The hosts become easier to attack or the host is predisposed to attack. Everyone will obey nature's laws Agree or not, all living things will obey natural laws of energy and matter. The wood is made up mostly of cellulose, hemicellulose and lignin. All of these substances have a carbon, hydrogen and oxygen framework and can be utilized by microorganisms as an energy source for their metabolisms. Animals do not have the enzymes to make the chemical conversions.
Many microorganisms do.
The energy in the remaining starch and wood is then used further. We would have no breakdown of once-living organisms. You can think of life as a journey, powered by the sun, of a highly ordered group of chemicals, borrowed from the soil. Death is the end of the journey when chemicals and their energy are returned to the soil to be used again for new life. Everything is recycled.