect of fire on soils persisted for decades. Recovery of vegetation was extremely slow by global standards, with delayed reinvasion of previously dominant species. There was low cover of the most fire-sensitive species 43–69 years after fire and much bare ground still evident, with the rate of revegetation declining through time. Gymnosperm shrubs increased at the expense of angiosperms in the unburned plots in the same period and cryptogams declined in both burned and unburned plots. These results suggest that the Tasmanian alpine flora cannot be characterised as resilient to infrequent large fire, although most species survive its incidence. The many centuries that it appears are necessary for coniferous heath to recover to its pre-burn state suggest that fires caused by increased ignitions from lightning and arsonists are the major issue for conservation of the vegetation type.

Succession after fire in alpine vegetation on Mount Wellington, Tasmania

The vegetation on either side of fire boundaries in the alpine zone of Mount Wellington, Tasmania, was surveyed in 1978 and 1998. This combination of spatial and temporal sampling gave data for 16, 31, 36 and 51 years since burning. These data were used to test for convergence in vegetation characteristics through time between the areas burned in 1947 and those burned in 1962 and to determine whether lifeform is a reasonable predictor of the successional dynamics of species. While convergence largely prevailed, some lifeforms and species diverged and lifeform was generally a poor predictor of species responses. For example, size class analyses of the larger shrub species indicated a wide variety of successional responses to fire. The tall shrubs on Mt Wellington have higher percentages of tolerators and species relying on the soil seed store for postfire regeneration than physiognomically similar vegetation in more fire-prone environments. Fifty-one years after fire, there is evidence of continuing floristic and structural change in the alpine vegetation that may be partly related to recent climatic warming.

Environmental relationships of floristic variation in the alpine vegetation of southeast Australia

. Australian alpine vegetation is confined to the southeast of the continent and the island of Tasmania. It exhibits strong geographic patterns of floristic variation. These patterns have been attributed to variation in edaphic conditions resulting from geographic variation in substrate, climate and glacial history. This edaphic hypothesis is tested using floristic and environmental data from 166 quadrats distributed throughout the floristic and geographic range of Australian alpine vegetation. Environmental vector fitting in three-dimensional ordination space, the number of significant environmental differences between all pairs of 17 floristic groups and overall statistical analyses of the environmental differences between communities suggest a primacy of climatic variables over edaphic variables in explaining the broad patterns of floristic variation. Continentality, summer warmth, summer rainfall and winter cold all provide a better statistical explanation of floristic variation than the most explanatory of the edaphic variables, extractable P. The environmental variables that best discriminate the groups at each dichotomy of the divisive classification of the floristic data are largely climatic at the upper two levels, with edaphic, topographic and biotic variables being generally more important than climatic variables at the lower levels. Many of the edaphic variables that were most important in discriminating dichotomous groups were relatively insignificant in the broader analyses, suggesting that it is important to partition large data sets for environment/floristic analyses. The results of such partitioning show that the environmental factors most important in influencing floristic variation in alpine vegetation in Australia vary by location and geographic scale.

Recovery in Alpine Heath and Grassland Following Burning and Grazing, Eastern Central Plateau, Tasmania, Australia

Long-term data from six sites in treeless subalpine and alpine vegetation in central Tasmania are used to document change in vegetation cover and life form dominance over time. All sites have been disturbed by burning and domestic stock grazing in the past. Although burning ceased at least 8 yr before initial measurements were taken, stock grazing still occurs at one site, and rabbits and native vertebrate herbivores (mainly wallabies) graze throughout the region. Vegetation cover increased across all sites over a 5- to 23-yr period at an average annual increment of approximately 1%. There was no significant relationship between the initial cover of bare ground and change in bare ground over time for most of the sites. Annual increases in vegetation cover were least in locations grazed by rabbits and native vertebrate herbivores and where domestic stock still grazed. Exclosures grazed only by rabbits had an intermediate rate of increase. Vegetation cover was found to increase most in ungrazed exclosures. The rates of increase in vegetation cover suggest that, in the absence of fire, it is a matter of decades before cover will be almost complete in the area.

