The pilot was guiding the balloon to a final approach for landing into a large clearing. He attempted to reduce a slight overshoot by operating the parachute vent, which is actuated by pulling on a line, of which the lower section is constructed of Kevlar material. When pulled, the lower parachute vent line became detached at a bowline joint, resulting in the balloon touching down near a large gum tree. After touchdown the envelope drifted onto the tree, sustaining substantial damage. The lower vent line was originally constructed from stainless steel but had been replaced with Kevlar in accordance with an engineering order from the manufacturer.