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| Titel |
Increased carbon sequestration in a Danish beech forest during 1996-2016: Observations and hypotheses. |
| VerfasserIn |
Kim Pilegaard, Andreas Ibrom |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250141576
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| Publikation (Nr.) |
 EGU/EGU2017-5106.pdf |
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| Zusammenfassung |
| A study of the net exchange of CO2 (NEE) between the atmosphere and a beech forest near
Sorø, Denmark, during 14 years (1996-2009) showed that the beech forest acted as an
increasing sink of CO2 [1]. A significant increase in gross primary production (GPP) and a
smaller and not significant increase in ecosystem respiration (RE) were also found.
Thus, the increased NEE was mainly attributed to an increase in GPP. The length of
the carbon uptake period (CUP) significantly increased, whereas there was a no
increase in the leafed period (LP). This means that the leaves stayed active longer. The
increase in the carbon uptake period explained about half of the increasing NEE.
The remaining increase was believed to be due to an observed increased uptake
capacity of the canopy and increased annual radiation efficiency[2]. The causes
for this were hypothesized to be a combination of increase in atmospheric CO2
concentration, higher summer precipitation, and increased availability of N. A higher
nitrogen content in the leaves was observed towards the end of the observation
period.
An updated analysis of the flux data, now including the years 1996-2016, confirms the
increasing trend in carbon sequestration of the forest, an increasingly longer growing season,
and a significant correlation of NEE and CUP, however, similarly to the first study, the
increase in CUP only explains about half of the total increase.
Here we investigate three hypotheses for the remaining reasons for the increase:
H1: increased canopy nitrogen content
H2: carbon dioxide fertilisation
H3: increased water availability due to changing precipitation patterns.
We describe the multiannual development of canopy photosynthesis capacity with
regression analysis and perform sensitivity studies with the canopy model MAESTRA [3] to
investigate the above hypotheses. The results will be presented, critically discussed and
interpreted with respect to general effects of global climate change and site specific, local
effects that affect forest dynamics.
[1] Pilegaard, K., Ibrom, A., Courtney, M.S., Hummelshøj, P. and Jensen, N.O., 2011.
Increasing net CO2 uptake by a Danish beech forest during the period from 1996 to 2009.
Agricultural and Forest Meteorology, 151: 934–946.
[2] Wu, J. et al., 2013. Modelling the decadal trend of ecosystem carbon fluxes
demonstrates the important role of biotic changes in a temperate deciduous forest. Ecological
Modelling, 260: 50-61.
[3] Duursma, R. and Medlyn, B., 2012. MAESPA: a model to study interactions between
water limitation, environmental drivers and vegetation function at tree and stand levels, with
an example application to [CO2] × drought interactions. Geosci. Model Dev, 5: 919-940. |
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