Author: Bert Cregg

Ok, ‘Hot’ might not be exactly the right word, but winter in the Midwest has certainly been warmer than average this year.  I did a little trolling around on Michigan State University’s Automated Weather Network website, which has been logging temperatures and other weather variables around the state for the past 15 years and compared our current winter here in East Lansing to recent years.  Since the middle of December our average daily temperatures are 5.2 deg. F above the previous 15-year mean.  The departure from the 15-year mean is even greater (+5.6 deg. F) when we look at minimum temperatures. 

15-year average Minimum daily temperature and Current-winter daily minimum for East Lansing, MI.

Minimum temperatures are especially important when discussing winter injury to landscape plants since extreme low temps (and the conditions immediately preceding them) are often responsible for many of our winter injury problems.  With a generally mild winter and only a few, brief temperature dips below average, one might expect that we will see few winter-related plant problems this spring.  However, prolonged exposure to temperatures above average means that plants are beginning to deharden early.  We see several signs of this already; such as witch-hazels blooming in protected locations and sap in maple trees running 2-3 weeks ahead of normal http://www.michiganradio.org/post/michigan-maple-syrup-producers-say-season-extra-early-year

February 28, 2012. Witch-hazel in bloom on MSU campus.

While other trees and shrubs may not provide the same outward signs, they are progressively becoming less cold-hardy by the day.  Unfortunately, temperatures, like the stock market, rarely move in a straight line. Here in mid-Michigan, temperatures in the single digits are possible throughout the month of March.  Given the preceding mild conditions, a sudden, severe cold snap still holds the potential to cause considerable damage to developing buds on trees and shrubs.  This type of late from damage may be evidenced by shoot die-back, bud-kill or death of newly-emerging shoots.  As always with winter injury, the final result won’t be known until late May or early June. 

I ‘like’ American Forests page on Facebook so I receive their periodic updates.  One item that caught my eye recently was a profile article on Dr. Greg McPherson, who is an urban forestry researcher with the USDA Forest Service in Davis, CA.  Even if you don’t recognize the name, if you have even seen any statistics on the economic and environmental benefits of trees in cities (energy conservation, carbon sequestration, etc), they probably cited information for McPhereon’s studies, either directly on indirectly,

http://www.americanforests.org/magazine/article/forest-frontiers-greg-mcpherson/

What really made me say “Amen, brother!” in the American Forest piece was McPherson’s response to the question, “What’s the biggest issue in urban forestry today?”  His reply, “Moving from the tree-planting paradigm to the tree-performance paradigm.”  Let’s face it, tree planting, for want of a better term, is sexy.  It’s relatively easy to raise money or get politicians to show up for a tree planting event and throw a few scoops of dirt with a ceremonial silver-plated shovel while the local media cameras are clicking.  

Image: Stephen Simpson/London News Pictures

But who is going to get excited about maintenance pruning? Or developing workable tree ordinances?  Or a pest management program?

Image: Susan Lesch

I’ve participated in various tree planting programs and it always gives me mixed emotions to hand out tree seedlings to second graders.  I’m glad they’re excited about getting a tree but also realize most of the seedlings that those 7-year-olds are running with will have the same lifespan as a goldfish that comes home in a plastic bag from the county fair.  Does this mean we should ban tree giveaways or planting events?  Of course not. Even if only a few seedlings survive the grubby hands of second-graders, that’s a plus and building their awareness of trees and their environment is the bigger issue.  But we also need to build public awareness of what it takes to maintain the urban forest and accrue all those benefits on the long term.  And most of those activities don’t make good photo ops or video clips for the local TV news.

In some places, we’re starting to get the message.  Here in Michigan our Department of Natural Resources awards Community Forestry grants.  The program will fund various activities but many grants are for tree planting.  If the application is for tree planting, the applicant must include a description of the maintenance practices that will be used to ensure the long-term success of the planting – forcing applicants to think about what happens after the trees are planted.  In addition the program also requires that applicants plant a diversity of species to help reduce issues with monocultures.  Small steps, but the ones we need to take to move from the tree planting paradigm to the tree performance paradigm. 

As part of my ‘other duties as assigned’, I have taken on an assignment to develop fertilizer prescriptions for landscape trees and shrubs based on soil samples submitted by homeowners to the MSU soils lab.  This has gotten me immersed in two sets of conflicting literature. 

