Jeff - Using shade cloth could result in two significant artifacts: (1) time of "canopy closure" and (2) inappropriate light quality at a given PPFD (photosynthetic photon flux density, µmol m-2 s-1 PAR).
If you just leave the shade cloth up the entire time, you are excluding a very important amount of light from the understory, which doubtless would have significant impacts on Alliaria. Earlier "canopy closure" -> less Alliaria success, IMHO. So ... perhaps you should track canopy closure in nearby forests and determine which dates to "close" the canopy and then "reopen" it later in the year. As we showed in the Smokies, there can be a month's difference in leaf-out time among species, and – as predicted – shade-tolerant species on mesic sites tend to leaf early, while shade-intolerant species on drier/less fertile sites tend to leaf later. Denser canopies not only reduce PPFD, they shift the red:far red ratio, which can have important morphogenetic effects. For an experiment the size you are contemplating, I don't think there is any practical way to shift the R:FR ratio appropriately. I believe that the plastic film we used in our lobeliad study, manufactured by the Mitsui Corporation, is no longer available, alas. Cheers, Tom Thomas J. Givnish Henry Allan Gleason Professor of Botany University of Wisconsin [email protected] http://botany.wisc.edu/givnish/Givnish/Welcome.html On 06/17/14, "Corbin, Jeffrey" wrote: > Hello Ecologgers - I am planning to conduct an experiment in which I > simulate several restoration strategies to control garlic mustard (Alliaria > petiolata) populations. I am leaning toward establishing new populations in > a meadow near my college's campus where I could more carefully control seed > input, etc. between plots. (The meadow is currently mowed, but mowing would > cease). I would erect a shading canopy with shade cloth over the plots to > more closely mimic the light environment that garlic mustard tends to > favor, and to also tamp down somewhat the meadow plants that would > ordinarily dominate such full-sun conditions. My hypotheses have to do with > comparing treatments that would all experience similar light levels, rather > than comparisons between light levels. > > My question: Does anyone have strong opinions about the artifacts of such a > shade cloth canopy? > > My thought is that the downsides of using shade cloth are offset by the > benefits of being able to create more of a "controlled laboratory" setup > than would be possible in a forested environment. I would be able to > control more variables (e.g. seed input, light levels) and therefore > isolate the particular variables (namely, my treatments) I am most > interested in. > > Obviously, though, if the artifacts of shade cloth are too great, then I > would not be able to apply my findings to the forested sites where such > questions would be meaningful. > > Thanks in advance for your thoughts. > > -Jeff > > -- > > ************************************ > > Jeffrey D. Corbin > > Associate Professor > > Department of Biological Sciences > > Union College > > Schenectady, NY 12308 > > (518) 388-6097 > > http://jeffcorbin.org > > ************************************ --
