Old Growth in BC

Highlights

The BC government defines “old growth” on the coast as forests older than 250 years, but old forests have unique ecological characteristics that aren’t considered in this definition.
The BC provincial government states that about 13 million hectares of the 50 million hectares of forested land in BC is old growth. However, 80% of these 13 million hectares is considered low productivityForest site productivity is the capacity of a forest to generate products (e.g., wood or biomass) on a certain site with a given tree species and a specified management regime. Site productivity depends both on natural factors inherent to the site and on management-related factors. and includes subalpine and bog forests and is expected to grow relatively small trees. This means that only 20% of the 13 million hectares the government considers old growth – i.e., 2,600,000 hectares – is productive old growth.

Old Growth Defined

The B.C. government’s current working definition for old growth forest is based on stand age, which is estimated from aerial photographs as well as on the ground inventory sampling. Forests of wet coastal and wet belt interior regions of the province are considered old growth if they include trees more than 250 years old. In dry interior forests, where tree species tend to be shorter-lived and stand-replacing wildfires and insect outbreaks are more frequent, old growth is generally defined as older than 120-140 years (Province of B.C., 2003Province of B.C. 2003. British Columbia’s forests: A geographical snapshot.).

However, an old growth forest is much more than a stand of old trees. Old growth is fundamentally an ecological concept and the simple working definition based on stand age does not consider structural and compositional attributes of the forest. Defining old growth without assessing structure may fail to identify the most biologically important forests (Braumandl and Holt, 2000Braumandl, T., Holt, R. 2000. Redefining definitions of old growth to aid in locating old-growth forest reserves. In Proceedings, From Science to Management and Back: A Science Forum for Southern Interior Ecosystems of British Columbia. C. Hollstedt, K. Sutherland, T. Innes, eds. S. Int. For. Ext. & Res. Partnership. p. 41–44.). Definitions should be based on multiple criteria, including tree age and size, disturbance pattern, forest structure and composition, and minimum area (B.C. Ministry of Forests, 1990British Columbia Ministry of Forests. 1990. Old-growth forests: problem analysis. Research Branch, Victoria, BC. 135 p.). The ecological uniqueness of old growth is well studied and widely recognized in BC. (MacKinnon, 1998MacKinnon A. 1998. Biodiversity and old-growth forests. In: Voller, J and S. Harrison, eds. Conservation biology principles for forested landscapes. UBC Press, Vancouver, British Columbia. pp. 146–184.; Hilbert and Wiensczyk, 2007Hilbert, J., Wiensczyk, A. 2007. Old-growth definitions and management: A literature review. BC J. Ecosyst. Manag. 8:15–31.; Gorley and Merkel, 2020Gorley, A., Merkel, G. 2020. A new future for old forests: A strategic review of how British Columbia manages for old forests within its ancient ecosystems.; Price et al., 2020Price, K., Holt, R., Daust, D. 2020. BC’s Old Growth Forests: A Last Stand for Biodiversity.). See the ecological values of old growth forests to learn more.

Amount of old growth forest in BC

The BC provincial government states that about 13 million ha (26% of the 50 million hectares of forested land) in BC is old growth based on provincial definitions of age >250 years on the coast and >120-140 years in the interior ().

However, stratifying the current amount of old growth in B.C. by reveals that:

About 80% of it (10 million ha) has low productivityForest site productivity is the capacity of a forest to generate products (e.g., wood or biomass) on a certain site with a given tree species and a specified management regime. Site productivity depends both on natural factors inherent to the site and on management-related factors. (site indexSite Index is a measure of the land’s productive potential for a particular tree species and is expressed as potential tree height at 50 years breast-height age. Breast-height age is the number of years required for a tree to grow from breast height (1.3 m above ground level) to its current height. Site index provides a standardized comparison of productive potential between sites, across a broad range of existing site conditions. <15 m), including subalpine and bog forests, and is expected to grow relatively small trees.
Only 8% of high-productivity sites (site indexSite Index is a measure of the land’s productive potential for a particular tree species and is expressed as potential tree height at 50 years breast-height age. Breast-height age is the number of years required for a tree to grow from breast height (1.3 m above ground level) to its current height. Site index provides a standardized comparison of productive potential between sites, across a broad range of existing site conditions. >20 m) in BC are old.
Less than 1% of BC’s forests (415,000 ha out of 50 million ha) support high-productivity old growth (site indexSite Index is a measure of the land’s productive potential for a particular tree species and is expressed as potential tree height at 50 years breast-height age. Breast-height age is the number of years required for a tree to grow from breast height (1.3 m above ground level) to its current height. Site index provides a standardized comparison of productive potential between sites, across a broad range of existing site conditions. >20 m).
Less than 0.1% (36, 00 ha) of forested land in BC supports very high productivity old growth (site indexSite Index is a measure of the land’s productive potential for a particular tree species and is expressed as potential tree height at 50 years breast-height age. Breast-height age is the number of years required for a tree to grow from breast height (1.3 m above ground level) to its current height. Site index provides a standardized comparison of productive potential between sites, across a broad range of existing site conditions. >25 m).
Of the 415,000 ha of high productivityForest site productivity is the capacity of a forest to generate products (e.g., wood or biomass) on a certain site with a given tree species and a specified management regime. Site productivity depends both on natural factors inherent to the site and on management-related factors. old growth, 108,000 ha is protected (e.g., in parks).
On the coast, only 10% or less of high-productivity forests are old, whereas more than half of low-productivity forests are old.

Future of old growth in BC

Populations of large old trees are critically declining in many ecosystems across the world () including BC. Intact old growth in BC has been described as being essentially irreplaceable and non-renewable (). As climate warms, regenerating forests of today will not replace the old growth stands that have been logged or removed. Pojar (2021) notes that some of today’s secondary forests could become centuries old (e.g., if managed under extended rotations) but future old forests will have a new mix of species and different soils and disturbance regimes compared to contemporary old growth forests.