Assessing the stem straightness of trees

Stem straightness is important in determining tree and log value. The ability to make an effective assessment before harvesting is useful for forest managers and practitioners to improve forecasting, planning, marketing and resource use. This Technical Note describes three methods for assessing stem straightness in standing trees: visual assessment, photogrammetric measurement and terrestrial lidar. It provides basic guidance on each of the techniques and recommendations for their use. If a low cost and high speed method is required the estimates provided by visual assessment may currently be the best option. However, the visual assessment method is highly subjective and only considers a relatively small part of the saleable stem. The other two methods are computer based and directly measure the shape of stems. The photogrammetric technique described here is highly accurate but technically demanding and time-consuming, so is currently only used for research applications. Terrestrial lidar can be used for plot-based measurements and is rapidly becoming more automated, which will considerably speed up the method and could make it more attractive to users.