Search

Questions: Livestock management in rangelands depends on the production of plant biomass. Biomass production is driven by the temporal and spatial variability in precipitation, but our understanding of how precipitation variability mediates grazing effects on biomass production is still fragmented. Along a 600-km precipitation gradient we extracted biomass data to ask the questions: (a) what are the effects of grazing intensity on biomass production; (b) does grazing intensity interact with plant species richness to affect biomass production; and (c) how do plant functional groups respond to grazing and precipitation?. Location: Mongolia. Methods: Biomass was sampled along 15 grazing intensity transects within the precipitation gradient over two consecutive years. We modeled spatial variability in above-ground plant biomass using mixed-effects models. Normalized difference vegetation index (NDVI) data were combined with field-sampled biomass data to correct for inter-annual precipitation variation. The effects of species richness were modeled with respect to possible interactions with grazing intensity, and the composition of plant functional groups was modeled with respect to possible interactions between grazing intensity and precipitation. Results: Biomass was negatively correlated with grazing intensity and this effect increased as precipitation increased. Biomass was positively correlated with species richness in both years, but the strength of this effect and the interaction between species richness and grazing intensity differed between 2014 and 2015 in line with highly variable precipitation between both years. The plant functional groups grasses, sedges, legumes, wormwood and forbs had contrasting responses to grazing and precipitation. Conclusion: Biomass production in drylands is more vulnerable to changes in precipitation variability and grazing intensities in relatively moist and productive rangelands than in dry and unproductive ones. Future rangeland management needs to address potentially increasing precipitation variability in order to promote desired forage plants, and to preserve the positive effects of biodiversity for biomass production.

Mongolia contains some of the largest intact grasslands in the world, but is vulnerable to future changes in climate and continued increases in the number of domestic livestock. As these are two major drivers of change, it is important to understand interactions between the impact of climate and grazing on productivity of Mongolia’s rangelands and the livelihoods they sustain. We use a gridded, spatially explicit model, the Rangeland Production Model (RPM), to explore the simultaneous and interacting effects of climate and management changes on Mongolia’s rangeland and future livestock production. Comparing the relative impact of temperature, precipitation, and grazing intensity, varied individually and in combination, we find that climatic factors dominate impacts on forage biomass and animal diet sufficiency. Site rainfall strongly mediates the impact of grazing on standing biomass, such that more productive or higher-rainfall sites are more vulnerable to increases in grazing pressure. Gridded simulations covering Mongolia’s Gobi-Steppe ecoregion show that while rangeland biomass is generally predicted to increase under future climate conditions, interactions among spatially varying drivers create strong heterogeneity in the magnitude of change.

In Germany, renewable raw materials are cultivated on approximately 15 percent of the agricultural area. Crops for biogas production have the largest cultivation area, followed by crops for biofuels. A minor role is played by the cultivation of crops for material use; these raw materials are mainly imported. Research is carried out into ecologically beneficial energy crops to develop greater crop diversity. To introduce these crops into practice, there is a need to promote the respective framework conditions. Peat moss cultivated on rewetted bog sites could offer an alternative to white peat extraction. Wood is the most important renewable raw material in Germany. In the meantime, around the same amount of wood (primary and secondary) is used to produce material and energy. In the forest, timber stocks are still increasing. However, while almost half of the forest land is planted with hardwood, the demand for roundwood (sawable wood in the rough) is overwhelmingly covered by softwood. This imbalance is a challenge for the future. Renewable raw materials have changed and enriched the agricultural landscape in Germany over the last 25 years. The politically desired change to the bioeconomy will intensify land use. Therefore, it is important to transfer the principles of sustainable land use and biomass production into the practice of agricultural production.

There are still major gaps in our understanding of rangeland degradation. Assessing the interactions between climate and grazing effects could help to explain what unifies and separates rangelands, and may therefore promote a more sustainable management of livestock. We studied 15 local land-use transects along a 600 km long climatic gradient in Central Asia to test the hypothesis that grazing effects differ between relatively moist equilibrium (EQ) and dry non-equilibrium (NEQ) rangeland systems. We analysed plant community composition, species diversity and indicator species for different grazing intensities. We found pronounced differences in community composition along our climate gradient, revealed climate-related grazing effects on richness, responses of Simpson's diversity, and also found different grazing indicator species along the larger transect. We conclude that in NEQ rangelands, grazing effects are limited to sacrifice zones and environmental filtering dominates vegetation composition. With increasing precipitation, resource availability gains in importance leading to more complex communities dominated by grazing-tolerant species under EQ dynamics. Hints for xerophytization in the transition zone between EQ and NEQ highlight the vulnerability of rangelands that temporally shift from one state to the other. This calls for extra care in the management of livestock numbers in these transition areas.

