Biomass and carbon accumulation in a fire chronosequence of a seasonally dry tropical forest

Seasonally dry tropical forests (SDTF) are a widely distributed vegetation type in the tropics, characterized by seasonal rainfall with several months of drought when they are subject to fire. This study is one of the first attempts to quantify above- and belowground biomass (AGB and BGB) and above- and belowground carbon (AGC and BGC) pools to calculate their recovery after fire, using a chronosequence approach (six forests that ranged form 1 to 29 years after fire and mature forest). We quantified AGB and AGC pools of trees, lianas, palms, and seedlings, and BGB and BGC pools (Oi, Oe, Oa soil horizons, and fine roots). Total AGC ranged from 0.05 to nearly 72 Mg C ha⁻¹, BGC from 21.6 to nearly 85 Mg C ha⁻¹, and total ecosystem carbon from 21.7 to 153.5 Mg C ha⁻¹; all these pools increased with forest age. Nearly 50% of the total ecosystem carbon was stored in the Oa horizon of mature forests, and up to 90% was stored in the Oa-horizon of early successional SDTF stands. The soils were shallow with a depth of <20 cm at the study site. To recover values similar to mature forests, BGC and BGB required <19 years with accumulation rates greater than 20 Mg C ha⁻¹ yr⁻¹, while AGB required 80 years with accumulation rates nearly 2.5 Mg C ha⁻¹ yr⁻¹. Total ecosystem biomass and carbon required 70 and 50 years, respectively, to recover values similar to mature forests. When belowground pools are not included in the calculation of total ecosystem biomass or carbon recovery, we estimated an overestimation of 10 and 30 years, respectively.     

Changes in topsoil carbon stock in the Tibetan grasslands between the 1980s and 2004

Climate warming is likely inducing carbon loss from soils of northern ecosystems, but little evidence comes from large-scale observations. Here we used data from a repeated soil survey and remote sensing vegetation index to explore changes in soil organic carbon (SOC) stock on the Tibetan Plateau during the past two decades. Our results showed that SOC stock in the top 30 cm depth in alpine grasslands on the plateau amounted to 4.4 Pg C (1 Pg=10¹⁵ g), with an overall average of 3.9 kg C m⁻². SOC changes during 1980s–2004 were estimated at −0.6 g C m⁻² yr⁻¹, ranging from −36.5 to 35.8 g C m⁻² yr⁻¹ at 95% confidence, indicating that SOC stock in the Tibetan alpine grasslands remained relatively stable over the sampling periods. Our findings are nonconsistent with previous reports of loss of soil C in grassland ecosystems due to the accelerated decomposition with warming. In the case of the alpine grasslands on the Tibetan Plateau studied here, we speculate that increased rates of decomposition as soils warmed during the last two decades may have been compensated by increased soil C inputs due to increased grass productivity. These results suggest that soil C stock in terrestrial ecosystems may respond differently to climate change depending on ecosystem type, regional climate pattern, and intensity of human disturbance.     

Change in CO2 balance under a series of forestry activities in a cool-temperate mixed forest with dense undergrowth

To evaluate the effects on CO₂ exchange of clearcutting a mixed forest and replacing it with a plantation, 4.5 years of continuous eddy covariance measurements of CO₂ fluxes and soil respiration measurements were conducted in a conifer-broadleaf mixed forest in Hokkaido, Japan. The mixed forest was a weak carbon sink (net ecosystem exchange, −44 g C m⁻² yr⁻¹), and it became a large carbon source (569 g C m⁻² yr⁻¹) after clearcutting. However, the large emission in the harvest year rapidly decreased in the following 2 years (495 and 153 g C m⁻² yr⁻¹, respectively) as the gross primary production (GPP) increased, while the total ecosystem respiration (RE) remained relatively stable. The rapid increase in GPP was attributed to an increase in biomass and photosynthetic activity of Sasa dwarf bamboo, an understory species. Soil respiration increased in the 3 years following clearcutting, in the first year mainly owing to the change in the gap ratio of the forest, and in the following years because of increased root respiration by the bamboo. The ratio of soil respiration to RE increased from 44% in the forest to nearly 100% after clearcutting, and aboveground parts of the vegetation contributed little to the RE although the respiration chamber measurements showed heterogeneous soil condition after clearcutting.     

