Author: Bert Cregg

Just a little bit of show and tell today.  The week before last the Central Region of the American Conifer Society (ACS) hosted the National ACS meeting here in Michigan.  Over 300 conferites gathered to discuss their favorite plants and share their conifer addiction.

The highlight of the meeting was a field trip to the Harper Collection of Rare and Dwarf Conifers at Michigan State University’s Hidden Lake Gardens.  The Harper collection, which was donated to MSU by noted plantsman Justin ‘Chub’ Harper is a world-class assemblage of conifers and includes over 550 plants displayed in a wonderfully-designed layout.

To add a little fun to the outing, each ACS member was give three pink pin-flags and asked to mark their three favorite conifers.  Tough to choose just three from this collection. 

ACS members descend on the Harper Collection

Adrian Bloom adds his vote to Metasequoia glytostraboides ‘Gold rush’

The elephant tree. Pinus strobus ‘Pendula’

Got my vote but wasn’t the winner: Taxodium distichum ‘Pendens’.  If the meeting had been in October when this tree is in fall color, this would have won hands down.

And the winner is… Abies concolor ‘Blue cloak’

In prepping grad students for their first big talk at a scientific meeting I always tell them everything will be fine – until the first data slide hits the screen.  The audience will nod knowingly during the introductory comments and even during the materials and methods, but data charts and tables are to scientists what chum is to hungry sharks.  So clearly I should have known better than to post figures without error bars in last week’s post.  In my defense, SigmaPlot, my program of choice for scientific graphing, currently resides on my old laptop which is running slower than molasses, so I did the ‘quick and dirty’ and used PowerPoint on my desktop.  Yes, my mother did raise me better than the present a measure of central tendency without an indication of dispersion.

So, duly chastised and humbled, I present the latest (July 12) volumetric soil moisture values from the SoMeDedTREEs.  N=8 for all means *=means are different at p=0.05.  The table below is more complete than last week’s post, which only presented the means from measurements just outside the container root ball.

Mean (std err) volumetric soil moisture of planetrees at MSU Hort farm, with and without 3” of ground red pine mulch

Inside container ball			MC%	std. err.
	15 cm	Mulch*	10.7	1.9
		No	6.4	0.6
	45 cm	Mulch	10.6	1.5
		No	10.5	1.7
Outside ball
	15 cm	Mulch*	21.9	1.3
		No	16.7	0.7
	45 cm	Mulch*	26.1	0.9
		No	23.1	0.9

As I noted a few posts back, this summer marks the 10^th anniversary of the discovery of emerald ash borer (EAB) in southeast Michigan.  While a lot of progress has been made on many fronts in the battle against EAB, the outlook for ash trees in North America still looks bleak for the foreseeable future.  Ash trees, both green and white ash, were popular choices as street and landscape trees throughout the Midwest and elsewhere.  In Michigan ashes comprised up to 30% of the overall tree cover in some communities.  Like chestnut blight and Dutch elm disease, EAB provides a cautionary tale of the destructive potential of invasive pests.  As global trade continues to increase (and the potential for exotic pest movement along with it), the most practical defense in the near term is to spread the risk and increase species diversity.  In spring 2003 Bob Schutzki and I installed an ash alternative species demonstration at the MSU Tollgate Extension Center in Novi, MI, near the epicenter of the EAB infestation.  As we near the completion of the 10^th growing season of the planting we can take stock of some of the better selections.

Dana (R) and Aniko assess the lindens

Hophornbeam Ostrya virginiana


Hardy rubber tree Eucomia ulmoides


Northern pine oak Quercus ellipsoidalis (R) can maintain good leaf color even when soil pH turns Q. palustris (L) chlorotic.

American Sentry linden Tilia americana ‘McKSentry’

Baumannii horsechestnut Aesculus hippocastanum ‘Baumannii’

State street maple Acer miyabei ‘Morton’

Thanks to our partners!

If you live anywhere east of Montana you know that two-thirds of the country has been roasting under record heat for the past few weeks.  While the weather has been a bane to farmers and many others, it has provided us with an ideal set of conditions to begin to look at the responses in the SoMeDedTREES project. 

