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| Titel |
Coincidences of climate extremes and anomalous vegetation responses: comparing tree ring patterns to simulated productivity |
| VerfasserIn |
A. Rammig, M. Wiedermann, J. F. Donges, F. Babst, W. von Bloh, D. Frank, K. Thonicke, M. D. Mahecha |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 2 ; Nr. 12, no. 2 (2015-01-20), S.373-385 |
| Datensatznummer |
250117778
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| Publikation (Nr.) |
 copernicus.org/bg-12-373-2015.pdf |
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| Zusammenfassung |
| Climate extremes can trigger exceptional responses in terrestrial
ecosystems, for instance by altering growth or mortality rates. Such effects
are often manifested in reductions in net primary productivity (NPP).
Investigating a Europe-wide network of annual radial tree growth records
confirms this pattern: we find that 28% of tree ring width (TRW) indices
are below two standard deviations in years in which extremely low
precipitation, high temperatures or the combination of both noticeably
affect tree growth. Based on these findings, we investigate possibilities for
detecting climate-driven patterns in long-term TRW data to evaluate
state-of-the-art dynamic vegetation models such as the Lund-Potsdam-Jena dynamic global vegetation model for managed land (LPJmL). The major problem
in this context is that LPJmL simulates NPP but not explicitly the radial
tree growth, and we need to develop a generic method to allow for a
comparison between simulated and observed response patterns. We propose an
analysis scheme that quantifies the coincidence rate of climate extremes
with some biotic responses (here TRW or simulated NPP). We find a relative
reduction of 34% in simulated NPP during precipitation, temperature and
combined extremes. This reduction is comparable to the TRW response patterns,
but the model responds much more sensitively to drought stress. We identify
10 extreme years during the 20th century during which both model and
measurements indicate high coincidence rates across Europe. However, we
detect substantial regional differences in simulated and observed responses
to climatic extreme events. One explanation for this discrepancy could be
the tendency of tree ring data to originate from climatically stressed
sites. The difference between model and observed data is amplified by the fact that dynamic
vegetation models are designed to simulate mean ecosystem responses on landscape or regional scales. We find that both simulation results and measurements
display carry-over effects from climate anomalies during the previous year.
We conclude that radial tree growth chronologies provide a suitable basis
for generic model benchmarks. The broad application of coincidence analysis in
generic model benchmarks along with an increased availability of
representative long-term measurements and improved process-based models will
refine projections of the long-term carbon balance in terrestrial
ecosystems. |
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