Land-use changes are the second largest source of human-induced greenhouse gas emission, mainly due to deforestation in the tropics and subtropics. CO 2 emissions result from biomass and soil organic carbon (SOC) losses and may be offset with afforestation programs. However, the effect of land-use changes on SOC is poorly quantified due to insufficient data quality (only SOC concentrations and no SOC stocks, shallow sampling depth) and representativeness. In a global meta-analysis, 385 studies on land-use change in the tropics were explored to estimate the SOC stock changes for all major land-use change types. The highest SOC losses were caused by conversion of primary forest into cropland (À25%) and perennial crops (À30%) but forest conversion into grassland also reduced SOC stocks by 12%. Secondary forests stored less SOC than primary forests (À9%) underlining the importance of primary forests for C stores. SOC losses are partly reversible if agricultural land is afforested (1 29%) or under cropland fallow (1 32%) and with cropland conversion into grassland (1 26%). Data on soil bulk density are critical in order to estimate SOC stock changes because (i) the bulk density changes with land-use and needs to be accounted for when calculating SOC stocks and (ii) soil sample mass has to be corrected for bulk density changes in order to compare land-use types on the same basis of soil mass. Without soil mass correction, land-use change effects would have been underestimated by 28%. Land-use change impact on SOC was not restricted to the surface soil, but relative changes were equally high in the subsoil, stressing the importance of sufficiently deep sampling.

A; et al., (2010). Bottom-up effects of plant diversity on multitrophic interactions in a biodiversity experiment. Nature, (468) Bottom-up effects of plant diversity on multitrophic interactions in a biodiversity experiment Abstract Biodiversity is rapidly declining1, and this may negatively affect ecosystem processes, including economically important ecosystem services. Previous studies have shown that biodiversity has positive effects on organisms and processes4 across trophic levels. However, only a few studies have so far incorporated an explicit food-web perspective. In an eight-year biodiversity experiment, we studied an unprecedented range of above-and below-ground organisms and multitrophic interactions. A multitrophic data set originating from a single long-term experiment allows mechanistic insights that would not be gained from meta-analysis of different experiments. Here we show that plant diversity effects dampen with increasing trophic level and degree of omnivory. This was true both for abundance and species richness of organisms. Furthermore, we present comprehensive above-ground/below-ground biodiversity food webs. Both above ground and below ground, herbivores responded more strongly to changes in plant diversity than did carnivores or omnivores. Density and richness of carnivorous taxa was independent of vegetation structure. Below-ground responses to plant diversity were consistently weaker than above-ground responses. Responses to increasing plant diversity were generally positive, but were negative for biological invasion, pathogen infestation and hyperparasitism. Our results suggest that plant diversity has strong bottom-up effects on multitrophic interaction networks, with particularly strong effects on lower trophic levels. Effects on higher trophic levels are indirectly mediated through bottom-up trophic cascades. However, only few studies so far incorporated an explicit food-web perspective 6 . In an 8-50 year biodiversity experiment, we studied an unprecedented range of above-and 51 belowground organisms and biotic interactions. A multitrophic dataset originating from 52 a single long-term experiment allows mechanistic insights that otherwise would not be 53 possible using meta-analysis of different experiments. We show that plant diversity 54 effects dampen with increasing trophic level and degree of omnivory. This finding was 55 consistent both for abundance and species richness of organisms. Further, we present 56 comprehensive above-belowground biodiversity food webs. Both above-and 57 belowground, herbivores responded more strongly to changes in plant diversity than did 58 carnivores or omnivores. Density and richness of carnivorous taxa was independent of 59 vegetation structure. Belowground responses to plant diversity were consistently weaker 60 than aboveground responses. Responses to increasing plant diversity were generally 61 positive, but negative for biological invasion, pathogen infestation and hyperparasitism. 62Our results suggest that plant diversity exhibits stron...

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Land-use change (LUC) is a major driving factor for the balance of soil organic carbon (SOC) stocks and the global carbon cycle. The temporal dynamic of SOC after LUC is especially important in temperate systems with a long reaction time. On the basis of 95 compiled studies covering 322 sites in the temperate zone, carbon response functions (CRFs) were derived to model the temporal dynamic of SOC after five different LUC types (mean soil depth of 30 AE 6 cm). Grassland establishment caused a long lasting carbon sink with a relative stock change of 128 AE 23% and afforestation on former cropland a sink of 116 AE 54%, 100 years after LUC (mean AE 95% confidence interval). No new equilibrium was reached within 120 years. In contrast, there was no SOC sink following afforestation of grasslands and 75% of all observations showed SOC losses, even after 100 years. Only in the forest floor, there was carbon accumulation of 0.38 AE 0.04 Mg ha À1 yr À1 in afforestations adding up to 38 AE 4 Mg ha À1 labile carbon after 100 years. Carbon loss after deforestation (À32 AE 20%) and grassland conversion to cropland (À36 AE 5%), was rapid with a new SOC equilibrium being reached after 23 and 17 years, respectively. The change rate of SOC increased with temperature and precipitation but decreased with soil depth and clay content. Subsoil SOC changes followed the trend of the topsoil SOC changes but were smaller (25 AE 5% of the total SOC changes) and with a high uncertainty due to a limited number of datasets. As a simple and robust model approach, the developed CRFs provide an easily applicable tool to estimate SOC stock changes after LUC to improve greenhouse gas reporting in the framework of UNFCCC.