On one hand is a raft of extension bulletins and ISA guidelines on tree fertilization, which typically suggest adding 2-4 lbs of nitrogen (N) per 1,000 sq ft of ground area – in some cases up to 6 lbs of N per 1,000 sq ft (Rose 1999).  To put that last number in perspective, that works out to 262 lbs of N per acre.  A typical recommendation for corn in Ohio is 150 lbs of N per acre.  Landscape trees need more fertilizer than a field of corn?

On the other side are numerous landscape studies, and even some nursery field studies, that suggest landscape trees simply don’t respond to fertilization (Day and Harris, 2007; Ferrini and Baietto, 2006; Harris et al., 2008; Robbins, 2006; Werner and Jull, 2009). 

So, what gives?  I mean, we know trees need nitrogen to make proteins, enzymes, chlorophyll, and all that good stuff.  We rake up leaves and haul them away each fall; short circuiting the natural nutrient cycle.  Urban trees should be starving for nutrients and begging to be fed, yet don’t grow any better when we fertilize them?  There are likely several factors at work.  First, many of the widely circulated recommendations are based, at least in part, on rates that might be applied in production forestry or nurseries where maximizing growth is a primary objective.  Also, as Dan Struve (2002) noted in his review, some recommendations were based on poorly designed studies.   Or, as Dan Herms (2002) hypothesized, trees may be allocating more resources to defensive compounds. 

Another answer may be found in some of the papers cited above.  In many cases, foliar N levels of the control (unfertilized) trees were already in sufficiency ranges.  In other words, even without fertilizer the trees had enough nutrients.  Part of this is a recent emphasis on the question of fertilizing at transplanting.  Trees coming in from a nursery are likely to be pretty jacked up with fertilizer – often referred to as a ‘nutrient loading’ effect.  Trees can be pretty efficient at internal nutrient re-cycling, so this effect can persist for a few years after transplanting. 

So where does all this leave me on my homeowner recommendation?  For some elements, like potassium and phosphorus, we can base a recommendation on the standard soil test included in the program.  Unfortunately there is no simple indicator of soil N availability (see Scharenbroch and Lloyd (2004) for a thorough discussion).  Foliar samples would be the best bet but aren’t part of our testing program.  At this point, I’m leaning toward a simple visual assessment – Do the trees/shrubs look healthy and have acceptable color? (check yes/no).  If ‘yes’, don’t fertilize.  If ‘no’ add 1-2 lbs N/ 1000 sq ft.

Your thoughts?   

References

Day and Harris. 2007. Arboric. and Urban Forestry 33:113-121.

Ferrini and Baietto. 2006. Arboric. and Urban Forestry 32:93-99.

Harris et al. 2008. Urban Forestry and Urban Greening 7(3): 195-206.

Herms. 2002. Environ. Entomology 31:923-933.

Robbins. 2006. So. Nursery Assoc. Proc. 51:113-117.

Rose. 1999. HortTechnology 9(4):613-617.

Scharenbroch and Lloyd. 2004. J. of Arboric. 30:214-229.

Struve. 2002. J. of Arboric. 20:252-263.

Werner and Jull. 2009. Arboric. and Urban Forestry 35:252-262.

A follow-up to Linda’s post about a recent study in Arboriculture and Urban Forestry that indicated mulch may not reduce evaporation of water from soil as we generally assume and which suggested that landscapers may want to re-evaluate their mulching practices.  As Linda noted, we have some real concerns about this conclusion and believe that proper mulching of landscape trees and shrubs has well-established benefits.

First, I don’t question the results present in AUF article.  As my grad students frequently hear me say, the data are the data.  But we need to bear in mind the paper is looking at one aspect of one of the impacts of mulching.  As Linda notes there are plenty of data to suggest that mulching does conserve soil moisture and she included some data from one of my studies which demonstrated this.  But there are other benefits to mulching beyond improving soil moisture.  I’d like to mention two here; one is a practical observation, the other is based on data from another study.

Preventing lawn mower blight and string trimmer trauma
From my observations and experience, one of the biggest and perhaps least appreciated benefits of mulch is keeping mowers and weed whips at bay.  I’m not aware of specific data, but damage by trimmers and mowers has to be near the top of the list of causes of mortality and long-term damage of new landscape trees.  A mulched zone around trees provides a buffer and simplifies maintenance operations. It’s an easy, simple and effective way to eliminate a major cause of tree distress.  A no-brainer.

