Effects of long-term N fertilization on nitrate leaching and vegetation responses in a spruce stand after severe wind damage

Wind damage in a forest stand can result in varying soil effects depending on the pre-history of the site, but areas with storm-felled trees can generally be expected to show more nitrate leaching than undamaged stands. Previous fertilization in such areas, especially with nitrogen (N) fertilizer, may further increase nitrate leaching. This study examined the effect of partial felling of a 42-year-old Norway spruce stand in the Skogaby experimental forest in Sweden during Storm Gudrun in 2005. Nitrate leaching was measured one year before and six years after the storm, in three experimental treatments: fertilization-irrigation with complete nutrient admixture (IF), fertilization with N-free nutrient admixture (V), and an untreated control (0). The 0 and IF treatments had some undamaged replicate plots, but V plots had no trees left after the storm. Compared with undamaged plots and the pre-disturbance level, nitrate leaching was significantly higher in all storm-felled plots, and in the soil solution nitrate dominated strongly over ammonium. Leaching peaked during the second and third post-storm years (2006-2007) and decreased to near pre-storm levels during the fifth and sixth years (2009-2010). Total nitrate leaching 2005-2010 was estimated to be 414, 233, and 218 kg N ha(-1) in the damaged IF, 0, and V plots, respectively. Total nitrate leaching in undisturbed plots in the IF and 0 treatments was 37 and 0.3 kg N ha(-1), respectively. Ground vegetation coverage, biomass, and biomass N increased with time and were negatively correlated with nitrate discharge. However, plant uptake of N only partly explained the significant decline in nitrate leaching between 2006 and 2010. This decrease could also be explained by N immobilization in fungi decomposing woody roots with low N concentrations

Markfaunans rumsliga spridning i betad och orörd stäpp i Chernozem-zonen i Ryssland

Långvarig boskapsdrift har visats ge tydliga förändringar av stäppväxtligheten samt vissa effekter på markens makrofauna. Syftet med detta arbete var att undersöka markfaunans rumsliga spridning i marken i naturreservatet i Kurskområdet, Ryssland. En parcell med orörd stäpp och en med betesmark (ko/ha) undersöktes. Prover insamlades med en jordborr (10 cm) till 15 – 20 cm djup. I varje parcell togs totalt 144 prover (6 rader om 24 prover). Proverna togs tättintill varandra. Markfaunan sorterades ut från varje jordprov för hand och analyserades tillsammans med provets vikt, stenighet, rötter och förna. Vår hypotes var att den rumsliga spridningen skulle vara mer homogen i en stäpp än i en betesmark där biocenosen är mer fragmenterad. Den orörda stäppen hade 2 gånger högre vikt av rötter och 20 gånger högre vikt av förna. Dessa skillnader medförde också skillnader i markfauna. Det totala antalet markdjur var högre i stäppen (349/m2) än i betesmarken (246/m2). I stäpp dominerade Staphylinidae (72 eks/m2), Scarabaeidae-larver(63) och Julidae (50). I betesmarken dominerade Curaelionidae-larver (40), Scarabaedae-larver (31), Elateridae larvi (39). Antalet Myriapoda var 60 gånger högre i obetad stäpp och saknades nästan i betesmarken. Vid jämförelsen av stäppytor och betesytor framgick att båda saknade daggmaskar, antagligen på grund av torkan. Markfaunas spridning var heterogenare i stäppen än i betesmarken. Heterogeniteten var hos somliga djurgrupper, t.ex. skalbaggslarver, som sped sig inom stäppytan på så sätt att de förekom med förhöjt antal samtidigt som de saknades på andra områden. I betesmarken spred sig larverna däremot jämnt. Den erhållna resultaten vederlägger hypotesen om en mer agreggerad fauna i en betesmark. Antal markdjur visade en positiv korrelation med förnans vikt, både i stäppen och i betesmarken, men korrelationskoefficienten var högre i stäppen. Förnan saknades nästan i betesmarken och där dominerade markdjur som spred sig mer homogent. Deras spridning var oberoende av förnans vikt

Short-term effects of thinning, clear-cutting and stump harvesting on methane exchange in a boreal forest

