sentences:  Most haze events have resulted from smoke from fires that occurred on peatlands in Sumatra and the Kalimantan region of Borneo island.Undisturbed humid tropical forests are considered to be very resistant to fire, experiencing rare fires only during extraordinary dry periods.A study published in 2005 concluded that there is no single dominant cause of fire in a particular site and there are wide differences in the causes of fires in different sites.