Young, thin bark is no match for mowers and trimmers

Mulch protects trees and simplifies maintenance operations

Reduced soil temperatures
We conducted a trial a few years ago to look at the impacts of plastic mulches to improve establishment and early growth of Christmas trees. http://www.hrt.msu.edu/assets/PagePDFs/bert-cregg/cregg-et-al-2009.pdf  In a bit of serendipity we added a treatment at the last minute because our research station had some leftover wood chips from another project.  The trees mulched with wood chips were not irrigated but grew almost as much as trees in the plots that were irrigated.  What was especially impressive was the insulating effects of the wood chip mulch.  We installed probes to measure soil temperature 2” below the soil surface that we logged continuously.  During a July heat wave we found that soil temperatures were up to 10^oC (18^oF) cooler on the wood chip mulch plots than on the bare-ground plots.  Reducing soil heat load has profound implications for reducing root respiration and improving overall root function.

Soil temperatures were continuously logged on bare ground plots (foreground) and plots with wood chip mulch (background)

Soil temps peaked at around 38C (100 F) on bare ground without mulch (green dots);  max. soil temps were about 28C (82F) with wood chips (purple squares).

As Linda noted in her comprehensive review article, mulching has a myriad of benefits for landscape trees and shrubs.  It is important that we continue to look at all the various aspects of mulching and understand how to maximize the benefits (or reduce negative impacts) of mulching but in doing so it’s important to not lose site of the bigger picture.  While individual studies may yield conflicting data, on the whole, the preponderance of evidence and practical considerations come down strongly in favor of mulching

Lots of people around the country seemed to take perverse pleasure in the snow and ice storm that paralyzed much of the Pacific Northwest recently.  From Boulder to Boston, northern residents that deal with snowstorms on a regular basis chortled at video clips of cars and buses slip-sliding away in western Washington.  Perhaps it’s just the Northwesterner in me getting a little defensive, but I’ve never understood why people feel the need to gloat over other people’s inability to cope with weather.  At the end of the day we’re all in the same boat.

I’ve lived in the Northwest, the Plains, the South and the Midwest.  And guess what?  Nobody can handle weather they’re not used to or equipped for.  On NPR the other day I heard a former Chicago resident now living in Seattle bragging how his former city dealt with snow and couldn’t understand why everyone was making such a big deal about a little snow.  I used to live in Georgia and people there were similarly perplexed when a few days of 100 degree heat killed hundreds of people in Chicago.  Likewise, I can remember my amazement shortly after I moved to Michigan and saw a scroll at the bottom of the morning TV news announcing 2-hour school delays for fog.  I’d never heard of such a thing.  If we had fog delays in Olympia, we’d have started half our school days at 10:30.

On the eve of the recent Northwest snowstorm I saw an interview on the Weather Channel with Seattle’s transportation manager, who said they had 30 snow plows standing by.  Custer had better odds.  To put things in perspective it would be like the city of Lansing having 6 plows (it has more than 60).  Seattle and western Washington are not equipped for snow, nor does it make any financial sense for them to do so.  Just like it doesn’t make sense for everyone in the Midwest to have central air or to equip every Michigan school bus with fog lamps.  Just remember, when you get ready to gloat over someone else’s weather misfortune, Mother Nature will always have the last laugh. 

I probably shouldn’t admit this but one of my all-time favorite movies is Steve Martin’s classic “The Jerk”.  Part of the appeal is that I have an affinity for low-brow humor in general but also because the movie contains some great lines; “I was born a poor black child”, and the classic scene when Martin’s character finds his name in the phonebook for the first time and runs around yelling, “The new phonebook’s here! The new phonebook’s here!” http://www.youtube.com/watch?v=kOTDn2A7hcY

I wasn’t quite as excited as Navin R. Johnson today, but pretty darn close.  The reason? The USDA (finally) released a new hardiness zone map for the US.  http://planthardiness.ars.usda.gov/PHZMWeb/
Why is this exciting news?  Well, for several reasons.  The earlier version of the USDA map was released 1990.  The 22-year-old map had several limitations.  First, it was 22 years old.  Secondly, the versions of the map that were available electronically did not reproduce well and had poor resolution when you tried to zoom in on a particular area.  This sometimes made it difficult to identify the hardiness zone for certain locations and limited the utility of the map for presentations and publications. 

