  Large eddy simulation allows to incorporate the important driving physics of
turbulent flow through forest- or vegetation-like canopies. In this paper we
investigate the effects of vortex stretching and coherent structures on the
subgrid-scale (SGS) turbulence kinetic energy (TKE). We present three
simulations (SGS-d/s/w) of turbulence-canopy interactions. SGS-d assumes a
local, dynamic balance of SGS production with SGS dissipation. SGS-s averages
the SGS contributions of coherent structures over Lagrangian pathlines. SGS-w
assumes that an average cascade of TKE from large- to small-scales occurs
through the process of vortex stretching. We compare the consequences of
considering a forest of the same morphology as immersed solids or an immersed
canopy. Our results show clear differences in the characteristics of flow and
turbulence, while both the cases exhibit canopy mixing layers. The results also
show that the consideration of vortex stretching resolves about $18$% more TKE
with respect to classical Deardorff's TKE model. These observations indicate
that the aerodynamic response of the forest canopy is linked to the morphology
of the forest cover. Sweep- and ejection-events of the spatially intermittent
coherent structures in forests as well as their role in transporting momentum,
energy, and scalars are discussed.
