Author/s Pablo Tejedo (1)* & Tanya O’Neill (2) (1) Departamento de Ecología, Universidad Autónoma de Madrid, Ciudad Universitaria de Cantoblanco, Madrid, Spain (2) School of Science, Waikato University, Hamilton, New Zealand * pablo.tejedo[at]uam.es Brief Overview Antarctic soils are particularly vulnerable to disturbance due to their biological and physical properties and naturally slow recovery rates that are suppressed by low temperatures and sometimes low moisture availability. As most human activities are concentrated in relatively small scattered ice-free areas, the potential for adverse human impacts is great. Antarctic soils provide habitat for fauna and flora which are regionally important and, in some cases, include endemic representatives. Thus, protection of this component of the ecosystem should be a priority. Human trampling and track formation as a result of field camp installation, scientific activities and tourism can produce some undesirable consequences on soils. These impacts affect soil physicochemical and biological properties at different scales, ranging from populations to communities, and even habitats. The longevity of disturbances depends on soil type, regional climate, impact severity, remediation effort (if any), and what components of the ecosystem are being affected. In some cases, impacts continue decades after disturbance. Scientists have analysed these impacts, soil vulnerability and recoverability, and guidelines have been proposed to minimize the consequences of human pressures on soil environments. Detailed Overview Summary Most of Antarctica is covered in ice, but isolated sites with exposed soils exist as cliffs, coastal margins, nunataks, and seasonally snow- and ice-free ground. The largest ice-free region in Antarctica is the McMurdo Dry Valleys with an area of c. 15,000 km21. Terrestrial life is concentrated in soils developed in these ice-free areas, which have a combined area of c. 49,500 km2, and are mainly confined to the Antarctica Peninsula, the Transantarctic Mountains, MacRobertson Land and Dronning Maud Land2. Most of these soils are characterised by a general lack of structural development and coherence, low organic matter, biomass and primary production, low moisture availability, slow decomposition rates, and limited soil biota3. These characteristics, combined with the general absence of higher vegetation (vascular plant species) and prevailing low temperatures, result in a greater vulnerability to human trampling4. Most human activities are concentrated in ice-free areas with easy access and mild climates (e.g. Antarctic Peninsula and associated archipelagos). The most intense ground disturbances occur in the vicinity of research stations or field camps and at key tourist sites. Other affected sites include areas of scientific importance, historical sites, lookout points for spectacular landscapes and coastal wildlife colonies (Fig. 1). Trampling can lead to changes in soil properties and surface features including increases in track width, penetration resistance and bulk density4-8. Trampling usually produces visible micro-relief changes4, 9-11 (Figs. 1 and 2), in addition to albedo alterations in some specific sites. Figure 2. The longevity of visible trampling impacts are different in different locations and materials. Vanda experimental treading trial, Wright Valley, McMurdo Dry Valleys: (A) Vanda Fan site, immediately after 200 passes, December 1993. (B) Vanda Fan site, after 17 years of recovery, December 2009. (C) Vanda Rocky site, 192 passes, December 1993. (D) Vanda Rocky site, after 17 years of recovery, December 2009. Photos A and C by Megan Balks. Several impacts on flora have also been identified, mainly in the Antarctic Peninsula where there is more extensive vegetation, the most obvious being reduction in vegetation cover and biomass around paths12 (Fig. 3). Soil animals are directly affected through increased mortality and, indirectly, by the decrease of habitat quality affecting fecundity, abundance, composition and structure of the soil community6, 7, 13. Certain microbiological parameters can be modified by foot traffic, including enzymatic activity and soil respiration13, 14. Trampling reduces the amount of available nutrients in Antarctic moss communities12. Additionally, it has been suggested that non-indigenous species establishment may be facilitated as a direct result of the foot traffic associated with human presence14, 15, although additional evidence is needed to determine the relative importance of this mechanism. Figure 3. Temporary closure periods have been successfully applied at some sites in the maritime Antarctic to halt the effects of trampling. During a monitoring study conducted by Spanish and Ecuadorian researchers in early 2012, a series of impacts on vegetation were detected around the tracks as a result of repeated foot traffic (A; photo by Javier Benayas and Luis R. Pertierra). This situation was presented in a Working Paper submitted to the ATCM XXXV, held in Hobart. As a consequence, Resolution 5 (ATCM XXXV, Hobart, 2012) was adopted. Resolution 5 recommended to restrict all access to the central part of Barrientos Island (other than for reasons of scientific research and monitoring related to the recovery of the site). Under this measure a large part of the affected area showed a marked improvement in only one year (B; photo by Belén Albertos and Daniela Cajiao) including reduction in foot imprint depth and at grass rooting development level. However, the scar produced by trampling in the area surrounding the track had not completely healed during the four year closure period (C; photo by Laura Muñoz and Daniela Cajiao). The measured severity of disturbances depends on soil type, regional climate, mode and intensity of disturbance (foot versus vehicle), how dynamic the landscape is, and what component of the ecosystem is being investigated. Disturbances resulting from foot