Life cycle inventories of roundwood production in northern Wisconsin: Inputs into an industrial forest carbon budget

Carbon budgets are developed to understand ecosystem dynamics and are increasingly being used to develop global change policy. Traditionally, forest carbon budgets have focused on the biological carbon cycle; however, it is important to include the industrial forest carbon cycle as well. The overall objective of this study was to quantify the major carbon fluxes associated with the production of Wisconsin's industrial roundwood, by using life cycle inventory (LCI) methodology to produce an industrial forest carbon budget. To achieve this objective we (1) developed carbon LCIs for the harvest process for three major forest ownerships (state, national, and private non-industrial), (2) developed carbon LCIs for a dimensional lumber and two oriented strand board (OSB) mills and (3) completed a scaled version of 1 and 2 to include more Wisconsin forestlands and to incorporate the other major processes within the industrial forest carbon cycle (e.g. primary mill, secondary mill, product use and product disposal processes of the industrial forest carbon cycle). The carbon budgets for the harvesting process of the Chequamegon-Nicolet National Forest (CNNF), the Northern Highland American Legion State Forest (NHAL), and the non-industrial private forests that participated in the managed forest laws of Wisconsin (MFL-NIPF) were 0.10, 0.18 and 0.11 tonnes C ha⁻¹ year⁻¹), respectively. The dimensional lumber and OSB products were both net carbon sources, and released 0.05–0.09 tonnes C/tonnes C processed). More carbon is sequestered than released within the industrial forest carbon cycle of Wisconsin's national (6 g C m⁻² year⁻¹), state (12 g C m⁻² year⁻¹) and non-industrial private forests (7 g C m⁻² year⁻¹). Using published net ecosystem production data we estimate that the net forest carbon cycle budget (sum of the biological and industrial C cycle, [Gower, S.T., 2003. Patterns and mechanisms of the forest carbon cycle. Ann. Rev. Environ. Resour. 28, 169–204]) for the CNNF ranges between −897 and 348 g C m⁻² year⁻¹. Life cycle inventories of wood and paper products should be clear and explicitly state what processes are included, so that results can be used by policy makers and future researchers.     

Modelling the effects of forest management intensification on base cation concentrations in soil water and on tree growth in spruce forests in Sweden

The study investigated the effects of forest residue extraction on tree growth and base cations concentrations in soil water under different climatic conditions in Sweden. For this purpose, the dynamic model ForSAFE was used to compare the effects of whole-tree harvesting and stem harvesting on tree biomass and the soil solution over time at 6 different forest sites. The study confirmed the results from experimental sites showing a temporary reduction of base cation concentration in the soil solution for a period of 20–30 years after whole-tree harvesting. The model showed that this was mainly caused by the reduced inputs of organic material after residue extraction and thereby reduced nutrient mineralisation in the soil. The model results also showed that whole-tree harvesting can affect tree growth at nitrogen-poor forest sites, such as the ones in northern Sweden, due to the decrease of nitrogen availability after residue removal. Possible ways of reducing this impact could be to compensate the losses with fertilisation or extract residue without foliage in areas of Sweden with low nitrogen deposition. The study highlighted the need to better understand the medium- and long-term effects of whole-tree harvesting on tree growth, since the results suggested that reduced tree growth after whole-tree harvesting could be only temporary. However, these results do not account for prolonged extraction of forest residues that could progressively deplete nutrient pools and lead to permanent effects on tree growth.

