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October 2000 through July, 2006
Principle Investigators: Gary Johnson, Jeff Gillman, Harold Pellett, Chad Giblin, Dave Hanson, Patrick Weicherding. University of Minnesota.
Introduction
In October, 2000, 186 trees representing 15 different species were planted in a randomized block design on Nicollet Island, Minneapolis, Minnesota. The purpose of our study was to evaluate tree performance over a three-year period on a harsh site with minimal maintenance provided. All trees were purchased containerized, ranging from number 10 to number 20 cans. The trees have been evaluated two times each year since the study began: in the autumn for end of the season caliper measurements and in the late spring/early summer for condition rating. Initially, the study was designed to conclude in 2003, but courtesy of the Minneapolis Park and Recreation Board, Division of Forestry, we have been able to continue the evaluation studies.
Nicollet Island is one of the oldest settlements in Minnesota, and the soil has been highly altered. Soil pH ranges from 7.8-8.6, drainage varies from poor to pitiful, all soil tests registered less than .5% organic matter, and compaction is a major problem. The trees were watered a total of four times the first year and mulched with wood chips in order to assist establishment. No subsequent care has been given to the trees.
Previous Studies
Other brownfield tree performance studies that we have conducted in the Twin Cities metropolitan area since 1992 have shown the following trees to be exceptional performers on harsh sites:
Acer negundo (boxelder) Populus deltoides (eastern cottonwood)
Acer platanoides (Norway maple) Prunus americana (American plum)
Acer rubrum (red maple) Pseudotsuga menziesii (Douglas fir)
Acer saccharinum (silver maple) Rhus glabra (smooth sumac)
Catalpa speciosa (northern catalpa) Rhus typhina (staghorn sumac)
Diervilla lonicera (bush honeysuckle) Viburnum lentago (nannyberry viburnum)
Fraxinus pennsylvanica (green ash)
Gleditsia (thornless honeylocust)
Picea glauca (white spruce)
Pinus nigra (Austrian pine)
The Trees
There were fifteen different varieties of trees selected for this study. Thirteen of these fifteen trees were partially modified genetically with Minnesota native trees resulting in the following cultivars:
Green Column Black Maple (Acer nigrum ‘Green Column’)
Freeman Maple (Acer rubrum x saccharinum ‘Feeeman’)
Sugar Maple (Acer saccharum)
Autumn Blaze White Ash (Fraxinus americana ‘Autumn Blaze’)
Common Hackberry (Celtis occidentalis)
Autumn Purple White Ash (Fraxinus americana ‘Autumn Purple’)
Fall Gold Black Ash (Fraxinus nigra ‘Fall Gold’)
Northern Gem Ash (Fraxinus nigra x mandshurica ‘Northern Gem’)
Northern Treasure Ash (Fraxinus nigra x mandshurica ‘Northern Treasure’)
Kentucky Coffeetree (Gymnocladus dioicus)
Heritage Oak (Quercus macrocarpa x robur ‘Heritage’)
Boulevard Linden (Tilia americana ‘Boulevard’)
Bur Oak (Quercus macrocarpa)
The two trees that were not native to Minnesota are:
Amur Maackia (Maackia amurensis)
Accolade Elm (Ulmus sp.)
A brownfield site is an area that once provided a suitable environment for plant life, but has since been dramatically altered. Examples of events that change sites include: the razing of buildings, previous superfund sites, new subdivisions, and as in the case of areas that often never “green up” again, leaving behind a lifeless “brownfield.” Plant failure at these sites is primarily due to dramatic changes to the soil. These changes include, but are not limited to: the loss of organic matter from the topsoil, water percolation problems, severe compaction, and an extreme shift in soil pH.
The trees that performed well on this site should be excellent selections for areas where circumstances are similar such as a subdivision. Today's subdivisions have conditions that closely emulate those of a brownfield. During the construction of a new development the original site is severely altered. First, the top six or so inches of soil is removed (this includes the majority of the organic matter). This is done so that the soil can be compacted to meet engineering standards for footings and concrete. The remaining soil often consists of compacted clay and rock. Clay often has a more alkaline pH than does organic matter, resulting in pH that is much higher than is optimal for plant growth. In addition, construction waste (e.g. insulation, treated wood, concrete, scrap metal) and chemicals leaks (hydraulic fluid, gasoline, water proofing fluid) from their machinery are buried and incorporated into the soil. All of this results in a newly created brownfield site.
People are encouraged to visit the Nicollet Island Brownfield site and make their own observations. Each tree has been tagged with its species name to help you easily
identify it.
Financial sponsorship
Funding for the purchase and maintenance of the trees in this study was provided be a grant form the UNITREE program, and the Minneapolis Park and Recreation Board (MPRB) Forestry Section.
In 1994, Foster Wheeler Twin Cities, Incorporated, agreed to provide funding for the UNITREE program for 25 years. Its purpose is to fund tree planting in neighborhoods adjacent to the University of Minnesota’s Twin Cities Campus, as well as on the campus, for the primary purpose of promoting energy conservation through urban reforestation.
The Tree Trust is a non-profit organization that was contracted by the University to implement the UNITREE grant awarded to the Nicollet Island Brownfield Site project.
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