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| Titel |
Estimating needle litterfall in Scots pine based on photosynthesis and stand structural development |
| VerfasserIn |
Boris Tupek, Liisa Kulmala, Mikko Peltoniemi, Aleksi Lehtonen |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250097921
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| Publikation (Nr.) |
 EGU/EGU2014-13548.pdf |
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| Zusammenfassung |
| Needle leaf litter modelled with constant foliar biomass turnover rates or with constant
proportion of gross primary production (GPP) may underestimate the climate change driven
impacts on ecosystem carbon balance. Changing climate may have adverse effects e.g. on the
timing of the needle leaf development and shedding quantity, which means litter-induced
variation may become more pronounced.
In this study, we investigated whether the meteorological conditions, GPP, and fraction of
absorbed photosynthetically active radiation (fAPAR) can be used to predict more precisely
trends and inter-annual variation of needle litterfall. Mutual dependence of these
factors would imply mechanistic linkages between precise estimation of leaf litter
and precise estimates of GPP, which is driven byfAPAR. The fAPAR depends on
the quantity of active foliage in canopy that depends on carbon allocation to the
foliage.
The needle litterfall, needle cohort counts, and basic tree measurements were conducted
between 1992 and 2012 on 7 Scots pine stands across Finland. Meteorological conditions for
each stand were available from the nearest weather station. The GPP was estimated with a
semi-empirical ecosystem model calibrated to Finnish environment given meteorological
conditions and fAPAR as inputs. The fAPAR depended on the modelled foliage and
measured litterfall. Litterfall was estimated as a difference between two fAPAR estimates.
First based on allometric foliage models and second based on allometric foliage models
scaled annually with the needle growth model. We tested our predictions against data from
two FLUXNET eddy covariance sites Hyytiälä and Sodankylä located in southern and
northern Finland.
We found that the non-functional longevity of the needle lifespan (sum of the period
when GPP is close to zero) was strongly correlated with the mean annual GPP level, and
could be used for estimating the mean number of the needle cohorts. The inter-annual
variation of the number of needle cohorts which correlated with the needle litterfall was
function of the GPP variation. Our results show that if structural changes are accounted
for in GPP estimation, then both GPP and litterfall predictions are more precise. |
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