Monocultures are so Last Century

Minnesota’s forests and urban tree canopy are facing a dramatic loss of ash trees thanks to the invasive emerald ash borer (EAB). First detected in the state in 2009, EAB has spread widely—now confirmed in most of Minnesota’s counties—and feeds on all native ash species, ultimately killing them outright. The state is home to more than 1 billion ash trees, and many communities have up to 60% of their urban canopy made up of ash—a distribution that means this pest doesn’t just harm individual trees, it reshapes entire landscapes.

One of the clearest lessons from EAB is that species diversity isn’t optional—it’s insurance. To avoid repeating the same mistake, Hoffman & McNamara’s Tree Diversity Guide organizes our grow list by botanical family, making it easier to spot overreliance, broaden palettes, and plan plantings that are better equipped to withstand the next pest, disease, or climate stressor. Choosing across families—not just species—helps build landscapes that are healthier, more resilient, and far less vulnerable to a single threat.