Showing papers by "Ernst Detlef Schulze published in 2008"

Old-growth forests as global carbon sinks.

Abstract: Old-growth forests remove carbon dioxide from the atmosphere at rates that vary with climate and nitrogen deposition. The sequestered carbon dioxide is stored in live woody tissues and slowly decomposing organic matter in litter and soil. Old-growth forests therefore serve as a global carbon dioxide sink, but they are not protected by international treaties, because it is generally thought that ageing forests cease to accumulate carbon. Here we report a search of literature and databases for forest carbon-flux estimates. We find that in forests between 15 and 800 years of age, net ecosystem productivity (the net carbon balance of the forest including soils) is usually positive. Our results demonstrate that old-growth forests can continue to accumulate carbon, contrary to the long-standing view that they are carbon neutral. Over 30 per cent of the global forest area is unmanaged primary forest, and this area contains the remaining old-growth forests. Half of the primary forests (6 times 10 8 hectares) are located in the boreal and temperate regions of the Northern Hemisphere. On the basis of our analysis, these forests alone sequester about 1.3 plusminus 0.5 gigatonnes of carbon per year. Thus, our findings suggest that 15 per cent of the global forest area, which is currently not considered when offsetting increasing atmospheric carbon dioxide concentrations, provides at least 10 per cent of the global net ecosystem productivity. Old-growth forests accumulate carbon for centuries and contain large quantities of it. We expect, however, that much of this carbon, even soil carbon, will move back to the atmosphere if these forests are disturbed

Carbon accumulation in European forests

Abstract: European forests are intensively exploited for wood products, yet they also form a sink for carbon. European forest inventories, available for the past 50 years, can be combined with timber harvest statistics to assess changes in this carbon sink. Analysis of these data sets between 1950 and 2000 from the EU-15 countries excluding Luxembourg, plus Norway and Switzerland, reveals that there is a tight relationship between increases in forest biomass and forest ecosystem productivity but timber harvests grew more slowly. Encouragingly, the environmental conditions in combination with the type of silviculture that has been developed over the past 50 years can efficiently sequester carbon on timescales of decades, while maintaining forests that meet the demand for wood. However, a return to using wood as biofuel and hence shorter rotations in forestry could cancel out the benefits of carbon storage over the past five decades. European forests are intensively exploited for wood products, yet they are also a potential sink for carbon. European forest inventories combined with timber harvest statistics from sixteen European countries show that between 1950 and 2000 forest biomass increased faster than the amount of timber harvests. Silviculture, which has developed over the past 50 years, can efficiently sequester carbon on timescales of decades, while maintaining forests that meet the demand for wood.

Organic carbon sequestration in earthworm burrows

Abstract: Earthworms strongly affect soil organic carbon cycling. The aim of this study was to determine whether deep burrowing anecic earthworms enhance carbon storage in soils and decrease C turnover. Earthworm burrow linings were separated into thin cylindrical sections with different distances from the burrow wall to determine gradients from the burrow wall to the surrounding soil. Organic C, total N, radiocarbon ( 14 C) concentration, stable isotope values ( δ 13 C, δ 15 N) and extracellular enzyme activities were measured in these samples. Anecic earthworms increased C stocks by 270 and 310 g m −2 accumulated in the vertical burrows. C-enrichment of the burrow linings was spatially highly variable within a distance of millimetres around the burrow walls. It was shown that C accumulation in burrows can be fast with C sequestration rates of about 22 g C m −2 yr −1 in the burrow linings, but accumulated C in the burrows may be mineralised fast with turnover times of only 3–5 years. Carbon stocks in earthworm burrows strongly depended on the earthworm activity which maintains continuous C input into the burrows. The enhanced extracellular enzyme activity of fresh casts was not persistent, but was 47% lower in inhabited burrows and 62% lower in abandoned burrows. Enzyme activities followed the C concentrations in the burrows and were not further suppressed due to earthworms. Radiocarbon concentrations and stable isotopes in the burrow linings showed an exponential gradient with the youngest and less degraded organic matter in the innermost part of the burrow wall. Carbon accumulation by anecic earthworm is restricted to distinct burrows with less influence to the surrounding soil. Contrary to the initial hypothesis, that organic C is stabilised due to earthworms, relaxation time experiments with nuclear magnetic resonance spectroscopy (NMR) did not reveal any enhanced adsorption of C on iron oxides with C stabilising effect. Our results suggest that earthworm activity does not substantially increase subsoil C stocks but burrows serve as fast ways for fresh C transport into deep soil horizons.

