Trees and People

Festivals to celebrate the blooming of trees are held all over the world, and can be a major tourist draw. Most famous among blooming festivals are the various celebrations of cherry blossoms in Japan, Washington DC and other places. The vagaries of weather means that blossoms often fail to appear at the scheduled time for festivities. Since festivals have to be scheduled well in advance, it is easy to miss the actual bloom date. As cities become warmer, both because of climate change and the urban heat island effect, blossoms are occurring much earlier, often well before tourists arrive to celebrate the event.

Authorities in Hirosaki, in northern Japan, are funding research by tree biologists to try to control blossoming so that it occurs when the festivals are scheduled. Since hundreds of thosands of tourists may descend on a properly timed festival, the city stands to lose a lot of money if it is unable to predict the timing of blossoming. Hirosaki is in a cooler area than most Japanese cities and the blossom time of cherries often coincided with Golden Week, a national week of holidays. Up to two million visitors go to Hirosaki when the blossoms coincide with Golden Week.

Scientists at Hirosaki University are experimenting with hormone sprays and injections and piling snow around cherry trees. To date, none of the treatments have been effective. This is not surprising. Once a tree's dormancy requirement has been met, the timing of flowering in temperate trees is tightly tied to degree days (heat accumulation above a threshold temperature). It seems very unlikely that hormonal control of flower timing is significant. Packing snow may cool the roots, but flower development is more likely dependent on air temperature. I suspect that the scientists will spend a lot of money without any significant outcome. Maybe it is time to reschedule Golden Week.

The article describing this issue doesn't address some important questions: how often is Golden Week missed, and has there been a trend toward earlier blooming over time? The article says that there has but does not describe the trend in sufficient detail. Also, the urban heat island effect, which is often much larger in cities than other sources of climate change, is not addressed. While little can be done over the short term regarding climate change, the urban heat island effect can be mitigated.

Horticulturists have selected and bred fantastic ornamental plants with showy, often dramatic flowers. Along the way to today's modern flowers, something has been lost. In the last 50 years, as breeders have selected for better or new colors, larger flowers, longer stems and longer shelf life, they seem to have inadvertently selected against smell. Many modern flowers lack odor or have minor smells compared to their wild ancestors or older cultivars. Now breeders are beginning to pay more attention to smell and to select modern cultivars for odor as well as appearance. Nursery catalogs are beginning to list smell along with color and other descriptors. The desire for strong fragrance is also behind the resurgence in traditional and heirloom varieties.

In Palo Alto, CA, an innovative volunteer program is improving the health of city trees. Volunteers working with the citizen organization Canopy are taking care of 1200 street trees planted in the last five years. The volunteers are examining the trees for water needs, support stake removal and problems. Problem trees are reported to the city arborist. They are also leaving leaflets with homeowners to remind them to care for the young trees and providing tips on their care. Water needs of young trees are particularly critical in the summer-dry mediterranean climate of coastal California.

While many cities have active tree planting programs, few have the budgets to properly care for the trees. Citizen organizations like Canopy are a great way to mobilize concerned residents to help care for street trees.