VARIATION OF LIVE AND DEAD FINE FUEL MOISTURE IN PINUS-RADIATA PLANTATIONS OF THE AUSTRALIAN-CAPITAL-TERRITORY

A study was made of the variation in moisture content of fine dead fue l (FFM) in relation to 1) differences of fuel type (needles, leaves, t wigs, bark), 2) different fuel locations (dead canopy and surface litt er), 3) contrasting management of plantations (unthinned-unpruned vs t hinned-pruned) and 4) environmental factors (air temperature (T) and r elative humidity (H); moisture content of duff (D) and topsoil (S)). T he variation of live (green needle) fine fuel moisture content (LFMC) in relation to needle age, canopy location (shaded vs unshaded) and se ason was also studied in Pinus radiata D. Don plantations over 2 years . Mean differences of moisture content between the several types of fu el exposed to the same atmospheric conditions were generally significa nt and ranged from 0.6% (pine twigs vs eucalypt twigs) up to 2.8% oven dry weight (ODW) (eucalypt bark vs recently cast pine needles). T and H were highly correlated between study sites in pine plantations and an official meteorological station at Canberra airport, 15 km away. In the pine plantations, mid afternoon moisture contents of pine needle litter (litter FFMs) were mostly higher than moisture contents of dead needles in canopies (aerial FFMs); the mean differences between litte r FFMs and aerial FFMs were statistically significant. FFMs in the unt hinned-unpruned plantation were also generally higher than those in th e thinned-pruned plantations. Regression analyses of relationships bet ween FFM and environmental variables showed that T and H in combinatio n explained a large proportion of the variation in aerial FFM but much less of the variation in litter FFM. However, the inclusion of either D or S in multiple regression models accounted for significant amount s of the variation in litter FFM. LFMC decreased with needle age and, for full-grown needles, was up to 25% (ODW) higher in shaded compared to unshaded canopy locations. Seasonal patterns of change in LFMC of f ull-grown needles were not well defined. Variation in the parameters a nd the precision of FFM regression relationships between fuel location s and stands with contrasting management demonstrate the site specific ity and limitations of empirical FFM models. The results suggest that for prediction of aerial FFM, models based on a combination of T and H are most appropriate; while, models that include a soil moisture vari able may predict FFM of litter fuels more accurately. However, the int rinsic variation in FFM revealed in this study indicates that such mod els, although providing a useful guide, may not predict FFM with the a ccuracy required for fire behaviour models during high fire danger wea ther - when fuel moistures are low.