To recap, we installed two experiments with 25-gallon container-grown ‘Bloodgood’ planetrees.  In both experiments we applied one of three treatments to the root systems at planting: 1) “Shaved” the outer  portion of the root system to remove  circling roots, 2) “Teased” apart the outer portion of the rootball to remove circling roots and 3) “Control” where we did nothing to the root system, or “Pop and drop” to use Linda’s terminology.  One set of 48 trees was planted at the MSU Beaumont Nursery where half the trees were fertilized (400 g of Osmocote 15-9-12) and half were not.   The second set of trees was installed at the MSU Hort Farm.  At this site I made an executive decision to change the Fertilizer treatment to a Mulch comparison based on our discussions related to a recent study that suggested mulching does not actually reduce evaporation or improve soil moisture. We applied 3” of ground red pine bark in a ring approximately 40” in diameter around each tree in the “Mulch” treatment and left the other half of the trees with bare ground.

Overview of SoMeDedTREEs site at MSU Hort farm

If I had a hammer…  Summer Intern Aniko Gaal demonstrates proper form for installing TDR rods in clay soil (also works for relieving frustrations with your choice of summer employment).

Obviously this is a long-term study and we’re a long ways from any definitive results – especially with regard to the impact of the root treatments on eventual root structure – but the point of this exercise is to allow GP blog readers to come along for the ride and get a glimpse of what goes into our research.  For the mulch study one of our primary objectives is to track changes in soil moisture and tree stress associated with mulching.   In order to monitor soil moisture we are using a technique called Time Domain Reflectometry or TDR for short.  A TDR system is basically a glorified coaxial cable tester.  The system sends out an electrical pulse to a set of metal rods that are buried in the soil and then measures the return signal.  The greater the moisture in the soil, the longer it takes for the signal to return.  The instrument converts this information into volumetric soil moisture (% volume water/volume soil).  For this study we installed rods at two depths 15 cm (6”) and 45 (18”). Rods were installed 12” from the trunk of the tree at the edge of the root ball (inside) and 24” from the trunk of the tree (outside).

Volumetric soil moisture at 15 cm and 45 cm depth of planetrees with and without mulch at MSU Hort farm, Summer 2012.

We planted the trees in mid-May and watered them from a portable water tank once a week until mid-June.   Since then we’ve left the trees on their own.   So far the trees actually seem to be fairing pretty well given the heat.  We have one tree that is beginning to drop a few leaves but most look pretty good.  Our soil moisture readings to date are consistent with a couple of related studies that we’ve done that show mulching increases soil moisture.  Soil moisture was greater at the 45 cm depth than at 15 cm and the difference between mulch and no mulch was greater at the shallow depth.  Still very early, obviously, but we will continue to update – sort of like FOX Radio news: “We report – you decide.”

Many blue spruce trees in our area are suffering from a progressive decline.  This is more than the usual combination cytospora canker & rhizospaera needlecast that tend to make most mature blue spruce look crappy.   The current syndrome has been linked to phomopsis blight and affected trees show increasing branch die-back and in some cases trees go from a having a few dead branches to completely dead in a 3-4 years.  Because of this alarming and pervasive issue, I’ve been asked to put together a list of alternative selections for blue spruce as part of my extension duties.

Whenever I put together one of these lists I always include my all-time favorite conifer; a graceful, elegant tree that is native to the Pacific Northwest but grows well in Michigan and fulfills a range functions in the landscape.  Of course that tree is… well, that’s the problem.  I’m not sure what to call it anymore.  In Mr. Chance’s 6^th period Botany class at Olympia High School 30-some years ago I learned it as Alaska yellow cedar, Chamaecyparis nootkatensis.  Had to get the Latin spelling right to get full credit.  When I moved to Michigan in 1999 I heard people talk about Alaska cypress or Nootka cypress.  Took me a minute but I figured it out.  At least I could take comfort in the scientific name.  After all, as Mr. Chance taught us, we use scientific names to eliminate confusion; using Latin since it is ‘dead’ language and not subject to change.

