(MPOV) Black Locust: the Sustainable Hardwood of our Future?

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Black Locust Tree, Source: Wikipedia

This is a duplicate post written originally for Metropolis POV.

Considered by some to be a nuisance tree, Black Locust (Robinia pseudoacacia), which grows across most of the US, may be an important resource in the near future; it could be the sustainable replacement to rainforest hardwoods.

Whether you are a landscape architect designing a park bench or an engineer designing a pedestrian bridge, the materials you select for your work must meet specific and often rigorous standards that involve strength, durability, cost, texture, and color. Many of us don’t appreciate the hard choices designers have to make.

Michael Van Valkenburgh, a landscape architect well known in New York for his role in designing Brooklyn Bridge Park, has lots of ideas to throw around when it comes to the materials his firm uses. When asked what lead to the realization of the potential for Black Locust, he said, “As a designer, there just seemed to be no satisfying alternative [to rainforest hardwoods] in sight: there were no types of North-American harvest lumber that could work as a substitute.” He explained how 15 years ago his firm, Michael Van Valkenburgh Associates, Inc., started thinking about Black Locust and how it was used in his childhood upstate on a dairy farm. “It was the choice for fence posts, due to its stellar rot resistance.”

Van Valkenburgh and his firm started researching the wood and experimenting with applications like the first boardwalk at the Chicago Botanic Garden which, he says, “was the breakthrough”. Proving the wood’s potential would not have been possible without a client who was willing to trust him and was willing to take a few risks. “Such clients are always critical for cultural change,” notes the landscape architect.

Van Valkenburgh was one of four presenters at a recent lecture concerning the use of Black Locust as a sustainable wood choice when compared to rainforest hardwoods. Their presentation is available on the American Society of Landscape Architects website.

Rainforest hard woods, which are harvested from tropical forests in countries like Brazil, are among the materials of choice when it comes to making products that need to have durability and longevity. The hardness of the wood means less wear and tear with heavy use, and less rot due to exposure to the elements.

“New York, like many cities, uses tropical hardwoods-in our case, for our extensive beach boardwalks and also for the walkway on the world-famous Brooklyn Bridge,” said Mayor Michael Bloomberg in early 2008. “’I’ve asked my Office of Long-Term Planning and Sustainability to work with the relevant city agencies, and present me, within the next 60 days, with a plan for reducing our reliance on such hardwoods.”

Rainforest hardwood harvesting involves deforestation of the tropical forests. One example is the Brazilian Walnut (Ipe), which grows sporadically throughout the rainforests of Brazil. Generally only one or two trees are found per acre, and in Brazil, 80% of logging practices are illegal, resulting in 80,000 acres of forest being destroyed every day. That is a lot of destruction for a product that is both beautiful and durable, and Van Valkenburgh agrees: “The harvesting of South American hardwoods for construction in the U.S. was dealing a devastating blow to the global atmospheric ecology.”  The hunt for a durable and beautiful product is where Black Locust steps in.  Visit this link for more information on rainforest hardwood use in NYC.

“It grows best in Appalachia,” said Don Lavender, a research and development engineer for landscapeforms, but it can grow pretty much everywhere in the United States.

“I love the color it turns,” said Van Valkenburgh prior to the presentation. Black Locust changes from a golden brown to a dark gray patina, as shown here.

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Source: ASLA Black Locust Presentation

One of the biggest selling points for Black Locust is its durability. Van Valkerburgh quipped, it “lasts a day longer then stone.” He proved his point by showing images of a bench at Lucy Vincent Beach awash in the high surf of Hurricane Irene.

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Source: ASLA Black Locust Presentation

Black Locust is extremely durable for several reasons; it is a dense wood with high levels of anti-oxidants, making it a wood unlike others harvested in North America. It is extremely rot and insect resistant. It’s so strong that another lecturer, Ted Zoli, an engineer with HNTB Corporation, showed it being used to build a pedestrian bridge for Brooklyn Bridge Park.

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Source: ASLA Black Locust Presentation

While some people scoff at the idea of using wood to build a bridge in NYC, Zoli shows that wood can be used as an excellent structural member under compression; with Black Locust being twice as strong as concrete, but significantly lighter.

While Black Locust is not like the other woods that grow in the US, it does have some challenges. As of now, it’s not a highly cultivated crop in the US. Eastern European countries, like Hungary, imported and planted vast groves of Black Locust 300 years ago and have since then selectively bred and cultivated it into a high-yield crop.

This is what convinced Van Valkenburgh and his team of the viability for Black Locust, “The ‘A-ha!’ moment finally came when Izabela Riano went to Hungary last spring,” he says, “and documented the extent of the locust industry there.” Riano, as representative of Michael Van Valkenburgh Associates, showed how Hungary is an immediate source for Black Locust that can be used in their practice while they encourage the expansion of domestic harvesting.

By comparison, Stephen Noone of Michael Van Valkenburgh Associates, Inc. showed images of Black Locust groves in the wild and Black Locust nurseries in Hungary– tall straight trees that are ideal for harvesting. Here is an image that shows the potential of Black Locust crop in the US.

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Source: ASLA Black Locust Presentation

The bottom line? Black Locust as a domestically grown product (good for the economy), it’s durable and beautiful (good for product design), and it can help reduce the use of rainforest hardwoods, preventing the destruction of tropical rainforests (good for the environment). The landscape architect is taking the first steps.  “We will be using locust harvested in Hungary to build a new garden fence and deck at the Cambridge office of Michael Van Valkenburgh Associates.”

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