- Introduction / Background / Justification
-Over a decade ago, a general theory of forest structure and dynamics (GTFSD) was proposed to account for power-law patterns of tree size and density scaling across forests (West et al. 2009; Enquist et al. 2009). The GTFSD assumes the origin of power-law scaling in forest ecosystems ultimately lies in the geometry of plant branching networks (West et al. 1999). It appeals to the intuition that forests are groups of trees fluxing energy and matter through branching resource distribution networks, analogous to the way that trees are groups of branches fluxing energy and matter through a single stem--the forest ‘is’ the tree. This work tests the idea that variation in the size structure of forest populations can be partially explained by the architectural branching traits of vascular networks in tree species.
- Objective(s)/Hypothesis(es)
i) Extract the branching traits of trees using LiDAR scans and census data to sample individual vascular networks from plot-level 3D scans

ii) Given the following hypotheses:

-Locally, branching traits vary across species

iii) Evaluate the corresponding predictions:

-Local deviations from the expected size distributions will be explained in terms of deviations from the expected branching geometry across species.

- Methods
We focus on the stem-radius frequency distribution which is the most fundamental representation of forest structure in GTFSD. Taking the expression for the density of individuals of a given mass, and the stem size of an individual of a given mass, we link the radius and length scaling of tree branches to the overall size distribution of individuals in a forest.

Size-frequency distributions were estimated from recent census data using standard methods (White et al. 2007).

Tree networks were extracted from 3D LiDAR data using spatial coordinates in stem census data and treeseg .
Once networks are sampled, processing will consist of fitting cylinders to individual branches to reconstruct the vascular hierarchy and measure branching traits (Raumonen et al. 2013)
- Results
-Radius scaling is uniform across tree species due to strong constraints on hydrodynamics in vascular transport. Variation in branch length scaling explained more variability in size structure across species.
- Implications/Conclusions
-Reconciling broad theories of organismal form and function with the magnitude of variation and diversity within ecosystems remains one of the central grand challenges in ecology. The relaxed GTFSD framework presented above could allow better predictions of scaling patterns within and across forests by measuring vascular networks.