Take note if a plugin changes anything in the worldspace and the tree mods/billboards being used. This is the vanilla list:
<TreeClover01 [TREE:000B8A62] billboard not found textures\terrain\lodgen\skyrim.esm\clover01_000b8a62.dds>
<TreeDeadShrub [TREE:000A731C] billboard not found textures\terrain\lodgen\skyrim.esm\deadshrub01_000a731c.dds>
<TreeFloraMountainFlower01Blue "Mountain Flower" [TREE:000BCF3D] billboard not found textures\terrain\lodgen\skyrim.esm\floramountainflower01blue_000bcf3d.dds>
<TreeFloraMountainFlower01Purple "Mountain Flower" [TREE:000BCF3A] billboard not found textures\terrain\lodgen\skyrim.esm\floramountainflower01purple_000bcf3a.dds>
<TreeFloraMountainFlower02Blue "Mountain Flower" [TREE:000BCF3F] billboard not found textures\terrain\lodgen\skyrim.esm\floramountainflower02blue_000bcf3f.dds>
<TreeFloraMountainFlower02Purple "Mountain Flower" [TREE:000B91F8] billboard not found textures\terrain\lodgen\skyrim.esm\floramountainflower02purple_000b91f8.dds>
<TreeFloraMountainFlower02Red "Mountain Flower" [TREE:000BCF3E] billboard not found textures\terrain\lodgen\skyrim.esm\floramountainflower02red_000bcf3e.dds>
<TreeFloraSnowberry01 "Snowberry" [TREE:000BCF33] billboard not found textures\terrain\lodgen\skyrim.esm\florasnowberry01_000bcf33.dds>
<TreeFloraThistle01 "Thistle" [TREE:000B91F0] billboard not found textures\terrain\lodgen\skyrim.esm\florathistle01_000b91f0.dds>
<TreePineShrub01 [TREE:0009DAA3] billboard not found textures\terrain\lodgen\skyrim.esm\pineshrub01_0009daa3.dds>
<TreePineShrub02 [TREE:0009DAA0] billboard not found textures\terrain\lodgen\skyrim.esm\pineshrub02_0009daa0.dds>
<TreePineShrub03 [TREE:000A7312] billboard not found textures\terrain\lodgen\skyrim.esm\pineshrub03_000a7312.dds>
<TreeSwordFernCluster01 [TREE:000B8A59] billboard not found textures\terrain\lodgen\skyrim.esm\swordferncluster01_000b8a59.dds>
<TreeSwordFernCluster02 [TREE:000B8A64] billboard not found textures\terrain\lodgen\skyrim.esm\swordferncluster02_000b8a64.dds>
<TreeSwordFernCluster03 [TREE:000B8A65] billboard not found textures\terrain\lodgen\skyrim.esm\swordferncluster03_000b8a65.dds>
<TreeSwordFernCluster04 [TREE:000B8A66] billboard not found textures\terrain\lodgen\skyrim.esm\swordferncluster04_000b8a66.dds>
<TreeSwordFernCluster05 [TREE:000B8A67] billboard not found textures\terrain\lodgen\skyrim.esm\swordferncluster05_000b8a67.dds>
<TreeSwordFernCluster06 [TREE:000B8A68] billboard not found textures\terrain\lodgen\skyrim.esm\swordferncluster06_000b8a68.dds>
<TreeThicket01 [TREE:000A7329] billboard not found textures\terrain\lodgen\skyrim.esm\thicket01_000a7329.dds>
TreePineForestSnow01 [TREE:0005C072] #8 using billboard textures\terrain\lodgen\skyrim.esm\treepineforestsnow01_0005c072.dds
TreePineForestSnow02 [TREE:0005C071] #6 using billboard textures\terrain\lodgen\skyrim.esm\treepineforestsnow02_0005c071.dds
TreePineForestSnow03 [TREE:0005C070] #3 using billboard textures\terrain\lodgen\skyrim.esm\treepineforestsnow03_0005c070.dds
TreePineForestSnow04 [TREE:0005C06F] #0 using billboard textures\terrain\lodgen\skyrim.esm\treepineforestsnow04_0005c06f.dds
TreePineForestSnow05 [TREE:0005C06E] #1 using billboard textures\terrain\lodgen\skyrim.esm\treepineforestsnow05_0005c06e.dds
TreePineForestSnowL02 [TREE:0005D2DA] #9 using billboard textures\terrain\lodgen\skyrim.esm\treepineforestsnowl02_0005d2da.dds
TreePineForestSnowL03 [TREE:0005D2D9] #7 using billboard textures\terrain\lodgen\skyrim.esm\treepineforestsnowl03_0005d2d9.dds
TreePineForestSnowL04 [TREE:0005D2D8] #5 using billboard textures\terrain\lodgen\skyrim.esm\treepineforestsnowl04_0005d2d8.dds
TreePineForestSnowL05 [TREE:0005D2D7] #2 using billboard textures\terrain\lodgen\skyrim.esm\treepineforestsnowl05_0005d2d7.dds
TreePineForestSnowL05 [TREE:0005D2D7] #4 using billboard textures\terrain\lodgen\skyrim.esm\treepineforestsnowl05_0005d2d7.dds