%0 Reviews %T Effect of ash fertilization on the understorey vegetation in drained Scots pine mires %A Hotanen, Juha-Pekka %D 2025 %J Suo - Mires and peat %V 76 %N 1-2 %U http://suo.fi/article/10846 %X

The suitability of ash for managing the nutrient ecology of forest-drained peatlands has been known for a long time (e.g. Lukkala 1951; Huikari 1953; Silfverberg & Huikari 1985). Extensive research has been conducted on the effects of different types and amounts of ash on the structure and functioning of drained peatland ecosystems (e.g. Silfverberg 1996; Moilanen et al. 2002; Huotari et al. 2008; Silfverberg et al. 2010; Piirainen et al. 2013; Peltoniemi et al. 2016; Hökkä et al. 2024). The effects of ash fertilization on greenhouse gas emissions and carbon balances of peatlands have also begun to be widely investigated (e.g. Ernfors et al. 2010; Moilanen et al. 2012; Silvan & Hytönen 2016; Väänänen et al. 2024). Efforts are being made to increase the areas of ash fertilization. However, the effects of ash fertilization on the structure of understorey vegetation in different habitats are poorly understood. The purpose of this study was to analyze the effects of wood ash amounts normally used in forestry on the structure of understorey vegetation in suitable habitats for ash fertilization, i.e. second-type peatlands that have developed from open and mixed-type mires (Laine et al. 2018).
The ash treatment plots (n = 10) and their controls (n = 10) were located in seven sites in the middle boreal zone, in the aapa mire region of Ostrobothnia. The year of ash fertilization, the amount of ash used, and the type of peatland varied. Ash fertilization enriched the undergrowth. The site type of peatland in the fertilized plots was at least one variant (+) higher (slightly more nutrient -rich type) than that of the controls (see also e.g. Silfverberg & Huikari 1985; Silfverberg & Hotanen 1989; Moilanen et al. 2002; Silfverberg et al. 2010, 2011). Ash fertilization also promoted drying and forest succession, meaning that mire vegetation changes more rapidly to forest vegetation. This was evident in the increased number of tree seedlings, mainly Betula pubescens (see also Huotari et al. 2008), as well as the increase in litter. This was also evident in the slight increase in Brachythecium spp. mosses living on the litter, and the decrease in most Sphagnum mosses. Ash fertilization increases microbial activity in the surface peat along with nutrient levels, speeding up the use and cycling of nutrients in the drained peatland ecosystem while simultaneously increasing tree growth and its evaporative effect.
Ash slightly increased the diversity of the undergrowth, i.e. the number of forest vegetation species, which was visible in the field layer. The total number of field and bottom layer species increased statistically suggestively (p < 0.1). A total of 63 species (partly group species) grew in the ash plots, compared to 52 species in the controls, respectively. The Dwarf shrubs decreased at the group level in the ash plots. Andromeda polifolia decreased in all drained peatland forest types studied (Vaccinium myrtillus type, MtkgII; Vaccinium vitis-idaea type, PtkgII; Dwarf shrub type, VatkgII, see e.g. Laine et al. 2018). Vaccinium vitis-idaea decreased in Dwarf shrub type, while Vaccinium myrtillus seemed to increase, but the change was not statistically significant. The cover of grasses and sedges was low in the plots, and the changes in species abundance were small. Calamagrostis purpurea benefited the most from the fertilization. Herbs also grew rather sparsely. However, the coverage of Dryopteris carthusiana, Epilobium angustifolium and Trientalis europaea increased because of ash fertilization. The nutrient addition from ash changes the competitive conditions of the vegetation. It also increases nitrogen mobilization in the surface peat. As a result, many grass and herb species become more abundant, while many bog dwarf shrub species adapted to low nutrient levels decline.
Ash fertilization did not significantly affect the overall abundance of Bryales. Brachythecium mosses increased, but they were still quite sparse after fertilization. Hylocomium splendens increased slightly, most notably in the V. vitis-idaea type ash plots. Polytrichum strictum suffered the most from ash fertilization. Due to the nutrient addition from ash fertilization and accelerated drying and forest succession, Sphagnum mosses also clearly declined, except for S. capillifolium, which increased slightly. The survival strategy of S. capillifolium is good: as a hummock surface species, it tolerates occasional drying excellently, quickly utilizes rain and spring and autumn moisture, and spreads effectively through spores; additionally, it withstands nutrient addition better than the most barren sphagnum mosses.