When I first started my job in the 1980s with the forest inventory section of the Ministry of Forests our field projects took place on public sustained yield units (PSYU) which had the latest air photos. In the 1970s the province had been organized into six regions which were broken down into timber supply areas (TSAs).
In the case of the Cariboo region there were the three TSAs based on the anticipated flow of logs to the main lumber processing facilities in Quesnel, Williams Lake and 100 Mile House. The chief forester was assigned the task of determining the allowable annual cut (AAC) of each TSA which had completed the most recent inventory.
The determination was reliable for a decade or more unless there was a major change to the original timber harvest land base (THLB) of the TSA. Unfortunately the Cariboo has had a number of events like forest insects attacks and wildfires that have impacted our original AAC determinations and necessitated a review.
I have included highlights of the “Impacts of 2021 Fires on Forests and Timber Supply in British Columbia “ published in April of 2022.
“The areas affected by wildfires in 2017 (1.2 million hectares), 2018 (1.3 million hectares) and in 2021 (0.9 million hectares) were the three largest in 102 years of recorded wildfire history in B.C.
The 2017 fires were mostly in the Central Interior of the province with three timber supply areas (TSA) (Quesnel, Williams Lake and 100 Mile House) accounting for about 80 per cent of the area affected. The 2018 fires were spread across the Northern Interior of the province with six TSAs (Cassiar, Lakes, Great Bear Rainforest North, Prince George, Fort Nelson, and Morice) accounting for about 73 per cent of the area burned.
The 2021 fires were scattered across the Southern Interior of the province with five TSAs (Kamloops, 100 Mile House, Okanagan, Lillooet and Merritt) accounting for about 54 per cent of the area burned. Three tree farm licences (TFL) (TFL 23, TFL 49 and TFL 59) account for a further 10 per cent of the area burned in 2021.
Almost all of these management units had previously experienced significant levels of lodgepole pine mortality during the mountain pine beetle epidemic. Wildfires occurred on the timber harvesting land base (THLB) as well as the non-THLB.
The THLB area within the fire perimeters was 700,000 hectares in 2017 (58 per cent of total area), 300,000 hectares in 2018 (23 per cent of total area) and 419,500 hectares in 2021 (54 per cent of total area). Within a fire perimeter some of the trees are completely burned, some can be salvaged for lumber production and some areas remain unburned.
To guide salvage operations after the 2017 fires, the ministry published Post-Natural Disturbance Forest Retention Guidance. Since the areas affected by wildfires were also significantly affected by the mountain pine beetle, the document focused on what forested areas should be reserved from harvest to protect non-timber values rather than on salvaging whatever remained in the fire perimeters.
In any management unit, the allowable annual cut (AAC) for the unit is directly related to the amount of timber on the THLB. After the 2017, 2018 and 2021 wildfires, staff from the Forest Analysis and Inventory Branch (FAIB) updated the forest inventories and assessed the timber supply projections for the most severely affected management units.
These assessments were done to determine whether the AAC for those management units needed to be revisited by the chief forester sooner than expected due to timber volume losses attributable to fires. To update the forest inventories, the following actions were taken: fire severity mapping was completed, ground sampling to estimate timber volume losses by severity class were completed, forest inventories were updated to account for timber volume losses using both the fire severity mapping and information from the ground samples.”
FAIB has determined that wildfires during the past five years do not pose a risk to timber supply for the coast and northern TSAs. The most recent timber supply reviews for the Lakes and Okanagan TSAs have accounted for wildfires which have occurred during the past five years. Timber supply reviews which will account for all past wildfires are underway for the 100 Mile House, Lillooet, Quesnel and Williams Lake TSAs.