3. Negative tourism impacts
Overcrowding, misuse of natural resources, the construction of buildings and infrastructure, and other activities associated with tourism, produce impacts on the environment. These impacts may be not only physical, but also cultural. In this chapter the most frequent and damaging tourism impacts at local level in regard to protected areas are analysed.
In general, the impacts of tourism vary according to the number and nature of tourists and the characteristics of the site. The individual tourist normally has a relatively small impact. Problems arise, however, if the number of tourists is large or the resource overused. Thus although tourism can be a lucrative source of revenue for a protected area, it can also represent a major management problem. As with most problems, the negative impacts of tourism can only be managed effectively if they have been identified, measured and evaluated. Once this has been done, tailored management responses can be created.
Tourism impacts on protected areas can be broadly classified in two categories: direct and indirect. Direct impact is caused by the presence of tourists, indirect impact by the infrastructure created in connection with tourism activities.
For the purposes of this book, direct tourism impacts on the environment have been classified as follows:
impacts on geological exposures, minerals and fossils
impacts on soils
impacts on water resources
impacts on vegetation
impacts on animal life
impacts on sanitation
aesthetic impacts on the landscape
impacts on the cultural environment.
These impacts (which are actually manifestations of change) are dealt with below, one by one. But it should be remembered that the ecological effects of tourism activities rarely occur singly.
Impacts which are likely to occur together, or to follow in sequence, can be predicted to some extent. Sites of more intense recreational activity will be the first parts of an area to be affected, and can be used to forecast changes likely to occur elsewhere in the event of increasing intensity of use or misuse.
For very ample discussions on tourism impacts in natural areas, see Kuss et al. (1990) and Speight (1973).
Impacts on geological properties, rock formations, minerals and fossils
Climbing and caving are the two activities that make most use of rock formations. But apart from minor abrasion of rock faces and the wearing away of surface travertine deposits, their effects appear to be negligible (Speight, 1973).
The collecting of minerals, rocks formations and fossils gives more cause for concern. One of the most dramatic examples of the effect of rock collecting is that of the Petrified Forest National Monument in Arizona. Souvenir hunters have totally stripped various sites of their fossil tree covering. Similarly, frost-net features in the Rocky Mountains National Parkland have been destroyed by visitors who have removed the stones that once outlined the frost polygons (Scott-Williams, 1967). In New Mexico, "rockhounding" has become so popular that the 100 hectare Rockland State Park in New Mexico has been set aside specifically for mineral collecting in order to relieve pressure in other areas (Mitchell, 1967).
In less developed countries, lack of surveillance contributes to fossil depletion. This is the case in the fossil area of San Juan Raya, Puebla, Mexico. Also, at many sites, the eagerness with which cave formations such as stalactites are sought has made the use of elaborate protection devices necessary.
Governments now realize that national parks and protected areas safeguard the natural environment and the cultural heritage of their countries. The Dryandra State Forest Reserve, Western Australia, preserves eucalyptus forests that host the endangered numbat (an endemic marsupial) (25); Portobello World Heritage Site, Panama, protects the remains of Spanish colonial fortifications (26); and Chichén Itzá Archeological Zone (a World Heritage Site) in Yucatán, Mexico, contains magnificent Maya ruins, surrounded by undisturbed deciduous forest (27).
Impacts on soils
Terrestrial and aquatic soils are treated here together, along with beach sands and estuarine muds, cave earths and screes.
Impacts on soils may be of several kinds. Soil removal and relocation is due mainly to the introduction of on-site facilities or site management, and can in effect "sterilize" land by burying its surface under buildings or car parks.
Soil creep, slides and scree movement can occur as a result of walking activity. Soil creep becomes noticeable when it results in terracette formation, which often accompanies the development of hillside contour or oblique paths, as seen in areas used for hiking and pony-trekking. A more dispersed downward movement of topsoil can be caused by visitors when they walk or scramble down a slope. Slopes of volcanoes of recent origin are particularly vulnerable. (Careless scrambling prevents natural vegetational succession). In a dense temperate woodland with an unconsolidated chalk-rubble-soil, unstabilized by ground vegetation, the average rate of downslope movement has been found to increase from 5 cm/year to 30 cm/year as a result of such activity. Use of paths can be sufficient to reactivate screes, that would otherwise be stabilized by ground vegetation.
