Forest disturbance from timber harvesting or wildfire may impact aquatic environments by increasing soil erosion, stream flow and nutrient loading through watershed systems.
*The greater commercial forest zone includes the commercial forest zone, Cold Lake Air Weapons Range and federal and provincial parks within and adjacent to the commercial forest zone.
What we are doing
Equivalent clearcut area (ECA) is a measure of the relative loss and recovery of hydrologic function for a forest canopy. Hydrologic function concerns the condition of water, including the quality, the quantity, when and how quickly water moves through a watershed. Typically, the greater the ECA, the greater the potential for changes to the natural hydrology of an area.
Experimental watershed studies indicate that flow increases are minimized when the equivalent clearcut area is limited to no more than 20 to 25 per cent in aspen-dominated watersheds, and 30 per cent in coniferous dominated watersheds. Hardwood forest stands can take up to 15 years, and softwood forests 35 years, to regain full evapo-transpiration and interception capacity following the harvest of cutblock.
Of the 29 watersheds in Saskatchewan, nine are found within Saskatchewan's greater commercial forest zone. Within those nine watersheds, 36 sub-watersheds intersect the commercial forest zone.
As of 2017, the equivalent clearcut area across the greater commercial forest zone averaged 17 per cent when wildfire and harvest area were considered. For the three preceding 10-year periods (2007, 1997 and 1987), equivalent clearcut area averaged 12 per cent, 12 per cent, and 5 per cent, respectively.
As of 2017, of the 36 sub-watersheds in the greater commercial forest zone, all but eight were below the 20 per cent equivalent clearcut area threshold for flow increases. Five of these eight sub-watersheds had the majority of their area outside of the commercial forest zone. In these cases, it is difficult to assess the true equivalent clearcut area because data for the majority of these sub-watersheds is incomplete.
The three remaining sub-watersheds had equivalent clearcut areas above the 20 per cent threshold and may actually see increases in flows. These three sub-watersheds are found within the Churchill River watershed and the Saskatchewan River watershed. In all of these cases, wildfire was the greatest contributor to equivalent clearcut areas. Harvesting contributed one per cent or less to the overall equivalent clearcut area.
When forest harvest disturbances are considered on their own, equivalent clearcut area is considerably less. As of 2017, the equivalent clearcut area within the greater commercial forest zone averaged two per cent when the harvest area alone was considered. For the three preceding 10-year periods (2007, 1997, and 1987), equivalent clearcut area averaged two per cent, two per cent and one per cent, respectively. Of the 36 sub-watershed within the commercial forest zone, none exceeded a 10 per cent equivalent clearcut area.
Roads and water crossings were not considered in this analysis, though they are an important forest disturbance. Currently, year of construction and year of reclamation data for roads within the commercial forest zone is incomplete.
Why it matters
The impacts of wildfire suppression strategies and the occurrence of large and frequent wildfires in recent years are apparent in the northern reaches of the commercial forest zone. For the 10-year period ending in 2017, sub-watershed equivalent clearcut areas show an increasing trend as one moves northward towards the commercial forest zone's northern boundary. This trend is less pronounced when the equivalent clearcut area is considered for 10-year periods ending in 2007, 1997, and 1987.
When wildfire and harvest areas are combined, the watershed health trend appears to be deteriorating based on an equivalent clearcut area analysis. As of 2017, the equivalent clearcut area within Saskatchewan's greater commercial forest zone averaged 17 per cent when wildfire-burned and harvested areas were considered. However, when harvest areas alone are considered, the watershed health trend appears to be more stable based on this equivalent clearcut area analysis. As of 2017, the equivalent clearcut area within Saskatchewan's greater commercial forest zone averaged two per cent when harvested areas alone were considered. This indicates that forest harvest practice, in the greater commercial forest zone, is consistently below the industry threshold of 20 per cent equivalent clearcut area. This implies that forestry harvest practices are a low threat to the natural flow within these watersheds.