Reconstructing the Past

Many modern conservation efforts are focused on returning the landscape back to its original state before the settlement of pioneers, yet even the rolling prairie that once covered most of Iowa shows only a sliver of the land’s biological history. The contemporary flora and fauna communities of prairie and cropland look very different from those of nearly 20,000 ago. The Late Wisconsinan glacial period lasted roughly from 21,000 to 15,000 years ago and drastically changed Iowa’s landscape through complete ice cover for thousands of years. While plants and animals exist and evolve together in certain locations, Baker et al.’s 1986 article from the Journal of Quaternary Science contends that these communities shift over time. Richard Baker and his colleagues at the University of Iowa worked together with researchers from Washington, North Dakota, and Minnesota to study the biological history of the Conklin Quarry in southeast Iowa to shed light on the ancient Iowan landscape. Their work compares ancient flora and fauna communities to those of the modern day in a study which may suggest a new way of approaching conservation. 

Conklin Quarry: a Picture of the Past

Conklin Quarry in Johnson Co., Iowa, contains a large collection of fossils from 18,000-16,000 year ago of a diverse array of organisms. These fossils include pollen, plants, insects, and small-mammals that were preserved in the deposits. While most sites that had been covered in ice, or full-glacial sites, have some of these fossil types, very few locations match the sheer breadth of samples from each group that Conklin Quarry has. This site’s rich selection of fossils represents the environmental spectrum during the Late Wisconsinan glacial period, a range of dates which is normally rare in fossils sites. In addition to the date range, the quarry has arctic plant remains found 1000km south of the nearest reported Wisconsinan arctic floras. This unique site provides important evidence for understanding both the glacial and postglacial development of flora and fauna today. 

Plant Fossils

In order to map flora communities of 18,000-16,000 years ago, Baker and his lab studied pollen and plant macrofossils. The pollen samples found were mostly degraded, although pine, spruce, and sedge species could be clearly identified. The samples found in Iowa from the Wisconsinan period contained low pollen concentrations, which match low pollen concentrations found in tundra and tree-line areas in eastern Canada today. Spruce and dwarf birch macrofossils were found in abundance, which are native boreal forest species and extend to the northern tree limit today. Many of the less common macrofossils represent arctic-alpine plants found today only in the tundra. Several species found normally grow along water, suggesting a pond was present at one time. Both the pollen and plant macrofossils match species found in eastern Canada presently, suggesting open conditions between the forest limit and the limit of tree species in a tundra environment. 

Insect and Vertebrate Fossils

The remains of the insects found were remarkably well preserved, showing species that could occur today within or near forest/tundra transition zone. Close analogues to the insect communities at the Conklin Quarry only exist today in tree-line environments where temperatures average 10-12°C in July (compared to 23°C Iowa today). The taxa of vertebrate macrofossils are found presently, like the insects, only in tundra environments. Some fossils, such as the singing vole, are found today only near running water, which suggests an ephemeral steam or a wet environment. 

 

Fig.1: Map of North America (1986). All flora and fauna populations represent 1986 conifer and insect populations found in Conklin Quarry site.

Communities Today

While both the plant and animal fossils represent species presently found in tundra, Baker et al. found that these communities shifted over time. The insect and animal species found in the quarry are present today in northern coastal regions in Canada and Alaska, while the plant species (conifers) grow primarily in a large swath across Canada (Fig.1). Between 18,000-16,000 years ago and now, the analogue communities, or flora and fauna that evolve and develop together, have changed. Baker et al.’s research shows that the evolution of communities is dynamic, and that flora and fauna populations dissociated from one another as glaciers retreated. These results suggest that biological communities can evolve, disassociate, and even disappear over time. Instead of focusing just on certain ecosystems, conservation efforts might find understanding the community evolution beneficial. If the relationships between various species change and even disappear over time, perhaps the aim to restore prairies to match their relic counterparts should be reexamined.

Baker, R.B., R. Sanders Rhodes II, T.J. Fresst, G.R. Hallberg, J.A. Janssens. 1986. “A full-glacial biota from southeastern Iowa USA.” Journal of Quaternary Science 1 (2) 91-107.

GRAINS OF TRUTH: IOWA'S PLANT HISTORY PRESERVED IN POLLEN

Key Terms

Hypsithermal: A period in geological history spanning approximately 9,000 to 5,000 years before present.

Radiocarbon Dating: A technique that utilizes the minute amounts of radioactive carbon in organic matter to determine an approximate age for the matter in question.

Pinus: The genus encompassing pine trees

Abies: The genus encompassing fir trees

Macrofossil: A fossil that can be observed without a microscope

            Newcomers to Iowa might see nothing but endless rows of corn. But beneath the state’s surface landscape lies evidence of a diverse and fascinating floral history. Ancient plant material buried below the row-crops reveals a narrative of evolution and competition amidst geological and environmental changes. Studying the plant communities of Iowa’s past can provide us with clues on the history of climate change, glacier activity, and humans’ effect on the landscape.

DIGGING, DATING AND IDENTIFICATION

            The pollen left in soil by plants over the course of time can be identified to the species level to provide a picture of historical species presence and abundance. To study pollen history, scientists often take cores of sediments. In his 1979 study, “Late Glacial and Postglacial Pollen and Plant Macrofossils from Lake West Okoboji, Northwestern Iowa,” Ken Van Zant took a soil core reaching approximately 12m below the surface of Lake West Okoboji, Dickinson County, IA. The site “was selected as a coring site because of the reported presence of late glacial sediments and the reported ability to penetrate the Hypsithermal sediments” (Van Zant 1979). After pulling the core, Van Zant divided the soil into segments for radiocarbon dating, which allowed approximate time periods to be assigned to points along the core’s vertical axis. He then sifted through the sediment for plant macrofossils and pollen samples, which he identified using pre-established keys.

THE PROOF IS IN THE POLLEN

            By examining changes in the composition of the fossil and pollen records over time and correlating them with data from radiocarbon dating, Van Zant was able to reconstruct a history of the region’s floral composition. The product of Van Zant’s labor was a set of hypothetical plant communities that probably have existed near Lake Okoboji, as summarized below:

(1)  Around 14,000 years B.P: Coniferous forest with abundant spruce and larch

(2)  13,500 years B.P: Mixed forest with lots of black ash

(3)  11,800 years B.P: Forest dominated by birch and alder

(4)  11,000 to 9,000 years B.P: Deciduous forest with abundant oak and elm

(5)  About 9,000 years B.P: Prairie beginning to compete with the forest

(6)  7,700 to 3,200 years B.P: Prairie becomes dominant

(7)  3,200 years B.P: Return of some forest, prairie still present

(8)  About 400 years B.P: Row crops and humans

QUESTIONS REMAINING

            Some trends described by Van Zant conflict directly with other scientists’ hypotheses. Specifically, Van Zant’s “late glacial sequence from Lake West Okoboji contains lower percentages of Pinus and Abies pollen than Durkee (1971) or Brush (1967) found,” (Van Zant 1979) referencing studies conducted in in other regions of Iowa. Van Zant’s somewhat simplistic answer to this disparity was that “perhaps fir and pine pollen were misidentified by Durkee and Brush” (Van Zant 1979). Ideally all three authors in question would have preserved voucher specimens of the pollen and fossils they examined in their respective studies; unfortunately, no such records were kept, meaning there is no way to be absolutely sure as to who was correct in their identification, though it does seem somewhat unlikely that both Durkee and Brush would have independently made the same mistake.

PUTTING TOGETHER THE PUZZLE

            Despite the points of dispute between findings by Van Zant, Durkee, Brush, and similar authors, their works have contributed and continue to contribute to a broader body of knowledge. In fact, scientific progress requires conflicting hypotheses, because they provoke subsequent studies that build on existing knowledge while seeking to resolve the inconsistencies. In one such study, Baker et al. (1996) used inferences from Van Zant (1979) to inform their own broader study, “Holocene Paleoenvironments of Northeast Iowa.” Subsequently, Williams et al. (2008) paired data from Baker et al. (1996) and similar studies with modern spatial simulation techniques to generate approximations of climatic and floral history across the Midwestern United States.

Locations of the studies referenced in the text

          Ultimately we should treat Van Zant’s study as one of many building blocks forming the foundation of our modern understandings of environmental history. Van Zant’s work also might serve as a reminder that the study of something as seemingly inconsequential as ancient pollen might provide us with useful knowledge in unexpected realms.

Baker, R.G., E. A. Bettis III, D. P. Schwert, D. G. Horton, C. A. Chumbley, L. A. Gonzalez and M. K. Reagan. 1996. “Holocene Paleoenvironments of Northeast Iowa.” Ecological Monographs 66(2):203-234.

Brush, G.S. 1967. “Pollen Analyses of Late-Glacial and Post-Glacial Sediments in Iowa.” In “Quaternary Plant Ecology” (H.J.B. Birks and R.G. West, eds.), pp. 173-189. Blackwells: Oxford University Press.

Durkee, L.H. 1971. “A Pollen Profile from Woden Bog in Northcentral Iowa.” Ecology 52:837-844

Van Zant, K. 1979. “Late Glacial and Postglacial Pollen and Plant Macrofossils from Lake West Okoboji, Northwestern Iowa.” Quaternary Research 12:358-380.

Williams, J.W., B. Shuman and P.J. Bartlein. 2009. “Rapid Responses of the Prairie-Forest Ecotone to Early Holocene Aridity in Mid-Continental North America.” Global and Planetary Change 66:195-207.

