[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

TT: Locust, Diatribe II

 -----------------------------------------------------------------------
Some notes on locusts, and a further diatribe on genetic diversity.  You can
find more on my web site, listed below.

1.  Thornlessness in locusts cultivars do not arise from breeding and
selection, but from people finding spontaneous mutants in the field.  The
very popular moraine locusts (thornless honeylocust, Gleditsia triacanthos
inermis) are propagated as seedlings and clones from a single huge tree in
western Wisconsin.  These breed true, so seedlings are also thornless.  Some
of the more recent cultivars are from selection efforts, but I believe that
even these originate from the thornless trees found in the wild.  Perhaps
some of the horticulturists on the list could comment.  In any case, progeny
of thornless females are generally thornless, and thornlessness is a natural
trait.

2.  Black locust, Robinia pseudoacacia, is an important early successional
species.   Originally from the Appalachians, its range was greatly increased
by Native Americans and by pioneers, especially for living fences (as with
our friend Osage-orange).  Today, it is the most widely planted North
American tree in southern Europe and North Africa.  Here at home, the tree
is beset with difficulties.  It not only has serious borer problems, as
Thomas Palmer pointed out, but also has a leaf miner that turn the leaves
brown by mid-summer in most of its range.

3.  Ron Neely is right on the money when he suggests that we should be
selecting for "polite" trees for cities.  I see nothing wrong with thornless
or fruitless cultivars, provided that adequate genetic diversity is
maintained.  I do, though, have a problem (and I hope we all do) with
covering entire cities with single clones of desirable cultivars.  The
danger of horticultural selection is not the introduction of thornless or
seedless cultivars, but the drastic narrowing of the genetic base presently
under way.  How many of us are aware, for example, that the largest
wholesaler of red maples is selling only two genotypes, or that the "modern"
honeylocust are mostly of clonal, not seedling origin?  We who are
interested in community forestry, rather than just in planting trees, ought
to be pressing the horticulture industry to abandon the current practice of
producing huge numbers of single clones of trees.  We need to restore
biodiversity to cities not only by increasing the number of species, but
also by increasing the number of genotypes within species.


Tom Kimmerer
Forest Biologist
University of Kentucky
Lexington KY 40546-0073
606-257-1824
Fax 606-323-1031
tkimmer@pop.uky.edu
Visit the TreeWeb at http://quercus.uky.edu/treeweb

-----Original Message-----
From: Owner-TreeTown@listbox.com [mailto:Owner-TreeTown@listbox.com]On
Behalf Of Thomas Palmer
Sent: Thursday, January 08, 1998 9:45 AM
To: TreeTown@Majordomo.Flora.Com
Subject: TT: Re: Locusts


 -----------------------------------------------------------------------
Here at Boston's southern edge, black locust is a common colonizer of
disturbed areas, often forming large patches (as if it spreads by root
suckers--does it?)

A longhorn beetle whose grubs inhabit this species, the locust borer, is
also common, and the yellow-striped adults are conspicuous on patches of
goldenrod in late summer.  Perhaps they are responsible for large amount of
deadwood seen amongst most locusts' smaller branches.

The locusts leaf out quite late--well into May--apparently later than any
other local species.  One drawback to them is that their shade is so light
that barbarous thickets of multiflora rose can flourish underneath them for
many years (these thickets fade rapidly under maturing black cherry, etc.).

Thornless honey locusts are common in street plantings, but do not
apparently escape.  There are, however, a few heavily-armed examples of the
parent species adventive here and there (they are not native to the area).
Does the thornless habit breed true?  Are the thorny adventives descendants
of the thornless plantings?

Thomas Palmer
Milton, MA



 ==============================(TreeTown)===============================


 ==============================(TreeTown)===============================
References: