Category: What About the Trees

Trees can be good plumbers

A short follow up to last weeks post on girdling roots.  Just to reiterate, the point of the post was that we need to be careful not to jump to conclusions when assessing tree problems.  It’s important to look beyond the first defect we see and consider additional causes.  And to also reiterate, girdling roots can be a serious problem and can lead to tree failures.  The photo below shows an example of tree that was both planted too deep and had stem girdling roots.  The result was a weakened area in the trunk, which was subject to breakage during a windstorm.

Many people also assume that girdling roots restrict flow of water and nutrients in the xylem.  They can, but trees also have the ability graft roots and re-establish connections between roots.  In the study I mentioned last week, Phillip Kurzeja and his co-workers  traced water flow in ’manifold roots’ (a series of interconnected, girdled roots) by injecting dye.  The trees were subsequently felled and de-barked, allowing the researchers to determine whether the roots were still functional.  As shown below the girdled roots were able to re-establish their vasculature and continue to translocate water up the stem. So trees can be efficient at fixing their own pipes!

Image: Phillip Kurzeja

It is important to note that this phenomenon occurs between roots but not between roots and the main trunk – hence the concern for impact of stem-girdling roots, especially for trees planted too deep.

Girdling roots: The source of all evil in the world?

One of the most widely discussed topics in arboriculture and tree care these days is the problem of girdling roots.  Virtually every conference or workshop on tree care has a speaker or speakers on how poor planting technique or poor nursery practices lead to girdling roots and their subsequent correlation with poor tree performance, tree failures, global warming, the soaring Federal budget deficit, and the batting average of the Seattle Mariners.  Before we go any further let me state categorically that I do not think girdling roots are a good thing; nor do I think any of the consequences mentioned are a laughing matter – especially the Mariners’ batting average.  I do think, however, that we often see a rush to judgment as soon as girdling roots are found on trees that are declining or have died.  I attribute at least part of this to the increased availability of air spades for excavating tree roots.  I have nothing against air spades; they are useful tools and a great way to non-destructively examine and treat roots and even move trees.  The problem is that often when people see a tree in decline they examine the roots, see a girdling root, conclude that was the problem and blame the person that planted the tree (unless they were the person that planted the tree, then they blame the nursery).

 

Example of oak tree with leaf scorch (Photo Phillip Kurzeja)

A recent study here at Michigan State presented by Phillip Kurzeja at the recent Arboriculture Society of Michigan ArborCon, points out the importance of looking beyond girdling roots in assessing tree problems.

The problem:  Oak trees at several locations on the MSU campus have been suffering severe leaf scorch.  In some cases virtually 100% of the leaves on the trees are affected and growth has been severely affected.  Examination of the trees by a pathologist ruled out bacterial leaf scorch, suggesting that the problem may be abiotic.  The researchers looked at a battery of variables including degree of leaf scorch, number of girdling roots, planting depth, soil compaction, foliar nutrition, leaf water potential, and leaf photosynthetic function.  Most importantly, they looked at these traits on trees without scorch as well as trees with scorch.

Evaluating girdling roots (Photo Phillip Kurzeja)

The results:  Trees with mild or severe scorch leaf scorch had girdling roots.  At this point one might have leapt to the conclusion that the girdling roots were responsible for the leaf scorch.  But girdling roots were also found in trees that did not have any leaf scorch.  In fact, in some cases the healthy trees had more severe girdling roots than trees with the worst leaf scorch.  So, what factors differed between trees with scorched and un-scorched leaves?  The researchers are still working on the analyses but the most obvious differences were that trees with leaf scorch were consistently planted deeper and had lower levels of foliar manganese than healthy trees.

 

The presentation I saw did not include data on soil pH or soil nutrient levels, so it’s impossible at this point to establish causal relationships among planting depth, foliar manganese, and leaf scorch.  But, for those who have to answer the ‘what’s wrong my tree?’questions, this study does point out the importance of keeping an open mind and looking at a variety of factors and not leaping on the first defect to appear.

Planting trouble: multiple trees in one hole

[I enjoyed Jeff’s Valentine story so much that I thought I’d stick to the theme of togetherness…for better or worse.]

A week or so ago a reader asked about the practice of planting three or four fruit trees in the same hole.  Having not heard of this before, I checked on the web and found many “how to” pages geared to home gardeners who either want a longer harvest of a particular fruit (early to late) or a mixture of different species.  Doesn’t it sound just great, especially for smaller urban yards?

One of these sites has these written instructions: “Plant each grouping of 3 or 4 trees in one hole at least 12 to 15 inches apart.”

Now, I’m sorry, but this is just asking for trouble down the road.  Readers of this blog know that root systems extend far past the drip line, and that roots from different trees are going to compete with one another.  You’ll end up with three unhappy trees, all jostling for space and resources, just like kids in the back seat during those long car rides.

But wait! you might say.  There’s research on high density tree planting, and it’s been shown to increase fruit yield on a per acre basis!

Yes, in fact there is a lot of planting density research on many different species of fruit trees.  What’s considered by researchers to be “high density” varies, but it rarely exceeds 2698 trees/acre (6666/ha for our international readers).  Optimal and sustainable levels of high density planting are also variable, as they depend on not only species but rootstock and the crown architecture; 1214/acre (3000/ha) might be a mid-range number.  This can be converted to a per-tree requirement of 36 sq. ft. or a 6’x6’ planting area.

How does this compare to the 12-15” recommendation given earlier?  If we’re generous and use the 15” recommendation, this translates to 6.25 sq. ft. per tree or 6970 trees/acre.  The 12” recommendation would lead to a whopping equivalent of 10,890 trees/acre.  (And no, it doesn’t matter if you’re using dwarfing rootstock or not; most of the higher densities in the literature are for dwarfing rootstocks.)

You don’t have to be a math whiz to see that these densities are totally out of line with reality.  Sure, you can probably keep overcrowded trees alive with lots of water and fertilizer, but they’ll be under enough chronic stress so that pests and disease might take hold, and fruit production will likely be poor.  And it’s about as far from a sustainable practice as you can get.

Scrambling for Answers

Yesterday a good friend of mine who works for a well respected tree company in town asked me whether I would be willing to talk about  tree conservation as it relates to the emerald ash borer.  Specifically he wanted me to make people aware of a statement produced by a group called the Coalition for Urban Ash Tree Conservation which you can find here which was produced by a number of well respected industry people and academics.  This statement basically says that we shouldn’t cut down all of our ash out of fear of the emerald ash borer but that we should, instead, treat some with various insecticides to conserve our ash.

I don’t have any major disagreement with the article, but it’s important to remember that every situation is different and that, while chemical treaments might be appropriate for one ash, another should hit the chipper.  As the emerald ash borer moves across the country we’ve got to assess what our ash are worth to us and decide when and where it’s appropriate to save them.  This is an extremely daunting task without easy answers.  The statement by the Coalition for Urban Ash Tree Conservation is good and very appropriate, but what would be even better is a guide to help people decide whether to leave trees alone, to cut them down, or to treat including all of the costs and consequences.

UPDATE:  As you might have expected, there is already a cost calculator out there — I just wasn’t aware of it.  Fortunately Katie was and left details in the comments section.  If you are interested in a calculation to figure out the cost of treating vs. removing ash go here http://www.ag.purdue.edu/entm/Pages/csadof.aspx and then click on EAB cost calculator — it’s on the left hand side.  It’s a very nice little tool!

When trees attack!

I’ve been suffering through my post-holiday, post-annual-reporting cold and/or flu, so I don’t feel as witty (or snarky) as I might otherwise be.  Instead, I feel like my body’s been invaded by a slowly spreading mass that reminds me…oh, I don’t know…of what trees can do when they encounter an immovable object.

Not much of a segue, I know, but I just had the urge to post some interesting photos after Holly’s photo-fest yesterday.  (Memo to self: not fun being Holly’s follow-up act.)  Anyway, you’ve seen what happens when growing trees encounter neglected plant tags:

And perhaps you’ve seen how roots laugh at puny planting pits:

So before you feel the urge to attach something – anything – “permanently” to a tree, keep in mind that they have no respect for authority…

…or even those who got them started in life:

Landscape conifers: The Good, the Bad, and the Underused

This week is our annual Great Lakes Trade Expo, the main trade show and education venue for Michigan nursery and landscape industry. One of my talks was for the Arboriculture track on landscapes conifers. The theme this year was “The Good, the Bad, and the Underused.” Hey, you try giving a dozen talks a year for 10 years and see if you can come up with an original title!

 

The selections were based the following, admittedly subjective, criteria.

The Good:  These are the all-around good guys.  Conifers that are well-adapted, good growers with good form and few pest problems.

The Bad:  The problem children of the conifer world.  Pest magnets, spoiled prima donnas, or incessantly overused.

The Underused:  Trees that have the virtues of ‘The Good’ but that tend not to attract attention.

 

Here are three of my selections for each of the categories.  I’m interested in nominees from other sections of the country and the world.

 

The Good:

Eastern white pine Pinus strobus This one flirts with the overused designation but I’ll give it a nod since it’s the state tree of Michigan and figured prominently in the state’s history when Michigan was the lumbering capital of the US in the late 19th century.  A fast growing tree that improves with age.

 

Eastern hemlock Tsuga canadensis   The answer to the age-old question, ‘What conifer to you recommend for shade?’  A little finicky on site, prefers moist but well-drained – who doesn’t.  But a great elegant looking tree.  The main down side is the specter of hemlock wooly adelgid looming to our south.

 

Alaska false cypress Chamaecyparis nootkatensis (Xanthocyparis nootkatensis).  Lot of confusion over the nomenclature but no question this is a great landscape tree.  Graceful, weeping habit; good growth rate; and few pests in this area (knock on wood).

 

The Bad.

Scots pine Pinus sylvestris  Is there a pest that doesn’t affect this tree?  Our Forest Entomologist, Dr. McCullough, had a grad student count up all the pests that affect Scots pine and they lost count after 30.  Borers, tip moths, needlecasts… the hits keep coming.  The problems are exacerbated around here because of abandoned Christmas tree plantations that serve as insect breeding grounds and fungal infection courts.

 

Austrian pine Pinus nigra  Austrian pine is a frustrating tree.   In some respects it is the perfect conifer for our region. A great looking tree with dark green needles.   Good growth rate, cold hardy, drought hardy, tolerates road salt.  Everything you could want in a tree and then some.  Then the trees get about 15 years old and the wheels fall off.  Diplodia tip blight, dothistoma needle blight…  Austrian pine is the ugly duckling in reverse; looks great when young and then, blechh…

 

Colorado blue spruce  Picea pungens  The tree everyone loves to hate, yet we keep planting it.  I suppose it’s the allure of the blue that people can’t resist.  It’s like that bad boyfriend; you know he’ll do you wrong but…  He’ll lure you in with those baby blues then start hanging out with those low-life Cooley adelgids, then hook up with rhizosphaera needlecast.  And by the time the cytospora cankers start hanging out you know this relationship is going nowhere.

 

The underused

Swiss stone pine Pinus cembra  Renowned conifer aficionado ‘Chub’ Harper used to remark, “I never met a cembra I didn’t like.”  Cembras are great trees, good growers with consistently good form.  Underused but worth looking for.

 

Korean fir Abies koreana  I wrote about Korean when in discussion alternative Christmas trees but it also makes a good landscape tree.  In our area we can expect about 1’ of height growth per year.   Symmetrical form; short needles with silvery undersides, and conspicuous cones.  Lot to like about Korean fir.

 

Dawn redwood Metasequoia glyptostaboides  A fast-growing deciduous conifer with wonderful pyramidal form.  Dawn redwood is also an interesting botanical story.  Only known to science from fossil records, an isolated population was discovered in China in the 1940’s.  Seed were imported into the U.S. and the tree has been found to be broadly adapted.

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Will cabling a tree’s crown make it stronger?

In a previous column (December 1, 2010) I discussed the problems that wet, heavy snow can cause for trees and shrubs – particularly evergreens.  In response my colleague Terry Ettinger mentioned a cabling technique discussed in the 2nd edition of Arboriculture (1991).  I think it’s worth looking at the science behind this practice and some of the unintended consequences.

Harris’s Arboriculture text is considered the bible for landscape professionals, including certified arborists.  In the late 1990’s, Dick Harris was joined by Jim Clark and Nelda Matheny, two other gifted academics who have crossed over into practical writing.  In the 4th edition of this book (published in 2004), the authors caution about routine use of cables and other support systems for tree crowns.  They state that “evidence for the use of support systems to strengthen tree structure is anecdotal” and based on my reading of the scant scientific literature on the topic I must agree.

Older articles and texts tend to provide how-to instructions and diagrams on various cabling and bracing techniques, but little to no evidence supporting the practice. More recently, studies have provided evidence that drilling holes for cables, wires, bolts etc. increase the likelihood of introducing disease into otherwise sound wood.  As the tree continues to grow and change over time, even the best of these systems may need to be modified or replaced.  In fact, the systems should be inspected and maintained annually.  Crown cabling is not a permanent, one-time fix – and sometimes it isn’t even a fix.  Failures still occur, often just above the point of attachment of bolts and cables.  In fact, many arborists believe cabling should be the choice of last resort.

Some current research is exploring noninvasive methods of securing crowns, such as belt systems, that provide support without creating additional problems. As with any new technology, long terms studies are pending. Given the potential risks and lack of reliable benefit, I would not recommend cabling or bracing unless there were no other choices for saving the crown of a tree.

What fir?

OK, it’s the middle of December so I get to indulge my passion for Christmas trees.  One of the most interesting projects I’ve gotten to work on during my time at Michigan State is a study to look at alternative species of firs (Abies spp) for Christmas trees and well as for landscape conifers.  Firs are fascinating trees that are distributed throughout temperate regions of the northern hemisphere.  There are about 50 species, many of which are important for timber, landscaping or Christmas trees.

 

For those of you that put off your Christmas tree shopping until the end (or want to start thinking about next year’s tree) here are three trees to keep an eye out for.

