[APWG] Ecosystem dynamics and 100 percent suppression by straw application Allelopathic straw keeping weeds out & moisture in duringdrought

[Wayne Tyson]

I have never seen 100 percent suppression of vegetative growth by anything, 
much less straw. I once concluded (erroneously) upon seeing a highly 
disturbed site "full" of the "worst" possible assemblage of alien weedy 
species I had ever seen, that it was "100 percent" devoid of any indigenous 
species after conducting a very cursory but pointed point/quadrat survey of 
the area, I soon discovered how wrong I was. Down between the weedy species 
I started finding small stands of "re-invading" indigenous species, 
successfully slugging it out with the weeds. Where these stands occurred, 
the invasives were clearly suppressed or entirely absent.

If Dremann cannot or will not cite the specific mechanisms of action 
relevant to the particular project he cites, I must continue to suspend 
belief until he supplies more evidence. I find his direction to a website 
insufficient to support his claims; moreover it is patronizing. I am well 
aware of the suppressive action of "shade," "robbing water," and "robbing 
nutrients," but am aware of no chemical action which has been demonstrated 
to be any percent effective in suppressing any weed growth, much less 100 
percent. I stand ready to be corrected and educated, based upon evidence and 
directly relevant scientific/scholarly/disciplined research. "Many" does not 
reveal what mechanisms of action are responsible for the claimed 100 percent 
suppression of the species Dremann mentions.

I do agree with Dremann that "straw," including that of standing or 
prostrate alien species, can be protective of surface evaporation as well as 
contribute to water infiltration and other beneficial effects. However, the 
presence of any straw can have adverse effects upon emerging vegetation as 
well. For example Robinson (????) studied this effect upon Stipa (Nasella) 
pulchra (dissertation at the University of Oklahoma, if my memory serves me 
correctly), and found that Stipa seedling survival was very low under such 
conditions. This, combined with our own observations, led us to develop the 
technique of planting very small seedlings in small colonies into the 
weed-infested areas. The colonies expanded, albeit slowly, in our 
experimental plots. We were never able to finish the large-scale project. We 
developed a unique planting method that was very cheap (as were the small 
seedlings), and, in terms of actual long-lasting results much more effective 
than mass-sowing, using far less seed, thus minimizing the depredation of 
wild stand seed stocks by over-collecting. As this work was never properly 
completed, we never published on it; however, we did mark the plots with 
buried iron markers that could probably be located with a metal detector 
today, some 32 years later, should anyone be interested in a follow-up.

WT

----- Original Message ----- 
From: "Craig Dremann - Redwood City Seed Company" <Craig at astreet.com>
To: <apwg at lists.plantconservation.org>
Cc: <craig at street.com>
Sent: Tuesday, November 13, 2012 1:10 PM
Subject: [APWG] Allelopathic straw keeping weeds out & moisture in 
duringdrought


> Dear Wayne and All,
>
> Thanks for your email.  I will comment below your email:
>
> Wayne--The grass-straw mulch is an interesting idea, and I certainly don't
> doubt
> that such a practice might have some utility in suppressing weeds, but I 
> am
> concerned about suppression of indigenous species as well.
>
> Craig--Native grass and wild oats straw are being used on a site that has
> been 100%  devoid of any natives for the last 12 years of monitoring, and
> you can see a painting of the site at http://www.ecoseeds.com/art3.html.
> Since the straw is 100% effective against annual weed grasses like cereal
> rye, Medusahead or cheatgrass, plus annual thistles like Italian and
> Yellow Star, I do not recommend straw to be used in areas where native
> seeds might still be in the soil seedbank.
>
> I wonder just which "allelopathogens" are responsible for the observed
> effects? What is their mechanism of action?
>
> There are many  Journal of Chemical Ecology articles an allelochemicals,
> that you can access through http://scholar.google.com and Dr. Liu and his
> team have been important authors since the early 1990s studying the
> allelochemicals involved.  His work was the first to sort out the
> allelochemical effects from the other plant suppression effects, like
> roots robbing water, or stealing nutrients, or shading of one plant by
> another, etc.
>
> Since most of the USA is in severe drought mode again, that you can see at
> http://droughtmonitor.unl.edu/ the straw mulch is keeping the soil
> surface moisture in place for much longer, perhaps twice as much moisture
> today--while we have a dry 40% relative humidity, barometer reading 30.20
> inches (no rain for a while),  and no dewfall at night--than in areas that
> do not have any mulch.
>
> Sincerely,  Craig Dremann (650) 325-7333
>
>
>
>
>
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