Maj-Britt Johansson

The influence of soil scarification on the turn‐over rate of slash needles and nutrient release

The effect of soil scarification on decomposition of green Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) needles and mineral nutrient release was investigated. The treatments studied were ploughing, disk trenching, mound on inverted humus and untreated control. The study was conducted on two clear‐felled sites with different ground moisture conditions, located in south Sweden. The needles decomposed and released their contents of N and Ca considerably faster on scarified areas than on untreated ones. For P, Mg and especially K, only minor differences between scarified and untreated areas were established. At the wet site, needle decomposition and nutrient mineralization were generally affected to the same extent by all three scarification methods studied. At the dry to fresh site, mounding and ploughing enhanced needle decomposition and nutrient mineralization more than disk trenching. The effect of different scarification methods on the long‐term production capacity of soil...

Decomposition of litter and soil organic matter—can we distinguish a mechanism for soil organic matter buildup?

This synthesis paper presents a model for estimating the buildup of soil organic matter in various types of coniferous forests. The knowledge used was obtained from a well‐studied forest with good Iitterfall data, decomposition information and validation measurements of the soil organic matter layer. By constructing a simple model for litterfall, and the information on maximum decomposition levels for litter, we could estimate the annual increase in soil organic matter and extend this to encompass stand age. The validation measurement and the estimated amount of soil organic matter differed by about 8 or 26% over a 120‐yr period, depending on the litterfall model. The estimated increased storage of soil organic matter as a consequence of climate change was found to be drastic. We thus found that the soil organic matter layer would grow about four times as fast as a result of the needle component only. This estimate was based on a comparison between latitudes with a difference of 17°.

Influence of mechanical site preparation on decomposition and nutrient dynamics of Norway spruce (Picea abies (L.) Karst.) needle litter and slash needles

Abstract Turnover rates and nutrient dynamics of Norway spruce ( Picea abies (L.) Karst.) needle litter and slash needles were followed for 3 and 4 years, respectively, in an unprepared clear-cut and in the soil ridges of a disc trenched clear-cut in central Sweden. In the soil ridges of the disc trenched clear-cut, needles decomposed faster than in the unprepared clear-cut. After 3 years of decomposition the remaining mass of needle litter was 40% in the disc trench ridges and 59% in the unprepared clear-cut. After 4 years the corresponding values for slash needles were 26% and 45%, respectively. In the ridges, slash needles decomposed somewhat faster than needle litter, but this difference was barely significant. Nutrient release was faster from needles in the ridges than in the unprepared clear-cut and this effect was more noticeable in slash needles. At the end of the experiment there were lower amounts remaining of all elements in needle litter (except K) and slash needles in the disc trench ridges than in the unprepared clear-cut. The results indicate that microclimatic conditions inside the disc trench ridges promoted the activity of predominant decomposing organisms. Differences between needle litter and slash needles can be attributed to different initial nutrient and lignin concentrations. Some implications of enhanced organic matter decomposition andmineralisation in the context of site fertility are discussed.

Organically bound halogens in coniferous forest soil : distribution pattern and evidence of in situ production

Abstract We examined organically bound halogens in a coniferous soil profile and in Norway spruce litter enclosed in litter bags and subjected to degradation in field. Throughout the soil profile the total amount of organically bound halogens (TOX, μg Cl/g soil) was related to organic matter, i.e. amounts decreased with increasing depth. In contrast, the organic chlorine to organic carbon ratio (mg Cl org :g C org ) increased with increasing depth, and a pronounced increase in this ratio was observed in the transition between the O-horizon and the A-horizon, strongly indicating that in situ production of organically bound halogens occur in soil. This conclusion was strengtened by the results of the litter bag study, which clearly showed that a net-production of organically bound halogens occurred during decomposition of the spruce needle litter. Furthermore, this part of the study showed that organically bound halogens are not a static factor of organic matter. On the contrary, the results strongly indicated that during decomposition of organic matter, organically bound halogens are subjected to both production, i.e. incorporation of inorganic halides into organic matter, and mineralisation, i.e. release of inorganic halides from organic matter. A method previously developed in our laboratory to determine TOX in soil was further evaluated; there were no indications that inorganic halides interfere with the determination.

Sequestration of carbon in the humus layer of Swedish forests — direct measurements

To determine sequestration rates of carbon dioxide (CO2) we calculated the carbon (C) storage rate in humus layers of Swedish forests with Podsolic soils, which account for 14.2 x 106 ha of the 22. ...

Decomposition of tree root litter in a climatic transect of coniferous forests in northern Europe: A synthesis

The purpose of this study was to understand the variation in root litter mass‐loss rates in a climatic transect across a large region ranging from the Arctic Circle (66°N) in Scandinavia to Berlin (52°N) in north‐east Germany, dominated by coniferous monocultural forests. To investigate the combined influence of litter quality and climate, data were used from 37 sites and plots at which root litters of three coniferous species (Pinus sylvestris, Pinus contorta and Picea abies) had been incubated. In spite of the considerable climatic differences among sites, there were no strong relationships between any climatic variable and the lst‐yr mass loss (range 17.0–40.9%). For the lst‐yr mass loss, the average annual temperature was the most rate‐regulating factor for all litter combined, with a value for R 2 adj of 0.186. Substrate quality also had an influence. Thus, for the whole region lignin concentration was significant, with a value for R 2 adj of 0.142. For the separated groups of pine and spruce stands ...

