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Woody fuel consumption experiments in an undisturbed forest
Forest Ecology and Management 234S (2006) S109
Abstract
Woody fuel consumption experiments in an undisturbed forest Kevin G. Tolhurst a, Wendy R. Anderson b, Jim Gould c a
School of Forest and Ecosystem Science, University of Melbourne, Water Street, Creswick, Vic. 3363, Australia b UNSW@ADFA, Northcott Drive, ACT 2600, Australia c Ensis, P.O. Box E4008, Kingston, ACT 2604, Australia
Keywords: Woody fuel consumption; Intensity; Decay; Size-class
This paper describes research which is part of project A1.3 (Fuel classification and availability) of the Australian Bushfire Cooperative Research Centre (CRC). Initial research was undertaken in Tumbarumba in south-eastern NSW, Australia when a methodology was developed and initial results obtained. The plots were burnt in February 2004 under dry summer conditions. The vegetation was predominantly mature Mountain Gum (Eucalyptus dalrympleana) and Narrow-leaf Peppermint (E. radiata) forest of about 30 m height. Volume consumption was measured by wiring large diameter (>2.5 cm) fuel along transects and measuring the circumference change of fuel of different diameters and decay states. Density was also related to diameter and decay class, so that biomass consumption could be modelled in terms of fuel characteristics. The high level of fuel moisture variability in coarse woody debris in natural forests is a significant problem for fuel consumption modelling. Moisture content in the large logs can show a dramatic change from inner to outer wood. Some logs show this change, whilst others vary little from exterior to core. Samples were taken from core and sapwood to determine moisture content. Sawdust was collected from cross-sectional chainsaw cuts to determine an average moisture content of the samples. Distinction was made between woody fuel predominantly suspended above the ground (suspended) and that lying
DOI: 10.1016/j.foreco.2006.08.145 E-mail addresses: [email protected] (K.G. Tolhurst), [email protected] (W.R. Anderson), [email protected] (J. Gould).
on the ground (grounded). Suspended fuel outer FMC was reasonably well related to fuel diameter (apart from the green wood). Inner suspended and inner and outer grounded fuel moisture contents were very variable 100% for a given diameter. Surprisingly moisture content was not well related to decay class—apart from the green wood. A significant difference in fuel moisture was found between woody material in contact with the ground and material suspended above it, suggesting that the modelling of fuel moisture and availability in natural forests is likely to be more complex than has been indicated by previously published research, which has largely been in recently harvested areas with less variation in the extent of woody fuel decay. In the three plots burned, there was a strong relationship between woody fuel consumption and fire intensity. The greater the degree of decay, the greater the proportion of woody fuel consumed by the fire. There was a tendency for a greater proportion of the smaller diameter classes of woody fuel to be consumed by the fires. This was most pronounced in the grounded woody fuels in high intensity fires and suspended fuels in low intensity fires. Grounded woody fuel tended to be moister than the suspended fuel, but it was also in closer proximity to fine surface and near-surface fuels. However, the effect of the surface and near surface fuels on woody fuel consumption could not be identified in these experiments.
Abstract
Woody fuel consumption experiments in an undisturbed forest Kevin G. Tolhurst a, Wendy R. Anderson b, Jim Gould c a
School of Forest and Ecosystem Science, University of Melbourne, Water Street, Creswick, Vic. 3363, Australia b UNSW@ADFA, Northcott Drive, ACT 2600, Australia c Ensis, P.O. Box E4008, Kingston, ACT 2604, Australia
Keywords: Woody fuel consumption; Intensity; Decay; Size-class
This paper describes research which is part of project A1.3 (Fuel classification and availability) of the Australian Bushfire Cooperative Research Centre (CRC). Initial research was undertaken in Tumbarumba in south-eastern NSW, Australia when a methodology was developed and initial results obtained. The plots were burnt in February 2004 under dry summer conditions. The vegetation was predominantly mature Mountain Gum (Eucalyptus dalrympleana) and Narrow-leaf Peppermint (E. radiata) forest of about 30 m height. Volume consumption was measured by wiring large diameter (>2.5 cm) fuel along transects and measuring the circumference change of fuel of different diameters and decay states. Density was also related to diameter and decay class, so that biomass consumption could be modelled in terms of fuel characteristics. The high level of fuel moisture variability in coarse woody debris in natural forests is a significant problem for fuel consumption modelling. Moisture content in the large logs can show a dramatic change from inner to outer wood. Some logs show this change, whilst others vary little from exterior to core. Samples were taken from core and sapwood to determine moisture content. Sawdust was collected from cross-sectional chainsaw cuts to determine an average moisture content of the samples. Distinction was made between woody fuel predominantly suspended above the ground (suspended) and that lying
DOI: 10.1016/j.foreco.2006.08.145 E-mail addresses: [email protected] (K.G. Tolhurst), [email protected] (W.R. Anderson), [email protected] (J. Gould).
on the ground (grounded). Suspended fuel outer FMC was reasonably well related to fuel diameter (apart from the green wood). Inner suspended and inner and outer grounded fuel moisture contents were very variable 100% for a given diameter. Surprisingly moisture content was not well related to decay class—apart from the green wood. A significant difference in fuel moisture was found between woody material in contact with the ground and material suspended above it, suggesting that the modelling of fuel moisture and availability in natural forests is likely to be more complex than has been indicated by previously published research, which has largely been in recently harvested areas with less variation in the extent of woody fuel decay. In the three plots burned, there was a strong relationship between woody fuel consumption and fire intensity. The greater the degree of decay, the greater the proportion of woody fuel consumed by the fire. There was a tendency for a greater proportion of the smaller diameter classes of woody fuel to be consumed by the fires. This was most pronounced in the grounded woody fuels in high intensity fires and suspended fuels in low intensity fires. Grounded woody fuel tended to be moister than the suspended fuel, but it was also in closer proximity to fine surface and near-surface fuels. However, the effect of the surface and near surface fuels on woody fuel consumption could not be identified in these experiments.