Drainage Design Manual - the City of San Luis Obispo

• Removal of Exotic VegetationThe removal of exotic tree and shrub species is often required to reestablish nativeriparian vegetation at a site, and is usually best performed prior to planting.Depending on the growth habits of exotic trees and shrubs, it may beadvantageous to leave certain non-invasive exotics on a site to protect somerevegetation plants from harsh windy and/or sunny exposures. As revegetationplants become established, exotic trees and shrubs can be selectively removedover time. This is a good practice where large groves of exotic trees occur thatprovide some wildlife habitat values and other benefits. In these situations,selected patches of trees can be removed gradually over a period of several yearsto protect the site until replacement plantings become established. Also, certaintrees can be killed and left in place as "snags" for wildlife. Procedures for exotictree and shrub removal are described as follows:After a qualified restoration specialist identifies all exotic shrubs and trees andprepares a removal plan, work can commence. Tree cutting and removal shouldbe performed in such a way that trees are felled into natural openings or otherareas to be cleared. Care must be taken to not damage existing native vegetation.Any branches of native trees that are damaged during exotic tree removal shouldbe pruned back to a branch as near as possible to the break point by a wellselectedthinning cut. Tree and shrub stumps of exotic species such as poplar,eucalyptus and pyracantha should be treated with a stump killer. Re-spouting canbe controlled with glyphospate herbicides (Roundup or Rodeo), if approved forsite conditions, or removed by hand. To promote natural degradation, the stumpsof non-sprouting species with ground level trunk diameters less than 304millimeters (12 inches) can be treated by drilling 25.4-milliammeter (1-inch)diameter holes 152 millimeters (6 inches) deep and 101 millimeters (4 inches) oncenter. All branches and debris from plant removal operations should be removedfrom the project site, chipped and spread, or otherwise left on the site as directedin the removal plan.As mentioned above, it may be advantageous to kill exotic overstory trees andleave them standing as snags for wildlife. This can be accomplished by girdling.Girdling cuts should be made late in the season to delay and diminish sprouting.Control sprouting with herbicides. If species of Populus (poplar) are cut down orgirdled, be prepared to respond to aggressive root sprouting.11.8 Planting LayoutLayout of plant materials should follow approved revegetation plans andspecifications as closely as possible. Prior to installation of any plant materials, thecontractor should place flags or markers at each planting site, using a different colorand/or number for each revegetation species. Areas where specified seed mixturesare to be planted can also be marked out. The contractor should provide thecontracting officer and/or a designated project inspector with an index correlating theSLO Creek Drainage Design Manual 152 February 2003