Temporally inter-comparable maps of terrestrial wilderness and the Last of the Wild

Wilderness areas, defined as areas free of industrial scale activities and other human pressures which result in significant biophysical disturbance, are important for biodiversity conservation and sustaining the key ecological processes underpinning planetary life-support systems. Despite their importance, wilderness areas are being rapidly eroded in extent and fragmented. Here we present the most up-to-date temporally inter-comparable maps of global terrestrial wilderness areas, which are essential for monitoring changes in their extent, and for proactively planning conservation interventions to ensure their preservation. Using maps of human pressure on the natural environment for 1993 and 2009, we identified wilderness as all ‘pressure free’ lands with a contiguous area >10,000 km2. These places are likely operating in a natural state and represent the most intact habitats globally. We then created a regionally representative map of wilderness following the well-established ‘Last of the Wild’ methodology; which identifies the 10% area with the lowest human pressure within each of Earth’s 60 biogeographic realms, and identifies the ten largest contiguous areas, along with all contiguous areas >10,000 km2.Wilderness areas are ecologically intact landscapes free of human pressures which cause significant biophysical disturbance of the natural environment1,2. This includes industrial activities such as land-clearing, dense human settlements, agriculture, industry, and infrastructure development3,4. Importantly, this definition does not exclude indigenous peoples and communities, who have been part of wilderness areas for millennia through deep bio-cultural connections to the land5,6.

Natural ecological and evolutionary processes continue largely unimpeded in wilderness areas, providing a suite of high-value ecosystem services7,8. These include regulation of hydrological cycles at multiple scales8,​9,​10, and significant organic carbon stocks11,12. Wilderness areas are also critically important for in situ biodiversity conservation, supporting the last intact mega-faunal assemblages3,13, wide ranging and migratory species14,15, and species sensitive to exploitation by or conflicts with humans16. Wilderness areas are also the last remaining places on Earth where scientists can study biodiversity and natural processes free from the influence of modern society.

Maps of terrestrial wilderness areas have previously been developed by mapping the extent of a number of human pressures on the environment at both global and regional scales3,17,18, using the logic that the areas free of human pressure constitute ‘wilderness’. These maps have proved useful for numerous ecological and conservation analyses18,​19,​20,​21. However, these maps provide a temporally static and now much outdated view of wilderness extent7,22,23, and there have been recent calls for a more updated product19.

Here we present two new data-sets of spatially and temporally intercomparable maps of global terrestrial wilderness areas for the years 1993 and 2009. We used the methodological framework outlined in the original ‘Last of the Wild’ work17 but utilized the recently updated ‘Human Footprint’ maps24. These are the most up-to-date and highest resolution globally standardized maps of cumulative human pressure on the terrestrial environment25. The Human Footprint is the only pressure map to have had its data validated24, and is widely regarded as the best available product of its kind26.

Our maps of wilderness areas have already been used to highlight catastrophic declines in wilderness extent over the last two decades, and show that conservation efforts has been greatly outpaced by these losses4. This has raised the profile of wilderness conservation globally12,27, and it seems that international targets for wilderness conservation may be developed shortly12,19. We anticipate that our maps will be important tools in the process of developing such targets, and for the conservation planning and decision making necessary to ensure representative protection of wilderness areas globallyThe human footprint
To map the global extent of wilderness we utilised the recently updated Human Footprint maps for 1993 and 200924,25 (Fig. 1). These are globally-standardised maps of cumulative human pressures on the terrestrial environment. At a 1 km2, they are the finest resolution cumulative threat maps available, as well as the most comprehensive, including data on eight human pressures globally: built environments; crop lands; pasture lands; population density; night-time lights; railways; major roadways; and navigable waterways. Following the original Human Footprint methodology17, individual pressures were placed within a 0–10 scale based on their estimated contribution to human pressure, and summed giving a cumulative score ranging from 0–50 for each pixel (some pressures are mutually exclusive, whilst others can co-occur). We converted the Human Footprint datasets from a continuous to an integer 0–50 scale by truncating. The integer Human Footprint datasets were used for all the analyses described in the paper. The following sections and Table 1 describe in detail how these datasets were handled to map pressure free lands and the Last of the Wild.Comparable maps of pressure free lands for 1993 and 2009
We created two global maps of wilderness in 1993 and 2009 by identifying all areas which are free of human pressure (Human Footprint=0), and have a contiguous area >10,000 km2. This size threshold has been used by others to identify wilderness areas3,7,19, and is consistent with the parameter values for identifying intact ecological communities in the International Union for Nature Conservation (IUCN) standards for identifying Key Biodiversity Areas30. Large wilderness areas separated by small areas of Human Footprint greater than ‘0’ were treated as two discreet wilderness blocks. Given the difficulty in restoring wilderness condition, locations which had a Human Footprint score >0 in 1993 but=0 in 2009 were excluded, as was Antarctica for its lack of suitable data.

Temporally inter-comparable maps of the ‘Last of the Wild’ for 1993 and 2009
We also created global maps of the ‘Last of the Wild’ for 1993 and 2009 following the methodology developed by Sanderson et al.17. First, we created a layer of biogeographic realms (hereafter simply ‘biorealms’) as a biogeographic framework for our analysis, based on the widely used Terrestrial Ecoregions of the World31. The biorealms represent combinations of the world’s 14 vegetated biomes and seven biogeographic realms (for example boreal forests exist in both the Palearctic and Nearctic realms). Following established practice we excluded Antarctica and other rock and ice ecoregions32,33. Our resulting map contained 60 out of a possible 67 biorealms because some sub-Antarctic and Pacific islands fall beyond the extent of the Human Footprint data (Supplementary File 1).

We calculated biorealm specific thresholds on the 1993 Human Footprint scale which ensured that at least 10% of each biorealm’s land area with the lowest Human Footprint in 1993 was captured. We then selected the ten largest contiguous blocks in each biorealm and all contiguous areas >10,000 km2 to create the Last of the Wild dataset for 1993. The same biorealm specific thresholds identified for the 1993 map for the 10% area with the lowest Human Footprint score for 1993 were also used to map the 2009 Last of the Wild so that it is possible to directly compare changes in wilderness extent across the two time periods. Finally, we created a map of the Last of the Wild for 2009 where we calculated the biorealm specific thresholds on the 2009 Human Footprint scale which ensured that at least 10% of a biorealms land area with the lowest Human Footprint in 2009 was captured (for the previous maps we used the 1993 threshold to ensure maps from the two time periods are comparable). This map is not comparable with the 1993 map, but is important since it shows the current best quality habitat left in all the biorealms.