Where There’s Smoke

by Carl Strang

Mid-November brought forest preserve district crews to St. James Farm to conduct controlled burns in the forest. These burns are a normal part of oak woodland ecology in northeastern Illinois, and they help control invasive plants. Occasionally the consequences of the burn extend beyond the brief time when the flames consume the dry leaf litter on the ground, and I noted two such incidents this time around.

Carpenter ants commonly hollow out the base of a tree as they tunnel through the dead wood at the core. If the accumulated sawdust catches a spark from the controlled burn, a slow growing smoldering coal can expand to the point where it consumes a significant amount of the remaining wood.

A victim of that phenomenon was the large white oak that harbored the great horned owl nest last winter.

A victim of that phenomenon was the large white oak that harbored the great horned owl nest last winter.

There had been a larger live stem, and a smaller dead stem (the fractured one in the photo) where the nest had been. The live stem’s base was thinned by the growing coal to the point where it went down, taking the nest stem with it.

The same burn had the remarkable effect of catching in another tree, already knocked down by a storm, which then smoldered for weeks.

Here is the tree 2.5 weeks after the burn, on December 5. The underside of the fallen stem was burning slowly from west to east, and the top of the stem protected the coal from the snowfall.

Here is the tree 2.5 weeks after the burn, on December 5. The underside of the fallen stem was burning slowly from west to east, and the top of the stem protected the coal from the snowfall.

Another heavier snowfall still did not stop the burn, here on December 12. This was a cold day, but a moderate west wind kept the coal alive.

Another heavier snowfall still did not stop the burn, here on December 12. This was a cold day, but a moderate west wind kept the coal alive.

At that point, however, the coal was no longer sheltered. When I returned on the 16th, I found the fire had gone out. It had lasted nearly a month.

 

Burn Season

by Carl Strang

The end of winter brings with it the prairie and savanna controlled burn season. Mayslake Forest Preserve got some of that attention, but it was more limited than the almost complete coverage of two years ago.

Only half of the north stream corridor prairie was burned, for instance.

Only half of the north stream corridor prairie was burned, for instance.

A thread of fire reached into the edge of the stream corridor woodland and ignited the tall stump which I regarded as the most likely nest site for the great horned owls last year. It continued to smolder for days.

Several feet of one side burned away, showing that the cavity had been wide open and quite deep.

Several feet of one side burned away, showing that the cavity had been wide open and quite deep.

I don’t know if any owl eggshell fragments could be found in the former base of the cavity, but it’s a moot point now as they won’t be able to use this platform again.

I don’t know if any owl eggshell fragments could be found in the former base of the cavity, but it’s a moot point now as they won’t be able to use this platform again.

It’s a moot point personally, too, as I will be retired next year and plan to shift my preserve monitoring to St. James Farm, a preserve closer to home.

Burn Aftermath

by Carl Strang

Mayslake Forest Preserve had much of its acreage burned for management purposes last spring, as described earlier. One result, aided by good amounts of seasonal rains, was a very lush, tall growth of prairie vegetation.

Part of one of Mayslake’s prairies on August 12.

Part of one of Mayslake’s prairies on August 12.

What impact did this have on the prairie insects, in particular the singing insects? I expected the species that lay their eggs in the tops of prairie plants would be impacted the most, but those that lay their eggs in the soil would be relatively unharmed. It was clear, though, that despite the unusual completeness of the burn, small patches of prairie here and there were missed by the fire, as were wetland and woodland edges, and there were portions of the preserve not included in the burn plan. These provided a reservoir from which affected species might spread.

My impression through the season was that the numbers of fall field crickets (a species which lays its eggs in the soil) were down from last year, but the numbers don’t bear this out. Counts on the whole in the various habitats are similar between this year and last. Likewise, the 3 species of common ground crickets are so abundant in all habitats that no quantitative comparison seems necessary.

Greenstriped grasshoppers overwinter as nymphs, and so are more vulnerable. If anything, however, their numbers seemed somewhat larger in all habitats, including burned ones.

Greenstriped grasshopper nymph

Greenstriped grasshopper nymph

Unfortunately, confusion about the species identity of meadow-dwelling tree crickets (described in a post earlier this week) prevented my gathering quantitative data last year. I did record numbers this year, though, and attended their locations through the season. It was clear that the earliest singers in this group were concentrated in unburned areas and around the edges of burned areas, where they might have hatched from eggs in the unburned adjacent habitats. As the season progressed, though, these tree crickets (mainly Forbes’s tree crickets) proved to be very mobile, and spilled into the hearts of the burned areas (where the forage no doubt was richer thanks to the burn, and where there was an advantage to escape the competition). Though numbers overall may have been down a little, there were plenty of these tree crickets to ensure a rapid population recovery.

