Maple Leaf Miners, Understory

by Carl Strang

In addition to the trailing strawberry bush (reviewed yesterday), I looked at leaf miners on understory sugar and black maples at Maple Grove and Meacham Grove forest preserves last week. As was the case with the other study, I was interested in the potential impact of controlled burning on the populations of the tiny moths whose caterpillars mine the leaves. Even after a year, the burned areas still had essentially no leaf litter.

Unburned areas at Maple Grove, and in a separate, off-study-area forest in Meacham Grove Forest Preserve, had plenty of litter remaining.

The upshot, though, is that I cannot identify any impact of that fire on leaf miner populations. This is not because they are all high, but rather because the four genera of miners have been consistently low at Meacham Grove for 15 years, now. This year, likewise, maple leaves were very clean at Meacham.

That result, I suspect, is more from the sustained intensive management at Meacham Grove over the years, with greater removal of understory maple saplings and more frequent and extensive burning. This is consistent with Meacham Grove’s forest having more of an oak component, a sign that it was exposed more to fire in its early days, fire that would have limited maple reproduction and dominance. The differences I have observed between the two forests in understory leaf miner populations thus may reflect a historically significant difference in the ecologies of the two preserves. Certainly the management at Meacham has produced an increase in botanical diversity of forest floor plants there.

In three of the four leaf miner genera, understory populations were higher this year at Maple Grove than at Meacham Grove. At Maple Grove, Caloptilia were present on 8% of understory leaves (2% at Meacham), probable Stigmella were on 3% (0% at Meacham), and Phyllonorycter were on a whopping 19% of understory leaves (0% at Meacham). The difference in Cameraria blotch mines, on 2% of Maple Grove leaves and 0% of Meacham Grove leaves, was not statistically significant (for more on these insects, go here). Though I did not take measurements, Phyllonorycter tent mines to the eye were much more abundant in the unburned, less managed forest block at Meacham Grove, and thus resembled Maple Grove.

At Maple Grove, two of the four insect groups increased over last year. That 19% figure for Phyllonorycter in fact is the highest since before 1996, and it is the fifth time that population has occurred on more than 10% of leaves in that period. The median annual value in those 15 years has been a healthy 6%. Caloptilia likewise have stayed strong, with a median matching this year’s value of 8%. This year’s frequency of 3% likewise is the median value for Maple Grove (probable) Stigmella. Cameraria has stayed low, with a median of 2% (also this year’s Maple Grove value). The respective medians for Meacham Grove have been 1%, 4%, 1%, and 0%. All of this discussion has been about the understory. The forest canopy may produce different results, which I’ll investigate in November.



  1. John said,

    September 24, 2010 at 1:34 pm

    Hi Carl,

    I came across your blog researching, of all things, DuPage County history but I’ve stayed interested as I’ve learned more about DuPage Co’s ecology too!

    I’ve got a question for you regarding the last few posts… what is your “take” on controlled burns?

    I’m coming from a novice standpoint, ecologically speaking, and I’m trying to envision what life would have been like for the world we live in 200+ years ago (yet, as I understand it, even then some Native American tribes did their own prescribed burns).

    On one hand, fires likely would have occurred more frequently than they naturally do now by virtue of the fact that there would have been more natural features to the land… likely more larger, older trees, no man-made conduits to attract and deflect lightening strikes, only natural barriers to prevent fires from spreading.

    On the other hand, the fires that did occur (speaking of the natural woodland or grassland type fires, not anthropogenic in nature) would be unhindered and would burn through the available fuel of fallen leaves, branches, and trees and thus, with the greater frequency of fires, they likely wouldn’t be as severe as the wildfires we get nowadays in more rural areas of Illinois or Wisconsin, or certainly the backcountries of Colorado and similar places.

    In the case of more frequent, less severe fires over large swaths of land, the entire ecology would be much healthier than what we know to day as “wilderness” in places like the Northwoods in Wisconsin or the back country in Colorado. Even our forest preserves which are certainly protected and cared for… but confining nature to such a limited area (and making it accessable and enjoyable to man) isn’t allowing nature to be nature. I am certainly thankful that we have the natural areas that do still exist and I wouldn’t trade what we have for something less… But do these areas need to be treated differently because each ecosystem doesn’t have the interaction with neighboring ecosystems (that are either similar in the case of deciduous or coniferous forests, or quite different, like a forest and a swamp)?

