Elephant ecosystems in decline
Study examining habitats across centuries reveals an urgent need for sustainable land-use and conservation strategies to avoid dangers for wildlife and human communities
Peer-Reviewed PublicationVIDEO: ANIMATION TRACKING THE LOSS OF SUITABLE HABITAT FOR ASIAN ELEPHANTS (YELLOW) BETWEEN 1700-2015. A STUDY PUBLISHED IN SCIENTIFIC REPORTS LED BY UC SAN DIEGO EXAMINING HABITATS ACROSS CENTURIES REVEALS AN URGENT NEED FOR SUSTAINABLE LAND-USE AND CONSERVATION STRATEGIES TO AVOID DANGERS FOR WILDLIFE AND HUMAN COMMUNITIES. view more
CREDIT: ASHLEY WEAVER
More than 3 million square kilometers of the Asian elephant’s historic habitat range has been lost in just three centuries, a new report from an international scientific team led by a University of California San Diego researcher reveals. This dramatic decline may underlie present-day conflicts between elephants and people, the authors argue.
Developing new insights from a unique data set that models land-use change over 13 centuries, a research team led by new UC San Diego faculty member Shermin de Silva found that habitats suitable for Asian elephants have been cut by nearly two-thirds within the past 300 years.
The largest living land animal in Asia, endangered Asian elephants inhabited grasslands and rainforest ecosystems that once spanned the breadth of the continent. Analyzing land-use data from the years 850 to 2015, the researchers describe in the journal Scientific Reports a troubling situation in which they estimate that more than 64% of historic suitable elephant habitat across Asia has been lost. While elephant habitats remained relatively stable prior to the 1700s, colonial-era land-use practices in Asia, including timber extraction, farming and agriculture, cut the average habitat patch size more than 80%, from 99,000 to 16,000 square kilometers.
The study also suggests that the remaining elephant populations today may not have adequate habitat areas. While 100% of the area within 100 kilometers of the current elephant range was considered suitable habitat in 1700, the proportion has since declined to less than 50% by 2015. This sets up a high potential for conflicts with people living in those areas as elephant populations alter their behavior and adjust to more human-dominated spaces.
“In the 1600s and 1700s there is evidence of a dramatic change in land use, not just in Asia, but globally,” said de Silva, an assistant professor in the School of Biological Sciences’ Department of Ecology, Behavior and Evolution, and founder of the nonprofit Trunks & Leaves. “Around the world we see a really dramatic transformation that has consequences that persist even to this day.”
Also contributing to the study were researchers from across the globe, including Smithsonian’s National Zoo and Conservation Biology Institute, University of Nottingham Malaysia, Frankfurt Zoological Society, Vietnam National University of Forestry, Wild Earth Allies, Zoological Society of London and Colby College.
“This study has important implications for our understanding of the history of elephant landscapes in Asia and it lays the groundwork for better understanding and modeling the potential future of elephant landscapes as well,” said Philip Nyhus, Professor of Environmental Studies at Colby College and one of the study co-authors.
In addition to Nyhus, three Colby undergraduate students contributed to the study. “This was a collaborative and multi-institutional effort,” added Nyhus, “and I was proud that Colby students contributed significantly to the models and analyses used in the study.”
Beyond the immediate impact on Asian elephants, the study offers the results as a mechanism to assess land-use practices and much-needed conservation strategies for all of the area’s inhabitants.
“We’re using elephants as indicators to look at the impact of land-use change on these diverse ecosystems over a longer time scale,” said de Silva.
Human impacts leading to reductions in the habitat ranges of several land-based mammal species have been well documented in the recent past. Climate change is also thought to have accelerated this decline over the past century. But assessing the impact of such changes on wildlife over the long-term has been difficult to study due to the lack of historical records.
The newly published findings were based on information from the Land-Use Harmonization (LUH) data set, produced by researchers at the University of Maryland. The data set provides historical reconstructions of various types of land uses—including forests, crops, pastures and other types—that reach back to the ninth century.
“We used present-day locations where we know there are elephants, together with the corresponding environmental features based on the LUH data sets, to infer where similar habitats existed in the past,” said de Silva. “In order for us to build a more just and sustainable society, we have to understand the history of how we got here. This study is one step toward that understanding.”
