Tourism and its effects on the environment were not foreseen in the 1972 Convention and were only included as a concept in the Recommendation. Today, however, tourism poses both an opportunity and a threat to UNESCO WHS. Recognition of a heritage site by UNESCO often helps the destination reinvent itself, innovate, and improve the resources and products devoted to tourism. However, the destination itself may not have an adequate or updated tourism management plan that considers the changes brought about by the UNESCO recognition. It can also create tension when tourism leads to site abuse, commodification, increased waste and resource exploitation (De Ascaniis et al. 2018). Although WHL accreditation means identifying, recognizing, and protecting natural hotspots of global value, WHL is now widely admitted as a marketing tool for tourism campaigns and strong support for attracting tourism (Huang et al. 2012). Placing on the list is conspicuous to policy makers as it makes the site stand out and enhances its attractiveness (Frey and Steiner 2011), resulting in generated income. Recently, the tourism literature has begun to realize the prepotent effectiveness of UNESCO recognition in increasing the attractiveness of tourism, without conclusive results (Yang et al. 2010; Su and Lin 2014; Patuelli et al. 2016). As a result, there has been a long-standing debate between heritage preservation and tourism development, as experts in various disciplines have expressed concerns about potential damage caused by over tourism to such sites(Yang and Lin 2014). This discussion has crucial importance, considering the relationship between sustainable planning, tourism, and heritage protection.
The sustainable tourism practices are now a necessity for the growth of tourism industry in heritage sites (UNESCO 2021c). Indeed, since 1994, sustainability has been increasingly integrated into the directions recommended by the WHC (Marcotte and Bourdeau 2012). Donations and support funds have been collected for many of the listed heritage sites. Protected area managers and conservationists around the world spend sizeable amount of money each year to conserve biodiversity (Castro and Locker 2000). However, these donations are often in serious conflict with the socioeconomic development needs of local residents (McNeely and Ness 1996).
The reason why some of the protected areas do not function well, despite sufficient management, may be mainly because of intensified human spatial use in the protected areas, causing changes in biodiversity and ecological function. Satellite-based analyzes reveal that intensive land use and human populations have swiftly increased in recent years around many protected areas (Hansen et al., 2013). Besides, the habitat destruction is a key component of species extinction (Bibby 1994; Brooks et al. 2002), with human activities being (Kozak 2013)responsible for the vast majority of existing habitat loss (Bawa and Dayanandan 1997). At this point, the size of the protected area is important in terms of the volume and functionality of the conservation activities due to the negative effects of tourism Parks and Harcourt (2002) note that small reserves are particularly prone to this effect, and conservation agencies are increasingly focusing on such areas.
Environmental impacts of tourism in heritage sites include ecosystem, season, management measures, tourist behavior and characteristics, scale and intensity of tourism operations (Buckley 2012, 2018; Koichi et al. 2013). Flora effects vary from botanical differences to usage type in the site. Forest floor plants are usually less tolerant to crush resistance, while open grassy habitats are harder.
Impacts on ground often include erosion and compaction. Tourism usually causes soil compaction because of recreational activities. This raises runoff from snow and rain, resulting in decreased water absorption, erosion, and vegetation loss. Soil compaction is inevitable but may be limited to certain areas. Turbidity in source is a frequent consequence of recreation activities and tourism infrastructure. Tourist activities are more likely to alter water quality in ways that harm aquatic flora and fauna if soils are more prone to erosion. The absence or malfunction of the sewerage and cesspool systems in the hotels can drive tourists away from the region. Organic waste from poorly treated sewage affects water quality. On coastlines, these wastes may cause pollution (Pedersen 2002).
Disturbances from wildlife watching affect some species more than others. Distinct species develop a tolerance for discomfort after an initial impact. The habit can be mistakenly viewed as favorable, as it draws visitors up to wildlife. But it can pose a problem: habitual wildlife can be in search for food, and they may injure or even kill visitors. When the tolerance levels of nesting birds are exceeded, they could leave their nests. Timid species permanently replace the recreation areas when they encounter visitors, while others such as deer may get used to it over time. However, some species are readily frightened than others, and even any simple factor can influence their breeding and feeding patterns (Pedersen 2002).
