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Living with lichens

We often hear that the US needs to boost its investment in science education to keep up with rest of the world. While we often think in terms of physics and chemistry when we think of science, we need to remember biology and ecology fit in the mix, too.

I bring this up because of a call a received a while back from a homeowner. The gentleman was concerned /borderline distraught that he would have to remove a prized maple tree from his front yard because it had “peculiar growths all over the trunk”. I told him it was difficult to diagnose a tree problem sight unseen but if he could send me some images, it might help me out.

The photo did indeed make ‘the problem’ obvious.

The growths were lichens. Lichens do not harm trees but I’m sure an unscrupulous tree service could have easily convinced the homeowner his tree needed come out had he not contacted me first. Lichens are actually two organisms; a fungus and an algae that form a symbiotic relationship and function very much like one organism The algae part of the lichen is photosynthetic, and therefore they are able to produce their own energy and do not take any resources away from the tree. In fact, lichens often grow on non-living substrates such as wood, concrete, tombstones, benches and so on. If a homeowner observes a dead tree or dead branch covered with lichens on it, this is a coincidence; the lichens did not cause the branch or the tree to fail. The tree trunk or branch simply provides a porous surface for the lichen to attach. Lichens are often fairly inconspicuous, but in some moist areas, such as the Pacific Northwest, they may form a mat that completely coats branches.

Fast facts about lichens

Lichens grow in some of the most inhospitable places on earth from deserts to tundras.

Lichens are commonly grayish-green, but may also be yellow or red, depending of the type of algae associated with the fungus.

Lichens are sensitive to air pollution, and researchers are investigating their use as a bio-indicator of air pollutants such as sulfur dioxide and ozone.

Lichens are fascinating organisms, if you are taking a liking to lichens try these websites:
http://www.nmnh.si.edu/botany/projects/lichens/
http://www.ucmp.berkeley.edu/fungi/lichens/lichens.html

Thomas Knight and the Water Wheel

Classes have begun, and this semester (and every spring semester) I have the opportunity to teach our introduction to horticulture class, otherwise known as Plant Propagation (Hort 1001). We usually have about 120 students, and I don’t want to brag or anything, but it is just about the best class out there. Watching the students learn about seeds, cuttings, and grafting in the labs is one of the most motivating things about my job (and it doesn’t hurt that the greenhouses are about 70 degrees while it’s 0 outside). But, as you might expect, there is a lecture too. Believe it or not, the lecture isn’t half bad. In fact, students actually ask questions in class. This past Tuesday during a lecture on seeds one of the students asked how the roots know how to grow down when they exit the seed. The answer is geotropism. Geotropism is a response by a plant to gravity. Some parts of a plant grow towards a gravitational pull (roots), and some grow away from it (shoots). One of the coolest experiments ever was a study done by a gentleman named Thomas Knight in the very early 1800s where he set up a water wheel which had seeds planted along the edges. As the wheel spun and the plants grew they responded both to the Earth’s gravity and to the force created by the spinning wheel. You can see the results below.

Knight also did some very interesting work showing that buds from older plants retained their physiological age when grafted onto younger plants. Basically that means that if you graft a bud from a mature ‘Honeycrisp’ apple onto a young seedling, that bud will produce a new shoot which produces ‘Honeycrisp’ apples before the rest of the tree produces apples.

Usually when we think of horticulture we think of L. H. Bailey – and we should – but let’s never forget Thomas Knight either.

Pussy Riot: How far should we go to eliminate destructive alien species?

A short article in our Sunday paper caught my eye this weekend. New Zealand economist Gareth Morris has launched a campaign to eliminate domestic cats from the country in order to preserve native bird populations. According to Morris and his supporters, cats represent a serious threat to many rare and endangered bird species in New Zealand, which has the highest rate of cat ownership in the world. Ironically, one of the reasons the article our paper caught my eye is I have been considering adopting a feral cat from a local program to control mice in our barn.

So, what do you think? Are cats useful companions and mousers or do you agree with Morris that they are ‘natural born killers’ that need to be eliminated?

Balance

By this time most of you have probably read all about Mark Lynas, the anti-GMO activist who decided that GMOs are actually a net benefit to society. I’ve been asked by a few people to comment on how I feel about Mr. Lyna’s changing sides. I think they expect me to be jumping up and down for joy. But that’s not how I feel at all. I’m happy when anyone decides to let research lead them to a conclusion rather than politics or gut feelings, but in this case it also makes me nervous. This is because some people tend to travel too far towards one side or another. I’m just as fearful of the damage that people who are radically pro-GMO may cause as I am of radically anti-GMO activists. And, in my opinion, this guy just seems to be radical. Saying that you have research that supports one side of an argument is fine, but in almost all cases there is research that supports the other side too, and you ignore it at your own peril. Balance people — Balance.

