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1.
Concerns over climate change have increased interest in carbon sequestration in agricultural lands. While the per-hectare carbon capture potential of rangelands is less than either cropland or forests, existing research suggests modest changes in carbon storage on rangelands can potentially alter the global carbon cycle. This paper examines the potential firm-level revenues from voluntary carbon offset programs, such as the Chicago Climate Exchange (CCX) Rangeland Soil Carbon Offset program. We estimate revenues for short-term voluntary offsets given historical prices and prices projected with potential cap-and-trade legislation. We also estimate revenues assuming 100-yr offsets are required to meet international sequestration standards. Simulation results indicate a relatively wide range of modest revenues from recent CCX contracts and carbon prices. The analysis suggests that recent carbon prices or low-end projected prices from cap-and-trade legislation are not likely to encourage producer participation. Medium and high carbon price projections for cap-and-trade legislation may make carbon sequestration a more attractive option for rangeland managers, but given potential requirements for projects to meet international guidelines for greenhouse gas offset projects, many issues remain before range managers may be interested in carbon sequestration as an enterprise.  相似文献   

2.
Drastic changes have occurred in Mongolia’s grazing land management over the last two decades, but their effects on rangelands are ambiguous. Temporal trends in Mongolia’s rangeland condition have not been well documented relative to the effects of long-term management changes. This study examined changes in grazing land use and rangeland biomass associated with the transition from the socialist collective to the current management systems in the Tsahiriin tal area of northern Mongolia. Grazing lands in Tsahiriin tal that were formerly managed by the socialist collective are now used by numerous nomadic households with their privately owned herds, although the lands remain publicly owned. Grazing pressure has more than tripled and herd distribution has changed from a few spatially clustered large herds of sheep to numerous smaller herds of multiple species. Landsat image–derived normalized-difference vegetation index estimates suggest that rangeland biomass significantly decreased (P < 0.001) from the collective to the postcollective periods. The observed decrease was significantly correlated with changes in the grazing management system and increased stocking density (P < 0.001), even when potential climate-induced changes were considered. Furthermore, field- and Satellite Pour l’Observation de la Terre imagery–based rangeland assessments in 2007 and 2008 indicate that current rangeland biomass is low. Spatial pattern analyses show that the low biomass is uniform throughout the study site. The observed decrease in rangeland biomass might be further accelerated if current grazing land use continues with no formal rangeland management institution or organized, well-structured efforts by the local herding households.  相似文献   

3.
碳交易市场现状及草地碳汇潜力研究   总被引:1,自引:0,他引:1  
本研究概述了国内外主要碳交易市场和各大洲典型碳示范项目的现状以及中国碳交易市场的潜力,分析了中国草地碳汇的潜力和草地碳汇交易的必要性。目前世界主要发达国家已建立各自的碳排放交易体系(如欧盟排放交易体系,芝加哥气候交易体系等),其中欧盟排放交易体系占主要地位,在全球碳交易市场中占据较大份额。国际上开展的固碳项目主要位于北美洲、南美洲、亚洲、非洲和大洋洲,主要采用再造林、减少森林砍伐、保护生物多样性、提高能源效率和进行可持续有效管理等方式,增加总固碳量,以减少CO2排放。中国碳交易主要遵循清洁发展机制(CDM),CDM项目注册和签发量均在全球占据较大份额,且项目主要分布于四川、云南、内蒙古等省份,主要为新能源和可再生能源项目两种减排类型。我国的核证减排量(CER)高达1028.98 Mt CO2e,位居世界第一。在7个碳交易试点省市顺利进行下,中国有望于2017年统一碳排放权交易市场。中国碳交易市场中配额项目累计成交量和成交额最高的是湖北碳市场,中国核证减排量(CCER)项目累计成交量最多的是上海碳交易市场。无论从较低的减排成本或从CDM项目市场规模来看,我国都具有较大的优势与潜力。目前CDM项目虽还未涉及草地碳汇,但草地作为我国面积最大的生态系统,具有巨大的碳汇潜力,将在未来的碳交易市场中占据重要地位。  相似文献   

