The vast Tsavo ecosystem features a huge diversity of habitats including mountains, rivers, forests, plains, lakes and wooded grassland. Once thickly wooded, Tsavo was transformed over the years into open bush and grassland by the great elephant herds which roamed endlessly across its red earth. These days, though the elephant numbers have been drastically reduced by a series of catastrophic droughts, they still leave a trail of destruction in their wake whilst even more damage is being done to the terrain by the off-road driving habits of the tour operators. Another hazard that park wardens must contend with is fire, especially during the long hot dry summers. Finally, due to the massive size and impenetrability of much of the park, tracking and monitoring the massive animal herds becomes virtually impossible and in the past this has resulted in disastrous poaching. In the 1960’s, for instance, Tsavo had the biggest population of black rhinos in Africa (between 6000 and 9000) but by 1981 they had been poached to barely 100 individuals. Today, most of the rhino have been moved to a sanctuary so that their numbers may gradually re-build and poaching is not tolerated, either by the Kenya Wildlife Service or the Kenyan government.