Multidimensional site description of peatlands drained for forestry

Abstract

Sites (n = 119) on drained mires located in the southern aapa mire zone in Finland were analysed by multivariate techniques. The compositional trends of the understorey vegetation were analysed by means of hybrid multidimensional scaling (HMDS). In addition to field classification, two-way indicator species analysis (TWINSPAN) and flexible unweighted paired group arithmetic average (FUPGMA) classifications were used. The 1st HMDS dimension primarily reflected variation along a gradient from spruce mire influence to hummock-level bog influence. Variation in nutrient status was also connected to this gradient. Factors underlying the 2nd dimension were variation in nutrient status and drainage succession (moisture). Some sample plots representing herb-rich or Molinia-rich types were separated along the 3rd dimension. The variation in understorey vegetation (i.e. the ordination space) showed high maximum correlation with stand volume r = 0.81, mean annual stand volume increment r = 0.76, and post-drainage dominant height r = 0.75. The covariation between the vegetation and peat bulk density in both the 0-10 and 10-20 cm peat layers was also strong: r = 0.55 and r = 0.80. The correlations for Hv.Post were 0.64 and 0.81, respectively. Of the total macronutrient concentrations, phosphorus (r = 0.73, r = 0.75) and nitrogen (r = 0.59, r = 0.64) were the most strongly correlated with species composition. The environmental sample variables were also presented by the vegetation units of numerical classification. Most of the recorded variables, including nutrient amounts (kg ha-1), were examined in site quality (fertility) classes by succession phases as well. Border variants or transitional forms of the site types were common. Additional vegetation criteria (e.g. surface-water influence) more closely defined the ecology of the site. In addition to the site quality classes, a considerable amount of information about the tree stands, vegetation diversity and peat properties was associated with the separation of the succession phases, i.e. in this study transforming (phase II) vs. transformed (final phase III) sites. In conclusion, the actual vegetation appeared to well reflect various aspects of the ecological conditions, even in labile communities of commercial forests on drained peatlands.