Fang Jingyun

Large scale patterns of forage yield and quality across Chinese grasslands

Understanding the patterns of forage quantity and quality and investigating the factors influencing these patterns are essential for the development of animal husbandry. However, there is very little field evidence focused on these issues at a large spatial scale. In the current study, we analyzed forage quantity and quality at 177 sites distributed in all the major grassland types across China, and explored the relationship between forage quantity and quality based on consistent sampling protocols. We also investigated potential factors influencing forage quality patterns across China. Our study indicates the Tibetan grasslands had both higher quantity and quality forage than the Inner Mongolian grasslands, and alpine meadow had the best quantity and quality forage because of the meadow’s high productivity and the crude protein and nitrogen free extract content of the meadow forage. For the main vegetation formations, Kobresia tibetica meadows and Achnatherum splendens steppes had the highest quantity, while Kobresia pygmaea meadows and Kobresia humilis meadows had the best quality. We also found that although environmental factors, such as temperature and soil fertility, could affect physiological processes and so influence forage quality, the large scale patterns of change were mainly a result of the differences in vegetation types. Finally, we reported a negative relationship between forage quantity and quality: higher forage quantity means more crude fiber but less ether extract and crude protein. These findings improve our understanding on the spatial patterns of forage quantity and quality, and provide solid evidence related to the future development of animal husbandry.

How many areas of grasslands are there in China

Grassland is the indispensable natural resources which covers a large area of terrestrial China and plays an important role in the ecological construction, ecological security, and food security of the country. The size of the grassland, i.e., grassland area, is its important natural property, which is the basis to estimate total grassland biomass and productivity. Therefore, an accurate estimate of the grassland area is of great importance in reasonable protection and utilization of the grassland resources. However, the estimated area of China’s grasslands varies greatly among different studies due to different data sources and grassland definitions. Climate determines geographical distribution of natural vegetation, and thus the distribution of a vegetation type can be retrieved based on regional characteristics of climate. In the semi-arid and arid regions of northern China, precipitation is the major limiting factor of vegetation distribution, especially for grassland. On the other hand, normalized difference vegetation index (NDVI) data well reflects the vegetation coverage and is strongly correlated with precipitation in the arid and semi-arid regions. Therefore, the distribution and area of grasslands can be retrieved using the relationship between precipitation and NDVI in the recognized regions of the grassland. For these reasons, we first roughly divide grasslands into two categories according to their concentrative degree of distribution: contiguous temperate grassland (northern grassland) and discrete subtropical grassland (southern grassland), and then quantify the range and area of the grasslands in these two different regions. Because the grassland distribution in the southern regions cannot be directly determined by climatic variables, we use the vegetation map of China to determine the range and area of the grasslands. For the northern grasslands, we first determine the thresholds of mean precipitation in the ecotones between grasslands and forests and between grasslands and desert vegetation, based on vegetation distribution in the vegetation map of China, and then use the precipitation thresholds to make sure the distributional limits of the grasslands. By conducting a regression analysis between average precipitation and the NDVI average value of vegetation growing season (May–September) over the past 30 years (1982–2011), we estimate the NDVI threshold for grassland and retrieved its potential distribution. The precipitation and NDVI thresholds for the grassland distribution in our study area are estimated to be 102–437 mm and 0.12–0.61 unit, respectively. Finally we document an estimate of the total grassland area of 293×104 km2 in China, with a small variation of 290×104–295×104 km2 over the past 30 years. Uncertainties remain in our estimations because the area might be overestimated or underestimated at regional scale. For instance, a part of deserts in northern Xinjiang was falsely determined as sparse grassland, because the NDVI values of these deserts exceeded the thresholds for grassland; and in the northern Tibetan Plateau, the sparse desert grassland, showing NDVI values lower than 0.05, was falsely determined as desert. Nevertheless, our estimate is generally consistent with that from the vegetation map of China and land cover data of China in 2010. Overall, this study develops a useful methodology which estimates the range and area of the grasslands based on the thresholds of precipitation and NDVI values and generates reliable estimates of the total grassland area in China.