Estimating the extent of selective timber harvesting in private native eucalypt forests with multi-temporal lidar

Abstract

ABSTRACT A large proportion of forests in New South Wales (NSW), Australia, are owned privately. Timber harvesting is permitted in some of these forests, subject to approval processes and operational procedures. Recent changes to the codes of practice require landholders to provide timely and detailed reports of harvesting operations. Previously, however, harvesting could occur any time in a 15-year period (the length of the approval), and detailed self-reporting was not required. Consequently, the extent of timber harvesting in private forests, as well as the environmental impacts, are poorly understood. In this paper, we present the results of a recent study that used multi-temporal airborne lidar samples to precisely map harvesting-related canopy change in a 1-year period (2020–2021). The lidar transects were collected in a robust design-based sampling framework to enable estimates across the broader area. The methodology we developed principally used the difference in canopy height models between the two lidar datasets, along with customised height and spatial thresholds, to distinguish harvesting impacts from noise and natural disturbances. The methods were applied to northeast NSW (where most private native timber harvesting occurs in the state) to estimate the area of forest disturbed by timber harvesting in 1 year. Of the area of private native forests with an approval plan in place (455 000 ha), we estimated that 1665 ha (±492 ha at the 95% confidence level), or 0.37% (±0.11%), was harvested between April 2020 and April 2021. The robust and objective methodology presented here represents what is understood to be the most detailed assessment of timber harvesting in NSW private native forests to date.