Understorey vegetation data of drained Picea abies peatlands in Finland

Understorey vegetation data of drained Picea abies peatlands and an example of SPSS syntax used in the article by Hotanen et al. in Silva Fennica. The study monitored the changes in the abundance of the species and species groups after selection harvesting of uneven-aged peatland stands. The aim was to understand the impact of selection harvesting on the understorey vegetation in drained Picea abies peatlands. The study experimentally examined changes in the abundance of plant species and species richness caused by selection harvesting of varying intensity. The study sites included four drained peatland sites located in the southern boreal zone in the municipalities of Janakkala, Multia, Heinävesi, and Juuka in southern Finland. On three study sites, two different thinning intensities were tested (with remaining stand basal areas of 12 m²ha⁻¹ and 17 m²ha⁻¹) and on the fourth ste (Multia), an intensity after which the stand basal area was 13 m²ha⁻¹. The spruce-dominated stands on the experimental plots were thinned to the target basal area so that the remaining stand included trees of various sizes, the emphasis of the harvest removal was on the upper half of the diameter distribution. The experimental plots were herb-rich and Vaccinium myrtillus drained peatland forest types. Vegetation was inventoried on each experimental plot from 15 systematically placed 1 m² vegetation squares before cutting in 2016, and two and six years after cutting in 2018 and 2022. Two-way repeated measures ANOVA was used to determine the effect of harvesting intensity and time since harvesting on the percent cover of the species or species group and the number of species. The models were fitted, and the marginal means were estimated using the UNIVARIATE procedure in IBM SPSS Statistics 29 (IBM SPSS Inc., Chicago, IL, USA). To achieve normality and homogeneity of variances, the percent covers were log-transformed prior to analysis. Post hoc least significant difference (LSD) pairwise comparisons of the estimated marginal means were done for multiple comparisons.