Vegetation forms and sub-forms¶

Map of vegetation formations in New South Wales

The 16 primary vegetation formations describe the floristic composition of vegetation communities across Australia and are the primary unit of organization for a series of fire behavior models.

External Documentation¶

Form, Structure & Composition¶

Formations and sub-formations, referred to here as forms and sub-forms, are a method of classifying land cover based on the types, abundances & properties of vegetation in an area.

These are often determined based on the life form of the vegetation (like trees, shrubs, or grasses), the horizontal and vertical structure of the ecosystem (like closed-canopy forests, open woodlands, or grasslands), and the bioclimatic conditions of the region (dry vs. wet sclerophyll forests).

Contemporary definitions of the vegetation forms and sub forms of New South Wales were defined by David Keith in his book Ocean Shores to Desert Dunes (2004).

DPIE—the Department of Planning, Industry and Environment—hosts a 200m resolution raster dataset with codes to lookup the forms and subforms for all of NSW. These data were used to create the formations map above, and are visualized in this notebook.

Vegetation form abundance across New South Wales

Arid and semi-arid woodlands/shrublands are the most common formations across NSW, comprising about 75% of the land surface.

Drivers of Turnover¶

Why are vegetation communities different—structurally and floristically—across New South Wales?

Bioclimatic Variation¶

Temperature and precipitation place abiotic constraints on the distributions of vegetation forms and on the total abundance of vegetation in an area, mostly by constraining photosynthetic activity. Plant communities have multiple mechanisms to adapt to these varying conditions, and most of the vegetation forms in NSW are oriented towards drought tolerance (like thick, hairy leaves).

Temperature and precipitation are also important for determining decomposition rates. Decomposition moves fastest during warm and wet conditions. But, like in other Mediterranean climates, there is often seasonal disparity between when temperatures are warmest and when rainfall is most abundant, leading to low natural decomposition rates in hot and dry systems.

In these systems, fire is a critical ecological process for promoting regular nutrient cycling as a supplement to decomposition. Fire is also critical for seedling germination in many Australian plants. These species are most common in areas that are a) hot, b) seasonally dry, yet c) not so much of either that photosynthesis is constrained enough to severly limit vegetation abundance.

Mean Land Surface Temperature data by formation

Dry sclerophyll forests are some of the most important forms for fire danger mapping because they meet the three qualifications above and are a typical fire-prone/fire-adapted formation. They also occupy a large climatic range, found in areas with both a high mean and high overall variance in temperatures. Wet sclerophyll forests, however, occupy a lower range of temperatures.

Mean Cloud Cover data by formation

The Alpine complex formation refers to high-altitude plant communities in the Great Dividing Range, characterized by frequent cloud cover and low temperature. These are cloud forests.

Rainforests, wet forests & heathlands group together in cloudy regions, as do grasslands, semi-arid woodlands & shrublands in cloudless ones.

Mean Leaf Area Index data by formation

LAI—Leaf Area Index—is a metric of vegetation abundance, increasing in areas with dense vegetation. Some of the cloud cover-based groupings above still hold, but some break down: rainforests and wet forests are both characterized by consistently high LAI, while heathlands have a lower average and higher variance than the other two.

Dry sclerophyll forests cover the largest range of LAI values, reflecting the wide variance in climatic conditions experienced by this form that drives the high diversity of the plant communities that comprise them.

Geobotany¶

Also known as phytogeography, geobotany describes how soil and geological features constrain plant biogeography. David Keith (2011) evaluated the relative importance of geodiversity and climatic variability in determining the spatial distributions of several vegetation types. I'll let the abstract say the rest:

The results indicate a strong non-random relationship between vegetation and geodiversity, with most vegetation types restricted to a narrow range of geological substrates. Partial variance analyses indicated that the influence of geodiversity on vegetation composition was stronger than, and largely independent of the influence of climate. Consistent with current theories, sclerophyllous vegetation formations and classes showed a strong association with geological units characterised by low levels of mineral nutrients. It was concluded that landscape patterns of geodiversity are likely to place significant constraints on the response of native vegetation to future climate change.

Soil and geology place boundaries on the potential geographic extents of different vegetation forms, which varies by vegetation type. It's probably worth checking out these global soil data in addition to searching for canonical data from DPIE or Geosciences Australia.

The Great Dividing Range¶

Topographic map of the Great Dividing Range

Also known as the Eastern Highlands, the Great Dividing Range is the collection of mountains, plateaus & hills along the east coast of Australia, which forms the fifth-longest land-based mountain chain in the world.

Several forms and sub-forms are defined by whether they are east or west of the divide. This is driven in part by differences in temperature and precipitation, with the west slopes being much warmer and drier due to a rain shadow effect.

These mountains also likely act as a barrier to dispersal for many plants. The drastic environmental and geological gradients of the range mean few species would be able to move up and down the slopes across the range, leading to isolation between communities. This creates differences in the floristic composition of communities east and west of the divide, which may also

Glossary¶

sclerophyll: drought-resistant vegetation characterized by hard, evergreen leaves that are adapted to prevent water loss. Often associated with Mediterranean climates, which are characterized by hot, dry summers and mild, wet winters.

Naming inconsistencies¶

The formation Grassy wet sclerophyll forests east of the Divide, as it's referred to in Watson 2012, is also known as Wet sclerophyll forests (Grassy subformation) in Keith 2004 and in the official formations raster metadata.