Sunlight-Sensitive Park Resources and Shadow Impacts
- Sunlight-sensitive park resources are those resources which are dependent on sunlight to maintain the overall usability and/or health of a park space, whether it be for human activity or horticultural needs.
- As the city develops, the extent and duration of shadows cast increases. Direct sunlight exposure becomes all the more important as a resource for people and nature, particularly in the city’s central greenspaces, the Boston Common and Public Garden, which are used by millions of people each year as places to relax, gather with the community, walk to work, and recreate.
- In considering the impact of shadows on these parks, it is necessary to assess how they affect the growth cycle and sustainability of the parks’ natural features, as well as the comfort and enjoyment of their users.
- The issue of human use and comfort is particularly important during the cold winter months when there is less available sunlight, especially during morning and afternoon commuting hours, when thousands of people pass through these parks daily. Human-related sunlight-sensitive resources during the warm months include use of the wading pool at the Frog Pond in the Common and the lagoon and Swan Boats in the Garden.
Horticulture and Shadow Impacts
- Trees and turf need 4 – 6 hours of direct sunlight.
- Less sunlight = less photosynthesis = less energy for trees and turf to grow
- Full day and yearlong analysis of cumulative shadows show that the Common and Garden are under significant shadow pressure
- The Tremont and Boylston edges of the parks in particular experience significant shadow pressure
- When trees and turf are in the shadows of buildings, soil surface temperatures may not reach normal levels.
- A lag time in warmth, and a shaded condition that can keep soil wetter, favor disease development. This is a contributing factor in the root rot some trees have suffered in the Garden, and the decline and removal of trees in the Tremont/Boylston corner of the Common
- Shade impacts the success of seed growth, with colder soil temperatures slowing and shortening their growing period.
- Grass is less tolerant of shade than trees. It is easy to grow grass, and easy to kill grass.