Humans have essentially engineered the problem by relocating, either directly or indirectly, pachyderm populations. According to the survey, described in the journal Ecology Letters, elephants prefer toppling trees in the 16- to 30-foot range, with annual losses of up to 20 percent in these height classes.
A strong elephant can topple over a tree in mere seconds. If you jump to around the 1:45 mark in the video below, you can see a mother elephant knocking over a tree so that her calves can enjoy the leaves and fruit.
The discovery presens a tough issue: Trees provide food, shelter, shade and more for numerous other species. But elephants are just doing what comes naturally to survive. "Save an Elephant, Kill a Tree" isn't exactly a catchy conservation phrase.
The losses were documented in the South African savannas of Kruger National Park. In the future, the data could help to inform conservationists about the needs and impacts of elephants.
High-tech lasers swept across the park, providing detailed 3-D images. The lasers were mounted on the fixed-wing Carnegie Airborne Observatory.
"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," lead author Greg Asner of Carnegie's Department of Global Ecology was quoted as saying in a press release.
"Our maps show that elephants clearly toppled medium-sized trees," he added, "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."
For years, scientists at the park have wondered what was happening to all of the trees and vegetation. They knew elephants were big eaters, of course, but thought herbivores, like rabbits, or fires might be doing in much of the greenery.
Some areas at the park have been closed off to all herbivores larger than a rabbit. Others permitted herbivores other than elephants to enter.
Because of this separation, the scientists were able to compare and contrast what happens to trees with or without elephants around.
The researchers discovered that nearly 9 percent of all studied tree species decreased in height in two years. The documented 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.
"This collaboration between external scientists and conservation managers has led to exciting and ground-breaking new insights to long-standing questions and challenges," Danie Pienaar, head of scientific services of South African National Parks, said.
"Knowing where increasing elephant impacts occur in sensitive landscapes allows park managers to take appropriate and focused action," Pienaar added. "These questions have been difficult to assess with conventional ground-based field approaches over large scales such as those in Kruger National Park."