**2. Tourism carrying capacity: A review of concept**

The concept of TCC, though emerged in the 1970s and 1980, has received significant attention in recent years as part of an effective strategy to address environmental, economic, and social issues [6–8].

There have been many attempts to define carrying capacity. It was stated that TCC is a specific type of environmental carrying capacity and refers to the biophysical and social capacity of the environment with respect to touristic activity and its development [9–10]. Middleton and Hawkins (1998) [11] defined carrying capacity as "a measure of the tolerance a site or building are open to tourists activity and limit beyond which an area may suffer from the adverse impacts of tourism." TCC can also be defined as "the maximum number of people that use tourism site without unacceptable effect on environmental resources while meeting the demand" [12].

Chamberlin (1997) [13] defines it as "the level of human activity an area can accommodate without the area deteriorating, the resident community being adversely affected or the quality of visitors experience declining." Clark [14] defines carrying capacity as a "certain threshold level of tourism activity beyond which there will occur damage to the environment, including natural habitats." He also states that the "actual carrying capacity limit in terms of numbers of visitors or any other quota or parameter is usually a judgement call based upon the level of change that can be accepted, regarding sustainability of resources, satisfaction of resource users, and socio-economic impact" [14]. The TCC represents "the maximum level of visitor use that an area can maintain, that is, the limit of human activity: if this level is exceeded, the resource will deteriorate" [15].

The UN World Tourism Organisation (WTO) defines TCC as "the maximum number of people that may visit a tourist destination at the same time, without causing destruction of the physical, economic, socio-cultural environment and an unacceptable decrease in the quality of visitors' satisfaction." Tourism operations in protected areas need to be planned carefully and monitor regularly to ensure their long-term sustainability. Otherwise, such operations will have negative consequences and tourism will contribute to the further deterioration of these areas. Many of the protected areas have promoted tourism for their social, economic, and livelihood opportunities of the local residents [15–19].

Individual tourist destinations were studied assessing the TCC all over the world [20–24]. It has been suggested that development of a tourist destination should be based on their innate capacities for tourism. TCC was considered as an appropriate tool for management and remains one of the most useful and applied techniques for tourism and recreation planning, if combined with other management tools [25, 26].

Coccossis and Mexa [6] showed that carrying capacity assessment remains a powerful concept that can be used for planning and management of sustainable tourism. Many studies calculated carrying capacity using physical, ecological, psychological, and economical approach. Because of expanding degree of environmental threat with growing tourism, a suitable method needs to be carried out and carrying capacity stays one of the applied and effective methods [27]. Hamed and Fataei [28] estimates the TCC to Fandoqloo forest in Iran using physical, real, and effective carrying capacities. Results of their study showed that each tourist spot has its specific priorities and the carrying capacity of each region differs according to the environmental conditions. Nghi et al. [23] assessed the environmental carrying capacities for Phong Nha-Ke Bang and Dong Hoi using three basic components: ecological, economic, and social. The authors have calculated the TCC in Dong Hoi and Phong Nha centers by using the adjustment from physical carrying capacity (PCC) to real carrying capacity (RCC) based on various limiting factors such as infrastructure and management capacities. Their results show that Dong Hoi center has the highest TCC and Phong Nha has a lower TCC than other centers in Quang Binh.

Lagmoj et al. [29] in their study evaluated TCC in three ways viz., PCC, RCC, and ECC, and found that "ECC is in low range due to lack of required facilities and infrastructures as well as manpower for management and providing tourism services for tourists." They estimated the "PCC in Khorma forest as 3712 persons/day while RCC, considering limiting factors including the number of very hot days and the number of wet days, is 2001 persons/day. The ECC, taking the management capabilities including the number of manpower and the budget, 69 persons/day was calculated for Khorma forest". Armin and Calichi [30] in their study of PCC, the factors viz., tourist flows, the size of the area, the optimum space available for each tourist and the visiting time, were considered. Their results showed that the total visitors to the park in 2012 were 220 visitors per day that actual average park visitation are higher than the estimated carrying capacity and stated that the expanding recreational use would affect production and other forest benefits in the long term and suggested that a recreational forest use plan must be adjusted by the planner to keep the park more exploiting.
