Ed, I think there are many clear example of allelopathy in trees, and this certainly could be one of them!
thanks for the interesting photos! ryan On Fri, Sep 25, 2009 at 12:17 PM, Edward Frank <[email protected]> wrote: > Ryan, Paul, ENTS, > > I posted to see what others had observed about the species and and to see > what everyone thought about the case of the difference in vegetation. I will > not dismiss the idea of shade having an impact, but I thin something else is > going on well. There is a long history of chemical warfare between plants > and insects. The plants make their leaves poisonous or taste bad to insects > to limit their feeding. it seems reasonable that they employ the same > tactics to cut down on competitition from other plants. There are several > well known examples of this. I bet the process is much more common than > anybody realizes at this time. > > Of you choices below I thin the hawthorns are arriving and modifying the > site. When you look at ld field settings there commonly are patches of > hawthorns. They seem to grow in small groves well before other species are > successfully colonizing the old fields. The patches of hawthorns themselves > are pretty much the only species growing in these patches to the exclusion > of other species. The ground in these patches is commonly pretty bare with > only dead leaves from the trees on the ground surface. The only other > species that seem to be able to grow among the hawthorns are apple trees and > in some areas grapevines. Root competition is a possibility. I am still > leaning toward alleopathy as the major mechanism involved, but these other > ideas could provide an alternative explanation. Thanks for the attached > document. > > Ed Frank > > "Oh, I call myself a scientist. I wear a white coat and probe a monkey > every now and then, but if I put monetary gain ahead of preserving > nature...I couldn't live with myself" - Professor Hubert Farnsworth > > ----- Original Message ----- > *From:* Ryan McEwan <[email protected]> > *To:* [email protected] > *Sent:* Friday, September 25, 2009 9:14 AM > *Subject:* [ENTS] Re: Alleopathy > > Very interesting observation and photos! > > One tricky thing is understanding the history. Are those hawthorns growing > in those spots because of something unique about the spot, which makes it > less conducive to grasses? Or are hawthorns randomly arriving and then > modifying the site. > > If the latter, you still have the trick of trying to separate resource > competition from allelopathic effects. Attached is a very interesting paper > from Ray Callaway's dissertation research where changes in grasses under the > canopy of oaks in california was apparently related to competition from > surface roots. > > Its funny, in the entomology literature allelopathy is used to describe the > anti insect herbivore chemistry in plants, and it is well-recognized > (pedestrian, even), but it is a subject of some debate among plant > ecologists. > > > ryan > > > > On Thu, Sep 24, 2009 at 6:11 PM, Paul Jost <[email protected]> wrote: > >> Ed, >> >> I agree with most of what you have said. However, hawthorns have a nearly >> unique branching habit that is wide spreading just a few feet above the >> ground, casting shade most of the day. Other taller and/or more upright >> trees only block sun briefly during mid-day. That being said, I have seen >> some cases of the vegetation change abruptly at the drip line of hawthorns, >> too. That suggests that the shade may have only a secondary influence. >> >> Paul >> >> >> On Thu, Sep 24, 2009 at 4:52 PM, Edward Frank <[email protected]>wrote: >> >>> Paul, >>> >>> I have considered this. It is my impression that the hawthorns are >>> encroaching into the fields covered by the grass. I think that many of the >>> smaller hawthorns are younger than the age of the grass fields. Shade >>> intolerance could be a part of the effect I am seeing, but under other >>> scattered trees of other species that occur within or surround the grassy >>> areas the grass is growing underneath them without any of these visible >>> differences. The shade from these trees do not seem to be limiting the >>> growth of the grass. The grass does not seem to be affected noticeably by >>> the shade of these trees and the hawthorns are not any more foliage dense >>> than these other species. It is just under the hawthorns that I see this >>> effect. That is why I am think alleopathy rather than shade effects. >>> >>> Ed >>> >>> "Oh, I call myself a scientist. I wear a white coat and probe a monkey >>> every now and then, but if I put monetary gain ahead of preserving >>> nature...I couldn't live with myself" - Professor Hubert Farnsworth >>> >>> ----- Original Message ----- >>> *From:* Paul Jost <[email protected]> >>> *To:* [email protected] >>> *Sent:* Thursday, September 24, 2009 5:15 PM >>> *Subject:* [ENTS] Re: Alleopathy >>> >>> Ed, >>> >>> I wonder if those hawthorns predate the reed canary grass and if the reed >>> canary grass is too shade intolerant to grow underneath them? I've seen >>> similar effects with hawthorns over other grasses. >>> >>> Paul >>> >>> >>> >>> >> >> > > > -- > Ryan McEwan > The University of Dayton > http://academic.udayton.edu/RyanMcEwan > > > > > > > -- Ryan McEwan The University of Dayton http://academic.udayton.edu/RyanMcEwan --~--~---------~--~----~------------~-------~--~----~ Eastern Native Tree Society http://www.nativetreesociety.org Send email to [email protected] Visit this group at http://groups.google.com/group/entstrees?hl=en To unsubscribe send email to [email protected] -~----------~----~----~----~------~----~------~--~---
