An empirical assessment of tree branching networks and implications for plant allometric scaling models

Abstract

Several theories predict whole-tree function on the basis of allometric scaling relationships assumed to emerge from traits of branching networks. To test this key assumption, and more generally, to explore patterns of external architecture within and across trees, we measure branch traits (radii/lengths) and calculate scaling exponents from five functionally divergent species. Consistent with leading theories, including metabolic scaling theory, branching is area preserving and statistically self-similar within trees. However, differences among scaling exponents calculated at node- and whole-tree levels challenge the assumption of an optimised, symmetrically branching tree. Furthermore, scaling exponents estimated for branch length change across branching orders, and exponents for scaling metabolic rate with plant size (or number of terminal tips) significantly differ from theoretical predictions. These findings, along with variability in the scaling of branch radii being less than for branch lengths, suggest extending current scaling theories to include asymmetrical branching and differential selective pressures in plant architectures.

Prediction of Human Glomerular Filtration Rate from Preterm Neonates to Adults: Evaluation of Predictive Performance of Several Empirical Models

“…There is also no consensus if there is a scientific basis to use any fixed exponent across all age groups even though in many instances there are several allometric exponents embedded within these age groups (4). Recent studies by many investigators have shown that the concept of quarter-power law or so-called theoretical allometry (fixed exponents of 0.25, 0.75, or 1.0) is incorrect (43)(44)(45)(46)(47)(48)(49)(50)(51). The exponents of allometry for drug clearance in preterm and term neonates are generally >1 (4,(8)(9)(10)(11)39).…”

Crown-fibre attribute relationships for enhanced forest inventory: Progress and prospects

“…The observation by Leonardo da Vinci that "all branches of a tree at every stage of its height when put together are equal in thickness to the trunk" (Richter 1888) has been interpreted as a feature of the tree's water transport system (Hari et al 1986), or as response to wind-induced stresses (Eloy 2011). In any case, there is a very strong relationship between the cross-sectional area of the tree stem at a point and the sum of the cross-sectional area of branches above that point (Hari et al 1986, Bentley et al 2013. A cumulative branch area constraint would ensure realistic branch amounts at the tree level, although climatic variation in the branchwood area to stemwood area ratio must be taken into account (Berninger et al 1995).…”

Effects of biophysical constraints, climate and phylogeny on forest shrub allometries along an altitudinal gradient in Northeast China

“…This is because small plants (e.g. herbs) lack some key features of trees: high stature, branching networks with a large number of branchings121314, and large amounts of secondary xylem15. For instance, for small plants MST predicted that (Table 1): H (height) ∝  D (Diameter), M L (leaf mass) ∝  M S (stem mass), M A (aboveground mass) ∝  D 3 and M A  ∝  H 3 (for details, see Appendix 1).…”