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The initial employment of tree rings in geomorphic studies was simply as a dating tool and only rarely were other environmental information and records of damage contained within the tree exploited. However, these annually resolved tree-ring records also preserve valuable archives of past geomorphic processes on timescales of decades to centuries. As many of these processes are significant natural hazards, understanding their distribution, timing and controls provides crucial information that can assist in the prediction, mitigation and defense against these hazards and their effects on society. This contribution aims at presenting a proposal on the types of growth disturbances to be included in future work focusing on geomorphic disturbance, the intensity of reactions, and on the minimum requirements needed for growth disturbances to be considered in event histories. We present possibilities and limitations of dendrogeomorphic applications in geomorphic research and propose a range of techniques and approaches that may become standard practice in the analysis and understanding of earth-surface processes and related natural hazards in the future.
A new 368-year tree-ring chronology (A.D. 1643–2010) has been developed in western North Dakota using plains cottonwood (Populus deltoides subsp. monilifera) growing on the relatively undisturbed floodplain of the Little Missouri River in the North Unit of Theodore Roosevelt National Park. We document many slow-growing living trees between 150–370 years old that contradict the common understanding that cottonwoods grow fast and die young. In this northern location, cottonwood produces distinct annual rings with dramatic interannual variability that strongly crossdate. The detrended tree-ring chronology is significantly positively correlated with local growing season precipitation and soil moisture conditions (r = 0.69). This time series shows periods of prolonged low radial tree growth during the known droughts of the instrumental record (e.g. 1931–1939 and 1980–1981) and also during prehistory (e.g. 1816–1823 and 1856–1865) when other paleoclimate studies have documented droughts in this region. Tree rings of cottonwood will be a useful tool to help reconstruct climate, streamflow, and the floodplain history of the Little Missouri River and other northern river systems.
The McKenzie Home is a one-story log structure located in Meigs County, Tennessee. The land tract where the cabin was originally built was purchased by the McKenzie family ca. A.D. 1820 to 1828, which makes the suspected construction date for the home sometime after 1820. Our objective was to date oak (Quercus spp.) cross-sections taken from original logs to accurately determine the year when the trees were cut and therefore when the structure was built. We created a master chronology from measurements taken along 12 radii from five oak sections using program COFECHA to first confirm internal crossdating among the measured radii and then using program ARSTAN to create a floating master chronology. Interactive detrending identified two likely disturbances that affected tree growth on all five oaks and these trends were subsequently removed using 32-year splines. The McKenzie floating chronology was then compared with a composite reference chronology created from four oak chronologies located in Tennessee, Kentucky, and Alabama. An interseries correlation coefficient of 0.412 (n = 169 years, t = 5.84, p < 0.0001) was obtained between the floating chronology and the anchored reference chronology, indicating a single year of tree harvesting in A.D. 1876. Cutting dates for the five samples indicate harvesting began in the early part of the growing season in 1876 and lasted until the end of the growing season or possibly into the dormant season of 1876–1877. The graphical and statistical crossdating evidence and cutting dates that confirm 1876 as the year of construction matches historical property and district records, which state the land was purchased by E.G. McKenzie, Sr. from his brother on 1 February 1876. The log structure has since been renamed the “E.G. McKenzie, Sr. Home.”
Two tulip poplars (Liriodendron tulipifera L.) growing at Monticello, the home of Thomas Jefferson, were recently removed because of potential damage to the house; however, their ages were uncertain. Jefferson's writings express his interest in tulip poplars and suggest that he may have planted at least one, but his documents are not conclusive. After the Thomas Jefferson Foundation purchased the property in A.D. 1923, expert opinions on the ages of these trees were divided. This study investigated the ages of both trees (referred to as northwest and southwest). Even though the southwest tree's bole was hollow and decay was present in the northwest tree, usable cross-sections were obtained. The southwest tree's cross-section was from an upper branch, whereas upper and lower cross-sections were extracted from the bole of the northwest tree. Ring widths were crossdated and statistically verified using an oak chronology from Monticello. The innermost rings of the southwest tree dated to A.D. 1852 and those of the upper and lower sections of the northwest tree dated to 1822 and 1808, respectively. These dendrochronological analyses in combination with historical photographs support the conclusion that the northwest tree and likely the southwest tree were Jefferson era, but the evidence for the southwest tree is less certain.
One of the most extensive dendrochronological field collections in South America was conducted by LaMarche and collaborators from 1973 to 1978. However, no robust chronologies had been developed from these species and/or sites because there were not enough samples collected, or simply because the materials were never processed. Here, I report on results from a re-examination of all Nothofagus dombeyi samples collected during LaMarche and collaborators' field sampling in South America. A tree-ring chronology was developed for the Alto Vilches site in Chile. For the other sites sampled by LaMarche and collaborators, there were not enough samples, or series were not sufficiently long to build a chronology or to provide adequate information about tree growth. The Alto Vilches (VIL) chronology extends into the early 1800s, and shows high mean sensitivity values and a strong common signal. As expected, the VIL chronology evidenced narrow rings for several years that correspond with low precipitation periods in Patagonia. Making available the information kept in unprocessed tree-ring samples reinforces the dendrochronological potential of this species and strengthens chronology networks developed for ecological studies in northern Patagonia. Finally, this study honors the initial work of LaMarche and collaborators and provides closure to a small part of it.