Dating Buildings and Landscapes with Tree-Ring Analysis

An Introduction with Case Studies

Darrin L. Rubino, Christopher Baas

• Éditeur: Routledge
• Année: 2019
• ISBN:
  9781351381956
• Édition: 1
• Sujet: Architektur
• Sous-sujet: Architektur Allgemein

This book presents guidance, theory, methodologies, and case studies for analyzing tree rings to accurately date and interpret historic buildings and landscapes.

Written by two long-time practitioners in the field of dendrochronology, the research is grounded in the fieldwork data of approximately 200 structures and landscapes. By scientifically analyzing the tree rings of historic timbers, preservationists can obtain valuable information about construction dates, interpret the evolution of landscapes and buildings over time, identify species and provenance, and gain insight into the species matrix of local forests. Authors Darrin L. Rubino and Christopher Baas demonstrate, through full-color illustrated case studies and methodologies, how this information can be used to interpret the history of buildings and landscapes and assist preservation decision-making.

Over 1, 000 samples obtained from more than 40 buildings, including high style houses, vernacular log houses, and timber frame barns, are reported. This book will be particularly relevant for students, instructors, and professional readers interested in historic preservation, cultural landscapes, museum studies, archaeology, and dendrochronology globally.

Chapter 1
Can you date my building

An introduction to tree-ring analysis for dating buildings and landscapes

1.1 Introduction

Trees are reliable timekeepers. Undoubtedly you have learned that trees can be aged by counting their rings – count the number of rings, and you know the age of the tree. Yes, trees can be aged by counting rings, but tree rings can tell more than just age (Figure 1.1). Trees are autobiographers. A tree records in its growth rings the annual layers of wood formed each year, a story written in one-year-long chapters. The size of a tree ring in a given year is determined by a variety of factors experienced by the tree in that year (amount of precipitation, temperature, light, etc.). Reading a tree’s “story” requires a researcher to translate unique patterns in growth (patterns of large and small tree rings) to gain a better understanding of what a tree has experienced over its lifetime. One can determine when a tree began growing, when it died, and how it reacted to changes in its environment. The science of tree rings is called dendrochronology (which roughly translates from its Greek roots to the study of time using trees). Using dendrochronological techniques (acquiring samples, prepping them for “reading,” assigning accurate dates to individual rings, etc.) researchers have been able to ask and answer a multitude of questions. For example, tree rings have been used to investigate and/or date insect outbreaks and natural disasters (volcanoes, windstorms, and fires) and to study long- and short-term climatic variability.

The wide application of tree rings to investigate the natural world is a testament to the versatility of tree-ring science. Many subdisciplines of dendrochronology have evolved, such as dendroecology (using tree rings to explore ecological questions and phenomena) and dendroclimatology (tree-ring analysis of climate). The subdiscipline of dendroarchaeology relates to the use of tree-ring methodology to date historical wooden objects. The wooden object could be a piece of furniture, a panel used in a painting, a ship, a musical instrument, or a building (Baillie 1982, 1995; Speer 2010). This text focuses on how tree rings and tree-ring science can be used to date historically constructed buildings and the landscapes in which they are found. Tree rings offer a unique ability to establish construction dates because they offer annual resolution. In other words, dendrochronological techniques allow for actual calendar dates to be assigned to individual tree rings – tree rings are precise! Dating historic buildings and landscapes has been done since the 1920s and is one of many methods used to establish construction dates (Stokes and Smiley 1968; Dean 1997; Nash 1999; Taylor 1999).

Figure 1.1
Cross section of a white oak beam from a southern Indiana log house. The tree rings in this timber were dated from 1696 to 1831; tree rings can be identified by the alternating light and dark woody tissue. Note that not all of the rings have the same width. The variation in ring size is related to the growth conditions experienced by a tree in a given year. Depending on the amount of resources available for growth, such as light or water, trees will produce larger or smaller rings. Tree rings, therefore, record what a tree experienced while it was growing. Since the last ring in this timber is next to the bark (arrow), we can determine that the tree was felled in 1831 and subsequently was used for construction.
Source: Authors.

1.2 An overview: can you date my building?

To introduce the reader to this text, we thought we would begin with a commonly asked question: “Can you date my building?” We are often asked by landowners, museum directors, and private citizens if we can provide construction dates for their buildings using tree-ring analysis. They are often initially perplexed by our answer of “maybe.” We have found that many stewards of historic buildings have heard of using tree-ring science to determine construction dates, but very rarely do they understand what is necessary for date determination. Once, while performing fieldwork on a barn, the owner came out after approximately two hours of work, asked us for the construction date, and wondered why we were still there! This experience was a bit of a revelation for us, and we realized that we needed to do a better job of explaining our methods and the potential and limitations of tree-ring analysis. What follows is an explanation of how we approach dating a structure and how we communicate with building owners before, during, and after an analysis is performed. We think it serves as a useful introduction to this text and gives the reader a basic summary of how we approach assigning dates to historical structures and landscapes.

