Alpine-steppe

Abstract: Question: Optimal partitioning and isometric allocation are two important hypotheses in plant biomass allocation. We tested these two hypotheses at the community level, using field observations from Tibetan grasslands. Location: Qinghai-Tibetan Plateau, China. Methods: We investigated allocation between above- and belowground biomass in alpine grasslands and its relationship with environmental factors using data collected from 141 sites across the plateau during 2001-2005. We used reduced major axis (RMA) regression and general linear models (GLM) to perform data analysis. Results: The median values of aboveground biomass (MA), belowground biomass (MB), and root:shoot (R:S) ratio in alpine grasslands were 59.7, 330.5 g m−2, and 5.8, respectively. About 90% of total root biomass occurred in the top 30 cm of soil, with a larger proportion in the alpine meadow than in the alpine steppe (96 versus 86%). As soil nitrogen and soil moisture increased, both MA and MB increased, but R:S ratio did not show a significant change. MA scaled as 0.92 the power of MB, with 95% confidence intervals of 0.82-1.02. The slope of the isometric relationship between log MA and log MB did not differ significantly between alpine steppe and alpine meadow. The isometric relationship was also independent of soil nitrogen and soil moisture. Conclusions: Our results support the isometric allocation hypothesis for the MA versus MB relationship in Tibetan grasslands.

Abstract: Serious grassland degradation is endangering the environment of the source regions of the Yangtze and Yellow Rivers (SRYYR). There is an urgent need to analyze and review the grassland resources, status of grassland degradation, factors causing grassland degradation, and measures for grassland protection and restoration so as to ensure sustainable development in the SRYYR. This review shows that: (1) The alpine meadow, one of the most important grassland types in the SRYYR, can be divided into four subtypes: typical alpine meadow, alpine swamp meadow, alpine steppe meadow and alpine shrub meadow. (2) There is approximately 357.13 × 104 ha degraded grassland in this area, which is 34.34% of the area of all the investigated grasslands in the SRYYR, and heavily degraded grasslands cover an area of 74.34 × 104 ha, approximately 20.82% of the degraded grasslands. (3) Alpine grassland degradation in the SRYYR follows the following sequence: non-degraded grassland lightly degraded grassland moderately degraded grassland heavily degraded grassland. (4) Grassland degradation in the SRYYR is caused by the integrated effect of anthropogenic and natural factors. The principal factors causing grassland degradation are thought to be long-term overgrazing and the destruction by rodents that follows, and climate warming, which accelerates the grassland degradation process. (5) Some effective management practices (e.g. rodent and ruderal weed control, establishment of artificial grassland, rational management of grassland, and optimizing livestock structure) and integrated countermeasures for the restoration of degraded grasslands have been developed in the SRYYR.