Ambrose

1. The 10-20-30 Rule Revisited:
Is It a Useful Standard for Urban Forest
Diversity?
Mark J. Ambrose
NC State University
mambrose@fs.fed.us
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

2. The “10-20-30 Rule”
• Plant no more than 10% of any one species, no more
than 20% of any one genus, no more than 30% of any
one family
• Dr. Frank Santamour, Research Geneticist at the US
National Arboretum (1990)
• Proceedings Paper
• “Rule of thumb”
• Risk mitigation
• No supporting data
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

3. Recent calls for a higher standard
• “5-10-20 rule” – standard adopted by Portland, OR
(2015, 2016) and other cities
• No more than 5% of any one genus (Ball 2015, 2016)
(http://www.urbanforestrytoday.org/videos.html)
• But are any of these “rules” attainable?
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

4. Motivation for this Analysis
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016
Generally, in urban forestry management, it is recommended that no single
species should account for more than 10% of the total population. Furthermore,
no single genus (a genus is a group of closely related species) should account for
more than 15% of the total population. Table 1 shows that Norway maple and
callery pear comprise approximately 22% and 16%, respectively, of the
inventoried street tree population, and combined with Park/Public Space trees,
they amount to approximately 30% and 23%, respectively, of the entire tree
population. Figure 1 shows that the genus Acer (maple) accounts for
approximately 33% of the City’s total inventoried tree population.

5. Motivation for this Analysis
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016
(Raupp et al. 2016)

6. Metrics, Populations, and Scale
• Street trees, park trees, public trees, or total urban forest
• Neighborhood, city, or region
• Number of stems vs. basal area
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

7. Stem Count vs. Basal Area
• Santamour presented his “rule” in terms of number of
stems (i.e., tree count)
• Tree count is useful for planting goals
• Most evaluations of urban forests against the 10-20-30
have used tree count
• But:
– Environmental services
– Tree value (e.g., effect on real estate values)
– Tree removal & replacement costs
. . . . all depend on tree SIZE.
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

8. Stem Count vs. Basal Area (cont’d)
• So, maximum Basal Area in any one species, genus, of
family may be a better measure of risk due to lack of
diversity
• Reformulated 10-20-30 Rule:
No more than 10% of basal area in any one species,
no more than 20% of basal area in any one genus, and
no more than 30% of basal area in any one family.
• One problem with using basal area: legacy effects
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

9. Data & Methods
• Collected inventory data from approx. 1300 inventories
covering over 1000 North American cities
• Street tree, Park tree, Public tree, Campus tree, & i-Tree
Eco sample inventories
• Complete inventory, statistical sample, or partial
inventory covering a “large” and/or clearly defined
portion of a municipality
• Most trees must be identified to species
• Almost all trees must have DBH recorded
• Inventories completed from 2000 to the present.
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

10. Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

11. Data Sources
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

12. Methods (cont’d)
• Calculated relative basal area and relative abundance
for each species, genus, and family.
• Tested the most dominant/abundant species, genus, &
family in each inventory against the 10-20-30 rule.
• For comparison, ran the same tests using Forest
Inventory and Analysis data by ecoregion.
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

13. Results: Abundance, all inventories
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

14. Results: Basal area, all inventories
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

15. Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016
Results: Species Level Failures
Species
Failures
by
Species
Total
Species
Level
Failures
Percent
of
failures Species
Failures
by
Species
Total
Species
Level
Failures
Percent
of
failures
Norway Maple 204 1149 17.75 Silver Maple 245 1234 19.85
Green Ash 176 1149 15.32 Green Ash 130 1234 10.53
Silver Maple 125 1149 10.88 Norway Maple 128 1234 10.37
Sugar Maple 86 1149 7.48 Sugar Maple 110 1234 8.91
Red Maple 51 1149 4.44 Pin Oak 54 1234 4.38
Crape Myrtle 39 1149 3.39 Siberian Elm 54 1234 4.38
Siberian Elm 33 1149 2.87 London Plane 35 1234 2.84
Hackberry 28 1149 2.44 Southern Live Oak 27 1234 2.19
Crabapple/Apple 22 1149 1.91 Hackberry 25 1234 2.03
Southern Live Oak 20 1149 1.74 American Elm 22 1234 1.78
Blue Spruce 19 1149 1.65 Eastern Cottonwood 18 1234 1.46
Honey Locust 17 1149 1.48 Douglas-fir 18 1234 1.46
Callery Pear 17 1149 1.48 Red Maple 17 1234 1.38
Pin Oak 17 1149 1.48 Northern Red Oak 16 1234 1.30
London Plane 16 1149 1.39 Loblolly Pine 15 1234 1.22
------------ Abundance ------------ ------------ Basal Area ------------

