In article ,
(Rodger Whitlock) writes:
| On 21 Feb 2003 08:40:36 GMT, (Nick Maclaren)
| wrote:
| Rodger Whitlock writes:
|
| ...The USDA zones were devised with
| a specific purpose in mind, hardiness of *woody* material in the
| continental USA.
|
| Perhaps I am too stringent, but I regard anyone who invents such
| a scheme without thinking of its potential for extension as being
| a fool...at the very least they should have considered
| its relevance to herbaceous crop plants.
|
| Not really (imo). The only important herbaceous crop that
| over-winters, and for which hardiness is therefore an issue, is
| fall-sown wheat, afaik. The other big grain crop grown in the US
| is corn (maize), which is invariably sown in the spring.

Winter wheat is woody? Boggle :-)

More seriously, I agree that the vast proportion of the agricultural
crops are not herbaceous, but they are not woody either, and the
average extreme minimum is quite inappropriate. There are many,
FAR better, measures for those, INCLUDING simple latitude! So I can
assume that either they were living in some fantasy world or were
thinking about the minority of perennial agricultural crops.

While the majority of those are woody, it is NOT a dominating
majority, not by any manner of means. Strawberries, asparagus
and globe artichokes have been grown commercially and on a large
scale in the USA for a long time, and there are a fair number of
other crops that may have been.

| And it may be that the deviser realized that a system suitable
| for herbaceous material was impractical as their hardiness
| depends on many other factors than just temperature, whereas the
| hardiness of woody material (sc. fruit trees) is really dependent
| only on the winter low temperature.

Well, if that were true, it would be a justification for using
the scheme, though NOT for claiming its generality. But it is
not true.

The survival of fruit TREES is dependent FAR more on the average
daily minimum than the average extreme minimum - bark is quite a
good insulator, you know! - especially as the former is FAR more
closely correlated with how deeply the soil freezes. The confusion
arises because, in the contiguous USA though not more generally,
the correlation between the two is extremely high.

The survival of fruiting branches is probably more dependent on
the extreme low, but isn't the main issue anyway. The main issue
is the frequency of late frosts and their effect on the flowers,
as any fruit grower can tell you! And there are plenty of ways
to measure that much more directly.

| Horticultural material doesn't have enough economic importance to
| count in this kind of study.

Agreed. I was and am damning them for doing a bad job of what they
set out to do, not what other people may claim.


Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:
Tel.: +44 1223 334761 Fax: +44 1223 334679