Controls on fluxes and export of dissolved organic carbon in grasslands with contrasting soil types

Abstract: Export of dissolved organic carbon (DOC) from grassland ecosystems can be an important C flux which directly affects ecosystem C balance since DOC is leached from the soil to the groundwater. DOC fluxes and their controlling factors were investigated on two grassland sites with similar climatic conditions but different soil types (Vertisol vs. Arenosol) for a 2.5-year period. Parts of both grasslands were disturbed by deep ploughing during afforestation. Contrary to what was expected, ploughing did not increase DOC export but surface soil DOC concentrations decreased by 28% (Vertisol) and 14% (Arenosol). DOC flux from the soil profile was negatively influences by the clay content of the soil with seven times larger DOC export in the clay-poor Arenosol (55 kg C ha−1 a−1) than in the clay-rich Vertisol (8 kg C ha−1 a−1). At the Arenosol site, highest DOC concentrations were measured in late summer, whereas in the Vertisol there was a time lag of several months between surface and subsoil DOC with highest subsoil DOC concentrations during winter season. DOC export was not correlated with soil organic carbon stocks. Large differences in 14C concentrations of 22–40 pMC between soil organic carbon and DOC in the subsoil indicated that both C pools are largely decoupled. We conclude that DOC export at both sites is not controlled by the vegetation but by physicochemical parameters such as the adsorption capacity of soil minerals and the water balance of the ecosystem. Only in the acidic sandy Arenosol DOC export was a significant C flux of about 8% of net ecosystem production.

Characterisation of ecosystem water-use efficiency of european forests from eddy covariance measurements

Abstract: . Water-use efficiency (WUE) has been recognized as an important characteristic of vegetation productivity in various natural scientific disciplines for decades, but only recently at the ecosystem level, where different ways exist to characterize water-use efficiency. Hence, the objective of this research was (a) to systematically compare different ways of calculating ecosystem water-use efficiency (WUEe) from eddy-covariance measurements, (b) quantify the diurnal, seasonal and interannual variability of WUEe in relation to meteorological conditions, and (c) analyse between-site variability of WUEe as affected by vegetation type and climatic conditions, across sites in European forest ecosystems. Day-to-day variability of gross primary productivity (GPP) and evapotranspiration (ET) were more strongly coupled than net ecosystem production (NEP) and ET, obviously because NEP also depends on the respiration that is not heavily coupled to water fluxes. However, the slope of daytime NEP versus ET (mNEP) from half-hourly measurements of a single day may also be used as a WUEe-estimate giving very similar results to those of the GPP-ET slope (mGPP), since the diurnal variation is dominated by GPP. Since ET is the sum of transpiration (linked to GPP) and evaporation from wet vegetation and soil surfaces (not linked to GPP) we expected that WUEe is increasing when days after rain are excluded from the analysis. However only very minor changes were found, justifying an analysis of WUEe related to vegetation type. In most of the studied ecosystems the instantaneous WUEGPP was quite sensitive to diurnally varying meteorological conditions and tended to decline from the morning to the afternoon by more than 50% because of increasing vapour pressure deficits (VPD). Seasonally, WUEGPP increased with a rising monthly precipitation sum and rising average monthly temperatures up to a threshold of 11, 14 and 18°C in boreal, temperate and Mediterranean ecosystems, respectively. Across all sites, the highest monthly WUEGPP-values were detected at times of positive anomalies of summer-precipitation. During drought periods with high temperatures, high VPD, little precipitation and low soil water content, the water-use efficiency of gross carbon uptake (WUEGPP) tended to decrease in all forest types because of a stronger decline of GPP compared to ET. However the largest variation of growing season WUEGPP was found between-sites and significantly related to vegetation type: WUEGPP was highest in ecosystems dominated by deciduous trees ranging from 5.0 g CO2 kg H2O−1 for temperate broad-leaved deciduous forests (TD), to 4.5 for temperate mixed forests (TM), 3.5 for temperate evergreen conifers (TC), 3.4 for Mediterranean broad-leaved deciduous forests (MD), 3.3 for Mediterranean broad-leaved evergreen forests (Mbeg), 3.1 for Mediterranean evergreen conifers (MC), 2.9 for boreal evergreen conifers (BC) and only 1.2 g CO2 kg H2O−1 for a boreal wetland site (BT). Although vegetation type and meteorology co-vary, the WUEGPP variation was hardly related to meteorology, as we could show by comparing similar meteorological conditions only. Furthermore we compared across-site WUEGPP only under conditions when the 10% high GPP rates were exhibited. The between site differences remained, and at all sites ecosystem reached higher WUEGPP levels under this condition. This means when vegetation is most productive usually it also maximises the amount of carbon gained per water lost. Overall our results show that water-use efficiency exhibits a strong time-scale dependency in the sense that at longer time-scale meteorological conditions play a smaller role compared to shorter time scale. Moreover, we highlight the role of vegetation in determining carbon-water relation at ecosystem level. Consequently, all predictions of changing carbon-water cycle under changing climate should take into this role and the differences between vegetation types. These results show the strong time-scale dependency of water-use efficiency

