基于秸秆补饲的青藏高原草地载畜量平衡遥感监测

为了快速准确地掌握青藏高原草地生产力/产草量及草畜平衡情况,促进藏区草地资源可持续利用,实现青藏高原生态与生产协调发展,有必要对青藏高原不同行政区域天然草地及补饲后的载畜能力和草畜平衡问题开展研究。该研究首先结合MODIS(moderate-resolution imaging spectroradiometer)的归一化植被指数(normalized difference vegetation index,NDVI)数据、青藏高原草地类型图、气象数据、土壤质地数据等数据,利用改进的CASA(carnegie-ames-stanford-approach)模型,对青藏高原草地产草量进行了估算,并分析了青藏高原草地天然产草量的空间分布情况。然后利用草谷比法估算了青藏高原饲用秸秆资源量及空间分布情况,计算得出各县市可利用的秸秆资源的载畜量情况。最后根据草地产草量、秸秆资源载畜量和实际载畜量,利用草畜平衡模型,模拟得出各县市的超载过牧情况。结果表明:2010年,青藏高原年产草量区域差异十分明显,西藏年产草量最大为2642.89万t,青海藏区次之,为2 307.60万t;云南藏区最低,为37.36万t。青藏高原天然草地总载畜量为8 363.04万只(羊单位,以下同),其中,青海省藏区为2 889.10万只,西藏为2 789.35万只,四川藏区为1 854.10万只,甘肃藏区为796.42万只,云南藏区为34.09万只。青藏高原饲用秸秆资源量为372.16万t,其中青海藏区和西藏的饲用秸秆资源总量占整个藏区的74.77%;其他3个省份的可饲用秸秆总量比例仅占25.23%。青藏高原饲用秸秆资源可饲养牲畜293.53万只,其中青海省藏区为172.48万只,西藏为46.80万只,四川藏区为31.94万只,甘肃藏区为19.69万只,云南藏区为22.65万只。青藏高原各县市超载过牧十分突出。在未补饲情况下,超载率超过5倍的县市占7.69%,2~5倍的占13.46%,1~2倍的占28.84%,超载率小于1倍的占38.82%,未超载的仅占11.19%。通过补饲秸秆资源,未超载过牧的县市比例未发生变化,但各县市的超载过牧情况有所改善。超载率超过5倍的县市比例下降了3.2个百分点,2~5倍的下降了4.49个百分点,1~2倍的增加了5.49个百分点,超载率小于1倍的增加了2.2个百分点。因此,今后青藏高原需根据草地资源及饲用秸秆资源的承载能力严格控制牛羊的养殖数量,实现生态环境和畜牧业的可持续发展。

Balance between actual number of livestock and livestock carrying capacity of grassland after added forage of straw based on remote sensing in Tibetan Plateau

Abstract: In order to quickly and accurately know grassland productivity and the balance between the actual livestock and carrying capacity of the grassland, to promote the rational use of grassland and ensure the sustainable development of ecological environment and animal husbandry on the Tibetan Plateau, it is necessary to estimate the stock capacity of natural grassland and grassland after supplementing feed, as well as understand grassland balance situation supplementing feed before and after among different administrative regions in the Tibetan Plateau. The study estimated the grass yield on the Tibetan Plateau and analyzed the yield's spatial distribution of natural grassland using an improved model of CASA combined with the data of NDVI from MODIS, grassland type maps, meteorological data, soil texture on the Tibetan Plateau. The paper adopt the method of straw-to-grain ratio to estimate the volume of straw forage among different administrative regions in the Tibetan Plateau and then to calculate the carrying capacity of the available straw resources of each county. According to the grass yield, carrying capacity of straw resource and the real number of livestock, the paper identified the overgrazing of all counties and cities with grass build balance model. The results showed that the annual grass yield of different regions in the Tibetan Plateau varied a lot in 2010, and the maximum was in Tibet with the largest grass yield of 26 428 890 tons, followed by Qinghai Province with the yield of 23.08 million tons, and Yunnan was the lowest, only 373 600 tons. The total livestock carrying capacity of natural grassland in the Tibetan Plateau was 83 630 365 (standard sheep unit, the same below), in which, the livestock carrying capacities of Qinghai, Tibet, Sichuan, Gansu and Yunnan were 28 890 963, 27 893 522, 18 540 968, 7 964 236 and 340 946, respectively. The overgrazing among each county and city in the Tibetan Plateau was very common. Without adding feed by straw forage, the quantities of the county and city with the overgrazing rate more than 5 times, between 2 and 5 times, less than 1 time accounted for 7.69%, 28.84% and 38.82% of total county and city, respectively. And the counties in which the actual number of livestock did not exceed the local maximum carrying capacity only accounted for 11.19%. In case of adding straw forage, the proportion of the counties without overgrazing remained the same, however the situation of overgrazing county improved. The proportions of the county with overgrazing rates more than 5 times, between 2 and 5 times, between 1 and 2 times decreased by 3.2%, 4.49%, 5.49%, respectively, and the proportion of the county with overgrazing rate less than 1 time increased by 2.2%. Therefore, it is necessary to strictly control the volume of cattle and sheep to match the carrying capacity of natural grassland and feeding straw resources, and to achieve sustainable development of ecological environment and animal husbandry.