Forest fire histories and tree age structures in Värriö and Maltio Strict Nature Reserves, northern Finland

Wildfires virtually disappeared from the Fennoscandian forests in the 20th century, but have left persistent legacies in forest structure. Here, I reconstructed past fires in three northern boreal landscapes (each 2 km x 2 km) from fire scars, and described the fire regime for the past 300 years. The average fire cycles (1700–1999) were 72 and 156 years in Pinus sylvestris-dominated landscapes, and 579 years in a Picea abies-dominated landscape. At the site level, the number of fires was clearly related to soil hydraulic properties. Age structures from 1800 live and dead trees showed strong cohorts associated with large fires in two of the landscapes. Although tree growth and regeneration in sub-arctic regions are considered highly climate-sensitive, fires have been a major driver of forest dynamics in these areas. Continued absence of fires will lead to considerable changes in the forest structure and species composition in the future.