Soil break-up due to the "powdering" of litter layers usually occurs on paths or tracks, and sometimes also over wider areas such as camp-sites. Disappearance of the soil litter layers due to fragmentation (and subsequent leaching/erosion) is one of the processes that usually occurs during the initial stages of path formation. (Many paths are simply strips of exposed soil.) It was found that the volume of leaf litter on a newly-opened temperate woodland nature trail, used by 8,000 people, decreased by 50% during the course of a single week. Conversely, grass litter increased in depth, reflecting the decline in ground vegetation. It has also been observed that the powder produced by the comminution of woodland leaf litter is dispersed by wind erosion. A similar phenomenon has been observed along trails and near car parks, in a peaty montane soil. Horses' hooves can also break up trail surfaces. Continued loss of soil litter layers is very detrimental to an ecosystem because it decreases nutrient recycling and reduces the populations of those organisms that carry out recycling processes (Kuss et al., 1990).
Soil compaction is caused mainly by trampling. It has been observed on chalk grassland, in caves, along lake shores, and on paths and tracks. It has also occurred as a result of compression — due to trampling — of the surface of frost polygons. Path compaction due to the passage of horses has also been noted (Kuss et al., 1990). Soil compaction is sometimes exacerbated by the passage of vehicles — for example on camping grounds. (Dunes too are vulnerable to the trampling of visitors and the passage of vehicles.) Indeed, most references consulted by Speight (1973) concern "camping" in woodlands. This may be an artifact of the disproportionate interest in campground management on the part of the US Forest Service in particular, but an alternative explanation is that camping is the recreational activity most likely to cause soil compaction and that woodland sites are the most susceptible. (A survey of 137 forest campgrounds in the USA found that 70% of them were suffering from compaction.) The facts are obscured by the use made of the word "camping" in American literature on compaction. "Camping" is used as an umbrella term to refer to anything from the simplest tent to the most complex mobile home.
Compacted soils may not always be reliably identified by eye; compaction recorded for a chalk grassland soil after the passage of 8,000 people was found to have disappeared after two week's respite. Evidently, continuous trampling reduces the ability of the soil to recover, due to the decrease in abundance of active roots.
Consequences of compaction include impeded drainage (which leads to increased run-off and erosion), decreased water and air availability to plant roots and soil organisms (causing alteration in soil organism populations and plant death), and decreased abundance of larger pore spaces (leading in turn to a decline in the populations of larger soil organisms). Present information on soil compaction is not sufficiently precise to allow prediction of damage resulting from given intensities and types of use. But it is known that compacted, puddled and churned-up soil surfaces increase surface run-off.
Puddling of the ground surface of trails used for horse riding can also impede drainage and result in the development of marshy surface conditions. (Puddling leads to "gleying" and other drainage problems and simultaneously destroys plant roots that would otherwise help re-establish vegetation cover.) Additionally, any facility with areas of impenetrable surface, such as roof-tops, hard-topped paths and areas of hard standing, will be susceptible to surface run-off. However, it is only areas of intense recreational activity, such as picnic sites and trails, that appear to be affected by significant changes in run-off and drainage. Texture of ground surface (e.g. covered with vegetation or bare), angle of slope, soil type (sands are less susceptible to drainage changes than finer-grained soils), initial drainage patterns and intensity of use can all influence run-off and drainage changes. Erosion is the most likely consequence of increased run-off.
Soil erosion at picnic sites, on paths and among sand-dunes is often attributed to the impact of recreational activities. But recreational activities are themselves almost never agents of erosion, their effect being only to provide circumstances in which forces of erosion, i.e. wind and water, are more likely to occur. Decrease in ground vegetation and increased soil compaction (which often occur together