Territory Stories

Top End Native Plant Society newsletter



Top End Native Plant Society newsletter

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TENPS newsletter


Top End Native Plant Society


Top End Native Plant Society newsletter; Top End Native Plant Society newsletter; E-Journals; PublicationNT




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Top End Native Plant Society; Periodicals; Plant; Darwin Region

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Top End Native Plant Society

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4 better understanding the interactions between trees and fire, and help develop coherent theory. Garry began by discussing some of the evolutionary strategies and growth patterns utilized by contrasting types of plants to protect themselves from fire. In all of the world's wet/dry savannah systems fire is a major driver of ecological processes. An important difference between savannahs in Australia and the rest of the world is the presence of eucalypts. On other continents savannah trees have evolved a strategy of shading by investing considerable energy into their structures, with substantial branches and often broad, large leaves. Shading both reduces competition with grasses and the impact of fires. Although this strategy assists them to better survive fires trees tend to be reduced to discrete clumps surrounded by grass. In contrast, Australia's eucalypts have evolved a strategy of putting energy into growing vertically and dropping all leaves and associated twigs that become shaded. Although this leads to a fuel build up around their bases the trees rapidly grow to a sufficient height to escape serious damage in fires. This strategy is breaking down where introduced weeds such as Gamba Grass (below) and Mission Grass are present. The latter burn so much hotter (above) than native grasses they pose a serious threat to the continued survival of savannah trees, including eucalypts. Garry noted that Gamba Grass might potentially grow as far south as the lower rainfall region around Elliott. Garry's investigations have led him to sites along a north-south line from the savannah of the Top End into arid Central and South Australia, and further afield into the Kimberley, the Great Western Woodlands of southern Western Australia and the southern forests of southeastern Australia. Gradients in the amount and seasonality of rainfall (see figure above) appear to influence the types of protection from fire that plants have developed. In northern Australia between 84%100% of rainfall occurs in the summer 6 months, central Australia may receive both summer and winter rain, and in the south most rainfall occurs in winter. Following the rainfall gradient north to south, Garry found the same (or equivalent) species of trees grow shorter for any given diameter. Eucalypt woodlands shorter with the rainfall gradient: Tall near Darwin and short near Tennant Creek. The shorter trees experience a lower fire frequency. In the north fires occur about every 2 years on average, compared to every 10-20 years in the south. So the chance of the shorter growing trees being harmed by fire is greater as we move south, but the frequency of this happening is much less. Are the trees in the south trading off energy otherwise expended to quickly grow tall and avoid fire (in the north) for other survival factors? The observations have led to more questions than answers at this stage. In the highly diverse Great Western Woodlands the trees are fire sensitive but the habitat appears

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