Species richness and identity affect the use of aboveground space in experimental grasslands

Abstract: Complementary resource use is regarded as a mechanism that contributes to positive relationships between biodiversity and ecosystem functioning. Here, we used a biodiversity experiment composed of nine potentially dominant species (grasses: Alopecurus pratensis, Arrhenatherum elatius, Dactylis glomerata, Phleum pratense, Poa trivialis; legumes: Trifolium pratense, T. repens; non-legume herbs: Anthriscus sylvestris, Geranium pratense) to test for differences among monocultures and mixtures and for effects of species richness and the presence of particular species on the use of aboveground space. The number of rooting shoots determined in a line transect increased from monocultures to mixtures. Particularly, the presence of A. elatius in mixtures caused a higher shoot density at the community level. The number of pin contacts per sampling point (cumulative cover) at the community level, analysed with the point intercept method, was higher in mixtures than monocultures, and higher in mixtures with than without A. elatius. The effect was attributable to increased densities across the strata of the vertical stand profile as well as to an increase in community height. The impact of species richness on the use of aboveground space differed considerably between individual species. A. elatius achieved increased densities across all strata of the stand profile, while D. glomerata reached higher densities with a more pronounced use of space in the upper strata with increasing species richness of mixtures. Cumulative cover of P. pratense and A. pratensis was not affected by species richness, while the remaining species decreased space use mostly in the upper strata with increasing species richness or in mixtures with the competitively superior A. elatius. Our study shows that potentially dominant species are limited in their ability for adaptive responses to canopy shading. Nevertheless, the differential responses to species richness of individual species with regard to vertical niche occupation resulted in positive diversity effects on aboveground space use at the community level.

Advection and resulting CO2 exchange uncertainty in a tall forest in central Germany.

Abstract: Potential losses by advection were estimated at Hainich Forest, Thuringia, Germany, where the tower is located at a gentle slope. Three approaches were used: (1) comparing nighttime eddy covariance fluxes to an independent value of total ecosystem respiration by bottom-up modeling of the underlying processes, (2) direct measurements of a horizontal CO2 gradient and horizontal wind speed at 2 m height in order to calculate horizontal advection, and (3) direct measurements of a vertical CO2 gradient and a three-dimensional wind profile in order to calculate vertical advection. In the first approach, nighttime eddy covariance measurements were compared to independent values of total ecosystem respiration by means of bottom-up modeling of the underlying biological processes. Turbulent fluxes and storage term were normalized to the fluxes calculated by the bottom-up model. Below a u* threshold of 0.6 m/s the normalized turbulent fluxes decreased with decreasing u*, but the flux to the storage increased only up...

Annual rainfall does not directly determine the carbon isotope ratio of leaves of Eucalyptus species.