Where did the 10-20-30 rule come from? Is it adequate?

We’ve been having an interesting discussion over on the Urban Forestry group on LinkedIn on the origins and suitability of the 10-20-30 rule for tree diversity in urban forests. For those that aren’t familiar, the 10-20-30 rule is a guideline to reduce the risk of catastrophic tree loss due to pests. The rule suggests an urban tree population should include no more than 10% of any one species, 20% of any one genus, or 30% of any family.

The first published reference to the 10-20-30 rule (often referred to as just the 10% rule) was by late Dr. Frank Santamour, Research Geneticist at the US National Arboretum in his paper Trees for urban planting: Diversity, uniformity, and common sense, which was presented at the 1990 Metropolitan Tree Improvement Alliance (METRIA) conference. While Santamour is commonly credited with the 10% rule he notes in his paper, “I am not sure who first propounded the “10% rule”, nor am I sure that anyone would want to take credit for it, but it is not a bad idea.”

The other question on the LinkedIn discussion is whether the 10-20-30 rule is adequate to ensure genetic diversity in urban and community forests. My personal is opinion is that the rule is inadequate but far preferable than the status quo in most communities. If we consider the current issue with emerald ash borer (EAB) in North America, following the 10-20-30 rule means we would accept the loss of 1/5^th of our urban canopy since both of the commonly planted ash species (Fraxinus pennsylvanica or F. americana) are highly susceptible to EAB. On the other hand, many community tree populations the US currently include 30% or more maples, so 10-20-30 would actually be an improvement.

A limitation to the 10-20-30 guideline that Santamour acknowledges is that the rule does not afford protection against insects with a broad host range such as gypsy moth or Asian long-horned beetle. However, while these pests can, and have, caused widespread damage they do not appear to threaten nearly total annihilation of an entire species or genus ala specialists such as chestnut blight, Dutch elm disease or EAB. Moreover, a wide diversity of species is still a better defense even against generalist pests, unless you happen to get lucky and plant a monoculture of the one tree they won’t destroy.

One of the inherent challenges in the 10-20-30 rule is implementation. What is the tree population in question? Are we talking about a city? A neighborhood? A block? If there are 10 trees on a block do they all need to be different species? Some have proposed corollaries to 10-20-30 such as the “Look around rule” (or “Look around, fool!” if you prefer the Mr. T version). This guide states if you’re getting ready to plant a tree; look around and if you already see that tree, plant something else. The problem with diversity on a very small scale is we can end up with the ‘menagerie effect’ – one of these, one of that, one of those – that often lacks aesthetic appeal. Ultimately this becomes a challenge for urban foresters and designers working together; how do we incorporate diversity guidelines within established design principles.

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Over-Interpreting

One of the things that scientists need to be able to do is to figure out what the research that they conduct means without over-interpreting it. This isn’t as easy as it seems, for example, if a particular pesticide at a particular dose kills mice, then should it also kill humans? Without testing we really don’t know – though we certainly have suspicions. If we allow our suspicions to take over and we say that, based on the mouse data, the pesticide necessarily does or doesn’t affect humans then we’re over-interpreting. Most (dare I say all?) scientists have been guilty of over-interpreting their results – or the results of others — at one time or another in their careers. It’s a hazard that comes with the job. Unfortunately it’s a hazard that comes with journalists jobs too — often over-interpreting what scientists say. Recently I had the opportunity to see an online lecture (a TED lecture) on this very topic and thought it was worth sharing.

Planting Edibles in Cities

The snow has just started falling and I’m already thinking about what I’m going to be planting next spring. Most of my plantings won’t be at my own house, they’ll be out in the cities of St. Paul and Minneapolis. We’ll be looking at all kinds of fun stuff like growing trees in various new types of containers, adding compost to planting holes in different circumstances, and even pruning methods. But one of the big things that we’re starting to look at are new trees for the urban environment. Cities have always spent time considering what they plant, but with the emerald ash borer ravaging the Midwest, now they’re thinking even harder. And because of the local food movement, suddenly the cities are at least considering trees like apples and hazelnuts on a trial basis (sure, there are some places that use them here and there, but they’re less than common). Of course, if this movement stalls, the cities would be upset at having so many “messy” plants around (that’s their big concern about edibles right now), but I don’t think it will. I’m actually pretty optimistic about using fruits and nuts on public property. Sure, some plants will fail because they get too many diseases or insects, or because they’re weak wooded, but some will make it too. I think hazelnut has a great chance in the right place (it would be too bushy for most boulevards….). Do any of you have a favorite edible that you think might work well in a city? Let me know, maybe we’ll try it!