4.
5.
In many developing countries where rangelands are a dominant land type and critically important in livelihoods of a significant portion of the population, severe rangeland degradation and/or conflicts over rangeland use can create significant social, economic, and environmental problems. In this paper, we review rangeland degradation in the developing world, its impacts and causes, discuss problems in applying rangeland science to improve rangeland conditions, discuss the role of rangeland scientists, and discuss our approach for enhancing rangeland science in international development. We suggest range scientists can provide valuable input and direction on issues of rangeland degradation (including state changes and impacts on ecosystem goods and services), provide guidance in methods and realistic opportunities for rangeland improvement to local users, government, and development organizations, and work to provide pastoralists with adaptive management in variable ecosystems. Conflict and poverty can create situations where a long-term goal of sustainable rangeland use is overwhelmed by short-term needs of safety and food security; however, providing science and training on sustainable management can make a difference where conflicts are not too severe and can help promote societal stability. Negative perceptions about aid are widespread, but the needs for improved conditions associated with multiple values of rangelands, and the needs of people utilizing these areas, are great. Conducting planning and projects with transparency and accountability will help promote more inclusive participation and successful projects. To be effective, a project needs to consider the needs of the people utilizing the project area but also provide to these communities information on values of the rangelands to other stakeholders (ecosystem services). Sustainable projects will require accountability and enhance self-reliance to allow community empowerment and adaptability to changes.  相似文献   

6.
Recent climatic trends and climate model projections indicate that climate change will modify rangeland ecosystem functions and the services and livelihoods that they provision. Recent history has demonstrated that climatic variability has a strong influence on both ecological and social components of rangeland systems and that these systems possess substantial capacity to adapt to climatic variability. Specific objectives of this synthesis are to: 1) evaluate options to mitigate greenhouse gas emissions and future climate change; 2) survey actions that individuals, enterprises, and social organizations can use to adapt to climate change; and 3) assess options for system transformation when adaptation is no longer sufficient to contend with climate change. Mitigation for carbon sequestration does not appear economically viable, given the small and highly variable carbon dioxide fluxes of rangeland ecosystems and the high transaction costs that would be incurred. In contrast, adaptation strategies are numerous and provide a means to manage risks associated with climate change. Adaptation strategies are diverse, including altered risk perception by individuals, greater flexibility of production enterprises, and modifications to social organizations that emphasize climatic variability, rather than consistency. Many adaptations represent “no regrets” actions because their implementation can be justified without emphasis on pending climate change. Adaptations specific to livestock production systems can include flexible herd management, alternative livestock breeds or species, innovative pest management, modified enterprise structures, and geographic relocation. Social-ecological systems in which adaptation is insufficient to counter the adverse consequences of climate change might undergo transformative change to produce alternative ecosystem services, production enterprises, and livelihoods. The rangeland profession is in a pivotal position to provide leadership on this global challenge because it represents the intersection of management and scientific knowledge, includes diverse stakeholders who derive their livelihoods from rangelands, and interacts with organizations responsible for rangeland stewardship.  相似文献   

7.
沈禹颖  杨子文 《草地学报》2008,16(4):319-323
在百年奥运即将开幕前夕,我国草学界成功举办了第21届国际草地大会暨第8届草原大会。本届大会展示了世界变化中的草地/草原,强调了草地/草原的多功能性。学术交流热点主要表现在:世界草地/草原普遍面临着退化的威胁,面对草地/草原生态环境研发经费减少的挑战,要求科学家准确选题,把握学科发展的新方向。可持续发展已成为主流指导思想和原则,是评价系统成功与否的标准;分子技术和模型构建在某些系统的相关研究中发挥了重要作用;牧草在人类食物链中的作用越来越重要,主要体现在食物质量和数量2个方面;全球经济一体化背景下国际合作更显重要。在理解草地/草原自然科学基础上综合其服务功能评估、土地使用权、市场、复杂性与变化性,政策和综合系统等人文、政策因子,是实现和谐草原、建设和谐社会的基础。  相似文献   

