# A Vulnerable Environment Study in Karst Regions between 1991 and 2017: A Bibliometric Analysis
## 1 Introduction  
Karst environment, the most vulnerable natural environment in the world, is easily influenced by human activities that have caused many environmental problems, such as environment degradation and disruption, and resulted in high economic cost [1; 2; 3]. The environmental degradation and disruption are characterized by drought, flood, soil erosion, reduction of vegetation coverage, rocky desertification, surface subsidence, loss of biodiversity, habitat fragmentation, changes in physiological and ecological characteristics of plant communities, pollution and depletion of water resources, and the accompanied poverty. The vulnerable environment with its attenuated sustainable development ability cannot adapt to the fast-paced social and economic development [1; 4; 5; 6; 7; 8].  
Currently, the understanding of the vulnerability of karst environment has reached a new height, which greatly facilitated the settlement of the degradation and pollution problems [9; 5; 10; 11; 12; 13; 14].  
Karst systems are highly dynamic and heterogeneous. The complicate hydrological, geochemical, and biological processes have great impact on the transfer of water, solute, and non-aqueous substance on large-scale spatial and temporal scale [15]. Meanwhile, the distribution of animals and plants and the activities of human beings are also greatly impacted by the hydrological network, rock solubility, and the unique landscape of karst systems [16]. However, the karst regions are faced with increasingpressure of ecological degradation due to the increasing population and demands of resources and the vulnerability of surface soil [14; 17; 18; 19; 20]. The formation and development of vulnerable karst environment are tightly connected with human activities, especially in developing countries. It has caused the deterioration of ecosystem services and ultimately forced local residents to live in greater poverty [4; 17; 20; 21; 22].  
In the past few years, a lot of researches about vulnerable karst environment have been undertaken. Some of the researches covered areas of characteristics of vulnerable karst environment, cause of formation, and ecological restoration and rehabilitation [11; 20; 23; 24; 25; 26], while others focused on the landscape of karst rocky desertification [5; 10; 18; 19; 27], the soil erosion in karst region [9; 28; 29; 30; 31], cave environment [32; 33; 34], aquifer and spring based water environment [35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45], carbon source and sink [46; 47; 48], eco-hydrology [49; 50], and protection and management of vulnerable karst environment [13; 51; 52]. Those researches addressed the major issues, yet there is still a lack of a general review that may reveal the trend of studies in this field. This paper gives a comprehensive analysis, from the angle of biliometrics, in the field of vulnerable karst environment and provides insights for further studies.  
This work helps to define the research clusters and researchers with a stronger impact on the field by identifying the mature and emerging research topics online using bibliometrics tools. Bibliometric analysis revealed the interests and new topics in the field and pointed out the possible directions of future studies [53]. Although the importance of researches on vulnerable karst environment has been increasingly emphasized, there is no bibliometric analysis popped up into our sight of searching. This work summarized the knowledge foundation and research frontiers in the field of vulnerable karst environment through bibliometric analysis on the literature in the \"Web of Science\" database from 1991 to 2017. It clarified current research hotspots and future research directions and provided scientific foundation for further studies in this field.