i-tree Streets: An Assessment of Virginia s Municipal Street Trees

Transcription

1 i-tree Streets: An Assessment of Virginia s Municipal Street Trees Eric Wiseman Associate Professor of Urban Forestry Dept. of Forest Resources & Environmental Conservation Virginia Tech arborist@vt.edu May 22, 2014 Northern VA Urban Forestry Quarterly Roundtable NOVA Comm. College Sterling, VA

2 PRESENTATION OVERVIEW Project background Project methods Study findings Study implications May 22, 2014 Northern VA Urban Forestry Quarterly Roundtable NOVA Comm. College Sterling, VA

3 PROJECT BACKGROUND Why street trees? o Street trees are immersed in the built environment o Citizens have a high level of interaction with them o Their assets and liabilities are readily noticed by the public o Citizens form their opinions and values of urban forests based on their experiences with street trees

4 PROJECT BACKGROUND Why emerald ash borer?

5 PROJECT BACKGROUND Midwestern urban forests were being devastated by EAB SE Michigan: 20 million dead ash trees (Anulewicz et al. 2007)

6 PROJECT BACKGROUND Native ash abundance was variable and uncertain Locality % Fraxinus as Street Trees Source 34 SD localities 36 Ball et al Minneapolis, MN 21 MPRB 2008 Gastonia, NC 19 Raupp et al Florence, KY 13 Raupp et al Lincolnshire, IL 13 Raupp et al Chicago, IL 12 Raupp et al Kansas City, MO 10 Raupp et al Toledo, OH 9 Raupp et al Marion, IN 5 Raupp et al New York, NY 4 Raupp et al. 2006

7 PROJECT BACKGROUND Native ash abundance was variable and uncertain

8 PRESENTATION OVERVIEW Project background Project methods Study findings Study implications May 22, 2014 Northern VA Urban Forestry Quarterly Roundtable NOVA Comm. College Sterling, VA

9 PROJECT METHODS Street tree assessment

10 PROJECT METHODS Zonation of state and identification of prospect localities

11 PROJECT METHODS Zonation of state and identification of prospect localities Zone Complete Sample Total

12 PROJECT METHODS Street tree inventory data collection Sample Inventory Method Sample Street Tree Inventories N=16 Sampling Intensity (% of streets sampled) Minimum 4% - Richmond Median 13% Maximum 33% - Buchanan Goal: 10% relative standard error for total street tree population estimate

13 PROJECT METHODS Street tree inventory data collection >1 DBH (lawn) >4 DBH (forest) Address Land Use Site Type Species DBH Condition Age Class

14 PROJECT METHODS Street tree inventory data analysis

15 PRESENTATION OVERVIEW Project background Project methods Study findings Study implications May 22, 2014 Northern VA Urban Forestry Quarterly Roundtable NOVA Comm. College Sterling, VA

16 STUDY FINDINGS Street Tree Abundance N = 22 Total Street Trees (#) Street Tree Density (#/sq. mi.) Street Trees per Capita Minimum 771 Buchanan 144 Abingdon 0.05 Alexandria Median 5, Maximum Interquartile Range 46,792 Richmond 1,980 Fredericksburg 0.90 Fredericksburg 2,072 11, Total 233,240

17 STUDY FINDINGS Street Tree Diameter Distribution % of Population N = in in in in in. >30 in. Trunk Diameter Class

18 STUDY FINDINGS Street Tree Composition N = 22 Native Ash Trees (#) Relative Abundance (%) Relative Importance (%) Minimum 0* Buchanan, Franklin 0* Buchanan, Franklin 0* Buchanan, Franklin Median Maximum Interquartile Range 1,391 Richmond 6.0 Wytheville 11.3 Abingdon Total 5,280

19 STUDY FINDINGS Street Tree Composition N = 22 Minimum Sum of Relative Importance of Top-5 Species 25.8% Harrisonburg Median 40.8% Maximum Interquartile Range 64.4% Franklin City 33.4% 47.9%

20 STUDY FINDINGS Street Tree Composition N = 22 Freq. in Top-5 of Relative Importance Median Relative Import. (%) Acer Quercus Pinus Cornus Fraxinus Max. Relative Import. (%) 33.5 Winchester 30.2 Richmond 28.7 Emporia 8.1 Martinsville 10.4 Abingdon

21 STUDY FINDINGS Street Tree Benefits & Value Wisconsin Department of Natural Resources Northeast Region

22 STUDY FINDINGS Street Tree Benefits & Value N = 22 Minimum Gross Annual Benefits ($) Replacement Value ($) Total Per Tree Total Per Tree $34,380 Buchanan $32.62 Martinsville $1,467,544 Buchanan $763 Roanoke Median $452,387 $67.79 $17,159,802 $2,594 Maximum $4,938,852 Richmond $ Falls Church $211,889,829 Richmond $5,229 Franklin City Interquartile Range $100,231 1,030,551 $ $5,606,673 33,004,551 $2,000 3,716 Total $18,845,893 $617,578,471

23 STUDY FINDINGS Street Tree Benefits & Value

24 STUDY FINDINGS

25 PRESENTATION OVERVIEW Project background Project methods Study findings Study implications May 22, 2014 Northern VA Urban Forestry Quarterly Roundtable NOVA Comm. College Sterling, VA

26 STUDY IMPLICATIONS SHORT-TERM Slow the spread and protect high-value trees

27 STUDY IMPLICATIONS SHORT-TERM Slow the spread and protect high-value trees SL.A.M. SUPPRESSION TACTICS Systemic Insecticides Prompt removal of infested trees Use of trap trees Harvesting and utilization of healthy trees

28 STUDY IMPLICATIONS LONG-TERM Diversify our urban forests Santamour's Ideal Distribution 30% 20% 10% Family Genus Species (Santamour 1990) A community forestry goal of a 10% limit on a single species could give a false indication of stability. (t)here is probably little concern about the diversity of families used as street trees, but not enough concern on the reliance on a limited number of genera a 10% limitation on genera may be our best measure of stability. (Ball et al. 2007)

29 STUDY IMPLICATIONS LONG-TERM Diversify our urban forests What is holding us back? o Ecology (site suitability: soil, space, pests, stress) o Social norms (citizens want fast-growing, colorful trees) o Design and management norms (symmetry and uniformity) o Nursery production (nurseries produce what consumers demand) What do we do about it? o Educate (perform assessments; identify and publicize threats) o Incentivize (tree replacement request preference for diverse spp.) o Subsidize (rebate or discount on diverse spp. sales) o Regulate (approved/prohibited spp. in policy or ordinance)

30 PRESENTATION SUMMARY Street trees are a critical component of Virginia s urban forest Pests are but one of the threats to the sustainability of street tree populations Potential threats of street trees can be evaluated using i-tree Streets An i-tree Streets asssessment provides valuable information for managing street trees and for educating the public and decision-makers May 22, 2014 Northern VA Urban Forestry Quarterly Roundtable NOVA Comm. College Sterling, VA