16. Results:
Genus level
Failures
Genus
Failures
by
Genus
Total
Genus
Level
Failures
Percent
of
failures Genus
Failures
by
Genus
Total
Genus
Level
Failures
Percent
of
failures
ACER 612 1017 60.18 ACER 612 1202 50.92
FRAXINUS 147 1017 14.45 QUERCUS 162 1202 13.48
QUERCUS 77 1017 7.57 FRAXINUS 124 1202 10.32
ULMUS 36 1017 3.54 ULMUS 80 1202 6.66
PINUS 27 1017 2.65 POPULUS 60 1202 4.99
POPULUS 16 1017 1.57 PINUS 45 1202 3.74
PICEA 14 1017 1.38 PLATANUS 21 1202 1.75
CELTIS 13 1017 1.28 CELTIS 16 1202 1.33
THUJA 7 1017 0.69 WASHINGTONIA 12 1202 1.00
GLEDITSIA 6 1017 0.59 PICEA 11 1202 0.92
LAGERSTROEMIA 6 1017 0.59 PSEUDOTSUGA 10 1202 0.83
PYRUS 6 1017 0.59 EUCALYPTUS 9 1202 0.75
EUCALYPTUS 5 1017 0.49 FICUS 4 1202 0.33
SABAL 5 1017 0.49 SALIX 4 1202 0.33
JUNIPERUS 4 1017 0.39 GLEDITSIA 3 1202 0.25
WASHINGTONIA 4 1017 0.39 SABAL 3 1202 0.25
MALUS 3 1017 0.29 CINNAMOMUM 2 1202 0.17
PLATANUS 3 1017 0.29 JUGLANS 2 1202 0.17
PRUNUS 3 1017 0.29 MORUS 2 1202 0.17
TILIA 3 1017 0.29 SEQUOIA 2 1202 0.17
CHILOPSIS 2 1017 0.20 THUJA 2 1202 0.17
RHAMNUS 2 1017 0.20 TILIA 2 1202 0.17
AILANTHUS 1 1017 0.10 AILANTHUS 1 1202 0.08
ARECASTRUM 1 1017 0.10 ARECASTRUM 1 1202 0.08
BUCIDA 1 1017 0.10 BUCIDA 1 1202 0.08
CORNUS 1 1017 0.10 CARYA 1 1202 0.08
CUPRESSUS 1 1017 0.10 CATALPA 1 1202 0.08
ILEX 1 1017 0.10 CUPRESSUS 1 1202 0.08
JUGLANS 1 1017 0.10 JUNIPERUS 1 1202 0.08
MELALEUCA 1 1017 0.10 LIRIODENDRON 1 1202 0.08
PSEUDOTSUGA 1 1017 0.10 MELALEUCA 1 1202 0.08
RHIZOPHORA 1 1017 0.10 PRUNUS 1 1202 0.08
ROYSTONEA 1 1017 0.10 PYRUS 1 1202 0.08
SALIX 1 1017 0.10 ROBINIA 1 1202 0.08
SCHINUS 1 1017 0.10 ROYSTONEA 1 1202 0.08
SEQUOIA 1 1017 0.10 SCHINUS 1 1202 0.08
SORBUS 1 1017 0.10
TAXODIUM 1 1017 0.10
------------ Abundance ------------ ------------ Basal Area ------------

