Black walnut (or American walnut) has a fine figure and quality. Its dark color makes it a prized alternative for many tropical timbers. As walnut trees become rarer in the wild, where it provides food for many birds and mammals, we had to ask: How sustainable is it to buy products made out of black walnut?

Black walnut wood is a sustainable material thanks to trees’ carbon sequestration, carbon storage in furniture, which are generally long-life, and carbon offset upon recycling. In addition, agroforestry can increase the value of land used for growing black walnut, sustaining the logging industry. 

In this article, we’ll go through the life-cycle of black walnut wood used for furniture and other household items. Then, we evaluate its sustainability, potentials, and shortfalls. And in the end, we’ll show you tips for buying sustainable walnut.  

Here’s How Sustainable Black Walnut Wood Is

Black walnut is a highly prized wood for fine furniture and veneer. This beautifully colored wood has exceptional durability and a great value at the end of life, making it a sustainable material.

“Sustainable: The ability to be maintained at a certain rate or level | Avoidance of the depletion of natural resources in order to maintain an ecological balance”

Oxford Dictionary

To understand the sustainability of black walnut wood, we assess the life-cycle of furniture products, such as shelves or cabinets. This life-cycle assessment (LCA) is a method to evaluate the environmental impacts of each stage in a product’s life-cycle, from the making to the recycling. Over the years, companies have strategically used LCA to research and create more sustainable products. 

In this article, we’ll use the cradle-to-grave perspective of the LCA, examining the five stages of the life-cycle of furniture made with black walnut wood. 

We can say that black walnut wood is sustainable. However, the actual environmental impact of a particular product, like a shelf or a cabinet, depends on many factors, especially the distance and mode of transportation. Let’s dive deeper into each stage and find out how it can be more sustainable. 

How Sustainable Is the Growing Black Walnut Wood

Growing black walnut is sustainable thanks to its potential for carbon sequestration (the capturing and storing of carbon), diverse land use, and its ability to reproduce naturally, sustaining the growing stock. 

What Type of Wood is Black Walnut and What Does This Mean for Sustainability

Black walnut is a hardwood tree with edible fruits and valuable wood. The black walnut species grows at a medium rate. In the best sites, young black walnut trees can grow as much as 36 to 48 inches per year. However, growth slows down as walnut trees mature. 

How Sustainable Does Black Walnut Wood Grow

Growing black walnut for making furniture is sustainable because of walnut trees’ carbon sequestration and their ability to reproduce naturally, sustaining the growing stock. Besides, the land can be used for multiple crops when choosing the right combination. 

The following section zooms into three reasons why growing black walnut can be sustainable:

• Carbon sequestration: Walnut trees can reach 100 to 150 feet in forest conditions where they have to compete for light with other species like oak or maple. The crown can grow very wide, as much as the height of the tree. Their large size means significant carbon sequestration over their lifetime, which is average at 150 years (with some black walnut trees live up to 400 years when the environment is perfect for their growth).
• Agroforestry land usage: In plantations, walnut trees are grown in widely-spaced rows because of their big crown. Then, there is an opportunity for agroforestry, growing other crops in-between trees. It could be pasture crops for harvesting or livestock grazing. Other high-value crops include raspberries or blueberries. After a few years, the walnut trees produce nuts, which is also a profitable harvest. Multi-cropping makes better use of the land while increasing the profits of planning walnut trees.
• Sufficient growing stock: The growing stock of black walnut is fairly sufficient, with a yearly 2.4 million m³ of black walnut accumulated in the forests even after harvesting. However, black walnut is not as available as, for example, white oak. The U.S. forests take 1.57 seconds to grow 1m³ of white oak but 13.09 seconds for 1m³ of black walnut. Still, it would take less than two seconds for new growth in the U.S. forest to replace the walnut wood needed for making a shelf.

Where Is Black Walnut Wood Usually Grown

Black Walnut (or American Walnut) is widely distributed in the eastern United States. Another walnut species prized for its wood is found in Europe and recognized as English Walnut (or Common Walnut). 

