Author: Bert Cregg

I’ve had an on-going discussion – OK, argument – with a fellow faculty member who does research on social dimensions of forestry, including urban forestry.  She contends that we basically know everything we need to know about growing trees in cities and that the real underlying problems in urban and community forestry these days are social issues.  This, of course, means that funding for urban forestry research, what little there is, should be directed at social sciences.  Needless to say, as a tree physiologist, I can point to lots of examples of trees in cities in pitiful conditions and under stress.  To which, my colleague would hasten to ask, “Is it because the urban forester (if the city can afford one) doesn’t know any better or because they don’t have the resources to do anything about it?”  Which is a valid point.  Most of the urban and community foresters I know are dedicated, well-educated, highly professional, and woefully under-staffed.  The Greening of Detroit, a community-based urban forestry non-profit, got its start several years ago because the city could not afford a tree planting program.  The city forestry department dedicated its meager resources to tree trimming; going into triage mode on a 125-year back-log of tree maintenance.  Why would a city plant trees when it can’t even care for the ones it has?

What got me thinking about this was a New York Times article on a rash of tree grate thefts in the city. http://cityroom.blogs.nytimes.com/2012/05/10/if-its-made-of-metal-thieves-increasingly-have-an-eye-for-it/  With the rising price of metal such as iron and copper, thieves are making off with just about anything made of metal including tree grates and man-hole covers.  We can probably start a whole other debate about tree grates and tree pits and whether they are effective, but, in any event, the city forestry department will now have to devote resources to replacing the stolen tree grates and figuring out ways to keep the replacements from disappearing as well.  

I’m not ready to concede that we know everything we need to know about growing trees, but the longer I’m at it, the more I see the need to integrate the biological and the social elements.  We can develop the best tree establishment and tree care protocols in the world but if there no money or no public support to implement them, it’s all for naught.

Well, students just finished finals here at MSU so I suppose it’s appropriate we put our faithful GP readers through their own gauntlet of quizzes…

Top marks to Terry for determining the damage on the conifer seedlings was due to incomplete overlap on the sprinklers the grower used for frost protection during our most recent freeze.  Our record-setting March warm up pushed budbreak ahead by about a month in most locations in the state.  Fruit crops (cherries, grapes, blueberries, and peaches) have been devastated but nursery crops and landscape trees came through relative unscathed until the freeze the weekend before last.

I know Linda normally handles quiz duties, but I received a couple of intriguing pictures last week.  Rather than just tell you all what’s going, I thought we’d have a little sport with it.

The photo below was taken last week ago at a container seedling nursery in western Michigan.  These are trays of container-grown spruces.  Most of the seedlings are green and growing but some are tip-damaged – with a specific pattern.  What’s going on and what caused the pattern?

Last August I posted some photos from a field tour in Austria where we saw an organic Christmas tree farm that used Shropshire sheep as their principle form of weed control.  The particular breed of sheep is suited to the task since they will graze on grass and weeds but not on conifers.  Since then I have shared the pictures elsewhere and found out the Shropshire sheep are also employed in the U.S. and the U.K. for similar purposes.  Recently, I have had several people share websites for a service known as ‘Rent-a-Ruminant’.  As with the Shropshire sheep, these services use grazers to control vegetation, but instead of sheep these companies use goats. 

Unlike sheep, goats are much less selective grazers; so call these guys in when you’re in need of land-clearing or invasive species removal.  I have seen Rent-a-Rumant advertised in the Pacific Northwest http://www.rentaruminant.com/goats-clear-land.html and in Australia http://thebegavalley.org.au/24484.html so clearly this is a widespread idea.   And, I suppose, an example of an old idea that’s new again.  As many GP blog readers probably know, I have issues with the ethics (not to mention efficacy) of exploiting grade-school children to pull garlic mustard or purple loosestrife in the name of invasive species control.  But using goats to control invasives?  That might be a solution everyone can get behind

Not baaaad work if you can get.  Rental ruminants chomping on English ivy in the Northwest. (Just for you, Linda)

Well, things continue to run fast and furious as we get rolling for a new round of field research projects.  But we did find a little time to break out the Cornhole set and initiate a new season at Daisy Hill farm.  Life is good!

After Jeff’s recent eclectic musical selection of Rasputina’s 1816, I thought I’d go a little more mainstream with Lynard Skynard’s ‘Swamp music’.  Turn it up and remember; if it’s too loud, you’re too old. http://www.youtube.com/watch?v=_wJWBcj7lsY

So, what got me thinking about the swampy backwoods down South and the late, great Ronnie Van Zant?  The arrival of pallet after pallet of bagged cypress mulch at every gas station/convenience store in the area.  Like the first robin, the annual appearance of bagged cypress mulch is another harbinger of spring.  Awhile back (Oct 2009 to be exact) I commented on efforts by some environmentalists to boycott cypress mulch.  The rationale behind the boycott is that cypress mulch is harvested from wetlands in Louisiana and Florida.  Many of these areas are environmentally sensitive and it is difficult to regenerate new stands after harvest because of frequent inundation.

