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Good Neighbors

Good Neighbors

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    Bottom: Installing “reduced” sidewalks—pavement with cutouts to allow room for tree roots—have significantly reduced broken pavement and made Hyde Park a more walkable neighborhood.

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    Top: In Los Angeles's Hyde Park neighborhood, buckled, cracked sidewalks such as this were a common eyesore. Photos: George Gonzalez

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    Tree roots can turn a city sidewalk into an impassable mess of broken-up concrete.

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Here are a few sidewalk design features to consider for preventing future problems:

  • Spacing it out: Placing a sidewalk and tree right on top of each other is a recipe for disaster. They should be a significant distance apart so that expanding roots don't eventually disrupt the pavement when the tree grows to adulthood.
  • “Meandering” sidewalks: Acurving pathway can provide ample room for trees, and the contours provide a unique aesthetic feature.
  • “Reduced” sidewalks: These straight lines have notched areas to allow room for tree growth.
  • Ramped sidewalks: An inclined path can give tree roots sufficient room to grow underneath; these are often used as a way to install a sidewalk in proximity to an established tree without disturbing roots.
  • Rubber sidewalks: A relatively recent development, these flexible pathways give to allow for root growth. An added benefit: precast panels can be lifted to maintain roots or infrastructure underneath, then simply dropped back into place—a feature that traditional concrete doesn't offer.
Making The Grade

A good forester monitors and evaluates the health of his city's trees. Gonzalez uses a five-point grading scale to gauge whether a tree is the picture of health, needs “medical” attention, or should be taken down:

A: exceptionally healthy, structurally stable, and attractive.

B: healthy, stable, and has a useful lifespan of five years or more.

C: in decline, creating extensive structural damage, and/or is the wrong species or size for its site.

D: declining, structurally unsound, and there's a good chance it'll die.

F: the tree is dead.

To preserve a tree, Gonzalez's team seeks to avoid cutting roots, compacting the surrounding soil, or changing drainage or grade within the root zone. Pruning, the most common maintenance, can be called for if the tree's crown is too high, low, or thick. The practice also can be used, after pavement is removed, to prevent future sidewalk damage. The risk: If not done properly, the branches could die, the tree could become unstable, root regrowth may increase, and the susceptibility to various conditions (drought or insect attack, for example) increases. Gonzalez recommends evaluating root-pruned trees periodically in the months after treatment to gauge their continuing health.