Do you love maple trees? We do too - but use these lessons we've learned to keep your trees flourishing.
There's no denying our love affair with maple trees. From the stunning fall colors of red maples to the graceful form of sugar maples, these beloved trees have captured the hearts of homeowners across the Twin Cities metro area. At Minnesota Landscapes, we absolutely love maples too – but we've learned valuable lessons from history about the dangers of putting all our eggs in one arboreal basket.
The story of urban tree diversity in Minnesota is a cautionary tale of boom and bust. Dutch elm disease fungus devastated shade trees in Minnesota in the 1970s, much like the emerald ash borer is doing today. Before the Dutch elm disease outbreak in Minnesota, elm and ash trees were found in very similar growing conditions. But this similarity in habitat preferences would prove to be both a blessing and a curse.
The Elm Era and Its Downfall
Prior to Dutch elm disease (DED), Minneapolis was estimated to have between 200,000 and 600,000 elms; there are now about 35,000 (that's just 5 to 17 percent of the original population). During the 50s and 60s, elms were a favored boulevard tree species used in the Twin Cities. This had to do with their quick growth rate, large size at maturity, and shade production. The carnage began in the 1970s.
Dutch elm disease (DED) causes wilt and death in all elm species native to Minnesota. The fungus that causes Dutch elm disease is an invasive species and was first introduced to Minnesota in 1961. The monoculture approach made the devastation swift and complete. With so many city streets lined with large elm trees, DED was able to move quickly through the city, wiping out entire blocks of trees. The urban forest was dominated by elms, and this allowed the disease to spread very quickly.
The Ash Replacement Strategy
After losing our elm canopy, we turned to ash trees as replacements. Unfortunately, when the elms were being replaced, the scales sort of tilted towards the green ash. Why? Because it is a very fast growing tree, with a large size at maturity, providing generous amounts of shade. Sound familiar? We were seduced by the same characteristics that made elms so popular.
All ash trees are susceptible to emerald ash borer (EAB). The most common ash species in Minnesota are black ash, white ash and green ash. Minnesota is home to an estimated 1 billion ash trees. One in five community trees are ash. In some communities, ash trees make up 60% of the trees.
The Emerald Ash borer was confirmed in Minnesota in 2009. This invasive species has killed tens of millions of ash trees across the United States. Once again, our monoculture approach left us vulnerable to catastrophic loss.
Now we're seeing the same pattern emerge with maples. Walk through neighborhoods in Minneapolis, St. Paul, Woodbury, or Eden Prairie, and you'll notice an abundance of newly planted maples replacing the ash trees we've lost to EAB.
Why Maples Are So Popular
Maple is the most common genus of deciduous street tree planted in eastern North America. Acer is also one of the most common tree genera planted in U.S. residential and commercial landscapes, parks, and public spaces. The reasons are compelling:
Current Diseases and Pests Affecting Maples
While we don't currently face a single devastating pest like Dutch elm disease or emerald ash borer for maples, they're not immune to problems. Maple trees are hosts for at least 81 potentially damaging arthropod pests. Common issues include:
Anthracnose is a common disease that causes dark, irregular leaf blotches on ash, oak, maple, birch, and other shade trees. It affects a wide variety of deciduous trees in Minnesota, including ash, oak, maple, and sycamore.
Common maple diseases include tar spot, verticillium wilt, anthracnose, leaf scorch, powdery mildew, and lichen. Treatment ranges from pruning dead branches to removing the entire tree and fumigating the soil to doing nothing at all, depending on the infection.
Verticillium wilt is a soil pathogen that infects the roots of the tree causing dieback in the corresponding branches above ground. Maple and lilac trees are very commonly affected.
The 10-20-30 Rule
Urban foresters recommend setting tree diversity targets to minimize the drastic effects of tree pest and disease outbreaks. The "5-10-20" rule recommends a species, genus, family ratio of no more than 5 percent of one species, no more than 10 percent of one genus, and no more than 20 percent of one family for an urban forest.