In response to the calls for a boycott, the Louisiana Forestry Association countered with a series of Cypress FAQ’s. http://www.laforestry.com/site/ForestFacts/Cypress/FAQ.aspx The Forestry Association, not surprisingly, deems the proposed boycott an overreaction, noting that cypress makes up only a small proportion of all timber harvested and that only about one-fifth of cypress harvested goes into mulch.  While it’s true that cypress is a comparatively minor species in terms of acres logged, much of this area includes some of the most sensitive ecosystems in the country.  And I was actually surprised to learn that the proportion of cypress that went into mulch was that high (20%).  Cypress timber is extremely valuable for decking and other high-end uses; I had always assumed mulch was a fairly minor component of the overall market.  But clearly, diverting a portion of the harvest to mulch could tip the balance and make some marginal logging operations profitable.

So, where do I come down on the boycott issue?  I suppose in a sense I boycott cypress mulch because I’ve never bought any and never intend to buy any.  Bob Schutzki and I conducted a study several years ago that showed that landscape shrubs grew as well or better when mulched with locally produced ground pine bark or ground hardwood bark than with cypress mulch.  Even mulch from ground recycled pallets (yes, that stuff dyed a red color not found in nature) did better than cypress.  So for me the issue has been moot.  Buy a local product and support your local forest products industry.

Despite Linda’s assertion to the contrary, I was not cow-tipping nor was I sampling micro-brews last week when I missed my regular post.  As usual, the beginning of spring is a busy time on the research side of my appointment.  This past week we began setting up for a major new project.  The goal of our newest study is to look at physiological traits of street trees that may enable them to better withstand future climate change. 

If you think about it, trees that are planted today may experience future climates in their lifetimes that will be different than the climates under which they were selected.  So how do we ensure that trees that are planted today can withstand a potentially different environment in 50 or 75 years?  It’s a very complex question.  An easy response would be to plant species or seed sources that have evolved in warmer, southern locations.  The problem is climate change is predicted to occur gradually so southern trees moved northward today will be subject to increased frost and freeze damage in the interim.

Grad student Dana Ellison (L) and undergrad research aide Aniko Gaal (R) pot up shade tree liners for a new project.

Another approach, and the one we are investigating, is that trees that are best suited for the future may be those that have a high degree of phenotypic plasticity.  What is phenotypic plasticity?  Simply stated is the relative ability of a species or genotype to acclimate to changes in their environment.  In our case we are going to look at the photosynthetic response of a range of street tree cultivars in order to identify their optimum temperature for photosynthesis or Topt.  But we know from other studies that Topt can vary depending on the environment to which trees are acclimated.  So we will acclimate our trees to a range of temperatures in a greenhouse study and determine which species or cultivars are best able adjust their physiology to changing environmental conditions.  In addition to the greenhouse study we will out-plant trees from the same cultivars in a parallel field study with the Greening of Detroit.  Working with the Greening we will identify sites around Detroit with contrasting temperature regimes and plant trees at these locations.  We will follow up with a similar suite of measurements as our greenhouse trial.

Will one study tell us everything we need to know about selecting street trees for a changing climate?  Of course not.  But it provides some important base line information and insights on approaching the problem.  Trees in urban and community forests are already operating at the margins and subject to myriad of stresses.  The argument can be made that urban ecosystems are among those most at risk under climate change.  Trees are an important component of many climate change mitigation strategies but they must be able to survive and grow in order to contribute this function.

The study “Urban tree selection in a changing climate” is funded by Michigan State University Project GREEEN, with material and in-kind support from J. Frank Schmidt and Sons Nursery, Nursery Supplies, Inc., Renewed Earth, Inc., and the Greening of Detroit.

Photos by Tom Fernandez

Ok, admit it.  If you’re over 40 or so, at some point in your life you’ve muttered that phase, likely more than once.  There is no doubt the younger generation can do things to get under your skin and raise your blood pressure.  But then they can turn around and do some pretty cool things, too.  The cool side was on ample display this weekend as over 750 college Horticulture students from 62 college and universities competed this weekend at the annual PLANET Student Career Days (SCD).  For the initiated, SCD is the landscaping Olympics for undergraduate students across the US (and a few from Canada to boot). The competition is organized by the Professional Landcare Network (PLANET) and sponsored by companies such as Stihl, Gravely, and Husqvarna.   Students competed in 28 events including arboricultural techniques, plant identification, skid-steer operation, sales presentation, paver construction and landscape installation.  The event moves around the country each year, and Kansas State hosted this year’s event in Manhattan. 

