Fuel accumulation following prescribed burning in young even-aged stands of karri (Eucalyptus diversicolor)

Summary

Accumulation of forest floor litter, elevated dead fuel < 25 mm diameter and live fuel < 4 mm diameter was studied over a ten year period following prescribed burning in young even-aged regrowth stands of karri. Patterns of accumulation were compared amongst three stands burnt by low intensity fires that did not scorch the overstorey, and one stand where the overstorey was fully crown scorched and in places completely defoliated by crown fire. Forest floor litter contributed the major proportion, by weight, of the total fuel load. The pattern of litter accumulation was similar at the three low scorch sites, but litter accumulated more slowly at the fully scorched and defoliated sites. Ten years after fire the average litter fuel load at the three low scorch sites was 27 t/ha (range 25–28 t/ha), which is a similar rate of litter accumulation to that recorded for mature karri forest. Twigs 6–25 mm in diameter comprised the majority of the elevated dead fuel load, with smaller proportions of fine twigs < 6 mm diameter and suspended bark and leaves. Fine twigs, and bark and leaves accumulated at a relatively constant rate over the ten years following fire but loadings of twigs 6–25 mm diameter peaked in the fifth year after fire. This was attributed to episodic input resulting from the collapse of fire-killed understorey shrubs. Live fuel was the smallest component of the total fuel load at any of the sites and varied between stands according to the species composition of the understorey shrub layer. Live fuel loads were greater where the overstorey had been severely damaged by fire. Total fuel loads (live and dead) at the low scorch sites ranged from 37 t/ha to 40 t/ha after ten years, which is considerably heavier than in many other eucalypt forest types.