Predicting soil depth using simple ground-based measurements of stem shape and taper in the butt swell section of individual Pinus radiata trees

ABSTRACT

Predicting soil depth using simple ground-based measurements of the tree stem has multiple benefits for precision (site-specific) forest management and estimating carbon stocks of plantation forests. Current methods of mapping soil depth rely on collecting a sufficient density of direct soil measurements, which is expensive and typically not feasible over extensive forest areas. The availability of detailed soil depth information under forest plantations is consequently sparse and this presents a significant impediment to precision forest management and the ability to estimate forest soil carbon stocks. In this study, we propose that the relationship between stem shape and taper in the butt swell of individual Pinus radiata trees and soil depth can be described in a simple empirical model. We demonstrate that shape and taper of the butt-swell section of the tree stem are as robust predictors of soil depth as individual tree height, and also have the advantage of being easy to measure from the ground. This finding has potential benefits for reducing the cost of soil data collection and improving fine-scale forest soil mapping.

KEYWORDS:

• Precision forestry
• soil surveys
• soil mapping
• soil depth
• stem form
• taper
• butt swell
• Pinus radiata

Acknowledgements

This work formed a component of the author’s PhD and we thank the thesis reviewers for their comments and feedback. We gratefully acknowledge the Cooperative Research Centre for Forestry for funding. We also extend thanks to Brian Jenkins (NSW Office of Environment and Heritage) for his assistance in classifying soils; Jan Rombouts (Forestry SA), Duncan Watt (State Forests NSW) and Christine Stone (State Forests NSW) for their assistance with data access, fieldwork and technical support; and Dr Jess Drake (Monash University) for her feedback on early drafts of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.