Nicollet Island brownfield study

Summary of data

Principal Investigators: Gary Johnson, Jeff Gillman, Harold Pellett, Chad Giblin, Dave Hanson, Patrick Weicherding.  University of Minnesota. October 2000 through July, 2006

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)
Acer platanoides (Norway maple)
Acer rubrum (red maple)
Acer saccharinum (silver maple)
Catalpa speciosa (northern catalpa)
Diervilla lonicera (bush honeysuckle)
Fraxinus pennsylvanica (green ash)
Gleditsia (thornless honeylocust)
Picea glauca (white spruce)
Pinus nigra (Austrian pine)
Populus deltoides (eastern cottonwood)
Prunus americana (American plum)
Pseudotsuga menziesii (Douglas fir)
Rhus glabra (smooth sumac)
Rhus typhina (staghorn sumac)
Viburnum lentago (nannyberry viburnum)

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’) (photo)
  • Freeman Maple (Acer rubrum x saccharinum ‘Freeman’) (photo)
  • Sugar Maple (Acer saccharum) (photo)
  • Autumn Blaze White Ash (Fraxinus americana ‘Autumn Blaze’) (photo)
  • Common Hackberry (Celtis occidentalis) (photo)
  • Autumn Purple White Ash (Fraxinus americana ‘Autumn Purple’) (photo)
  • Fall Gold Black Ash (Fraxinus nigra ‘Fall Gold’) (photo)
  • Northern Gem Ash (Fraxinus nigra x mandshurica ‘Northern Gem’) (photo)
  • Northern Treasure Ash (Fraxinus nigra x mandshurica ‘Northern Treasure’) (photo)
  • Kentucky Coffeetree (Gymnocladus dioicus) (photo)
  • Heritage Oak (Quercus macrocarpa x robur ‘Heritage’) (photo)
  • Boulevard Linden (Tilia americana ‘Boulevard’) (photo)
  • Bur Oak (Quercus macrocarpa) (photo)

The two trees that were not native to Minnesota are:

  • Amur Maackia (Maackia amurensis) (photo)
  • Accolade Elm (Ulmus sp.) (photo)

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.  Here’s a map of the planting locations by species (PDF).

Results

Mortality Rate: Mortality rate was calculated as an overall percentage and then broken down into mortality rate of trees that were adjusted, versus non-adjusted trees. Adjusted trees were those that were found buried too deeply in the containers when the trees were purchased. The excess soil and roots that were above the first main-order roots for these trees were subsequently removed prior to the beginning of the study. The range of excess soil that had to be removed was from 4-9 inches.
Overall, the mortality rate for the 97 adjusted trees was 13/97= 13%
The mortality rate for the 89 non-adjusted trees was 24/89=27%
Total trees in the study =186.

Growth rate: Growth rate was determined as a percentage increases in stem caliper (stem diameter measured at 6-12 inches above ground).

Condition Ratings: Separate condition rating for the stem and canopy were determined annually for each tree. Ratings were based on a four point system with 0 representing dead and 4 representing no “flaws” for the species. Stem condition ratings were based on wholeness and health of the stem tissue, with points subtracted for bark loss and/or cambial death…for any reason. Canopy condition rating were based on the characteristic of the species, specifically live crown ration, density, balance (symmetry), as well as dieback. Leaf size and color was not taken into consideration.

Acer nigrum “Green Column”

Mortality rate                                            46%
Mortality rate, adjusted trees                   50%
Mortality rate, non-adjusted trees            40%
Growth rate                                               54%
Condition ratings:
Stem Ratings 3.5+                        4/7
Stem Ratings <1.5                        2/7
Canopy Rating 3.5+                      6/7
Canopy Rating <1.5                      1/7

Acer rubrum x saccharinum “Autumn Blaze”

Mortality rate                                            17%
Mortality rate, adjusted trees                   11%
Mortality rate, non-adjusted trees            33%
Growth rate                                             116%
Condition ratings:
Stem Ratings 3.5+                                  10/10
Stem Ratings <1.5                       0/10
Canopy Rating 3.5+                     9/10
Canopy Rating <1.5                     0/10

Acer saccharum “Fall Fiesta”

Mortality rate                                            62%
Mortality rate, adjusted trees                  20%
Mortality rate, non-adjusted trees           88%
Growth rate                                              89%
Condition ratings:
Stem Ratings 3.5+                                    3/5
Stem Ratings <1.5                        0/5
Canopy Rating 3.5+                      4/5
Canopy Rating <1.5                      1/5

