Leaf Physiognomy Offers clues to the Past

By Eric Atkins

There are many techniques that can be used to offer insight to the past–a family of proxies that range from gas found in ice cores to fossilized feces. I have always been interested in fossils. The allure of something so ancient was introduced to me as a child. At the age of eight, I found a veiny imprint of a leaf in a chunk of sandstone. Fossils are a great tool for looking into the past. For nearly a century by paleoclimatologists and paleoecologists have been using leaf physiognomy as a proxy to deduce past climate environments. By looking at leaf mass per area, teeth area, number of teeth, and degree of blade dissection we can extrapolate information about past climates.

Fossilized Platanus leaf, Paleocene, Alberta, Canada. Via Wikimedia Commons.

Fossilized Platanus leaf, Paleocene, Alberta, Canada. Via Wikimedia Commons.

In recent years this type of proxy has evolved along with technology. Continue reading

The past’s mark on the present as seen through LIDAR

By Erika Lyon

Light Detection and Ranging, also known as LiDAR, is a form of remote sensing used by various professions to examine landscape features in three-dimensions.  Imaging is generally performed by aircraft (though not always) that use lasers, scanners, and GPS to measure reflected light from Earth’s surface.  This light describes changes in distance between the aircraft and surface features (National Ocean Service 2013).  For terrestrial systems, a near-infrared laser is used to collect data (this is known as topographic LiDAR), while aquatic systems make use of green light, which can break through water surfaces (bathymetric LiDAR) (National Ocean Service 2013).  Data on height, latitude, and longitude of geographic features are generated and used to create models of the landscape (National Ocean Service 2013).  LiDAR’s applications have been used in the fields of archeology, geology, and paleontology to study natural and human history, but it is not fully utilized in paleoecological studies.  LiDAR is a powerful remote sensing tool that can provide invaluable information about Earth’s surface and can be especially useful for looking at evidence of past events and land use.

Past events can leave behind footprints on the Earth’s surface, and these footprints may not be easily distinguished from an aerial or satellite imagery alone.  For example, during the summer months of 2012, I inventoried abandoned mine lands in the Midwest, which are notorious for their dangerous highwalls and sinkholes that are often hidden from view by overgrown trees and shrubs.  LiDAR was a very valuable tool in the field because it made many of these hazardous features evident (Fig. 1).  Needless to say, I didn’t go to a mine site without a LiDAR hillshade map.

Fig. 1: Example of an aerial photo (left) and LiDAR hillshade image (right) of an abandoned surface mine.  Maps, like the ones above, are often utilized by state agencies to assess site conditions of abandoned mines.  For more maps of Iowa’s abandoned mines (including 1930s, 1950s, 2008 aerials, and LiDAR hillshade) click here. (Images created by GeoTREE and the Iowa Department of Natural Resources).

Fig. 1: Example of an aerial photo (left) and LiDAR hillshade image (right) of an abandoned surface mine.  Maps, like the ones above, are often utilized by state agencies to assess site conditions of abandoned mines.  For more maps of Iowa’s abandoned mines (including 1930s, 1950s, 2008 aerials, and LiDAR hillshade) click here. (Images created by GeoTREE and the Iowa Department of Natural Resources).

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Using the past to manage the future

By: Rob Brown

Disturbances such as climate change, biological invasions, pollution, and many others, have led to organizations to emerge with the purpose of restoring and conserving our natural resources. Both paleo- and modern ecological data can help inform resource managers as they implement restoration and conservation strategies.

Figure 1. Nutrient runoff has led to increased algal blooms in lakes and ponds and organizations to implement restoration projects. By Ildar Sagdejev, via Wikimedia Commons

Figure 1. Nutrient runoff has led to increased algal blooms in lakes and ponds and organizations to implement restoration projects. By Ildar Sagdejev, via Wikimedia Commons

 

Restoring ecosystems

Traditionally, the aim of restoration is to restore ecosystems to a natural baseline, or a pre-human disturbance state. However, Jackson and Hobbs (2009) made three observations that complicate finding natural baselines. Continue reading

The pitfalls of transfer functions (and how to avoid them!)

