Answer:
Evaporated via combustion.
Step-by-step explanation:
The loss on ignition (LOI) and Ash content are inorganic analytical techniques used to determine the percentage by mass of hydrocarbon in compounds. This process allows volatile matter and possibly impurities found in a material to evaporate, leaving behind the true chemical constituents of the material.
The 10kg lost could be moisture content of the tree, or other volatile matter which has escaped on combustion of the tree.