About the same time I came to MSU a new conifer was discovered in Vietnam.  The new tree, Vietnamese golden cypress, was originally described as Xanthocyparis vietnamensis.  Moreover, this new species was closely related to nootkatensis, so both were added to the new genus.  Subsequently it was argued that the genus Callitropsis was originally used for Xanthocyparis nootkatensis before it became Chamaecyparis.  So, based on precedent Callitropsis was the proper genus for nootkatensis and vietnamesis.  Got it?  Well, as Lee Corso would say, Not so fast my friend…   Here’s the rest of story from the font of all knowledge, Wikipedia:

‘In 2010, Mao et al. performed a more detailed molecular analysis and placed Nootka Cypress back to Cupressus. However, this is disputed, as the tree would compose a monophyletic subgenus. "The argument that it warrants treatment as a monotypic genus is not without merit, in which case the correct name is Callitropsis nootkatensis."’

Then the Wikipedia poster shows their true colors.

‘Although acceptance of the revised classification of this tree is widespread among botanists, inertia in the horticultural and forestry industries (both typically very slow to adopt the results of botanical research), mean the name Chamaecyparis nootkatensis is likely to continue being listed in many situations.’

So let me get this straight.   Taxonomists have put the tree in four different genera within ten years and in one sentence current molecular analysis puts the tree in Cupressus (which the International Botanic Congress approved last year) but that’s disputed by other botanists – and WE’RE the idiots because we won’t jump on board?!

Posted by Sara Tanis and Bert Cregg

NOTE: Last week I gave an update on the 10-year anniversary of the discovery of the emerald ash borer in the U.S.  In response to the post, Sonia John raised a couple of points:

“Please share your knowledge about the status of efforts to: 1. introduce insect species or other biocontrols that predate the EAB, and 2. evaluation of the degree of resistance to EAB of Asian (and European) Fraxinus spp. as well as Asian/N.American hybrids)” 

Sonia is right on the mark because these two areas of investigation probably represent the best long-term solution to the EAB issue.  As I mentioned last week, EAB was a relatively obscure insect in its native range in Asia, rarely causing any significant damage.  This suggests that native (Asian) ashes are resistant, native biocontrols keep it in check, or both.

In order to reply to Sonia’s post I enlisted the aid of Sara Tanis.  Sara is a Ph.D. student in the Department of Forestry at MSU (and a former MS student of mine) and is studying variation in susceptibility to EAB among ash species for her dissertation.

 

Biocontrols 
Almost from the moment that EAB was first identified, USDA and US university scientists have been working with their Asian counterparts to identify diseases or other insects that keep EAB under control in Asia.  From this work, researchers have identified several parasitic wasps that affect EAB.  Some of the wasps lay their eggs on EAB eggs – when the wasp larvae hatch they feed on the EAB eggs.  Other wasps lay eggs on the EAB larvae and then the wasp larvae feed on the EAB larvae – yeah, pretty gross.  (for more information visit http://www.emeraldashborer.info/biocontrol.cfm).  A state of the art bio-control research facility has been established by USDA-APHIS in Brighton, Michigan to rear these parasitoids and to date they have been released in several locations throughout infested areas of the United States.   We know the wasps are highly effective in parasitizing EAB eggs and larvae in China.  The question is whether we can establish viable and self-sustaining populations in the US.  

  

In addition, a native parasitoid Atanycolus cappaerti, a Braconid wasp described in 2009, is also proving to be successful in curbing EAB densities.  At the MSU Tree Research Center, we have seen more than 70% parasitism on EAB in black ash and green ash trees.  Hopefully turn-about will be fair play and lack of co-evolution will back-fire on EAB and our all-American native wasp can do a number it.  All together now: USA! USA! USA!

 

Everybody’s All-American? Atanycolus cappaerti  Photo: David Cappaert

Variation in resistance among species.