In mixed forests, black walnut trees can inhibit many plants’ growth around the trees, either through taking up all the light or emitting a toxic substance called juglone via their roots and leaves. However, its fruits and leaves feed a variety of birds and mammals. Black walnuts produce mast crops (large numbers of drupes) on average twice every five years. The mast makes up a significant part of the diet of mammals like eastern fox squirrels. 

Illegal logging of black walnut in the U.S. is unfortunately not non-existent because the wood has long been prized for fine furniture and veneer for its attractive color and extended durability. 

Improperly managed logging (including illegal activities) can cause many problems for forest equality and diversity. One example is when loggers only cut down the biggest and tallest trees. That pattern would cause a reduction in the genetic diversity and quality of the trees within the stand, leading to gradual degradation of tree quality. 

The best way for you to tackle problems caused by illegal logging on an individual level is to make sure that the black walnut of your desired products is sourced sustainably. We will point you in the right direction with black walnut in a later section. 

In total, logging of forestry products from plantations accounts for 26% of forest loss, which is a combination of deforestation and forest degradation. However, the loss in bio-diverse forests in tropical climates is more significant (and sometimes less properly recorded) than in temperate, well-managed logging forests. 

How Sustainable Is the Manufacturing of Black Walnut Wood

Turning black walnut wood into furniture has a relatively low carbon footprint because wood waste can be recycled fully as by-products or biomass pellets to offset the carbon emissions during harvesting and processing. 

The first step of manufacturing black walnut furniture involves cutting down trees and turning them into lumber in a sawmill. The carbon emissions here come from electricity usage. 

The next step is to dry lumber and turn it into furniture. Black walnut dries fairly fast, three times faster than slow drying woods like oak or hickory. It means a low energy consumption for kiln drying. Besides, a high proportion of energy can come from burning wood waste. At least 90% of all thermal energy used for kiln drying in the U.S. hardwood sector is derived from biomass.

In one calculation, total emissions material extraction and processing, manufacturing, and transporting a walnut shelf in the U.S. to the U.K. amounts to 59 kilograms of CO₂ equivalent. In this production, carbon offset is 63 kilograms coming from the substitution of fossil fuels through the reuse of wood waste. It means the black walnut shelf is carbon negative. 

How Sustainable Is the Transportation of Black Walnut Wood

Transporting is a carbon-intensive stage in the life-cycle of black walnut furniture due to the emissions associated with operating the hauling vehicles that take timber to sawmills and factories, then furniture to stores.   

The actual emission during this stage depends on the type of vehicles used, the fuel they need, and the distance the wood travels. Calculations made by the Norwegian Forest and Landscape Institute showed that smaller wood hauling trucks emitted more CO₂ per transported cubic meters of timber: 1.25 times more than larger wood hauling trucks, 1.3 times more than sea vessels, and six times more than freight trains. The cost efficiency is higher when the distance increases and emissions are reduced when using biofuels. 

Let’s make the massive impact of transportation on the sustainability of wood more concrete: In one calculation, transporting a black walnut shelf from the U.S. to the U.K. would account for 50% of the total CO₂ emission. One more reason to ensure that your wood is sourced locally – especially when it’s so readily available as black walnut wood.

Typically, the sustainable options would be locally manufactured walnut furniture, transported by rail or large trucks using biofuel. 

How Sustainable Is the Usage of Black Walnut Wood

Using walnut wood furniture can be sustainable thanks to the carbon capture during the products’ long life. 

Black walnut wood is highly durable and rot-resistant. Its straight, dark, heavy, strong, fine-grained heartwood makes fine furniture. As the price goes up, it is increasingly used for veneer. Black walnut furniture lasts for a long time, contributing to black walnut wood being a sustainable material. 

When wood is decayed, either naturally in the forest or because of damage caused by usages at home, the carbon stored in the wood is released back to the atmosphere. Therefore long-lasting furniture can be considered as a good way of keeping the carbon out of the atmosphere. If the wood is then reclaimed for making another piece of furniture, its positive carbon storage environmental impact is even higher. 

