Abstract
Abstract. In the forests of south west Western Australia dramatic declines in tree health have been observed in recent years. The species Eucalyptus wando has exhibited loss of crown foliage in increasing stages of severity; this condition is referred to as wandoo crown decline and can lead to death. Determining the extent and timing of these declines is difficult on the ground due to the large distribution of E. wandoo and the observation of tree declines at a range of locations and dates over the last 40 years. Understanding the distribution, severity and timing of these declines is essential to the identification of the causes of these impacts. Investigation of time series Landsat imagery can inform on locations of crown foliage loss and the time periods these losses occurred in. Applying a vegetation index to a 20 year sequence of imagery enabled periods of decline to be identified. Employment of trend analysis of four date time series demonstrated the dynamics of wandoo crown cover. Comparisons of periods of decline with the variations of cover density over the entire image sequence facilitated the identification of possible locations and timing of wandoo crown decline impacts. Changes in crown cover observed by the imagery analysis were compared to field surveys.
Highlights
1.1 MotivationOver the last forty years Eucalyptus wandoo crowns have demonstrated varying losses in canopy initially on terminal branches in some cases leading to death
Trend analysis has been employed in this investigation as it has proven useful in investigating vegetation cover dynamics in the south west of Western Australia and in other parts of Australia (Wallace and Thomas 1998, Curry et al 2008, Wallace et al 2006)
This study aims to interrogate the time series of imagery and use shorter trend periods to inform the questions posed by the Wandoo Recovery Group
Summary
Over the last forty years Eucalyptus wandoo (wandoo) crowns have demonstrated varying losses in canopy initially on terminal branches in some cases leading to death. This is described as wandoo crown decline (WCD). Lack of knowledge about the timing and spread of phenomenon makes it difficult to understand and manage. These issues have instigated the following questions: 1) Where does wandoo crown decline (WCD) occur? Time series satellite imagery can be utilised to inform these questions and improve understanding of WCD over the last 20 years across its mapped occurrence
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