Why Monocultures Fail
This near monoculture approach has made urban forests vulnerable to outbreaks of pests and diseases – as it happened with the emerald ash borer and the Dutch elm disease that decimated tree populations throughout cities in the United States and Canada.
The legacies of past monocultures create time-lagged vulnerabilities to pest and disease outbreaks. When approaching urban forestry from a management perspective, it is useful to expand the conception of urban forests beyond trees to include the associated biotic and abiotic components, including people, institutions, and infrastructure as part of an integrated socio-ecological system.
The Benefits of Diversity
Multispecies tree planting has long been applied in forestry and landscape restoration in the hope of providing better timber production and ecosystem services. Multispecies plantings, on average, have taller and thicker trees and greater aboveground biomass accumulation than monocultures.
Tree species diversity measures the richness and evenness of tree species within an urban forest. Species richness refers to the total number of different tree species present, while species evenness indicates how evenly those species are represented. High species diversity is characterized by a variety of tree species represented evenly.
As your design-first landscaping contractor, we've learned from the past and are committed to creating resilient, diverse urban forests. Our approach includes:
Comprehensive Species Selection
We work with clients throughout the Twin Cities metro area – from White Bear Lake to Apple Valley – to select trees that complement both the landscape design and contribute to overall urban forest health. This means incorporating:
Professional Assessment and Planning
Our expert arborists conduct thorough site assessments to determine the best species for each location. We consider:
Integration with Landscape Design
Tree selection is seamlessly integrated into our comprehensive landscape design services. We ensure that tree diversity enhances rather than complicates the overall design, creating beautiful and functional outdoor spaces that will thrive for generations.
Minneapolis is mixing tree species in a more random fashion to prevent a single pest or disease from wiping out an entire block's trees. This is really great to see – we are making progress. The city learned that had there been a broader mix of tree species, the disease would not have had such a devastating impact. Increased tree diversity, even in an urban setting, really makes sense.
Back in the day, the city of Minneapolis used to plant trees by the block. For instance, an entire city block was all green ash and the next block might be all hackberry. Now we are seeing that planting plans include a greater variety of tree species used in a more random pattern.
Diversify Your Landscape
If you're planning to plant trees on your property in Eagan, Cottage Grove, or any Twin Cities community, consider:
Consider Native Alternatives
While maples are beautiful, consider incorporating native Minnesota trees such as:
Professional Guidance Matters
If we are to plant and sustain city forests that will delight and inspire the residents and visitors in our urban centers, we need both diversity and uniformity of plant material to reduce the costs of maintenance and reduce the use of potentially dangerous pesticides.
We're not saying don't plant maples – they truly are magnificent trees that deserve a place in Minnesota's urban forest. What we're advocating for is thoughtful, diverse planting that learns from the mistakes of the past.
With extreme weather events like storms, floods and droughts on the rise, increasing tree diversity through strategic planting and management is vital for making urban forests more resilient.
At Minnesota Landscapes, we help clients throughout Mendota Heights, Afton, Shoreview, and surrounding communities create landscapes that are both beautiful and resilient. We love maples, but we love healthy, diverse urban forests even more.
Don't repeat the mistakes of the past. Let Minnesota Landscapes help you create a diverse, resilient landscape that will thrive for generations to come. Our comprehensive outdoor solutions integrate tree selection and planting with expert landscape design to create outdoor spaces that are as sustainable as they are stunning.
Contact Minnesota Landscapes today to discuss how we can help you make thoughtful tree choices that contribute to a healthier urban forest while creating the outdoor space of your dreams. Together, we can ensure that future generations inherit diverse, resilient urban forests rather than the boom-and-bust cycles of the past.
Remember: loving maples means planting them responsibly as part of a diverse urban ecosystem. Your trees – and your community – will thank you for it.