17. Results:
Genus
level
Failures
Genus
Failures
by
Genus
Total
Genus
Level
Failures
Percent
of
failures Genus
Failures
by
Genus
Total
Genus
Level
Failures
Percent
of
failures
ACER 612 1017 60.18 ACER 612 1202 50.92
FRAXINUS 147 1017 14.45 QUERCUS 162 1202 13.48
QUERCUS 77 1017 7.57 FRAXINUS 124 1202 10.32
ULMUS 36 1017 3.54 ULMUS 80 1202 6.66
PINUS 27 1017 2.65 POPULUS 60 1202 4.99
POPULUS 16 1017 1.57 PINUS 45 1202 3.74
PICEA 14 1017 1.38 PLATANUS 21 1202 1.75
CELTIS 13 1017 1.28 CELTIS 16 1202 1.33
THUJA 7 1017 0.69 WASHINGTONIA 12 1202 1.00
GLEDITSIA 6 1017 0.59 PICEA 11 1202 0.92
LAGERSTROEMIA 6 1017 0.59 PSEUDOTSUGA 10 1202 0.83
PYRUS 6 1017 0.59 EUCALYPTUS 9 1202 0.75
EUCALYPTUS 5 1017 0.49 FICUS 4 1202 0.33
SABAL 5 1017 0.49 SALIX 4 1202 0.33
JUNIPERUS 4 1017 0.39 GLEDITSIA 3 1202 0.25
WASHINGTONIA 4 1017 0.39 SABAL 3 1202 0.25
MALUS 3 1017 0.29 CINNAMOMUM 2 1202 0.17
PLATANUS 3 1017 0.29 JUGLANS 2 1202 0.17
PRUNUS 3 1017 0.29 MORUS 2 1202 0.17
TILIA 3 1017 0.29 SEQUOIA 2 1202 0.17
CHILOPSIS 2 1017 0.20 THUJA 2 1202 0.17
RHAMNUS 2 1017 0.20 TILIA 2 1202 0.17
------------ Abundance ------------ ------------ Basal Area ------------

18. Family
Failures
by
family
Total
Family
Level
Failures
Percent
of
failures Family
Failures
by
family
Total
Family
Level
Failures
Percent
of
failures
Aceraceae 428 708 60.45 Aceraceae 515 975 52.82
Oleaceae 110 708 15.54 Fagaceae 120 975 12.31
Fagaceae 42 708 5.93 Oleaceae 97 975 9.95
Pinaceae 41 708 5.79 Pinaceae 70 975 7.18
Rosaceae 19 708 2.68 Ulmaceae 55 975 5.64
Ulmaceae 18 708 2.54 Salicaceae 52 975 5.33
Arecaceae 11 708 1.55 Arecaceae 19 975 1.95
Salicaceae 9 708 1.27 Platanaceae 12 975 1.23
Celtidaceae 6 708 0.85 Celtidaceae 11 975 1.13
Cupressaceae 6 708 0.85 Myrtaceae 7 975 0.72
Fabaceae 6 708 0.85 Fabaceae 4 975 0.41
Myrtaceae 5 708 0.71 Cupressaceae 3 975 0.31
Bignoniaceae 2 708 0.28 Moraceae 3 975 0.31
Tiliaceae 2 708 0.28 Rosaceae 3 975 0.31
Lythraceae 1 708 0.14 Anacardiaceae 1 975 0.10
Platanaceae 1 708 0.14 Juglandaceae 1 975 0.10
Rhizophoraceae 1 708 0.14 Taxodiaceae 1 975 0.10
Tiliaceae 1 975 0.10
------------ Abundance ------------ ------------ Basal Area ------------
Results: Family Level Failures

19. Results by
State/
Region:
Abundance
(count) (%) (count) (%) (count) (%) (count) (%)
AL, AR, LA, & MS 13 11 84.62 11 84.62 3 23.08 12 92.31
Alberta & Manitoba 7 7 100.00 7 100.00 5 71.43 7 100.00
Arizona & New Mexico 11 5 45.45 4 36.36 5 45.45 8 72.73
California 98 70 71.43 22 22.45 15 15.31 74 75.51
Colorado & Wyoming 38 29 76.32 20 52.63 11 28.95 33 86.84
DC, MD, VA, & WV 40 31 77.50 18 45.00 5 12.50 33 82.50
Delaware & NJ 58 53 91.38 51 87.93 40 68.97 56 96.55
Eastern Canada 34 33 97.06 30 88.24 18 52.94 34 100.00
Florida 20 20 100.00 19 95.00 16 80.00 20 100.00
Hawaii 1 0 0.00 0 0.00 0 0.00 0 0.00
Iowa 95 95 100.00 94 98.95 79 83.16 95 100.00
Illinois 18 15 83.33 15 83.33 8 44.44 16 88.89
Indiana 30 29 96.67 30 100.00 23 76.67 30 100.00
Idaho & Montana 64 56 87.50 53 82.81 46 71.88 60 93.75
Kansas 52 51 98.08 40 76.92 14 26.92 51 98.08
Michigan 34 32 94.12 31 91.18 28 82.35 33 97.06
Minnesota 34 13 38.24 28 82.35 21 61.76 32 94.12
Missouri 40 35 87.50 27 67.50 10 25.00 36 90.00
NC, SC, & GA 39 38 97.44 32 82.05 13 33.33 39 100.00
North Dakota 42 42 100.00 42 100.00 40 95.24 42 100.00
Nebraska 70 66 94.29 54 77.14 22 31.43 67 95.71
New York 89 85 95.51 87 97.75 78 87.64 87 97.75
New England 54 50 92.59 53 98.15 35 64.81 53 98.15
Ohio 28 19 67.86 23 82.14 16 57.14 25 89.29
Pennsylvania 32 28 87.50 27 84.38 20 62.50 30 93.75
Pacific NW 47 42 89.36 34 72.34 25 53.19 45 95.74
South Dakota 57 57 100.00 52 91.23 37 64.91 57 100.00
Tennessee & Kentucky 9 8 88.89 6 66.67 4 44.44 8 88.89
Texas & Oklahoma 24 24 100.00 20 83.33 10 41.67 24 100.00
Utah & Nevada 46 43 93.48 27 58.70 15 32.61 43 93.48
Wisconsin 72 62 86.11 60 83.33 46 63.89 66 91.67
Species failures Genus failures Family failures Overall failures
# of
inventories
State/Region

