windthrow

D. Braun dbraun at u.washington.edu
Fri Mar 22 13:13:00 EST 1996



On 21 Mar 1996, Peter Sibbald wrote:

> In article <4iq1ov$do2 at cc-server9.massey.ac.nz>,
> Arnold Chamove <A.S.Chamove at massey.ac.nz> wrote:
> >It is said that windthrow is caused by trees growing so fast
> >that the roots do
> >not anchor them sufficiently when the weather gets wet and so
> >they blow over.
> >
> >If a low nitrogen, high K fertilizer were used, it should
> >inhibit the growth
> >in height but stimulate the root development.
> >Is this true?
>
> I have seen windthrow caused by at least two factors which your solution
> will not cure. One is where the rock is close to the surface and there
> just isn't enough soil to hold the tree up in that one bad gust you get
> every 30 years. The other is where "selective" logging has thinned a
> forest to the point where the trees no longer shelter each other. There
> may be other causes of blowdown but I cannot comment..
>
> peter sibbald

Why the "quotes" around selective?  I wonder if you are thinking of
so-called selective cuts which leave weak co-dominant trees about which
bow, die, or blow down with high frequencies after logging.  This need not
be the case.

It is true that windthrow is often associated with partial cuts.  However,
the amount depends on the diameter/height and live crown ratio of the
leave trees.  If done in stands where these are relatively low, the chance
of windthrow is increased compared to stands in which these values are
high.  Also, within a stand, the trees which are left can be the dominant
trees, or the weaker co-dominant trees which have lower ratios and
therefore are more likely to blow down; unfortunately, the latter is often
the choice.

Recently, there has been increasing emphasis on green tree retention, in
order to create more diverse stands with greater complexity in ecosystem
function, and stand structure, to provide habitat for more late successional
species, among other reasons. For the most part, this effort has been on
public lands in the western US, but it is increasing on private lands as well.
In drier interior forests, it has always been widespread as an aid to
regeneration, becasue of the effect of leave trees on microclimate; it
is a newer management direction in moister forest which has
traditionally been managed for timber with clearcutting.This effort's
success depends on both the stands that are
selected for partial cuts, and the trees marked in the selected stands.
Of course, soil rooting depth, root and butt rots, hardpans, and
surrounding topography and presence/absence of surrounding stands and
canopy height of the surrounding stands are additional variables.

		Regards, Dave Braun




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