As a result of water regulation measures and the subsequent introduction of intensive use practices, riverine floodplains have suffered severe habitat and species losses. With the changed economic conditions and decrease in animal stocking rates after 1990, opportunities arose for the partial restoration of species-rich vegetation areas in East Germany. Sixty permanent plots were established in the lower Havel Valley in the federal state of Brandenburg from 1993 to 1999. We studied the effects of extensification and partial rewetting in this area during a monitoring programme that lasted until 2018. For this purpose, groundwater levels, historical land use, and soil chemical parameters were investigated, and the soil seed bank and phytosociological releves were sampled. Previous research has shown that an extended period of intensive grassland use eliminates the possibility of success in short- to medium-term natural restoration because of the lack of suitable propagules. Our question was as follows: how does a floodplain grassland respond to extensification and decreased water regulation in an area that experienced a shorter period of intensification in the past, such as the lower Havel floodplain? Tests of soil samples showed a depleted soil seed bank at the beginning of the monitoring period, but the seed bank was less depleted than those in other areas. Using cluster analysis followed by discriminant analysis, we identified water regime parameters and historical land-use intensity as the main drivers of vegetation differentiation. The classification resulted in the differentiation of vegetation into 13 plant communities. Plant communities were combined into 5 main groups based on their location in the ordination diagram of a detrended correspondence analysis. The shift in group centroids over time correlated with increases in the species diversity and moisture level for all groups. The altered species composition as a result of the changed water regime after 1990 influenced the usability of the grassland differently depending on the relief level. At the end of monitoring, vegetation at sites in the mesic moisture range was determined to have the highest fodder quality observed in this study. With increasing mean groundwater levels, the forage quality of the vegetation decreased until it was so low that the vegetation was hardly suitable for use as animal forage. The plant species diversity was negatively correlated with the plant-available P and Ellenberg N indicator value. Plant-available P, K and Mg showed evidence of leaching during the later study period. The abundance of red-listed species and extensive-use indicator species increased over the course of the study period. This positive trend was reversed by the extreme flood event in the summer of 2013. However, the high species richness and the species compositions of the reference communities were not equal in the other communities, even after almost 30 years of extensification. This finding underlines the importance of the few remaining meadows that are rich in typical floodplain species as donor areas of autochthonous seeds. The results of this study are discussed in light of sustainable management practices and global climate change.

The phreatophytic tree species Populus euphratica Oliv. (Euphrates poplar) forms riparian (tugai) forests along the Tarim River at the northern and eastern fringe of the hyper-arid Taklamakan Desert (Xinjiang province, NW China). These forests are threatened by decreasing groundwater levels due to excessive withdrawal of water for agricultural irrigation. At three plots each at the middle (Yingbazar) and the lower reaches (Arghan) of the Tarim River, we investigated the long-term effects of different water supply due to different distances to the groundwater (from 2 to 12 m) or to additional supply with water from reservoirs, which is being conveyed to the Tarim River's lower reaches since 2000 to conserve and restore the poplar forests. We conducted tree-ring analyses for the time period 1946–2011 and quantified the water use at the tree (Etree) and the stand level (Estand) using the Granier method. For the last four decades of investigation, the average tree-ring width and basal area increment (BAI), the cumulative Etree (May–August) and Estand were significantly higher on the plots with the largest water supply than on the plots with the largest distance to the groundwater. However, the maximum values of xylem sap flow density and Etree values averaged for the vegetation period did not differ significantly among plots and between sites. These transpiration values and the relatively large BAI even at a large distance to the groundwater indicate that—in contrast to previous studies—Euphrates poplars can grow vigorously even at a groundwater depth of up to 12 m. Supply with additional water resulted in a marked increase in BAI. Lower Estand at lower water supply can be explained with a sparser stand density. Interannual fluctuations in the water supply resulted in distinct alterations in BAI in trees that grow at a short distance to the water table or are supplied with additional water. Against the background of limited water availability in the region, we recommend concentrating the conveyance of additional water to forest stands with a short distance to groundwater to keep those forests fully functional and to maintain their ability to regenerate.