Abstract
Forests cover around 30% of the Earth’s land area but are becoming
increasingly fragmented. In many parts of the world, edge effects
dominate most of the forested area. Inhomogeneous landscapes and
non-ideal weather conditions generate fluid dynamical features that
cause observations to be inaccurately interpreted, biased, or
over-generalized. We discuss progress towards capturing the complicated
reality of forests in turbulence-resolving models. Scalar transport does
not necessarily follow the flow in complex terrain, meaning scalar
quantities are rarely at equilibrium around patchy forests, and
significant scalar fluxes may form in the lee of forested hills. Gaps
and patchiness generate significant spatial fluxes that current models
and observations neglect. Atmospheric instability, driven by
differential heating of the canopy, increases the distance over which
fluxes adjust at forest edges. For deciduous forests, the effects of
patchiness differ between seasons; eddies reach further into rougher,
leafy canopies. Air parcel residence times are likely much lower in
patchy forests than homogeneous ones, particularly around edges.
However, the modeled probabilities of gusts are sensitive to the model
setup, including any stochastic element. Eulerian parametrizations now
allow researchers to investigate forest chemistry and particle
deposition in the turbulent flow. The reconfiguration of plants under
wind loading can be captured efficiently by modifying the velocity
dependence of the aerodynamic drag. Future challenges include: (i)
targeted observations in patchy landscapes; (ii) developing
parametrizations of turbulent transfer applicable to larger scales;
(iii) developing numerically efficient improvements to model forest
structure; and (iv) simulating a greater range of weather conditions.