Kristen de Graauw is a dendroarchaeologist: that’s someone who studies the plant material in old human-made structures, such as buildings, artefacts and furniture. She is a recent PhD graduate from West Virginia University. In her recent work in the Journal of Biogeogrpahy, she describes the role of human occupation in shaping the distribution and dynamics of North American forests. Kristen shares how these insights were made possible from analysis of tree rings in historical log buildings.
Kristen K. de Graauw climbing into the hayloft of a late 1700s barn to inspect logs for sample collection.
Institute. Recent graduate from West Virginia University.
Academic life stage. PhD (graduated 2019).
Major research interests. Dendroarchaeology, Forest History and Ecology, Physical Geography, Environmental Science.
Current study system. Currently, my major research focus is on using tree-ring data from historic log buildings (typically Quercus alba, Liriodendron tulipifera, Pinus species) to explore forest history in eastern North America. This is a relatively new area of research exploration, and I’m finding that historic log buildings hold great potential for recording forest dynamics during the 1500s-1800s, a period not well represented in live tree records in eastern North America. My specific interests are related to changes in land management from Indigenous to European immigrant occupation and how those changes shaped our understanding of modern forests.
Recent paper in Journal of Biogeography. de Graauw, K.K. & Hessl, A.E. 2020. Do historic log buildings provide evidence of reforestation following the depopulation of Indigenous Peoples? Journal of Biogeography 47(3).
Motivation behind this paper. My co-author and I were compelled to undertake this project after reading Koch et al. (2019) in Quaternary Science Reviews. In this study, the authors hypothesized that there was mass forest regrowth in the Americas following the depopulation of Indigenous Peoples and that the increase in biomass ultimately led to the coldest portion of the Little Ice Age. A fascinating study! I was already using tree-ring data from historic log buildings to reconstruct forest age structure and disturbances during the European immigration period and recognized the potential of using my data to address the forest regrowth portion of the Koch et al. (2019) hypothesis. European immigrants’ historic log buildings were constructed in areas that were likely previously inhabited by Indigenous Peoples, so they were an ideal data source to use in this investigation of potential land management change.
(left) The Barracks, a late 1700s log building used in this study. (right) The Pitsenbarger farm, an example of historic log homesteads from the mid-1800s in the central Appalachian Mountains.
Key methodologies. Until recently, tree-ring data from historic log buildings were not generally used to investigate ecological questions. My dissertation provides one of the first formal introductions to the topic and this paper provides the first application (I believe) of historic logs to address an ecological question. We collected samples from 18 log buildings and compared recruitment dates (estimate of tree establishment), early radial growth (fast versus slow growth in first 100 years), and growth release events (an indication of canopy status, i.e. “open” or “closed”) with 8 old-growth forests to test for evidence of reforestation. We hypothesized that if there was evidence of forest regrowth following depopulation it would be present in historic log buildings because they represent areas suitable to human occupation, but not present in old-growth forests because these sites are generally located in areas not suitable for habitation.
Unexpected challenges. One of our greatest challenges was locating the specific tribes that inhabited the Ridge and Valley region of the central Appalachian Mountains in the 1600s. We wanted to accurately present the tribes that lived in this region at that time, and more specifically we wanted to understand their unique land management strategies. However, published records of the Indigenous Peoples at that time are relatively sparse and we were left with broad language groups that likely inhabited the region. We have since been informed about the Native Land App (native-land.ca), which provides a user-friendly map interface for locating territory boundaries of tribes in North America. While there are still some gaps in the data in our region, we now have a better understanding of who lived here in the 1600s and can begin to explore their land management techniques with the help of archaeologists and ethnographers.
Major results and contributions to the field. By comparing initiation, growth, and release events of historic logs (representing habitable areas) versus old-growth forests (representing areas unsuitable for human habitation), our data demonstrates that there were significant differences in tree growth in these two site types and that the timing of tree initiation coincided with the estimated timing of Indigenous depopulation from the region. However, tree recruitment dates across site types (historic buildings and old-growth forests) were also consistent with a sub-continental drought event in eastern North America, which may have led to tree mortality and subsequent recruitment. If we can replicate these results across a broader area in eastern North America, specifically in places where the sub-continental drought did not occur and/or where depopulation occurred earlier or later than the drought, it would suggest that forests encountered by European immigrants were largely created through cessation of large-scale land management at the time of European contact and depopulation (migration, mortality) of Indigenous Peoples.
The next steps in this research? The next step is to repeat our study using tree-ring data from historic log buildings in other portions of eastern North America. We are specifically interested in working in the southeast and along the coastal region. In doing this, we will test for forest regrowth and compare it with the estimated timing of depopulation in these regions, which would be different from the timing of depopulation in the central Appalachian Mountains. If we find evidence of forest regrowth that is coincident with estimated depopulation in the southeast and in coastal regions, it would suggest that Indigenous depopulation led to major forest changes in eastern North America. Such a finding would also contribute evidence to the “cooling” hypothesis posed by Koch et al. (2019) if evidence of reforestation is contemporaneous with the nadir of carbon drawdown (circa 1610 CE).
(left) Sanded white oak (Quercus alba) cores collected from a historic log building in the central Appalachian Mountains. (right) Kristen K. de Graauw collecting core samples from logs in a barn.
If you could study any organism on Earth, what would it be and why? Well, trees are my “thing”. I love mighty oaks, specifically white oak (Quercus alba), so I already study my favorite organism! But it would be amazing to work with older wooden archaeological materials/artifacts in other parts of the world.
Any other little gems you would like to share? My colleagues like to give me grief about how easy it must be to collect samples in a log building versus a forest, but what most people don’t consider is the massive amount of wildlife (spiders, snakes, mice, raccoons, etc), dead wildlife (see wildlife – and a cow!), animal feces, rusty objects, and general accumulation of human artifacts over centuries that I encounter in these historic buildings. Each building has its own theme, or “personality”, and some are more horrendous (and/or hazardous) than others. The most challenging building I worked in, though, was a museum full of beautiful antiques. I worry enough about carefully collecting cores from these centuries-old logs – the last thing I want to worry about is getting sawdust on a priceless quilt!