Acknowledgments
We thank Gancho Slavov for encouragement to produce this article, Alvin Yanchuk and Dave Kelly for comments on early drafts and suggestions, Richard Primack for providing some references, and Stuart Fraser, Jennifer Lau and anonymous reviewers for helpful comments and suggestions. RDB was in receipt of office facilities from Scion, and MJB.’s contribution was covered by the New Zealand Ministry for Business Innovation and Employment through the Science Strategic Investment Fund (administered by Scion, the New Zealand Forest Research Institute Ltd).