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| Titel |
Quantifying the effects of harvesting on carbon fluxes and stocks in northern temperate forests |
| VerfasserIn |
W. Wang, J. Xiao, S. V. Ollinger, A. R. Desai, J. Chen, A. Noormets |
| 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 ; 11, no. 23 ; Nr. 11, no. 23 (2014-12-04), S.6667-6682 |
| Datensatznummer |
250117709
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| Publikation (Nr.) |
 copernicus.org/bg-11-6667-2014.pdf |
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| Zusammenfassung |
| Harvest disturbance has substantial impacts on forest carbon (C) fluxes and
stocks. The quantification of these effects is essential for the better
understanding of forest C dynamics and informing forest management in the
context of global change. We used a process-based forest ecosystem model,
PnET-CN, to evaluate how, and by what mechanisms, clear-cuts alter ecosystem
C fluxes, aboveground C stocks (AGC), and leaf area index (LAI) in northern
temperate forests. We compared C fluxes and stocks predicted by the model
and observed at two chronosequences of eddy covariance flux sites for
deciduous broadleaf forests (DBF) and evergreen needleleaf forests (ENF) in
the Upper Midwest region of northern Wisconsin and Michigan, USA. The
average normalized root mean square error (NRMSE) and the Willmott index of
agreement (d) for carbon fluxes, LAI, and AGC in the two chronosequences were
20% and 0.90, respectively. Simulated gross primary productivity (GPP)
increased with stand age, reaching a maximum (1200–1500 g C m−2 yr−1)
at 11–30 years of age, and leveled off thereafter (900–1000 g C m−2 yr−1).
Simulated ecosystem respiration (ER) for both plant
functional types (PFTs) was initially as high as 700–1000 g C m−2 yr−1
in the first or second year after harvesting, decreased with age
(400–800 g C m−2 yr−1) before canopy closure at 10–25 years of
age, and increased to 800–900 g C m−2 yr−1 with stand
development after canopy recovery. Simulated net ecosystem productivity
(NEP) for both PFTs was initially negative, with net C losses of 400–700 g C m−2 yr−1
for 6–17 years after clear-cuts, reaching peak
values of 400–600 g C m−2 yr−1 at 14–29 years of age, and
eventually stabilizing in mature forests (> 60 years old), with a
weak C sink (100–200 g C m−2 yr−1). The decline of NEP with age
was caused by the relative flattening of GPP and gradual increase of ER. ENF
recovered more slowly from a net C source to a net sink, and lost more C
than DBF. This suggests that in general ENF may be slower to recover to full
C assimilation capacity after stand-replacing harvests, arising from the slower
development of photosynthesis with stand age. Our model results indicated that
increased harvesting intensity would delay the recovery of NEP after
clear-cuts, but this had little effect on C dynamics during late succession.
Future modeling studies of disturbance effects will benefit from the
incorporation of forest population dynamics (e.g., regeneration and
mortality) and relationships between age-related model parameters and state
variables (e.g., LAI) into the model. |
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