Forestry in a Climate of Change Urban Trees and Construction: Minimizing Damage to Maximize Ecosystem Benefits Richard J. Hauer, Ph.D. Assistant Professor of Urban Forestry College of Natural Resources University of Wisconsin-Stevens Point Social Economic Environmental Trees Have Values Society of American Foresters, National Convention, November 5 9, 2008, Reno, NV and Liabilities A Problem When the Grey Battles the Green (Green versus Grey) When Streets or Sidewalks are Repaired, Widened, and Improved Trees and values can be impacted But it Need not Be! What s Wrong with This Tree? Bio. Logical in the Urban Forest Why do Trees Die? Never Killed a Tree The Mortality Spiral and The Decline of Trees 1
Tree Defense Mechanisms There is a Limit Damaging Factors with Street and Sidewalk Repair Grade Change (Fill and Removal) Soil Compaction ph Alteration Root Severing Trunk and Branch Wounding Hydrology Changes Must be an Act of August 1978 City of Milwaukee, Storms and the Start of Preventing Loss of Trees Start of Construction Damage Prevention Jim Kringer Hired 1981 Tree Uprooting Up to 400 annually Now few (as few as two annually) Technical Services Coordinator Fines ($100/Diameter Inch) Scientific Investigation Contractor Meetings (pre to post) Today 99% of trees saved during construction et al. Street Tree Decline and Construction Activities Short-term and Long-term Effects on Tree Survival, Health, and Growth 2
Project Objectives: Street and Sidewalk Repair Long-term effects (20 25 years) Survivability (Mortality) Tree Health (Condition Rating) Growth Diameter Change Increment Core Analysis Compare to short-term study (4 8 years) Conducted in 1989 Hypotheses No difference between control and construction trees in survival/mortality condition rating diameter change Use 0.05 significance level Methods Known data and tree locations from previous study Collected street tree data in Milwaukee, WI in summer 1979 1989 2005 Statistics: Analysis of Variance Multiple Regression Model Tree Condition Lawn Width Construction or Control Past Tree Condition 1979 and 1989 Tree Diameter Construction Activity Tree Species (Dependent Variable) (between curb and sidewalk) (past and present) (percent) (size) (sidewalk, curb, street) Methods Data Collected: Construction date Blind Condition rating (CTLA as Guide): Roots: 1-5 Trunk: 1-5 Larger Branches: 1-5 Limbs and Branches: 1-5 Foliage/Growth: 1-5 Randomly chosen core samples Non Apparent Norway Maple Decline Advanced 3
Results: Tree Survival Table 1. Percent survival of trees subjected to construction or no construction (control) since 1979. Results: Tree Survival Table 2. Percentage survival of trees subjected to construction or no construction (control) since 1979. Treatment 1979 1989 Survival (%) Construction 432 334 77.3 Control 413 336 81.4 Treatment 1979 2005 Survival (%) Construction 432 275 63.7 Control 413 268 64.9 Treatment 1989 2005 Survival (%) Construction 334 275 81.8 Control 336 268 79.8 Results: Tree Survival Table 3. Percentage survival of trees subjected to construction or no construction (control) since 1989 and after implementation of construction damage minimization program. Street Reconstruction on Tree Survival Four Percent Greater Mortality, 1989 Study No difference 2005 Study, Why? Survival (%) 2005 Survival (%) 1989 Treatment 1989 Alive 2005 Alive Construction 168 136 81.0 77.3 Control 502 407 81.1 81.4 Education Design and Planning When Streets are Widened and Improved, Tree Spaces Shrink But do they have to? 4
Figure 1. Condtion rating of street trees subjected to construction damage during street, curb, and sidewalk repair and undamaged control trees. (Bars are Std. Error of Mean) Figure 2. Percent condition rating of study trees that died between 1989 and 2005. (Bars are Std. Error of Mean) g (Percent) Condition Ratin 100 90 80 70 60 50 40 30 20 Pre-Construction P=0.935 77.2 77.2 p<0.000 76.7 71.0 5.7% Diff Control 76.0 Damaged P=0.116 74.6 1.4% Diff g (Percent) C on dition R ating 100 90 80 70 60 50 40 30 20 p<0.000 76.7 71.0 73.0 Control p<0.000 62.8 Damaged 10 10 0 1979 1989 2005 0 Alive in 1989 Dead by 2005 Results: Regression Model Table 4. Regression model Beta Coefficients relating lawn width, damage, and past tree condition on current tree condition. 1989 2005 Lawn Width 0.027 0.022 Construction -6.045-2.341 Past Tree Condition 0.433 0.142 1989 2005 Adj. R Square.19.043 Significance >0.000 >0.000 No Difference Between Control and Construction >>> Type of Construction Activity >>> Tree Species >>> Tree Diameter Year Species Control Construction Total Percent 1989 Norway Maple 163 98 261 39.0 1989 Green Ash 84 86 170 25.4 1989 Honeylocust 24 56 80 11.9 76.3 2005 Norway Maple 153 56 209 38.5 2005 Green Ash 101 53 154 28.4 2005 Honeylocust 68 10 78 14.4 81.3 Results: Diameter Change Study Time Period: 1979 1989 Treatment n Mean Change Control 336 0.4842 Construction 334 0.4907 No Significant Difference Overall 670 0.4874 p=0.368 Study Time Period: 1989 2005 Treatment n Mean Change Control 405 0.4342 Construction 136 0.4479 No Significant Difference Overall 541 0.4376 p=0.325 Summary of Findings Suggests City of Milwaukee Construction Damage Prevention Resulted in Reducing Tree Mortality Less Reduction in Tree Condition Growing space important part of preventing construction damage Short- and Long-term diameter similar among control and construction trees Effects of construction activity most pronounced soon and residual effect was not found 5
The End! Research Partners Dr. Richard Hauer, University of Wisconsin-Stevens Point, Assistant Professor Ms. Kelly Mumm, University of Wisconsin-Stevens Point, Undergraduate Research Asst. Mr. Randy Krouse, City of Milwaukee, District Urban Forestry Manager Dr. Robert Miller, University of Wisconsin-Stevens Point, Emeritus Prof. of Urban Forestry University of Wisconsin-Stevens Point, University Professional Development Grants City of Milwaukee Urban Forestry Division Tree Fund, John Z. Duling Grant Wisconsin Arborist Association 6