8.
Rapidly increasing demand for food, fiber, and fuel together with new technologies and the mobility of global capital are driving revolutionary changes in land use throughout the world. Efforts to increase land productivity include conversion of millions of hectares of rangelands to crop production, including many marginal lands with low resistance and resilience to degradation. Sustaining the productivity of these lands requires careful land use planning and innovative management systems. Historically, this responsibility has been left to agronomists and others with expertise in crop production. In this article, we argue that the revolutionary land use changes necessary to support national and global food security potentially make rangeland science more relevant now than ever. Maintaining and increasing relevance will require a revolutionary change in range science from a discipline that focuses on a particular land use or land cover to one that addresses the challenge of managing all lands that, at one time, were considered to be marginal for crop production. We propose four strategies to increase the relevance of rangeland science to global land management: 1) expand our awareness and understanding of local to global economic, social, and technological trends in order to anticipate and identify drivers and patterns of conversion; 2) emphasize empirical studies and modeling that anticipate the biophysical (ecosystem services) and societal consequences of large-scale changes in land cover and use; 3) significantly increase communication and collaboration with the disciplines and sectors of society currently responsible for managing the new land uses; and 4) develop and adopt a dynamic and flexible resilience-based land classification system and data-supported conceptual models (e.g., state-and-transition models) that represent all lands, regardless of use and the consequences of land conversion to various uses instead of changes in state or condition that are focused on a single land use.  相似文献   

9.
Invasive annual weeds negatively impact ecosystem services and pose a major conservation threat on semiarid rangelands throughout the western United States. Rehabilitation of these rangelands is challenging due to interannual climate and subseasonal weather variability that impacts seed germination, seedling survival and establishment, annual weed dynamics, wildfire frequency, and soil stability. Rehabilitation and restoration outcomes could be improved by adopting a weather-centric approach that uses the full spectrum of available site-specific weather information from historical observations, seasonal climate forecasts, and climate-change projections. Climate data can be used retrospectively to interpret success or failure of past seedings by describing seasonal and longer-term patterns of environmental variability subsequent to planting. A more detailed evaluation of weather impacts on site conditions may yield more flexible adaptive-management strategies for rangeland restoration and rehabilitation, as well as provide estimates of transition probabilities between desirable and undesirable vegetation states. Skillful seasonal climate forecasts could greatly improve the cost efficiency of management treatments by limiting revegetation activities to time periods where forecasts suggest higher probabilities of successful seedling establishment. Climate-change projections are key to the application of current environmental models for development of mitigation and adaptation strategies and for management practices that require a multidecadal planning horizon. Adoption of new weather technology will require collaboration between land managers and revegetation specialists and modifications to the way we currently plan and conduct rangeland rehabilitation and restoration in the Intermountain West.  相似文献   

10.
The assessment of rangeland productivity in semi-extensively grazed arid rangelands is a prerequisite for livestock management in relation to sustainable use of pastoral resources. The objective of this study was to assess rangeland productivity based on normalised difference vegetation index (NDVI) images. Data on phytomass were measured on 61 field samples in arid rangelands of Morocco, covering various rangeland categories during autumn (November) and spring (April), i.e. when phytomass is at low and high levels, respectively, for two consecutive years (2008 and 2009). Dekadal EROS Moderate Resolution Imaging Spectroradiometer (eMODIS) NDVI data were linearly regressed to field measurements for these four periods. Results show that phytomass values were correlated with NDVI during spring, with R2 and RMSE values of 0.82 and 0.3 t ha?1, respectively. This study indicates there is a high potential for operational use of remotely sensed data to estimate rangeland phytomass of semi-extensively grazed rangelands.  相似文献   

11.
Rangelands account for almost half of the earth’s land surface and may play an important role in the global carbon (C) cycle. We studied net ecosystem exchange (NEE) of C on eight North American rangeland sites over a 6-yr period. Management practices and disturbance regimes can influence NEE; for consistency, we compared ungrazed and undisturbed rangelands including four Great Plains sites from Texas to North Dakota, two Southwestern hot desert sites in New Mexico and Arizona, and two Northwestern sagebrush steppe sites in Idaho and Oregon. We used the Bowen ratio-energy balance system for continuous measurements of energy, water vapor, and carbon dioxide (CO2) fluxes at each study site during the measurement period (1996 to 2001 for most sites). Data were processed and screened using standardized procedures, which facilitated across-location comparisons. Although almost any site could be either a sink or source for C depending on yearly weather patterns, five of the eight native rangelands typically were sinks for atmospheric CO2 during the study period. Both sagebrush steppe sites were sinks and three of four Great Plains grasslands were sinks, but the two Southwest hot desert sites were sources of C on an annual basis. Most rangelands were characterized by short periods of high C uptake (2 mo to 3 mo) and long periods of C balance or small respiratory losses of C. Weather patterns during the measurement period strongly influenced conclusions about NEE on any given rangeland site. Droughts tended to limit periods of high C uptake and thus cause even the most productive sites to become sources of C on an annual basis. Our results show that native rangelands are a potentially important terrestrial sink for atmospheric CO2, and maintaining the period of active C uptake will be critical if we are to manage rangelands for C sequestration.  相似文献   