How Sustainable Is the End-of-Life of Black Walnut Wood

The end-of-life stage for black walnut furniture is sustainable when the wood is reused or burned as a bioenergy. 

There are a few scenarios for wood products – furniture, flooring, and household items – at the end of their life. 

They can end up in landfills and don’t decompose. In this case, it keeps its role as carbon storage. 

Wood products can also be upcycled and reused, extending their role as carbon storage and reducing the CO₂ emitted as much as four times when comparing, for example, a recovered hardwood flooring with a new one. 

In another end-of-life scenario, products like a black walnut door can be burned for biomass energy displacing coal or natural gas in generating electricity. In one calculation, the carbon offset is more than the total carbon emissions for a black walnut shelf. Half of the amount comes from manufacturing waste and the other half from end-of-life recycling. 

With smaller household items, like a doorknob or a small chair, the offset won’t be as high as there is much less waste for burning. However, if such products are made from manufacturing wood waste as by-products, their carbon footprint is minimal.  

How Can You Buy Black Walnut Wood More Sustainably

The key to sustainably buying any wood is to check on relevant environmental and original certifications. Reliable certifications for sustainable woods are: 

• Forest Stewardship Council: 

An FSC certification ensures that the black walnut wood comes from responsibly managed forests that provide environmental, social, and economic benefits.

• Program for Endorsement of Forest Certification: 

PEFC’s approaches to sustainable forest management are in line with protecting the forests globally and locally and making the certificate work for everyone. Getting a PEFC certification is strict enough to ensure the sustainable management of a forest is socially just, ecologically sound, and economically viable but attainable not only by big but small forest owners. 

Why Is It Important to Buy More Sustainable Wood

Buying sustainable wood also means helping to prevent illegal or unsustainable logging, which harms the forests’ biosystems and accelerates climate change. 

Logging of forestry products from plantations accounts for 26% of forest loss. Cutting down trees for wood has a lesser impact on carbon storage than digging up the whole forest floor and turning it into farms or mines. However, if logging is not sustainably managed, it can badly damage wildlife.

When logging happens in tropical forests – the bio hotspots of our planet – the biodiversity loss can be much more damaging. Subtropical and tropical forests are packed with unique wildlife – endemic mammals, birds, and amphibians. The displacement of such wildlife during poorly managed logging would be a major contributor to global biodiversity loss. 

Sustainable management of forests also means that trees are cut down for timber only when they are mature. These trees will then be able to regrow and eventually replace the loss of canopy, absorb carbon from the atmosphere and reduce the effect of climate change.

Final Thoughts

Making furniture from black walnut wood is sustainable as long as the material comes from sustainably managed forests. A sustainable approach would be to use any black walnut furniture for a long time, upcycle the material to extend its usage, and arrange for it to be fully recycled – or, even better, upcycled.

Stay impactful,

Sources

• Science Direct: Life-cycle assessment (LCA)
• MIT SMR: Strategic Sustainability Uses of Life-Cycle Analysis
• European Environment Agency: cradle-to-grave
• U.S. Forest Service: Black Walnut
• Association for Temperate Agroforestry: Eastern Black Walnut and Agroforestry
• Impactful Ninja: How Sustainable Is White Oak Wood? Here Are the Facts
• American Export Hardwood Council: American Hardwood’s Life Cycle Assessment Tool
• American Hardwood: Environmental Life Cycle Assessment
• ALDERLEAF Wilderness College: Black Walnut Tree
• MILWAUKIE HARDWOODS: Drying Lumber
• Science Norway: Larger logging trucks give less CO₂ emissions
• FOREST LEGALITY INITIATIVE: Black Walnut
• Research Gate: Life cycle primary energy and carbon analysis of recovering softwood 
• Forest Stewardship Council
• Program for Endorsement of Forest Certification
• Our World in Data: Epidemic Mammal Species