Forest management practices can alter soil conditions, affecting the consumption and production processes that control soil methane (CH4) exchange. We studied the short-term effects of thinning, clear-cutting and stump harvesting on the CH4 exchange between soil and atmosphere at a boreal forest site in central Sweden, using an undisturbed plot as the control. Chambers in combination with a highprecision laser gas analyser were used for continuous measurements. Both the undisturbed plot and the thinned plot were net sinks of CH4, whereas the clear-cut plot and the stump harvested plot were net CH4 sources. The CH4 uptake at the thinned plot was reduced in comparison to the undisturbed plot. The shift from sink to source at the clear-cut and stump harvested plots was probably due to a rise in the water table and an increase in soil moisture, leading to lower gas diffusivity and more reduced conditions, which favour CH4 production by archea. Reduced evapotranspiration after harvesting leads to wetter soils, decreased CH4 consumption and increased CH4 production, and should be accounted for in the CH4 budget of managed forests

A maximum likelihood estimator of a Markov model for disease activity in Crohn's disease and ulcerative colitis for annually aggregated partial observations.

Crohn's disease (CD) and ulcerative colitis (UC) are chronic inflammatory bowel diseases that have a remitting, relapsing nature. During relapse, they are treated with drugs and surgery. The present study was based on individual data from patients diagnosed with CD or UC at Herlev University Hospital, Copenhagen, Denmark, during 1991 to 1993. The data were aggregated over calendar years; for each year, the number of relapses and the number of surgical operations were recorded. Our aim was to estimate Markov models for disease activity in CD and UC, in terms of relapse and remission, with a cycle length of 1 month. The purpose of these models was to enable evaluation of interventions that would shorten relapses or postpone future relapses. An exact maximum likelihood estimator was developed that disaggregates the yearly observations into monthly transition probabilities between remission and relapse. These probabilities were allowed to be dependent on the time since start of relapse and on the time since start of remission, respectively. The estimator, initially slow, was successfully optimized to shorten the execution time. The estimated disease activity model for CD fits well to observed data and has good face validity. The disease activity model is less suitable for UC due to its transient nature through the presence of curative surgery

Heterotrophic respiration and nitrogen mineralisation in soils of Norway spruce, Scots pine and silver birch stands in contrasting climates

Different tree species are often associated with different soil properties. Earlier studies have shown that Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.), the two dominant tree species in Fennoscandia, often generate soils with larger carbon (C) and nitrogen (N) pools than silver birch (Betula pendula Roth.). Consequently, we hypothesised that spruce and pine would create soils with slower turnover rates than birch. To test this, C and N pools and C and N mineralisation rates were determined in different soil layers (humus, 0–10 cm, 10–20 cm mineral soil) at two sites with contrasting climatic conditions. One site (Tönnersjöheden) was located in the temperate zone in SW Sweden and one (Kivalo) in the north boreal zone in N Finland. At both sites, experimental plots with the three tree species had been established more than 50 years before the study. Samples from the different soil layers were incubated at 15 °C in the laboratory for 30 days, and C and N mineralisation rates were determined. In addition, earthworm abundance was estimated at Tönnersjöheden but not at Kivalo (no sign of bioturbation). At Tönnersjöheden, soil C and N pools (g C or N m−2) were ranked spruce > pine > birch. C mineralisation rate (mg CO2–C g−1 C d−1) was higher in the birch plots than in the other plots, but because of larger C pools in the spruce plots, field C mineralisation (g CO2–C m−2 year−1) was higher for spruce than for pine and birch. Field net N mineralisation (80–90 kg N ha−1 year−1) did not differ significantly between tree species, but nitrification rates (μg NO3–N g−1 C d−1) in the topsoil were higher in the birch plots than in the other plots. The birch plots had larger populations of earthworms and a higher degree of bioturbation than any of the coniferous plots, which probably explains the higher turnover rate of birch soil organic matter (SOM). At Kivalo, C and N soil pools were significantly larger in spruce than in birch plots, and C mineralisation rate was higher in birch and spruce humus than in pine humus. Net N mineralisation rate and annual field net N mineralisation (<4 kg N ha−1 year−1) were estimated to be very low, with no effect of tree species. Thus, the hypothesis of a ‘birch effect’ was supported at Tönnersjöheden, but only partly at Kivalo. The main difference seemed to be that the earthworms at Tönnersjöheden accelerated SOM decomposition under birch, whereas earthworm stimulation was negligible at Kivalo, probably because of climate-related limitations

Carbon and nitrogen pools and fluxes above and below ground in spruce, pine and birch stands in southern Sweden

