Research in real time

It’s been a busy spring around the Cregg lab.  In many ways, it feels more like mid-summer than mid-May.  One of the items my students and I have been with is installation of the Social Media Designed Tree Transplant Study (SoMeDedTreeS).  As loyal Garden Professor blog readers will recall, we conducted a Survey Monkey poll last fall to help develop a study plan to investigate tree transplanting practices of container-grown trees.  Based on the results of the survey we designed a study to look the effects of root-ball manipulation and post-transplant fertilization on 96 planetrees.  

Well, the time has arrived.  Last week we completed the first of two installations of the study – the second will be installed at the MSU Beaumont nursery soon.  Graduate research assistant Dana Ellison and summer research intern Aniko Gaal finished planting the first 48 trees last week at the MSU Hort Farm.  These two did yeoman’s (yeowoman’s?) work in handling the trees, applying the treatments and getting in the trees in the ground.  

Sometimes the best man for the job is a woman…

All of the trees are ‘Bloodgood’ planetrees that we have grown on in 25 gal. containers for past two years. The study was installed as a 3 x 2 factorial in a complete block design.  We have 3 root-ball manipulations: “shaving” the outer 1 in. of the rootball to remove circling roots; “teasing” apart the outer part of the rootball to pull appear circling roots; and “control” just pop off the container and drop ‘em in the hole.  The second part of the design is fertilization; with or without.  This results in 6 combinations (3 root-ball manipulations x 2 fert levels) times 8 reps = 48 trees total. 

Graduate Research Assistant Dana Ellison teases apart a root-ball

Summer Intern Aniko Gaal shaves a root-ball. Step one: remove the ‘pancake’ of roots  from the bottom.

Not to complicate life too much but I am considering a change to the protocol.  We will continue with the original rootball manipulation and fertilization trial at the second installation at Beaumont nursery.  In each test we would have 48 trees and 8 reps, which is better than a lot of landscape tree studies.   But given our recent discussion about mulching, I propose substituting with a mulch vs. without mulch treatment instead of the fert vs no fert at the Hort Farm installation.  We will water the trees once or twice a week to help get them established and then cut off the irrigation after about a month (simulating a city forestry department getting a budget cut and having to lay-off its temporary crews).  We will monitor soil moisture and tree water status in the subsequent months.   

Trees after planting

Before I make the change in the study, however, I’d like to get some feedback from our readers lest anyone feel there’s been a bait and switch.

21 thoughts on “Research in real time”

  1. Reaearch
    is not my strong suit, but this seems like too many variables. Don’t we already have a lot of research on fertilizing at planting? If you only tested the rootball treatments, you could have 16 trees per sample, which seems more likely to yield significant results.

    Similarly, if you start mixing mulch into the equation, you end up,with more variables and smaller samples. Current research suggests mulching the rootball is detrimental; to me, this suggest you would need a sample with no mulch, one with mulch over the rootball, and one with mulch starting outside the rootball, which further dilutes the samples.

    I know I am nobody in this situation, but I vote to stick with the rootball manulation and save the other stuff for another study.

  2. The approach and measurements would be similar. A couple of key differences – 1) we’re dealing with large, container-grown stock and 2) these are shade trees and not conifers. We got some nice data from the earlier study, but there are lots of ‘Yeah, buts’ when we try to apply to shade trees. As in ‘Yeah, but those were conifers’ or ‘Yeah, but that was a well-drained sandy loam’, etc… People will always find things to object to but I think we have a really good study system here.

  3. treedweller, Yes, there’s a trade-off, we’ll be conducting two smaller studies instead of one larger one. Looking at the root-ball manipulations we’ll have a total of 32 of e
    ach type between the two plantings. If really does make a difference, I think it will show up. I’m curious on the “research suggests mulching the rootball is detrimental” comment. Is there a reference you can share? Not being flip – I can be swayed by good data.

  4. @Treedweller, please do let us know about this research. Having published a pretty exhaustive review of the literature on this topic in 2007, I am really curious about such work. It flies in the face of the vast majority of published articles on the topic of mulching at planting.

  5. I think the mulch/no mulch experiment will mimic more what homeowners would do as I do not know many people who fertilize their trees after planting. Grass yet, trees no. Are you going to do some volcano mulching?

  6. I heard the bit about not mulching the rootball at a couple of different conferences. I will have to dig for the citation, but I will try. I thought it was more commonly known. As I recall, it was fairly new research at the time and perhaps we are only talking about one project. I will be back, with or without a reference.