12.
青藏高原高寒草原碳增贮潜力的初步研究   总被引:2,自引:0,他引:2  
青海省西部地区的高寒草原分为高寒草甸草原、高寒草原化草甸和高寒草原3种类型;按照草地利用现状,分为原生草地、退化草地和人工草地3种土地利用格局。以原生草地为参照,通过比较不同草地类型和土地利用格局草地碳贮现状,探索其碳的增贮潜力。结果表明:原生高寒草原、退化高寒草原、高寒草原化草甸、退化草原化草甸、高寒草甸草原、退化草甸草原和人工草地的土壤-植物系统中总有机碳贮量分别为45.07±0.68,30.41±0.5,84.21±0.61,66.11±0.62,98.85±0.11,80.02±0.22,43.77±0.16tC·hm-2,其中原生高寒草原与高寒草原化草甸、高寒草甸草原、退化高寒草原有机碳储量差异显著。对退化草地进行人工恢复,具有显著的碳增贮潜力,高寒草甸草原、高寒草原化草甸、高寒草原和人工草地的理论碳增贮潜力分别为18.82±0.51,18.15±0.15,14.65±0.78,1.29±0.21tC·hm-2。气候变化导致的青藏高原干暖化,对高寒草原有机碳贮量的影响主要体现在由高寒草甸草原和高寒草原化草甸向高寒草原的演替上。  相似文献   

13.
The management of rangelands over the past decade in Zimbabwe has been on the decline. This has resulted in degraded and depleted communal rangelands. A number of recommendations by various government departments, researchers and non-governmental organisations have been implemented. These focused on improving communal grazing areas throughout the country. Notable examples include the livestock destocking policy, introduction of grazing schemes, improved forage grasses, veld legume reinforcement and agro-forestry technology. However, success in improving communal grazing areas has been limited, with forage productivity in communal areas declining, soils still eroding, as well as loss of flora and fauna diversity. The objectives of this paper are to review factors limiting efforts to improve communal grazing areas, constraints to adoption of rangeland technologies necessary to achieve desired plant community for livestock production, and present recommendations to overcome the challenges. The review concludes that there has been limited farmer participation in efforts to improve communal grazing areas and livestock productivity, thus the low adoption of technologies to improve the grazing areas. It is therefore recommended to use participatory approach methodologies to assist communal livestock farmers to improve their grazing areas.  相似文献   

14.
A survey was conducted between April and July 2007 to generate information on dry season feeding management and livestock poisoning in the southern rangelands of Ethiopia. A total of 119 pastoralists were interviewed using a semi-structured questionnaire. Moreover, additional information was obtained through informal discussions. The study revealed that pastoralists have rich knowledge of natural resource management and utilization and employ various strategies such as migration, collection of grasses and pods, and cutting branches to overcome feed scarcity during dry/drought periods. Migration of livestock and people to areas with better grazing is the widely used strategy. However, the implementation of this strategy is diminishing as a result of changes such as bush encroachment, expansion of settlements, and crop cultivation in dry-season grazing lands. The respondents also indicated the presence of poisonous plants in the rangeland, and about 20 such plants were identified by the respondents. Various species and classes of livestock are reported to be affected by toxic plants particularly in the dry and early rainy seasons when feed is in short supply. A more extensive survey is required to document all poisonous plants in the rangelands and to identify the major toxic principles in the different species. Future development interventions should consider the prevailing constraints and potentials of the rangelands with active participation of the pastoralists.  相似文献   

