other soil. On top of that, mound soils have been found to contain more water than their surroundings, a clear advantage for plant growth in savannas. The high tree densities on termite mounds attract high densities of browsing herbivores, due to the high nutrient contents in foliage from trees growing on mounds, or perhaps due to the high quantities of food and shelter on mounds. Brazilian caatinga mounds The caatinga ecoregion in northeast Brazil has about 200 million termite mounds spread over an area the size of Great Britain. Some of the mounds are tall and wide, and they are spaced about apart. Underneath the mounds are networks of tunnels that required the excavation of of dirt. Scientists performed radioactive dating on 11 mounds. The youngest mound was 690 years old. The oldest was at least 3,820 years and possibly more than twice that. The mounds were built by Syntermes dirus termites, which are about half an inch long. Deforestation in the region helped to reveal the extent of the mounds to scientists. One scientist stated that the mounds apparently represent "the world's most extensive bio-engineering effort by a single insect species". See also Amitermes meridionalis, magnetic termite mounds of northern Australia Notes Termites Biogeomorphology