Forests cover 1854.7 ha of HNP. The forests are at the south edge of the Siberian Taiga. 66.2 % of the forests are birch and poplar forests, 23.6% of which being birch forests and 10.2% being poplars. The forests of the park grow in moist areas and at the backside of mountains, away from direct sunlight. A few individual Pine trees survive in the forest. Since the official protection of the Hustain Nuruu in 1993, no forest fire has happened.
Yet, the forests have degraded in the last year likely due to climate change. 70% of the Khushuut mountain forest has dried up. As a result of the degradation, forest insect pest has increased substantially. A random inspection of one tree showed that it was pest-infested. As a matter of fact, most of the trees suffer various degrees of infestations from harmful insects. For instance, bushes such as the cotoneaster and ribes diacantha have been damaged by moths. The Hustai Trust planted pine trees and broad-leaved trees that did not survive. Gobi elm trees grow in abundance along the mountain gullies. A few elm trees grow in the sand dunes of Moltsog Els. Shrubs and bushes grow in high density along the Tuul River but suffer from human activity as local people cut the bushes for everyday use.