Modelling soil carbon sequestration of intensively monitored forest plots in Europe by three different approaches (original) (raw)
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The impact of nitrogen deposition on carbon sequestration in European forests and forest soils
Global Change Biology, 2006
An estimate of net carbon (C) pool changes and long-term C sequestration in trees and soils was made at more than 100 intensively monitored forest plots (level II plots) and scaled up to Europe based on data for more than 6000 forested plots in a systematic 16 km  16 km grid (level I plots). C pool changes in trees at the level II plots were based on repeated forest growth surveys At the level I plots, an estimate of the mean annual C pool changes was derived from stand age and available site quality characteristics. C sequestration, being equal to the long-term C pool changes accounting for CO 2 emissions because of harvest and forest fires, was assumed 33% of the overall C pool changes by growth. C sequestration in the soil were based on calculated nitrogen (N) retention (N deposition minus net N uptake minus N leaching) rates in soils, multiplied by the C/N ratio of the forest soils, using measured data only (level II plots) or a combination of measurements and model calculations (level I plots). Net C sequestration by forests in Europe (both trees and soil) was estimated at 0.117 Gton yr À1 , with the C sequestration in stem wood being approximately four times as high (0.094 Gton yr À1 ) as the C sequestration in the soil (0.023 Gton yr À1 ). The European average impact of an additional N input on the net C sequestration was estimated at approximately 25 kg C kg À1 N for both tree wood and soil. The contribution of an average additional N deposition on European forests of 2.8 kg ha À1 yr À1 in the period 1960-2000 was estimated at 0.0118 Gton yr À1 , being equal to 10% of the net C sequestration in both trees and soil in that period (0.117 Gton yr À1 ).
Forest Ecology and Management, 2009
Changes in the Earth's atmosphere are expected to influence the growth, and therefore, carbon accumulation of European forests. We identify three major changes: (1) a rise in carbon dioxide concentration, (2) climate change, resulting in higher temperatures and changes in precipitation and (3) a decrease in nitrogen deposition. We adjusted and applied the hydrological model Watbal, the soil model SMART2 and the vegetation model SUMO2 to asses the effect of expected changes in the period 1990 up to 2070 on the carbon accumulation in trees and soils of 166 European forest plots. The models were parameterized using measured soil and vegetation parameters and site-specific changes in temperature, precipitation and nitrogen deposition. The carbon dioxide concentration was assumed to rise uniformly across Europe. The results were compared to a reference scenario consisting of a constant CO 2 concentration and deposition scenario. The temperature and precipitation scenario was a repetition of the period between 1960 and 1990. All scenarios were compared to the reference scenario for biomass growth and carbon sequestration for both the soil and the trees.
Impact of long-term nitrogen addition on carbon stocks in trees and soils in northern Europe
Biogeochemistry, 2008
The aim of this study was to quantify the effects of fertiliser N on C stocks in trees (stems, stumps, branches, needles, and coarse roots) and soils (organic layer +0-10 cm mineral soil) by analysing data from 15 long-term (14-30 years) experiments in Picea abies and Pinus sylvestris stands in Sweden and Finland. Low application rates (30-50 kg N ha À1 year À1 ) were always more efficient per unit of N than high application rates (50-200 kg N ha À1 year À1 ). Addition of a cumulative amount of N of 600-1800 kg N ha À1 resulted in a mean increase in tree and soil C stock of 25 and 11 kg (C sequestered) kg À1 (N added) (''N-use efficiency''), respectively. The corresponding estimates for NPK addition were 38 and 11 kg (C) kg À1 (N). N-use efficiency for C sequestration in trees strongly depended on soil N status and increased from close to zero at C/N 25 in the humus layer up to 40 kg (C) kg À1 (N) at C/N 35 and decreased again to about 20 kg (C) kg À1 (N) at C/N 50 when N only was added.
