Yesterday (Part 1 Summary):
A megafauna of elephants, zebras, lions, tigers, pecarries, bears, sloths, teratorns (huge vultures), camels, caribou, deer, elk, bison, etc. existed in a vast prairie & savanna ecosystem from the Plains to the Midwest in prehistoric times from millions of years ago, right up to the last glaciation.
Massive grazers & browsers were instrumental (along with an occasional lightning-induced wildfire & droughts) in maintaining this grassland environment for millions of years. The incredible amount of pristine grass & vegetation to graze led to huge animals that dwarf the larger African animals of today. Gigantic teratorns fed on the carcasses of dead grazers & lions & tigers the size of small cars roamed this aboriginal wilderness.
Prairie & oak savanna pollen show up in coring of old glacial lakes in southern & south-central Illinois from 130,000 years ago. Also, tortoise species that require a warm climate with a lack of freezing temperatures in winter also are in these layers. At the same time, Sweetgum leaves have been found buried in this layer near Toronto, Ontario, well north of their present native range. This shows a mild climate of prairie & savanna, lush growth ideal for grazers in the Midwest.
The prairie ecosystem may have migrated up from Chile as the Rockies rose & produced a rain shadow in the Plains.
The Plains' to Midwest immobile part of Earth's crust called a craton led to lack of any mountains of large barriers to grazing or wildfire limitations.
Multiple coverings of glacial till plains & lake plains by four glacial episodes in our area kept the relatively flat environment.
Dry, windy climate on the edge of each glaciation let dry climate western vegetation move east & grow in the area.
After the last glaciation, one main climate period & two sub-periods allowed prairie & savannas to flourish, even despite the "mega fauna" going exinct as humans entered the scene in our area.
Over the past 10,000 years, there are three periods of interest regarding prairie & savanna expansion in our area. One is the "Hypsithermal" also known as the "Xerothermic Period" or "The Prairie Period", the "Roman Period" & the "Medieval Optimum". These are all periods of apparent warm, dry weather with higher incidence of wildfires in our region.
In these periods, western & overall Plains vegetation made a massive leap eastward & species that favor cooler, wetter conditions migrated northeastward. This is especially prevalent in the "Hypsithermal", which was a period generally 5000-8000 years ago. Aspen & birch grew north of the Arctic Circle (with charcoal evidence of even some wildfires), oak rapidly expanded through Quebec & cooler, wetter-favoring hemlocks died out & also migrated. Extensive charcoal deposits are found in the layer from this period in Chesapeake Bay. A big uptick in prairie grass & flower pollen shows up in all the lake & bog corings from this period in the Midwest. Many areas of the Plains became devoid of vegetation, resulting in massive movement of sandhills in Nebraska. Varves in lake sediment in Minnesota show increased wind & accumulation of salts show drier climate.
Corings from local lakes & bogs (Otterbein bog, Cranberry Bog, etc., from Warren, Tippecanoe, Howard, Hamilton, Marion counties) by scientists at Butler University show a sharp uptick in oak & overall prairie pollen. In fact it all peaked in this period when looking overall at the past 10,000 years of sediment. Think of this prairie "tide" sweeping eastward all the way to Pennslyvania with outliers from Massachusetts to Delaware & Piedmont savanna from North to South Carolina. Now, think of this tide receding as wetter & cooler weather returns. As the prairie tide goes back west, tidal pools of prairie species (plant & animal) are left.
Notice the oak pollen peak in the core of Fox Prairie Bog (Hamilton County, Indiana) during the Hypsithermal. Maple pollen dropped substantially.
Even when the first Europeans arrived "tidal pools" existed.....& they do today.
Many of these tidal pools became completely cut off from the main arm of prairie & new subspecies of plants evolved. A good example is the Narrow-leaf Coneflower.
One main Plains population of this type of coneflower, the Narrowleaf Coneflower. Its range covers a massive area:
The second species, the Pale Purple Coneflower is found farther eastward in the tallgrass prairie.
Of interesting note is the fact that both species are very similar. This is an overall large area of two species that often dominate prairies & savannas.
The Purple, Bush's & Tennessee Coneflower all appear to be results of the tidal pool recedence of Narrow-leaf & Pale Purple Coneflower. However, do notice the tidal pools of Pale Purple Coneflower as far east as North Carolina in the map above.
Black Hickory is a savanna tree & common co-hort of the cross-timbers area of Texas (savanna buffer zone between prairie & forest). It is also frequent in Arkansas, where it is a common component of oak-hickory savannas, prairies & oak-hickory woodland there.
However, there are "tidal pools" of it in southwestern Indiana & southern Illinois. I found a random patch of the tree growing in dry sandy soil in southwestern Indiana's Daviess County & have a pressed & mounted specimen. It was found in an area where Prickly Pear Cactus grows & many Plains & southern U.S. pine savanna species are found. The soil is sandy, dry & warm, providing a good place for some of these species that came in with the tide to remain after the tide receded.
In Indiana & Illinois' "tidal pool", the tree has larger leaves & fruit. It is subspecies Carya texana variety arkansana. Farther to the southwest the tree is the typical Carya texana variety texana.
Post Oak is the prairie & savanna tree in Texas & Oklahoma like the Bur Oak is the prairie tree in our area, Illinois to Iowa & Kansas. It is also found in southern Indiana. It is actually a savanna/barrens/prairie indicator species on the loess & lake plains of southwestern Indiana. In the woods, it needs fires to maintain itself, as it is a very slow grower, needs full sun to grow & cannot compete with more aggressive species. Whole, massive post oak barrens & savannas existed in southern Illinois when the first European settlers arrived there.
Oddly, there is a tiny, single population of it near the Wea west of Lafayette. This is a small tidal pool hanging on when Post Oak's range expanded northward likely during the Hypsithermal. The drier, warmer soils of that area likely led this very small population pocket to hang on.
Same applies to fauna or animals.
Check out the range of "THE bird of the prairies", the Greater Prairie Chicken. It needs large expanses of prairie to mate & breed. Its range use to follow prairies at its peak from North Dakota to Texas to Indiana & Kentucky & then on the coastal prairies of Louisiana & the coastal prairies of the East Coast.
Here's the thing, like a tidal pool, the East Coast population was a sub-species called the "Heath Hen" that hung on there as the main Plains & tallgrass prairie population receded. The Heat Hen is now exinct. The Greater Prairie Chicken population in southeast Texas to Louisiana is the "Attwater's Prairie Chicken", which is nearing extinction. The other populations of Greater Prairie Chicken have shrunk to a few remnants in refuges of Illinois, Missouri with other populations in Oklahoma to Kansas, northward to North Dakota. A new danger today is the plowing of pasture & prairie land for row crop production in the Plains & the oil shale boom in the Dakotas.
Tens of thousands use to be found before the prairies were plowed in our area. The last one in Indiana was sighted in Newton County in 1970.
Greater Prairie Chicken:
The Greater Prairie Chicken's & all of its "tidal pools" of subspecies probably originated from the single large population of Lesser Prairie Chicken that occurs on the prairies in the Plains just east of the Rockies. It use to have a much larger range, but oil development & irrigated agriculture have caused its numbers to dwindle.
Lesser Prairie Chicken:
So what maintained these prairies & savannas when the climate favors forests? No way that lightning occurred enough when the grass was dry & dormant to create wildfires to sustain these environments. The season with the greatest lightning is summer when the prairie is lush & green & will not burn. What gives? That is Part 3 tomorrow.