New insights into tree architecture from mobile laser scanning and geometry analysis

The structure and dynamics of a forest are defined by the architecture and
growth patterns of its individual trees. In turn, tree architecture and
growth result from the interplay between the genetic building plans and
environmental factors. We set out to investigate whether (i) latitudinal
adaptations of the crown shape occur due to characteristic solar elevation
angles at a species’ origin, (ii) architectural differences in trees are
related to seed dispersal strategies, and (iii) tree architecture relates
to tree growth performance. We used Mobile Laser Scanning (MLS) to scan
473 trees and generated three-dimensional data of each tree. Tree
architectural complexity was then characterized by fractal analysis using
the box-dimension approach along with a topological measure of the
top-heaviness of a tree. The tree species studied originated from various
latitudinal ranges but were grown in the same environmental settings in
the arboretum. We found that trees originating from higher latitudes had
significantly less top-heavy geometries than those from lower latitudes.
Therefore, to a certain degree, the crown shape of tree species seems to
be determined by their original habitat. We also found that tree species
with wind-dispersed seeds had a higher structural complexity than those
with animal-dispersed seeds (p < 0.001). Furthermore, tree
architectural complexity was positively related to the growth performance
of the trees (p < 0.001). We conclude that the use of 3D data from
MLS in combination with geometrical analysis, including fractal analysis,
is a promising tool to investigate tree architecture.