Soil Organic Matter Changes In A Spruce Chronosequence On Swedish Former Agricultural Soil: I. Carbon And Lignin Dynamics

Afforestation of former agricultural soils is an important tool to reduce atmospheric CO2 levels because of the high capacity of both biomass and soil to store carbon (C). The long-term effect of afforestation on the role of soil as C sink was investigated in a chronosequence of 18-, 29-, 64-, 73-, and 91-year-old Picea abies stands, established on former agricultural soils in southwestern Sweden. The forest floor was sampled both as a whole and in the three horizons (unaltered, semialtered, and altered organic horizons), whereas the mineral soil was sampled at 0 to 5, 5 to 15, and 15 to 30 cm depth. The physicochemical characterization of soil, C and nitrogen content, and lignin characterization by the cupric oxide oxidation method was conducted. Within the first decades of afforestation, the soil properties reflected the former soil management, and C accumulation involved mainly the organic layer (3.41-5.92 Mg C ha−1), where the new litter was accumulating, and coniferous lignin showed a low degree of degradation. Meanwhile, the mineral soil behaved as a C source (95.5-80.2 Mg C ha−1), loosening the C inherited from the previous land use probably because of the nutrient needs of the growing trees that accelerated organic matter mineralization. Vanillyl moieties were almost absent, and the syringyl units, derived from angiosperms, were considerably oxidized, indicating a low C input from the conifer litter and high degradation of the inherited organic material. With age, the C stock started to increase both in the organic and mineral layers, reaching 191.5 Mg ha−1 in 91 years. The accumulation in organic soil was accompanied by a litter nitrogen impoverishment and decrease of soil pH, which probably limited the microbial community to fungi, able to degrade lignin. In the oldest stands, the lignin material seemed to be intensively altered, mainly in the deeper organic horizons, where aromatic, mobile, acidic compounds were produced and/or translocated down in the profile. This could contribute to organic matter incorporation into mineral layers and to mineral weathering, driving the soil toward the restarting of the podzolization process. From these results, it seemed that even if the previous land use caused an initial acceleration of organic matter mineralization, soil started to accumulate C when the influence of the new vegetation dominated. The soil became a major C sink with a long forest growth of about a century. The accumulation was strongly affected by litter composition, which changed with spruce age.

Biomass, decomposition and nutrient release of Vaccinium myrtillus leaf litter in four forest stands

Biomass and nutrient transfer (N, P, K, Ca, Mg) of bilberry (Vaccinium myrtillus L.) leaf litter fall, as well as decomposition and nutrient release, were studied in four mature forest stands situated in Central and South Sweden. Bilberry leaf litter fall amounted to between 33 and 55 kg ha‐1 yr‐1 in the four stands. Only minor differences between sites were noted for litter concentrations of N, P and Ca, whereas K and Mg showed somewhat larger variability. Relative amounts of the five nutrient elements in the litter fall were generally in the order N > Ca > K > Mg > P. The amounts of nutrients returned to the forest floor by the annual leaf litter fall in the stands ranged from 0.4 to 0.8 kg ha‐1 for N, 0.4 to 0.6 kg ha‐1 for Ca, 0.2 to 0.7 kg ha‐1 for K, 0.1 to 0.2 kg ha‐1 for Mg and 0.04 to 0.08 kg ha‐1 for P. The decomposition of the local bilberry leaf litter was followed by means of litterbags during three years. At all sites there was an extremely rapid mass loss from the litter (between 45% and 54...

Indications that site preparation increases forest ecosystem carbon stocks in the long term

ABSTRACT Mechanical site preparation (MSP) causes a mixing disturbance of the soil, which may increase decomposition of soil organic matter and subsequent carbon (C) dioxide emissions to the atmosphere. MSP also promotes the establishment and growth of tree seedlings, and hence ecosystem C fixation. However, there are uncertainties regarding the net effects of MSP on C stocks at the ecosystem scale. To assess decennial effects of MSP on ecosystem C stocks, C stocks in soil, ground vegetation and trees at three experimental forest sites with Pinus contorta, Pinus sylvestris and Picea abies in Sweden were sampled and measured for ca. 25 years in a control and after three MSP treatments: disc trenching, mounding and ploughing. After 25 years, all of the MSP treatments resulted in larger ecosystem C stocks than the control treatment due to positive effects on the tree biomass C stock. The tree C stock was highest after ploughing, intermediate after mounding or disc trenching and lowest in untreated control plots at all experimental sites. The MSP treatments did not affect the soil C stocks down to 30 cm. We recommend mounding or disc trenching to promote C sequestration as they disturb sites’ ecological, aesthetic and recreational values less than ploughing.