There have been persistent rumors for last 6 or 7 years that the USDA would release a better, updated map.  In addition to the shortcomings of the old map in terms of resolution, many felt the map didn’t accurately reflect more recent climatic conditions.  In 2006 the National Arbor Day Foundation released an updated hardiness map using more current climatic data.  This map indicated that many locations were 1 or even 2 hardiness zones warmer than the 1990 USDA map.  In addition, the Arbor Day map was available as a hi-res TIF file suitable for PowerPoint presentations and had a ‘zone-finder’ feature based on zip codes.

I haven’t had a lot of time to work with the new USDA map, but my initial reaction is a thumb’s up.  Like the Arbor Day map, the new USDA map has a zone finder based on zip code that makes it easy to find the zone in your area. The map is interactive, allowing users to zoom in or out.  As with MapQuest and other on-line maps we’ve grown accustomed to, it allows the user to select a roadmap or satellite background and choose different levels of transparency or opacity.

Whenever I discuss hardiness zones, I always include the caveat that these maps are based on average annual minimum temperatures.  That is, they are based low temperatures we are likely to see in an average year.  Not sure about where you live, but I have yet to see an average year in my adult life.  There are many years when we will get below our USDA hardiness zone temperature.  Human nature says we want what we can’t have and gardeners love to push the boundaries of their hardiness zone – people in zone 4 love to grow zone 5 plants; people in zone 5 love to grow zone 6 and so on.  Just because the new map may say you’re a zone warmer; your climate hasn’t changed, the map is just based on better and more recent data.

Like many, I was interested last week by the announcement that a University of Connecticut professor responsible for some of the research on resveratrol, a plant-based phenolic compound linked to various health benefits, had been accused of falsifying and fabricating data.  According to published reports, UConn officials found 145 cases of faked data that turned up in 26 published research articles by Dr. Depak Das.  Resveratrol occurs in many plants but most notably in grape skins and seeds, and one of the compounds associated with health benefits of red wine.   

http://www.cbsnews.com/8301-504763_162-57357720-10391704/red-wine-researcher-dr-dipak-k-das-published-fake-data-uconn/

Needless to say, reports of Dr. Das’s wrongdoing were disappointing to those of us that enjoy an occasional glass of Caberbet Sauvignon or Merlot.  More importantly, although Dr. Das’s research was a relatively minor part of the resveratrol story, these types of reports invariably provide grist for the mill for those that like to question the motives and veracity of scientists.  Only Dr. Das can ultimately comment on his motivation for the con job.  Dr. Das is a tenured professor and head of his university’s Cardiovascular Research Center so presumably career advancement was not a primary factor in the ruse.

In theory, a well designed and well executed study that provides useful results should be publishable.  In reality, the adage that ‘it’s difficult to publish negative results’ often proves true.  I’m not familiar with Dr. Das’s studies or the data he’s reported to have faked, but suppose, for example, he had found that resveratrol did not reduce heart attack risk.  Assuming the trials were experimentally valid, there is still value in that knowledge; it could save others from conducting expensive but likely fruitless research or it may suggest other avenues of research.   Unfortunately, it’s often easier to publish positive results and use those data as the basis for future grant development.  I’m not privy to all the details at this juncture, but I wouldn’t be surprised if this started off as fudging a few numbers, which, in turn, formed the basis for other proposals and started a self perpetuating cycle.

As I noted, Dr. Das is an established scientist near the top of his game.  But the need to keep science clean extends to all levels.  In some regards, the pressure to fudge data is greatest at the entry level.  At research intensive universities, young assistant professors must generate enough grant funding and publications to secure tenure within six years of their hire.  Denial of tenure means time to hit the road.  Many universities are even opting to not reappoint some new faculty at the three-year mid-point review, which was often perceived as a ‘rubber stamp’ in the past.

Falsifying data in science is analogous to gambling in sports.  Both represent the ‘third rail’.  People wonder why baseball came down so hard on Pete Rose.  Once gambling is introduced in sports, fans assume the outcome is predetermined and the sport is done.  Likewise, science runs the risk of becoming irrelevant if the public assumes that researchers are only going to conclude whatever will get them published or help them land the next grant.  It sounds like UConn and the US Office of Research Integrity are preparing to throw the book at Dr. Das.  If he’s guilty as charged, they have to.

Just a quick post today.  Today is the second Monday in January which means: 1) classes resume here at MSU and 2) it’s the first day of the Great lakes Trade EXPO in Grand Rapids, which is sponsored by the Michigan Nursery and Landscape Association and Michigan Turf Foundation.  I’m on tap for two presentations this afternoon.  