     

Managing forests infested by spruce beetles in south-central Alaska: Effects on nitrogen availability,understory biomass,and spruce regeneration

In Alaska, an outbreak of spruce beetles (Dendroctonus rufipennis) recently infested over one million hectares of spruce (Picea spp.) forest. As a result, land management agencies have applied different treatments to infested forests to minimize fire hazard and economic loss and facilitate forest regeneration. In this study we investigated the effects of high-intensity burning, whole-tree harvest, whole-tree harvest with nitrogen (N) fertilization, and conventional harvest of beetle-killed stands 4 years after treatment, as well as clear-cut salvage harvest 6 years after treatment. We measured available soil ammonium and nitrate and estimated N loss from leaching using in situ cation and anion resin exchange capsules. We also assessed spruce regeneration and responses of understory plant species. Availability and losses of N did not differ among any of the management treatments. Even a substantial application of N fertilizer had no effect on N availability. Spruce regeneration significantly increased after high-intensity prescribed burning, with the number of seedlings averaging 8.9 m⁻² in burn plots, as compared to 0.1 m⁻² in plots that did not receive treatment. Biomass of the pervasive grass bluejoint (Calamagrostis canadensis) was significantly reduced by burning, with burn plots having 9.5% of the C. canadensis biomass of plots that did not receive treatment. N fertilization doubled C. canadensis biomass, suggesting that N fertilization without accompanying measures to control C. canadensis is the least viable method for promoting rapid spruce regeneration.     

Scenario analyses for the effects of harvesting intensity on development of forest resources,timber supply,carbon balance and biodiversity of Finnish forestry

We used national scenario analyses to examine the effects of harvesting intensity on the development of forest resources, timber supply, carbon balance, and biodiversity indicators of Finnish forestry in nine 10-year simulation periods (90-year simulation period) under the current climate. Data from the 11th National Forest Inventory of Finland were used to develop five even-flow harvesting scenarios for non-protected forests with the annual harvest ranging from 40 to 100 million m³. The results show that the highest annual even-flow harvest level, which did not decrease the growing stock volume over the 90-year simulation period, was 73 million m³. The total 90-year timber production, consisting of harvested volume and change in growing stock volume, was maximized when the annual harvest was 60 million m³. Volume increment increased for several decades when harvested volume was less than the current volume increment. The total carbon balance of forestry was the highest with low volume of harvested wood. Low harvested volume increased the values of biodiversity indicators, namely volume of deciduous trees, amount of deadwood and area of old forest.     

Scenario analysis of the impacts of forest management and climate change on the European forest sector carbon budget

Analysis of the impacts of forest management and climate change on the European forest sector carbon budget between 1990 and 2050 are presented in this article. Forest inventory based carbon budgeting with large scale scenario modelling was used. Altogether 27 countries and 128.5 million hectare of forests are included in the analysis. Two forest management and climate scenarios were applied. In Business as Usual (BaU) scenario national fellings remained at the 1990 level while in Multifunctional (MultiF) scenario fellings increased 0.5–1% per year until 2020, 4 million hectare afforestation program took place between 1990 and 2020 and forest management paid more attention to current trends towards more nature oriented management. Mean annual temperature increased 2.5 °C and annual precipitation 5–15% between 1990 and 2050 in changing climate scenario. Total amount of carbon in 1990 was 12 869 Tg, of which 94% in tree biomass and forest soil, and 6% in wood products in use. In 1995–2000, when BaU scenario was applied under current climatic conditions, net primary production was 409 Tg C year⁻¹, net ecosystem production 164 Tg C year⁻¹, net biome production 84.5 Tg C year⁻¹, and net sequestration of the whole system 87.4 Tg C year⁻¹ which was equal to 7–8% of carbon emissions from fossil fuel combustion in 1990. Carbon stocks in tree biomass, soil and wood products increased in all applied management and climate scenarios, but slower after 2010–2020 than that before. This was due to ageing of forests and higher carbon densities per unit of forest land. Differences in carbon sequestration were very small between applied management scenarios, implying that forest management should be changed more than in this study if aim is to influence carbon sequestration. Applied climate scenarios increased carbon stocks and net carbon sequestration compared to current climatic conditions.     