Meeting US biofuel goals with less land: the potential of Miscanthus

Biofuels from crops are emerging as a Jekyll & Hyde – promoted by some as a means to offset fossil fuel emissions, denigrated by others as lacking sustainability and taking land from food crops. It is frequently asserted that plants convert only 0.1% of solar energy into biomass, therefore requiring unacceptable amounts of land for production of fuel feedstocks. The C₄ perennial grass Miscanthus × giganteus has proved a promising biomass crop in Europe, while switchgrass ( Panicum virgatum ) has been tested at several locations in N. America. Here, replicated side-by-side trials of these two crops were established for the first time along a latitudinal gradient in Illinois. Over 3 years of trials, Miscanthus × giganteus achieved average annual conversion efficiencies into harvestable biomass of 1.0% (30 t ha⁻¹) and a maximum of 2.0% (61 t ha⁻¹), with minimal agricultural inputs. The regionally adapted switchgrass variety Cave-in-Rock achieved somewhat lower yields, averaging 10 t ha⁻¹. Given that there has been little attempt to improve the agronomy and genetics of these grasses compared with the major grain crops, these efficiencies are the minimum of what may be achieved. At this 1.0% efficiency, 12 million hectares, or 9.3% of current US cropland, would be sufficient to provide 133 × 10⁹ L of ethanol, enough to offset one-fifth of the current US gasoline use. In contrast, maize grain from the same area of land would only provide 49 × 10⁹ L, while requiring much higher nitrogen and fossil energy inputs in its cultivation.     

Holocene carbon burial by lakes in SW Greenland

The role of the Arctic in future global change processes is predicted to be important because of the large carbon (C) stocks contained in frozen soils and peatlands. Lakes are an important component of arctic landscapes although their role in storing C is not well prescribed. The area around Kangerlussuaq, SW Greenland (66–68°N, 49–54°W) has extremely high lake density, with ∼20 000 lakes that cover about 14% of the land area. C accumulation rates and standing stock (kg C m⁻²), representing late- to mid-Holocene C burial, were calculated from AMS ¹⁴C-dated sediment cores from 11 lakes. Lake ages range from ∼10 000 cal yr  bp to ∼5400 cal yr  bp , and reflect the withdrawal of the ice sheet from west to east. Total standing stock of C accumulated in the studied lakes for the last ∼8000 years ranged from 28 to 71 kg C m⁻², (mean: ∼42 kg C m⁻²). These standing stock determinations yield organic C accumulation rates of 3.5–11.5 g C m⁻² yr⁻¹ (mean: ∼6 g C m⁻² yr⁻¹) for the last 4500 years. Mean C accumulation rates are not different for the periods 8–4.5 and 4.5–0 ka, despite cooling trends associated with the neoglacial period after 4.5 ka. We used the mean C standing stock to estimate the total C pool in small lakes (<100 ha) of the Kangerlussuaq region to be ∼4.9 × 10¹³ g C. This C stock is about half of that estimated for the soil pool in this region (but in 5% of the land area) and indicates the importance of incorporating lakes into models of regional C balance at high latitudes.     

Climate-induced changes in high elevation stream nitrate dynamics

Mountain terrestrial and aquatic ecosystems are responsive to external drivers of change, especially climate change and atmospheric deposition of nitrogen (N). We explored the consequences of a temperature-warming trend on stream nitrate in an alpine and subalpine watershed in the Colorado Front Range that has long been the recipient of elevated atmospheric N deposition. Mean annual stream nitrate concentrations since 2000 are higher by 50% than an earlier monitoring period of 1991–1999. Mean annual N export increased by 28% from 2.03 kg N ha⁻¹ yr⁻¹ before 2000 to 2.84 kg N ha⁻¹ yr⁻¹ in Loch Vale watershed since 2000. The substantial increase in N export comes as a surprise, since mean wet atmospheric N deposition from 1991 to 2006 (3.06 kg N ha⁻¹ yr⁻¹) did not increase. There has been a period of below average precipitation from 2000 to 2006 and a steady increase in summer and fall temperatures of 0.12 °C yr⁻¹ in both seasons since 1991. Nitrate concentrations, as well as the weathering products calcium and sulfate, were higher for the period 2000–2006 in rock glacier meltwater at the top of the watershed above the influence of alpine and subalpine vegetation and soils. We conclude the observed recent N increases in Loch Vale are the result of warmer summer and fall mean temperatures that are melting ice in glaciers and rock glaciers. This, in turn, has exposed sediments from which N produced by nitrification can be flushed. We suggest a water quality threshold may have been crossed around 2000. The phenomenon observed in Loch Vale may be indicative of N release from ice features such as rock glaciers worldwide as mountain glaciers retreat.     

