The Pogues song 'Death is not the end" often comes to mind when I see fallen trees. This one has been down for many years and is supporting an abundance of life externally, internally and under the ground. A symbol of the resilience of life, resurrection and, for me, hope.
I believe garden designers usually recommend an area for the equivalent of a 'fallen tree', to promote insect and bird life in the garden. Nice shot here, you can really see the trunk being reclaimed by nature.