 


Korean fir Abies koreana We have several growers in Michigan that are now growing Korean fir.  It has relatively short needles that have a bottle-brush arrangement on the stem.  The color is often described as dark green, but I’d say the needles tend more to a true green or Kelly green with a silvery underside.

 


Concolor fir also makes a great landscape conifer

Conolor fir Abies concolor  I grew up in the Northwest so I always knew this tree as white fir until I moved to the Midwest.  In any case, it’s a great tree.  Long, soft-blue needles.  Depending on the seed source they can be as blue as a blue spruce.  The main draw-back here in Michigan is that concolor tend to break bud early, which makes them susceptible to frost damage in the spring.  Their citrus-like scent is hard to beat.

 


Danish growers compete for the best Nordmann fir in the “Fight for the Golden star” at their annual tree fair.

Nordmann fir  Abies nordmanniana  Denmark is the leading producer of Christmas trees in Europe and Nordmann fir is their principle species.  The Danes like Nordmann because of its deep, dark green color and natural form and symmetry.  Europeans don’t like their Christmas trees sheared so they rely heavily on genetics and selection to find trees that naturally have good form. We’re starting to see more Nordmann in the US, both here in the Midwest and in the Northwest.  Growers complain that the trees are slow-growing to start but I think some US consumers are looking for a more open, natural-looking tree and Nordmann can fill this niche.

Saving your ash

My earlier post regarding plans to replace the monoculture of ash trees at the Gateway Arch Monument in St. Louis, MO with a monoculture of Lindens prompted a question about options for treating ash trees for emerald ash borer.  This is a complex topic so I wanted make sure I had time and space to respond completely.

 

First, the best and most current source of information regarding treatments for EAB is the Multi-state bulletin “Insecticide Options for Protecting Ash Trees from Emerald Ash Borer” which is available as a full-color .pdf on the EmeraldAshBorer.info website.  Anyone who lives in or near EAB-affected areas and is considering treating their ash trees should take the time to download and read this bulletin.

 

Here are some key points to consider if you want to save you ash:

It is possible to protect ash trees from EAB with insecticides.  There are several examples in and around the original core infestation area in Detroit where arborists have successfully protected trees since EAB first was identified in 2002.  There are two general options; protective cover sprays and systemic applications.  For most trees, protective cover applications will require professional application with specialized high-pressure spray equipment.  Most systemic application will also need to be applied by professional applicators, except for small trees that can be treated with soil drenches of systemic insecticide.  To date, the most effective systemic product is emamectin benzoate, sold under the trade name TREE-äge.  In various tests, emamectin has shown the highest level of control among products tested and is also the only product that consistently provides more than one year of control.  Imidacloprid is also effective as a systemic but will need to be re-applied annually for the best level of control.

 

The likelihood of successfully treating an ash tree declines rapidly once trees begin to show noticeable crown-die-back.  In certain cases, researchers have been able to save EAB-infested trees showing some crown die-back, but once 50% of the crown is affected the tree is likely a goner.

 

Once started, treatments will need to continue in perpetuity.  To me, this is the biggest factor homeowners need to consider if they’re thinking about treating their ash trees.  To the best of our knowledge, EAB is here to stay.  EAB populations may begin to decline once most of the ash trees in a region have been wiped out, but trees in woodlots and forests that have been killed will continue to sprout, providing host material to maintain an endemic population of beetles for the foreseeable future.  Systemic applications can provide control but the products will need to be re-applied every year (imidacloprid) or every other year (emamectin) to be effective.

 

Effectively treating trees larger than 4” in diameter will require applications by a certified pesticide applicator and may cost several hundred dollars per tree.  Homeowners need to carefully consider the cost of on-going treatments versus removal and replacement.

 

Mention of trade names does not imply in endorsement.  Read and follow label directions when applying pesticides.

Snow falling on cedars…not always a good thing

Seattle had its first snowfall last week – a mere 3-6″ – and the city shut down.  (Yes, those of you in the snowier parts of the midwest and east can laugh…but we’ve got hills.  That’s the main problem.)  It was unusally cold, so the snow that fell was the light, fluffy kind that I remember from our Buffalo years.

Every year someone writes to ask whether they should remove the snow from their trees and shrubs.  Here’s what I suggest:

1)  If it’s very cold and the snow is dry and light, I advise leaving the snow on.  It serves to insulate tissues from freeze damage.

2)  If the snow is wet and heavy (i.e. temperatures are not that cold), you should remove as much as possible.  The insulation isn’t necessary, and the weight load can permanently damage trees and shrubs.

This damage can’t be easily repaired; the only alternatives are to cut bent trunks and branches out entirely (no stub cuts!), or to tie them up.  Not being into plant bondage, I generally cut bent branches away.