Despite the high level of protection provided to natural heritage sites, the balance of protection and use has deteriorated due to the negative effects of the above-mentioned tourism activities. Exotic species are increasingly infesting protected areas (Stohlgren and Schnase 2006) and some native species have become extinct in protected areas. (Brashares et al. 2001). These extinctions are often attributed to the isolation of nature reserves (Wilcove and May 1986). In addition, tourism activities sometimes rise near the boundaries of protected areas and can replace wildlife (Hansen and DeFries 2007). In order to prevent this situation and to develop conservation activities, it has been proposed to create buffer zones around the protected areas (Noss 1983).
3.1. Carrying Capacity and Related Issues
Carrying capacity is introduced as a conceptual tool for managing tourism pressures in heritage sites. For heritage sites, the carrying capacity is expressed as 'the number of people who visit the site without causing irreversible damage to its natural and built environment and without degrading the quality of the visitor's experience' (Jinshi 2014). Carrying capacity can serve as a frame of reference for a variety of purposes, depending on the characteristics of the site (size, site characteristics, community, tourism, and visitors) and the adoption capacities of the local system (institutional, economic, social, and cultural) and implementing visitor management policies. Carrying capacity should be evaluated in the context of heritage site and/or destination management plans. Tourism management and careful planning, as well as respect for the well-being of destination’s permanent residents, are other issues that both researchers and managers must constantly consider (Wall 2020). Discussions about human pressure on resources go long way back, but in the tourism context, research focusing on carrying capacity in North American national parks is in lead (Dodds and Butler 2019).
The negative effects of tourism occur when the environment exceeds the limit of coping with tourism activity within the limits of acceptable change. Uncontrolled tourism poses potential threats especially to the sustainability of natural areas. In recent years, because of tourism mishandling and profit maximizing policies, many tourist areas and local communities and the wildlife have suffered from tourist concentrations. For this reason, over tourism (Seraphin et al. 2018; Cheung and Li 2019) leads to the failure of existing policies that promote tourism, continuous and increased cultural site destructions, natural heritage degradation, and harm to local communities. Tourism is being studied as an important topic of conservation and management as it is probably the most important commercial use for protected natural areas (Spenceley 2018). However, ignoring environmental concerns in tourism development in heritage (natural) areas is a factor that will threaten sustainability (Badola et al. 2018).
Post-organized infrastructure construction in natural heritage sites initiates a complex process chain that is often unfeasible to reverse. Infrastructure has a variety of indirect and direct ecological impacts on the environmental areas with a spatial extent through to several kilometers (Ibisch et al. 2016; Tverijonaite et al. 2018). Better access to natural area destinations not only impacts its immediate surroundings along the way; but it also affects satisfaction among visitors, as well-organized roads result in higher visitor traffic. This could cause an increased demand for more service development and infrastructure (Haraldsson and Ólafsdóttir 2018). While visitors prefer to relax in a natural and unspoiled environment, they are probably disappointed if the infrastructure and crowd level at a particular nature destination are too high. This paradox shows the importance of protection- use balance.
Ecotourism can procure an additional economic ground for the conservation of biodiversity and natural areas. Also, it has been seen as a sustainability tool, especially for developing countries where resources for environmental management are limited or non-existent (de Oliveira Silva et al. 2005). Protected areas need more flexible ownership structures and funds to improve monitoring systems and achieve equity and efficiency through nature-based tourism (Su and Xiao 2009). To ensure sustainability, it is necessary to consider scientific and empirical evidence, and also to make decisions by integrating cultural, social and political factors (Xu et al. 2014). Protection and management can be achieved with a balance in supporting local communities while preserving the characteristics of the natural area that allows for such tourism development (Bello et al. 2016; Lucrezi et al. 2017). Considering the visitation and environmental pressures in protected areas (Rodríguez-Rodríguez 2012), there is a need for continuous update and follow-up on conservation and management for response framework and an optimal visitor impact assessment.