Indicator description

Why is it indicative

What does the data show

Data

Acknowledgment

Indicator description

The distribution and severity of tree decline. This indicator is also part of the condition statement for the indicator Extent and condition of native vegetation.

Why is it indicative

This indicator is a direct measure of the condition.

What does the data show

• Tree decline is the most extensive form of land degradation in Tasmania (Grice 1995).
   
• It is estimated that 42% (861,000 ha) of private land in Tasmania supports trees that are suffering from either extreme, severe or moderate tree decline.
   
• In Tasmania tree decline extends throughout the low rainfall (below 900 mm annual rainfall) districts, with the most extensive and extreme cases in the Midlands such as around Tunbridge and Woodbury as well as in the upper Derwent Valley such as around Ouse.
   
• The Northern Midlands and south-east bioregions support the most extensive and extreme cases of tree decline in Tasmania.
   

Data

There has been no additional Statewide information gathered on the areas affected by tree decline since the previous State of the Environment report in 1997.

The only systematic Statewide survey of tree decline was conducted in 1992, which was part of the Statewide soil and land degradation assessment coordinated by Grice (1995). These assessments were conducted on private land only.

The maps and tables below show the results from this survey.

Land systems containing areas of tree decline on private land, 1992

Caption: The tree decline problem has increased since 1992 with tree decline expanding into many new areas. The white areas (i.e. non-private land) were not assessed for the presence of tree decline.

Notes: Legend: Class 0: No assessment possible: Trees absent. Class 1 Nil to minor: Less than 10% of branches within the trees' canopy are dead. Class 2 Moderate: 10-40% of branches within the trees' canopy are dead. Class 3 Severe: 40-80% of branches within the trees' canopy are dead. Class 4 Extreme: Trees dead or dying with more than 80% of branches dead.

Source: Grice (1992) and DPIWE.

Area of private land affected by tree decline in Tasmania by severity class, 1992

Class 0	Class 1	Class 2	Class 3	Class 4
No assessment possible - Trees Absent	Nil to minor -- Less than 10% of branches within the trees', canopy are dead	Moderate - 10 - 40% of branches within the trees', canopy are dead	Severe - 40-80% of branches within the trees', canopy are dead	Extreme - Trees dead or dying with more than 80% of branches dead
162,000 ha	1,039,000 ha	648,000 ha	161,000 ha	52,000 ha

Source: Adapted from Grice (1995)

Acknowledgment

State of the Environment - Tasmanian Indicator.