Cost of turning forest residue bioenergy to carbon neutral

Harvesting branches, unmerchantable tree tops and stumps for bioenergy reduces the carbon stock and the sink capacity of forest. We analyzed forest management changes that are financially viable for a forest owner to compensate for carbon loss resulting from the forest harvest residue extraction, and thus lead to truly carbon-neutral forest bioenergy. The management options studied included forest fertilization, elongated rotation periods, varying the type of forest residues extracted, and leaving high stumps. The costs of carbon loss compensation varied widely from 5 to 4000 € ha^− 1 between the management options. The lowest costs resulted from harvesting quickly decomposing branches combined with low levels of fertilization. Harvesting all residues and applying intensive fertilization regimes or postponing final felling generated the highest costs. A requirement for fast carbon loss compensation increased the costs. The results indicated that changes in the forest management improve the carbon benefits of forest bioenergy, and some of these changes are inexpensive for the forest owner. The optimization results suggested that the longer time period was allowed for the carbon loss compensation, the fewer cost-effective silvicultural measures existed in the optimal combination of management regimes for the compensation.     

Long-term effects of repeated urea fertilization in Douglas-fir stands on forest floor nitrogen pools and nitrogen mineralization

In six Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] stands in the Puget Sound Region in Western Washington/USA, forest floor C and N pools were quantified on control plots and on plots that had been fertilized repeatedly with urea 8–30 years ago (total amount of applied N 0.9–1.1 Mg ha⁻¹). Additionally, net N mineralization and nitrification rates were assessed in field and laboratory incubation experiments. Forest floor C/N ratios were decreased on the fertilized plots of all sites compared to the respective control plots. The decreases were particularly strong at sites with initial C/N ratios larger than 30. On sites with low productivity (site index at age 50: <33 m), N fertilization resulted in considerable increases in forest floor N pools. Net N mineralization and nitrification during 12-week field incubation was negligible for the unfertilized and fertilized plots of all except one site (Pack Forest), where the stand had been clear-cut 2 years ago. The increases in N mineralization rates during 12-week laboratory incubation induced by repeated N fertilization showed an inverse relationship to the time elapsed since the last fertilizer application, and were generally larger at sites with initial forest floor C/N ratios >30. For the investigated sites, fertilization effects on net N mineralization sustained for at least 11 years after the last fertilizer application. Nitrification correlated strongly with the forest floor pH; significant formation of NO₃⁻ was observed only for O layers with a pH (H₂O) higher than 4.5.     

Simulation of carbon and water budgets of a Douglas-fir forest

The forest growth/hydrology model FORGRO–SWIF, consisting of a forest growth and a soil water model, was applied to quantify the inter-annual variability of the carbon and water budgets of a Douglas-fir forest (Pseudotsuga menziessii (Mirb.) Franco) in The Netherlands. With these budgets, the water use efficiency, the amount of water needed to fix a certain amount of carbon, and its variability was estimated. After testing the model performance in simulating daily carbon and transpiration fluxes, and soil water contents of this forest ecosystem, the model was applied to a 10-year period of meteorological data. Two forest parameterisations were used: the non-thinned situation of 1995, and the thinned situation in 1996. Relations between forest water use and forest growth were quantified with the model. The model performed satisfactory, an R² value for daily carbon fluxes of 0.58 and for daily transpiration fluxes 0.81. The forest showed to be a clear carbon sink, in the climax situation between 1000 and 1210 g C m⁻² per year. In the thinned situation the carbon uptake was more than halved to values between 430 and 620 g C m⁻² per year. The calculated yearly WUE’s for the forest were between 2.5 and 4.3 g C m⁻² mm⁻¹ and for the total ecosystem between 1.1 and 2.0 g C m⁻² mm⁻¹. The thinned forest had clearly lower WUE’s than the non-thinned forest. The importance of including interception evaporation as forest water use is discussed, and the results showed the importance of integration of forest growth and forest water use for calculating yearly carbon and water budgets.     

