Forest ecosystems and the changing patterns of nitrogen input and acid deposition today and in the future based on a scenario (original) (raw)
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Major changes in forest carbon and nitrogen cycling caused by declining sulphur deposition
Global Change Biology, 2011
Sulphur (S) and nitrogen (N) deposition are important drivers of the terrestrial carbon (C) and N cycling. We analyzed changes in C and N pools in soil and tree biomass at a highly acidified spruce site in the Czech Republic during a 15 year period. Total S deposition decreased from 5 to 1.1 g m À2 yr À1 between 1995 and 2009, whereas bulk N deposition did not change. Over the same period, C and N pools in the Oa horizon declined by 116 g C and 4.2 g N m À2 yr À1 , a total decrease of 47% and 42%, respectively. This loss of C and N probably originated from organic matter (OM) that had accumulated during the period of high acid deposition when litter decomposition was suppressed. The loss of OM from the Oa horizon coincided with a substantial leaching (1.3 g N m À2 yr À1 at 90 cm) in the 1990s to almost no leaching (<0.02 g N m À2 yr À1 ) since 2006. Forest floor net N mineralization also decreased. This had consequences for spruce needle N concentration (from 17.1 to 11.4 mg kg À1 in current needles), an increase in litterfall C/N ratio (from 51 to 63), and a significant increase in the Oi + Oe horizon C/N ratio (from 23.4 to 27.3) between 1994 and 2009/2010. Higher forest growth and lower canopy defoliation was observed in the 2000s compared to the 1990s. Our results demonstrate that reducing S deposition has had a profound impact on forest organic matter cycling, leading to a reversal of historic ecosystem N enrichment, cessation of nitrate leaching, and a major loss of accumulated organic soil C and N stocks. These results have major implications for our understanding of the controls on both N saturation and C sequestration in forests, and other ecosystems, subjected to current or historic S deposition.
Does nitrogen and sulfur deposition affect forest productivity
2010
We studied the effects of atmospheric nitrogen and sulfur deposition on forest productivity in a 10year-old, aggrading forest stand at the Fernow Experimental Forest in Tucker County, WV. Forest productivity was expressed as total aboveground wood biomass, which included stem and branch weight of standing live trees. Ten years after stand regeneration and treatment initiation, total aboveground wood biomass was compared among three treatments: whole tree harvest (WT), whole tree harvest plus annual nitrogen (N) and sulfur (S) additions at two times ambient deposition rates (WT+NS), and whole tree harvest plus N, S (two times ambient), and dolomitic lime (WT+NS+CA) additions. Furthermore, future stand productivity was estimated for a subsequent 70 years using growth projection simulator SILVAH. Total aboveground wood biomass at 10 years was not significantly different among treatments (ANOVA: F = 1.20, p = 0.33, n = 9). Mean total aboveground wood biomass values for the WT, WT+NS, and WT+NS+CA treatments were 47.5 (± 15.3) Mg ha-1 , 53.0 (± 14.3) Mg ha-1 , and 51.0 (± 15.5) Mg ha-1 , respectively. The dominant tree species was pin cherry (average aboveground dry weight of the three treatments was 38.2 Mg ha-1). Lack of significant differences in the aboveground wood component at the stand level suggests that 10 years of three times ambient rates of nitrogen and sulfur deposition and mitigation did not impact the ability of this site to produce woody biomass. At the species level, however, yellow-poplar had significantly higher diameter at breast height and aboveground wood biomass in the WT+NS+CA stands, indicating the potential for N, S, and Ca additions to impact individual species' growth over forest succession. Projected aboveground wood biomass at stand age 80 was 230.3 Mg ha-1 , 229.9 Mg ha-1 , and 349.7 Mg ha-1 for the respective treatments WT, WT+NS, and WT+NS+CA. Our results suggest that although N and S additions alone do not increase stand growth, N, S, and dolomite additions increase growth of individual species within the first 10 years of stand development. Based on this early biomass increase, long-term growth in the WT+NS+CA treatment may increase 34 percent by forest age 80.