15.
Grassland conversion into croplands in the Prairie Pothole Region of the United States is a persistent hurdle toward mitigating climate change. Several carbon offset markets have been designed to reward landowners for keeping lands in their native state when incentives to convert are high. We explore the role of a critical determinant in such programs: the additionality threshold. This factor, if appropriately selected and applied, reduces the participation of landowners that would choose to enroll in the program but would not have converted their land under business-as-usual conditions. Using a simple model relating land quality and land use to economic rents, we simulate potential avoided grassland conversion offset market participation across a range of cropland over pasture rent difference threshold (RDT) values. We find mitigation potential and simulated program costs are widely variable depending on this parameter and assume carbon prices: across the five states studied, the full range is 0.41 tCO2e • yr−1 (0.2 RDT, $10 •·t−1 carbon price) to 4.6 million tCO2e • yr−1 (1.2 RDT, $40 tCO2e • t−1 carbon price), assuming average land use change emissions values for pastureland in the region. Total program costs for these offsets also exhibit a wide range, spanning $2−$120 million • yr−1 depending on parameterization. Results across the full range of RDTs (0.2−2) demonstrate a tendency toward higher RDTs for achieving high levels of avoided emissions, with cost efficiency being maximized in the 1.4−1.8 range for RDTs. A state-level breakdown of results demonstrate the importance of modeling economic trends in land use and setting region-specific additionality thresholds for avoided grassland conversion offsets. Although our study is specific to grassland conversion in one region of the United States, similar offset markets exist elsewhere, where additionality concerns are paramount. We believe our framework can be useful in improving protocol design.  相似文献   

16.
Rangelands make an important contribution to carbon dynamics of terrestrial ecosystems. We used a readily accessible interface (COMET VR) to a simulation model (CENTURY) to predict changes in soil carbon in response to management changes commonly associated with conservation programs. We also used a subroutine of the model to calculate an estimate of uncertainty of the model output based on the similarity between climate, soil, and management history inputs and those used previously to parameterize the model for common land use (cropland to perennial grassland) and management (stocking rate reductions and legume addition) changes to test the validity of the approach across the southwestern United States. The conversion of small grain cropland to perennial cover was simulated acceptably (<20% uncertainty) by the model for soil, climate, and management history attributes representative of 32% of land area currently in small grain production, while the simulation of small grain cropland to perennial cover + legumes was acceptable on 73% of current small grain production area. The model performed poorly on arid and semiarid rangelands for both management (reduced stocking) and restoration (legume addition) practices. Only 66% of land area currently used as rangeland had climate, soil, and management attributes that resulted in acceptable uncertainty. Based on our results, it will be difficult to credibly predict changes to soil carbon resulting from common land use and management practices, both at fine and coarse scales. To overcome these limitations, we propose an integrated system of spatially explicit direct measurement of soil carbon at locations with well-documented management histories and climatic records to better parameterize the model for rangeland applications. Further, because the drivers of soil carbon fluxes on rangelands are dominated by climate rather than management, the interface should be redesigned to simulate soil carbon changes based on ecological state rather than practice application.  相似文献   

17.
草地对全球气候变化的响应及其碳汇潜势研究   总被引:10,自引:3,他引:7  
 本研究用综合顺序分类法(CSCS)分析了1950-2000年和2001-2050年期间的草原类型演替及碳汇动态。证明中国草地的碳汇主体依次是冻原和高山草地、温带湿润草地、斯泰普草地和半荒漠草地大类,占中国潜在草地总面积的85.52%,年碳汇潜力占中国潜在草地年碳汇潜力的93.29%。全球草地的碳汇主体是萨王纳、冻原和高山草地大类,两者的面积和占全球潜在草地总面积的48.50%,年碳汇潜力占全球潜在草地年碳汇潜力的72.22%。在全球气候暖干化的强(A2a)、弱(B2a)情景下,与当前(1950-2000年)情景相比,中国将呈现草地面积减少,林地面积增加的态势;与中国的趋势相反,全球将呈现草地面积增加,林地面积减少的态势。在全球暖干化的A2a和B2a模式下,草地年碳汇潜力,中国将分别提升14.6%和18.5%,全球将分别提升17.3% 和16.8%。但两者的增长方式不同,全球是以温带湿润草地大类年碳汇潜力大幅增加为特征,而中国是以负增长为特征。我国的暖干化趋势在草地年碳汇潜力上的反映较之全球更强烈。尽管造成全球气候暖干化的自然因素远非人力所能控制,但系统问题只能靠系统综合的办法治理。这是草地工作者当前的使命。  相似文献   

