A maple tree grows in front of my house, between the sidewalk and the street.
The tree was planted as a spindly sapling in 1960. The next year, the city widened the street, restricting the growth potential of the tree. In 1982 a vehicle swiped the tree trunk. Ten years ago, the city removed (with no great care) a large branch, nearly a secondary trunk, growing to the southwest over the street. In 2010, a fierce rain and wind storm tore a number of branches, large and small, from the north side of the tree (the side facing the house).
In 1998, a neighbor planted an oak tree about 50 feet from the maple, also between the sidewalk and the street. Six years ago, a vehicle hit the oak and ran. (One hoped the damage to the vehicle was extensive.)
In the past 2 years, the maple has been seen to grow towards the oak. Of course, this tends to balance it following its truncation and wind damage. It also seems intent on squelching that oak. I suppose the roots of each sense the other with chemical receptors, but whatever the means, the goal of the maple seems clear: conquest. Each spring the maple puts out seeds and leaves. Each fall it withdraws its sugars from the leaves and drops them. This year it is also dropping seeds in the fall. The branch extending to the west may well have grown 6 feet that direction this year alone.