One of the main points to hit home here is the fact that even though Asian ash are considered “resistant” in their native habitat, in North America where EAB population densities are extremely high, they do succumb to EAB attack despite their co-evolutionary history.  Here at MSU, Andrea Anulewicz has done extensive host preference work using a variety of ash species including those found west of the Rockies (F. anomala), south in the Carolinas (F. caroliniana), Europe (F. excelsior and F. ornus), and an evergreen species found in Central America (F. uhdei).   All of these ash species have proven to be viable hosts for both adults and larvae.  However, EAB do prefer some ash species over others.  At the top of the menu are green ash and black ash, less preferred is white ash, and least preferred is blue ash, our hope for the future.   In the field, of the five ash species that EAB has encountered to date, blue ash appears to be the most resistant or the least preferred ash species native to North America.  In order to quantify differences in EAB related mortality between blue ash and white ash, we inventoried all living and dead trees in two woodlots in Southeast Michigan in 2010
620
-2011.  We found approximately 68% (402 out of 590 trees) of the blue ash trees in these sites were alive, and most (60%) appeared healthy!  We calculated that these trees were subject to at least 178,000 beetles (calculated from dead ash phloem area) over the course of a 15+ year invasion.  That is a lot of beetles.  In contrast, only 29 of the 312 white ash trees survived, and these were likely too small to be infested during the peak of EAB invasion (around 2005).   Blue ash survival has also been reported in Ontario and Ohio.  Many of us assumed that there would be 99% ash tree mortality across North America.  Don’t get me wrong, many forests and urban areas DO have mortality this high because of the ash species found there.  However, we now have something positive to report.  Evidence suggests blue ash trees will persist in forests ravaged by EAB.  In addition, blue ash resistance might also enhance bio-control efforts.  The combination of a less susceptible host and a specialized parasitoid could maintain EAB populations at densities blue ash trees could sustain and possibly aid in slowing the spread of EAB across the US.  At this time, we don’t know the exact mechanism of blue ash resistance, but we are working on it.  Bert serves on my graduate advisory committee, so I’m sure he will keep you up to date as we learn more.  There are likely several factors that contribute, once isolated, we hope to incorporate these mechanisms into other ash species and introduce less susceptible ash tress back into the landscape. 

Variation in susceptibility to EAB between blue and white ash

USDA and Ohio State researchers are working with the Dawes arboretum to hybridize North American and Asian ashes.  This work is based on the model that the American Chestnut Foundation has used to breed blight-resistant chestnuts; starting with an Asian – American hybrid (1/2 Asian; ½ American) and then making repeated back-crosses with the American species to increase the desired horticultural characteristics while maintaining the resistance from the Asian parent.   Clearly this is a long-term proposition and so far the efforts have been slowed by poor crossibility among species and insect damage to seed.   Moreover, earlier hybrids that have been produced crossing Manchurian ash have not exhibited any resistant qualities.  Breeding work, of course, is always a numbers game.  As a point of comparison, the USDA National Arboretum’s program to select Dutch elm resistant American elms found only 11 survivors out of 21,000 seedlings screened for tolerance.

This summer marks an anniversary of sorts.  Shortly after I joined the faculty at Michigan State University in the fall of 1999 MSU Extension began to get reports of dead and declining ash trees in and around Detroit.  Since ash trees had relatively few serious pest issues and none that routinely caused mortality, the mysterious ash decline was attributed to cumulative environmental stresses, ash yellows or various site factors.  In the summer of 2002, however, a little-known exotic beetle from Asia, emerald ash borer (Agrilis planipennis) was identified as the causal organism.  The beetle was so obscure that the first insects collected had to be sent to an entomologist in Eastern Europe for identification.  The summer of 2002 has become a point demarcation for those that work in landscape horticulture or urban forestry in the Midwest and East; now it’s before EAB and after EAB.  Prior to 2002,  EAB was completely unknown in the US, today it has been identified in 15 states and 2 Canadian provinces.

EAB range June 2012

In the intervening 10 years we have learned a lot about the beetle.  In fact, it seems likely that we have learned more about EAB in 10 years than just about any tree pest in history.  I did a quick Google Scholar search and there have been nearly 600 articles published with ‘emerald ash borer’ in the title since 2002. Below are some highlights of what we’ve learned.

In lower Michigan, EAB is able to complete its life cycle in one year.  Adults emerge in early summer, feed on ash tree foliage, mate, and lay eggs on ash tree bark.  When the eggs hatch the larvae burrow into the tree and feed on phloem under the bark leaving extensive galleries.  The larvae eventually pupate and overwinter before emerging as adults the next summer, leaving a characteristic D-shaped exit hole.

