Terrestrial laser scanning (TLS) data on tree crown morphology and neighbourhood competition from both Cuellar and Alto Tajo, Spain

1. Tree crown morphology is a key driver of forest dynamics, determining
not only the competitiveness of an individual but also the competitive
effect exerted on neighbouring trees. Multiple ecological theories,
including Metabolic Scaling Theory (MST), predict crown morphology from
first principles, but typically lack consideration of competition. The
accurate quantification of crown morphology to test theoretical
predictions, and the canopy interactions that could alter them, has
historically been limited by the simplicity and associated error of
traditional crown measurements. 2. In this study, we calculate high
resolution two and three-dimensional crown metrics from Terrestrial Laser
Scanning data for 1441 Pinus. sylvestris, P. nigra, Quercus. faginea and
Q. ilex trees from a water-limited forest community in central Spain and
test height-crown metric scaling relationships. We demonstrate new TLS
methods to define symmetric and asymmetric neighbourhood metrics based on
tree height, crown size and neighbour projected crown area, and test the
importance of neighbourhood genus diversity on crown morphology by
separating competition from congeneric and heterogeneric neighbours. 3.
Competition negatively impacted all crown metrics except crown depth where
only P. nigra showed sensitivity. Asymmetric competition was the strongest
driver of pine crown morphology, but oaks were more sensitive to symmetric
competition, in line with shade tolerance expectations. Congeneric
competition reduced Q. faginea crown size and changed its shape, but we
found no significant effects of heterogeneric neighbours. Most species and
crown dimensions had height-crown scaling exponents below those predicted
by MST, which may be due to water-limitation effects. Pines and oaks
showed large differences in crown depth to height scaling, with the former
shallower and the latter deeper, in contrast to theoretical predictions.
4. Synthesis. Our study is the first to demonstrate the ability of TLS to
characterise crown morphology from leaf-wood separated clouds and
competitive neighbour effects in a water-limited forest community, and to
use TLS metrics to test ecological crown scaling theory. Most crown
metrics scaled below theoretical predictions. Pines were more sensitive to
competition by larger neighbours and oaks to crowding from all neighbours,
with competition from neighbours of the same genus having a consistently
negative effect.