Post-fire species composition and regeneration of understory vegetation in a boreal forest in central Sweden

Post-fire survival, composition and regeneration of understory species in the boreal forest have shown to be affected by several factors, where consumption of the organic soil layer together with altered soil properties play important parts. There has however also been shown that the pre-fire site characteristics affect the post-fire understory vegetation. This study aimed to investigate the effects of fire and pre-fire site characteristics on understory regeneration and composition at a local scale in a boreal forest. Classification of species richness of the understory species together with measurements of biomass in terms of leaf area index (LAI) and normalized difference vegetation index (NDVI) were performed in a Pinus sylvestris forest in the Gärsjön catchment area, three years after a stand-replacing wildfire. Data of site index, fire severity on soil and moss, fire severity on shrubs, stand age, and remaining humus depth were also used. A total of 36 species of vascular plants (10 forbs, 14 graminoids, 5 dwarf shrubs, 2 ferns, 1 shrub and 4 trees) together with 3 species of bryophytes were recorded in the area. The study revealed that understory species composition was explained by remaining humus depth and site index. The regeneration of the understory was affected differently, where LAI was affected by site index, and NDVI was connected to both site index and fire severity on soil and moss. LAI and NDVI differed in their sensitivity in capturing differences among plant species, where higher values of LAI were associated to species such as E. sylvaticum, P. erecta, C. arundinacea and J. conglomeratus, while NDVI was related to both the ground and field layer, with high values associated to a high abundance of C. canescens and C. ovalis. According to my result, it can be concluded that NDVI is a more appropriate measure of post-fire re-establishment and recovery of understory vegetation in the boreal forest.