The construction industry produces about 40% of the world’s atmospheric carbon, as a consequence of the high heats needed to manufacture concrete and steel. Mass timber is seen as a sustainable solution to reducing the carbon footprint associated with building construction. Timber logging, however, has its own negative impacts on the environment. Trees sequester atmospheric carbon, but are they as effective in doing so if they are regularly cut in logging rotations?
The results of this study on the deforestation of tropical forests show that carbon absorption and storage are heavily decreased for at least 10 years after logging.
Timber groves that are replanted for future logging generally consist of a monoculture of trees that do not function nearly as well as natural forests. They are not well-suited as habitat for animals and insects and lack the underbrush and down woody debris that add nutrients back into the food web and are representative of a healthy forest.
FSC Certified Forests
Sourcing timber from FSC certified forests can be one potential solution to more sustainable timber sourcing. FSC forests must meet a set standard of principles. A specific forest management plan is created for each individual forest and forests are surveyed regularly to insure the FSC principles are adhered to. Studies that have surveyed the environmental, social, and economic outcomes of FSC certified forests have found positive results as illustrated below.
Creating engineered timber products from hardwood lumber has potential to be a method in which parts of the world that are not located near softwood trees can source their timber. The American National Standard for Performance-Rated Cross-Laminated Timber (PRG) does not currently include hardwood species to prepare lamella (lumber used in the production of CLT). Only 10% of sawmills have the resources to produce standard grade hardwood lumber.
Researchers from Virginia Tech produced CLT panels from National Hardwood Lumber Association grade wood. They then conducted strength tests following American Plywood Association procedures. Preliminary studies have shown there is ample evidence to support the viability of CLT hardwood production. Yellow Poplar CLT exhibited 30 times higher CLT strength values than that of Yellow Pine.
Researcher recommendations include:
- Recognizing hardwood lumber by the PRG 320 standard
- Including hardwood CLT in the PRG 320 standard
- Producing commercial SGHL (standard grade hardwood lumber)
- Operating CLT mills in areas where hardwood is abundant
Another potential solution to finding more sustainable timber sourcing methods is to use salvaged timber to create engineered wood products. This can include timber from wildfire mitigation operations, in which trees are cut to decrease the potential hazards associated with wildfires, as well as from forests that have been impacted by insect or fungal outbreaks.
Researchers at Michigan Technology University tested the flexural and shear performance of CLT made from White Spuce salvaged from a recent budworm outbreak. They made CLT panels from 3 categories of salvaged, beetle-killed White Spruce.
Category 1: Includes live trees with any amount of green foliage
Category 2: Dead-standing trees that have assumed to have died relatively recently
Category 3: Dead-standing trees assumed to have been dead for some time
The results show that the amount of structural degradation in the trees that were impacted by the budworm infestation was quite negligible. This study illustrates the potential for salvaged timber use in the production of CLT panels.
Mass timber has a lot of promise in offering sustainable solutions to the carbon output of the construction industry. However, the sustainability of timber depends on the methods of sourcing. As further studies are published, we are offered more sustainable ways for timber sourcing and creating engineered wood products. Once a demand is created, the timber industry will catch up and these solutions will become more commonplace options.