The influence of nutrient and water availability on carbohydrate storage in loblolly pine

We quantified the effects of nutrient and water availability on monthly whole-tree carbohydrate budgets and determined allocation patterns of storage carbohydrates in loblolly pine (Pinus taeda) to test site resource impacts on internal carbon (C) storage. A factorial combination of two nutrient and two irrigation treatments were imposed on a 7-year-old loblolly pine stand in the Sandhills of North Carolina. Monthly collections of foliage, branch, stem, bark, and root tissues were made and total non-structural carbohydrate analyses were performed on samples collected in years 3 and 4 after treatment initiation. Seasonal fluxes of carbohydrates reflected the hypothesized use and storage patterns. Starch concentrations peaked in the spring in all tissues measured; however, minimum concentrations in aboveground tissue occurred in late winter while minimum concentrations in below ground tissue occurred in late fall. Increased nutrient availability generally decreased starch concentrations in current year tissue, while increasing starch in 1-year-old woody tissue. Irrigation treatments did not significantly impact carbohydrate flux. The greatest capacity for starch storage was in below ground tissue, accounting for as much as 400 kg C/ha per year, and more than 65% of the total stored starch C pool. The absolute amount of C stored as starch was significantly increased with increased nutrient availability, however, its relative contribution to the total annual C budget was not changed.     

Microbial activity,nutrient dynamics and litter decomposition in a Canadian Rocky Mountain pine forest as affected by N and P fertilizers

To study the specific effects of N and P fertilizers on soil microbial processes under field conditions, a pine forest in southern Alberta was fertilized with ammonium nitrate and urea (0 and 188 kg N ha⁻¹, respectively) singly and in combination with triple super phosphate (0 and 94 kg P ha⁻¹, respectively). Microbial respiration (BR), substrate induced respiration (SIR), metabolic quotient (qCO₂) and rates of microbially mediated key processes were monitored in the forest floor FH material during the growing periods of spring 1990 to fall 1992. A transient increase in soil NH₄⁺ availability was detected following N addition but significant increases in PO₄³⁻ availability were detected throughout the study as a result of P enhancement. Microbial variables were unaffected by N addition, whereas soil organic matter and SIR was increased with P fertilization. Microbial BR and qCO₂ were reduced with P fertilization suggesting more efficient utilization of C. Increased net mineralization of P in the P-fertilized plots was found during the second and third summers after fertilization, following immobilization of P during the first year. In contrast, NH₄⁺-N mineralization in the N-fertilized plots was significantly increased only during the first year. Rates of nitrification were unaffected by either N or P addition. Decomposition of pine litter was enhanced with N addition only during the first year and P had no effect on decomposition. Addition of N and P at these rates does not appear to impose a major ecological stress to the soil ecosystem.     

Changing stock of biomass carbon in a boreal forest over 93 years

The growing stock more than doubled from 1.6 to 3.4 million m³ between 1912 and 2005 in forests on an area of 387 km² in southern Finland. The stock expansion continued for 93 years noting interim results, which were available for 1959, 1982, 1994 and 1999. Forested area in the region hardly changed. Carbon sequestration was mainly a result of a long-term recovery from forest degradation, a legacy of land use in the 18th and 19th centuries. Tree demography responded to management change especially of mature stands: Average tree size and stocking density of stands increased. On average the expanding biomass stock sequestered 18 tons C annually per km² (18 g C per m²). In comparison, the emissions of fossil carbon in the region were estimated at 12 tons C per km² (12 g C per m²) on average. However, fossil CO₂ emissions exceeded biomass sequestration in recent decades. The powerful and persistent expansion of the carbon stock was an unintended co-benefit of forestry, which was motivated by the intention to improve timber yield. On the more negative side the change in management introduced clear-cuts, and a loss of diverse elements of the pre-industrial biota.     

