Long-term spatial organization of understorey vegetation in boreal Pinus sylvestris stands with different fire histories

We examined the composition and spatial structure of the understorey vegetation at two sites with different fire histories in a mature Pinus sylvestris L. forest in eastern Finland. The entire study area had regenerated after a fire in the early 19thcentury. Besides, a part of the area was subsequently hit by a surface fire in 1906, which divided the study area into two parts. Vegetation and environmental variables measured from the these two parts, the 1800+ burn site and the 1906 burn site, have considerably different spatial pattern. Deciduous shrubs and ground layer, consisting primarily of bryophytes, had a more distinct patch structure at the 1800+ burn site than at the 1906 burn site, while with lichens the situation was the reverse. Cover of the field layer, dominated by evergreen shrubs, was significantly higher at the 1800+ burn site than at the 1906 burn site. At both sites, the spatial pattern of plant functional types was obviously strongly regulated by the spatial influence of living trees. Gradual formation of strong clonal patch structures of V. myrtillus, V. vitis-idaea and mosses, seems to be another important process affecting the properties of the understorey vegetation. The post-fire recovery of the understorey community was slow: in the 1906 burn site, the community composition and spatial structure were still in transition after almost 90 years since the last fire.