The impacts of drought can be devastating and long-lasting, from the loss of valuable crops and trees to increased wildfire risk. Droughts are difficult to predict since they are caused by the interaction of precipitation, temperature, and topography. A team of researchers from Coweeta LTER, led by Dr. Bijan Seyednasrollah, has developed a drought monitoring method that relies on remotely sensed data, operates in near real-time, and correlates very well with traditional methods.. [read more]
The Nuñez years draw to a close with the defense of a fine thesis, papers coming out, and all those post-doc interviews. Stay in contact!
Awards ceremony at the von Humboldt Foundation last week with Christian Pape. Also honored from Duke was Anne Yoder, Biology Department. more here…
The lives of more than two billion people are affected by drought and could benefit from monitoring plant stress in real time. The extensive data collection and in-situ calibration that would be needed for continental scale estimates are difficult to implement in ways that could provide assessments of current conditions.
We used a simple relationship between the atmosphere and plants to extract real-time plant stress. Ordinarily, plant canopies are cooled by leaf water loss through stomata. These small pores in leaf surfaces lose water as they admit CO2 from the atmosphere. This evaporative cooling limits the canopy-atmosphere temperature differential, explaining why summertime mid-day temperatures within forest canopies are cooler than in cities. This cooling mechanism is driven by water uptake from the soil and remains effective until plants are moisture-limited, leading to stomatal closure, and surface heating. This simple relationship led us to speculate that the canopy-atmosphere differential, or “thermal stress”, could provide a real-time index of moisture limitation and of plant water consumption in warm seasons.
Combining the measurements from thousands of land-based weather stations and satellite-based ‘skin temperature’ of the canopy, Seyednasrollah et al. found thermal stress to be a reliable indicator of drought-induced water stress at the continental scale. Comparisons with land-based measurements showed that a 1 °C change in thermal stress is comparable to 1 to 1.2 mm of daily evapotranspiration, depending on site and climate conditions. Read more here.
Clark contributed to the Forests chapter:
Earth’s climate is now changing faster than at any point in the history of modern civilization, primarily as a result of human activities. The impacts of global climate change are already being felt in the United States and are projected to intensify in the future—but the severity of future impacts will depend largely on actions taken to reduce greenhouse gas emissions and to adapt to the changes that will occur… [read the report]
The amount of water available to a tree determines its susceptibility to drought. It has been one of the big unknowns in predicting responses to climate change. Here we show that it can be measured:
We apply this model to multiple seasonal droughts with tree transpiration measurements to demonstrate how species and size differences modulate moisture availability across landscapes. The depletion of individual moisture reservoirs can be tracked over the course of droughts and linked to biomass growth and reproductive output. This mass balance approach can predict individual moisture deficit, tree demographic performance, and drought vulnerability throughout forest stands based on measurements from a sample of trees, more here
A warming climate is changing the pace of spring green-up. Using remote sensing and a new approach that quantifies the rate of green-up, Seyednasrollah et al show that green-up is fast in the mountains and relatively insensitive to temperature anomalies, while slow development in warm, coastal forests can respond to temperature swings. Confirming experimental evidence, this study shows that spring is compressed in cold climates, delayed in onset but then rapidly progressing to full leaf expansion. Conversely, mountainous forest green-up is more susceptible to intensifying drought and moisture deficit, while coastal areas are relatively resilient. Canopy thermal stress slows leaf development following dry years, but accelerates it following wet years. The study is published in Remote Sensing of Environment.
Arbuscular mycorrhizal (AM) fungi in the soil may influence tropical tree dynamics and forest succession. The mechanisms are poorly understood, because the functional characteristics and abundances of tree species and AM fungi are likely to be codependent. We used generalized joint attribute modeling to evaluate if AM fungi are associated with three forest community metrics for a sub-tropical montane forest in Puerto Rico. (read more …)
“Congratulations on your most most downloaded article in Global Change Biology (GCB), “The impacts of increasing drought on forest dynamics, structure, and biodiversity.” Your paper is one of 2016’s 15 most-downloaded, according to Web of Science®.”
The latest release represents a substantial revision of many parts of the code, in R studio:
On Thursday, December 8, Jim Vose, project leader of the U.S. Forest Service Integrated Forest Science accepted the Chief’s Award – one of the highest honors in the Forest Service — in the category of “Sustaining Forests and Grasslands.” Vose accepted as leader of a team that the award honored for “understanding the impacts of drought on the nation’s forests and grasslands: providing a scientific foundation for effective management responses.” read more…
The National Assessment was led by Jim Vose, Jim Clark, Charlie Luce, and Toral Patel-Weynand: Effects of Drought on Forests and Rangelands in the United States: A Comprehensive Science Synthesis,
The EnviBayes section of ISBA this year has granted two best posters awards at the ISBA World Conference in Forte Village (June 13th – 17th, Cagliari, Italy). Joint Species distribution modeling: dimension reduction using Dirichlet processes by Daniel Taylor-Rodriguez, postdoc at the Department of Statistical Science Duke University, with Kimberly Kaufield from North Carolina State University, Erin Schliep of University of Missouri, James Clark and Alan Gelfand of Duke University.
The paper is accepted at Bayesian Analysis, bayesanaly2016.
Daniel Taylor-Rodriquez led this analysis and produced best poster, awarded by the Env Section of ISBA.ISBAposter2016
early view in Ecology
Trait analysis aims to understand relationships between traits, species diversity, and the environment. Current methods could benefit from a model-based probabilistic framework that accommodates covariance between traits and quantifies contributions from inherent trait syndromes, species interactions, and responses to the environment… read more
Predicting whole-tree water use requires models that accommodate the variation in sap flux between wood types and by depth into the tree. We develop a method for scaling-up flux observations. As an illustrative example, we predict sap flux for a forest in North Carolina, quantifying changes in water use with tree species and size. We include computer software for generating whole-tree flow estimates with other observations in Excel® and the R programming language.
Three papers published, a fourth ready to submit, see Publications