One of India's most rare and treasured aromatic trees is the sandalwood . The bark of the cinchona tree contains quinine, a substance used to combat malaria. Malaria is a tropical disease carried by mosquitoes. In northern India, grow a wide variety of broadleaf trees, such as alder, birch, laurel, and maple, and conifers. The area is also known for its rhododendrons, bamboo, and dwarf willow. Juniper, silver birch, and silver fir are abundant in the uppermost, alpine environment of the western Himalaya. Further down the mountain slopes grow forests of spruce, silver fir, and deodar (East Indian cedar).