Research blogging: history of the Iowa flora

The following seven posts on this site will be written by students in Grinnell's BIO 305 course ("Evolution of the Iowa Flora.") My assignment prompt follows.

"Blog posts, podcasts (and presumably other two-syllable, internet-facilitated neologisms) are increasingly common ways to communicate science to the public. The creators of such pieces sometimes highlight the findings of a particular article, explaining the research and its relevance in terms that interested on-specialists can understand. That’s what I’m asking you to do.

Assignment. Compose a 3-4 page (double-spaced) essay that informs a scientifically literate lay audience about a research article on the history of the Iowa flora. You may use a conventional word processor like Word to prepare your post, but we will eventually edit it and convert it for web-delivery.

In this 'history' unit of the course we will read and discuss a series of articles that provide entry points into the literature on historical studies of the Iowa flora. In your blog posts, you will communicate other articles—selected from a set I’ve assembled, or discovered on your own."

My students (see their smiling faces above, as they pose with Opuntia humifusa at the Eddyville Dunes; from left they are Meg Schmitt, Elena Jaffer, Adele Crane, Carissa Shoemaker, Anthony Wenndt, John Seng, and Dan Connelly) selected seven articles about paleoecology or restoration ecology. Some of the articles are recent; some aren't so recent. All of them reveal something worth sharing about Iowa's natural (or unnatural, or used-to-be-natural-or-is-now-extinct-or-somewhere-in-Canada) vegetation.

Dog Day Afternoon

On a hot, early September afternoon, in Iowa’s drought of 2012, eleven students in Grinnell’s BIO 368 (Ecology) class gathered infrared thermometers and GPS receivers and set out to characterize the thermal environment of the Grinnell College campus (above left). Each of three teams of four students devised their own sampling scheme for an assigned area of campus—south, central, or north.  We used interpolation in ArcMAP to transform the raw data—which consisted of point estimates of surface temperature, air temperature, and relative humidity—into contour maps (e.g., surface temperature, above right).

As I expected (but didn’t tell the students), the outcome revealed a range of sampling strategies. The “southern group” traveled from west to east, starting out with ambitions of sampling the whole area in a dense, regular grid. With enough time, this scheme would have been comprehensive and representative.  Time ran short, however, compelling them to abandon those plans. At the (SE) end, they collected data in a less dense, haphazard fashion. The sample points of the “central group” were not in a formal grid and not quite haphazard, but they were broadly and more or less regularly distributed throughout their area. “The northern group” took sample points in lines along walkways and, especially, along the peripheries and of their assigned area, as if they were looking for a way out of a box.

Had we been a social psychology (or primate behavior) course, we might have used this “finding” to analyze how group dynamics led to contrasting decisions. Being an ecology class, we used the experience to identify best-practice environmental sampling approaches. Then, acknowledging the limitations of the data set, we asked what the preliminary findings could tell us about the thermal properties of contrasting surfaces and of different campus areas.

Some highlights

·      In that summer’s severe drought, exposed, un-irrigated lawns near the east-campus dorms were almost as hot as pavement. “Weedy” areas of those lawns, however, were 5-10 degrees Celsius cooler than adjacent turfrass. It is likely that the relatively deep-rooted weeds (such as prostrate knotweed, Polygonum aviculare) had access to soil water (and in that way, created evaporative cooling by transpiration) that shallow-rooted turf grasses did not.

·      Paved areas south of the Bear Athletic Center were the hottest place on campus. Warmth that might have been welcome on chilly winter days was barely bearable.

·      With the exception of the east campus lawns, vegetated areas were distinctly cool. Irrigated athletic fields—presumably, again, because of evaporative cooling—and areas under dense tree cover (e.g., west of the south campus dorms) were coolest.

Temperature affects all the organisms that share Grinnell College, including us. For the sake of our summer comfort, does this pilot study mean that we ought to irrigate the whole campus? Cover all the open fields with shade trees? Let weeds take over the lawns? Re-vegetate the parking lots? Respectively: (1) no, that would be an expensive, environmentally unsustainable use of water; (2) no, we need some open lawns for recreation and views; (3) no, we wouldn’t want those “weeds,” anyway, but maybe we should consider replacing some areas of conventional turf grass with deeper-rooted, native alternatives; and (4) no, but maybe we should be wary about installing more parking lots. In any event, we should think about the kind of habitat we create when we put together a college campus.

BIO 368, 2012: Leslie Bean (class of 2013), Cory Brooke-DeBock (2012), Brendan Byrne (2014), Tayler Chicoine (204), Erik Dixon-Anderson (2014), Savannah Duby (2013), Carla Eckland (2013), Griffin Lentsch (2013), Kaya Matson (2014), Pavlo Nikolaidis (2014), and Jordan Young (2014)