Elephants are ecotonal species where humans aren’t a threat

Elephants are considered to be well-adapted to the ecotone. They have been described as ‘edge species’ with a liking for the ecotone between forest and disturbed area, at least where fresh water is available.  Although their former use of a greater variety of habitats is acknowledged, they are still described by some as favoring ecotones with an "interdigitation of grass, low woody plants, and forest” over continuous forest, where they are thought to live at low densities. 

While this certainly appears to be the case in general, the exception may be where human poaching threat is high and elephants take refuge in forested areas where they appear to feel equally at home in high canopy forest as in a habitat mosaic. The ecology of savanna elephants in Afro-montane forest is little studied in E. Africa, and while some populations move between open and closed habitats, others are resident in closed forest year-round. So how does an ecotonal species successfully exploit undisturbed forest? The old networks of elephant trails, and their intersections, in forests may provide some good clues. 
Until we know more, generalizations should not be made when describing elephants' effects on sympatric species. Likely, the cascade effects that ensue a local extinction of elephants will be more detrimental to biodiversity than the community-level changes that take place after elephants have modified vegetation where they are compressed into small reserves. Linking local populations is key; here are two of the best papers on the subject: van Aarde & Jackson 2007 and Gillson and Lindsay 2003. 
For more on elephants' need for refugia see Graham et al. 2009.