I hope you know what I just said, because I'm not sure I do.
At any rate I was struck by the similarity of some of his thoughts to ones I posted waaaaay back at the beginning of ABITT's life.
I didn't really go into detail, and seeing Vixsin's incredibly well-organized, well-laid-out, and detailed explanations led me to want to do something similar to my original post. A decent chunk of this will overlap with the mechanics discussion in my first Primer on Tree Healing post, but I think this will be a more understandable method of going about it.
For reference, here are the healing spells available to Resto Druids, in no particular order, with the abbreviations I'll be using for them in parenthesis:
Rejuvenation(R), Regrowth(RG), Lifebloom(LB), Nourish(N), Swiftmend(SM), Healing Touch(HT), Wild Growth(WG), and Tranquility(T).
Here's some more reference material for you, in the form of talents which affect these spells (leaving off talents that affect them all relatively equally):
Empowered Rejuvenation(ER), Empowered Touch(ET), Gift of the Earthmother(GotE), Improved Rejuvenation(IR), Improved Tranquility(IT), Living Seed(LS), Naturalist(Na), Nature's Bounty(NB), Revitalize(Re), Tranquil Spirit(TS), Genesis(G), Moonglow(M), Nature's Splendor(NS), Nature's Majesty(NM).
Whew. That's a lot of linkage! You probably didn't bother reading all the popups from that (much less actually clicked the links), but that's ok, I don't think you actually need to know what all of them are. In a minute or ten I'll try to make it all make sense.
Now, instead of just leaving them all shotgunned at you, I'll try to associate each of these talents with the spells that they improve. To whit, in all my noobish-html-table-skill (if it looks bad, I'm blaming the post editor for removing supposedly unnecessary nbsp's or something):
I hope that makes half as much sense to you and/or looks half as good as I had originally intended. If so, I count it a win.
Without going into even more excruciating detail, the point I'm trying to get across is that while you can't really take enough talents to be the best at everything as a Tree (there's too much to spread it all around,) the talents that assist individual spells help enough of a variety that you won't be limiting your abilities in one area to work in another. If you've focused on one role or the other, you're going to be better at it - but not much!
Note that a lot of the talents that benefit Nourish also benefit Healing Touch. You take these if you want to pretend that you're a paladin healer - you get to focus on having a fast cast smaller heal and a longer cast big heal. These Trees tend to be a little better at being tank healers than raid healers. A lot of times you'll also pick up talents for Lifebloom as a tank healer - that's really where it shines.
If you've gone the other route, Wild Growth, Rejuvenation, and Regrowth, you'll tend to be a better raid healer.
You don't have to skip more than 1 or 2 of these talents, but you DO have to make cuts somewhere. There's even another talent (Nature's Grace) that I didn't mention, which would benefit Regrowth, Nourish, and Healing Touch (and maybe even Lifebloom too!), and I have all of these talents except for Nature's Grace, Tranquil Spirit, and Naturalist. So, I've currently got a small advantage for raid healing over tank healing.
Note that I said small - I could honestly find 3 points (probably from IT and/or Re) to take Nature's Grace, or maybe all 5 from those two spots to take Tranquil Spirit, and even without those you're talking about a difference of 10% mana cost of HT and N, or 20% casting speed increase for 3 seconds on crits. Those are nice bonuses but the majority of my heals would remain the same. Lifebloom, pretty much the quintessential tank-healing HoT, wouldn't change at all.
Gear and glyphs, of course, also figure in, but much like the last few talent points, you're talking about small shifts rather than big ones - if you focus all the way one way or another it can make a somewhat significant difference, but if you don't want to pigeonhole yourself, it won't hurt you either!
These last three points mean that, barring strange itemization or off-the-wall talent specs, Trees don't have to change specs to focus on tank or raid healing! They're not going to be bad at either no matter what spec they have!
How so, you ask? Well let me tell you.
They change the spells that they are using. That's why we have so many!
Assigned as a tank healer, my spells of choice are going to be Lifebloom, Rejuvenation, Regrowth, Nourish, Wild Growth, Swiftmend, and Healing Touch, in... roughly... that order.
Assigned as a raid healer, my spells of choice are going to be Rejuvenation, Wild Growth, Swiftmend, Nourish, and Regrowth, and again, in more or less that order.
Notice the major differences - as a tank healer, spells that have a casting time are added (as in HT), or moved closer to the top of the priority list (a la Nourish and Regrowth), where as in my raid healing I focus more on spells that are instant cast (to allow me to heal more players in shorter time).
Just as with all aspects of being a druid, we are VERSATILE - perhaps moreso than a lot of folks realize - and our only true limitations as a healer are that we don't have a way to shield another player, and we can only remove curses and poisons.
Don't be afraid, as a Tree, to tell your raid leader that yes, you CAN tank heal, or that you're more comfortable with it than raid healing, because you're perfectly capable of that role!
... and I'm still unhappy with this post, but I'm gonna put it up anyway, 'cuz that's how I roll... for today, at least.