Leaning Towards Shorter Trees

Italian stone pine (Pinus pinea)

Italian stone pine (Pinus pinea)

A week ago, a gigantic pine tree fell over and crashed into a house in Sherman Oaks. Luckily, no one was hurt, but what happened should serve as a reminder of the hazards presented by large trees in residential neighborhoods.
Large trees are meant to grow in forests, in fields, along river banks, and in parks. They are problematic in neighborhoods of densely packed houses. Common sense dictates that the mature height of a tree, particularly a leaning tree, should be less than its distance from any nearby structures. Yet, time and again, you find towering pine, eucalyptus, and sycamore trees growing within a few feet of residences, especially multistory residences. It is as though the landscape architects involved in these projects considered it a challenge to plant trees that would grow taller than the adjacent roof line. They overlooked the fact that such trees, in time, would become a source of anxiety every time the wind blew.
It was only about 250 years ago that an Englishman, William Kent, widely considered to be the first landscape architect, brought nature into our backyards. Before Kent, landscapes were not integrated into domestic living space. If there was a garden spot outside your door, it was devoted to growing vegetables. Architecture was a fine art, and the thought of obscuring the contours of a building with trees was unthinkable. Kent leaped the fence, bringing lawn, plants and trees right up to the front door.
In our own time, nostalgia for a rapidly vanishing rural landscape and a longing for grandpa’s farm and the woodsy countryside that surrounded it led to creation of the so-called urban forest. Trees seem to satisfy a deep, elemental need, at least until you have to worry about them falling over.
The truth is that as long as a tree grows straight up toward the sky, there is no cause for alarm, no matter how tall it gets, even if its leaves or needles clog your rain gutters and its roots bust your underground pipes every now and then.
Canary Island pines (Pinus canariensis), for example, have such strong apical dominance or determination to grow vertically that they can be planted very close to a structure and never lean. Italian stone pine (Pinus pinea), Aleppo pine (Pinus halapensis) and Afghan pine (Pinus eldarica), on the other hand, should not be planted in urban areas other than in parks or other open spaces.
If leaning pine trees have a tendency to fall, leaning eucalyptus trees prefer to break apart limb by limb. The reason for this is that eucalyptus wood is highly brittle.
When to be concerned
Actually, there is a simple way of testing whether a tree is in danger of falling. Stand next to the base of any tree and look up. Draw an imaginary vertical line from where you are standing toward the sky. If the canopy (branches and foliage) of the tree is evenly distributed, more or less, on the two sides of your imaginary line then, according to the laws of physics, your tree is balanced and probably safe from falling.
If, on the other hand, most of the tree’s canopy is growing on one side of the imaginary line, you want to either prune the tree at once to restore canopy balance or remove it altogether. Trees whose canopies are observed to be entirely over to one side of this line are serious candidates for immediate removal.
Q: Can you help me identify this tree? I have noticed it for several years along the 101 freeway, especially through Tarzana-Woodland Hills. The tree becomes loaded with orange-yellow blooms every spring. The trees are very tall, with pinnate-type leaves that are very long and narrow. The leaves are light-colored on the underside. The tree trunk appears to have rough bark similar to an oak. It appears to grow in a conical shape, like a pine.
— Kathy Cryer, North Hills
A: This tree is known as silk oak (Grevillea robusta). It is not related to oaks but matches them in size. It comes from Australia. It grows easily from seed, and its seedlings, with dark green, ferny foliage, are excellent subjects for patio containers. This tree should not be grown near the house because it becomes enormously tall, creates deep shade under which nothing will grow and produces a constant litter of leaves.

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