A slow unpicking of the landscape thread? Changes in tropical savanna birds on a gradient of habitat modification over 12 years of monitoring
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Context
In south-eastern Australia, land clearing has been extensive, resulting in an avifauna that has been significantly depleted. In northern Australian tropical savannas, land clearing is much less but increasing.
Aims
To examine the relative change in bird community composition of a Queensland tropical savanna over a 12-year period where sites represent a gradient of habitat modification. I investigate if these changes trigger avifauna disruption in the wider intact woodlands.
Methods
The data were collected from 60 sites sampled seven times between 2004 and 2016, using an eight-count repeat census in each site, in each year of survey. The data was examined via a range of non-parametric multivariate method.
Key Results
The analysis of bird community composition indicated that variation was not parallel across the habitat modification gradient (i.e., cleared, thinned sites displayed higher temporal change and instability). The strongest directional change and temporal turnover in β-diversity was strongly linked to the gradient of modification from cleared to thinned, to intact.
Conclusions
In this study I demonstrated that, where tree clearing has commenced or trees are thinned (even though it is only a small percentage of the total land cover), this initiates bird community instability, though the surrounding intact vegetation seemed to remain unaffected up until 2016.
Implications
Regional changes in bird populations can take many decades to appear after substantial disturbance, and continued monitoring of landscapes being progressively cleared, should be a priority to identify and prevent irreversible collapse of the avifauna, such has occurred in south-eastern Australia.
