Arboriculture

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.

Los Angeles has a great web site for information on its street trees, including permitting and street tree care guidelines. This kind of citizen information could serve as a model for other cities.

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.

Moving large ornamental trees is a common arboricultural practice, and often a rather dramatic one. In South Africa, Kruger National Park staff and volunteers had to move two large baobab trees because they were too close to buildings. The trees, one weighing more than 16,000 pounds, were hand dug and lifted onto trucks. The trees were moved to a new park entrance on the Mozambique border, part of an initiative to link parks in South Africa, Mozambique and Zimbabwe.

Baobab, Adansonia spp. and related species, is a genus of bizarre trees with extremely stout stems that store large amounts of water. Folk wisdom says that the baobab was planted upside down by devils or gods.