Changes in soil organic carbon under biofuel crops

One potentially significant impact of growing biofuel crops will be the sequestration or release of carbon (C) in soil. Soil organic carbon (SOC) represents an important C sink in the lifecycle C balances of biofuels and strongly influences soil quality. We assembled and analyzed published estimates of SOC change following conversion of natural or agricultural land to biofuel crops of corn with residue harvest, sugarcane, Miscanthus x giganteus , switchgrass, or restored prairie. We estimated SOC losses associated with land conversion and rates of change in SOC over time by regressing net change in SOC relative to a control against age since establishment year. Conversion of uncultivated land to biofuel agriculture resulted in significant SOC losses – an effect that was most pronounced when native land was converted to sugarcane agriculture. Corn residue harvest (at 25–100% removal) consistently resulted in SOC losses averaging 3–8 Mg ha⁻¹ in the top 30 cm, whereas SOC accumulated under all four perennial grasses, with SOC accumulation rates averaging <1 Mg ha⁻¹ yr⁻¹ in the top 30 cm. More intensive harvests led to decreased C gains or increased C losses – an effect that was particularly clear for residue harvest in corn. Direct or indirect conversion of previously uncultivated land for biofuel agriculture will result in SOC losses that counteract the benefits of fossil fuel displacement. Additionally, SOC losses under corn residue harvest imply that its potential to offset C emissions may be overestimated, whereas SOC sequestration under perennial grasses represents an additional benefit that has rarely been accounted for in life cycle analyses of biofuels.     

Amazonian peatlands: an ignored C sink and potential source

In tropical lowlands, peatlands are commonly reported from Southeast Asia, and especially Indonesian tropical peatlands are known as considerable C sinks and sources. In contrast, Amazonia has been clearly understudied in this context. In this study, based on field observations from 17 wetland sites in Peruvian lowland Amazonia, we report 0–5.9 m thick peat deposits from 16 sites. Only one of the studied sites did not contain any kind of peat deposit (considering pure peat and clayey peat). Historic yearly peat and C accumulation rates, based on radiocarbon dating of peat samples from five sites, varied from 0.94 ± 0.99 to 4.88 ± 1.65 mm, and from 26 ± 3 to 195 ± 70 g C m⁻², respectively. The long-term apparent peat and C accumulation rates varied from 1.69 ± 0.03 to 2.56 ± 0.12 mm yr⁻¹, and from 39 ± 10 to 85 ± 30 g C m⁻² yr⁻¹, respectively. These accumulation rates are comparable to those determined in the Indonesian tropical peatlands. Under altered conditions, Indonesian peatlands can release globally relevant amounts of C to the atmosphere. Considering the estimated total area of Amazonian peatlands (150 000 km²) close to that of the Indonesian ones (200 728 km²) as well as several factors threatening the Amazonian peatlands, we suggest that the total C stocks and fluxes associated with Amazonian peatlands may be of global significance.     

