birch, dark red
樺 centers on the birch tree, a tree known for its distinctive bark. The dark red meaning likely refers to the reddish-brown hue of birch bark or wood.
樺 combines 木 (tree) with 華, which likely contributes the sound カ and may also suggest the birch's showy or colorful bark, though the exact historical motivation is uncertain.
A tree 木 with a showy, flowery 華 appearance: the birch tree stands out with its striking bark, like a flower among trees.
For カ, imagine a birch tree with bark that looks like it's covered in colorful cars: car -> カ, and the birch tree is the canvas.
Japanese white birch (Betula platyphylla var. japonica)
birch (esp. Japanese white birch)
Karafuto (Japanese name for Sakhalin)
Koreans residing on Sakhalin island
monarch butterfly (Danaus plexippus)
dwarf birch (Betula nana)
Erman's birch (Betula ermanii); Russian rock birch
chaga mushroom (Inonotus obliquus)
birch tree (esp. the Japanese white birch, Betula platyphylla var. japonica)
Treaty of Saint Petersburg (1875); Russo-Japanese treaty in which Japan exchanged Sakhalin for the Kuril Islands
capelin; caplin (Mallotus villosus)
great grey owl (Strix nebulosa)
Sakhalin husky (dog breed)
willow ptarmigan (Lagopus lagopus); red grouse
pink salmon (Oncorhynchus gorbuscha); humpback salmon
greater spotted eagle (Aquila clanga)
ornamental variety of double weeping rosebud cherry
reddish yellow
Japanese foliage spider (Chiracanthium japonicum)
European silver birch (Betula pendula); European white birch