Water quality impacts of forest fertilization with nitrogen and phosphorus

The drinking-water quality of streamwater in forests is typically very good, exceeding the quality of water in areas with other types of land use. Streams draining agricultural lands in the United States average about nine times greater concentrations of nitrate and phosphate than streams draining forested areas. Forest fertilization commonly increases nutrient concentrations in streamwater, and large increases could lead to unacceptable degradation of water quality. This review summarizes information from studies of forest fertilization around the world, and evaluates the responses of streamwater chemistry. In general, peak concentrations of nitrate-N in streamwater increase after forest fertilization, with a few studies reporting concentrations as high as 10–25 (mg N)/l as nitrate. Increases in average concentrations of nitrate are much lower than the peak values, and the highest annual average nitrate-N concentration ever reported was 4 (mg N)/l. Relatively high concentrations of streamwater nitrate-N tend to occur with repeated fertilization, use of ammonium nitrate (rather than urea), and fertilization of N-saturated hardwood forests. Ammonium-N concentrations may also show large peaks following fertilization (up to 15 (mg N)/l), but annual averages remain <0.5 (mg N)/l. Fertilization with phosphate can lead to increased peak concentrations of >1 (mg P)/l, but annual averages remain <0.25 (mg P)/l. No evidence has been reported of detectable effects of forest fertilization on the composition or productivity of stream communities, but more detailed studies may be warranted (especially in relation to P fertilization). Major limitations in current knowledge include the effects of repeated fertilization in short-rotation plantations, fertilization of large landscapes rather than small stands, and the effects of fertilization on streamwater chemistry in tropical plantations.     

Applicability of a forest simulation model for estimating effects of nitrogen deposition on a forest ecosystem: Test of the validity of a gap-type model

Ecosystem models have been used to compile scattered information on various ecosystem processes and to test the hypotheses about ecosystem responses to various simultaneously changing environmental factors. In spite of the widespread use of models, there have been comparatively few quantitative evaluations of model projections compared to long-term observations under changing environmental conditions (e.g. increased nitrogen deposition). In this study we tested the validity of a gap-type forest simulation model (SIMA) in order to extend the applicability of the model for the prediction of how nitrogen deposition influences the production of a boreal forest ecosystem. The validity of the model was tested by comparing the prediction of the model with independent data from long-term fertilization experiments. The predictions provided by the SIMA model agreed fairly well with the results of long-term fertilization experiments. Both the experiments and the model simulations showed similar increases in stem-wood production and in growing stock as a consequence of repeated nitrogen fertilization over the 30-year study period. The addition of nitrogen increased the total production by 30–53% according to field experiments and by 39–63% according to model computations. In both the model calculations and the field experiments, organic matter accumulated in the soil after the addition of nitrogen. The increase in the amount of soil organic matter can be explained as being due to the increased biomass production and the resulting increase in litterfall. According to the model computations, annual litterfall of needles on the mesic site varied from 970 kg ha⁻¹ to 3050 kg ha⁻¹ and this agreed well with measured litterfall of the stand.     

Effects of chronic nitrogen amendment on dissolved organic matter and inorganic nitrogen in soil solution

