In discussing the nature of the Old Forest in in Letters on page 419 Tolkien states:
I know how much Tolkien loved nature and trees in particular, and how the destruction of forest in England and in Europe in were viewed as a great loss by him. Yet on another way I have always felt there is a theme in LOTR that is on the loss of people and things to other people and things. I am thinking of the Dunlanders/Wildmen who fight against Rohan because of the injuries they have suffered at the hands of the people of Rohan. I think the Ents and their reduction of territory and the injuries inflicted on them and their forest by Saruman are another example that is related to the Old Forest here. The Southerners and their conflict with Gondor and the Numernorians there must have felt injured in the past and thus allied against Gondor with Sauron. Perhaps an exception are the Druedain who aid Théoden and his army who have suffered loss and reduction (injuries) at the hands of Numennorians (2nd Age) and of Gondor after its founding."In all my works I take the part of trees as against all their enemies. Lothlórien is beautiful because there the trees were loved; elsewhere forest are represented as awakening to consciousness of themselves. The Old Forest was hostile to the two legged creatures because of the memory of many injuries."
Verilyn Flieger points out in Taking the Part of Trees: Eco-Conflict in Middle-earth, J.R.R. Tolkien and His Literary Resonances: Views of Middle-earth that
Though I may not agree that a reader may not know who the Black Riders are since a close reading combined with inference allows a reader to infer who they are, I do agree with her that the first real villain that they meet is a tree. I also like how on page 123 of A Reader's Companion the power and influence of Old Man Willow as "his song and thought ran through the woods on both sides of the river. His grey thirsty spirit drew power out of the earth and spread like the fine-root threads in the ground, and invisible twig fingers in the air, till it had under its dominion nearly all the trees of the Forest from the Hedge to the Downs.""it may come as something of a chock to be reminded that the first real villain to be met in LR is a tree. I except the Black Riders, since at this point in the narrative we have not met, but only seen and heard them. We do not know who or what they are or what they want (not sure I agree with this if one had read closely the Shadow of the Past a reader could connect the Black Riders to the Nine that Gandalf had mentioned or at least draw an inference to them). But we know more than enough about Old Man Willow. Huge, hostile, malicious (I love her description here), his trapping of Merry and Pippin in his willowy toils, his attempt to drown Frodo, give the hobbits their first major setback, and come uncomfortably close to ending their journey before it has properly started. [p. 148]
So it is Old Man Willow who when he learns of the intrusion of the hobbits into the Forest has the trees force paths that lead them to him. Malicious and hostile are indeed great descriptions of this living being.
An interesting side note is that the four hobbits here have Tinderboxes while Bilbo had matches. Perhaps matches were too expensive to have or as I have always said, matches are very unreliable on a journey (especially a hiking one) where as a tinderbox is much more reliable.
Hammond and Scull have a great discussion on page 128 of the names of Tom Bombadil and of their origin. Tom Bombadil is the name the hobbits of Buckland gave to him which to me implies that they were aware of him and of his presence in the Old Forest. I wonder if the hobbits blamed Tom Bombadil for the malice of the Old Forest and thus feared him, or was he just a myth that few had actual knowledge of like Farmer Maggot?
An answer is suggested in his Preface to The Adventures of Tom Bombadil and Other Verses from the Red Book. "Tolkien suggests that the two Bombadil poems were written by hobbits in Buckland, and show that the Bucklanders knew Bombadil, though, no doubt, they had as little understanding of his powers as the Shire-Folk had of Gandalf's: both were regarded as benevolent persons, mysterious maybe and unpredictable but nonetheless comic." I wonder if Tom's view as being a benevolent person came from the episodes of the four hobbits here or if there were other experiences with other hobbits that led to this reputation?
Tom Shippey commenting on how Tom Bombadil's speech has a rhythm that suggests verse says:
"Shippey in J.R.R. Tolkien: Author of the Century develops the theme further by suggesting that his voice and verse reflect his nearness to nature:"does not yet seem to have discovered, or sunk into, prose. Much of what he says is printed by Tolkien as verse, but almost all of what he says can be read as verse, falling into strongly-marked two-stress phrases, with or without rhyme and alliteration, usually with feminine or unstressed endings . . . . The point is though that while we appreciate it as rhythmical (unlike prose), we also do not mark it as premeditated or artificial (unlike verse)."
"He is a kind of exhalation of the earth, a nature-spirit . . . a highly English one: cheerful, noisy, unpretentious, to the point of shabbiness, extremely direct, apparently rather simple, not as simple as he looks. The fact that everything he says is in sort of verse, whether printed as verse or not, and that the hobbits too find themselves 'singing merrily, as if it was easier and more natural than talking', make him seen not an artist, but someone from an age before art and nature were distinguished, when magic needed no wizard's staff but came from words alone. Tolkien may have got the idea from the singing wizards of the Finnish epic the Kalevala, which he so much admired."
Of all the things stated here, I really love the notion, the idea that Tom goes back to a time when magic came from words alone, that words were power (which they are). There was no medium needed to channel magic or power. That is a very ancient notion and very powerful.
In terms to regarding Tom's nature Tolkien points out in Letters p. 192 in a draft to Peter Hastings "that although he is master of his natural little realm, Tom Bombadil hardly even judges, and as far as can be seen makes no effort to reform or remove even the Willow."
I find that interesting that even though in the text he threatens actions against Old Man Willow, Tom never takes action except to command the Willow to sleep and drink deep. How often do we want to change or remove something we don't find agreeable instead of finding a way to minimize it, yet leave it living on and continuing on?
Again, I took all of my info from A Reader's Companion but only because I really like many of the thoughts brought forth in their discussion.