Illinois’ Kankakee Sands

by Carl Strang

In the Chicago region when someone mentions the Kankakee Sands, usually they are referring to the Nature Conservancy project in Newton County, Indiana. There is, however, a nature preserve in southeastern Kankakee County, Illinois, also known as “Kankakee Sands,” which also is worth knowing about.

The preserve has very high quality oak savanna and prairie ecosystems.

The preserve has very high quality oak savanna and prairie ecosystems.

I paid my first visit to this site on Friday, and left with a good dozen singing insect county records.

Most species were sand-soil singers I had encountered before, but this was my first sprinkled grasshopper.

Most species were sand-soil singers I had encountered before, but this was my first sprinkled grasshopper.

He was buried in a grass clump, offering no chance of a good photo. Fortunately he was open to climbing onto my finger for a portrait. The all-black pronotum sides are unique.

The most common orthopterans were tinkling ground crickets and straight-lanced meadow katydids, unsurprising on this sand soil.

One of the many male straight-lanceds from Friday.

One of the many male straight-lanceds from Friday.

I was pleased also to find that my new friend the handsome grasshopper is common there.

Handsome grasshopper, male.

Handsome grasshopper, male.

Female handsome grasshoppers were a bit bigger and green rather than brown.

Female handsome grasshoppers were a bit bigger and green rather than brown.

Both mottled sand grasshoppers and Boll’s grasshoppers also were there, the former often punctuating the scenery with their bright yellow hind wings in flight.

Boll’s grasshopper also has yellow hind wings. These are concealed when both species are at rest.

Boll’s grasshopper also has yellow hind wings. These are concealed when both species are at rest.

There also were plenty of bush katydids.

Most were curve-tailed bush katydids.

Most were curve-tailed bush katydids.

One, slightly smaller, proved to be a male fork-tailed bush katydid.

One, slightly smaller, proved to be a male fork-tailed bush katydid.

Kankakee Sands are worth a visit on either side of the state line.

 

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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.

Ridge Trim “Mohawk”

by Carl Strang

As I tell the story of Mayslake Forest Preserve, from time to time I have to insert a focus on the outstanding effort by the volunteer restoration team. Led by stewards Conrad Fialkowski and Jacqui Gleason, this group is largely responsible for the high quality plant communities on the preserve, their maintenance and their enlargement. One of this year’s foci has been the south end of the savanna ridge, above the east end of May’s Lake. Long covered by an understory of dense buckthorn, in recent years the ridge gradually has been exposed through the patient techniques Conrad has tested over the years. The end is drawing near.

The many brush piles and the cleared ground attest to the volume of intense physical labor put in by these dedicated people in recent months.

Only a topknot stand of buckthorn remains at the peak of the ridge’s south end.

The remaining buckthorn in the background stands above soil as bare as in the cleared foreground. The cleared area will be seeded with bottlebrush grass, beginning to establish the native vegetation that will claim the space beneath the oaks.

Clearing is only part of the work, as the team gathers tens of pounds of seed from the preserve’s native plants, which they then spread in the opened areas. This effort cannot be praised enough.

Brush Pile Burn Concern

by Carl Strang

Last fall I had a concern, which apparently I did not share in this blog, that some of the brush piles on Mayslake Forest Preserve’s savanna ridge might have been placed too close to some of the Hill’s oaks.

The piles were composed of cut buckthorn and other invasive shrub stems. They were expertly stacked by the volunteer restoration team, and burned by Forest Preserve District staff in winter.

Last week I took a look at the oaks closest to the burn scars. For the most part they appeared unaffected by the fires. One tree did show some scorching on its bark.

Here you can see the blackened bark surface on the side toward the fire.

That tree’s lowest branch, which had overhung the brush pile, was not completely killed, but it had only one sprig of green leaves. The other twigs apparently were dead. Otherwise, that tree had a reasonably full canopy.

The top of the oak with the scorched bark.

I have to conclude that my concern was misplaced. There may have been some damage my eyeball assessment could not discern, but the trees all should survive. Hill’s oak is a savanna species, after all, and so must have some resistance to fire.

Birds, Buckthorn and Oaks Final

by Carl Strang

As I mentioned in my previous post on this subject, the songbird migration was nearly done by mid-May. In fact I have only 3 observations to add to the ones from the early part of the season, two in the oaks and one in the buckthorn-dominated woodland. That mildly reinforces my earlier conclusion, that the only reason buckthorn woodlands appeal to birds early in the season in our area is that oaks, which dominate most of our woodlands, leaf out late. In this year when the oaks were in leaf throughout the migration season, songbird migrants nearly abandoned the insect-depauperate buckthorn at Mayslake Forest Preserve and spent their time in the oak woodlands.