By Erin Hayes-Pontius

Paleoecology, or the study of organisms and their environments in past times, has a specific branch known as paleolimnology, which deals with records left by lakes. Beyond being pleasant places for swimming, fishing, and other recreation, lakes are particularly valuable for paleo records. Not only do lakes archive the goings-on within themselves, but they also archive goings-on within their drainage basins. In the case of Lake Champlain, it has a drainage basin nearly 17 times that of its surface area (21,326 km2 : 1,269 km2), making it extra sensitive to changes in climate (Fig. 1).

Due to lakes’ positions at low points on the landscape, they integrate everything that happens within their drainage basin and are therefore important “sentinels of change” (Williamson et al. 2009).

Figure 1. Lake Champlain’s drainage basin. From Wikimedia Commons

Figure 1. Lake Champlain’s drainage basin. From Wikimedia Commons

Over time, a variety of things fall into lakes, such as diatoms (single-celled algae), pollen, chironomid midges, or needles, to name a few, and these things get buried by sediment. In some lakes- some, certainly not most- sediment deposits occur quickly enough to leave annual layers; if this interests you, definitely check out Rob’s post from a little while back. Unfortunately, this does not happen most of the time, and we’re left with a much coarser resolution to deal with. Rather than knowing about the diatom species every year, we may only know ‘who’ was there every few years, every decade, or even every few decades. Despite these challenges, lakes are still- and will continue to be- widely used in paleoecology. Continue reading

Splinters in Dendrochronological Analyses

By Audrey Cross

A tree corer used to drill into a trunk, and two tree cores. Rings are counted from these cores and used to date events or reconstruct climate change.  Wikimedia Commons.

A tree corer used to drill into a trunk, and two tree cores. Rings are counted from these cores and used to date events or reconstruct climate change. Wikimedia Commons.

In dendrochronology, most analyses rely on a number of underlying assumptions. For wood that was used by humans, a tree might have been used immediately after it died, and it could be found at a site nearby where the tree had lived. However, humans could obtain wood in different ways; it could be found, as with driftwood; recycled, as with beams in houses; or transported, as with boats.

The study of driftwood proposes an interesting twist to dendrochronological analysis because the amount of time that wood can spend in transport can vary greatly. Continue reading

Fecal proxies

By Dulcinea Groff

Dung fungus spores of Sporormiella australis. From Funghi Paradise.

Dung fungus spores of Sporormiella australis. From Funghi Paradise.

Feces of prehistoric organisms remaining in the sediment records harbor information that can lead to a picturesque reconstruction of an ecosystem from long ago.  It is quite remarkable how many examples of fecal proxies exist and provide more information than just an indication of the presence or absence of an animal.  In the early 1800’s, an eccentric paleontologist named William Buckland was the first to describe coprolites or fossilized feces.  When feces become fossilized the organic components are replaced with minerals and any clue as to what the organism ate is replaced.  Therefore, coprolites may not be very useful in understanding the ecology of past environments and organisms.  Instead, other things associated with feces become proxies in paleoecological studies. Continue reading

The Glaciation Fascination

By Rayna Campbell

The Earth’s history shows a wild mix of climates. Ranging from the toxic CO2-filled atmosphere of the earliest years, to global tropical conditions, to periods of intense and violent volcanic disturbances. In the incredibly short period of time humans have inhabited the earth, the climate has not had much time to change. But if we look back into our history, the last glacial maximum, or “The Ice Age” only occurred about  21,500 years ago (Editors). On the scale of geological time, this is very recent. So recent, in fact, we are still able to look to our paleoecological records and “see” evidence of the changes the environment went through during the presence of these huge ice masses.