The logistics of the event are astounding.  For example, in the paver construction, wood construction, and landscape installation events, 40 teams are given the exact same set of materials and tools.  When the starting horn sounds the teams are given their plan and then allowed two hours to complete the job.  Watching 40 two or three person teams racing against each other and the clock to complete their project is truly inspiring; as is the camaraderie and sportsmanship.  At PLANET SCD everything is on the up and up. No performance enhancing substances, no under the table payments; just college kids working their hardest to do their best for themselves and their team.  And everyone can contribute.  The plant geek who can nail plant ID or the persuasive saleswoman-to-be who gets their customer to sign on the line can score as many points for their team as the athletic tree climber or skilled equipment operator.  So, what’s the matter with kids these days?  When you watch them compete in SCD: not a darn thing.

For more on PLANET student career days, including a pretty cool video clip  on last year’s event go to: http://www.studentcareerdays.org/

For the record: BYU-Idaho was the overall winner this year.  MSU finished 4^th and Virginia Tech was 9^th. 

Students compete in Landscape CAD at PLANET SCD

Team MSU is all smiles after the Landscape Installation event in the mud-pit

MSU Horticulture club President Jackie Grow (left) closes the deal en route to a 3rd place finish in Sales Presentation

Last week I decided to continue my discussion on cold hardiness and so now, of course, temperatures are forecast in the mid-70’s for this week.  Oh well, I’m still convinced we’ve got one more blast of winter to go and some of this will still matter to someone.

One of the questions posed in response to last week’s post was how much cold hardiness changes during the winter.  Before I get into that, it’s good to review how cold hardiness can be quantified.  Cold hardiness is essentially how much cold a plant can withstand before it suffers damage.  There are two common ways by which this can be measured.  The simplest and most straightforward method is through a whole plant (or whole shoot) freeze test.  In this test, entire plants, usually seedlings, are placed in freezer that is programmed to drop the temperature progressively colder, say from 3 deg C to -36 deg. C

At set intervals, often 3 deg. C, a group of plants are removed.  The plants are allowed to slowly thaw and are then examined for needle damage or bud kill.  At the warmest temperatures, plants are undamaged.  As we examine plants subjected to colder temperatures, we’ll begin to find some with damage.  Eventually we’ll find a temperature where all the plants are damaged.  When we plot the percent of damaged plants versus temperature we can identify an LT50, or lethal threshold where 50% of plants are damaged.

Examples of determining bud damage during whole shoot freeze tests.

The second common assay for cold hardiness is termed Freeze-induced electrolyte leakage or FIEL.  FIEL testing is similar to the whole plant freeze test except that instead of freezing the entire plant or shoot, just a small portion of tissue, such as a conifer needle segment is needed.  The FIEL test is based on the fact that plants can withstand inter-cellular ice (ice between cells) but not intra-cellular ice (ice within cells).  When intra-cellular ice forms it disrupts the cell membranes and cell contents are released into solution.  The amount of leakage of cell contents into solution can be easily measured using a standard conductivity meter.  Again, we can estimate an LT50 by plotting the amount of damage versus exposure temperature.

By assessing cold hardiness periodically through the winter, we can assess changes in hardiness associated with acclimation and de-acclimation processes.  A classic study by Karen Burr and her colleagues demonstrates how quickly acclimation can change.  In their study they tracked cold hardiness of conifer seedlings that we exposed to acclimating conditions (short days and progressively colder temps) and then de-acclimating conditions (longer days and warming temps).  The resulting chart demonstrates how dynamic cold hardiness can be.  When we describe plans based on Hardiness zone we’re talking about their maximum hardiness or the temps they can stand in the mid-winter period.  But note how quickly the lethal temperature rises during de-acclimation.
Seasonal trend in phases of cold hardiness: Acclimation, Maximum hardiness, and De-acclimation

Typically, our most common winter injury problems occur during the de-acclimation phase as temps warm and hardiness is lost.  We saw a dramatic example of this several years ago in western Michigan when an early March warm-up with temperatures in the 50’s F was followed by nights with temps as low a -5 deg.  This resulted in widespread bud-kill in conifer plantations.  With a week of highs in the 60’s and 70’s forecast, it’s easy to see why our current warm-up has everyone nervous.

Maximum and minimum temperatures from a west Michigan weather station