| As the largest grassland ecosystem in China,natural grassland is not only an important production material for grassland animal husbandry but also plays an important ecological service value such as wind-dreaking and sand fixing,soil and water conservation,carbon sequestration,and oxygen release.However,with the grazing pressure brought by the rapid population growth in pastoral areas,coupled with the development concept of prioritizing economic benefits, extensive production methods and the lack of awareness of grassland ecological protection,the unreasonable use of natural grasslands represented by overload overgrazing has caused different degrees of grassland degradation in pastoral areas,seriously threatening the ecological security of the country and the sustainable development of pastoral area economy and society.Forage-livestock balance,as the main measure of grassland ecological protection in pastoral areas at present,has improved the current situation of overload in pastoral areas,but has not solved the conflict between herders’ livelihood development and grassland ecological protection goals from herders’ point of view,leading to unsatisfactory implementation effect in some pastoral areas and the difficulty of the task of forbid grazing and reduce livestock.In response to this,the country has proposed the development model of grass husbandry,through the development of artificial irrigated grassland,replacing the grazing pressure of natural grassland with the huge productivity of fine grass industry,achieving a win-win situation of ecological protection of natural grassland in pastoral areas aed increasing the income of herders.However,China’s pastoral areas are in the arid and semi-arid regions where water resources are most scarce,and the development of grass husbandry has undoubtedly intensified the contradiction of water use in pastoral areas,and how to use limited water resources to develop pastoral grass husbandry has become the main problem facing the ecological protection of pastoral grasslands.Therefore,it is of great academic value and practical significance to introduce water elements into the pastoral forage-livestock balance system and to study the pastoral water-forage-livestock balance and optimal allocation of water-forage resources for pastoral grassland ecological protection.This study refers to existing research on water balance and forage-livestock balance and combines high-quality development theory,non-equilibrium theory,and critical field theory to establish a balance mechanism between water,forage,and livestock systems in arid pastoral based on the ecological protection priority.Taking three typical arid pastoral areas,namely,Sunan,Ulan,and OtogBanner,as research objects,we build a water-forage-livestock balance model of typical pasture areas,point out the problems and shortcomings in the development of grass husbandry in typical pasture areas,propose corresponding optimal allocation schemes,carry out research on the optimal allocation of water and forage resources in pasture areas,and propose strategies for the optimal allocation of water and forage resources for the development of grass husbandry in pasture areas,to provide a decision basis for the development of grass and pasture in pasture areas.The research conclusions of the thesis are as follows:(1) Based on the existing research on water resource balance and forage-livestock balance,the mutual feedback coupling mechanism between humans,water,forage,and livestock in the pastoral water-forage-livestock system is established by analyzing the logical structure of circulation and flow of water,forage,livestock elements and the balancing framework with human,water,grass,and livestock as the core in the pastoral water-forage-livestock system.The results show that the balance logic of the water-forage-livestock system in the pastoral area is to determine the forage output with water resources,determine the livestock carrying capacity with water resources and forage output,and finally,achieve the water resource balance in the pastoral area with artificial forage and livestock as water users (i.e.determine grass with water,determine livestock with aquatic grass,and balance marine animal),forming a closed balance transmission chain from water to forage to livestock and then to water.Operational research methods should be used to optimize the system balance.(2) Based on the non-equilibrium theory and the key field theory,according to the production mode of grass husbandry in pastoral areas,a process balance-based water,forage,and livestock balance model was established to calculate the reasonable livestock carrying threshold in typical pastoral areas.The results showed that,due to the non-equilibrium of the grassland ecosystem,the difference in livestock carrying capacity in pastoral areas under different water conditions was more than 1.2 times,and the difference in some pastoral areas with water shortage could reach 8.2 times,which was not conducive to the development of grassland and animal husbandry in pastoral areas.It is suggested that the livestock-carrying capacity in normal water years should be taken as the reasonable livestock-carrying threshold for the development of grass husbandry in the pastoral area.From 2016 to 2030,the scale of livestock carrying capacity in Sunan pastoral area should be controlled at 900 thousand sheep units to 1.182 million sheep units,and the development scale of artificial grassland should be 7072.3hm2 to 7827.1hm2;the scale of livestock carrying capacity in Ulan pastoral area should be controlled at 507 thousand sheep units to 604 thousand sheep Unit,and the development scale of artificial grassland should be 2374.4hm2 to 3782.4hm2;the scale of livestock carrying capacity in OtogBanner pastoral area should be controlled at 956 thousand sheep units to 1.472 million sheep units,and alfalfa development scale is 4143.9hm2 to 7278.3hm2,corn class development scale is 10549.7hm2 to 16499.5hm2.