Sorry, I did not made myself clear in the last sentence of my message.

In fact what I want to animate is the terrain material itself, not the material used in the ecosystem objects.

I want to have a terrain change materials :
Jungle -> cut down trees -> eroded grassland

I made other tries with Infinite 7.4 and 7.5 PLE.
It is possible to have material animation, but not if the first two materials include ecosystems. .

What I could get is a transition of this type:
normal material -> normal material -> ecosystem material

With any other combination, there is no animation and no material keyframe created.
If I start with an ecosystem material, there is no material animation possible at all.

I tried to trick it by first creating an animation with standard materials and then replacing them with ecosystems. This destroys the existing keyframes.

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