Category: Uncategorized

Does native matter?

We’ve had lots of lively discussion on my post regarding the Mark Davis et al. comment in Nature on natives and exotics. I have been traveling and otherwise occupied and have not had a chance to comment so I feel a little like the kid that kicked the anthill and then ran away. Fortunately, Holly was gracious enough to forego her post today (I promise to return the favor, Holly!) so I can chime back in.

Obviously there are lots of layers to the debate but one of the main items in the discussion is whether there is an inherent ecological advantage in planting natives over exotics.  At this point the focus always seems to shift to herbivory and the question of whether native insects will eat non-native plants.  There are certainly examples each way; some insects are generalists while others are highly specific.  More importantly, however, plants fill many other roles in the environment beyond serving as food for insects.   Moreover, species composition is just one aspect of diversity.  The ecological function of landscape is also determined by how we manage other factors such as structural diversity and age class distributions.  In his book “Bringing Nature Home” Doug Tallamy shows a picture of a bland, sprawling suburban landscape ( p. 24) and notes “this highly simplified community is made up of a few species of alien ornamental plants that provide neither food nor shelter for wildlife.”  OK, I’ll buy that.  But would the situation change if the blue grass was changed to a native grass kept mowed to 2” and the two widely spaced shade trees were changed to natives?  Doubtful.   The structural complexity; that is, the number and arrangement of grasses, annuals, shrubs, and trees, is likely a bigger driver of ecosystem function than whether the plants are native or exotic.

In his thoughtful comments on the blog post Vincent Vizachero sums up, “I stand by my view that the general heuristic of favoring native plants over alien plants is better than the alternative of not caring about origin at all.”   I can buy that as well, but with the caveat that other factors are equal.  The rub, of course, is that other factors are rarely equal.  And I suppose this is where the pragmatic approach discussed by Davis et al.  resonates with me.  In my position I do a lot of programming on trees for urban and community forests.  I go through a list of criteria to consider for tree selection.  Here are some of the key factors I usually discuss:

Adaptation There is no argument that there are well-documented environmental, economic and social benefits to trees in urban and suburban areas.   But in order to fulfill these roles trees must be able to survive where they are planted.  This means being adapted to abiotic and biotic environmental conditions which are often adverse.  In this region of the country there are some native trees that fit the ‘tough trees for tough places’ bill, such as swamp white oak, bur oak, and honey locust.  Many other natives, especially understory species, are much more difficult to site.

This street planting in Lansing alternated green ash and Norway maple.  

Available space This seems like a no-brainer, but it’s amazing how often this gets overlooked and we end up with too much tree and too little space.  Again, we have some great small native trees; Carpinus, redbud, striped maple.  But these can be limited in their site adaptability.

Ash stumps

Diversity  In Michigan some communities have lost 30% of their tree cover to the emerald ash borer.  Have we learned our lesson about improving species diversity?  Not really.  But we need to keep trying.  Exotic pests are here and here to stay.  Does anyone believe that global trade will decrease in the near future?  Does anyone believe that there will be quantum leap in our ability to detect and intercept hitch-hiking pests?  In order to continue to accrue the benefits of urban and community forests we need to continue to diversify our portfolio; this includes a mix of natives and exotics.  I doubt there will ever be sufficient data to prove one way other, but it seems reasonable to me that an urban and community forest balanced among 20-25 native and exotic species will be better able to withstand the slings and arrows of weather and pests better than one made up of 8-10 natives.

Excerpt from Davis et al. letter to Nature on natives vs aliens

In yesterday’s post I linked to a letter in Nature by Mark Davis and a number of other ecologists on the role and native and alien plants.  Unfortunately the journal requires a subscription.   Copyright laws prevent me from re-printing the entire article, however, below is an excerpt from the conclusion, which I think captures most of their message.

