Fine fuel moisture for site- and species-specific fire danger assessment in comparison to fire danger indices

- Fire danger index performance was evaluated based on fine fuel moisture.
- This method can be carried out even in areas with moderate fire danger.
- Differences between sites and forest types can also be detected.
- Beech to pine differences were due to the litter layer rather than micrometeorology.

Fire danger index performance as well as site- and species-specific fire danger is generally derived from fire occurrence records. However, in areas with a moderate overall fire danger, these analyses may be hampered by a small number of fires by unit area or generally missing fire data. However, as fire danger is expected to be linked to micrometeorology and dead fine fuel moisture, the use of litter and 10-h fuel moisture measurements for the aforementioned analyses was successfully tested in eight forest stands in southern Germany, using Spearman's rank correlation and various plotting techniques. The results show a reasonable ranking of fire danger indices. Furthermore, significant differences of litter moisture/fire danger between coniferous and deciduous forest stands exist at low to medium fire danger that fade away as fire danger increases. A comparison to standardized 10-h fuel moisture measurement revealed that differences between Scots pine and European beech litter moisture are not based on micrometeorological conditions in the forest stands, but rather on differences of the litter layer itself or the underlying soil.