In this research excerpt, the latest temporally inter-comparable maps of the terrestrial Human Footprint are presented, as well as an assessment of change in human pressure at global, biome, and ecoregional scales.
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by several authors of the School of Earth and Environmental Sciences of the University of Queensland, Australia.
Humans have influenced the terrestrial biosphere for millennia, converting much of Earth’s surface to anthropogenic land uses. Nevertheless, there are still some ecosystems that remain free from significant human pressure, thereby providing crucial habitats for imperilled species and maintaining the ecosystem processes that underpin planetary life-support systems. As a consequence, calls for the global identification, monitoring, and retention of the remaining lands that are relatively free of direct anthropogenic disturbance are increasing.
Over the past two decades, cumulative pressure maps that combine remotely-sensed data with survey data are being increasingly used to assess the full range of human pressures on land spatially. These advances have facilitated the mapping of Earth’s remaining marine and terrestrial wilderness, improved measures and estimates of species extinction risk underpinned broader assessments of human impacts on ecosystems and biodiversity and enabled the identification of protected areas and world heritage sites in danger. The results of these mapping efforts are influencing global policy discussions and informing on-the-ground decisions about where to undertake biodiversity conservation action.
Here, we provide the latest global maps of cumulative human pressure for the years 2000, 2005, 2010, and 2013, and use them to assess how changes in human pressure are altering Earth’s terrestrial ecosystems. We used a human footprint threshold of <4 (on 0 – 50 scale) to identify where land is considered ecologically intact (below the threshold) or highly modified and thus ecologically degraded (equal to or above the threshold). Areas below this threshold are ecosystems that may be subject to some level of human pressure (for example low-density transitory human populations or pasture lands grazed at a low intensity), but still contain the majority of their natural habitat and ecological processes.
This threshold has been found to be robust from a species conservation perspective because once surpassed, species extinction risk increases dramatically , and several ecosystem processes are altered.
We assess transitions from intact to highly modified land at global, biome, and ecoregional scales and ascertain which nations contain Earth’s remaining intact systems, and had the greatest amounts of habitat loss. Previous global assessments of human pressure have attempted to identify at risk ecosystems by determining a ‘safe limit’ of biodiversity loss for ecosystem functionality, assessing protection levels, and analysing habitat conversion using land cover. But all of these ignore a broad range of threats that occur beyond land use such as accessibility via roads, railways and navigable waterways, human population density, and light pollution. These pressures have environmental impacts well beyond the local development footprint.
As such, our results provide the latest spatially explicit understanding of the state of human pressure on the natural environment, and how it is changing over time. We show that the human footprint methodology can be continually updated and, when more recent data becomes available, allow for assessment of habitat loss at scales relevant to planning activities.
State of Terrestrial Earth
As of 2013, 55.8 million km2 (41.6%) of Earth’s surface was intact (which includes wilderness, human footprint of <4), and 33.5 million km2 (25.0%) was wilderness (human footprint of <1). The remaining (human footprint of >4) 78.4 million km2 (58.4%) was under moderate or intense human pressure (and therefore highly modified), which was widespread, encompassing over half the area of 11 (or 78.6%) of Earth’s 14 biomes. Temperate broadleaf and mixed forests were the most altered biome, with 11.6 million km2 (91.0%) being highly modified, followed by tropical and subtropical dry broadleaf forests with 2.72 million km2 (90.5%), and Mediterranean forests, woodlands and scrubs with 2.88 million km2 (89.7%). Wilderness areas have all but disappeared in many biomes, for example, only 82,000 km2 (0.81%) remained in temperate grasslands, savannahs, and shrublands, 29,000 km2 (0.96%) in tropical and subtropical dry broadleaf forests, and just 12,000 km2 (1.69%) in tropical and subtropical coniferous forests. Earth’s 14 biomes consist of 795 ecoregions, which represent distinct biotic assemblages and abiotic features (such as landforms) at a finer scale than biomes. We found the entire extent of 46 (5.76%) ecoregions were highly modified. These 46 ecoregions span 10 biomes, with the majority located in tropical and subtropical moist broadleaf forests (n=17, 37.0%), tropical and subtropical dry broadleaf forests (n=6, 13.0%), and temperate broadleaf and mixed forests (n=6, 13.0%). One-quarter of all ecoregions (n=187) have lost all wilderness. The majority of land in tundra, boreal and taiga forests, and deserts and xeric shrubland biomes remains intact. At the ecoregion level, just 52 (6.53%) still have >90% of their land intact, and a mere 21 (2.64%) are >90% wilderness. These ecoregions with >90% wilderness are found in just four biomes, tundra (n = 12), boreal forests/taiga (n = 5), tropical and subtropical moist broadleaf forests (Rio Negro campinarana and Juruá-Purus moist forests), and tropical and subtropical grasslands, savannahs and shrublands (Northwestern Hawaii scrub).
Contemporary changes in human pressure
Between 2000 and 2013, 25.4 million km2 (18.9%) of Earth’s terrestrial surface deteriorated (human pressure increased), while only 8 million km2 (5.96%) improved (human pressure decreased). This increase in human pressure was substantial across 1.89 million km2 of Earth’s intact lands, an area the size of Mexico, that these places can be classified as highly modified (i.e. they transitioned from below to above the human footprint threshold of 4). During the same time period, over 1.1 million km2 of wilderness was lost (human footprint increasing above 1), with 67,000 km2 of that wilderness becoming highly modified (human footprint increasing from below 1 to above 4).
Intact lands were lost in all biomes during the assessment period, with the highest loss occurring in tropical and subtropical grassland, savannah and shrublands (655,000 km2 was lost representing 11.3% of all intact lands within the biome, an area approximately the size of France; Figure 4). The tropical and subtropical moist broadleaf forests and mangrove biomes also lost substantial areas of intact land (559,000 km2, 6.90% and 9,000 km2, 14.7% respectively). While the largest absolute loss of intact lands occurred in savannah and woodland ecoregions, the largest proportional losses occurred in tropical forest ecoregion types. For example, intact areas were completely lost in seven forested ecoregions including the Louisiade Archipelago rainforests (Papua New Guinea), and Sumatran freshwater swamp forests (Indonesia).
You can read the complete research paper here.