We synthesised results on soil carbon (C) and nitrogen (N) fluxes and the accumulation of soil organic C and N under adjacent 50-year-old Norway spruce, Scots pine and silver birch stands growing on similar soils and evaluated the different processes involved. C and N budgets were calculated. Spruce stands had larger stocks of C and N in biomass and soil than birch stands, with pine intermediate. The differences in soil stocks were mainly found in the organic layer, whereas differences in the mineral soil were small. The study showed that there is no simple answer to what is causing the differences in soil C and N stocks, because several processes are interacting. Spruce and pine trees had higher biomass and litter production than birch trees, but total litter inputs showed no significant difference between stands, because the rich ground vegetation under pine and birch contributed with substantial litter inputs, in contrast to the poor ground vegetation under spruce. Decomposition rate (per g of C) was markedly higher under birch than under spruce and pine resulting in lower C and N stocks in the organic layer. This effect was amplified by higher abundance and biomass of earthworms, favoured by higher pH and palatable litter under birch. Earthworm bioturbation probably both increased decomposition rate and damaged the ectomycorrhizal network with negative consequences for the formation of mycorrhizal litter and C storage. In conclusion, the direct effects of spruce, pine and birch litter on C and N pools and fluxes were modified by indirect effects of understorey structure, pH and earthworm responses

Carbon and nitrogen pools and mineralization rates in boreal forest soil after stump harvesting

The use of forest-derived biomass has steadily increased in Finland and Sweden during the past decades leading to more intensive forest management practices in the region, such as whole-tree harvesting, both above- and belowground. Stump harvesting results in a direct removal of stump and coarse-root carbon (C) from the stand and can cause extensive soil disturbance, which has been suggested to increase C mineralization. In this study, the effects of stump harvesting on soil C and nitrogen (N) mineralization, and soil surface disturbance were studied in two different clear-felled Norway spruce (Picea abies) sites in Central Finland. The treatments were whole-tree harvesting (WTH, removal of stems and logging residues), and WTH and stump harvesting (WTH + S). Both sites, Honkola (2 stands) and Haukilahti (6 stands) were mounded. In both treatments, soil samples were taken from different soil layers down to a total depth of 20 cm in the mineral soil from (i) mounds, (ii) undisturbed soil and (iii) pits. The sampling was performed 11-12 years after treatments. Soil C and N mineralization rates were determined in laboratory incubation experiments. In addition, total C and N pools (g m(2)) were estimated for each disturbance class and soil layer. Soil C and N pools had a tendency to be lower following stump harvesting, but no statistically significant treatment effect was detected. Stump harvesting increased soil mixing as indicated by a significant decrease in C concentration in the mound disturbance class. There was no significant effect of stump harvesting on soil C mineralization rates. A combination of mineralization rates and soil pool data showed that field C mineralization (g CO2-C m(-2) yr(-1)) did not significantly differ between stands where stumps were removed or were retained. Further, stump harvesting did not seem to have any stimulating effect on soil CO2 efflux 11-12 years after treatment. (C) 2016 Elsevier B.V. All rights reserved.Peer reviewe

Effects of long-term N fertilization on nitrate leaching and vegetation responses in a spruce stand after severe wind damage

Wind damage in a forest stand can result in varying soil effects depending on the pre-history of the site, but areas with storm-felled trees can generally be expected to show more nitrate leaching than undamaged stands. Previous fertilization in such areas, especially with nitrogen (N) fertilizer, may further increase nitrate leaching. This study examined the effect of partial felling of a 42-year-old Norway spruce stand in the Skogaby experimental forest in Sweden during Storm Gudrun in 2005. Nitrate leaching was measured one year before and six years after the storm, in three experimental treatments: fertilization-irrigation with complete nutrient admixture (IF), fertilization with N-free nutrient admixture (V), and an untreated control (0). The 0 and IF treatments had some undamaged replicate plots, but V plots had no trees left after the storm. Compared with undamaged plots and the pre-disturbance level, nitrate leaching was significantly higher in all storm-felled plots, and in the soil solution nitrate dominated strongly over ammonium. Leaching peaked during the second and third post-storm years (2006-2007) and decreased to near pre-storm levels during the fifth and sixth years (2009-2010). Total nitrate leaching 2005-2010 was estimated to be 414, 233, and 218 kg N ha(-1) in the damaged IF, 0, and V plots, respectively. Total nitrate leaching in undisturbed plots in the IF and 0 treatments was 37 and 0.3 kg N ha(-1), respectively. Ground vegetation coverage, biomass, and biomass N increased with time and were negatively correlated with nitrate discharge. However, plant uptake of N only partly explained the significant decline in nitrate leaching between 2006 and 2010. This decrease could also be explained by N immobilization in fungi decomposing woody roots with low N concentrations