As for meadow katydids, they all to some extent concentrate in wetlands, which were scorched in places but not thoroughly burned. There again appeared to be plenty of survivors to reproduce and fill the habitat.

Perhaps the most interesting observation relevant to this question this year was a big drop in wasps of the genus Sphex. There were a lot of these last year, crowding into the areas where swamp milkweeds were blooming. The great black wasp and great golden digger specialize in capturing katydids to feed their young, and potentially can influence populations significantly. I saw only a very few of those wasps this year. As they overwinter underground, I doubt the fire had anything to do with their absence. Whatever the cause, their departure further assured a successful reproductive season for the katydids of Mayslake.

Great golden digger

Great golden digger

The upshot of all of this is that the extensive spring burns, while they may have had some minor and spotty effects on singing insect populations (and, by extension, other invertebrates), did not devastate any populations as far as I can tell. This was somewhat surprising, but in retrospect it becomes clear that it would take an extraordinarily complete and extensive burn to have a long-term impact. Refugia within and without the burn area seem likely to carry populations through enough to recover from this disturbance.

Burned Area Recoveries

by Carl Strang

The extensive areas at Mayslake Forest Preserve that received controlled burns this spring are responding vigorously, as rains and warming temperatures have supported rapid plant growth.

The fire killed the smooth sumac stems, but this is a fire-adapted species of the prairies, and new shoots are rising.

The fire killed the smooth sumac stems, but this is a fire-adapted species of the prairies, and new shoots are rising.

Though the dried herbaceous tops burned thoroughly, the wooded and wetland edges of prairies and meadows, as well as areas dense with shrubs, were less affected.

The outer, peripheral ranks of woody stems were killed, but the denser central stands survived.

The outer, peripheral ranks of woody stems were killed, but the denser central stands survived.

Of course my particular interest is in how the singing insects fared. Last week I was able to make early observations of green-striped grasshoppers, which were nymphs at the time of the burn. While it was clear that grasshoppers were few in the centers of larger burned areas, there were occasional individuals even there. Smaller areas, and edges of larger burn zones, had good numbers of grasshoppers, and so there are plenty to repopulate the prairies and meadows.

The Greening of Mayslake

by Carl Strang

The once blackened, burned portions of Mayslake Forest Preserve are responding to the increased heat absorption of that dark soil surface, as well as to the release of minerals in the ashes, and plants are growing rapidly.

The savanna ridge, among the last portions to be burned, already was this green a week ago.

The savanna ridge, among the last portions to be burned, already was this green a week ago.

Among the flowers blooming in that burned area is the early buttercup.

Among the flowers blooming in that burned area is the early buttercup.

Bellworts likewise have responded with full stems and flowers.

Bellworts likewise have responded with full stems and flowers.

In the prairies, which experienced their controlled burns earlier, the green reveals that a number of taller stems still stand, their tops unscorched.

This tempers my expectation that insects whose eggs overwinter in such stems might be absent from the burned areas.

This tempers my expectation that insects whose eggs overwinter in such stems might be absent from the burned areas.

Elsewhere, other plants are in their spring glory.

Dutchman’s breeches continue to multiply in the (unburned) south savanna.

Dutchman’s breeches continue to multiply in the (unburned) south savanna.

Weeping willow flowers may not be colorful, but they offer an interesting texture to those trees in this season.

Weeping willow flowers may not be colorful, but they offer an interesting texture to those trees in this season.

The green is a welcome change in the landscape.

The Burn Extended

by Carl Strang

As I reported earlier, Mayslake Forest Preserve had a thorough controlled burn of its highest quality restored prairies in late March. On Monday I discovered that had not been the end of it. The Forest Preserve District’s crew returned and conducted a burn of the north savanna and adjacent meadow areas.

The top of the savanna ridge after the burn.

The top of the savanna ridge after the burn.

This burn likewise was a good one, leaving little in the way of last year’s dead herbaceous growth. This is the most complete burn coverage of the preserve in the 5 years I have been there, and along with the vegetation went the eggs and nymphs of many species including tree crickets, meadow katydids, and greenstriped grasshoppers. From a scientific standpoint this is more opportunity than it is disaster, as there are no rare species at Mayslake. The remaining, unburned meadows and wetlands, as well as a few pockets that did not burn well, will be source areas for the spread and repopulation of the burned areas by survivors. Also, the fire probably did not affect the species whose eggs were in the soil or treetops, including fall field crickets, ground crickets, and some katydids.

The burn extended into adjacent meadows to the east and north.

The burn extended into adjacent meadows to the east and north.

I will be able to make a number of comparisons to assess the impact of the fire. How well will the affected insect species spread from the refugia, and where will they go first? Will there be differences between burned and unburned areas in the unaffected species, which stand to benefit from the higher quality plant growth in the wake of the burn? What will be the species count differences between years in the various habitat blocks? What about the impact of specialist predators and parasites? The first species to note will be the greenstriped grasshopper, which has been common in the early season.

