Tree Species and Diversity Recommendation

With the discovery of Emerald Ash Borer (EAB) in Boulder and the known devastation that it causes to Ash trees (Fraxinus species), the use of these trees in the landscape is strongly discouraged. The reason why the loss of the Ash tree has had such a large effect on the community is because the Ash tree makes up 15% to 20% of the total tree population. The number of Ash trees may be greater in some communities and HOAs.

A healthy urban forest has species diversity that will limit the effect a disease or insect infestation of a single tree species has on the forest. When replacing Ash trees, it is recommended that several tree species be used. Use the Diversity Schedule to help determine the number to tree species to plant based on the number of trees that need to be replaced.

Number of Trees Diversity Percentage ≤ 4 100% genus 5 to 8 50% genus 9 to 15 33% genus 16 to 50 20% species, 30% genus, 40 % family > 50 10% species, 20% genus, 30% family

Listed below is a list of street trees that are a suitable replacement of the Ash tree.

City and County of Broomfield Recommended Shade Trees Botanic Name Common Name Proven Comments Deciduous Trees Acer campestre Maple, Hedge

Acer miyabei Maple, Miyabe

Acer negundo Boxelder, Pink Sensation

Acer platanoides Maple, Norway Is prone to sunscald and leaf scorch in hot dry sites

Acer rubrum Maple, Red Develops chlorosis in alkaline soils

Acer saccharum Maple, Sugar Prefers well drained, neutral to acidic soils

Acer tataricum Maple, Tatarian X Moderately Drought-Tolerant

Acer truncatum x platanoides 'Warrenred' Maple, Pacific Sunset

Acer x freemanii Maple, Autumn Blaze Develops chlorosis in alkaline soils

Aesculus glabra Ohio Buckeye X Some chlorosis; prone to leaf scorch in hot dry sites

Aesculus hippocastanum Horsechestnut X Moderately Drought-Tolerant

Carpinus betulus Hornbeam, European Needs protected site Botanic Name Common Name Proven Comments Catalpa ovata Catalpa, Chinese X

Catalpa speciosa Catalpa, Western X Moderately Drought-Tolerant

Celtis occidentalis Hackberry X Drought-Tolerant

Corylus colurna Filbert, Turkish Moderately Drought-Tolerant

Ginkgo biloba Ginkgo

Gleditsia triacanthos Honeylocust X Drought-Tolerant

Gymnocladus dioicus Kentucky Coffeetree X Drought-Tolerant

Quercus bicolor Oak, Swamp White Develops chlorosis in alkaline soils

Quercus buckleyi Oak, Texas Red X

Quercus imbricaria Oak, Shingle X

Quercus macrocarpa Oak, Bur X Moderately Drought-Tolerant

Quercus muehlenbergii Oak, Chinkapin X Moderately Drought-Tolerant

Quercus robur Oak, English X

Quercus robur 'Fastigiata' Oak, Columnar English X

Quercus rubra Oak, Red Develops chlorosis in alkaline soils

Quercus shumardii Oak, Shumard X

Sophora japonica Japanese Pagoda Tree

Tilia americana Linden, American X Not tolerant of road salts, prone to heat scorch

Tilia americana 'Redmond' Linden, Redmond X Not tolerant of road salts, prone to heat scorch

Tilia cordata 'Greenspire' Linden, Greenspire X Not tolerant of road salts, prone to heat scorch

Tilia tomentosa Linden, Silver - 'Sterling Silver' Not tolerant of road salts, prone to heat scorch

Tilia x euchlora Linden, Crimean Not tolerant of road salts, prone to heat scorch

Tilia x flavescens Linden, Glenleven X Not tolerant of road salts, prone to heat scorch

Ulmus americana Elm, American - 'Valley Forge' Use DED resistant verities

Ulmus japonica x wilsoniana Elm, Frontier

Ulmus minor x U. parvifolia Elm, Accolade

Zelkova serrata Japanese Zelkova