1.2.1 Buildings and landscapes

The first step of dating a building’s construction requires a thorough examination of the timbers used in its construction. Even though they may be quite old and were not constructed with the benefits of modern technology, historic buildings and landscapes are complex. Trees were harvested, and timbers were fashioned using time-tested techniques. How a building is constructed and its role in a landscape must be understood to fully interpret it. In Chapter 2, we provide a framework, a sort of set of guidelines, of how to interpret buildings and landscapes.

1.2.2 Understanding how trees grow

One needs to have a basic knowledge of the biological processes that lead to the formation of tree rings to truly appreciate the results obtained when dating the timbers of historically erected buildings. The production of annual growth increments by trees is a complex process that is influenced by a wide variety of factors. In Chapter 3, we introduce the reader to the basic botanical concepts needed to understand tree-ring formation, tree growth, and how wood is formed.

1.2.3 Basics of tree-ring science

Like the understanding of basic botany, an understanding of the basics of tree-ring science is necessary to interpret and appreciate the results of any investigation focusing on providing a construction date for a building. In Chapter 4, we discuss the basic principles of dendrochronology. Dendrochronological examination of a building can provide information about a building that is unavailable from any historic source. Without a thorough understanding of how dates are assigned to tree rings, a simple construction date will surely be a less powerful piece of information when one is trying to interpret or restore a historical structure.

1.2.4 Obtaining a construction date

Most building owners and managers are quite interested in how we arrive at a construction date for a building or landscape. This interest likely stems from both curiosity and also a need to know how their buildings will be impacted by the sampling process. A thorough understanding and description of how we sample structures, prepare samples for study, and analyze data is imperative; Chapter 5 provides a description of field and laboratory work required for determining a building’s construction date. In order to date a building’s construction, many factors must be taken into consideration. In other words, obtaining the “right” samples is paramount for dating a building’s construction. Given how important these considerations are in the dating process of historic buildings and landscapes, we provide them here early in the text so that the reader can better appreciate what is necessary to answer the “Can you date my building?” question and to appreciate the important factors that must be kept in mind while reading subsequent chapters:

• Presence of bark or wane. In order to give an accurate construction date to a building, it is necessary to determine when the trees used to erect it died. Determining a death or felling date of a tree requires assigning a calendar date to the last year it formed a ring. This is the ring adjacent to the bark (Figure 1.1) or a ring associated with wane (the outermost ring if the bark has been removed or sloughed off. Wane is identified by noting a smooth, rounded outer surface on a log that is free of tool marks (Figure 1.2). When multiple timbers from a structure have the same or similar death dates we can determine the construction date of a building. If none of the accessible timbers of a building have bark or wane, calendar dates can still be assigned to the tree rings in the timbers, but an exact construction date cannot be determined (Figure 1.3).

Figure 1.2
Floor joists from a southeastern Indiana barn. These ash floor joists (arrows) exhibit wane, a smooth outer surface with no bark present. If the outermost ring in these joists can be dated, the felling or death date of the tree can be determined. When several timbers from throughout a building have the same or comparable death date, one can determine a construction date for a building.
Source: Authors.

Figure 1.3
Cross section of a white oak post from a log house. This timber was made by removing woody tissue from a fallen tree so that a square shape was achieved. This timber has no bark or wane, and it is not possible to determine how many rings were removed when it was squared. Therefore, the exact year of felling cannot be determined. The outermost ring in this sample is 1813 so we know this timber was put into service at some undeterminable year after 1813. The structure from which it was taken was built sometime after this date.
Source: Authors.

• Timber accessibility. Dating historically erected buildings requires extraction of wood samples from timbers from throughout a structure. In some structures, such as barns, sampling is fairly straightforward, because the timbers are readily accessible. Buildings such as houses and churches pose sampling problems because construction timbers are covered with plaster or other wall finishes, and access to structural timbers is not possible without causing major damage. In these buildings, we rely on sampling in crawlspaces, cellars, and attics (Figure 1.4). During renovations we have had great success in accessing timbers for dating (Figure 1.4; see also the Huxford House in Chapter 10, the Wyneken House in Chapter 8, and Musée de Venoge in Chapter 9).

Figure 1.4
To provide accurate construction dates for a building, samples from timbers must be obtained for analysis. Top: Sampling in buildings with finished walls is often done in cellars or crawlspaces, since the floor joists of the ground floor are usually accessible. Bottom: During renovation, samples are easily extracted, since wall coverings have been removed. During the renovation of Eleutherian College (Chapter 9), all of the baseboards (white boards in the foreground) were removed from the plastered walls. We were able to access and sample a large number of timbers without causing damage to finished walls. The vertical wooden timbers (center) are wall studs.
Source: Authors.

• Multiple samples are needed. Determination of a building’s construction date requires more than dating a single timber. Historical buildings have stood for extended periods of time (approximately two-century maximum where we work, but much, much longer in other parts of the world such as Europe and Asia). During this time, the fabric of buildings is routinely altered, and renovations and additions are made (see the Fauntleroy House, Chapter 11). New timbers are added to repair damaged timbers due to rot and insect damage (see Delphi’s Canal Park, Chapter 8). Additionally, buildings are often erected fully or in part with recycled timbers (see the Thiebaud and Posey...