Kill the tree to save it?
Are you cutting to conserve? There is a better way of finding out a tree’s secrets than cutting it down, says Meine van Noordwijk
Before you embark on another destructive sampling campaign to study allometrics for yet another tree species, please consider whether the non-destructive Functional Branch Analysis (FBA) model can do the job for you.
If your tree is in the normal parameter range for FBA characteristics it is likely that existing generic equations can be safely applied. The relationship between what you see when you stand in front of a tree and what you get when you harvest it is largely understandable and captured in the algorithms. Further empirical data collection can best be focussed on what appear to be the tails of the distribution, in trees that don’t look normal. And the FBA methodology guides you in capturing data on how strange any tree actually is. If your tree looks strange, chances are that it is an outlier that needs specific attention.
‘FBA is a promising non-destructive method that can produce accurate tree biomass equations when applied to trees which exhibit fractal branching architecture’, argue David W. MacFarlane and fellow researchers (I am one of them) in a study published this month.
We based our conclusion on a comparison of FBA with species-specific and mixed-species tree biomass equations derived from destructive sampling of trees in Western Kenya. There is some bias in the FBA, however, as well as uncertainty owing to variations in the branch diameter and length relationship but, all in all, the benefits probably outweigh the costs of more destructive sampling.
That’s not to say that choosing a particular method is easy. There are different schools of thought on whether a ‘one equation fits all trees’ approach is the best. One school prefers the use of generic equations (unless they are obviously way off the mark) while the other prefers fresh empirical data for every new species and situation. The latter involves a lot of cutting (the aptly named ‘destructive sampling’) in the name of conserving because most of the information needed for understanding a species is contained in the biggest trees.
Allometric scaling equations have been used by scientists to estimate the biomass and carbon content of trees during inventories of forests. Typically, the equations relate the diameter of the tree’s trunk at ‘breast height’ to the tree’s mass. These calculations have been proven to be accurate and, besides, a forest cannot be physically weighed. However, getting the initial data does involve cutting down sample trees, measuring and weighing them in order to develop a predictive equation for the whole forest.
Beyond pure empirics, however, there is a theory about tree architecture and the fractal geometry that underpins it that was made operational more than a decade ago in the FBA algorithm, captured in a spreadsheet model. This ‘pipe model’ theory assumes that a tree consists of unit pipes that support a respective proportion of foliage by connecting each piece of foliage to the roots, with various calculations that support this. But can you trust that theory? We suggest that you can.
Edited by Robert Finlayson
Read the article
MacFarlane DW, Kuyah S, Mulia R, Dietz J, Muthuri C, van Noordwijk M. 2014. Evaluating a non-destructive method for calibrating tree biomass equations derived from tree branching architecture. TREES. DOI: 10.1007/s00468-014-0993-2.
Read about Functional Branch Analysis
Van Noordwijk M, Mulia R, Harja D. 2013. Functional branch analysis (FBA): tree architecture and allometric scaling. In: van Noordwijk M, Lusiana B, Leimona B, Dewi S, Wulandari D, eds. Negotiation-support toolkit for learning landscapes. Bogor, Indonesia: World Agroforestry Centre (ICRAF) Southeast Asia Regional Program. p. 90–93.
This work is linked to the CGIAR Research Program on Forests, Trees and Agroforestry