South savanna at Mayslake, showing oaks well leafed.

So far all the analysis has been of the total species counts of neotropical migrants that do not nest at Mayslake. However, some of those species are brush specialists that might be expected to prefer the buckthorn over the more open oak woodlands regardless of what is happening in the canopy.

The Tennessee warbler is an example of a canopy species, on the other hand, which will not want to spend a lot of time foraging down in the buckthorn, though they might want to have it handy for resting and as a refuge from predators.

When I look at the two years’ data, sorting out brush from non-brush birds, the most curious observation is that hardly any brush-loving birds stopped by Mayslake this year. Only two birds out of the total sample of 30 were of brush species. Last year, 38 of 166 were brush birds. Looking at 2011, then, both brush and non-brush birds preferred the buckthorn woodland early in the season, though the preference was stronger for the brush species. Late last year, after the oaks were leafing out, non-brush species preferred oaks while the brush birds did not show a strong preference for either woodland type.

All of these data, coming as they do from one site over a short period of time, amount to a pilot study at best. Nevertheless, they support the notion that the apparent preference of migrant songbirds for woodlands dominated by invasive shrubs is an illusion. Birds avoid the buckthorn and prefer restored native woodlands when the latter are in leaf, capable of providing both food and essential shelter.

Birds, Buckthorn and Oaks

by Carl Strang

Now that the early part of the migration season is past, I can do a preliminary test of the Birds-Buckthorn-Oaks hypothesis. The idea is that migrating birds seem to prefer buckthorn infested woodlands early in the migration season because the buckthorn understory provides shelter unavailable in restored, oak-dominated woodlands because usually the oaks have not yet leafed out to provide food and shelter. Data from last year supported this idea, because late-season migrants showed a shift from the buckthorns to the newly leafing oaks. This year a further, better test was made possible by the warm early season stimulating oaks to break buds early, so that they were well in leaf for the early part of the migration season. So, what did the data show? I compiled the numbers of neotropical migrants that don’t nest on Mayslake Forest Preserve that I counted prior to May 19 (when oaks began leafing last year), comparing last year’s counts to this year’s. The results were stark: I counted only 5 of those birds in the buckthorn woodland, compared to 22 in the restored savannas (compared to 80 and 34, respectively, last year. Numbers were low this year, in part because my back strain limited my outings, but also a lot of migrants seemed to be bypassing Mayslake).

Things are moving along. This olive-sided flycatcher, a late season migrant, stopped by Mayslake on May 14, earlier than usual.

Using last year’s proportions to calculate expected values if there had been no difference between years, the values would have been 18.9 in the buckthorn-dominated woodland, 8.1 in the savanna. It should come as no surprise that the resulting chi-squared test statistic showed a highly significant difference (34.07, even with only 1 degree of freedom, is far above the threshold). With the migration progressing so rapidly, I don’t know if there will be enough observations in the late season to consider separately, but if so there will be an additional post. Either way, I am satisfied that the data support my point.

Another Year’s Squirrel Data

by Carl Strang

At the end of March I completed my third year of collecting data on habitat preferences of fox and gray squirrels at Mayslake Forest Preserve. The basic question is whether the usual preference of fox squirrels for savanna habitat and gray squirrels for forest will hold in an area where the savanna is high quality and the forest is low quality.

Fox squirrel

Over the first two years it was clear that both species preferred the savanna, but that preference has been stronger in the fox squirrel. This year the results were a little different. The area involved, 54.6 acres altogether, is 64% savanna and 36% forest. In the first year, 82% of fox squirrel observations were in savanna, 90% in the second year and 92% in this year just ended. The corresponding numbers for gray squirrels were 73%, 79% and 65%. That last number was perhaps the most remarkable, gray squirrels in the past year appearing in the exact proportions of the two habitat types on the preserve.

Gray squirrel

That is the only number in this entire study that shows no statistically significant difference from expected values (actually, the chi-squared test statistic is calculated from the numbers of observations rather than the percentage values; this year I had 157 observations of fox squirrels, 75 of gray squirrels). I continue to gather these data each year because the preserve continues to change, thanks to the efforts of the restoration team. High quality savanna is improving, and low quality forest is being cut back.

