Ulf Sikström

Contrasting effects of wood ash application on microbial community structure, biomass and processes in drained forested peatlands

The effects of wood ash application on soil microbial processes were investigated in three drained forested peatlands, which differed in nutrient status and time since application. Measured variables included the concentrations of soil elements and phospholipid fatty acids (PLFAs), net nitrogen (N) mineralization, nitrification and denitrification enzyme activity, potential methane (CH(4)) oxidation, CH(4) production and microbial respiration kinetics. Wood ash application had a considerable influence on soil element concentrations. This mirrored a decrease in the majority of the microbial biomarkers by more than one-third in the two oligotrophic peatlands, although the microbial community composition was not altered. The decreases in PLFAs coincided with reduced net ammonification and net N mineralization. Other measured variables did not change systematically as a result of wood ash application. No significant changes in microbial biomass or processes were found in the mesotrophic peatland, possibly because too little time (1 year) had elapsed since the wood ash application. This study suggests that oligotrophic peatlands can be substantially affected by wood ash for a period of at least 4 years after application. However, within 25 years of the wood ash application, the microbial biomass seemed to have recovered or adapted to enhanced element concentrations in the soil.

Effects of low-dose liming and nitrogen fertilization on stemwood growth and needle properties of Picea abies and Pinus sylvestris

Abstract Stemwood growth, needle weight and nutrient concentrations in needles after liming and nitrogen fertilization were studied in two randomized block trials. The treatments were a single application of 500 kg lime per hectare, 1000 kg limer per hectare, 150 kg N per hectare and combinations of the two compounds. The trials are situated in the southern part of Sweden on mesic mineral soils. One of the experiments was located in 32–55-year-old highly productive Picea abies stands and the other in a 31-year-old Pinus sylvestris stand. As calculated by growth-ring analysis, liming alone did not significantly affect the growth during a 10-year period following treatment. Nitrogen fertilization increased growth in pine, but not in spruce. Lime in combination with N gave about the same effect in pine as the pure N treatment, whereas lime and N interacted in spruce and resulted in increased stemwood growth. Current-year needles were sampled during the winter, weighed and analysed for nutrient concentrations. In the N-treated plots the N concentration increased in both tree species, whereas the needle weight increased only in pine. In two cases, lower concentrations were indicated. In the first, there was a tendency of decreased N concentrations in spruce needles after liming. In the second, the magnesium concentrations decreased in needles of both species, especially in the treatments that included nitrogen. The concentrations of the measured nutrients were never below levels considered to imply a severe deficiency.

Is tree growth in boreal coniferous stands on mineral soils affected by the addition of wood ash

Increasing use of forest fuels for energy production is generating greater quantities of wood ash. In Sweden, it is recommended that this ash should be returned to the forest to counter soil acidification and avoid potential future nutrient deficiencies, but the effects on tree growth require clarification. Thus, 10 field experiments were established in Sweden in 1990–2006 to study the effects of adding wood ash of various origins, doses and combinations of both ash and nitrogen on stem growth in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst.) stands on mineral soil. Observations after 5–15 years show that growth responses were strongest when N was added, either alone or with wood ash. Growth responses to additions of wood ash without N were small and variable and statistically insignificant at all study sites. However, there were indications that adding wood ash may increase stem-wood growth at fertile sites and decrease it at less fertile sites. Hence, at fertile sites, it may compensate for the growth reductions that normally follow whole-tree harvests, at least temporarily, presumably due to its effects on soil N turnover. At less fertile sites, adding N is probably essential to counteract these growth reductions.

Effects of wood ash fertilization on forest floor greenhouse gas emissions and tree growth in nutrient poor drained peatland forests