18.
Rangeland extent is an important factor for evaluating critical indicators of rangeland sustainability. Rangeland areal extent was determined for the coterminous United States in a geospatial framework by evaluating spatially explicit data from the Landscape Fire and Resource Management Planning Tools (LANDFIRE) project describing historic and current vegetative composition, average height, and average cover through the viewpoints of the Natural Resources Inventory (NRI) administered by the Natural Resources Conservation Service and the Forest Inventory and Analysis (FIA) program administered by the US Forest Service. Three types of rangelands were differentiated using the NRI definition encompassing rangelands, afforested rangelands, and transitory rangelands. Limitations in the FIA definition permitted characterization of only two rangeland types: rangeland and rangeland vegetation with a small patch size. These classes were similar to those from the NRI definition but differed in tree canopy cover threshold requirements. Estimated rangeland area resulting from the NRI- and FIA-LANDFIRE models were 268 and 207 Mha, respectively. In addition, the NRI-LANDFIRE model identified 19 Mha of afforested rangelands due principally to encroachment and increased density by species classified as trees belonging to the genera Quercus, Prosopis, and Juniperus. The biggest discrepancies between acreage estimates derived from NRI- and FIA-LANDFIRE models occurred in oak, pinyon-juniper, and mesquite woodlands. The differences in area estimates between the NRI and FIA perspectives demonstrate the need for development of unified, objective methods for determining rangeland extent that can be applied consistently to all rangelands regardless of ownership or jurisdiction. While the models and geospatial information developed here are useful for national-scale estimates of rangeland extent, they are subject to the limitations of the LANDFIRE data products.  相似文献   

19.
There is rapidly growing national interest in grazing lands’ soil health, which has been motivated by the current soil health renaissance in cropland agriculture. In contrast to intensively managed croplands, soil health for grazing lands, especially rangelands, is tempered by limited scientific evidence clearly illustrating positive feedbacks between soil health and grazing land resilience, or sustainability. Opportunities exist for improving soil health on grazing lands with intensively managed plant communities (e.g., pasture systems) and formerly cultivated or degraded lands. Therefore, the goal of this paper is to provide direction and recommendations for incorporating soil health into grazing management considerations on grazing lands. We argue that the current soil health renaissance should not focus on improvement of soil health on grazing lands where potential is limited but rather forward science-based management for improving grazing lands’ resilience to environmental change via 1) refocusing grazing management on fundamental ecological processes (water and nutrient cycling and energy flow) rather than maximum short-term profit or livestock production; 2) emphasizing goal-based management with adaptive decision making informed by specific objectives incorporating maintenance of soil health at a minimum and directly relevant monitoring attributes; 3) advancing holistic and integrated approaches for soil health that highlight social-ecological-economic interdependencies of these systems, with particular emphasis on human dimensions; 4) building cross-institutional partnerships on grazing lands’ soil health to enhance technical capacities of students, land managers, and natural resource professionals; and 5) creating a cross-region, living laboratory network of case studies involving producers using soil health as part of their grazing land management. Collectively, these efforts could foster transformational changes by strengthening the link between natural resources stewardship and sustainable grazing lands management through management-science partnerships in a social-ecological systems framework.  相似文献   

20.
We evaluated Arizona Cooperative Extension’s Rangeland Monitoring Program with the use of focus groups and a self-administered mail survey of grazing permittees and natural resource agency employees. Our primary objectives were to 1) determine whether Extension is reaching its target audience, 2) describe the monitoring practices and attitudes of permittees and agency staff, 3) determine whether there is a relationship between permittees’ exposure to Cooperative Extension and their monitoring and management practices, and 4) identify the monitoring information needs and preferences of permittees and natural resource agency staff. We found that Arizona’s rangeland monitoring Extension program has been effective in reaching a large part of its target audience, and a significant proportion of Arizona permittees monitor on public, private, and state-owned rangelands. However, overall monitoring adoption rates remain low. Extension contact is associated with use of monitoring and other beneficial management practices, and permittees and agency employees report that monitoring increased their knowledge and led to changes in management. Monitoring by permittees improves agency–permittee relationships in many cases. Most permittees and agency employees believe that their respective peers are the most reliable source of monitoring information and prefer to receive information from Extension through face-to-face contact at workshops or personalized on-site assistance. The evaluation revealed important social dimensions of rangeland monitoring. Extension agents play a key role in facilitating the social process of monitoring, as well as providing technical training in monitoring skills. Further study is needed to investigate whether permittee monitoring actually leads to better management, improved economic returns, or increased tenure security.  相似文献   

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