Calculation of Functionnal Diversity according to the Oikos paper :

Mouchet M., Guilhaumon F., Villéger S., Mason N., Tomasini J. A., Mouillot D. Towards a consensus for calculating dendrogram-based functional diversity indices. 2008. OIKOS (Volume 117 Issue 5, Pages 794 - 800)

Code by François Guilhaumon (francois.guilhaumon@univ-montp2.fr) Xtree, Getlength.inner and Getlength functions by Owen Petchey (o.petchey@sheffield.ac.uk)