Mass timber requires sustainably managed forests

At the International Mass Timber Conference last month in Portland, Jason McLennan of McLennan Design, the architect who designed the Bullitt Center in Seattle and the creator of the stringent green building certification the Living Building Challenge, gave a keynote address. In his speech, he stated that he believes we are at a tipping point where wood construction will take over the commercial building industry much the way the automobile replaced the horse and buggy in the early 20th century.   But there is a catch. Jason says that for this to happen, architects need to know that forest management practices are sustainable. For general information on mass timber construction in Oregon, review recent and future blogs by Director of Forest Products Timm Locke. For a discussion of whether Oregon forests are being sustainably managed, read on.

So what is sustainable forest management, and why does it matter? The earliest definition of sustainable forest management was based on sustained yield. One widely accepted definition of sustained yield is that harvest should not exceed growth in the long term. The following figure from Oregon Forest Facts 2017-18 shows growth, harvest and mortality for the various ownership classes of Oregon forestland. When harvest plus mortality is less than total growth, we have sustained yield.

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Overall, Oregon timber harvest plus mortality equals about 62 percent of wood volume growth for the 2011-2015 period, according to U.S. Forest Service Forest Inventory and Analysis data. All ownership classes are also individually at a place where harvest plus mortality is less than total growth. For private forests, harvest plus mortality equals 86 percent of growth. For state forests, harvest plus mortality equals 76 percent of growth. And for federal forests, harvest plus mortality equals only 38 percent of growth.

At first glance, all forest ownership classes in Oregon are sustainable in terms of timber harvest, but a sustainable forest needs to be a healthy forest. Many federal forests in Oregon are overstocked with trees. When mortality is 29 percent of growth, this is not a healthy forest. When harvest plus mortality equals only 38 percent of growth, the overstocking will get worse over time, which leads to an unhealthy forest with an increased risk of severe fire and insect attack.

A more recent definition of a sustainable forest that is used by independent, third-party forest sustainability certification programs would be “a living complex system that includes a diversity of species along with a balanced production of environmental, social/cultural and economic benefits.” Forest certification systems such as the Sustainable Forestry Initiative (SFI), American Tree Farm System (ATFS) and the Forest Stewardship Council (FSC) are the three forest certification systems that are commonly used in Oregon. These systems document how well forests meet the systems’ sustainability criteria.

The table below shows the acreage certified in Oregon under the various systems. SFI is the largest, and many of the large private landowners have their forestlands certified, for a total of almost 4 million acres. ATFS is the system preferred by smaller private landowners, with a total of about 800,000 acres certified. FSC is used by some small woodland owners and by conservation groups that own forestland, for a total of less than 200,000 acres in Oregon. Public lands in Oregon are typically not certified.

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One conclusion I reach with this data is that Oregon forests are in good shape from a sustainability standpoint. This could be one of the reasons we are a leader in the mass timber movement – and that is definitely not “horse and buggy” thinking.

For the forest,

Mike Cloughesy

Director of Forestry


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