It seems as though this is a historical (rather than spiritual or religious) perspective, yet we don't really have much clue about the historical druids. We have startlingly problematic accounts even by the same authors. The most important is that of Caesar. His account appears in book VI of the BG (sections 13-18), and begins with a separation of the Gallic people into classes. Apart from the plebes or common folk, according to Caesar there are only two important classes: druides and equites. The primary role Caesar ascribes to the druids is one of priesthood. They are rebus divinis intersunt, sacrificia publica ac privata procurant, religiones interpretantur ("concerned with divine things, attend to sacrifices public and private, [and] interpret religious matters"). The druids, however, are not simply religious leaders, but by extension hold a more general authority and prominence in Gallic society. It is the druids, Caesar writes, who de omnibus controversiis publicis privatisque constituent ("regulate all controversies public and private") including criminal action, and have the capacity to impose both rewards and penalties (praemia poenasque). The druids appear to be the figures of authority in Gaul.
But the very importance Caesar grants to the druids, however, is a reason for questioning his description. As first noted by Fustel de Coulanges in his La Gaule Romaine, if the druids were as central to Celtic society as Caesar asserts, the complete absence of any mention apart from the short aside in book VI is rather remarkable. Time and time again in the BG Caesar describes in great detail places, people, and even creatures he either personally encounters or is told about. Shortly after his description of the druids, Caesar devotes line after line to various animals in Germany, including a unicorn. Given his familiarity with Gaul, its peoples, and important individuals he encountered during his campaigns, the invisibility of the druids in BG is indicative of its unreliability.
This is particularly true considering information we possess about the druids apart from Caesar. Cicero, in his De Divinatione, affirms indeed that druids do exist in Gaul because he knows one: Divitiacus of the Aedui (of whom he says, in I.90, "Siquidem et in Gallia Druidae sunt, e quibus ipse Divitiacum Haeduum
cognovi/ if indeed there are druids in Gaul, [and there are because] I knew one of these myself, Divitiacus the Aeduan."). This is the same individual whom Caesar refers to as Diviciacus and whom he writes quite a bit about. Yet not once does he mention that Diviciacus is a druid.
How can a governing caste, so vital to social functioning across all of Gaul, exist in the way Caesar describes in book VI, and yet at the same time be insignificant enough that he felt mention of specific druids, their roles in the war as spiritual and communal leaders, their actions or inactions during Caesars time in Gaul, and so on, to be completely unnecessary? Of all the descriptions of the druids we possess which have survived from antiquity, Caesars is by far the most important. It is at once the lengthiest description of the druids and their role and is provided by a contemporary who was in an excellent position to know who the druids were.
Furthermore, in the handful of references given in other sources (many of which likely depend upon Caesars account), nowhere do we find greater prominence ascribed to the druids as leaders of Celtic society than in the passage from book VI of the BG.
How then can we say with any great confidence much of anything about the druids? Even etymological speculation is just that: speculation.
I would make my own tree calendar if I used one, based on the trees native to my area and what they are doing at a given time of year. See, to me, doing that kind of thing screams "druid" more than blindly following lore from a land you don't even live in. >_<;