Athrotaxis cupressoides forms stands of varying size class and age class structure in the high subalpine
and alpine environments of Tasmania. As with some other southern hemisphere gymnosperms with
great longevity, A. cupressoides does not successfully regenerate in dense forest stands without disturb-
ance but does so in many open stands. Vegetative regeneration through root suckers occurs in many
such stands. Suckers are most frequent in bogs and least evident in blockstreams. There has been little
successful seedling or sucker regeneration in open stands in the east of the range of the species since
European occupation of the Central Plateau. Exclosure experiments and field observations show that
seedlings, suckers and adult foliage are heavily grazed by introduced placental and native marsupial
mammals.
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.
Athrotaxis selaginoides and A. cupressoides are potentially interbreeding species with partly overlapping
ranges. The two Athrotaxis species occur in a wide range of floristic types, with A. selaginoides being
concentrated in thamnic and implicate rainforest communities and A. cupressoides in open montane
communities. As is consonant with its distribution pattern and the cold resistance of its adult foliage,
A. cupressoides seedlings are more frost resistant than those of A. selaginoides. Preliminary experiments showed no difference between the two species in resistance to waterlogging or drought. However,
stand structure data indicate that A. selaginoides can survive better in shaded conditions than its
congenor. This pattern of ecological differentation is consistent with an origin by parapatic speciation.
Seedling surveys indicated that landslide faces provide opportunities for Athrotaxis selaginoides and Nothofagus cunninghamii to regenerate in thamnic and high altitude callidendrous rainforest. The spatial distribution of mature A. selaginoides stems at some sites suggests that they have originated on past landslides. Leptospermum scoparium and Eucalyptus vernicosa seedlings were also present at some of the sites investigated. Therefore, landslides may provide regeneration opportunities for these species in rainforest communities in the absence of fire. The physical attributes of A. selaginoides suggest that the species would be advantaged by canopy disturbance of the scale caused by landslides as opposed to smaller treefall gaps. The cooler climate, higher levels of slope instability, avalanches and snowstorms during the last glacial would have been well suited to this species.
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