Restoration Experiment Results Inform Stewardship Efforts
|Western red cedar with the combination mulch and irrigation supplement treatment.|
In fall 2005, Mercer Island Parks Department initiated a restoration experiment to improve tree survival. The first season of the experiment suggests that certain planting techniques yield greater survivorship of transplanted trees.
Typically, the main goal of restoration efforts is greatest possible transplant survival rate. The experiment, therefore, tested the survival rate of two native tree species, Western hemlock and Western red cedar, when planted with one of four planting treatments: (1)arborist wood chips applied as a mulch, (2)installation of an irrigation supplement in the form of a starch-based gel, (3)a combination of mulch and irrigation supplement and (4)a control in which trees were planted with no additional material. Areas with thinning tree canopies within Pioneer, Island Crest, Mercerdale Hillside and Upper Luther Burbank Parks were cleared of invading Himalayan blackberry thickets in order to house the experiment and aid in long-term canopy regeneration.
Monitoring and data analysis were performed by two UW graduate students. Results from the first growing season revealed that significantly more trees planted with the combination of mulch and irrigation supplement survived as compared to the other three treatments. Likewise, reduced percentage of weed cover and a related reduction in the time required to remove weed regrowth surrounding trees planted with mulch or the combination of mulch and irrigation supplement also suggest this combination treatment as a viable improvement to restoration efforts. While second season results are currently being analyzed and are expected to reinforce first season findings, a connection between the type of vegetation already present and the probability of a transplant surviving is also being explored.
These results highlight the importance of a moisture source at the time of transplant and are guiding continued restoration efforts within MI forested parks. Pacific Northwest homeowners may also find these results helpful when attempting to augment native tree plantings on their properties. Further information regarding this study may be obtained by contacting Paul West at 206.275.7833.