- Scientists have been divided on what habitats to prioritise for conservation: natural, intact lands or fragments within human-modified areas.
- A team addressed this debate by developing a global index ‘contextual intactness’ by taking into account several factors including the human footprint of a location and the biodiversity in it, by using a new modelling framework.
- The study revealed that only 18.6 percent of global high-value habitat that supports biodiversity is protected, and that both intact wild areas and degraded, human-modified landscapes are crucial to maintaining biodiversity.
Scientists are undivided on the need to conserve natural habitats to maintain biodiversity, but divided on which ones to prioritise: intact wild habitats, or fragmented, degraded lands that are becoming increasingly common? However, both these habitats could play crucial roles in maintaining biodiversity worldwide, finds a recent study published in Proceedings of the National Academy of Sciences.
The world’s biodiversity is distributed across protected and non-protected areas, both of which face several threats. Increasing land degradation caused by human activities (including conversion of natural ecosystems into croplands to meet increasing rates of human consumption) is pushing the world towards a sixth mass species extinction, undermining the well-being of at least 3.2 billion people and intensifying climate change, found a 2018 report by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES).
According to another study, India is among the countries that could sustain high biodiversity loss (of birds, mammals, reptiles and amphibians) due to agricultural intensification. The cutting up of intact habitats into several smaller isolated fragments is a worry too: in 2015, an analysis found that such habitat fragmentation reduces biodiversity by 13 to 75 percent and affects important ecosystem functions in many ways.
Landscapes have to be conserved, but should intact natural expanses be prioritised over smaller, fragmented areas in people-modified landscapes? With studies revealing the importance of both protected areas (such as the finding that local biodiversity is higher in protected areas worldwide than outside them) and non-protected ones, scientists have been divided on this.
The world’s ‘contextual intactness’
To address this debate, a team including Karel Mokany (Commonwealth Scientific and Industrial Research Organisation, Australia) developed a global index, the “contextual intactness” of habitats across the world. They took into account two factors: the current habitat condition of every terrestrial location (every one square-kilometre grid, that is), and the similarity in species assemblages in that location relative to every other biologically similar location.
To develop the index, the team updated the human footprint (HFP) map for the world using data including human population density and land transformation and categorised areas according to four levels of the HFP: wilderness areas with zero HFP, low disturbance (HFP between 1 to 3), modified areas (where HFP is 4 to 9) and highly modified areas that had the HFPs of greater than 10.
The team then combined this with estimates of species assemblage similarities between pairs of locations using BILBI (Biogeographic Infrastructure for Large-scaled Biodiversity Indicators), a newly-developed modelling framework that has been used to develop several indicators including the Biodiversity Habitat Index endorsed by the Convention on Biological Diversity to report Aichi Targets of nations. The team used more than 100 million (10 crore) species occurrence records from the open-access Global Biodiversity Information Facility spanning more than 410,000 species (vertebrates, invertebrates and vascular plants) across the world’s bio-realms.
Put together, these data provided a value of contextual intactness (ranging from 0 to 1) for every location in the world. The team found that biomes that had one of the lowest levels of contextual intactness (and highest HFP) included temperate broadleaf and mixed forests (found in areas including central China, eastern North America and the Himalayas, according to the terrestrial ecoregions classification by the World Wildlife Fund). The boreal forests or taiga of central and east Russia had the highest contextual intactness.
The inset figure here depicts areas with higher levels of contextual intactness in dark shades, while different colours indicate the human footprint levels (wilderness areas are in blue and low disturbance-areas in green, while orange and pink reflect modified and highly modified areas). While some parts of the Himalayas are in orange and green (with dark shades too, indicating higher contextual intactness), regions including some parts of central and northeastern India are in dark shades of pink and orange.
Defining “high-value”, conservation-worthy habitats as those with contextual intactness of more than 0.5 (locations that are better off – such as having lower HFP – than more than half of the similar habitat) and overlaying this with a map of the world’s protected areas, the team found that only 18.6 percent of global high-value habitat is currently protected. The largest areas of unprotected high-value biodiversity habitat fell under wilderness and areas facing low human disturbance. Even modified areas were important for biodiversity; the tropical forests of southeast Asia, for instance, have faced “widespread degradation of natural habitats”, so even the remaining modified natural habitats are of high value, write the authors in the study. The debate of what to protect – intact natural landscapes or areas facing high human pressures – is nuanced, and an “unnecessarily artificial” dichotomy, argue the scientists.
“By its very nature, almost all countries will have very important habitat for retaining biodiversity,” wrote lead author Mokany in an email to Mongabay-India. “This analysis uses the human footprint map as one of its inputs, and the human footprint across India is very high, due to the high population density. These high pressures from humans make the remaining areas of habitat really important for biodiversity, even where that habitat may have been degraded by humans.”
Though India’s protected areas (PAs) span only five percent of its area, they have played a crucial role in conserving India’s biodiversity, argued scientists including Mousumi Ghosh-Harihar in their review of protected areas and biodiversity conservation in 2019. However, the team also noted how some habitats such as grasslands are not adequately represented in such PAs. Using the approach of contextual intactness could help prioritise conservation units in such often ignored habitats as well as pockets within high human use areas (e.g. urban forests, sacred groves, wetlands) which still harbour significant biodiversity, commented Ghosh-Harihar, postdoctoral fellow at the National Centre for Biological Sciences.
Remnant habitats within heavily human-modified regions have become the last foothold for many narrowly distributed species and biological communities, but because they are not ‘intact’ in absolute terms, convincing decision-makers, landowners, and even conservationists, about their significance can be quite challenging, commented scientist Anand M. Osuri of the Nature Conservation Foundation-India.
“Contextual intactness offers a new way of thinking and communicating about the importance of such habitats, and could help ensure that conservation strategies do not neglect the biodiversity of historically and heavily human-dominated regions.”
Mokany et al 2020. Reconciling global priorities for conserving biodiversity habitat. PNAS 117 (18), 9906-9911.
Ghosh-Harihar et al 2019. Protected areas and biodiversity conservation in India. Biological Conservation 237, 114-124.
Elsen et al 2017. The importance of agricultural lands for Himalayan birds in winter. Conservation Biology 31(2), 416-426.
Kehoe et al 2017. Biodiversity at risk under future cropland expansion and intensification. Nature Ecology and Evolution 1, 1129–1135.
Gray et al 2016. Local biodiversity is higher inside than outside terrestrial protected areas worldwide. Nature Communications 7, Article number 12306.
Dudley et al 2009. The Links between Protected Areas, Faiths, and Sacred Natural Sites. Conservation Biology 23 (3), 568-577.
IPBES (2018): The IPBES assessment report on land degradation and restoration. Montanarella, L., Scholes, R., and Brainich, A. (eds.). Secretariat of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, Bonn, Germany. 744 pages.https://doi.org/10.5281/zenodo.3237392
Haddad et al 2015. Habitat fragmentation and its lasting impact on Earth’s ecosystems. Science Advances 1 (2), e1500052.
Banner image: Savanna grassland in Tamil Nadu. Savanna grasslands are among the biomes with a higher human footprint and are among the often ignored habitats in need of conservation attention. Photo by T. R. Shankar Raman/Wikimedia Commons.