Testing the Birds and Buckthorn Hypothesis

by Carl Strang

A year ago I posted a hypothesis that this most unusual of seasons will allow me to test. To recap: When restored savannas are compared to woodlands with buckthorn and honeysuckle thickets in the understory in early May, when the bird migration is entering its peak, it seems that the birds prefer the invasive-degraded areas to the native savannas. Some birders take this as evidence that restoration is bad for birds. My hypothesis was that this observation is tied to the fact that oaks, the dominant trees in our savannas and woodlands, are among the latest trees to break bud and leaf out. Therefore they are not supporting leaf-eating insects, and also not providing the shelter that the birds need on their daytime migratory stops. As I pointed out a few weeks ago, like our flowering phenology, the oaks broke buds a few weeks early this year.

Remember this photo? I took it in early April, more than a month before oaks typically reach this point.

The stage thus is set. I have the records of where I saw the migrants last year, a late year when the oaks were not leafing out until the second half of May. I remarked in my notes that they were doing so around May 19, so I will take that as my dividing point. I can look at last year’s data, and this year’s, and see if the birds lose their apparent preference for the buckthorn woodlands now that they have leafy oaks as an alternative.

As a starting point I compared the bird counts from April 20 to May 18 last year to those from May 19 to May 31, when migration was essentially done. I considered only species that spend their winters south of the continental U.S. and that do not breed on the Mayslake preserve, to keep things as uniform and unbiased as possible. Even with those restrictions, I had 22 species to work with. For the moment ignoring species by species comparisons, here are the 2011 totals. In buckthorn woodlands before May 19, I made 80 observations of birds in the target group. The corresponding total for restored savanna areas in that same time period was 34 (these counts are not normalized for the relative areas of the two habitats, but the buckthorn area I used for this comparison is smaller, at 5.7 acres, than the savanna at 8.5). So the data support the notion that, at least early in the migration season before the oaks leafed out, the lower quality, buckthorn- and honeysuckle-dominated woodland harbored more birds. What about the latter part of the migration season, after May 18? Things had slowed down at that point, and the migrant species composition changed somewhat, but the totals last year were 24 observations in the buckthorn woodland and 28 in the savannas. Clearly the tide turned after the oaks began to leaf out (for the statistics cognoscenti, the chi-squared contingency table produced a test statistic value of 14.36 at 1 degree of freedom, highly significant). I will report on what happens this year, but if my hypothesis is correct, the oak savanna should prove more attractive to these migrants this year in both parts of the season.

Literature Review: Savanna Ecology

by Carl Strang

A pair of papers in Science last year described global surveys of savannas and the ecological conditions that produce them. Their results were not surprising, but valuable in further documenting the ecology of these woodlands with their trees scattered more widely than in forests. They defined forests as woodlands with tree cover greater than 50-60%. Above 2500mm of annual rainfall, a region will be forested. Between 1000 and 2500mm, an area can be forest or savanna, with fire tipping the balance. In savannas, low tree cover promotes the spread of fire, and fire limits tree cover. Lengthy dry seasons and lower rainfall amounts tend to produce savanna.

By their standards, this woodland at Mayslake Forest Preserve probably would be called forest rather than savanna.

When actual tree cover is measured, forests characteristically have 80%, and savannas 20%. There are few woodlands that measure close to the cutoffs separating these categories, supporting the idea that forest and savanna represent alternative stable states, or “attractors.” All of this is relevant to northeast Illinois. We fall in the range of rainfall where forest would cover the ground, but the rain is in the lower end of that range, and fire historically produced a prairie landscape with patches of savanna and, where rivers or topographic breaks produced little fire shadows, bits of forest. Here are the references:

Staver, A. Carla, Sally Archibald, and Simon A. Levin. 2011. The global extent and determinants of savanna and forest as alternative stable states. Science 334: 230-232.

Hirota, Marina, et al. 2011. Global resilience of tropical forest and savanna to critical transitions. Science 334:232-235.

Savanna Pioneers

by Carl Strang

I went up to the former friary site at Mayslake Forest Preserve on Monday, and found something new.

One of four recently planted bur oak trees.

The small trees at first glance seemed lost in the expanse of the site, separated as they were by distances of about 50 yards. This is, however, an appropriate spacing for a savanna, and even if no other trees were to grow there, when full grown these trees would look just right with prairie plants growing between them.

That condition will not be met, however. As I have mentioned in the past, the woodland at the north edge of the site is ready to send acorns and other propagules south, and with the aid of squirrels soon will expand into the open space. I am glad to see that the decision has been made to acknowledge and support that process through the planting of these four pioneers.

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