Abstract: Leaf carbon isotope discrimination (delta13C) was widely considered to directly reflect the rainfall environment in which the leaf developed, but recent observations have queried this. The relationship between delta13C and rainfall was explored in Eucalyptus species growing along a rainfall gradient in Australia. The leaves of 43 species of Eucalyptus and the closely related Corymbia species produced in 2003 were sampled in September 2004 at 50 sites and grouped into 15 locations along a rainfall gradient in southwest Western Australia. At 24 sites, the same species and same trees were sampled as in a study in September 2003 when leaves produced in 2002 were sampled. The rainfall in 2004 was on average 190 mm (range 135-270 mm) higher at all locations than in 2003. In the leaves sampled in 2004, the mean carbon isotope discrimination (delta13C) across the 15 locations decreased 2.9 per thousand per 1000 mm of rainfall, the specific leaf area (SLA) increased by 2.9 m2 kg(-1) per 1000 mm of rainfall and the nitrogen (N) content decreased by 1.56 g m(-2) per 1000 mm of rainfall. In contrast, a comparison between the leaves produced in the drier 2002 year compared with the wetter 2003 year showed that there was a strong correlation (r2= 0.85) between the SLA values between years and a trend for higher values with increasing SLA, but the values of delta(13)C were on average only 0.38 per thousand lower (more negative) at all locations in the wetter year, equivalent to a decrease of 2.0 per thousand per 1000 mm of rainfall. The results suggest that while there may be constitutive differences in leaf morphology, SLA and N content per unit area, increasing rainfall or cloudiness associated with higher rainfall increases SLA and decreases N content per unit area. We conclude that rainfall does not directly influence delta13C, but induces leaf morphological and physiological changes that affect the resultant delta13C.

Adaptive survival mechanisms and growth limitations of small-stature herb species across a plant diversity gradient.

Abstract: Several biodiversity experiments have shown positive effects of species richness on aboveground biomass production, but highly variable responses of individual species. The well-known fact that the competitive ability of plant species depends on size differences among species, raises the question of effects of community species richness on small-stature subordinate species. We used experimental grasslands differing in species richness (1-60 species) and functional group richness (one to four functional groups) to study biodiversity effects on biomass production and ecophysiological traits of five small-stature herbs (Bellis perennis, Plantago media, Glechoma hederacea, Ranunculus repens and Veronica chamaedrys). We found that ecophysiological adaptations, known as typical shade-tolerance strategies, played an important role with increasing species richness and in relation to a decrease in transmitted light. Specific leaf area and leaf area ratio increased, while area-based leaf nitrogen decreased with increasing community species richness. Community species richness did not affect daily leaf carbohydrate turnover of V. chamaedrys and P. media indicating that these species maintained efficiency of photosynthesis even in low-light environments. This suggests an important possible mechanism of complementarity in such grasslands, whereby smaller species contribute to a better overall efficiency of light use. Nevertheless, these species rarely contributed a large proportion to community biomass production or achieved higher yields in mixtures than expected from monocultures. It seems likely that the allocation to aboveground plant organs to optimise carbon assimilation limited the investment in belowground organs to acquire nutrients and thus hindered these species from increasing their performance in multi-species mixtures.

Monitoring Carbon Stock Changes in European Soils: Process Understanding and Sampling Strategies

Abstract: Soils are the main reservoir for carbon (C) in terrestrial ecosystems. On a global average, they contain about 2–3 times as much organic carbon (OC) as the atmosphere or standing biomass, namely about 1500–2000 Gt (Janzen 2005). It is well established that this reservoir is not inert, but in a dynamic stage of accumulation or decomposition. These processes are influenced by human activities. A major anthropogenic disturbance of soils is a land-use change from forest or natural grassland to agricultural soils (Johnson and Curtis 2001; Guo and Gifford 2002), and the permanent mechanical disturbance by ploughing. Prairie soils, for instance, lost 50% of their original soil C after 50 years of cultivation, and at a rate of about 70 g m y (Matson et al. 1997). The remaining 50% are temporary stabilized against decomposition by various mechanisms (Gleixner et al. 2001), but also this C can be mobilized under changing conditions, although at a much slower rate. Apparently, there is no organic matter in soils which is totally protected against microbial attack. But accumulation or degradation of soil C are influenced by environmental conditions and management. The total amount of soil C is so large that an activation of this reservoir could result in a significant increase in CO 2 emissions, relevant for the Earth’s climate. In a recent study, Bellamy et al. (2005) demonstrated a C loss across England over the past 20 years which is equivalent to the fossil fuel reduction of England since 1990 (Schulze and Freibauer 2005). On the contrary, studies in forests suggest that there is a long-term accumulation of C despite forest management (Schulze et al. 1996), but this sink is small and becomes most likely only measurable if management comes to a halt (Mund and Schulze 2006). Thus, soils are another example for a ‘slow in, rapid out’ behavior as defined by Korner (2003). Nevertheless, soils have accumulated C across Europe since the pleistocene retreat of glaciers, and contain C which is more than 1000 years old. This net C accumulation from the past could turn into a net C source in the future because of human activity and climate change. Since soils are very dynamic systems, it appears necessary to take changes in soils into account when estimating a global or national C balance. Such a soil monitoring program will include the determination of C pools at national or continental