“Most human and natural communities now consist both of long-term residents and of new arrivals, and ecosystems are emerging that never existed before. It is impractical to try to restore ecosystems to some ‘rightful’ historical state. For example, of the 30 planned plant eradication efforts undertaken in the Galapagos Islands since 1996, only 4 have been successful. We must embrace the fact of ‘novel ecosystems’ and incorporate many alien species into management plans, rather than try to achieve the often impossible goal of eradicating them or drastically reducing their abundance. Indeed, many of the species that people think of as native are actually alien. For instance, in the United States, the ring-necked pheasant, the state bird of South Dakota, is not native to the great plains of North America but was introduced from Asia as a game bird in the latter half of the nineteenth century.

“Specifically, policy and management decisions must take into account the positive effects of many invaders. During the 1990s, the US Department of Agriculture (USDA) declared several species of introduced honeysuckles to be alien (harmful), and banned their sale in more than 25 states. Ironically, from the 1960s to the 1980s, the USDA had introduced many of these same species in land reclamation projects, and to improve bird habitats. Recent data suggest that the agency’s initial instincts may have been appropriate. In Pennsylvania, more non-native honeysuckles mean more native bird species. Also the seed dispersal of native berry-producing plants is higher in places where non-native honeysuckles are most abundant (Gleditsch, J. M. & Carlo, T. J. Diversity Distrib. 17, 244-253 (2010).

“Clearly, natural-resource agencies and organizations should base their management plans on sound empirical evidence and not on unfounded claims of harm caused by non-natives. Another valuable step would be for scientists and professionals in conservation to convey to the public that many alien species are useful.

“We are not suggesting that conservationists abandon their efforts to mitigate serious problems caused by some introduced species, or that governments should stop trying to prevent potentially harmful species from entering their countries. But we urge conservationists and land managers to organize priorities around whether species are producing benefits or harm to biodiversity, human health, ecological services and economies. Nearly two centuries on from the introduction of the concept of nativeness, it is time for conservationists to focus much more on the functions of species, and much less on where they originated.”

Ecologists weigh in on native-exotic debate

Charlie Rohwer, a frequent guest contributor to the Garden Professors, brought to my attention a recent letter in Nature by Mark Davis and 18 other ecologist entitled, “Don’t judge species on their origins.” Davis is a leading authority on invasive species and author the book Invasion Biology. In their article, Davis and his co-authors make many of the same points that I’ve made here on the blog (Are natives the answer? Dec. 14, 2009; Restoration ecologists you need us – part 2. Aug. 9, 2010) regarding the native/exotic debate. The main point is that we need to develop a more pragmatic approach to managing landscape systems and this includes natives and exotic species; it’s not an either/or question anymore, not that it ever really was.

A couple of excerpts from their letter:

“It is time for scientists, land managers and policy-makers to ditch this preoccupation with the native–alien dichotomy and embrace more dynamic and pragmatic approaches to the conservation and management of species — approaches better suited to our fast-changing planet.”

“Clearly, natural-resource agencies and organizations should base their management plans on sound empirical evidence and not on unfounded claims of harm caused by non-natives. Another valuable step would be for scientists and professionals in conservation to convey to the public that many alien species are useful.”

The pragmatic approach that Davis and his co-authors (and I) advocate recognizes a several realities:

Exotics can fill many of the same ecological roles and niches as natives, Doug Talamy’s book notwithstanding.

Any inherent “ecological superiority” of natives over exotics has long since been negated by anthropogenic land-use change, alien pests, and climate change.

Attempts to eradicate alien species are largely warm-fuzzy exercises with little likelihood of success without liberal use of industrial-strength herbicides.

WOW again (Why oh Why?)

I’m going along with the “dead tree” theme of the week, but doing a little prognosticating at the same time.  Bert and Holly showed you tree demise on site; I’m going to show you tree demise in the making.  We can call this “dead plant walking.”

