I currently have pseudo-wood farms in a mod I'm working on.
They're going to take 2 years to grow, and use a custom reaction to draw out the wood, seeds, and other stuff. The current GROWDUR is just a placeholder. You'd want it in the league of 8000 or something if you want it to take that long, I believe. They'll appear on the map, but harvesting them doesn't yield anything. You'll have to change FREQUENCY and CLUSTERSIZE in order for you to gather them outside.
In reactions_other:
[REACTION:PROCESS_CUSTOM_TREE]
[NAME:separate tree]
[BUILDING:CUSTOM_WORKSHOP:CUSTOM_M]
[REAGENT:A:1:PLANT:NO_SUBTYPE:PLANT_MAT:CUSTOM_TREE:PLANT]
[PRODUCT:100:1:WOOD:NO_SUBTYPE:PLANT_MAT:CUSTOM_TREE_WOOD:WOOD]
[PRODUCT:100:1:SEEDS:NO_SUBTYPE:PLANT_MAT:CUSTOM_TREE:SEED]
[SKILL:PROCESSPLANTS]
I'm not sure if that's the correct skill token.
In plant_standard:
[PLANT:CUSTOM_TREE]
[NAME:test tree][NAME_PLURAL:test tree][ADJ:test trees]
[USE_MATERIAL_TEMPLATE:STRUCTURAL:STRUCTURAL_PLANT_TEMPLATE]
[MATERIAL_VALUE:20]
[BASIC_MAT:LOCAL_PLANT_MAT:STRUCTURAL]
[PICKED_TILE:23][PICKED_COLOR:4:0:1]
[GROWDUR:2200][VALUE:20]
[USE_MATERIAL_TEMPLATE:SEED:SEED_TEMPLATE]
[MATERIAL_VALUE:50]
[SEED:test tree seed:test tree seeds:4:0:0:LOCAL_PLANT_MAT:SEED]
[PREFSTRING:rich berries]
[WET][DRY]
[SPRING][SUMMER][AUTUMN][WINTER]
[BIOME:ANY_LAND]
[FREQUENCY:0]
[CLUSTERSIZE:0]
[SHRUB_TILE:23]
[SHRUB_COLOR:4:0:1]
[DEAD_SHRUB_TILE:198]
[DEAD_SHRUB_COLOR:0:0:1]
[PLANT:CUSTOM_TREE_WOOD]
[NAME:test tree][NAME_PLURAL:test tree][ADJ:test trees]
[USE_MATERIAL_TEMPLATE:STRUCTURAL:STRUCTURAL_PLANT_TEMPLATE]
[BASIC_MAT:LOCAL_PLANT_MAT:STRUCTURAL]
[USE_MATERIAL_TEMPLATE:WOOD:WOOD_TEMPLATE]
[STATE_NAME:ALL_SOLID:test tree]
[STATE_ADJ:ALL_SOLID:test tree]
[PREFIX:NONE]
[DISPLAY_COLOR:7:0:1]
[TREE:LOCAL_PLANT_MAT:WOOD][TREE_TILE:23]
[PREFSTRING:sweet scent]
[SOLID_DENSITY:670]
I'm not actually sure if I had to make two seperate entries for the plant itself and the wood, but I did anyways.