EAB life cycle – National Plant Gemplasm System

Host range.  When EAB was first discovered very little was known about the insect, even in its native range in China and Korea.  At the time, information from its native populations suggested that EAB could affect trees outside the genus Fraxinus.  Research in the US, however, has clearly demonstrated that EAB adults can only feed on Fraxinus foliage and EAB larvae can only develop by feeding on ash tree phloem.  So there is little likelihood that EAB will ‘make the jump’ to other tree species outside of Fraxinus.  That’s the good news.  The bad news is that all North American ashes are susceptible to EAB.  There are some differences in relative susceptibility; green ash trees are probably the most susceptible, while blue ash trees will hang in there the longest. Eventually, though, all North America ashes will succumb.

How not to stop an exotic invasion.  While much of what we’ve learned about EAB has been through systematic research, we have also learned by trial and error.  Immediately after EAB’s discovery regulators decided the best approach was try to eradicate the pest.  Historically eradication efforts have not been very successful but decision-makers at the time may have been buoyed by the recent successful eradication of Asian long-horned beetle in the Chicago area.  To make a long story short, EAB eradication failed.  In 2002 the EAB infestation was made up of a core population in and around Detroit and a series of isolated outlier populations.  The eradication strategy was analogous to fighting a forest fire – build a perimeter around the main hot spot and eliminate outlying ‘spot fires’ as soon as they appear.  With EAB the fire fighting analogy broke down for two reasons.  First, it was impossible to contain the main population since the insect was continually carried out of the core area, largely by campers moving firewood (It’s a Michigan thing).  Secondly, fire-fighters can rapidly respond to isolated spot fires because smoke identifies the location almost immediately. With EAB there is typically a 2-3 year lag period once the beetle moves into an area until trees begin to show symptoms.  By that time the population is well established and has likely already spread beyond any potential containment. 

Saving your ash. In 2002 there was no data on effectiveness of insecticides against EAB.  Therefore researchers and extensions specialists, did not provide recommendations for arborists to control it.  Several arborists ignored our advice and treated trees in the core infestation areas in Detroit with insecticides.  In some cases those trees are still alive.  So were the arborists right and were we wrong?  I think both groups did what they had to do.  As scientists and extension specialists we can’t make recommendations in the absence of data.  In many cases the arborists took a ‘sledgehammer’ approach, using multiple products and multiple applications. They saved some trees but they probably used more chemical than they needed to and probably hit some beneficial and other non-target insects along the way.  Today, with the benefit of nearly decade of research, we have effective controls for individual trees, primarily using trunk-injected systemic insecticides.

http://www.emeraldashborer.info/files/Multistate_EAB_Insecticide_Fact_Sheet.pdf

What’s next.  The range of EAB continues to expand.  While it is possible to protect individual trees, we need to remember those trees will require treatment in perpetuity to survive.   The development of hybrid ashes – similar to what has been done with elms – seems like to most likely scenario that will get ashes back into the landscape.  In the meantime, EAB joins chestnut trees and elms as another reminder of the need to diversify our landscape in order to reduce risks associated with exotic pests.

Admitting you’re wrong is difficult.   For exhibit A see the recent discussion between me and Jeff over alternative nursery containers.  We all like to think we’re open-minded but  when push comes to shove we all end up like the Fonz on Happy Days when it comes time to say ‘I was wrrrrr… I was wrrrr….  I was not exactly right.”  http://www.youtube.com/watch?v=uwkU8-d1gIk   As scientists we’re supposed to be objective and base our judgments on verifiable data and careful and repeatable observations.  But, as humans, we all have biases and preconceived notions that are hard to get around.

So here’s a challenge for our Garden Professors readers (and my fellow  GP’s too).  Give an example of a case where you’ve changed your mind about a landscape or gardening practice or product.  And what did it take to change your way of thinking and make you say, “Ya know, maybe I was not exactly right.”