I’ve done a few WOW postings in the past, often with a focus at what you might find at a nursery or big box store.  Here’s a recent find at an unnamed BBS, in the “topiary” section:

Unless you intend to have a giant stake as part of your topiary statement, this tree (actually a juniper) will morph into a prostrate form before your very eyes. Fortunately, it probably won’t live long once transplanted since it’s so overdue for potting up that the pot has split:

You can just imagine the nest of woody roots fusing into a functionless mass, can’t you?

Run, don’t walk, away from nursery plants like this.  You’ll be glad you did.

Read and follow label directions…

Every extension specialist or educator that mentions any kind of pesticide in a talk or article always includes the disclaimer ‘Read and follow all label directions.” However that caveat ranks somewhere between “Your seat cushion may be used as a flotation device” and “Do not remove tag under penalty of law” as the most ignored phrase in the English language. While we can probably rationalize ignoring the last two (If a jetliner ditches in the middle of the Atlantic is a seat cushion really going to save you? And when was the last time you saw someone led away in handcuffs for pulling the tag off a mattress?); failing to pay attention to pesticide labels can have some real and immediate consequences.

 

I got called recently to inspect some tree and shrub damage at an industrial park in suburban Detroit.  (Because the case potentially involves some legal issues, I won’t mention names of any parties).  The industrial park included several hundred acres, much of it turf and landscape beds of trees and shrubs.  The park had its own groundskeeper but contracted out its spray applications.  A couple summer’s ago the staff groundskeeper complained several times to the contractor that they weren’t doing a sufficient job of keeping up with the weeds in the landscape beds.  The typical vegetation management tools of choice on this site were spot applications of Round-up (glyphosate) and hand-weeding.  For reasons that are not completely clear, this time the contract applicator reached for a jug of Sahara.    Even if you don’t know what Sahara is; what image does the name conjure up?  Parched. Barren. Lifeless.  Sahara is a combination of two herbicides (Diuron and Imazapyr) designed for complete vegetation control in non-cropland areas such as parking lots and rights of way.  And, unlike Round-up, Sahara provides foliar and root activity.  This is a product you use when you want complete burn-down and you don’t want anything growing there for a long time.

 


A hedge maple 2 years after herbicide application

Unfortunately, that was not the desired result in this location.  Within a week of the application, dozens of trees and shrubs all over the industrial park were either dead or wishing they were dead.  The smoking gun was not too hard to find.  The applicators had duly noted the herbicide application in their logbook and presence of active ingredient was confirmed in soil samples.  Although the parties are still working a settlement, the bids for replacing the affected trees and shrubs are well into six figures.

 


The unkindest cut of all.  These green ash were regularly treated with imidacloprid to protect against emerald ash borer.  An herbicide ap took them out instead.


Two years after application there are still bare zones where Sahara ran off from mulch rings and landscape beds.

Of course, all of this death and destruction (and legal wrangling) could have been avoided simply by…  Reading and following the label directions.  The Sahara label notes in several places that contact with roots can damage trees and other plants, including this explicit statement under a heading in all bold letters, PRECAUTIONS FOR AVOIDING INJURY TO NONTARGET PLANTS:  “Injury or loss or desirable trees may result if Sahara is applied on or near desirable trees or on areas where their roots extend.”  Sounds pretty clear to me folks – don’t use this stuff near plants unless you want them to die.

 

So, next time you or someone working for you has any question about what a pesticide does:  Read and follow label directions….

Update on root-rotted Cornus kousa

A little more than a year ago I posted a Friday quiz based on a failing Cornus kousa.The answer explained that our landscape has, in part, a perched water table that effectively rotted most of the roots of this poor tree over several years.  Last spring we moved it to a different section of our landscape where we know the drainage is better, and I’ve been monitoring its recovery since that time.


Cornus kousa leaves in 2007


Cornus kousa leaves in 2011

We were gratified to see that the leaves this year are significantly larger than those of previous years.  This tells us that root function has resumed, providing enough turgor pressure to expand the leaves to normal size.  It was especially helpful that we had one of the rainiest springs on record.