Changes in organic carbon distribution with depth in agricultural soils in northern Belgium, 1960–2006

In most studies concerning the carbon (C) exchange between soil and atmosphere only the topsoil (0–0.3 m) is taken into account. However, it has been shown that important amounts of stable soil organic carbon (SOC) are also stored at greater depth. Here, we developed a quantitative model to estimate the evolution of the distribution of SOC with depth between 1960 (database 'Aardewerk') and 2006 in northern Belgium. This temporal analysis was conducted under different land use, texture and drainage conditions. The results indicate that intensified land management practices seriously affect the SOC status of the soil. The increase in plough depth and a change in crop rotation result in a significant decrease of C near the surface for dry silt loam cropland soils, (i.e. 1.02 ± 0.23 kg C m⁻² in the top 0.3 m between 1960 and 2006). In wet to extremely wet grasslands, topsoil SOC decreased significantly, indicating a negative influence of intensive soil drainage on SOC stock. This resulted in a decline of SOC between 1960 and 2006 in the top 1 m, ranging from 3.99 ± 2.57 kg C m⁻² in extremely wet silt loam soils to 2.04 ± 2.08 kg C m⁻² in wet sandy soils. A slight increase of SOC stock is observed under dry to moderately wet grasslands at greater depths corresponding to increased livestock densities in the region. The increase of SOC in the top 1 m under grassland ranges from 0.65 ± 1.39 kg C m⁻² in well drained silt loam soils to 2.59 ± 6.49 kg C m⁻² in moderately drained silt loam soils over entire period.     

Near-zero recent carbon accumulation in a bog with high nitrogen deposition in SW Sweden

We present data on the accumulation of carbon and nitrogen into an open oceanic ombrotrophic bog, SW Sweden, with high levels of anthropogenic nitrogen deposition. The aim was to investigate if this peatland currently acts as a sink for atmospheric carbon. Peat cores were sampled from the top peat layer in five different vegetation types. Small pines were used to date the cores. The cores bulk density and carbon and nitrogen content were determined. A vegetation-classified satellite image was used to estimate the areal extent of the vegetation types and to scale up these results to bog level. The rate of current carbon input into the upper oxic acrotelm was 290 g m⁻² yr⁻¹, and there were no significant differences in accumulation rates among the vegetation types. This organic matter input to the acrotelm was almost completely decomposed before it was deposited for storage in the deeper peat layers (the catotelm) and only a small fraction (≪1%) or 0.012 g m⁻² yr⁻¹ of the carbon would be left, assuming a residence time of 100 years in the acrotelm. Nitrogen accumulation rates differed between the vegetation classes, and the average input via primary production varied from 5.33 to 16.8 g m⁻² yr⁻¹. Current nitrogen input rates into the catotelm are much lower, 0–0.059 g m⁻² yr⁻¹, with the highest accumulation rates in lawn-dominated communities. We suggest that one of the main causes of the low carbon input rates is the high level of nitrogen deposition, which enhances decomposition and changes the vegetation from peat-forming Sphagnum -dominance to dominance by dwarf shrubs and graminoids.     

On linking multiyear biometric measurements of tree growth with eddy covariance-based net ecosystem production

Annual measurements of the diameter growth and litter fall of trees began in 1998 using a 1.0 ha permanent plot beneath a flux tower at the Takayama flux site, central Japan. This opened up an opportunity for studies that compare the interannual variability in tree growth with eddy covariance-based net ecosystem production (NEP). A possible link between multiyear biometric-based net primary production (NPP) and eddy covariance-based NEP was investigated to determine the contribution of autotrophic production and heterotrophic respiration (HR) to the interannual variability of NEP in deciduous forest ecosystems. We also defined the NEP^* as the measurable organic matter stored in an ecosystem during the interval in which soil respiration (SR) measurements were taken. The difference of biometric-based NEP^* from eddy covariance-based NEP within a given year varied between 55% and 105%. Woody tissue NPP (stems and coarse roots) varied markedly from 0.88 to 1.96 Mg C ha⁻¹ yr⁻¹ during the 8-year study period (1999–2006). Annual woody tissue NPP was positively correlated with eddy covariance-based NEP ( r ²=0.52, P <0.05). However, neither foliage NPP ( r ²=0.03) nor HR ( r ²=0.06) were correlated with eddy covariance-based NEP. Therefore, it was hypothesized that interannual variability in the ecosystem carbon exchange was directly responsible for much of the interannual variation in autotrophic production, especially carbon accumulation in the woody components of the ecosystem. Moreover, similar interannual variations of biometric-based NEP^* and eddy covariance-based NEP with small variations in SR and foliage NPP suggest a constant net accumulation of carbon in nonliving pools at the Takayama site.     

