Doesn't work with version Alien Biomes 0.6.4 When using a grenade, when fragments are scattered, instead of generating a tree, a message happen - you cannot build on the "biome name". If you disable Alien Biomes , then trees are generated.

Alien Biomes does have a changelog entry for 0.6.2 that seems to be related to your finding.

Some trees have additional tile restrictions. This prevents grassland trees from appearing on dirt and dryland trees appearing in desert.

But I can't seem to reproduce this. Could you elaborate a bit?

I downloaded the latest version of Factorio (1.1.27), got Alien Biomes 0.6.4 and the current version of this mod (1.1.1) and it seemed to work fine. I tried in 2 new games across different biomes and it worked as intented. New trees are created from existing nearby trees without issues.

Then I don’t know, all versions are new, I’m like this
https://www.youtube.com/watch?v=qfYWRKYJbhc
Mods list
https://i.ibb.co/n1xhrpQ/mods-2021-03-22-01-30-08.png
When I turn off Alien Biomes and Alien Biomes HR Terrain Textures then on all open chunks the ground and trees disappear, but it's worth going up and opening a new chunk where there are trees and everything works fine.

Edit
It seems this is due to other mods, if you leave only Alien Biomes and Sapling Capsule generation works. My apologies

Edit2
I think I found the criminal
Underwater Pipes https://mods.factorio.com/mod/underwater-pipes
Turned it off and it worked.

Edit3
And the last question, is the covered area not considered as the land on which trees can grow?
https://www.youtube.com/watch?v=OIW_4V9mHKE

No worries :)

That last thing is caused by Alien Biomes. That's certainly the "additional tile restrictions" that was mentioned in their changelog. Without Alien Biomes, trees are planted like usual on landfill.

Fixed on my side. I forgot to filter for underwater-pipe entities on on_trigger_created_entity event.

Btw i looked through the code of this mod and noticed that the event filter there is for tree-01. That's a regular tree which could be spawned by any other mod and could trigger this mod's functionality.
May i suggest to create a separate placer with its own name space?

Hi dodo, thanks for participating :)

May i suggest to create a separate placer with its own name space?

I haven't played Factorio in a while, so I might postpone it to a later date. It doesn't seem to be "criminal" at the moment ;) But I understand your suggestion. I opened it as an issue on GitHub so hopefully I won't forget.

May I suggest another addition for the issue?

Adding flag raise_built = true to create_entity would allow mods like Trees to recognize new trees (e.g. updating cache).

May I suggest another addition for the issue?

Adding flag raise_built = true to create_entity would allow mods like Trees to recognize new trees (e.g. updating cache).

Will do. Thanks for the hint :)