Increased atmospheric deposition of N to forests is an issue of global concern, with largely undocumented long-term effects on soil solution chemistry. In contrast to bulk soil properties, which are typically slow to respond to a chronic stress, soil solution chemistry may provide an early indication of the long-term changes in soils associated with a chronic stress. At the Harvard Forest, soil solution was collected beneath the forest floor in zero tension lysimeters for 10 years (1993–2002) as part of an N saturation experiment. The experiment was begun in 1988 with 5 or 15 g N m⁻² per year added to hardwood and pine forest plots, and our samples thus characterize the long-term response to N fertilization. Samples were routinely analyzed for inorganic nitrogen, dissolved organic nitrogen (DON), and dissolved organic carbon (DOC); selected samples were also analyzed to determine qualitative changes in the composition of dissolved organic matter. Fluxes of DOC, DON, and inorganic N were calculated based on modeled water loss from the forest floor and observed concentrations in lysimeter samples. The concentration and flux of inorganic N lost from the forest floor in percolating soil solution are strongly affected by N fertilization and have not shown any consistent trends over time. On average, inorganic N fluxes have reached or exceeded the level of fertilizer application in most plots. Concentrations of DOC were unchanged by N fertilization in both the hardwood and pine stands, with long-term seasonal averages ranging from 31–57 mg l⁻¹ (hardwood) and 36–93 mg l⁻¹ (pine). Annual fluxes of DOC ranged from 30–50 g m⁻² per year. DON concentrations more than doubled, resulting in a shift toward N-rich organic matter in soil solution percolating from the plots, and DON fluxes of 1–3 g m⁻² per year. The DOC:DON ratio of soil solution under high N application (10–20) was about half that of controls. The organic chemistry of soil solution undergoes large qualitative changes in response to N addition. With N saturation, there is proportionally more hydrophilic material in the total DON pool, and a lower C:N ratio in the hydrophobic fraction of the total DOM pool. Overall, our data show that fundamental changes in the chemistry of forest floor solution have occurred in response to N fertilization prior to initiation of our sampling. During the decade of this study (years 5–14 of N application) both inorganic N and dissolved organic matter concentrations have changed little despite the significant biotic changes that have accompanied N saturation.     

Natural disasters and economic development drive forest dynamics and transition in China

China has been implementing the world's most ambitious afforestation and forest conservation programs and undergoing rapid forest expansion since 1990s, thus, understanding the forest dynamics in China has global implications for sustainable forest management. Through analyzing forest area, biomass dynamics, and factors influencing deforestation and forest restoration, we found that the natural disasters and economic development drove forest dynamics and transition in China. The growth of the economy and population drove up demand for forest products, facilitating deforestation. The booming economy also boosted government's investment in forest restoration and conservation programs. Natural disasters damaged and frequently destroyed forests, but they also served as stimuli for the authorities to adopt remedy forestry policies and programs that ultimately led to forest increase. Nationwide, increasing peaks of annual afforestation were observed in the late 1950s, early 1980s, and early 2000s, and the newly increased area closed for forest restoration reached the peak in 1998. All these peaks were closely associated with peaks of natural disasters (i.e., floods, drought, and dust storm events). Based on the dynamics of forest area, biomass and forest consumption over the past 40 years, forest transition occurred during the late 1980s to the early 1990s, and it also strengthened the carbon (C) sink function of forests in China (with an increasing rate of 0.137 Pg C yr.⁻¹ during 1994–2008). Overall, our study highlighted the influences of natural disasters and economic development on the forestry policies and forest C dynamics in the newly industrialized country.     

Impacts of atmospheric deposition on New Jersey pine barrens forest soils and communities of ectomycorrhizae

A gradient of increasing N deposition was identified in a southwestern to northeastern transect through the New Jersey pine barrens. The effect of this change in N deposition rate on soil chemistry and ectomycorrhizal morphotype community of pitch pine was studied by sampling from the field under mature pine trees, by planting bait seedlings into the field and in a greenhouse study where seedlings were given differential rates of N applications (0, 35, 140 kg ha⁻¹ equivalent). The field transect showed a significant but small increase in N deposition from 0.35 to 0.72 kg N ha⁻¹ (during the ca. 6 months of the study) equating to 7.84 ± 0.50 kg ha⁻¹ year⁻¹ at the northernmost site, 5.31 ± 0.70 at the middle and 3.66 ± 0.61 kg ha⁻¹ year⁻¹ N at the southwestern most site. Along this transect the ectomycorrhizal morphotype abundance and richness declined significantly under pitch pine. The decline in richness was significantly correlated with the N deposition rate. Bait pitch pine seedlings planted into one of the field sites and fertilized with increasing levels of N showed a reduction in ectomycorrhizal morphotype richness with increased N addition. In a greenhouse study, pine seedling biomass was inversely related to N addition. Nitrogen content of plants increased with increasing N supply, but P content of plants decreased, suggesting that P is a limiting nutrient in this ecosystem. Extractable N from the upper soil horizons increased in cores to which tree seedlings had been added as N addition increased. This indicates an approach to a critical loading of N for these oligotrophic soils, where N supply exceeds seedling N demand. In treeless cores N supply appears to exceed microbial immobilization potential even when no exogenous N is applied. As N supply to greenhouse seedlings increased, ectomycorrhizal morphotype richness declined. By combining data from the field and greenhouse studies, specific ectomycorrhizal morphotype groups were identified by their response to added N. Cortinarius- and Lactarius-like morphotypes were restricted to low levels of N availability. Suilloid- and Ascomycete-like morphotypes were more abundant as soil N availability increases, whereas Russula-like types showed an inverse relationship to N availability. We discuss the results from these oligotrophic sandy soils in comparison with European data derived from richer soils, where mycorrhizal fungal community responses appear to occur only at much higher levels of exogenous N. We attribute these differences to the evolved adaptations of pitch pine and their symbionts to growth in highly oligotrophic environments.     