Take home lesson:  if a tree or shrub is failing in its current location, it’s worth digging up to see what’s going on.  Bad soil conditions?  Move it to a better location.  Bad roots?  Time to hone your root pruning skills.  But wait until fall to do this.  Transplanting this time of year is the most difficult for plants because of the increased water demands of warmer temperatures and expanding leaves.

Our visiting GP takes on fertilizers

Like many readers of this blog, I’m like a kid in a candy store where plants are sold.  I try to justify the extra cost of a large annual pot instead of a scrawny 4-pack, or I imagine I’ll find room for that lime green Heuchera and my wife will learn to love it.  But unless I keep my blinders on and stick to the shopping list, I’ll probably leave with a fertilizer.  This year, I’ve purchased 12-0-0, 5-6-6, sulfur, and some 5-1-1 liquid.  Those go with my 6-9-0, 11-2-2, 9-0-5, 2-3-1, and 4-6-4.  I can explain why I ‘need’ each one.  I have a decent idea what my soil is like because I’ve had it tested (though I’m due for another test). But I’ve always questioned how those bags of fertilizer can know exactly what my garden needs.  The rates listed on the bag imply they’re universal under all circumstances and will give great results if the directions are followed.   Is that true?   And at what cost?

For example, 2 of the bags are listed as ‘lawn’ fertilizers (the veggie garden doesn’t care about that though).  But if I apply these to my lawn at the rate listed and 4 times per year, I’m adding 3-4 pounds of nitrogen per 1000 ft2.  That’s a reasonable rate if I irrigate and bag my clippings, but I don’t do either.  Therefore, I only need ~1 pound of nitrogen, not 3 or 4 (see this publication for more info). I just saved myself some money by disobeying the bag. That extra nitrogen isn’t useful for making MY lawn healthy.

One of my fertilizers is labeled ‘tomato’.  If I do exactly as the bag tells me for tomatoes, I would be applying the equivalent of 400 pounds of nitrogen and almost 500 pounds of phosphate per acre.  So what?  Well if I look at a guide for how to grow tomatoes commercially, I’d notice that the recommended nitrogen rate is 100 to 120 pounds per acre, and phosphate is 0 to 240 pounds per acre.  Yes, those are commercial guidelines, but they shouldn’t be too far off from garden recommendations. And of course, recommendations should always be based on soil tests.  But 4 times the N and 2 to infinitely more times the amount of phosphate than is required? That’s likely a waste of money at least. And yes, those recommended guidelines are real: you CAN grow food without adding phosphate or potassium-containing fertilizers.  If the plants you’re growing don’t need much and your soil has plenty, you don’t need to add any.

Say I’ve got an acre of onions (Fig. 1; not quite an acre). One of the bags of fertilizers, were I to follow its instructions for fertilizing ‘vegetables’, tells me that I should add 100 pounds of nitrogen and 120 pounds of phosphate and potash at planting (per acre), followed by half that partway through the season (next to the row). The commercial production guidelines tell me that the nitrogen rate is similar to what the bag of ‘vegetable’ fertilizer says, but I actually need about 7 times less phosphate and potash (based on my soil test results; I have quite a bit of P and K already in my clay-loam soil). I don’t want to add stuff my soil doesn’t need, so I use my shelf full of bags, a scale for weighing pounds of fertilizer per cup, and some math to come up with a custom fertilizer regime that suits my soil and the onion’s needs (see Table 1, and remember that the numbers are for MY soil, not necessarily yours).

One problem with using extra fertilizer may be in the extra cost (wasting nutrient the plant won’t use), but that depends on what fertilizer it is and how much it costs. Another problem may not be immediately apparent, and that is nutrient deficiencies. Too much phosphorus can cause zinc deficiencies, for example. Excesses of some nutrients can create greater chances for pest and disease problems. One big problem with using too much is the potential for these extra nutrients to go where they shouldn’t be, like in groundwater, rivers, lakes, and streams. And as Jeff has mentioned, phosphorus fertilizers won’t be around (cheaply) forever.

