Tree-Ring Talk

Progress report on reanalysis of the Hawley-Bell collection: Tree-ring chronology building and 14C dating at the religious and political centers of pre-contact eastern North America

During the twelfth century A.D. Indigenous societies across the Mississippi River Basin transformed: populations aggregated into towns around dramatic monumental constructions that represented the seat of polities, communities adopted foreign styles, and more centralized leadership roles emerged. While the general outline of Mississippian history is known, exactly how people came to abandon old cultural practices in favor of the Mississippian pattern is not understood, nor are the historical details of individual mound centers.

The Missouri River: A Story of Two Basins

The Missouri River is unusual because of its two main source regions, one in the high headwaters and one close to the mouth of the river.  In this talk, I report the results of research which explored the hydroclimatology of the basin to better understand the climatic controls on the two parts of the basin, the contribution of the snowmelt-driven streamflow to total Missouri River flow, and the nature of droughts in the instrumental record.  I will also discuss the first comprehensive set of streamflow reconstructions for the upper Missouri River, and the Turn-of-the-21st Century

High-resolution field reconstructions of Mediterranean hydroclimate during the last millennium

The Mediterranean region is projected to experience severe drying trends and more extreme hydroclimate events as a consequence of anthropogenic climate change over the next century.   In some places, this signal may have already emerged from natural variability.  Here we provide content for recent and future changes using new high-resolution spatial reconstructions of multiple hydroclimate fields from a tree-ring network that spans the last millennium.

Back To The Future With Tree-Ring Standardization: Maybe Schulman Did It The Right Way

This talk reflects over 45 years of research and contemplation by me on the tree-ring standardization problem. There is no optimal solution to this problem because the statistical properties of the raw ring-width data we typically process are very complicated and their expressions of radial growth over time are totally unobserved. It has recently become apparent to me that we spend too much time letting the computer do the standardization for us without taking time to look at the data.

Connecting tributary erosion to downstream floodplain forest establishment in a large river network

Sediment eroded from the headwaters of a large basin strongly influences channels and ecosystems far downstream, but the connection is difficult to trace. Disturbance dependent riparian trees are thought to rely upon floods for creation of the sand bars necessary for establishment, but pulses of sediment should also promote formation of this habitat.

Living with the star: Carbon-14 excursions in tree rings as the evidence for extreme solar activity

The annual 14C data in tree rings is an outstanding proxy for uncovering extreme solar energetic particle events (SEP, also called SPE -solar particle event) in the past. Signatures of extreme SEP events have been reported in 774/775CE, 992/993 CE, and ~660 BCE.

Tree-rings to biomass trajectories: uncertainty and fading records

Tree-rings provide evidence of past aboveground carbon storage that can be used to inform and constrain ecosystem model predictions. However, formal state data assimilation requires the characterization of the uncertainty associated with the data being assimilated. In addition, aboveground biomass reconstructions from living trees typically suffer from the fading record problem- that trees that once contributed to the aboveground biomass pool may have died.

Is understanding the past enough to predict the future? Global tree-ring data show complex impacts of climate change.

A deep-rooted concept in the dendrosciences is to infer climate or ecosystem variability from statistical relationships established between tree-ring and instrumental data. By extent, these relationships can then be extrapolated into past or future time frames, for example, to anticipate the impacts of anthropogenic climate change on forest ecosystems. Problematically, evidence is mounting that matters are not so simple and that the uncertainties associated with temporal and spatial scaling of tree-ring data are substantial.

Stable isotopes of tree rings reveal seasonal-to-decadal patterns during the emergence of a megadrought in the Southwestern US

Recent evidence has revealed the emergence of a megadrought in southwestern North America since 2000. In this occasion I will talk about how we examined tree-ring growth and stable isotope ratios in Pinus ponderosa at its driest niche edge to investigate whether trees growing near their aridity limit were sensitive to the megadrought climatic conditions during or before the establishment of the current megadrought.

Multicentennial perspectives on extreme climate and natural disasters in the northeastern Pacific

Over the past decade, the northeastern Pacific has witnessed repeated and severe heatwaves that have profoundly impacted the functioning and productivity of marine and adjacent terrestrial ecosystems. However, there remains considerable and long-standing uncertainly regarding NE Pacific climate variability prior to 1900 CE and the extent to which recent extremes are atypical in a longer-term context.

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