Organizers of last week’s International Mass Timber Conference in Portland, Ore., devoted a whole track of the three-day event to environmental and sustainability aspects of the mass timber sector — an indication of the importance of sustainability to the tall timber building brand.
Manufacturing of cross laminated timber, or CLT — the product used to construct tall timber buildings — has the potential to revitalize the timber sector and the rural communities in Oregon that have fallen on hard times because of the widespread closure of timber mills across the state, reports Oregon Business.
But experts concede the environmental benefits of CLT are complex and difficult to measure.
Structural engineers look at the lifecycle emissions of CLT when assessing the environmental impact of tall timber buildings. The lifecycle analysis takes account of the greenhouse gas emissions from the harvesting of the wood, through the manufacturing and construction of tall timber buildings, to their eventual demolition.
When taking this cradle-to-grave assessment, the environmental benefits of CLT are not clear.
A set of newly published studies evaluated nearly forty years of data on the impacts of biomass utilization on soil, tree, and plant recovery and found minimal impact using certain forest harvesting techniques.
The experiments, initiated in 1974, were conducted by scientists from the U.S. Forest Service Rocky Mountain Research Station on the Coram Experimental Forest, located in Northwestern Montana. In order to evaluate the ecological consequences of large-scale biomass harvesting, scientists implemented three different tree removal techniques on the landscape – group selection (remove small groups of trees), clearcut (remove all timber), and shelterwood (retain some trees for shade and structure) – all using cable logging. On all three sites the soil was left relatively undisturbed from the harvesting and varying amounts of downed wood were left to promote soil organic matter and wildlife habitat. For some sites, prescribed fire was applied to reduce fuels and fire danger. Scientists then tracked these sites over 38 years to provide a contemporary look at the long-term impacts of biomass utilization on forest productivity (e.g., tree growth).