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| Titel |
Short-term effects of whole-tree and stem-only harvesting on C and N fluxes in two Picea abies stands, Norway |
| VerfasserIn |
O. Janne Kjønaas, Nicholas Clarke, Toril Eldhuset, Ari Hietala, Hugh Cross, Kjersti Holt Hanssen, Tonje Økland, Holger Lange, Jørn Frode Nordbakken, Ingvald Røsberg |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250110422
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| Publikation (Nr.) |
 EGU/EGU2015-10416.pdf |
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| Zusammenfassung |
| Tree harvest and different harvesting methods may affect the soil carbon (C) pool in forest
ecosystems. In conventional stem-only timber harvesting (SOH), branches and tops that
are left in the forests may contribute to the build-up of the soil carbon pool. In
whole-tree harvesting (WTH), inputs of organic matter from branches and tops are
strongly reduced. We established field experiments at Gaupen, SE and Vindberg, SW
Norway, to study the short-term effects of SOH and WTH on processes affecting the
accumulation and loss of soil C. Logging residues on the WTH plots were collected in piles
that were removed after 6 months, rendering two sub treatments (WTH-pile and
WTH-removal areas). We weighed selected trees and logging residues, surveyed
understorey biomass production, quantified pre-harvest soil C and nutrient pools down
to 30 cm. Soil respiration was measured and soil water sampled monthly during
the growing season, while temperature and moisture were measured continuously.
Organic and mineral horizons were incubated at different temperatures to estimate
potential C and N mineralization, and deep sequencing of the ITS2 barcode region of
fungal DNA was performed on the samples. Litterbags were deployed in the SOH
plots.
The logging residues amounted to 2.2-2.4 kg C m-2. At Gaupen, the mean in situ soil
respiration rates increased following harvest with all treatments, but were significantly higher
in WTH-pile and SOH relative to the WTH-removal areas in the first year as well as the
fourth year of treatment. The former rates included aboveground decomposing needles and
twigs but excluded coarser branches. The observed increase in the WTH-removal areas may
be related to decomposing roots, as well as to increased C mineralization partly due to the
higher soil temperatures following harvest. Soil temperature was the single most important
factor explaining the variability in soil respiration rates over all treatments. At Vindberg, a
decrease in soil respiration was observed with all treatments in the second and third
years following harvest. At both sites, decomposition of logging residues from
needles was more rapid relative to twigs and fine roots. The decomposing residues
released a substantial amount of nitrogen which was gradually reflected in the soil
water at 30 cm soil depth. A considerable increase in the NO3-N concentration
also in the WTH-removal areas in the second year following harvest suggests an
increase in N availability from decomposing fine roots and/or soil organic matter. The
increased N availability in the WTH-removal areas was supported by results from short
term lab incubations of undisturbed soil from the forest floor. The changes in the
WTH-removal areas were also reflected in the soil fungal diversity: saprophytic ascomycetes
on decaying plant material showed a striking increase in all treatments. For the
WTH-removal areas, this may, again, be related to the increased input of root litter; however,
the decrease in mycorrhizal basidiomycete species and the vigorous increase of
ascomycetes following harvest may also affect the C mineralization of soil organic matter. |
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