I’ll start.  I have long been dubious about is the use of plant growth retardants (PGR’s) on landscape plants.  PGR’s are chemicals that reduce plant growth, usually by inhibiting shoot elongation.  There are a variety of PGR’s on the market but most work by inhibiting plant growth hormones such as gibberilin or auxins.  PGR’s have long been used by bedding plant producers to make plants more compact and easier to handle and ship.  One PGR, paclobutrazol, has been heavily marketed in recent years to control growth in landscape trees and shrubs.  The effectiveness of paclobutrazol at controlling plant growth has been well established in the literature, though there are some exceptions.  My long-held skepticism toward the landscape application of PGR’s stems from a couple factors.  First, the marketing claims are pretty fantastic: Not only does it control growth but it improves drought tolerance, heat tolerance, insect resistance, and disease resistance (no word on how it does on getting spots out of rugs).  Second, just because something works on containers of annuals in a greenhouse doesn’t mean it will work on trees and shrubs in the field with variable soils, weather, etc.  Third, why bother?  If something is growing too fast; back off the fertilizer, head it back with the Felco’s, or take it out and put something more appropriate there.

What changed my mind.  I’ve seen a couple of effective applications of PGR’s on trees and shrubs that have made me re-evaluate my opinion.  One was at a program at the Indiana Arborists Association a couple years ago.  The study tracked pruning cycles following utility line clearance pruning.  They found that treating trees with paclobutrazol following pruning reduced re-sprout growth and extended the cycle time between pruning by 2 to 3 years – which is a big deal to utility arborists.  More recently, I’ve been observing shrubs here on campus that our landscape service group has been treating with paclobutrazol after pruning.  Typically many shrubs are rejuvenated after pruning and put on a big flush of growth.  The PGR application was effective in keeping this in check.  (Some examples with burning bush appear below). Even to my highly skeptical eye, the treated plants just looked a heck of lot better than the untreated.

Do I believe all the marketing claims made about PGR’s for landscape plants?  No. But for extending pruning cycles and keeping plants in check, I have to admit I was not exactly right. 

Burning bush with PGR app.

Burning bush without PGR app. (Note treated and untreated were growing in same bed)

By controlling growth after pruning PGR application can help keep these shrubs in line and lengthen the time between pruning cycles.

My wife and I were in Washington DC a few weeks back for a wedding.  I’ve been to DC a handful of times and it is one of my all-time favorite places to visit.  I love history so the memorials, monuments and Smithsonian museums are all high on my list.  But DC has a lot to offer plant geeks as well.  In honor of Memorial Day and the unofficial start of summer vacation season, here are my top three DC Horticultural Highlights.

National Botanic Garden.  Located nearly adjacent to the US Capitol, the Botanic Garden is easy to miss if you’re not looking for it.  The garden is comparatively small but offers a nice respite from the hustle and bustle (and interminable school groups) of the rest of the National Mall.  It’s also a cooler oasis to beat the heat if you visit the Mall in the summer and offers some unique views of the Capitol.  The conservatory has great on-going and rotating exhibits.  A current one was on medicinal plants.

The National Arboretum.  The Arboretum is a little more of challenge to get to and probably best if you have a car.  Some highlights include the Gotelli collection of dwarf conifers, the grove of state trees, and The National Bonsai & Penjing Museum.  Be sure to check on hours of operation before you go.  The first time I visited the Arboretum I arrived at 4:30 thinking I would have a several hours of prime late afternoon and evening light for pictures, only to find out they closed at 5:00.

Arlington Cemetery. Arlington is a special place is so many ways.  If you’re an American, these are images steeped in our collective consciences; the tomb of the Unknowns, the Kennedy gravesites, the Challenger memorial, and tens of thousands of headstones marking those that gave the last full measure of devotion.  The grounds are wonderfully tended and, like the Botanic Garden, provide a break from the din on the nearby National Mall.  The Cemetery grounds include dozens of memorial trees and several state Champion trees. Motorized trams are available but if you can walk a couple miles it’s a fascinating and moving place for a stroll.  Arlington is easily accessible by DC Metro or walk across the Memorial Bridge at the Lincoln Memorial end of the Mall.

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.