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Organized Oral Session

Session: A change is already here: Implications of intensifying drought for terrestrial ecosystems

OOS 33-4 - Impacts of intensified drought across space and time: Results from the International Drought Experiment

Wednesday, August 17, 2022

4:15 PM – 4:30 PM EDT

Location: 520C

Presenting Author(s)

KW

Kate D. Wilkins

Postdoctoral Fellow
Colorado State University, United States

Co-author(s)

MS

Melinda D. Smith

Colorado State University
Fort Collins, Colorado, United States
MH

Martin C. Holdrege

USGS Southwest Biological Science Center
PW

Peter A. Wilfahrt

University of Minnesota, United States
LG

Laureano A. Gherardi

University of California, Berkeley
TO

Timothy J. Ohlert

University of New Mexico
SC

Scott L. Collins

Distinguished Professor
University of New Mexico
Albuquerque, NM, United States
JD

Jeffrey S. Dukes

Professor
Purdue University Departments of Forestry and Natural Resources & Biological Science
West Lafayette, IN, United States
AK

Alan K. Knapp

Colorado State University, United States
RP

Richard P. Phillips, Ph.D.

Professor
Indiana University
Bloomington, IN, United States
OS

Osvaldo E. Sala

Professor
Arizona State University
Tempe, Arizona, United States
AT

Anna Tatarko

University of Nevada, Reno
AF

Andrew Felton

Chapman University
Logan, UT, United States
I(

International Drought Experiment Network (IDE)

NA

Background/Question/Methods
Grasslands and shrublands cover >40% of Earth's land surface and play an important role in global carbon cycling. These ecosystems are often plagued by short-term (one-year) droughts that are predicted to intensify with climate change. Previous experiments suggest that these ecosystems vary widely in their sensitivity to drought—possibly due to differences in study methods and because extreme drought is rarely imposed. Our research sought to better understand the effects of extreme drought on these ecosystems by 1) more accurately quantifying the effects of single year, extreme drought on aboveground net primary production (ANPP), 2) determining if the mean drought effect differed between grassland and shrubland ecosystems globally, and 3) reducing uncertainty in the magnitude of drought responses resulting from differences in experimental design. To achieve these goals, we used data from a coordinated distributed experiment across a broad range of grassland and shrubland sites globally: the International Drought Experiment or IDE. IDE sites constructed infrastructure that uses a passive approach to impose an extreme, 1-in-100-year drought based on each site’s historic precipitation record. Sites measured annual ANPP, a fundamental component of the global carbon cycle, as a metric for drought-induced impact to ecosystem function in these grasslands and shrublands.

Results/Conclusions
In total, 94 of 136 sites met our criteria for inclusion. These criteria included deploying infrastructure in replicated plots capable of imposing a site-specific, historically-based extreme drought for a full growing season and following all other IDE protocols. The 94 sites in this analysis were arrayed across six continents in 20 countries and spanned broad climatic and edaphic gradients. On average, IDE sites reduced precipitation by 52%, which decreased aboveground net primary production (ANPP) by ~26% regardless of ecosystem type. However, there was substantial variation across sites, from catastrophic ( >80%) loss in ANPP to complete drought resistance (no change in ANPP). Our experimental approach resulted in an unprecedented number of sites (n = 40) experiencing a statistically extreme one-year drought, with less severe drought imposed in the remaining sites. Differences in drought severity explained 44% of variation in ANPP responses among ecosystems. When only those ecosystems exposed to historically extreme drought were considered, ANPP decreased by 40%, but variation in drought responses remained high. Our results demonstrate that ecosystem sensitivity to short-term drought varies dramatically, even with standardized approaches and comparably extreme droughts. Such inherent variability will challenge local-scale drought mitigation efforts as the climate changes.