If a pine wood is surrounded by a white oak one chiefly, white oaks may be
expected to succeed when the pines are cut. If it is surrounded, instead
by an edging of shrub-oaks, then you will probably have a dense shrub-oak
thicket.
I have no time to go into details, but will say, in a word, that while the
wind is conveying the seeds of pines into hard woods and open lands, the
squirrels and other animals are conveying the seeds of oaks and walnuts
into the pine woods, and thus a rotation of crops is kept up.
I affirmed this confidently many years ago, and an occasional examination
of dense pine woods confirmed me in my opinion. It has long been known to
observers that squirrels bury nuts in the ground, but I am not aware that
any one has thus accounted for the regular succession of forests.
On the 24th of September, in 1857, as I was paddling down the Assabet, in
this town, I saw a red squirrel run along the bank under some herbage,
with something large in its mouth. It stopped near the foot of a hemlock,
within a couple of rods of me, and, hastily pawing a hole with its
forefeet, dropped its booty into it, covered it up, and retreated part way
up the trunk of the tree. As I approached the shore to examine the
deposit, the squirrel, descending part way, betrayed no little anxiety
about its treasure, and made two or three motions to recover it before it
finally retreated. Digging there, I found two green pig-nuts joined
together, with the thick husks on, buried about an inch and a half under
the reddish soil of decayed hemlock leaves,--just the right depth to plant
it. In short, this squirrel was then engaged in accomplishing two objects,
to wit, laying up a store of winter food for itself, and planting a
hickory wood for all creation. If the squirrel was killed, or neglected
its deposit, a hickory would spring up. The nearest hickory tree was
twenty rods distant. These nuts were there still just fourteen days later,
but were gone when I looked again, November 21, or six weeks later still.
I have since examined more carefully several dense woods, which are said
to be, and are apparently exclusively pine, and always with the same
result. For instance, I walked the same day to a small, but very dense and
handsome white-pine grove, about fifteen rods square, in the east part of
this town. The trees are large for Concord, being from ten to twenty
inches in diameter, and as exclusively pine as any wood that I know.
Indeed, I selected this wood because I thought it the least likely to
contain anything else. It stands on an open plain or pasture, except that
it adjoins another small pine wood, which has a few little oaks in it, on
the southeast side. On every other side, it was at least thirty rods from
the nearest woods. Standing on the edge of this grove and looking through
it, for it is quite level and free from underwood, for the most part bare,
red-carpeted ground, you would have said that there was not a hard wood
tree in it, young or old. But on looking carefully along over its floor I
discovered, though it was not till my eye had got used to the search,
that, alternating with thin ferns, and small blueberry bushes, there was,
not merely here and there, but as often as every five feet and with a
degree of regularity, a little oak, from three to twelve inches high, and
in one place I found a green acorn dropped by the base of a pine.