Carbon and nutrients loos in aboveground biomass along a fire induced forest-savanna gradient in the Gran Sabana,southern Venezuela

Forest degradation and savannization are critical environmental issues associated with forest fires in the Gran Sabana, southern Venezuela. Yet little is known about the ecological consequences resulting from the conversion of forest to savanna in this region. In this study we quantified the change in C and nutrients in aboveground biomass along a fire induced gradient consisting of unburned tall primary forest (TF), slightly fire-affected medium forest (MF), strongly fire-affected low forest (LF) and savanna (S). Total aboveground biomass (TAGB) decreased from 411 Mg ha⁻¹ in TF to 313 Mg ha⁻¹ in MF, 13 Mg ha⁻¹ in LF and 5 Mg ha⁻¹ in S. The pools of C and nutrients in TAGB decreased 13–25% from TF to MF, 88–97% from TF to LF and 97–98% from TF to S. In TF and MF, about 40% of C and over 80% of base cations (Ca, K and Mg) was stored in TAGB, whereas the bulk of N and P were stored in the soil (90% of N and 72% of P). This distribution of elements was different in LF and S, where about 50% of base cations were stored in TAGB, and more than 94% of C, 98% of N and 87% of P were stored in the mineral soil. The large amount of elements stored in the biomass of the tall unburned forest demonstrates the high sensitivity of this ecosystem to fire. The change from tall forest to low forest and savanna implies large losses of C and nutrients stored in aboveground biomass and soils (namely 390–399 Mg C ha⁻¹, 11–13 Mg N ha⁻¹, 70–72 kg P ha⁻¹, 783–818 kg K ha⁻¹, 736–889 kg Ca ha⁻¹, and 200–225 kg Mg ha⁻¹). Such drain of C and nutrients in soils extremely low in silicates, which can replenish the lost nutrients by weathering reduces the recuperation chance of these ecosystems and therefore their future capacity to sequester C and accumulate nutrients.     

Effects of enhanced nitrogen deposition on foliar chemistry and physiological processes of forest trees at the Bear Brook Watershed in Maine