Celtis occidentalis

Mortality rate                                              8%
Mortality rate, adjusted trees                   11%
Mortality rate, non-adjusted trees              0%
Growth rate                                             102%
Condition ratings:
Stem Ratings 3.5+                       11/11
Stem Ratings <1.5                         0/11
Canopy Rating 3.5+                     10/11
Canopy Rating <1.5                       0/11

Fraxinus americana “Autumn Blaze”

Mortality rate                                              8%
Mortality rate, adjusted trees                     0%
Mortality rate, non-adjusted trees            14%
Growth rate                                               89%
Condition ratings:
Stem Ratings 3.5+                       10/11
Stem Ratings <1.5                         0/11
Canopy Rating 3.5+                     10/11
Canopy Rating <1.5                       0/11

Fraxinus americana “Autumn Purple”

Mortality rate                                             0%
Mortality rate, adjusted trees                    0%
Mortality rate, non-adjusted trees             0%
Growth rate                                            126%
Condition ratings:
Stem Ratings 3.5+                       12/12
Stem Ratings <1.5                        0/12
Canopy Rating 3.5+                    12/12
Canopy Rating <1.5                     0/12

Fraxinus nigra “Fall Gold”

Mortality rate                                              17%
Mortality rate, adjusted trees                     8%
Mortality rate, non-adjusted trees              8%
Growth rate                                                95%
Condition ratings:
Stem Ratings 3.5+                       10/12
Stem Ratings <1.5                        0/12
Canopy Rating 3.5+                     6/12
Canopy Rating <1.5                     0/12

Fraxinus nigra x mandshurica “Northern Gem”

Mortality rate                                         0%
Mortality rate, adjusted trees               0%
Mortality rate, non-adjusted trees        0%
Growth rate                                           99%
Condition ratings:
Stem Ratings 3.5+                        9/12
Stem Ratings <1.5                        1/12
Canopy Rating 3.5+                     6/12
Canopy Rating <1.5                     1/12

Fraxinus nigra x mandshurica “Northern Treasure”

Mortality rate                                          8%
Mortality rate, adjusted trees                  0%
Mortality rate, non-adjusted trees         20%
Growth rate                                            100%
Condition ratings:
Stem Ratings 3.5+                       12/12
Stem Ratings <1.5                       0/12
Canopy Rating 3.5+                   10/12
Canopy Rating <1.5                     0/12

Gymnocladus dioicus

Mortality rate                                          31%
Mortality rate, adjusted trees                 40%
Mortality rate, non-adjusted trees          25%
Growth rate                                           75%
Condition ratings:
Stem Ratings 3.5+                       9/9
Stem Ratings <1.5                        0/9
Canopy Rating 3.5+                     5/9
Canopy Rating <1.5                     0/9

Maackia amurensis

Mortality rate                                          17%
Mortality rate, adjusted trees                 20%
Mortality rate, non-adjusted trees          14%
Growth rate                                           63%
Condition ratings:
Stem Ratings 3.5+                       8/8
Stem Ratings <1.5                        0/8
Canopy Rating 3.5+                     7/8
Canopy Rating <1.5                     0/8

Quercus macrocarpa x robur “Heritage”

Mortality rate                                         42%
Mortality rate, adjusted trees                0%
Mortality rate, non-adjusted trees         56%
Growth rate                                           71%
Condition ratings:
Stem Ratings 3.5+                      5/7
Stem Ratings <1.5                       1/7
Canopy Rating 3.5+                     2/7
Canopy Rating <1.5                     1/7

Tilia americana “Boulevard”

Mortality rate                                         31%
Mortality rate, adjusted trees                14%
Mortality rate, non-adjusted trees         50%
Growth rate                                           57%
Condition ratings:
Stem Ratings 3.5+                      4/9
Stem Ratings <1.5                       1/9
Canopy Rating 3.5+                     8/9
Canopy Rating <1.5                     0/9

Quercus macrocarpa

Mortality rate                                         15%
Mortality rate, adjusted trees                25%
Mortality rate, non-adjusted trees         11%
Growth rate                                           49%
Condition ratings:
Stem Ratings 3.5+                       10/10
Stem Ratings <1.5                        0/10
Canopy Rating 3.5+                     6/10
Canopy Rating <1.5                     0/10

Ulmus “Triumph”

Mortality rate                                          0%
Mortality rate, adjusted trees                  0%
Mortality rate, non-adjusted trees           0%
Growth rate                                          249%
Condition ratings:
Stem Ratings 3.5+                      12/12
Stem Ratings <1.5                       0/12
Canopy Rating 3.5+                    12/12
Canopy Rating <1.5                     0/12

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.
Gary Johnson
Gary is a Professor Professor of Urban and Community Forestry within the Department of Forest Resources/Extension at the University of Minnesota. His work addresses a variety of urban natural resource issues.

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