The research team notes that the historical range of elephants is likely to have extended well beyond protected areas, which are of insufficient size to support elephant populations in Asia. They included lands under traditional systems of management that were altered within the past three centuries. The loss of these traditional practices, the authors suggest, may be a major reason behind the loss of habitat.
Much more work, the authors argue, is needed to understand possible changes facing these habitats in the future. Considering the people—along with wildlife—at the frontiers of elephant-human conflict zones, the researchers caution that attempts at habitat restoration need to be guided under a reckoning of social and environmental justice for historically marginalized communities.
“Exploring the relationship between past land management practices and the distributions of elephant ecosystems would be a useful direction for future studies from the perspectives of both ecological and social policy,” they note in the report.
The full author list of the study includes: Shermin de Silva, Tiffany Wu, Philip Nyhus, Ashley Weaver, Alison Thieme, Josiah Johnson, Jamie Wadey, Alexander Mossbrucker, Thinh Vu, Thy Neang, Becky Shu Chen, Melissa Songer and Peter Leimgruber.
In Sri Lanka, a large Minneriya reservoir built by King Mahasen in the third century provides Asian elephants with a year-round water supply and floodplain vegetation for foraging.
The global space available for Asian elephant habitats has been in rapid decline since the 1700s.
CREDIT
Report coauthors
Asian elephants inhabit dry deciduous forests, seen here in Sri Lanka, as well as lush rainforests.
CREDIT
Shermin de Silva
JOURNAL
Scientific Reports
METHOD OF RESEARCH
Data/statistical analysis
SUBJECT OF RESEARCH
Animals
ARTICLE TITLE
Land‑use change is associated with multi‑century loss of elephant ecosystems in Asia
ARTICLE PUBLICATION DATE
27-Apr-2023
COI STATEMENT
Shermin de Silva is the founder and president of Trunks & Leaves, a non-profit organization that supports research and public awareness of Asian elephants.
Ecology: Over 64% of suitable elephant habitat lost across Asia since 1700
Habitats suitable for Asian elephants (Elephas maximus) across Asia have decreased by over 64% – equating to 3.3 million square kilometres of land – since the year 1700, estimates a study published in Scientific Reports. The authors suggest that habitat loss from 1700, after centuries of relative stability, coincides with the colonial-era use of land and subsequent agricultural intensification in South Asia.
Asian elephants live in a range of habitats including grasslands and rainforests, but with increasing human use of land and habitat loss, elephants can come into conflict with humans. To assess the historical distribution of elephant habitats and land-use change, data on elephants and environmental factors can be modelled to infer habitat suitability across an area and over time.
Shermin de Silva and colleagues estimated the change in the spread and fragmentation of Asian elephant ecosystems in 13 countries between the years 850 and 2015 and calculated the change in suitable habitat from 1700 to 2015. Habitats were categorised as suitable if they exceeded a threshold defined and modelled according to ecological criteria including the percent of primary forests and pastures, non-forested vegetation, cropping and irrigation patterns, wood harvest rates and urbanization, amongst other factors.
The authors compared an area within 100km of the current range of elephants in Asia and found that in 1700, 100% of the area could have been considered suitable habitat but by 2015 less than half was considered suitable (48.6%). They suggest that mainland China, India, Bangladesh, Thailand, Vietnam, and Sumatra have each lost more than half of their suitable elephant habitat range, with the greatest declines in China (around 94% of suitable habitat lost) and India (around 86% of suitable habitat lost). Estimates of land in Borneo suggest it has gained habitat that is suitable for elephants. The authors suggest that the decrease in suitable habitat for Asian elephants may drive potential conflict between elephants and people.
The authors conclude that it is important to consider the history of the landscape to understand the distribution of elephants in Asia and to help develop more sustainable land-use and conservation strategies to meet the needs of both elephants and people.
###
Article details
Land-use change is associated with multi-century loss of elephant ecosystems in Asia
DOI: 10.1038/s41598-023-30650-8
Corresponding Authors:
Shermin de Silva
Trunks and Leaves Inc., Pittsfield, USA
Email: Shermin@trunksnleaves.org
Please link to the article in online versions of your report (the URL will go live after the embargo ends): https://www.nature.com/articles/s41598-023-30650-8.
JOURNAL
Scientific Reports
