Airborne technology helps manage elephants

August 06, 2012

Washington, D.C. - For years, scientists have debated how big a role elephants play in toppling trees in South African savannas. Tree loss is a natural process, but it is increasing in some regions, with cascading effects on the habitat for many other species. Using high resolution 3-D mapping, Carnegie scientists have for the first time quantitatively determined tree losses across savannas of Kruger National Park. They found that elephants are the primary agents--their browsing habits knock trees over at a rate averaging 6 times higher than in areas inaccessible to them. The research also found that elephants prefer toppling trees in the 16-to-30 foot (5-8 m) range, with annual losses of up to 20% in these height classes. The findings, published in Ecology Letters, bolster our understanding of elephant conservation needs and their impacts, and the results could help to improve savanna management practices.

"Previous field studies gave us important clues that elephants are a key driver of tree losses, but our airborne 3-D mapping approach was the only way to fully understand the impacts of elephants across a wide range of environmental conditions found in savannas," commented lead author Greg Asner of Carnegie's Department of Global Ecology. "Our maps show that elephants clearly toppled medium-sized trees, creating an "elephant trap" for the vegetation. These elephant-driven tree losses have a ripple effect across the ecosystem, including how much carbon is sequestered from the atmosphere."

The technology used for monitoring trees is Light Detection and Ranging (LiDAR), mounted on the fixed-wing Carnegie Airborne Observatory (CAO). It provides detailed 3-D images of the vegetation canopy at tree-level resolution using laser pulses that sweep across the African savanna. The CAO's lasers can detect even small changes in each tree's height, and its vast coverage is far superior to previous field-based and aerial photographic evaluations.

The scientists considered an array of environmental variables spread over four study landscapes within Kruger and in very large areas fenced off to prevent herbivore entry. For years, four of these exclosures have kept out all herbivores larger than a rabbit. Two other partial enclosures have permitted entry of herbivores other than elephants. The scientists identified and monitored 58,000 individual trees from the air, inside and outside of these exclosures and across the landscape in 2008 and again in 2010. They found that nearly 9% of the trees decreased in height in two years, and that the mapped changes in treefall were linked to different climate and terrain conditions. Most tree losses occurred in lowland areas with more moisture and on soils high in nutrients that harbor trees preferred by elephants for browsing. Critically, the partial exclosures definitively identified elephants, as opposed to other herbivores and fire, as the major agent of tree losses over the two-year period.

"These spatially explicit patterns of treefall highlight the challenges faced by conservation area managers in Africa, who must know where and how their decisions impact ecosystem health and biodiversity. They should rely on rigorous science to evaluate alternative scenarios and management options, and the CAO helps provide the necessary quantification," commented co-author Shaun Levick.

Danie Pienaar, head of scientific services of the South African National Parks remarked, "This collaboration between external scientists and conservation managers has led to exciting and ground-breaking new insights to long-standing questions and challenges. Knowing where increasing elephant impacts occur in sensitive landscapes allows park managers to take appropriate and focused action. These questions have been difficult to assess with conventional ground-based field approaches over large scales such as those in Kruger National Park."
-end-
The Carnegie Airborne Observatory and this study are made possible by the Andrew Mellon Foundation, Gordon and Betty Moore Foundation, W. M. Keck Foundation, Grantham Foundation for the Protection of the Environment, Mary Anne Nyburg Baker and G. Leonard Baker Jr., and William R. Hearst III.

The Department of Global Ecology was established in 2002 to help build the scientific foundations for a sustainable future. The department is located on the campus of Stanford University, but is an independent research organization funded by the Carnegie Institution. Its scientists conduct basic research on a wide range of large-scale environmental issues, including climate change, ocean acidification, biological invasions, and changes in biodiversity.

The Carnegie Institution for Science (CarnegieScience.edu) has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments throughout the U.S. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

Carnegie Institution for Science

Related Elephants Articles from Brightsurf:

How do giraffes and elephants alter the African Savanna landscape?
Through their foraging behavior across the diverse topography of the African savanna, megaherbivores may be unknowingly influencing the growth and survival of vegetation on valleys and plateaus, while preserving steep slopes as habitat refugia.

New findings highlight threatened status of forest elephants
Conservation efforts for the African forest elephant have been hindered by how little is known the large animal, according to researchers.

Researchers study elephants' unique interactions with their dead
Stories of unique and sentient interactions between elephants and their dead are a familiar part of the species' lore, but a comprehensive study of these interactions has been lacking -- until now.

A chronicle of giant straight-tusked elephants
About 800,000 years ago, the giant straight-tusked elephant Palaeoloxodon migrated out of Africa and became widespread across Europe and Asia.

Capturing elephants from the wild hinders their reproduction for over a decade
Capturing elephants to keep in captivity not only hinders their reproduction immediately, but also has a negative effect on their calves, according to new research.

Sisters improve chances of reproduction in Asian elephants
Researchers at the University of Turku found that the presence of a maternal sister was positively and significantly associated with annual female reproduction in a population of working elephants in Myanmar.

Future of elephants living in captivity hangs in the balance
Scientists at the University of Sheffield and University of Turku are looking at ways to boost captive populations of Asian elephants without relying on taking them from the wild.

Wildlife tourism may negatively affect African elephants' behavior
Increasing numbers of tourists are interested in observing wildlife such as African elephants, and income generated from tourism potentially aids in the protection of animals and their habitats.

Sex differences in personality traits in Asian elephants
Scientists from the University of Turku, Finland, have found that male and female Asian elephants differ in their personality.

New welfare tool to help improve the lives of elephants in human care
Zoos and safari parks in the UK are using a special new tool to help them more successfully monitor the wellbeing of elephants in their care, thanks to a study led by The University of Nottingham.

Read More: Elephants News and Elephants Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.