Complex sentence: Diablo has been preserved in the years since Bowerman's study was completed, as well as areas where other buckwheat records were established however the eastern areas of the plant's range are threatened by development pressure.
Split into simpler sentences: Diablo has been preserved in the years since Bowerman's study was completed, as well as areas where other buckwheat records were established. However, the eastern areas of the plant's range are threatened by development pressure.