Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Ann Hamblin, Bureau of Rural Sciences, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06748 5
Introduction of novel biota into native habitats and communities (continued)
Impact of agriculture on native vegetation [L Indicator 4.2]
A second indicator, developed for the National Collaborative Project on Indicators of Sustainable Agriculture (NCPISA), assessed the impact of agriculture on native vegetation types using the 34 categories of vegetation developed by Graetz et al. (1995). Details of the method were provided in SCARM (1998). This indicator ranked:
- the area of original vegetation protected,
- the area of original vegetation disturbed, and
- the proportion of original remnant vegetation occurring on agricultural land.
|AER 10 temperate slopes and plains||67%|
|AER 8 wet temperate coasts||64%|
|AER 5 semi-arid tropics and subtropical plains||58%|
|AER 6 subtropical slopes and plains||57%|
|AER 9 temperate highlands||55%|
|AER 11 arid interior||48%|
Source: SCARM (1998).
The representation of the full range of vegetation types is low in nearly all agro-ecological regions (AERs) other than the north-eastern wet tropics and the temperate highlands (Figure 47). In all other regions, over half the vegetation types have less than 10% of their area in the conservation estate.
Figure 47: Percentage of native vegetation types that have less than 1% representation in reserves, and more than 75% of the vegetation types on agricultural land disturbed, in various agro-ecological regions.
Source: adapted from SCARM (1998)
The proportion of vegetation types that are disturbed on agricultural land is also high across much of the continent. Of the 34 different vegetation types classified by Graetz et al. (1995), the arid interior (AER 11), temperate slopes and plains (AER 10) and semi-arid subtropical plains (AER 5) all have 20 or more. These regions, together with the subtropic slopes, temperate highlands, and temperate slopes and plains, all have more than 50% of vegetation types significantly disturbed over more than 75% of their range.
This degraded remnant vegetation patch shows the problem of no fencing, with older dying trees.
Source: Bureau of Resource Sciences
The highest impact of agriculture on representative native vegetation, and the largest number of underprotected vegetation types, occur in AERs 5 and 6-the great sweep of semi-arid and subtropical plains and slopes stretching in an arc through the Northern Territory and Queensland to northern New South Wales. This region is not heavily populated and much of it is used for pastoral activities, but the proportion of land in the conservation estate is very low.
The agro-ecological regions used for reporting the sustainability of agricultural systems in Australia in 1998 were too large for most remnant vegetation that occurs on agricultural land to be closely identified. However, the NCPISA analysis does show that much of it is at risk from current agricultural activities such as grazing. Grazing stops seedling recruitment, alters the composition of understorey species, and may destroy older and weakened trees or shrubs through rubbing and browsing. Eventually the remnant patch succumbs to disease, parasitic invasion (e.g. mistletoe or strangler vine) and old age. Most of the smaller (< 1 ha) patches of unfenced native vegetation and isolated trees dotting park-like agricultural landscapes in southern Australia are probably already doomed to extinction by these means.