Biogeochemistry, 2008
The change of current pools of soil C in Norway spruce ecosystems in Sweden were studied using a process-based model (CoupModel). Simulations were conducted for four sites representing different regions covering most of the forested area in Sweden and representing annual mean temperatures from 0.78C to 7.18C. The development of both tree layer and field layer (understory) was simulated during a 100-year period using data on standing stock volumes from the Swedish Forest Inventory to calibrate tree growth using different assumptions regarding N supply to the plants. The model successfully described the general patterns of forest stand dynamics along the Swedish climatic transect, with decreasing tree growth rates and increasing field layer biomass from south to north. However, the current tree growth pattern for the northern parts of Sweden could not be explained without organic N uptake and/or enhanced mineralisation rates compared to the southern parts. Depending on the assumption made regarding N supply to the tree, different soil C sequestration rates were obtained. The approach to supply trees with both mineralised N and organic N, keeping the soil C:N ratio constant during the simulation period was found to be the most realistic alternative. With this approach the soils in the northern region of Sweden lost 5 g C m À2 year À1 , the soils in the central region lost 2 g C m À2 year À1 , and the soils in the two southern regions sequestered 9 and 23 g C m À2 year À1 , respectively. In addition to climatic effects, the feedback between C and N turnover plays an important role that needs to be more clearly understood to improve estimates of C sequestration in boreal forest ecosystems.
Soil Biology & Biochemistry, 2011
Forests cover one-third of the Earth’s land surface and account for 30–40% of soil carbon (C). Despite numerous studies, questions still remain about the factors controlling forest soil C turnover. Present understanding of global C cycle is limited by considerable uncertainty over the potential response of soil C dynamics to rapid nitrogen (N) enrichment of ecosystems, mainly from fuel combustion and fertilizer application. Here, we present a 15-year-long field study and show an average increase of 14.6% in soil C concentration in the 0–5 cm mineral soil layer in N fertilized (defined as N+ hereafter) sub-plots of a second-rotation Pinus radiata plantation in New Zealand compared to control sub-plots. The results of 14C and lignin analyses of soil C indicate that N additions significantly accelerate decomposition of labile and recalcitrant soil C. Using an annual-time step model, we estimated the soil C turnover time. In the N+ sub-plots, soil C in the light (a density < 1.70 g cm−3) and heavy fractions had the mean residence times of 23 and 67 yr, respectively, which are lower than those in the control sub-plots (36 and 133 yr in the light and heavy fractions, respectively). The commonly used lignin oxidation indices (vanillic acid to vanillin and syringic acid to syringaldehyde ratios) were significantly greater in the N+ sub-plots than in the control sub-plots, suggesting increased lignin decomposition due to fertilization. The estimation of C inputs to forest floor and δ13C analysis of soil C fractions indicate that the observed buildup of surface soil C concentrations in the N+ sub-plots can be attributed to increased inputs of C mass from forest debris. We conclude that long-term N additions in productive forests may increase C storage in both living tree biomass and soils despite elevated decomposition of soil organic matter.► Long-term fertilization leads to detectable increases of soil carbon in 0-5 cm layer. ► Long-term fertilization increases the decomposition of soil organic carbon. ►Increased soil carbon is attributed to elevated inputs from increased productivity.
Forest soils and carbon sequestration
Forest Ecology and Management, 2005
Soils in equilibrium with a natural forest ecosystem have high carbon (C) density. The ratio of soil:vegetation C density increases with latitude. Land use change, particularly conversion to agricultural ecosystems, depletes the soil C stock. Thus, degraded agricultural soils have lower soil organic carbon (SOC) stock than their potential capacity. Consequently, afforestation of agricultural soils and management of forest plantations can enhance SOC stock through C sequestration. The rate of SOC sequestration, and the magnitude and quality of soil C stock depend on the complex interaction between climate, soils, tree species and management, and chemical composition of the litter as determined by the dominant tree species. Increasing production of forest biomass per se may not necessarily increase the SOC stocks. Fire, natural or managed, is an important perturbation that can affect soil C stock for a long period after the event. The soil C stock can be greatly enhanced by a careful site preparation, adequate soil drainage, growing species with a high NPP, applying N and micronutrients (Fe) as fertilizers or biosolids, and conserving soil and water resources. Climate change may also stimulate forest growth by enhancing availability of mineral N and through the CO 2 fertilization effect, which may partly compensate release of soil C in response to warming. There are significant advances in measurement of soil C stock and fluxes, and scaling of C stock from pedon/plot scale to regional and national scales. Soil C sequestration in boreal and temperate forests may be an important strategy to ameliorate changes in atmospheric chemistry.
