Many of Haiti's people, the poorest in the Americas, routinely cut down trees for fuel—either to burn "raw" or turn into charcoal.
As a result, the destruction of Haiti's natural forests is almost total, making the Caribbean country one of the most deforested in the world.
As Haiti's trees have disappeared, landslides have become a major concern, especially during the rainy season, and the destabilizing effects of an earthquake on soil only worsen the problem.
Natural Buffers Depleted in Haiti
Forest canopies serve as natural buffers against wind and rain, and the deep roots of trees help keep the granular soil from shifting.
"If you remove the trees, you have no buffer. So the water"—and soil—"tends to very quickly move downhill," said Mark Ashton, a professor at the Yale School of Forestry and Environmental Studies.
During an earthquake, hillside stability is further threatened as the ground is shaken.
"Anywhere you have strong motion and steep terrain, you have extremely high risk of slope failure and landslides, and they can be extremely large," said Colin Stark, a geophysicists at the Lamont-Doherty Earth Observatory in New York.
Earthquake Plus Rain Equals Trouble
Among the rare bright spots for Haiti this week are that its capital, Port-au-Prince, is on relatively flat land—making the landslide threat one less thing to worry about—and that the earthquake struck during the dry season.
"The worst kinds of landslides would be if you had an earthquake on rain-soaked soil," Yale's Ashton said.
The surrounding hilly regions may not be so lucky, he added. Even without landslides, post-earthquake pictures show collapsed houses sliding downhill.
"It's where foothills are that the worst landslides will occur," he said. "That's also where people tend to build their houses."