Effect of leaf age on CAM activity in Littorella uniflora

In this study the effect of ontogenetic drift on crassulacean acid metabolism (CAM) was investigated in the aquatic CAM-isoetid Littorella uniflora. The results of this study strengthen the general hypothesis of CAM being a carbon-conserving mechanism in aquatic plants, because high-CAM capacity (45–183 μequiv. g⁻¹ FW) was present in all leaves of L. uniflora irrespective of age. Since possession of CAM in aquatic plants allows CO₂ uptake throughout the light/dark cycle, presence of CAM in all leaves influences the carbon balance of L. uniflora positively. On average for all lakes, different leaf classes accounted for 11–36% of the total dark CO₂ uptake by the individual plant.

The capacity for both CAM and photosynthesis declined with increasing leaf age, and was in the oldest leaves only 25–53% of the capacity in the youngest. The photosynthetic capacity was estimated to be sufficiently high to ensure refixation of the CO₂ released from malate during decarboxylation in the daytime. In line with this, a linear coupling between CAM capacity and photosynthetic capacity was found. Parallel to the change in photosynthetic capacity, an age-related change in total ribulose-bisphosphate carboxylase/oxygenase (rubisco) activity from 732 μmol C g⁻¹ DW h⁻¹ in the youngest leaves to 346 μmol C g⁻¹ DW h⁻¹ in the oldest was observed. In contrast, no significant change in phosphoenolpyruvate carboxylase (PEPcase) activity with leaf age was observed (means ranged between 46 and 156 μmol C g⁻¹ DW h⁻¹).     

Simulated chronic nitrogen deposition increases carbon storage in Northern Temperate forests

High levels of atmospheric nitrogen (N) deposition in Europe and North America were maintained throughout the 1990s, and global N deposition is expected to increase by a factor of 2.5 over the next century. Available soil N limits primary production in many terrestrial ecosystems, and some computer simulation models have predicted that increasing atmospheric N deposition may result in greater terrestrial carbon (C) storage in woody biomass. However, empirical evidence demonstrating widespread increases in woody biomass C storage due to atmospheric N deposition is uncommon. Increased C storage in soil organic matter due to chronic N inputs has rarely been reported and is often not considered in computer simulation models of N deposition effects. Since 1994, we have experimentally simulated chronic N deposition by adding 3 g N m⁻² yr⁻¹ to four different northern hardwood forests, which span a 500 km geographic gradient in Michigan. Each year we measured tree growth. In 2004, we also examined soil C content to a depth of 70 cm. When we compared the control treatment with the NO₃⁻ deposition treatment after a decade of experimentation, ecosystem C storage had significantly increased in both woody biomass (500 g C m⁻²) and surface soil (0–10 cm) organic matter (690 g C m⁻²). The increase in surface soil C storage was apparently driven by altered rates of organic matter decomposition, rather than an increase in detrital inputs to soil. Our results, for study locations stretching across hundreds of kilometers, support the hypothesis that chronic N deposition may increase C storage in northern forests, potentially contributing to a sink for anthropogenic CO₂ in the northern Hemisphere.     

Terrestrial export of highly bioavailable carbon from small boreal catchments in spring floods

1. We assessed the terrestrial export of organic carbon, which effectively supported aquatic bacterial production (BP), from small boreal catchments during spring flood. We analysed stream runoff from nine small catchments with different proportions of peat mires and coniferous forests by monitoring the dissolved organic carbon (DOC) flux in combination with conducting bacterial bioassays.
2. Multiple linear regression analysis showed that BP during 7-day-dark bioassays (BP₇; μg C L⁻¹day⁻¹) was explained by both the quantity and quality (low-molecular weight fractions) of the DOC. BP₇ can be used as a measure of export of terrestrial organic carbon that is highly bioavailable.
3. Total export of DOC during spring flood from the different catchments ranged from 20 to 27 kg ha⁻¹ and was negatively correlated to forest cover (%). However, the export of BP₇ carbon was positively correlated to forest cover and varied from about 0.1 kg ha⁻¹ in mire-dominated streams to about 0.2 kg ha⁻¹ in forest-dominated streams.
4. The high bioavailability of forest carbon suggests that forests are the main contributors of BP-supporting carbon in boreal streams although mires have higher area-specific export of DOC.     

