I am an ecologist and unapologetic tree hugger, and I spend much of my time in parks looking up at the trees' canopy. Now that the autumn leaves have mostly fallen from the trees in the Common, the Mall, and the Public Garden, the natural forms of the trees are revealed. Some of them are beautiful and iconic of the species - the classic vase shaped form of the American Elm, for instance, which is instantly recognizable from any distance. The bushy, spreading form of an open grown Red Maple is distinctive, as is the characteristic branching of the Horsechestnut tree, which always reminds me of an athlete flexing his muscles. The old Japanese Pagoda tree's graceful lines are more akin to a ballerina than a weightlifter. During the dormant season, the many varieties of "weeping" forms are clearly visible as their branches trail down towards the ground - cherries, willows, and beeches. But you may notice something else as well - some of the oldest, most venerable trees appear to have been lopped off at the top! Why on earth would an arborist prune a tree in such an unsightly way?
The answer is relatively simple, but might not be immediately obvious. The very largest trees in these parks are approaching the end of their natural lifespans, which vary from species to species but which don't generally exceed 200-300 years. Many of these older specimens have some hidden rot in their heartwood, which leaves them potentially vulnerable to damage from high winds during New England's famous nor'easters, thunderstorms, and hurricanes. Extreme weather events are expected to increase in intensity and frequency as the effects of our changing climate are manifested in our region. To protect against blowdowns, the Friends of the Public Garden have been implementing a strategy called "Load reduction pruning". Many trees have been pruned to strategically reduce the weight of the canopy. After our last major wind event, we only lost one large limb in the Public Garden, which is a great accomplishment after a high-wind storm!
In most trees this load reduction pruning is hardly noticeable to the untrained eye, but there are a few trees in which it's quite noticeable - some of the oldest trees in our parks, including the two elms that frame the steps in front of the State House, and one of the oldest weeping willows by the lagoon in the Public Garden. In these cases, the pruning allows the trees to persist despite extensive age-related die-back in the canopy, and for much of the year, to most passers-by (who are not gazing up at the canopy), the tree serves the general purpose of a tree, albeit with somewhat odd proportions. It is only when the leaves have fallen that the odd proportions are fully revealed. I like to think that we value the lives of the older trees perhaps more because of the many years they've seen, and tolerating (and understanding) their odd shape in the winter is a small price to pay to have these familiar Boston arboreal citizens persist into the 21 st century.
