Using LIDAR to measure the impact of tree height on yield and kernel recovery in mature macadamia orchards

Abstract

As the macadamia industry has matured, a presumed relationship between tree age and declining yields has been identified as a potential threat to the industry’s future sustainability. Despite some evidence to support performance decline in older trees, there is evidence that some farms continue performing well despite tree age.
There is both anecdotal evidence and logic to suggest that yield declines in older orchards may be related to tree height rather than age. Clarifying relationships between tree height and productivity could provide the quantitative information required to inform growers about the value of tree height reduction strategies in older orchards. This project aimed to source existing Light Imaging, Detection and Ranging (LIDAR) tree height data for a sample of mature macadamia orchards and relate this to annual yield and kernel recovery data sourced from the macadamia benchmarking project (MC15005).
LIDAR can be used to rapidly collect detailed information on tree or canopy height. For this project, existing LIDAR data was sourced and processed by an external partner (GES Mapping) for nine orchards in the older NSW Northern Rivers macadamia growing region. This canopy height information was then related to whole-orchard yield and quality data from the project “Benchmarking the macadamia industry 2015-2018”.
The project did not find clear relationships between macadamia canopy height and yield or quality, partly due to the low number of suitable orchards available for analysis. This low number was due to the spread of LIDAR mapping over many years, as well as a difference in the resolution of the benchmarking and LIDAR data sets. Also affecting the ability to identify relationships was the age of relevant LIDAR data. However clear understanding of how best to overcome these limitations was gained and practical recommendations made, including collaboration between current macadamia research projects.