Thinning and Wind-Firmness

What evidence is there that thinned stands are more “windfirm”? It seems not much, and there is a lot of caution about thinning in stands subjected to high winds.

From a Nova Scotia Government doc on thinning:

Approximately one-third of the trees can be removed during a commercial thinning. As with any partial cutting technique, risks of blow-down and breakage increase as more trees are removed.

Unthinned buffers are often left along exposed edges of the treatment area to create more windfirm conditions

Commercial thinning should not be considered in areas where soils are shallow, drainage is poor or where
stands are exposed to wind. Stands that have been previously treated by precommercial thinning are apt to be more
windfirm than those with no prior treatment.

Are irregular stands more windfirm?
W.L. Mason, Forestry: An International Journal of Forest Research, Volume 75, Issue 4, 2002, Pages 347–355.
ABSTRACT: Abstract
The proposed transformation of substantial areas of even‐aged plantation forests in Britain to irregular structures (‘continuous cover forestry’) has raised concerns about the likely wind stability of irregular stands. A review of the literature suggests that the major difference between irregular and regular stands is the lower (i.e. more stable) height : diameter ratio associated with the dominant trees in the former. This appears to be a consequence of the greater wind loading that these dominant trees have to withstand. Wind tunnel studies show no difference in wind profile within or above the two types of canopy. There have been few comparative root investigations in the two types of stand and no differences in rooting depth have been reported, although changes in root architecture could be anticipated as a result of greater wind loading. The implications of these findings upon windthrow risk in regular and irregular Sitka spruce stands has been explored using the Forest GALES wind risk model on sites of different wind exposure. The results suggest no difference in wind risk on sheltered sites. On sites of moderate exposure, an irregular stand at close to ‘steady state’ conditions could be more wind stable than a conventionally thinned regular stand. However, this advantage disappears with increasing exposure. The conclusion is that the promotion of irregular stands may provide structures with more stable characteristics, but these cannot be considered in isolation from the prevailing wind climate and the local site type.

Foresters’ Perceptions of Windthrow Dynamics in Northern Minnesota Riparian Management Zones
Jeremy C. Steil et al., 2009. NORTH. J. APPL. FOR. 26(2)/ Nuanced, cautions about thinning in relation to wind.

Windthrow in riparian buffer strips: effect of wind exposure, thinning and strip width
Jean-Claude Ruel et a;., 2001. Forest Ecology and Management Volume 143, Issues 1–3, Pages 105-113. “…Windthrow was not related to strip width or thinning”