Long-Term Changes in Forest Growth: Potential Effects of Nitrogen Deposition and Acidification
Water Air and Soil Pollution, 2001
In spite of numerous experimental studies, it has, sofar, not been possible to link historic changes inforest growth to acid deposition at regional scales,partly due to difficulties in modeling the ecologicalcomplexity of forests. We analyzed radial incrementdata from increment cores from >31 000 spruce forestplots in southern Norway from 1954–1996. Using acombination of a bio-stratification model to controlconfounding factors, and a catchment model foracidification, we demonstrate for the first time aspatial and temporal co-variation between forestgrowth and both nitrogen deposition and acidification,as indicated by acidity critical loads exceedances.Increases in growth during the 1960–1970s, followed bya subsequent decline in the 1980–1990s, were bestexplained by combined actions of acidification,nitrogen deposition and climatic stress on forestgrowth. While forest conditions varyprimarily with natural growing conditions, the resultssuggest that boreal forests are sensitive to moderatelevels of nitrogen and sulphur deposition whereacidity critical loads are low, and that effects maybe observed over relatively short time scales.
2017
Nitrogen (N) and sulfur (S) depositions are much mitigated over the conterminous U.S. (CONUS) but deposition exceedance still exists on forest soil. In addition, the empirical approach is usually used but only provides a spatially constant critical load (CL). Therefore, the CL derived from steady-state mass balance equation is used to study the CL exceedance on forest soil over the CONUS. The multimodel mean (MMM) of global climate-chemistry models in 2000s indicates that total (wet+dry) N deposition alone over 10.32% of forest soil exceeds the CL, but a higher percent (30.16%) is observed by the N+ S deposition, which highlights the necessity of considering S deposition. In 2050s, less CL-exceeded forest soil is projected and the exceedance amount is lower as well, mainly attributed to the strong reduction of projected NOX and SO2 emissions. By first projecting the future CL due to the climate change, the CL exceedance could further decrease as the air temperature is projected to i...
Atmospheric Environment, 2002
The integrated biogeochemical model, PnET-BGC, was used to simulate the response of soil and surface water at the reference watershed (W6) at the Hubbard Brook Experimental Forest, New Hampshire, to changes in atmospheric deposition. The performance of the model was assessed using two objective statistical criteria, the normalized mean absolute error, and the efficiency, in order to compare simulated results with observed values between 1980 and 1998. Model results showed good agreement with measured concentrations of stream Ca 2+ , and SO 4 2À , while stream NO 3 À and Al concentrations and soil solution Ca/Al ratios were over predicted after 1990. Model simulations showed that there was some improvement in soil and stream chemistry in response to the 1990 Amendments to the Clean Air Act (CAAA) compared to conditions without this legislation. However, the 1990 CAAA will not result in substantial changes in critical indicators (e.g. soil base saturation, soil solution Ca/Al, stream pH, acid neutralizing capacity (ANC) and Al concentrations). The slow recovery rates suggest that additional reduction in strong acid inputs will be required to significantly alleviate ecosystem stress from acidic deposition. Simulation of the impact of equivalent reductions in SO 4 2À and NO 3 À deposition indicated slightly greater recovery under the SO 4 2À reductions compared with NO 3
Nitrogen Saturation in Temperate Forest Ecosystems
BioScience, 1998
e tivity remain elevated in industrialized regions of the world and are accelerating in many developing regions (Galloway 1995). Although the deposition of sulfur has been reduced over much of the United States and Europe by aggressive environmental protection policies, current nitrogen deposition reduction targets in the US are modest. Nitrogen deposition remains relatively constant in the northeastern United States and is increasing in the Southeast and the West (Fenn et al. in press). The US acid deposition effects
Exceedance of critical loads of nitrogen and sulphur and its relation to forest conditions
European Journal of Forest Research, 2005
The calculation of critical loads and their exceedance is one method to describe the vulnerability of forests to environmental stress caused by anthropogenic impact. Exceedance of critical loads for acidifying inputs and nitrogen was compared to different indicators of the soil and forest conditions in the German part of the extensive forest monitoring (ICP Forests/EU Level I), including more than 1,800 plots. In addition, an empirical relationship between the C/N ratio of the forest floor humus layer (C/N Humus) and the estimated nitrogen output for ten plots of the intensive monitoring (ICP Forests/EU Level II) was established in order to estimate the potential nitrogen output on Level I plots dominated by Norway spruce. Regarding all tree species assessed, the exceedance of critical loads for nitrogen and sulphur is negatively correlated with pH and base saturation up to 30 cm soil depth. The sulphur deposition and the exceedance of critical loads are highly correlated with the sulphur content of leaves and needles, whereas the respective relations for nitrogen were lower. The crown condition was weakly positively related to the sulphur content in tree leaves and needles. For Norway spruce sites, high exceedance of critical loads for nitrogen and nitrogen deposition corresponded well with low C/N Humus. In regions with high nitrogen load and low C/N ratios in the humus layer, the calculated nitrogen output was high. The results support the concept of critical thresholds in that way that their exceedance can impair forest ecosystem functions like nitrogen retention.