traffic and field camps usually cover a small area, but are often clearly visible16. Foot tracks form readily in certain vulnerable soils and may remain visible for many years after the event4, 10. Vehicular traffic also results in ground disturbances which are often much more extensive and persistent17. Ground disturbance is often greatest where the overlying desert pavement is disturbed and underlying fine material exposed4, 13, 18. In the McMurdo Dry Valleys, distinct walking tracks formed in soft material after as few as 20 pedestrian transits and are still visible up to 23 years after disturbance4 (Fig. 2, A and B). Non-cohesive soils with sandy pebble-gravel textures are also vulnerable to trampling, and damage is immediate7. In contrast, soils with a high surface-boulder cover and/or a large particle-size fraction are the least susceptible4 (Fig. 2, C and D). Other areas with aeolian sand dunes or coarse volcanic soils are readily disturbed, but the physical effects of regular foot traffic can disappear after one year due to the freeze-thaw activity and wind action7, 10 (Fig. 1, D). Experimental manipulations in soils located in the maritime Antarctic demonstrated that the effects of soil compaction could be completely reversed within 3-5 years if the area was closed to any human traffic during this period7. The same interval of time has been suggested for bryophyte and associated invertebrate communities to develop on previously bare soil19. There are several instruments to manage the impacts of pedestrian traffic in Antarctica20. The Scientific Committee on Antarctic Research (SCAR) has developed the ‘‘Environmental code of conduct for terrestrial scientific field research in Antarctica’’. This proposes two measures with reference to trampling: (1) to stay on established trails when available, and (2) to avoid walking on areas that are especially vulnerable to disturbance (e.g. peat soils, moss carpets, desert pavement, or muddy areas). Apart from these general recommendations, the Antarctic Treaty Parties have developed a collection of ‘‘Site guidelines for visitors’’ to provide specific instructions on the conduct of activities at the most heavily visited Antarctic sites, taking into account the environmental values and sensitivities specific to each site. Some measures for controlling the effects of trampling are mentioned, including the demarcation of closed areas to protect vulnerable features and the establishment of walking routes to avoid vegetation trampling. Finally, the management plans for some Antarctic Specially Managed Areas (ASMA) and the Antarctic Specially Protected Areas (ASPA) include instructions for protecting the environment during fieldwork or visits which help to limit impacts to soil. All these existing codes of conduct have to date contributed to controlling the scale of many of the potential impacts generated by trampling. These recommendations require regular assessment and, where necessary, revision to ensure their continued effectiveness in the face of the predicted increases in the intensity of human activities. Future work could usefully address the variability seen in responses of different soil types to trampling impacts. For example, the effectiveness of the use of established paths that cross vegetation-free soils, is highly dependent on context7, 10. At some sites of low intensity trampling, small changes at the soil surface recover relatively rapidly, in less than one annual cycle, suggesting that sometimes the dispersal of activity across wider corridors may be the most appropriate option rather than formation of a well-defined and long-lasting track. However, research has shown, for paths with high intensity use and those located in steep-sloped sites, that constraining use to a single well-defined track, on stony or bouldery surfaces wherever possible and avoiding muddy areas, keeps disturbance to a minimum7, 9, 18. It is clear that both environmental conditions and expected use levels must be taken into account in determining when and where it is more appropriate to concentrate or disperse human activities7. A coordinated approach using an agreed suite of biophysical or chemical indicators to assess the vulnerability and recoverability of different Antarctic soil surfaces to human trampling would assist environmental managers and the tourism industry in choosing the most appropriate, site specific, strategy to minimize physical and biological impacts. Key Events 1991 Special Antarctic Treaty Consultative Meeting (SATCM) XI adopts the Protocol on Environmental Protection to the Antarctic Treaty. Annex I Environmental Impact Assessment requires persons responsible for an activity in Antarctica to predict its significance and likely environmental impacts. 1993 Development of assessment criteria for human impacts on Antarctic soils by Campbell, Claridge and Balks. 1994 Recommendation XXVIII-1, entitled Guidance for visitors to the Antarctic, was adopted by the Antarctic Treaty Consultative Parties. It includes the directive of “Do not damage plants, for example by walking, driving, or landing on extensive moss beds or lichen-covered scree slopes”. It is the first mention of how to avoid an impact produced by trampling within a Treaty document. The International Association of Antarctica Tour Operators (IAATO), which includes most of the operators in this trade sector, applies a version of this recommendation as a code of conduct for their clients. 1995 Experimental investigation of impacts of trampling on Ross Island and in the Dry Valleys. 2005 First Site guidelines for Visitors published. These documents usually include recommendations for controlling the undesirable effects of trampling. 2008 The Environmental code of conduct for terrestrial scientific field research in Antarctica is approved by SCAR and COMNAP. 2016 The SCAR Code of Conduct for Activity within Terrestrial Geothermal Environments in Antarctica is agreed.