Credit portfolio selection with decaying contagion intensities

We develop a fixed‐income portfolio framework capturing the exponential decay of contagious intensities between successive default events. We show that the value function of the control problem is the classical solution to a recursive system of second‐order uniformly parabolic Hamilton–Jacobi–Bellman partial differential equations. We analyze the interplay between risk premia, decay of default intensities, and their volatilities. Our comparative statics analysis finds that the investor chooses to go long only if he is capturing enough risk premia. If the default intensities deteriorate faster, the investor increases the size of his position if he goes short, or reduces the size of his position if he goes long.     

基于生态系统承载能力核算的西藏高原草地资源区划研究

随着经济发展,全球生态系统和景观正经历着快速变化。作为基本生态系统单元之一,草地生态系统以其独特的生态系统服务功能与区域经济发展模式而面临着严峻挑战。西藏高原地区草地生态系统服务功能演变及退化已成为高原生态安全屏障保护与建设面临的主要问题。文章基于家畜饲草料资源多样性,首先将西藏草地资源划分为不适合和不能放牧区域以及适合放牧区,对于适合放牧区域,在分析草地载畜量、补饲载畜量、牲畜存栏量地域差异及其影响因素基础上核算生态系统承载力,提出草地承载力监测评估、畜牧业可持续发展、草地生态保护对策建议。研究发现:全区不适合和不能放牧草地36.95万km2,占全区草地总面积的44.37%;农区可供牲畜食用的精饲料总量与粗饲料总量分别为23.71万t与27.50万t,全区补充饲料载畜量为115.18万羊单位;从载畜量区划来看,那曲、当雄等县超载严重,八宿、察隅等县略为盈余。     

Rotational grazing adoption in cattle production under a cost‐share agreement: does uncertainty have a role in conservation technology adoption?

Rotational grazing has been promoted as a best management practice with environmental benefits and associated higher revenue. Its adoption rate has been relatively low. This study investigates the role of uncertainty in the adoption of rotational grazing with a cost‐share by cattle producers. Mail survey results indicate that 63–71 per cent of cattle producers are uncertain about adoption with a government cost‐share. The study suggests that the possibility of uncertainty should be considered in cases where willingness‐to‐pay is elicited in the context of adoption of technology.     

Using participatory mapping and a participatory geographic information system in pastoral land use investigation: Impacts of rangeland policy in Botswana

Since the 1980s, the spatial extent of communal grazing lands in Botswana has been diminishing due to rangeland privatisation and fencing associated with animal health policies. Spatial comparisons of pastoral land use transformations are particularly important where accessibility to grazing and water resources remains at the core of sustainable pastoralism policies. Achieving success in pastoral development research requires a sound understanding of traditional pastoralists’ information systems, including the nature of local spatial knowledge. This study explores local spatial knowledge through participatory mapping and a Participatory Geographic Information System to understand and analyse pastoralists’ grazing patterns, spatial mobility and the impacts of subdivisions and privatisation policies in Botswana’s Ngamiland rangelands. The study uses focus group discussions, historical analysis through key informant interviews, and participatory mapping exercises along with community guided transect walks. The resulting maps provide insights into the traditional tenure patterns of land use and the impacts of rangeland policy on traditional livestock spatial mobility and access to grazing lands. Privatisation and rangeland enclosures have resulted in the restricted movement of livestock and overstocking of floodplains and riparian rangelands, with some natural water pans becoming inaccessible to local communities. We conclude that the integration of local spatial knowledge can be used to foster better articulation and understanding of pastoralists’ tenures, which are often lacking in communal land administration systems. Such integrated analysis can contribute to sustainable pastoral land management policy toolkits in semi-arid rangeland environments and enable better land tenure and management decision making for sustainable land management.     

Effects of European Union agricultural policies on the sustainability of grazingland use in a typical Greek rural area

Recent changes in the Common Agricultural Policy (CAP) introduced different definitions regarding the eligibility of various types of land used by grazing animals. In particular, shrublands and other low-quality areas which have traditionally been used as grazinglands are now not eligible for European Union income support payments. Subject to these changes, a large part of livestock farms will be affected, being partially or fully deprived of EU income support. In addition to these policy-driven changes, pasture-fed livestock farms in Greece are faced with a unique system of grazingland allocation, as all grazing areas in the country are state-owned. These areas are allocated for a short period either directly to farmers who are permanent residents of the Municipalities or to other livestock farmers through an auction system, which does not take into account the grazing capacity thus bringing about environmental degradation. This paper investigates the effects of CAP changes and of this communal land allocation system based on the findings of a typological analysis. The study focuses on a typical Greek territory in terms of land uses, economic activities and sociodemographic developments. Data from a questionnaire survey are used to build a typology of local livestock farms in terms of their nutritional management and land use characteristics and then the profile of each type is investigated through the estimation of a Multinomial Logit Model where the dependent variable is the cluster participation. Three distinct types of farms (clusters) are determined. Cluster 1 includes traditional farms which rear sheep and goats and bovine for meat, which are highly dependent on grazingland uses and EU income support. Cluster 2 farms – mainly sheep and goat – have evolved a ‘double’ dependency on land in the form of grazingland but also of cropland for feedstuff production, which renders them more resilient to policy changes. Finally, Cluster 3 farms are intensive dairy cattle farms and use artificial (cultivated) privately-owned grazinglands and cropland for feedstuff production. Market-oriented measures are proposed for each type and suggestions for an integrated land use plan are made, including long-term leasing of land and the consideration of environmental criteria for land allocation, thus rendering farmers responsible for keeping their land in a good production state.     

