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All across San Francisco one can find beautiful examples of full-grown, mature Blackwood Acacia trees gracing various neighborhoods, providing an attractive foreground to neighboring buildings, enhancing nearby property values, and quietly helping to combat climate change. Yet in our own Westwood Highlands neighborhood, these attractive trees are routinely butchered by well-meaning homeowners who pay to have their limbs hacked off, in the belief that Blackwood Acacias require this kind of extreme “pruning” to improve their appearance and maintain their long-term health. This belief is completely mistaken. The kind of brutal pruning routinely imposed on Blackwood Acacias by some of our Westwood Highlands neighbors not only prevents these trees from ever attaining their full natural beauty and stature, but severely weakens them and renders their limbs far more susceptible to decay and breakage. Westwood Highlands appears to be the only neighborhood in San Francisco where these beautiful trees are treated as if they were ornamental sycamores or plane trees fit only for radical pruning. This is probably because of the error of one tree pruner hired by the Homeowners’ Association many years ago to prune all the Blackwood Acacias planted in the Westwood Highlands development. This particular contractor drastically cut back the limbs of the already mature Blackwood Acacias in the apparent belief that this was the proper way to maintain the trees. This unhealthy style of pruning Blackwood Acacias now seems to have become a local tradition in Westwood Highlands. And it has caused problems. The kind of brutal “hacking off” of limbs visible on trees in our neighborhood has permanently damaged the trees, actually shortening their life span. Once mature limbs are hacked off, the new branches that eventually grow back are weaker, and much more susceptible to decay and easy breakage in the wind. Trees “pruned” and hacked off in this manner are also unsightly — they simply don’t look natural or as beautiful as full-grown trees do. The principal pruning of these trees must be done when they are very young — no more than three or four years old. Older trees need different kinds of pruning — much less invasive or dramatic. Properly cared for by a knowledgeable tree pruner every two years or so, the limbs of a Blackwood Acacia will not die and fall off prematurely. Instead, the tree will grow naturally into a beautiful specimen, with strong limbs and branches. Such a tree enhances the value of the property on which it grows. Homeowners should be aware of an additional reason for properly pruning and caring for their trees. Under recent revisions of the Urban Forestry Ordinance in the San Francisco Municipal Public Works Code, “significant trees” located on private property are now given the same protection as public street trees, so that a permit is required before any such tree can be removed. Such “significant trees” are defined to include any trees, whether or not on private property, that are within 10 feet of a public right-of-way, and are either 20 feet or greater in height, 15 feet or greater in canopy width, or having 12 inches or greater diameter of trunk measured at 4.5 feet above grade. For more information, call 3-1-1 and ask for DPW’s Urban Forestry Division. For good advice on proper pruning of Blackwood Acacias, contact Frank Fredericks of City Trees at (415) 626-8535. See also The Trees of San Francisco, by Mike Sullivan, published by Friends of the Urban Forest (here is a review by the Neighborhood Parks Council). To see a photo of a mature Blackwood Acacia from Mike Sullivan's book, see this preview from Google Book Search. Locations of well-established mature Blackwood Acacias in San Francisco:
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