MPRB Autumn Update: Taking Stock of the Evolving Urban Forest

Via an October 30 e-newsletter from the Minneapolis Park and Rec Board:

As leaves fall and trees settle into dormancy for the coming winter, MPRB forestry staff are wrapping up removals of ash and other tree categories for the season. To maintain and even expand the urban forest, we also planted some 8,300 trees this year.

About 1,800 were planted in parks and the balance of 6,500 went into boulevards along Minneapolis streets. Oak trees and coffeetrees, nearly 1,000 of each in various cultivars and species, were among the most-planted categories; planetrees were a close third. 

Numbers of Note

Of course, an urban forest is more than the sum of its trees. But some numbers are worth noting.

For example, 900 oak trees may sound like a lot, but to put it in perspective: Oak still comprise just 7% of Minneapolis' street trees - and that's up from only 2% in 2004. Meanwhile, coffeetrees have moved from less than 1% to 3%. These single-digit gains are how we measure success in developing a diverse urban forest. 

Two other measures of this type of success, also illustrated in the charts below: 

• The number of tree categories that comprised 2% or more of the total trees planted in 2018: Parks got 20 categories, while streets got 18.
  
  
• Overall, 16 tree categories comprised 1% or more of the overall street tree population in 2018 - up from only nine categories back in 2004.

Seeing the forest for the trees: Diversity rules!

As shown in the charts above and below, MPRB's overall mission is to ensure variety, which protects the entire urban forest from the kind of blight brought by diseases like Dutch elm or insects like emerald ash borer.

Some key MPRB practices advance this mission:

• Plant hundreds of tree types from dozens of categories
• Mix three to five or more tree categories on any individual city block
• Limit any tree category within a neighborhood to 10% (that's a limit, not a goal)
  
  

In practice, that limit 10% limit means that MPRB continues to plant tree categories that currently represent only single-digit percentages in parks and along streets. Over time, this lowers the percentages for categories that currently dominate - maples, lindens and yes, even elms - as shown in the street-tree charts below.

MPRB street tree population, then and now

Up-and-coming trees

As diversity develops throughout the urban forest, you may begin to see more of these categories: 

• Maackia - A great option for our climate and urban conditions, maackia cultivars are becoming more readily available. Their small size makes them a good option on streets where space is limited. 
  
  
• Corktree - If we could get more, we'd plant more! But supplies are limited, since it takes years for nurseries to respond to changes in the demand for specific trees; most of the corktrees that MPRB procures are five to seven years old. 
  
  
• Larch (aka Tamarack) - Locals may be familiar with this tree from the Quaking Bog in Theodore Wirth Park - but the larch holds promise in parks and even along streets; MPRB is monitoring plantings in both locales. 

Remember: Water trees weekly!

After the leaves have fallen, but before you put away the garden hose for the winter, use it to give a good, long drink to young trees on your property and along nearby streets: It's essential in helping them get through the winter.

Find out more about MPRB's park care and maintenance and its stewardship of the urban forest and park trees.