Wood ash (3.1, 3.3 or 6.6 tonnes dry weight ha(-1)) was used to fertilize two drained and forested peatland sites in southern Sweden. The sites were chosen to represent the Swedish peatlands that are most suitable for ash fertilization, with respect to stand growth response. The fluxes of carbon dioxide (CO(2)), methane (CH(4)) and nitrous oxide (N(2)O) from the forest floor, measured using opaque static chambers, were monitored at both sites during 2004 and 2005 and at one of the sites during the period 1 October 2007-1 October 2008. No significant (p>0.05) changes in forest floor greenhouse gas exchange were detected. The annual emissions of CO(2) from the sites varied between 6.4 and 15.4 tonnes ha(-1), while the CH(4) fluxes varied between 1.9 and 12.5 kg ha(-1). The emissions of N(2)O were negligible. Ash fertilization increased soil pH at a depth of 0-0.05 m by up to 0.9 units (p<0.01) at one site, 5 years after application, and by 0.4 units (p<0.05) at the other site, 4 years after application. Over the first 5 years after fertilization, the mean annual tree stand basal area increment was significantly larger (p<0.05) at the highest ash dose plots compared with control plots (0.64 m(2) ha(-1) year(-1) and 0.52 m(2) ha(-1) year(-1), respectively). The stand biomass, which was calculated using tree biomass functions, was not significantly affected by the ash treatment. The groundwater levels during the 2008 growing season were lower in the high ash dose plots than in the corresponding control plots (p<0.05), indicating increased evapotranspiration as a result of increased tree growth. The larger basal area increment and the lowered groundwater levels in the high ash dose plots suggest that fertilization promoted tree growth, while not affecting greenhouse gas emissions.

Damage to Picea abies Regeneration After Final Cutting of Shelterwood with Single- and Double-grip Harvester Systems

Logging-related damage to forest regeneration is a problem during final cutting in the shelterwood system. In order to compare the effects of logging methods, damage to natural Norway spruce [Picea abies (L.) Karst.] regeneration caused by single- (SGH) and double-grip harvester (DGH) systems was studied in three shelterwoods (132-234 m3 ob ha-1) in Sweden. Between 38 and 65% of the original seedlings (6 400-25 400 ha-1

Effects of pre-harvest soil acidification, liming and N fertilization on the survival, growth and needle element concentrations of Picea abies L. Karst. seedlings

There are concerns that the anthropogenic acidification of Swedish forest soils may have severe effects on forest yield, and it has been suggested that liming could be used to counter this problem. The aim of this study was to investigate the survival, growth and element concentrations of C+1 needles of Picea abies (L.) Karst. seedlings planted on plots that had been acidified (in 12 annual treatments totalling 600 or 1200 kg S ha−1 in the form of elemental sulphur), limed (12×500=6000 kg lime ha−1 in the form of CaCO3) or N-fertilized (3×200=600 kg N ha−1 in the form of urea) prior to harvest. Seedlings growing on plots given a combination of the N plus low S treatments were also tested. None of the treatments, given to triplicate plots, significantly influenced seedling survival during the first five growing seasons. Furthermore, none of the treatments significantly affected growth, although the average growth rate was slightly higher for limed plots. The survival and growth of the seedlings are discussed in relation to differences in the cover of field-layer vegetation between the treatments after the final felling. Needles from seedlings in the limed plots showed significantly lower concentrations of Mn and Al, and higher concentrations of Ca and Zn compared with needles from seedlings in the other plots (i.e. control, high S or N-treated). The K concentration in the needles was significantly higher in limed plots than in high-S plots. Changes of element concentrations observed in the soil, associated with the treatments, where in some cases reflected in the needle concentrations.

Effects of Previous High N Addition on Nutrient Conditions in Above-ground Biomass of a Picea abies Stand in Sweden

Deposition of air pollutants, together with intensified harvesting practices, has led to concern about the declining base cation status and the acidifying effects in the soil, with possible implications for silviculture. The aim of this study was to analyse the effects of a previous high N addition on the nutritional status in the above - ground part of a tree stand. We sampled various biomass fractions in a highly productive Norway spruce (Picea abies (L.) Karst.) stand in the province of Värmland, western Sweden. The experimental plots had been fertilized with urea four times at intervals of 5 yrs, the last time being 13 yrs before our study. The total amount of N added was in the range 480 - 2400 kg ha?1. Despite the high N addition and an insignificant growth increase following N input, there were no obvious residual changes of nutrient concentrations in the above - ground parts of trees.

Ditch network maintenance in peat-dominated boreal forests: Review and analysis of water quality management options

The objective of this study was to evaluate the potential of different water management options to mitigate sediment and nutrient exports from ditch network maintenance (DNM) areas in boreal peatland forests. Available literature was reviewed, past data reanalyzed, effects of drainage intensity modeled, and major research gaps identified. The results indicate that excess downstream loads may be difficult to prevent. Water protection structures constructed to capture eroded matter are either inefficient (sedimentation ponds) or difficult to apply (wetland buffers). It may be more efficient to decrease erosion, either by limiting peak water velocity (dam structures) or by adjusting ditch depth and spacing to enable satisfactory drainage without exposing the mineral soil below peat. Future research should be directed towards the effects of ditch breaks and adjusted ditch depth and spacing in managing water quality in DNM areas.