The first one is a bit of post-mortem on the Imprelis issue that dominated some of our lives back in the summer.  My talk, "Imprelis: What went wrong?’ looks back over the development of the Imprelis debacle.  The final verdict on how the EPA allowed the registration on an herbicide with such devastating non-target effects probably won’t be fully known until the dust settles on the legal process. Bottom line: the testing that was done was not adequate and either DuPont or the EPA (or both) dropped the ball.

My second talk, thankfully, is a little more upbeat.  In "Little Big Men" I discuss the use of miniature and dwarf conifers for landscaping.  I even get to talk about one of my new interests: railway gardening.  I haven’t taken the plunge yet – not enough time or nearly enough money – but I think I may have found a hobby for retirement.  For those that have access to the Oregon Association of Nurseries Digger magazine, Elizabeth Peterson wrote a very nice feature on railway gardens in their September issue.
 
Courtesy: Elizabeth Peterson
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NOTE: Linda and I switched places this week so we could get the Garden Professors survey up on Monday – See Linda’s post for the link – please take a minute to give us your feedback!

I recently received a copy of a newsletter from the USDA Forest Service Pacific Northwest Research Station that included a summary of an article recently co-authored by one of the Station’s scientists on the effect of urban tree cover on pregnancy outcomes of new mothers in Portland, OR http://www.fs.fed.us/pnw/sciencef/scifi137.pdf

According to the summary, researcher Geoffrey Donovan and his colleagues found that babies born to pregnant mothers who lived in neighborhoods with high amounts of tree cover were more likely to have higher birth weights than babies born to mothers living in areas with less tree cover.  Of course, being a skeptical (cynical?) Garden Professor my first reaction was, “Well, duh…expectant mothers that live in areas with more tree cover are probably living in better neighborhoods, are wealthier, better educated, and have lots of other things going for them that we typically associate with better pregnancy outcomes.” 

The summary put out in the PNW Station newsletter was scant on these details so I went on-line and dug out the original paper (citation below).  As I suspected the authors noted that, “Women with greater access to urban trees were more likely to be non-Hispanic white, younger, have fewer previous births, and live in newer, more expensive houses closer to private open space compared to women with less access to urban trees.”  However, they were able to account for these effects in their statistical analysis and still found that birth weight increased with the amount of tree cover near the mothers’ homes.

As we’ve all heard many times, correlation is not causation and it is unclear exactly how tree cover improves pregnancy outcomes.  One of the most likely explanations for the tree cover effect is that having more trees around reduces stress levels, resulting in better birth outcomes.  Trees can also reduce noise and other forms of pollution as well.  Regardless of the mechanism, this study may provide one more bit of ammunition for urban forestry advocates that go to battle for trees in our cities.

Donovan, G.H.; Michael, Y.L.; Butry, D.T.;Sullivan, A.D.; Chase, J.M. 2011. Urban trees and the risk of poor birth outcomes. Health & Place. 17(1): 390–393.

PS: Don’t forget to take our survey!

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One thing I’ve always enjoyed about living in Michigan is that we are virtually guaranteed to have a white Christmas each year.  This is in stark contrast to western Washington where I grew up where a white Christmas was a relatively rare event.  In fact, to make the locals feel better, one of the popular songs on the radio play lists during the holidays is “Christmas in the Northwest is a gift God wrapped in green.”  Actually, He usually wraps it in grey fog or drizzle but hey, it’s a nice sentiment.

And for the Great Lakes region and much of the eastern US, a white Christmas may not turn out to be such a sure thing after all.  Snowfall in the East is way off compared to last year.  According to data from National Operational Hydrologic Remote Sensing Center http://www.nohrsc.noaa.gov/nsa/index.html?region=Northern_Great_Lakes&year=2011&month=12&day=14&units=e , only about one-third (33.7%) of the Great Lakes region had snow cover as of last week and the average depth was only 0.9”.

This is quite a difference from a year ago in mid-December when 99.7% of the Great Lakes region was covered with an average of 9” of snow.

Of course, this is Michigan and things can change in hurry.  But right now the forecast for the next couple days is for temps in the upper-30’s and low 40’s.  There’s a chance of snow showers on Saturday so we’ll keep our fingers crossed and hang our hats on a Christmas eve snow for our White Christmas.

May your days be merry and bright, and may all your Christmases be white!