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Remotely assessing hollow availability using aerial photographs


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Koch, AJ and Baker, SC 2011 , 'Remotely assessing hollow availability using aerial photographs' , Biodiversity and Conservation, vol. 20 , pp. 1089-1011 , doi: 10.1007/s10531-011-0018-z.

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Tree hollows provide critical habitat for many species worldwide. The conservation of hollow-bearing trees presents a particular challenge for forest managers, partly
due to difficulties in predicting their occurrence across a landscape. We trialled a novel approach for assessing relative hollow availability, by remotely estimating mature crown cover and senescence from aerial photographs in Tasmania, Australia. These estimates were tested against plot-based field assessments of actual occurrence of hollow-bearing trees. In dry forest we conducted ground-based surveys of hollows for all mature trees ([50 cm dbh) in 37 half-hectare plots. In wet forest, we conducted helicopter-based surveys of hollows for all mature trees in 45 oldgrowth plots (0.29–4.63 ha). Aerial photographs
(1:10,000–1:25,000) were used to classify the senescence and cover of mature crowns in each plot. Regression analysis showed that, in dry forest, hollow-bearing tree
densities were strongly related to the remote assessment of mature crown cover, with an 8% increase in variability explained if senescence was also included (R2 = 0.50). In wet forest, mature crown cover alone was the best model (R2 = 0.53 when outliers were removed). Assessing senescence was less important in dense wet forests than dry forest
because trees take longer to form mature-shaped crowns and so mature-shaped crowns are more likely to have hollows. These results suggest that, with skilled photo-interpretation, aerial photographs can be useful for remotely assessing the relative density of hollowbearing
trees. This approach has the potential to greatly improve conservation planning for hollows and hollow-dependent fauna.

Item Type: Article
Authors/Creators:Koch, AJ and Baker, SC
Journal or Publication Title: Biodiversity and Conservation
DOI / ID Number: 10.1007/s10531-011-0018-z
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