[VIPS] Ideotype question (fwd)

'Toby' H D Bradshaw toby at u.washington.edu
Mon Oct 16 12:18:55 EST 1995


>From: Paul Heilman <heilman at coopext.cahe.wsu.edu>
>
>It seems to me that the danger in the ideatype approach is that it can be
>entirely too simplistic.
>
>Since high production depends on the crowding together of trees that are
>simply efficient at using their allotted space throughout their lifetimes
>(untill harvest),  much more is involved than:
>
>Juvenile branching advantages.  Syleptics do give early advantages but not
>so much as to be a key to high production. 

It does seem as though sylleptics have more to do with early radial
growth than with later growth, but are we willing to give up that
early growth in a 6-year rotation?

I'm also curious about the possible effect of sylleptics in the upper
crown contributing to reduced stem taper, which would improve
harvest index (since the current year's growth and often part of
the previous year's increment is below the 2 inch minimum used
for chips).

>Crown characteristics.  Support of the tree and other root system functions
>with minimum allocation of carbon to roots must be important to high
>production.

Jerry Leverenz also made this point.

>Same for behavior in stool beds, rooting from cuttings with high survival in
>plantations,  high harvest index for bole wood( w/o bark), disease and
>insect resistance, wood quality, tolerance to adverse site conditions,
>resistance to animal damage, etc

I agree that the "ideotype" extends beyond the crown, but we have
to start someplace!  :)

>For other than biomass and pulp, it is important to have straight boles with
>minimal taper.

See above on taper.  It seems as though syllepsis has its biggest effect
on diameter growth of the previous year's height increment, and so
sylleptic branches could be economically important throughout the
rotation, despite the fact that they aren't doing much at the base
beyond the first two or three years.

>Now if we can make some real progress on those features, maybe we can afford
>the luxury of crown ideatype breeding.

I would say that crown ideotype breeding need not be driven by purely
economic concerns, but can be justified as basic research with potential
commercial application down the road.

Don Dickmann has suggested that a "total ideotype" be treated as a
quantitative trait, but he recognizes that this approach will dilute
the effectiveness of selection on particular components of the ideotype,
such as crown geometry.

I think *experimental* ideotype breeding for crown characters has a
lot to recommend it -- the modelers have made explicit predictions
about the relative productivity of trees with varying crown characters,
and we're now in a position to apply genetics to help them test their
models.

-Toby Bradshaw
toby at u.washington.edu




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