Effects of enhanced nitrogen deposition on nutrient foliar concentrations and net photosynthesis of sugar maple (Acer saccharum Marsh.), American beech (Fagus grandifolia Ehrh) and red spruce (Picea rubens Sarg.) were evaluated at the Bear Brook Watershed in Maine (BBWM). The BBWM is a paired-watershed forest ecosystem study with one watershed treated since 1989 with bimonthly dry ammonium sulfate ((NH₄)₂SO₄) additions at a rate of 25.2 kg N ha⁻¹ year⁻¹, while the other watershed serves as a reference. The (NH₄)₂SO₄ treatment resulted in significant increases in foliar N concentrations for all three species and significant reductions in foliar Ca, Mg and Zn concentrations for American beech and red spruce. Treatment effects on foliar concentrations of other nutrients were not significant in any species. Despite higher N concentrations in all species, only treated sugar maple showed significantly higher photosynthetic rates. The non-response in net photosynthesis to higher foliar N in American beech and red spruce might be attributed to their low foliar Ca and/or Mg concentrations. Higher net photosynthetic rates in sugar maple might be explained by the higher foliar N and by the ability of this species to maintain an adequate Ca and Mg supply. Results suggested that nutrient imbalances due to inadequate supply of Ca and Mg might have counteracted a potential increase in net photosynthesis induced by higher N concentrations in American beech and red spruce.     

Long-term sustainability of forest ecosystems on sandstone in the Vosges Mountains (France) facing atmospheric deposition and silvicultural change

Since the 1980s, atmospheric deposition acidity has generally decreased in European forest ecosystems. However, at many sites, little or no sign of recovery has been observed yet. Concerns are rising about the sustainability of these ecosystems because of reduced nutrients inputs in atmospheric deposition and the increase in biomass harvesting to supply bio-energy.We used a silver fir plot of the French monitoring network (RENECOFOR, site SP57) typical of the ecosystems on sandstone in the Vosges Mountains, to investigate its functioning and its response facing past and possible future changes. We (1) calculated 12-year-mean “input-output” nutrient budgets, (2) measured the change in soil exchangeable cations and anions, (3) used monitoring data to calibrate a process oriented biogeochemical model, NuCM, that was then used to (4) simulate the consequences of two main scenarios and their combinations: constant or reduced atmospheric deposition, and traditional or whole-tree harvesting.Mean term changes in exchangeable nutrients and input-output budgets showed a loss of exchangeable sulphate and base cations, the level of which depended on the method. This combined efflux induced an acidification of soil solution and an alkalinisation of the soil. The model NuCM was successfully calibrated and scenarios were implemented. A slight recovery was simulated when deposition was maintained constant but combined acid and nutrient atmospheric deposition reduction delayed recovery. Whole-tree harvesting drastically decreased soil fertility compared to traditional silviculture. Hence, biomass harvesting in forests on poor soils may counter recovery in the future.     

Nitrogen budgets for Scots pine and Norway spruce ecosystems 12 and 7 years after the end of long-term fertilisation

The magnitude of nitrogen storage and its temporal change in forest ecosystems are important when analysing global change. For example, the accelerated growth of European forests has been linked to increased nitrogen deposition, but the changes in the N inputs that cause long-term changes in ecosystems have not yet been identified. We used two Swedish forest optimum nutrition experiments with Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) to study the long-term fate of N applied to these forest ecosystems. In the pine experiment, in addition to fertiliser (NPK) application, soil acidity was manipulated by application of lime and dilute sulphuric acid. From the spruce experiment, we selected treatments with similar fertiliser doses as in the pine experiment and with and without lime addition.We quantified various terms in the N budget 12 years (pine) and 7 years (spruce) after the last N addition. In the pine stand the NPK-treatment was the only treatment to produce a significant increase in N in the tree biomass (97% above control), whereas in the spruce stand the N additions increased tree N in all treatment combinations (207% above control). In the pine stand the relative distribution of nitrogen between trees and soil did not vary across treatments, with trees containing around 12% of ecosystem N and humus containing around 44% of soil N. The increases in N stocks in the pine stands were mainly in the soil. In contrast, in the spruce ecosystem trees accumulated most of the added N and the increase in the soil was restricted to the humus layer.In the pine ecosystem, large losses of added N (between 254 and 738 kg ha⁻¹ out of 1040 kg ha⁻¹ added as fertiliser) occurred, whereas in the spruce ecosystem we recovered more N than could be accounted for by inputs (between 250 and 591 kg ha⁻¹). There was no clear pattern in the interaction between acidification/liming and N additions.