Data from: Shade tolerance controls the spectrum of crown sizes and its response to local competition across European and North American tree species: Implications for light interception strategies

The size of a tree and its crown are key drivers of its ability to
intercept light. These characteristics are also constrained by
biomechanical and hydraulic limitations, leading to tremendous variations
in crown size and tree height between species. To date, there is no
consensus on how covariation between crown characteristics (i.e., tree
height, crown diameter and relative crown depth) control the spectrum of
crown sizes, nor on the species characteristics (i.e., species climate
niche or functional traits) that govern their variation. Using
species-specific allometric relationships accounting for local competition
data on individual crown characteristics of tree species across Europe and
North America, we showed that the spectrum of tree crown size is mainly
driven by two independent axes: one correlating tree height with relative
crown depth, and another linking crown diameter to crown volume. While
both angiosperms and gymnosperms exhibited similar patterns of covariation
for these crown characteristics, distinct ecological strategies emerged
for maximum tree height. We also highlighted that shade-tolerant species
were characterized by wider and deeper crowns and showed reduced
sensitivity to local competition in relative crown depth, indicating
enhanced competitive resilience. Finally, simulations of light
interception in virtual stands performed using a ray tracing algorithm
highlighted the importance of different crown characteristics in various
competitive contexts. Tree height was the primary determinant of light
interception in low competitive contexts, common in early successional
stages, whereas relative crown depth and crown diameter played a more
significant role in high-competitive contexts typical of late succession.
These findings suggest that shade-tolerant species, with their deeper
crowns, are better equipped to intercept light under competition and
ultimately emphasize the ability of shade tolerance to improve the realism
of forest dynamic models as it can be used as an indicator of crown size
and its response to competition.