20. Results by
State/
Region:
Basal
Area
(count) (%) (count) (%) (count) (%) (count) (%)
AL, AR, LA, & MS 13 13 100.00 12 92.31 11 84.62 13 100.00
Alberta & Manitoba 7 7 100.00 7 100.00 7 100.00 7 100.00
Arizona & New Mexico 11 10 90.91 9 81.82 8 72.73 11 100.00
California 98 84 85.71 50 51.02 33 33.67 85 86.73
Colorado & Wyoming 37 34 91.89 34 91.89 24 64.86 37 100.00
DC, MD, VA, & WV 41 34 82.93 37 90.24 19 46.34 39 95.12
Delaware & NJ 58 54 93.10 56 96.55 45 77.59 58 100.00
Eastern Canada 34 31 91.18 31 91.18 25 73.53 34 100.00
Florida 20 20 100.00 19 95.00 18 90.00 20 100.00
Hawaii 1 1 100.00 0 0.00 1 100.00 1 100.00
Iowa 96 96 100.00 96 100.00 88 91.67 96 100.00
Illinois 18 18 100.00 17 94.44 13 72.22 18 100.00
Indiana 30 30 100.00 30 100.00 29 96.67 30 100.00
Idaho & Montana 64 62 96.88 62 96.88 54 84.38 64 100.00
Kansas 52 52 100.00 48 92.31 25 48.08 52 100.00
Michigan 34 32 94.12 34 100.00 32 94.12 34 100.00
Minnesota 35 11 31.43 32 91.43 28 80.00 34 97.14
Missouri 40 40 100.00 37 92.50 27 67.50 40 100.00
NC, SC, & GA 39 39 100.00 39 100.00 35 89.74 39 100.00
North Dakota 42 42 100.00 42 100.00 38 90.48 42 100.00
Nebraska 70 70 100.00 69 98.57 41 58.57 70 100.00
New York 91 91 100.00 90 98.90 84 92.31 91 100.00
New England 54 54 100.00 54 100.00 50 92.59 54 100.00
Ohio 30 25 83.33 27 90.00 21 70.00 29 96.67
Pennsylvania 33 33 100.00 32 96.97 23 69.70 33 100.00
Pacific NW 47 45 95.74 39 82.98 31 65.96 46 97.87
South Dakota 58 57 98.28 54 93.10 47 81.03 58 100.00
Tennessee & Kentucky 9 9 100.00 9 100.00 7 77.78 9 100.00
Texas & Oklahoma 24 24 100.00 22 91.67 16 66.67 24 100.00
Utah & Nevada 46 44 95.65 43 93.48 33 71.74 46 100.00
Wisconsin 72 72 100.00 71 98.61 62 86.11 72 100.00
State/Region
# of
inventories
Species failures Genus failures Family failures Overall failures

21. Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016
Results by Inventory Type
(count) (%) (count) (%) (count) (%) (count) (%)
Whole City 102 77 75.49 65 63.73 30 29.41 92 90.20
College Campus 45 31 68.89 20 44.44 9 20.00 34 75.56
Facilities Trees 1 1 100.00 0 0.00 0 0.00 1 100.00
Golf Course 1 1 100.00 1 100.00 0 0.00 1 100.00
Park Trees 53 40 75.47 32 60.38 17 32.08 43 81.13
Public Trees 432 381 88.19 318 73.61 212 49.07 402 93.06
Street Trees 662 618 93.35 581 87.76 440 66.47 643 97.13
(count) (%) (count) (%) (count) (%) (count) (%)
Whole City 103 84 81.55 88 85.44 53 51.46 101 98.06
College Campus 45 44 97.78 40 88.89 31 68.89 45 100.00
Facilities Trees 1 1 100.00 0 0.00 0 0.00 1 100.00
Golf Course 1 1 100.00 1 100.00 1 100.00 1 100.00
Park Trees 53 51 96.23 45 84.91 33 62.26 53 100.00
Public Trees 433 408 94.23 388 89.61 298 68.82 425 98.15
Street Trees 668 645 96.56 640 95.81 559 83.68 660 98.80
---------------------------------------- Abundance ------------------------------------
Inventory Type
# of
inventories
Species failures Genus failures Family failures Overall failures
---------------------------------------- Basal Area --------------------------------------
# of
inventories
Species failures Genus failures Family failures Overall failures
Inventory Type

22. Results: Genus relative basal area
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016
Relative basal area
of most dominant genus

23. Results: FIA data (species)
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

24. Results: FIA data (genus)
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

25. Results: FIA data (family)
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

26. Results: FIA data (overall)
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

27. Results: FIA data (species)
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

28. Results: FIA data (genus)
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

29. Conclusions
• Most cities fail the “10-20-30 Rule” standard regardless
of region or inventory type
• Many cities don’t even come close to meeting the
standard
• Most natural forests in the US also fail
• Maple, ash, and/or oak exceed the ”rule” in most cities
• Most cities fail both in terms of abundance and basal
area
• No city would meet a “5-10-20 rule” or a 5% genus rule
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

30. Concluding thoughts
• Relative basal area is superior to relative abundance in
evaluating risk due to lack of diversity
• Family (30%) portion of the “10-20-30 Rule” contributes
little
• Focusing on genus-level diversity makes sense
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

31. Concluding thoughts
• Competing goals for urban forest:
– Diversity within cities
– Species that are well suited to the urban environment
and the climate region
– Diversity among cities (γ diversity)
– Native species (or not?)
– Water use considerations
• Constraints on diversifying urban forests:
– Species availability in nursery trade
– Species that have been proven successful
Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016

32. Acknowledgements:
– John Campanini, Rhode Island Tree Council
– Fred Cowett, Dept. of Horticulture, Cornell University
– Eric Berg, Nebraska forest Service
– Kim Bomberger, Kansas Forest Service
– Jason Grabosky, Rutgers University
– Emma Bruemmer Hannigan, Iowa Dept. of Natural Resources (DNR)
– Meaghan Eastwood, Toronto & Region Conservation Authority
– Ian Hanou, Plan-It Geo
– David Howlett, Nevada Division of Forestry
– Jamie Kirby, Montana DNR & C
– Frank Koch, USFS-SRS, Eastern Forest Threat Assessment Center
– Eric Kuehler, USFS, Athens, GA
– Nick Kuhn, Missouri Dept. of Conservation
– Linden Lampman, Washington DNR
– Andy Lister, USFS-NRS, Forest Inventory & Analysis
– Pam Louks, Indiana DNR
– Kamie Long, Colorado State Forest Service
– Scott Maco, Davey Trees
– Kim Miller, Wisconsin DNR
– Eric North, U of Minnesota, Dept. of Forest Resources
– Dave Nowak, USFS-NRS, Urban & Community Forestry
– Micah Pace, Texas A & M Forest Service
– Meridith Perkins, Utah Div. of Forestry, Fire, and State Lands
– Alix Rogstad, Arizona State Forestry
– Kevin Sayers, Michigan DNR
– John Sugg, Treefull Communities, LLC
– Aaron Wang, South Dakota Dept. of Agriculture, Resource Conservation & Forestry
– P. Eric Wiseman, Virginia Tech
– Brian Wolyniak, Penn State Extension
– Many, many others from across the US and Canada who supplied data!!

33. Partners in Community Forestry,
Indianapolis, IN, November 16-17, 2016
Thank You!
Questions/Comments?
Mark J. Ambrose
North Carolina State University
Dept. of Forestry & Environmental Resources
Office: (919) 549-4078
FAX: (919) 549-4047
mambrose@fs.fed.us