OFR 151.pdf - CRC LEME

1.3 Flora, vegetation and climate
1.3.1 Flora
An important distinction exists between flora and vegetation. A flora comprises the plant
species present in an area irrespective of their relative abundance or life form. Vegetation
denotes the abundance and structural arrangement of the taller or more common species.
Plant community is used to denote relatively stable associations between particular species,
which in combination make up particular vegetation types. Species making up the major
vegetation types in Australia are given in Specht (1970, 1982).
1.3.2 Vegetation
Vegetation has a staggering potential to alter global and regional environments in the shortterm
and over geological time. For example, on average plants contain less than 0.5 g carbon
cm 3 and form a ‘veneer’ that is less than 100 m thick between the 100 km deep lithosphere
and 10 km high atmosphere. Nevertheless, the global vegetation manages to cycle 60
gigatonnes (60 x 10 15 g) of carbon between the lithosphere, biosphere and atmosphere each
year (Naeem 1999).
Similarly, methane produced by the bacterial decomposition of organic matter in wetlands has
been implicated as a major factor in global warming. A brief but intense period of global
warming and massive perturbation of the global carbon cycle during the Paleocene-Eocene
transition (Paleocene-Eocene thermal maximum) almost certainly was due to the catastrophic
release over ~20 ka of methane, which previously had been ‘frozen’ as hydrates in sea floor
sediments (Rohl et al. 2000).
1.3.3 Biomes
Biomes are defined as broad stable ecosystems of plants and animals, which occupy climatic
regions defined by unique combinations of precipitation and temperature, and seasonal
variation in these parameters. Plant biomes are broad vegetation classes defined by
combinations of dominant physiognomic character (life form, leaf-form, phrenology).
Terrestrial and most aquatic ecosystems are underpinned by plants whose life-forms/size
(trees, shrubs, herbs), growth rates and distributions are shaped not only by the prevailing
climate but also by soil fertility, drainage and moisture status (edaphic factors).
Global biomes
The strong association of particular life forms with particular climatic regimes allows plant
biomes to be defined using a combination of climatic, physiognomic and physiological
characters (Christopherson 1997). Because of functional convergence between unrelated
plants growing under the same physical environment, it is possible to use ecophysiological
data to compare or combine data from regions with taxonomically different floras (Prentice et
al. 1992).
Eleven terrestrial plant biomes can be recognised globally (Table 1). Most biomes are named
after the tallest/most abundant (dominant) plant stratum present, i.e. the one most exposed to
climate. They are rainforest, savannah (grasslands with scattered trees), grassland (grasslands
lacking woody species), shrublands, desert and tundra. Each is characterised by a distinctive
flora with equally distinctive morphological and ecophysiological adaptations. The transition
between biomes is recognisable by changes in the physiognomic character of the vegetation
as a whole, in the relative proportions of the component plant communities, or in the relative
abundance of the dominant plant species.
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