A communities Eden – grazing Exclosure success in Ethiopia

The traditional significance of livestock to rural communities in Ethiopia has resulted in intense pressures on available grazing areas, resulting in vegetation loss, reduced infiltration and increased runoff, greater erosion and land degradation. Unfortunately, the uptake of sustainable land management (SLM) practices in communal grazing land is constrained by a lack of land tenure security. Recently the International Fund for Agricultural Development, working with the Government of Ethiopia, has invested in the capacity of local administrations, to improve land demarcation and the issuance of both individual and community land certificates. This is concurrent with the promotion of improved SLM, particularly zero grazing of communal lands, known by communities as Exclosures. This pilot study reports the biophysical changes observed in four different Exclosures in the Amhara region compared to adjacent communal lands. Irrespective of age, it was found that vegetative cover, biodiversity levels and infiltration rates, all increased in Exclosures, enhancing ecosystem services and function. Results suggest that Exclosures are most effective for large sites with effective cut and carry forage systems. It is evident that the issuance of land titles increases the adoption of SLM practices. Further studies are required to assess the economic and social impacts of Exclosures.     

OPTIMAL INVESTMENT IN CREDIT DERIVATIVES PORTFOLIO UNDER CONTAGION RISK

We consider the optimal portfolio problem of a power investor who wishes to allocate her wealth between several credit default swaps (CDSs) and a money market account. We model contagion risk among the reference entities in the portfolio using a reduced‐form Markovian model with interacting default intensities. Using the dynamic programming principle, we establish a lattice dependence structure between the Hamilton‐Jacobi‐Bellman equations associated with the default states of the portfolio. We show existence and uniqueness of a classical solution to each equation and characterize them in terms of solutions to inhomogeneous Bernoulli type ordinary differential equations. We provide a precise characterization for the directionality of the CDS investment strategy and perform a numerical analysis to assess the impact of default contagion. We find that the increased intensity triggered by default of a very risky entity strongly impacts size and directionality of the investor strategy. Such findings outline the key role played by default contagion when investing in portfolios subject to multiple sources of default risk.     

草原文化基因传承浅论

草原文化遗传基因的载体是包含人居、草地和畜群三者共生的放牧系统单元,亦即人居、草地、家畜三者共生的,三位一体基本元素。放牧系统单元包含两重结构。第一层是草地—草食动物(家畜)构成的牧食系统;第二层结构是在草畜系统之外,加入人为因子,扩大为人居—草地—家畜的共生体。放牧系统的驱动力是能量按照一定的序的运动模式,需要满足生存空间需求与营养源网络两方面条件。科学实验和生产实践证明,划区轮牧是保持放牧系统单元完整性的唯一途径,它把放牧的序覆盖全部草地面积和全部放牧持续时间,适用于不同的时空阈限。我国需克服对放牧的诸多认识误区,建立放牧系统单元的概念,采取保持放牧系统单元完整的划区轮牧是维系草原生态,传承草原文化的关键所在。     

退牧还草区农牧民家庭收入结构转型效益

农户家庭收入结构转型效益的研究对于揭示政策影响下农户家庭经济收入增长的内在本质具有重要意义。从不同退牧还草模式的角度,采用半结构访谈的数据采集方法与分位回归模型,分析了不同生态功能区农牧民家庭收入结构的转型效益。结果表明:生态补偿方式与收入转型需求错位,生态功能区农牧民家庭收益普遍降低,补偿性收入所占比重较大;受农牧民家庭经济特征影响,各种收入来源对农牧民家庭的收入效益贡献不一;资源禀赋和社会经济的地区差异,以及当地传统生产生活习惯与退牧还草政策的影响,各生态功能区农牧民家庭收入结构转型效益存在差异。退牧还草生态工程体系缺乏完善,尤其替代生计补偿缺乏针对性,有碍于农牧民家庭收入结构的有效转型。     

种草养畜——农区畜牧业持续稳定发展的必然趋势

我国广大农区只有将牧草纳入农田耕作制，走以草养畜、以草或畜禽粪便养地、用养结合的农牧业共同发展的生态农业道路，才能使畜牧业突破传统种植业生产的饲料数量有限、蛋白质含量低的双重约束，为人们提供满足营养需要的畜产品。