Structurally complex canopies create heterogeneity in resource
availability (Hypothesis 2)
We confirmed our second hypothesis that structurally complex canopies
increase heterogeneity of light and soil resources at the forest floor.
The structural complexity of the tree canopy influenced the distribution
of light within forests in space and time. In this study, structural
complexity increased with an increasing number of gaps in the canopy,
resulting in an heterogenous diversity of moving sun flecks at the
forest floor. In these sun flecks, the amount of light can be over two
orders of magnitude higher than in the shade (Chazdon and
Pearcy
1991). This can be beneficial for some species which are able to handle
the sudden increase, or detrimental for those which are sensitive to
full sunlight. As the sun is moving during the day, the spatial
configuration of leaves, twigs and stems will affect how long a certain
spot or certain plant will be irradiated. Furthermore, the different
incidence angles of the sun during the year will influence the spatial
alignment of the sun flecks. This also affects in which phenological
stage a plant is standing in full light or shade. Hence, on a very small
scale numerous species could be adapted to the many different light
conditions present over space and time. For soil resources, we found
that C:N ratio and potassium content increased with canopy complexity,
particularly for SSCI and DBHsd. A higher canopy complexity causes a
heterogeneous distribution of plant material in forest stands. In
combination with heterogeneous light distribution on the forest floor
and eventually heterogeneous water input, decomposition of organic
matter is altered at the small scale level which leads to heterogeneity
of the C:N ratio. In addition, DBHsd also increased light heterogeneity.
As the DBH is strongly correlated with tree age, results imply that a
stand with different age classes will increase light heterogeneity. The
correlation of potassium with canopy complexity was very weak although
it is possible there is a covariance with other variables.