Storms can cause Europe-wide reduction in forest carbon sink

Disturbance of ecosystems is a major factor in regional carbon budgets, and it is believed to be partly responsible for the large inter-annual variability of the terrestrial part of the carbon balance. Forest fires have so far been considered as the most important disturbance but also other forms of disturbance such as insect outbreaks or wind-throw might contribute significantly to the largely unexplained inter-annual variability, at least in specific regions. The effect of wind-throw has not yet been estimated because of lack of data on how carbon fluxes are affected. The Gudrun storm, which hit Sweden in January 2005, resulted in ca. 66 million m³ of wind-thrown stem wood on an area of ca. 272 000 ha. Using a model (BIOME-BGC) calibrated to CO₂ flux measurements at two sites, the annual net ecosystem productivity during the first year after the storm was estimated to be in the range −897 to −1259 g C m⁻² yr⁻¹. This is a much higher loss compared with harvested (clear-cut) forests in Europe, which ranged between ca. −420 and −100 g m⁻² yr⁻¹. The reduction in the carbon sink scaled to the whole wind-thrown area was estimated at ca. 3 million tons C during the first year. By historical data on wind-throw in Europe combined with modelling, we estimated that the large Lothar storm in 1999 reduced the European carbon balance by ca. 16 million tons C, this is ca. 30% of the net biome production in Europe. We conclude that the impact of increased forest damage by more frequent storms in future climate change scenarios must be considered and that intermittent large wind-throw events may explain a part of the large inter-annual variability in the terrestrial carbon sink.     

Nitrogen effects on net ecosystem carbon exchange in a temperate steppe

It has widely been documented that nitrogen (N) enrichment stimulates plant growth and net primary production. However, there is still dispute on how N addition affects net ecosystem CO₂ exchange (NEE), which represents the balance between ecosystem carbon (C) uptake and release. We conducted an experimental study to examine effects of N addition on NEE in a temperate steppe in northern China from 2005 to 2008. N was added at a rate of 10 g N m⁻² yr⁻¹ with NH₄NO₃ alone or in combination with phosphorous (P, 5 g P₂O₅ m⁻² yr⁻¹) in both clipped and unclipped plots. Over the 4 years, N addition significantly stimulated growing-season NEE, on average, by 27%. Neither the main effects of P addition or clipping nor their interactions with N addition were statistically significant on NEE in any of the 4 years. However, the magnitude of N stimulation on NEE declined over time. N addition significantly increased NEE by 60% in 2005 and 21% in 2006, but its effect was not significant in 2007 and 2008. N-induced shift in species composition was primarily responsible for the declined N stimulation over time. The gradually increasing coverage of the upper canopy species ( Stipa krylovii ) and standing litter accumulation induced light limitation on the lower canopy species ( Artemisia frigida ). Thus, N-induced shifts in plant species composition strongly regulated the direct effects of N addition on C sequestration in the temperate steppe.     

Artificial drainage and associated carbon fluxes (CO2/CH4) in a tundra ecosystem

Ecosystem flux measurements using the eddy covariance (EC) technique were undertaken in 4 subsequent years during summer for a total of 562 days in an arctic wet tundra ecosystem, located near Cherskii, Far-Eastern Federal District, Russia. Methane (CH₄) emissions were measured using permanent chambers. The experimental field is characterized by late thawing of permafrost soils in June and periodic spring floods. A stagnant water table below the grass canopy is fed by melting of the active layer of permafrost and by flood water. Following 3 years of EC measurements, the site was drained by building a 3 m wide drainage channel surrounding the EC tower to examine possible future effects of global change on the tundra tussock ecosystem. Cumulative summertime net carbon fluxes before experimental alteration were estimated to be about +15 g C m⁻² (i.e. an ecosystem C loss) and +8 g C m⁻² after draining the study site. When taking CH₄ as another important greenhouse gas into account and considering the global warming potential (GWP) of CH₄ vs. CO₂, the ecosystem had a positive GWP during all summers. However CH₄ emissions after drainage decreased significantly and therefore the carbon related greenhouse gas flux was much smaller than beforehand (475 ± 253 g C-CO₂-e m⁻² before drainage in 2003 vs. 23 ± 26 g C-CO₂-e m⁻² after drainage in 2005).     