Exploratorien für funktionelle Biodiversitätsforschung

Abstract: In Mitteleuropa prägt der Mensch seit vielen Jahrhunderten durch vielfältige Bewirtschaftungsformen die Landschaftsstrukturen. Die biologische Vielfalt wurde dadurch teilweise erhöht (ELLENBERG 1996, STÖCKLIN et al. 2007), aber gegenwärtig nimmt sie vor allem aufgrund anhaltender großund kleinskaliger Veränderungen der Landnutzung ab (MEA 2005). Die Veränderungen des Landnutzungstyps und dessen Intensität beruhen auf Entscheidungen der Bewirtschafter. Sie werden von der Verfügbarkeit und den Kosten für Arbeitskräfte und Maschinen sowie von den zu erwartenden Gewinnspannen und Subventionszahlungen für bestimmte Güter und Dienstleistungen bestimmt. Da alle Ebenen der Biodiversität – genetische Diversität, Artendiversität und die Diversität an Lebensgemeinschaften und biologischen Interaktionen zwischen Individuen (WILSON 1992) – durch Landnutzungsänderungen beeinflusst werden können, sind für ein umfassendes Verständnis von Landnutzungseffekten auf die Biodiversität Studien auf all diesen ökologischen Ebenen notwendig.

A roadmap for a continental-scale greenhouse gas observing system in Europe

Abstract: The global growth rate of CO 2 emissions from fossil fuel burning and other industrial processes has been accelerating from 1.1% year in 1990–1999 to more than 3% year in the period 2000–2004 (Raupach et al. 2007). This increase has contributed to an observed increase in the atmospheric growth rate of CO 2 ; during 1990–1999, the atmospheric CO 2 growth rate was estimated at 3.1 Pg C year; for the period of 2000–2005, this is estimated at 4.2 Pg C year (Denman et al. 2007). The increase in emissions has put the growth rates of atmospheric carbon in recent years at the top end of the SRES (Special Report Emission Scenarios) prepared by the Intergovernmental Panel on Climate Change (IPCC) (Nakicenovic et al. 2000). These scenarios are the most important forcing agents used in current climate models to predict the effects of greenhouse gases and aerosols on the Earth’s climate. The dominant factor causing the imbalance appears to be a faster increase in fossil fuel emissions relative to the sink capacity of the land and oceans. The analysis of Raupach et al. (2007) and the various chapters of this book point to the clear need to continue observing the carbon cycle as a means of both to verify and to fingerprint the source of emissions. Raupach et al. furthermore suggest that increased understanding of where the emissions are accelerating, and where decarbonisation of energy use takes place, has important implications for global equity and burden sharing in the costs of global change. This makes understanding the global carbon balance an issue of direct and fundamental relevance to society. Under the Kyoto protocol, the majority of industrial countries have agreed to a reduction of emissions and take other measures to reduce the amount of greenhouse gases in the atmosphere. The effectiveness of greenhouse gas emission reductions needs to be monitored through observations. Although countries regularly report to the United Nations Framework Convention on Climate Change (UNFCCC), this reporting is partial, not always verifiable and not in any way related to the atmospheric increase which it is aimed at to halt. This book also shows how the current greenhouse gas monitoring can be improved upon by new techniques and methods. Denman et al. (2007) noted for the IPCC’s Fourth Assessment Report that the budget of anthropogenic CO 2 can now be calculated with improved accuracy. On