Fig. 1) Glacial striations. Image courtesy of GNS Science (2009)

On the rocky coasts of lovely Maine in the summer, trips to the seaside provide not only a relaxing retreat from the summer heat, but a wealth of information about glacial movement thousands of years ago. Continue reading

Attaching dates to lake sediment cores: precise dating using varves

By: Rob Brown

There are many proxies paleoecologists use to determine past environments and communities (insects, pollen, diatoms, packrat middens, tree rings, etc.), many of which have been discussed on this blog previously. These proxies can be used to answer questions ranging from seasonal to millennial time scales. With the exception of tree rings, which were previously discussed on this post by Erin our reconstructions are often limited by errors in dating methods. However in some lakes, sediments are deposited in visible annual layers called varves. Varved sediments offer a unique situation where the temporal resolution necessary to determine annual to decadal changes relevant to a human lifetime can be achieved.

Figure 1. Varve sediment from Newbury, Vermont, USA. Note the alternating light and dark bands and different thicknesses. From Tufts University North American Glacial Varve Project

Figure 1. Varve sediment from Newbury, Vermont, USA. Note the alternating light and dark bands and different thicknesses. From Tufts University North American Glacial Varve Project

What are varves and where are they found?

Simply put, a varve is an annual layer of sediment that forms in distinct layers (Figure 1). A single year’s deposit includes a light (summer) layer and a dark (winter) layer.

Varves don’t form in all lakes, in fact they are found in very few. The main factor controlling varve formation is climate variability; there must be large seasonal differences in both temperature and precipitation. This sets up the succession of biotic life and the physical and chemical structure of the lake necessary to form the contrasting layers. Additionally, there needs to be no disturbance of the sediment once it is deposited. Processes such as underwater currents, sediment slumping (think underwater mudslides), degassing (air bubbles within the sediment), or bioturbation (organisms physically mixing the sediment) all mix the sediment layers and the annual deposits are lost (O’Sullivan, 1983). Continue reading

Dendrochronology: the trees tell stories too

By Erin Hayes-Pontius

To add to the seemingly never-ending list of proxies paleoecologists use to study the past, here’s another one: trees. If you have been following this blog for a little while, you probably read about what pollen can tell us, but using the trees themselves, rather than their pollen, can tell an entirely different story. Studying the pollen that accumulates in lake sediments has the distinct advantage of providing a record that is as old as the lake itself, which can sometimes be up to millions of years old. However, because of how long it takes lake sediments to accumulate, we cannot always be very confident of the date a particular layer of sediment represents. In contrast, trees generally provide a much shorter record than pollen, but because of their annual rings, give us an annual record to work with.

treecore

A device used to extract thin cores from trees (Wikimedia Commons: Beentree 2006).

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Small but Mighty: Insects as Proxies

By Wayne Heideman

Insects have been on the Earth for a long time and their presence can affect their surrounding environment. It is important to look at insects in the past as they can provide us with insight on how they can act in the present and in the future. In a paleoecological sense, insects can be studied in a number of ways. One way is to look at plant-insect interactions through plant fossils (herbivory) and peatlands (habitat). Another technique is through amber and observing the insect in a snapshot of time. Lastly, sediment cores in lakes can capture insect presence, notably Chironomidae (non-biting midges) larvae and Coleoptera (beetles). All three are viable means of observing past insect use but they all have their strengths and weaknesses which should be assessed before using a specific method.

A picture of three different types of insect damage on plants. A) Shows a frass trail as well as an oviposition site marked by the arrow. B) Shows a high degree of herbivory, only leaving fine veins and C) shows areas of leaf case shelter sites. From Wilf 2008.

A picture of three different types of insect damage on plants. A) Shows a frass trail as well as an oviposition site marked by the arrow. B) Shows a high degree of herbivory, only leaving fine veins and C) shows areas of leaf case shelter sites. From Wilf 2008.

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