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Northern Forest DroughtNet 

Understanding impact of precipitation change
on northern forest ecosystems

H. Asbjornsen, K. Jennings, C. McIntire, A. Coble, M. Vadeboncoeur
in collaboration with Lindsey Rustad (USFS), John Campbell (USFS), Pam Templer (Boston University), Melinda Smith (Colorado State), and others.

One of the ways that climate change is likely to affect the Northern Forest region is through the increased frequency and severity of drought events. However, our understanding of how the Northern Forest, which is adapted to humid temperate conditions, will respond to moderate to extreme droughts is limited. Given the important role that these forests play in protecting and regulating water resources, enhancing our knowledge about impacts of drought is critical to ensuring effective forest management and adaptation to climate change.

Specific project objectives include:
  1. Develop a standard methodology for conducting drought experiments in forest ecosystems
  2. Implement a prototype drought experiment
  3. Synthesize existing data on precipitation change and its ecological impacts in the northeastern U.S.
  4. Raise awareness in the Northeast about drought as an important and yet overlooked forest health issue

Combined, we will contribute to the capacity of scientists, managers, and the public in the northern region to plan for and adapt to future changes caused by anticipated increases in extreme drought events and impacts on forest and water resources.

We have recently established two throughfall-exclusion experiments:  one starting in spring 2015 in a maple-beech-birch stand at the Hubbard Brook Experimental Forest (in collaboration with CCASE), and one starting in fall 2015, in two pine-oak stands at Thompson Farm in Durham, NH.  These manipulations are designed to remove ~50% of throughfall from a plot, simulating a severe drought in the region. This experiment will allow us to measure growth response of trees subjected to a water-limited climatic regime and quantify the impacts this may have on tree health, water use, carbon sequestration, wood production, and soil water availability.

We are collaborating closely with researchers involved in creating a NSF-funded International DroughtNet Research Collaboration Network that will facilitate the establishment of a coordinated global network of drought experiments utilizing standard protocols. Changing water relations in ecosystems across the globe is an important current topic of research, but temperate forests are currently underrepresented in the literature. Thus, this research will allow us to produce relevant data sets that can inform local decision-making as well as be integrated into a global-scale understanding of terrestrial water dynamics. Response variables of interest being measured include:
  • Volumetric soil moisture content
  • Soil respiration and temperature
  • Root production and biomass
  • Whole tree water using heat-based sapflow methodology
  • Litter fall and decomposition rates
  • Sub-annual stem dendrometer measurements
  • Leaf water potential and gas exchange

This work is funded by USDA via a grant from NSRC, and by the New Hampshire Agricultural Experiment Station.

This work was featured in a story in EOS Spheres in March 2016 and a UNH Press Release in April 2016.

Drought Plot 2 under construction at Thompson Farm in 2015: