Live fuel moisture is the moisture content of living leaves, needles and stems, and it behaves nothing like dead fuel moisture. A plant regulates its own water, so live fuel moisture responds to soil water, root depth, species and season over weeks and months rather than to today's humidity. Values are high by the dry-mass definition — often \( 200\% \) in spring foliage, falling towards \( 60\% \) in a stressed late-summer shrub. Fire practitioners watch thresholds: many chaparral systems become capable of carrying crown fire once live fuel moisture in the dominant shrub drops near \( 60\% \), and sampling programmes clip and oven-dry foliage every two weeks to track it. Old growth and new growth on the same plant differ, so what is sampled must be stated. The confusion this resolves is assuming a humid week has rehydrated the living canopy; it has not, because the canopy was never in equilibrium with the air. After this Concept you can explain why green vegetation can still carry a fast-moving fire late in a drought year.
Fuel moisture is a wildland fire science metric expressing the water content of vegetative fuel as a percentage of its dry weight, calculated as (wet weight − dry weight) / dry weight × 100. It is a …