Its incredible biodiversity in plant life is due to a combination of several unique factors: its setting in one of the richest plant regions of the world (the tropical biogeographical region known as western Malesia which comprises the island of Sumatra, the Malay Peninsula, and the island of Borneo), the fact that the mountain covers a wide climatic range from near sea level to freezing ground conditions near the summit, the jagged terrain and diversity of rocks and soils, the high levels of rainfall (averaging about 2700 mm a year at park HQ), and the climatic instability caused by periods of glaciation and catastrophic droughts which result in evolution and speciation.