    I know there’s a lot here… but these are things I have thought about. I’ve come to the realization that what I know as “Wilderness” isn’t what wilderness was 200+ years ago. It’s hemmed in. It’s wild (with a lowercase w). It’s muted, in some respects. And, to be honest, it’s rotting. The amount of dead underbrush and combustable matter has been gathering for decades if not longer in many places… and we as a species have gotten really, really good at building big expensive houses in very picturesque locations.

    I just think about the recent encroachments by invasive species. Where would the Ash Borer’s have gone if we had allowed our natural areas to burn naturally for the last 200 years? Would the effect of the Pine beetle in Colorado have been nearly as devestating as it has been? Maybe those invasive species are hearty enough to withstand a fire and it wouldn’t have mattered (heck, there’s a chance it would have been even worse), but maybe the outbreaks could have been stopped naturally before they got out of control.

    In the case of the Pine beetle, there is now so much fuel that it may be a disaster waiting to happen on a scale much greater and more severe than it would have been if burning had not been supporessed.

    Sorry for the diatribe of sorts… I oftentimes find myself in an epic battle with myself… wanting to see what types of things man can build and create yet not wanting to lose the beauty and majesty that is God’s green earth.

    So, getting back to my original question… what is your position on controlled burns? Should they be done at all? Or if they should be done, how often and in which types of locations?

    • natureinquiries said,

      September 25, 2010 at 6:48 am

      Hi, John,
      Thanks for a long and thoughtful comment. Since you begin by expressing your interest in history, perhaps the first part of my perspective I should share is that there is no such thing as a landscape uninfluenced by human activities in our part of North America, since the time that landscape originated with the departure of the last glacier (as it melted away, people already were here to wave bye-bye, and though their population was small they were having significant impacts through hunting large animals faster than these were able to replace themselves).

      Since people were here all along, we can’t really know how things might have been different, for instance what North America would have been like if fires were all started by lightning. The rich diversity of prairie plants, at least in the tallgrass areas, would seem to imply evolution in an environment where fire was an important disturbing factor, so I’m inclined to regard fire-influenced communities as a given.

      Once the argument reaches that point, land managers have to accept that maintaining biodiversity (keeping populations of all the native species, common and rare) is going to involve creating disturbance. We have seen plenty of instances of local extinctions when disturbance is prevented. (Perhaps I should explain that the effect of disturbance is to prevent a few species of competitive dominants from taking over). When a restoration project begins, disturbance in our local dry-land ecosystems usually involves brush clearing. Once a native plant community is established, fire is usually the tool of choice. This is in part because of history, in part because it’s relatively efficient, and perhaps in part because we can’t claim to know all that goes on and so stick with what worked for thousands of years. Fire does have more benefits than simply being a disturbance factor.

      That said, there is some debate about how often and how much to burn. Perhaps the biggest alarm is raised by insect ecologists, who point to the loss of invertebrate diversity when an entire block of, say, prairie is burned. The conservative thing to do is burn only part at a time, allowing an unburned area to preserve insects and other invertebrates that otherwise might be eliminated. Some land managers get so focused on the plants that they forget this important point. That is less a problem in a place like DuPage County, where ecosystem blocks are small and history has removed most of the rarer species already. In our larger projects you don’t see wholesale fires, and over time as high quality communities develop, it will be possible to reintroduce missing species or, in some cases, they may find their way back.

      I think that covers most of your question. Our picture of this area 200 years ago is lacking in detail, but we do know the landscape was diverse. Fire was an important factor, but it didn’t go everywhere. Our north-south rivers created fire shadows, with forested areas on the east banks where fires seldom went (thanks to the prevailing westerly winds). Wet areas and topographic breaks also stopped fire from being ubiquitous.

      I hope this helps.


  2. November 10, 2010 at 7:01 am

    […] this year’s measurements of leaf miners in black and sugar maples. Earlier I reported the results for the understory. This time I was looking at fallen leaves to index leaf miner abundance in the forest as a whole. […]

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