Closing the loop

Just a short post today as I am participating in an Extension planning meeting for most of the day. One up-side to the meeting is we are meeting and having lunch at Brody Dining hall here at MSU. If you’re around my age and attended college in the 80’s, the thought of eating at a dormitory dining hall might elicit memories of a hair-netted cafeteria lady glopping amorphous slop on your tray next to the mystery meat of the day. Boy, how times have changed. Today, the quality of dining hall food is point of competition for universities angling for students. The Brody dining center is set up like a food court, daily choices for students include a fresh salad bar, southwest food, sushi, made to order pizza, home-style comfort food, even kosher food.

The dining halls are also part of MSU’s sustainability initiative. Food wastes from the dining halls are collected and sent to an anaerobic digester and composted at the MSU Student Organic Farm. The compost is used at the recently completed Bailey hoop-houses on campus to produce salad green and herbs for use in the dining halls, providing a closed-loop system. Is the food produced in the hoop-houses going to make the dining halls completely self-sufficient? Probably not in the foreseeable future. But they do provide a good opportunity to promote horticulture. The project has generated numerous press articles and there are posters around the dining hall highlighting the project. In an age when many bemoan the public’s disconnect between farm and fork, the Bailey GREENhouses remind students, especially those that might not think about it otherwise, where their food comes from.

Does fertilization increase insect herbivores?

Always fun when you find a research paper that confirms what you’ve suspected all along. I ran across a paper last week in the Annals of Applied Biology entitled ‘Fertilisers and insect herbivores: a meta-analysis’ (Butler et al. 2012. Ann Appl Biol 161: 223–233). I’m interested in the topic because in recent years a dogma has emerged that if you fertilize a landscape tree it will be immediately devoured by insects. In this study the authors conducted a meta-analysis (basically a compilation of studies on a given topic and then combining and analyzing the aggregated results) and looked at dozens of studies of the response of insect herbivores to fertilization to answer the question, does fertilization increase insect damage? The answer was absolutely no surprise to me: It depends.

What does it depend on? First, what type of insect. Secondly, what kind of fertilizer. For example, fertilizing with nitrogen greatly increases populations of sucking insects. This makes sense when you stop to think that aphids and other sucking insects have to consume a lot of phloem sap –which is essentially sugar water – in order to get sufficient nutrients. Nitrogen fertilization did not significantly increase populations of chewing insects, however. This could be related to off-setting effects of improved nutritional quality of leaves versus increased presence of defense compounds or leaf toughness. For other fertilizer elements Butler et al. found that phosphorus decreased insect populations in 2/3^rd of the studies (14 out of 21) and that potassium decreased insects in 7 out of 10 cases. As with nitrogen only, complete fertilizers (NPK) tended to increase insect populations, especially for sucking insects.

I should hasten to point out some limitations of the study as it relates to tree fertilization. First, of course, is the British spelling of fertilizer. Second, the study mainly dealt with fertilization in agronomic crops, not trees. Lastly, the authors only included studies on insect adults. In many cases insect larvae, not adults, are the most damaging life stage, especially for insects that affect trees. Nevertheless, the study highlights the difficulty of making generalizations when discussing host stress and insect interactions. In addition to type of insect and type of fertilizer, we could have added nutritional status of the plant before fertilization to the ‘It depends’ list. My rule of thumb is that trees shouldn’t be fertilized unless a problems is noted by visible symptoms, a soil test, and/or a foliar test – and preferably by more than one of these.

Bottom line: Before you buy into the notion that fertilizing a tree is going to increase insect problems make sure you know what type of pest you’re dealing with, what type of fertilizer and the current nutrient status of the tree.

How Can Natives and Exotics Possibly Coexist?

Natives vs. exotics. We’ve heard that before haven’t we Bert? Well, here’s an interesting little nugget published recently in the journal Ecology Letters. Exotics and natives are different, and their differences allow them to coexist. In this study exotics were superior to natives in terms of growth, but were fed upon more by herbivores. Interesting. Of course there are lots of different types of exotics and natives, but the plants that these researchers looked at had been living together for about 200 years. I think that’s something that the invasive extremists and apologists consistently forget – until relatively recently the average person didn’t spend that much time thinking about native or exotic, and yet the world never turned into a desert and neither the natives nor the exotics disappeared. I’m not saying we shouldn’t think about native vs. exotic differences at all, just that sometimes we concentrate on this distinction too much. Plants tend to be able to fend for themselves.