Impacts of grazing by vertebrate herbivores on the flower stem production of tall alpine herbs, Eastern Central Plateau, Tasmania

Some species and genera of tall herbs that are widespread both in Tasmanian and in mainland Australian alpine vegetation are dominant or codominant over large areas in the Australian Alps, while being typically subordinate species in Tasmania. This difference has been attributed to the impact of vertebrate herbivores, which are abundant in the Tasmanian high country but rare in or absent from the higher altitudes in the Australian Alps. The present study tests the hypothesis that lack of dominance (>50% cover) of tall alpine herbs in Tasmanian alpine and subalpine areas could be at least partially caused by grazing of their reproductive parts. Both in experimental plots and a clipping experiment, tall herbs produced more flowering stems under lower grazing/clipping pressure. In the field, the greatest reduction in flowering occurred under a grazing regime of sheep plus rabbits plus native herbivores. There was no consistent difference in the number of flowering stems between rabbit-grazed and rabbit plus native-grazed areas. However, there was a significant negative relationship between the number of flower heads and wallaby scats and a non-significant positive relationship between the number of flower heads and rabbit scats, suggesting that wallabies, not rabbits, were largely responsible for flower head depletion. Many species had more flowering stems in rabbit plus native vertebrate-grazed areas than in ungrazed exclosures. Therefore, it seems possible that the effects of vertebrate herbivory on flowering may have contributed to the lack of tall alpine herbfields in Tasmania.

Changes in alpine vegetation related to geomorphological processes and climatic change on Hill One, Southern Range, Tasmania, 1989-2000

Photographs of 84 plots in alpine vegetation, largely consisting of fjaeldmark and bolster heath, on Hill One, Southern Range, Tasmania, were taken in both 1989 and 2000 to compare cover characteristics. Between these two observations, vegetation cover declined in the fjaeldmark, largely as a result of erosion. Declines also occurred on the active depositional lobes, through burial of bolster heath. Within the parts of Hill One where vegetation cover was not lost, graminoids decreased and Pterygopappus lawrencei increased in the bolster heath and tall shrubs displaced bolster heath. Thirty-six per cent of the rocks visible in the 1989 photographs had moved by 2000, the mean area of the individual rocks that moved being 95 cm2. Larger rocks were moved on the exposed western slope than on the leeward eastern slope. Analyses of climatic data from nearby stations for 1979–2000 indicated a decline in both precipitation and temperatures and an increase in the frequency of the highest wind speeds, all of which are consistent with the nature of vegetation and geomorphological changes that occurred on the mountain, although a climatic cause is far from proven. Localised cooling and drying, in the two hottest and wettest decades recorded for the globe, emphasises the importance of local data in determining the possible impacts of climatic change on biota.

Explaining a sharp transition from sedgeland to alpine vegetation on Mount Sprent, southwest Tasmania

Regular altitudinal sampling of the vascular plant species composition of treeless vegetation on Mount Sprent, Tasmania revealed gradual change between 510 and 820 m, and between 930 and 1050 m, but steep change between 830 and 920 m. The zone of sharp change was the boundary between lowland sedgeland dominated by Gymnoschoenus sphaerocephalus and alpine vegetation. Edaphic and topographic conditions varied relatively little along the transect. Two years of temperature and precipitation data were obtained from sites on either side of the boundary, a site near the summit and a site near the lower limit of the sedgeland. These data indicate that the phytosociological zone of change is coincident with a sharp change in mean temperature conditions between the two central sites. Variation in precipitation appears largely unrelated to phytosociological conditions at this scale. This climatic break appears to be consistent in its characteristics with a frequent subsidence inversion layer, and could explain the similar sharp boundaries found elsewhere on Tasmanian mountains. The phenomenon may be widespread in maritime mountains.

Natural and cultural histories of fire differ between Tasmanian and mainland Australian alpine vegetation

We ask how and why mainland Australia and Tasmania differ in the natural and cultural history of alpine fire. Indigenous people seem unlikely to have extensively burned the alpine landscape in either of mainland Australia or Tasmania, whereas anthropogenic fire increased markedly after the European invasion. In Tasmania, where lightning ignition is uncommon, alpine fires have been rare post-1980, whereas mainland alpine vegetation has been extensively burned. The current distributions of the eight Australian alpine plant species that have no mechanisms for recovery from fire suggest that climate and natural fire barriers have been important in their survival. Mainland Australian pre-fire vegetation cover is typically attained in less than a decade, whereas in Tasmania, half a century or more after fire, bare ground persists at high levels, and continues to decrease only where mammalian herbivores are excluded. These differences appear to be ultimately related to the climatic contrast between the maritime mountains of Tasmania and the continental mainland mountains, through the effects of continentality on snow cover, which, in turn affect marsupial herbivore grazing, exposure of soil and vegetation to extreme microclimatic conditions and the degree of shrub dominance.