Trees care for us – we need to care for trees
Portland's trees provide us with immense benefits - $27 million a year in environmental benefits alone not to mention increased property values and healthier, quieter, cooler, and safer neighborhoods. As cities in the eastern U.S. have lost in rapid succession their elms, chestnuts, and now ash trees to introduced pests and blights, they have become painfully aware of the high cost of not having a healthy urban forest. The structural value of Portland's urban trees as they currently stand is estimated at $5 billion dollars. That's an enormous gift to us from previous generations. Each of us can protect that living legacy by taking simple steps to care for the trees around us.
Our frequently gray, cloudy days make it seem like it's always raining in Portland. But the truth is that the city receives less than 2 inches of rain over the summer months. The majority of the city's trees come from parts of the world where summer rainfall is several inches a month. Young trees of these species are especially at risk of dying during our dry months. Even if trees don't die of thirst, their growth is stunted and they are more at risk from attack by pests. To help:
- give young trees at least 10 to 15 gallons of water once a week from about April to the end of September
- Native Oregon white oaks and many California oak species, after their first year should not be watered in the summer as this can cause deadly root rots for those trees.
Keep grass at bay
The thick, mat-like roots of grass are extremely good at absorbing water. They can easily outcompete young trees for moisture, stunting the tree’s growth or leading to its death. Many trees also die when lawn mowers and wire weed whackers cut into the bark as people try to cut grass near a tree's trunk. To help: keep grass at least 3 feet from any tree trunk.
Don't compact soils
One of the least recognized causes of urban tree decline is soil compaction. We can see soil compaction in parks where hundreds of people walk over the same ground. This can quickly turn a lawn into a trail of hard ground. Clay soil like we have in much of Portland takes on the consistency of a brick when driven on or parked on. Rainfall doesn't easily penetrate such hardened soil, depriving trees of life-giving moisture. To help:
- never drive or park over the root zone of a tree
- never store heavy items underneath trees
- keep to sidewalks and driveways when walking or bicycling
Trees are not billboards
Don't nail anything to a tree. Puncturing the bark injures a tree, giving access to diseases and insect pests. For the same reason, don't carve your initials or love notes into a tree's bark. Your sweetheart won't think it's romantic that you harmed a tree to declare your devotion!
Prune with a light touch
Ornamental trees look best and are usually healthiest when allowed to reach their natural size and shape. Once a tree has had time to establish, prune to remove:
- dead or broken branches
- crossing branches
- suckers at the base of the tree
- water shoots (vertical shoots sticking straight up from branches)
- low branches growing into the street or sidewalk
Never top a tree (remove all branches across the upper half of a tree). Utility crews sometimes have to do this for trees at risk of growing into overhead powerlines but it should never be done to other trees.
Don't cut a branch in the middle or leave stubs. Take the branch you want to remove back to where it joins another main branch or the trunk. Make cuts just outside the root collar (small swelling) where a branch joins another one or the trunk.
To avoid weakening a tree, remove no more than 10 to 15 percent of a mature tree in any given year. For young trees, take off no more than 20 to 25 percent of a vigorously growing younger tree after it has become established.
Remember, you need a permit to prune street trees. You can easily apply for this free permit online!
Find more details about the value of Portland trees below:
- Portland’s Urban Forest Canopy Assessment and Public Tree Evaluation 2007, and Tree Canopy Monitoring 2012.
- Trees in the city: Valuing street trees in Portland, Oregon. Geoffrey H. Donovan & David T. Butry
- The effects of urban trees on the rental price of single-family homes in Portland, Oregon. Geoffrey H. Donovan & David T. Butry
- The effect of trees on crime in Portland, Oregon. Geoffrey H. Donovan & Jeffery P. Prestemon
- The value of shade: Estimating the effect of urban trees on summertime electricity use. Geoffrey H. Donovan & David T. Butry
- Street trees in the urban forest canopy: Portland, Oregon. Joseph Poracsky & David Banis
- Urban Forest Canopy Cover in Portland, Oregon, 1972-2002. Joseph Poracsky & Michael Lackner
Reduce carbon dioxide, a key greenhouse gas by:
- Binding up carbon in their wood
- Reducing the heating and air conditioning demands of nearby buildings
Decrease stormwater runoff by:
- Intercepting rain on leaves, branches and bark
- Increasing infiltration through the tree’s root system
- Reducing soil erosion
Make us happy by:
- Beautifying the built landscape
- Providing shade to cool air near our homes
- Dampening noise
- Providing nesting sites, shelter and food for birds
- Increasing resale values
Improve our air quality by:
- Absorbing pollutants
- Intercepting particulates, such as soot, which worsens asthma
- Releasing oxygen
- Lowering air temperatures
- Reducing energy demand