Do the work of figuring out what kind of soil you have and what’s in it, what your fruits and veggies need, and what kinds of fertilizers can do the job for you.  Heck, you can even organize your fertilizers based on “cost per pound of nitrogen” to see where the best bang for your nitrogen buck will be.  But none of us are THAT obsessed about our fertilizers, right?…. [$ per bag / (pounds per bag * (% nitrogen/100))].

As a reminder, the numbers on your fertilizers are percent nitrogen, phosphorous (as ‘phosphate’, P2O5), and potassium (as ‘potash’, K2O).  One cup is 16 tablespoons, and an acre is has length of one furlong (660 feet) and width of one chain (66 feet), or 43,560 square feet.  Side rant: metric rocks.

Safety first?

I was driving around town recently and saw a tree service crew clearing up some storm damaged trees. Because of my line of work I usually do a little rubber-necking and try to assess why type of tree came down and what issues may have preceded it’s demise. In this case, however, I was struck not by the trees but by the tree crew. What I saw left me speechless. Well, here, see for yourself…

 

No eye protection.  No hearing protection.  No sign of a hardhat, face-shield, or chaps by the chainsaw.  No personal protective equipment anywhere as near as I could tell.  Of course the photo illustrates a lot of what’s wrong with the landscape and tree service industry.   Economists tell us that this industry has a ‘low barrier to entry’; in other words any one with a chain saw and a pickup truck can put an ad in the classifieds and call themselves a tree service.   As a consumer, you may not care if the employer makes their employees where personal protective equipment (PPE).  But if they don’t care about their employees’ safety, what else don’t they care about?

 

Periodically I’ll write an article for a newspaper or other media on selecting an arborist.  I always make the point that you get what you pay for and urge consumers to compare bids and companies carefully.  Truly professional tree services have to cover the cost of hiring and retaining quality employees, worker training, proper equipment (including PPE), and insurance.  If you skip over those things, like Fly-by-night tree service here, it’s probably not too hard to come out with the low bid.

Science Education and Lichens

Seemingly once a week we see a report in the news about how Science and Math education in the US lags behind many developed countries around the world.  http://articles.cnn.com/2011-05-15/us/education.obrien.response_1_math-and-science-national-robotics-competition-education?_s=PM:US

While we typically think of Chemistry and Physics when discussing science education, biology is in there too.

 

I bring this up because I am continually amazed at how little many people know about basic biology.  Some of this funnels its way into extension calls and e-mails.  A couple of weeks ago I got a call from a distraught homeowner in a Detroit suburb.  “My maple trees are dying”, he told me sincerely.  “There are growths all over them.  They’re big trees.  What do I need to do to save them?”

 

I tried to get as much information as I could over the phone: How old are the trees? What kind of maple? Describe the site.  Describe the symptoms.  I told him the problem didn’t sound like typical issues with maples in our area (i.e., not manganese chlorosis, tar spot, gall mites, or verticillium wilt).  Diagnosing problems sight unseen is difficult so I asked if he could get me some digital photos.  “Yeah, my son has a digital camera.  We can do that.”  Later that week I got a series of digital photos like the one below.

Lichens on maple

I informed him the growths on the trees were lichens, a combination of a fungus and algae; they’re normal and they don’t harm trees.  I gave him a quick biology lesson on lichens and pointed out that some of the pictures he sent were of lichens growing on the sidewalk.  The algae part of the lichen is photosynthetic so they just need a place to hang out – a tree, a sidewalk or a piece of wood all work fine.

British soldier lichens

One of my all time favorite bumper stickers says, “If you think education is expensive, try ignorance”.  I suspect if this homeowner had happened to call an unscrupulous tree service instead of MSU Extension, they would have been more than happy to ‘treat’ the problem and sign him up for their deluxe 8-step pest and micro-nutrient maintenance plan.  Sometimes a little knowledge can go a long ways.