Scientists in Scion’s Geomatics team have found that wilding conifers can be detected in grasslands using a combination of Lidar and multi-spectral values obtained from aerial imagery. Their research was recently published in the journal Remote Sensing.
Self-propagating conifers are invading indigenous and semi-native grass and shrublands across large areas of New Zealand. Recent estimates place the total area affected by wildings at 1.7 M ha and this area is growing, with a rate of spread estimated at 5%–6% per annum. Detecting and eradicating wildings before they start to produce cones is vital to controlling conifer spread and minimising their ecological and economic impact. However, identifying juvenile and scattered trees is complex and labour-intensive. Current methods rely on helicopter and ground-based surveys that are expensive and require highly skilled observers.
Remote sensing offers an alternative method to detect wilding pines automatically. The Scion group have developed a method for wilding conifer detection by combining Lidar data and aerial imagery. Fusing the two datasets was the key to developing the technique. Lidar was useful for providing elevation data for detecting taller isolated trees in short vegetation, while the spectral properties of the wildings were useful for differentiating them from other trees and shrubs.
This is the first time that Lidar has been combined with aerial imagery and used for wilding conifer detection. The approach offers a promising method for detecting wilding pines in relatively complex terrain with short tussock grassland intermixed with shrub species. Implementing the approach may be an effective and efficient means of monitoring and controlling the spread of invasive conifers over large areas of New Zealand.
Photo: The Lidar point cloud coloured with aerial imagery including the near-infrared band. Wilding conifers are clearly visible in the landscape and could be detected automatically..
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