Lawn, Meadow or Wetland? Evaluating Plans for a City Park

Four Plans for Linden Park

1Linden Park is a city park with an 8,000 m² lawn that slopes down to Mill Creek. After heavy rain, water runs across the mowed grass and into the creek, carrying soil and lawn fertilizer with it. Healthy ecosystems provide services that people depend on, such as soaking up rain, keeping water clean and pollinating plants. The city's parks board wants to replace part of the lawn to support more kinds of living things and to protect the creek, so it asked a seventh-grade class at Eastgate Middle School to help compare four plans.

2Plan A adds large beds of annual flowers, which are planted each spring and bloom mostly in midsummer, and keeps the rest as lawn. Plan B turns much of the lawn into a meadow of native wildflowers and grasses that bloom at different times from April to October, with a 10 m wide strip of native shrubs along the creek. Plan C plants a row of shade trees along the creek and keeps the rest as lawn. Plan D digs a wetland pond with a wooden boardwalk.

3The board set three constraints. A plan must cost no more than $25,000 to install and no more than $6,000 a year to maintain, and it must leave at least 3,000 m² of open lawn for a youth soccer field. The board's criteria are more kinds of pollinators and birds, more rain soaked into the ground and a cleaner creek.

4The class first studied small examples of each kind of planting that already grow in the park or nearby. They marked a 10 m by 10 m plot in each one and, on one sunny morning in each season, counted how many different pollinator species, such as bees, butterflies and hover flies, visited the plot in 30 minutes (Table 1). There was no wetland nearby, so Plan D has no plot. The city's engineer then estimated the costs of each plan, how much of the rain falling on the area would soak in, and how much open lawn would be left (Table 2 in Section 2).