Tree-Ring Talk

Evaluating the abruptness of dendrochronologically-reconstructed western spruce budworm outbreaks

Reconstructed insect regimes provide information on outbreak interval length, periodicity, duration, and associations with climatic patterns. We explored patterns associated with western spruce budworm outbreak initiation, dating “foremost years” as when the percentage of trees recording defoliation reached a prescribed limit, and quantified outbreak abruptness as the number of years between when 25 and 50% of the trees were defoliated. We re-analyzed budworm data from Colorado and New Mexico to demonstrate the utility of these statistics.

Coupling between summer North Atlantic jet variability and European forest productivity and growth

Dynamically-driven extreme weather events have large ecological, social and economic consequences including large tree-growth reductions and forest mortality. These events are likely to become globally more frequent and intense under increased anthropogenic forcing and associated changes in coupled atmosphere-ocean circulation. The jet stream latitude (JSL) over the North Atlantic-European domain provides a synthetic and robust physical framework that integrates climate variability not accounted for by atmospheric circulation patterns.

Arctic Amplification: Do rivers matter? A tree-ring case study of seasonal streamflow changes in the Yenisei River Basin (Russia)

The Yenisei River is the largest contributor of freshwater and energy fluxes among all rivers draining to the Arctic Ocean. We quantify larch tree growth response to river discharge at the upper reaches of the Yenisei River in Tuva, South Siberia. Two regression models built from tree-ring width chronologies are applied to reconstruct winter (Nov–Apr) and annual (Oct–Sept) discharge. This new hydrological archive doubles the length of the instrumental discharge record at the Kyzyl gauge and resets the temporal background of discharge variability back to 1784.

Diversity in dendrochronology

In 2016, only 6% of US Geoscience PhDs went to students from underrepresented minorities, leading Bernard et al. (2018) to conclude that no progress has been made on diversity in 40 years. The situation is similar in the field of dendrochronology. In this talk I will discuss the biases in the publication process, in academic careers, and in various forms of recognition that lead to this lack of progress. I will focus my talk on biases against women scientists, for which the most scientific evidence is available.

Miracle March, August flooding, and October atmospheric rivers: Seasonal wet extremes & the tree-ring record

Moisture-sensitive trees provide exceptional long-term records of streamflow, snowpack, and rain within the context of our changing climate. The delivery of a large portion of annual moisture in a short period of time can present a challenge to our interpretation of these records. This is particularly true in arid and semi-arid regions, where late-spring snowpack, summer convective storms, or autumn atmospheric rivers can provide a high percentage of annual water in a season that might not be aligned with tree growth.

Using tree-ring chronologies to calibrate a forest gap model in Denali National Park

Merging robust statistical methods with complex simulation models is a frontier for improving ecological inference and forecasting. However, bringing these tools together is not always straightforward particularly with tree-ring data. Matching tree-ring data with model output, determining starting conditions, and addressing high dimensionality are some of the complexities that arise when attempting to incorporate tree-ring data with mechanistic models directly using sophisticated statistical methods. To illustrate these complexities and pragmatic paths forward, we

Tree rings and the Truckee River: paralleling the past and the present

The Truckee River Basin, located on the Nevada-California border, is an area of extreme hydrologic variability, being subject to both prolonged multi-decadal droughts and devastating floods; however, due to its brief instrumental record, understanding the full range of this variability is limited. To address concerns over the potential severity of the current post-2000 drought, I created a new streamflow reconstruction of the Truckee River.

A spatial field reconstruction of North American summer air temperatures derived from a tree-ring blue intensity network 

Spatially-resolved climate field reconstructions are opportune for analyzing spatial anomaly patterns and characterizing regional-scale trends resultant from climate change. To date, few fine-scale (<5o by 5o) spatially-resolved paleo-temperature datasets exist in the Northern Hemisphere, especially those with representation of locations below 40oN.

A multimillennial snow water equivalent reconstruction from giant sequoia tree rings

The first dendroclimatic reconstruction of May 1 Snow Water Equivalent (SWE) was developed from a Sequoiadendron giganteum regional tree-ring chronology network of 23 sites in central California for the period 90-2012 CE. The reconstruction is based on a significant relationship between May 1 SWE and tree-ring growth and shows climate variability from inter-annual to inter-centennial time scales. A regression-based reconstruction equation explains up to 55% of the variance of SWE for 1940-2012.

Forests, climate, and tree rings: forecasting the future state of complex systems

At this stage in the Anthropocene, answering questions about the future state of ecological systems has become critical – the future growth of trees exposed to changing climate, tree species’ future geographic distributions, and the future role of forests in the global carbon cycle – yet ecological systems are complex. Summarizing four lines of research, I will illustrate how the use of tree-ring and forest inventory data can help address questions about and improve prediction of forest and climate system dynamics.

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