I have feels :(

This was seriously great, and so interesting. Honestly, you come up with things that I could only ever attribute to you, if I had found them in the wild. Props to you on being able to write human society from the point of view of a tree (metal beetles, bark, etc)-each description was a joy. Perhaps I'm just needy, but I would have liked an ending with just a scosche of acknowledgment from Acacia to Birch, instead of his innate satisfaction/assurance that he had fulfilled his promise. But it IS your universe, and if you say it was fulfilled, then it was fulfilled. RIP Acacia and Birch

So, let me get this straight. A Birch and an Acacia become friends, then one realizes he's human, then escapes to bring her a piece of wallpaper as a gift to fufill a promise to kiss her.

He becomes a tree, and waits until he gets sick and nearly dies, (may even be alluding to cancer?) Then some police haul him away for being a creeper. Then he gets practice talking, and now he gets to kiss the girl that nhst so happens to be dying as well.

Did I get everything? Ok.

The unreliable narration is the key to why this piece stands out so brilliantly. Birch's inability to understand who he is makes the story out as a tragedy. It's a psuedo love story, because the love is more of a promise than a conversation between two people.

As for things I'd personally change, they are few and far between. Romantic elements could be squeezed in there. Maybe a small conversation at the beginning between Acacia and Birch to set a funny or romantic mood depending on when they meet. Then let the story take a darker and darker turn towards the end.
There's also a strange neutrality to everything. Dr Taylor is probably the only person who is vaguely complemented on her appearance (oaks are thick, so is she curvy, or fat?) And his own appearance before becoming a tree. Come to think of it, it's always people's faces he seems to forget about. The strangest part is that both the Girl and Birch are experiencing the same delusion. This sort of makes the delusions more fantastic.

Lovely and bittersweet - and what is romantic than dedication?

This is so sweet, and so heartfelt and painful and yet so funny. I love the constant thread of plant-notes through the narration: "brooding like only a tree can" and "nuggets of delight" are hilarious, and "a raindrop slid down his cheek" is just beautiful. The ending is sad and bittersweet, and the whole piece has a great subtle magic to it right from the first words. The only criticism I can levy, and this is a stretch, is that it's not really a romance, per se; while we do get that sense of longing and of love through the whole story, I'm not sure if that quite ticks over into the romance category. But that hardly stops it from being a deep and emotional tale and I heartily commend you for it.