Complex sentence: When the fire swept the area the forest was dense and mature with heavy fuel loads from dead trees, which also had dead limbs which extended to the ground providing a fuel ladder for it to easily spread into the tree tops.
Split into simpler sentences: When the fire swept the area the forest was dense and mature with heavy fuel loads from dead trees. Trees also had dead limbs which extended to the ground providing a fuel ladder for the fire to easily spread into the tree tops.