(3) Based on the asynchrony between the theoretical development area and the actual area of the artificial grassland,this paper puts forward the actual livestock carrying capacity of the pastoral area,integrates the advantages of the theoretical and actual livestock carrying capacity of the pastoral area,sums up the relationship between the livestock carrying capacity of the pastoral area and the theoretical and actual livestock carrying capacity,and uses the livestock volume to carry out the backward verification of the water-forage-livestock system,to establish the evaluation system of the water-forage-livestock system balance in the pastoral area,and carry out the balance analysis of the aquatic grass livestock system in the pastoral area.The results showed that the balance of water-forage-livestock systems in the pastoral area could be divided into six types:system bearing,artificial grassland hysteresis overload,artificial grassland overload,overgrazing overload,overgrazing and artificial grassland overload,and resource overload.The water-forage-livestock system in typical pastoral area is seriously overloaded.Only the Shule River and Heihe River sub-regions in Sunan pastoral area can maintain the balance and stability of the water,grass,and livestock system in the current 2016 wet year.Overload in the pastoral area is mainly overgrazing overload and overgrazing and artificial grassland overload,accounting for 78% of the overload in the pastoral area.The main reason for overload is that the scale of livestock in the pastoral area and the development of artificial grassland are unreasonable.In addition,through the analysis of the key fields in the pastoral area,the coexistence of overloading and under loading of the utilization of water and forage resources are common in typical pastoral areas,which indicates that the mismatch between the utilization mode of water and forage resources and the distribution of resources is also the main problem in the development of grass husbandry in the pastoral area.(4) Based on the study of grassland ecological service value and grassland grazing disturbance in pastoral areas,the ecological value of grassland in pastoral areas is quantified.With the ecological value and production value of grassland in pastoral areas as the goal,the optimal allocation model of water and grass resources in pastoral areas is established.The allocation scheme set is set from the aspects of grassland rotational grazing time,livestock slaughter rate,irrigation water use efficiency and artificial forage sale.NSGA Ⅱ algorithm is used to solve the problem,and then the combined weighting TOPSIS model is used to optimize the scheme.The results showed that the allocation results achieved the win-win goal of improving the grassland ecological service value and increasing the income of herdsmen in pastoral areas.Compared with the results of the water forage livestock balance,the grassland ecological service value and income of herdsmen in typical pastoral areas increased by 14.4%and 8.6% respectively.Compared with natural grazing,the allocation results can not only ensure the balance of water,grass and livestock systems in pastoral areas,but also promote the balanced development of grassland production functions and ecological functions in pastoral areas.In addition,according to the allocation results,the optimal allocation strategies of water grass resources in different level years of corresponding typical pastoral areas are proposed,providing decision-making basis for the development of grassland and animal husbandry in pastoral areas.(5) By comparing the optimal allocation results of the seasonal grazing prohibition pastoral area and the seasonal rotational grazing pastoral area,the impact of the two grazing modes on the development of grass husbandry was analyzed.The results showed that the key to the double increase of ecological production benefits of grass husbandry development in the pastoral area was to increase the artificial replacement rate of natural forage and reduce the use of natural forage alone.In the seasonal grazing prohibition pastoral area,the use of forage in the process of grassland and animal husbandry production was determined through the grazing system,so that the artificial replacement rate of natural forage reached 46.7%,less than 40%higher than that of the seasonal rotational grazing pasture.From the perspective of allocation effect,the grassland ecological service value and herdsmen’s income in typical pastoral areas with seasonal grazing prohibition increased by 12.8% and 11.9% respectively,and the comprehensive effect was higher than that in seasonal rotational grazing areas.However,the use of fixed forage will inevitably lead to the independent use of natural forage,and the development of grass husbandry will inevitably lead to the decline of the allocation effect of grassland ecological value.In addition,seasonal grazing prohibition is difficult to adapt to the advantages of water and grass resources in pastoral areas,and structural water or grass shortage is likely to occur when resources are tight,which limits the further development of grass husbandry.Finally,it is proposed that the development of grass husbandry in pastoral areas is not suitable in areas with water shortage. |
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