2019
The effects of atmospheric nitrogen deposition (N dep) on carbon (C) sequestration in forests have often been 60 assessed by relating differences in productivity to spatial variations of N dep across a large geographic domain. These correlations generally suffer from covariation of other confounding variables related to climate and other growth-limiting factors, as well as large uncertainties in total (dry + wet) reactive nitrogen (N r) deposition. We propose a methodology for untangling the effects of N dep from those of meteorological variables, soil water retention capacity and stand age, using a mechanistic forest growth model in combination with eddy covariance CO 2 exchange fluxes from a Europe-wide network of 65 forest flux towers. Total N r deposition rates were estimated from local measurements as far as possible. The forest data were compared with data from natural or semi-natural, non-woody vegetation sites. The carbon sequestration response of forests to nitrogen deposition (dC/dN) was estimated after accounting for the effects of the co-correlates by means of a meta-modelling standardization procedure, which resulted in a reduction by a factor of about 2 of the uncorrected, apparent dC/dN value. This model-enhanced analysis of the C and N dep flux observations at the scale of the European network suggests a mean overall 70 dC/dN response of forest lifetime C sequestration to N dep of the order of 40-50 g (C) g-1 (N), which is slightly larger but not significantly different from the range of estimates published in the most recent reviews. Importantly, patterns of gross primary and net ecosystem productivity versus N dep were non-linear, with no further responses at high N dep levels (N dep > 2.5-3 g (N) m-2 yr-1) partly due to large ecosystem N losses by leaching and gaseous emissions. The reduced increase in productivity per unit N deposited at high N dep levels implies that the forecast increased N r emissions and increased N dep levels 75 in large areas of Asia may not positively impact the continent's forest CO 2 sink. The large level of unexplained variability in observed carbon sequestration efficiency (CSE) across sites further adds to the uncertainty in the dC/dN response. 1 Introduction Atmospheric reactive nitrogen (N r) deposition (N dep) has often been suggested to be a major driver of the large forest carbon (C) sink observed in the Northern Hemisphere (Reay et al., 2008; Ciais et al., 2013), but this view has been challenged, both 80 in temperate (Nadelhoffer et al., 1999; Lovett et al., 2013) and in boreal regions (Gundale et al., 2014). In principle, there is a general consensus that N limitation significantly reduces net primary productivity (NPP) (LeBauer and Treseder, 2008; Zaehle and Dalmonech, 2011; Finzi et al., 2007). However, the measure of carbon sequestration is not the NPP, but the long term net ecosystem carbon balance (NECB; Chapin et al., 2006) or the net biome productivity at a large spatial scale (NBP; Schulze et al., 2010), whereby heterotrophic respiration (R het) and all other C losses, including exported wood products and 85 other disturbances over a forest lifetime, reduce the fraction of photosynthesized C (gross primary production, GPP) that is actually sequestered in the ecosystem. There is considerable debate as to the magnitude of the "fertilisation" role that atmospheric N r deposition may play on forest carbon balance, as illustrated by the controversy over the study by Magnani et al. (2007) and subsequent comments by Högberg (2007), De Schrijver et al. (2008), Sutton et al. (2008), and others. Estimates of the dC/dN response (mass C stored 90 in the ecosystem per mass atmospheric N deposited) vary across these studies over an order of magnitude, from 30-70 g (C) g-1 (N) (