  7. @Treedweller, as far as I know these are all from one person’s research program. I’m not going to disparage this person, because he’s published some good things, but one article makes this assertion in the abstract with no supporting data. In contrast, there are many articles demonstrating that mulch does benefit new transplants, including one published by Dr. Cregg.
    I’ve been concerned for some time about abstracts often not being representative of what the research results support (and many times people only read the abstracts). Peer review is supposed to catch this. In any case, the weight of the published evidence to date strongly supports mulching after tree installation (though there are some mulches that are better than others). That’s why we recommend the practice.

  8. LCS,
    [br]I, too, am a strong advocate for mulching correctly, but I would be curious to know how many of the studies that support mulching tried Gilman’s approach: leave the rootball exposed or thinly mulched, but follow existing protocol for mulching the area beyond the root ball. I am not trying to say all the previous research is wrong and this one study is right, but I also am reluctant to dismiss it solely because it hasn’t been replicated. Someone has to be first, right?
    You did inspire me to dig out my old Journal of Arboriculture to read the complete paper. Worth noting that he only recommends this practice during the initial period of establishment–only a few weeks in his Florida test site. Sorry to say, I do not know of an online link to the study, which compared this practice to traditional mulching in various depths, no mulching with chemical control of competing flora around the stems, and letting grass grow all the way to the trunks (7 trees per sample)–pretty complicated data set even without adding rootball manipulation.
    [br]To my mind, this points to the need for discrete studies on mulching and rootball manipulation instead of lumping them together in one.

    [br]But, again, I am a practitioner, not an academic, so I do not mean to criticize. I eagerly await the results regardless. Thanks for listening.

  9. @Treedweller, the paper I read didn’t look at trees or tree responses at all. It is solely an experiment using containers of soil, water and mulch. IMO, this experiment should not have been used as evidence against mulching new transplants. Now, if there’s another paper out there looking at tree response and/or stress related to mulching, I’d like to see that.

  10. Bert, how were the trees originally grown? Did you grow them yourself or were they containers from a nursery? I’m wondering about the likelihood of circling or girdling roots at the center of the root ball.

  11. LCS, the study I read tracked growth response in 49 live oaks (/Q. virginiana/) through seven different treatments. “Journal of Arboriculture” 30(5), pp. 311-316. It came out sept. 04. You threw me a second—I wondered how I could have overlooked the lack of actual trees. I do not know what study you saw. From the article: “Mulch placed over the root ball appeared to intercept water, which resulted in greater tree stress and reduced survival following light applications of water in the months after transplanting compared to trees with no mulch over the root ball.” and, “. . . keeping the ground free of vegetation had the same effect on survival and growth as mulching the first year after planting.” Trees were in sandy soil, FWIW.

  12. @Treedweller, the article I was referring to was published in January of this year.
    I had read the 2004 article several years ago. I’m not able to tell if the mulch they used was pine bark, which would not be something I’d recommend anyway. Bark mulches tend to be heavily suberized, and this waxy compound will most definitely repel water. Wood chips, on the other hand, are conducive to water interception and retention.

  13. Linda,
    We grew all the trees from bare-root liners graciously donated by J. Frank Schmidt and Son Nursery. The trees were originally potted in 25
    gal. containers in spring 2010 and grown on for 2 years. We destructively harvested a subset of trees (18) for biomass and nutrient analysis (including roots) in the fall. The roots looked good. The main issue I saw was some large girdling roots starting to form on the outer portion of the roots. These are removed when we have the root ball. For the tease treatment we clip them with the Felco’s.

  14. TreeDweller thanks for comments and the reference. Linda, the quote is in the Gilman and Groboski paper (p. 314). A couple of things to note here. They were planting oaks in full leaf in late summer in Florida. Based in their discussion, trees under these conditions would die in 3-5 days without irrigation. Certainly mulch can intercept small rainfall events and prevent moisture from reaching the rootzone, but on balance the ability to conserve moisture will greatly offset this effect.

  15. Thanks, Bert. At least you got bare root stock, meaning you know you’ve got good roots to start with. Looking forward to the results!
    Back to the mulch debate. Sorry, Bert, I’d pulled up the wrong Gilman paper (he had two in that issue back to back). And I would agree that planting deciduous trees in a hot and dry climate during the summer is going to confound the results.

  16. LCS, the first study in the paper used pine bark. The second (with the unmulched ball sample) used mulch “derived from freshly chipped /Taxodium distichum/ L. wood without bark.”

    I think part of the reason for the timing and sparse irrigation was to simulate likely conditions of trees planted in public spaces. I suspect a study that looked at trees grown by a homeowner in his front yard and lovingly watered according to accepted standards would yield different results. But does that necessarily mean there is nothing useful to learn from this research?

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