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| Titel |
Forest fire effects on transpiration: process modeling of sapwood area reduction |
| VerfasserIn |
Sean Michaletz, Edward Johnson |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250032289
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| Zusammenfassung |
| Transpiration is a hydrological process that is strongly affected by forest fires. In
crown fires, canopy fine fuels (foliage, buds, and small branches) combust, which
kills individual trees and stops transpiration of the entire stand. In surface fires
(intensities -¤ 2500 kW m-1), however, effects on transpiration are less predictable
becuase heat transfer from the passing fireline can injure or kill fine roots, leaves, and
sapwood; post-fire transpiration of forest stands is thus governed by fire effects on
individual tree water budgets. Here, we consider fire effects on cross-sectional sapwood
area. A two-dimensional model of transient bole heating is used to estimate radial
isotherms for a range of fireline intensities typical of surface fires. Isotherms are
then used to drive three processes by which heat may reduce sapwood area: 1)
necrosis of living cells in contact with xylem conduits, which prevents repair of
natural embolism; 2) relaxation of viscoelastic conduit wall polymers (cellulose,
hemicelloluse, and lignin), which reduces cross-sectional conduit area; and 3) boiling of
metastable water under tension, which causes conduit embolism. Results show
that these processes operate on different time scales, suggesting that fire effects on
transpiration vary with time since fire. The model can be linked with a three-dimensional
physical fire spread model to predict size-dependent effects on individual trees, which
can be used to estimate scaling of individual tree and stand-level transpiration. |
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