Invasive Plant Removal

Questions and Answers

* Pictures captioned in yellow text are heavily infested with invasive plants.

53rd Street Open Space   What are the invasive non-native plants? Why is native habitat important? What are native plants? Why is ivy bad on trees?  Why is ivy bad when growing on the ground? So what if the trees disappear? What are the non-economic benefits of our urban forest? Why should I remove invasives and do restoration now?  Why not wait?  What can I, a private landowner, do? What is to prevent the ivy and other invasives from just growing back?  Who do I call if I want to have ivy or other invasive plants removed from my property? What do I use to cover the bare soil after the ivy or other invasive plants have been removed?   If you have additional questions submit them to rmoore@eds.org and those deemed to be of general interest will be posted here.

Why not just let nature take it's course?  That would work except for the fact that we have introduced non-native invasive plants that overtake our native plants and alter the natural regrowth of our native plants.  Our island will not be the same place in the future if we do not get the invasives under control.  Native ground cover and habitat will be overrun by ivy and we will have ivy deserts.  Our mature tree will gradually disappear with no new young tree to replace them because ivy suppresses the sprouting of seedlings!

What are the invasive non-native plants?  The most common non-native invasives on Mercer Island are:

• English ivy

• Himalayan blackberry

• English holly

• English laurel

Other invasives are Japanese knotweed, giant hogweed, clematis, field bindweed, creeping buttercup, reed canary grass, policeman's helmet and herb Robert.  Almost all of the invasives were originally introduced as landscaping plants that escaped into the natural environment. 

Why is native habitat important?  The birds, butterflies, mammals, reptiles and amphibians that live here are adapted to nesting, feeding and living in the plants, shrubs and trees that were here before we, the settlers, arrived.  If you remove their habitat, they too will disappear.

What are native plants?  Native plants are the plants that existed in this area of Washington before 1860, the year of the arrival of the white settlers in Washington.

Why is ivy bad on trees? 

• The added weight of the ivy can cause mature trees to come down in a storm.  For example, on a large tree in Olympic National Park, 2,100 pounds of ivy was removed from a single tree. 

• Once ivy is in the tree canopy it shades out the trees leaves or needles.

• English ivy can strangle tree, especially at the base of the trunk.  

• Dense ivy cover deprives the tree's bark of normal contact with air and microorganism.

• Thick ivy mats accelerate rot.

• Fast-growing ivy competes for nutrients and water.

Why is ivy bad when growing on the ground? Ivy provides nesting places for rats and other vermin. English ivy's shallow root structure makes it a poor choice for erosion control and it can contribute to erosion in some cases. Ivy limits understory regeneration of native trees, shrubs and plants by blocking sunlight and shading out native plants. (i.e. No regrowth of native plants.) Fast-growing ivy competes with native plants for nutrients and water. Ivy changes the natural succession of the forest.  If you look around your will see few young tree to replace the mature trees when they come down.  Ivy also creates "ivy deserts", where other plants, native to our environment, do not grow.

So what if the trees disappear?  There is no upside to the loss of urban forest.  Every community that has made the decision to lose urban forest has been on the decline.  There are measurable economic savings to a healthy urban forest:

• Trees improve property values; homes with mature trees sell much better.
• Trees reduce air pollution by removing carbon dioxide from the air, reducing the greenhouse effect.  Our forests are our lungs.  Diminished air quality can be traced back to a lack of urban forest.
• Trees reduce storm water runoff costs by naturally controlling water runoff.  Engineering solutions to surface water runoff are much more expensive.  Functioning forests work better for storm water and ground water cleanliness than any engineered solution.
• Trees reduce energy costs by shading houses.
• Trees reduce the air temperature by giving off droplets of water.
• Trees help muffle sounds such as cars.

What are the non-economic benefits of our urban forest?  Urban forests have a soothing effect on people and produce a higher quality of life.  The strength and vitality of a community is directly related to the amount of green in that community.  People who are sick heal faster when they can see a green environment.  Crime rates are lower in communities with urban forest.   What can I, a private landowners do?  Home owners are strongly encouraged to clear ivy from their trees and remove ivy and other invasive plants from the "natural areas" on their property.  For more information on ivy removal see the IvyOut website at http://www.ivyout.org/

Why should I remove invasives and do restoration now?  Why not wait?   It does not make good economic sense to wait.  Waiting involves a quadruple whammy to costs and effort. The invasives do not stop growing.  The longer you wait, the more invasive plant material will need to be removed.  The longer you wait, the fewer viable native seeds will be available under the ivy for regrowth, increasing the costs of replanting and the loss of local genetic diversity. The invasives keep spreading and destroying more native plants as they grow.  More native plants will have to be purchased and replanted to fill the space left by the invasives. The cost of removing invasives, buying and replanting native plants will only increase with time.  It takes a generation to grow a mature tree.

What is to prevent the ivy and other invasives from just growing back?  Your property needs to be monitored for regrowth and remove the invasive regrowth annually.   This is no where as difficult as the initial removal.  If you spent 100 hours initially removing ivy, the second year will take 10 ours and future years will only take an hour.

Who do I call if I want to have ivy or other invasive plants removed from my property?  If you have landscaped property, you can get a gardening service to remove ivy and other invasives.  Get multiple bids.  I will probably be cheaper to have it done in the winter when gardening services are less busy and looking for work.  Also the roots are removed more easily in the winter.

If you own a ravine or other undeveloped you you might try getting a bid from EarthCorps, a non profit organization.

What do I use to cover the bare soil after the ivy or other invasive plants have been removed?  Bare soil needs to be protected from heavy rains.  The rain can cause erosion and close the pores in the soil.  Be sure to protect soil from where ivy has been pulled by planting trees, shrubs and ground cover and putting down a mulch.  Initially, it can be covered with 4-6" of wood chips. (Usually available for free from tree services.)  Beauty bark is not a good choice.  For a good article on the reasons for using arborist wood chips and not beauty bark see the article by Linda Chalker-Scott formerly of University of Washington at