European-wide GIS-based modelling system for quantifying the feedstock from Miscanthus and the potential contribution to renewable energy targets

Reliable estimates of feedstock resources are a prerequisite to the establishment of a biomass based-industry for energy and non food products. Field trials in the European Union (EU) show that Miscanthus spp. can produce high yields. Here we use a model (MISCANMOD) coupled with a GIS environment to estimate the contribution that Miscanthus could make to projected national electricity consumption. We describe the integration of different data sets, transformation procedures, and spatial analyses using GIS to produce energy statistics for the EU-25. Overall, Miscanthus grown on the 10% of arable land which is currently in set-aside could generate 282 TWh yr⁻¹ electricity. This would meet 39% of the EU-25 target of 723 TWh yr⁻¹ of electricity from renewable energy sources (RES) by 2010. As RES targets rise, land available for energy crops is also expected to increase. We consider three additional scenarios where Miscanthus could be grown on 10%, 20% and 35% of all agricultural land and we estimate it could generate respectively 345, 691 and 1209 TWh yr⁻¹ of electrical energy. At a national scale France, Poland and Germany have the highest potentials for Miscanthus production based on agricultural land area (respectively 83, 52, 49 TWh yr⁻¹ when 10% agricultural land is used). Finally, we reduced the scale to the EU NUTS2 (Nomenclature of Territorial Units for Statistics) regions to examine regional generation capacities. Key regions have been identified where national RES targets are exceeded. These regions could become net exporters of renewable energy.     

Storage and turnover of carbon in grassland soils along an elevation gradient in the Swiss Alps

Amount, composition, and rate of turnover of soil organic carbon (SOC) in mountainous cold regions is largely unknown, making predictions of future responses of this carbon (C) to changing environmental conditions uncertain. We hypothesized increasing amounts and declining turnover times of soil organic matter (SOM) under permanent grassland with increasing elevation and decreasing temperature. Samples from an irrigated transect in the Swiss Alps (880 to 2200 m elevation, mean annual temperatures +8.9 to +0.9 °C) were analyzed. Soil C stocks ranged from 49 to 96 t C ha⁻¹ (0–20 cm) and were not related to elevation, though the highest site stored least C. Particulate organic carbon (POC) increased significantly with elevation and accounted for > 80% of the total soil C at 2200 m (0–5 cm). Mean residence times (MRTs) of POC computed by means of radiocarbon dating were in the order of years to decades and were positively related to elevation in the topsoil. At higher elevations, the estimated total C flux through the soil profile mainly depended on this fraction. MRT of mineral-associated matter ranged from decades to centuries and was not systematically related to elevation, but positively related to the soil mineral surface area and it increased with soil depth. Turnover rates from simulations with the soil C model RothC exceeded those from ¹⁴C measurements by a factor of 1.7–3.3 which suggests that C dynamics at these sites is overestimated by the model. Size of model pools and amount of C in soil fractions were only weakly correlated, thereby challenging previously postulated hypotheses concerning the correspondence of pools and fractions for grasslands at higher elevations.     

Tree population dynamics in Kibale National Park, Uganda 1975–1998

Changes in species composition, stem abundance, and basal area of trees taller than or equal to 10 m in a medium altitude tropical rain forest at the Ngogo study area, Kibale National Park, Uganda are described for the period between 1975 and 1998 ( n  = 23 years). Two enumeration episodes were conducted in 263 plots of 5 m by 50 m during 1975–80 and 1997–98. During this period, species richness decreased by 3% (from 92 to 89). Species diversity (H') also declined slightly from 2.97 to 2.86. The number of trees recorded in the sample plots decreased by 8% (from 2545 to 2329), while basal area decreased from 49.48 m² ha⁻¹ to 48.68 m² ha^−1. However, stem abundance and basal area increased for some species.