Mayslake Burns

by Carl Strang

Smoke rose in thick columns on Thursday as the Forest Preserve District’s controlled burn program reached Mayslake Forest Preserve. Mayslake has well-established restored prairies, and the burn cleared off the dead tops of last year’s growth. The fire released minerals back to the soil, opened the way for the living roots to send new, unimpeded shoots skyward, blackened the soil further to facilitate plant growth by soaking in solar heat, and knocked back undesirable, competing woody plants.

A prairie burn is an impressive thing to watch.

A prairie burn is an impressive thing to watch.

Goldilocks would appreciate the decision to burn on a given day. Everything has to be just right. There needs to be some wind, but not too much. The area has to be large enough but not too large, and bounded by mowed areas or other fire stoppers. The vegetation needs to be dry enough. Finally, the burn crews need to be sufficiently equipped and trained to manage the burn safely.

Ranger staff keep watch from all sides.

Ranger staff keep watch from all sides.

Sometimes burns are incomplete due to the plants being too wet, but this time the prairies burned well. A walk through a recently burned area is worth taking, as it reveals what was hidden by all that herbage: the microtopography of the land, which can help determine exactly which plants grow where; the networks of animal trails, large and small; skeletons of animals that lived their last moments there. No freshly killed animals, though. They have their ways of escaping the flames.

Tiny low spots can host a few plants that prefer slightly wetter soils.

Tiny low spots can host a few plants that prefer slightly wetter soils.

The day after the Mayslake burn I found a number of animals taking advantage of the change. Killdeers and robins ran unimpeded over the cleared ground. Migrating sandhill cranes took advantage of thermals rising from the blackened soil to gain altitude during their journey north. In a few days, the warming soil will release and activate insects, and eastern phoebes likely will congregate to feed on them.

A robin hunts on the newly opened ground.

A robin hunts on the newly opened ground.

Sandhill cranes on the thermal elevator above the burn site.

Sandhill cranes on the thermal elevator above the burn site.

Another month, and the ground will be thick with new green shoots. The prairie always grows better in a burn year. (Note: This post first appeared last week as a Nature Note in the Forest Preserve District of DuPage County’s Observe Your Preserve website. )

Woodcock Season

by Carl Strang

Two years ago I posted my first report on woodcocks at Mayslake Forest Preserve. That year there were two displaying males, and my impression was that the habitat was marginal.

Woodcocks are in the shorebird group, but are a fully terrestrial species. Photograph taken at Willowbrook Forest Preserve.

Last year there were none displaying on the few evenings I checked for them. Last week I led a night hike group into the most likely area for woodcocks, and we heard peents by 2-3 males. They were between the north savanna and Route 83, noisy with traffic but with enough open brush that nesting is conceivable.

Two days ago the birds’ choices became restricted by a prescribed burn. This was long overdue. It was concentrated in the savanna.

The burn removes dead tops of last year’s herbaceous plants. The blackened soil absorbs more solar heat, minerals are released to the ground, and the plants don’t have to fight their way through the tangle.

The burn area also included some of the male woodcocks’ dancing ground.

With the area even more open now, dancing spots may have been improved.

Some adjacent unburned areas could work as nesting habitat.

I could imagine a nest under the pines, for instance.

Other brushy areas, though the fire came right up to them, remain viable.

The litter beneath the bushes in the background was untouched by the flames.

Maybe I’m being a cockeyed optimist, but given that this burn was badly needed, helping in the battle against invasive plants, I remain hopeful that negative impacts on species such as the woodcock were minimal.

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.

Trailing Strawberry Bush 2010

by Carl Strang

Last week I began to collect this autumn’s forest herbivore data. Today I’ll focus on the trailing strawberry bush at Meacham Grove Forest Preserve. In last year’s account of this study I expressed concern about a second controlled burn of this forest floor area in 3 years. The 2007 burn had knocked back the plants, and though they had recovered some in 2 years I wondered how they might respond to another burn happening so soon. I am not the only interested party, of course.

These deer I saw while collecting the data are affected by the fall burns, possibly for the better, and the removal of litter may help the plants by removing some insect herbivores. But it was clear that some trailing strawberry bush plants were scorched. As I checked my study colonies of the plants last week I found them looking green and scarcely touched by herbivory. They still are very small, and none produced fruit (2000 was the last year when any of the colonies fruited). Though they were smaller than in 2009, the difference was not statistically significant whether colony size was measured as overall length by width (median value of that product reduced from 5.5 square meter in 2009 to 0.95 in 2010) or by the total ground coverage of the scattered bits composing each patch (median value reduced from 0.28 to 0.1 square meter). Though some of the colonies now are very small, what remains appears healthy, and in general the fire appears to have reduced their competition from other forest floor plants.

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