The lower altitudes are covered with dry mixed deciduous forest , while hill evergreen forest grows above 800 m , as well as in shady and narrow zones in the valleys . Extensive wildfires are deliberately set off by local farmers in the mountain forests of the Khun Tan Range every year between February and April towards the end of the dry season . One of the purposes of this somewhat radical activity is to trigger the growth of the '' Astraeus odoratus '' mushroom ( ; '' het pho '' ) that fetches a high price on the Thai market . Often speculators hire people to set forests on fire in order to claim land title deeds for the areas that have become " degraded forest " . Although the large trees are not too badly affected , the periodic fires negatively affect the wildlife of vast areas of the mountain chain . These yearly wildfires are the main cause of the intense air pollution in Northern Thailand and contribute to the floods in the country by completely denuding the undergrowth of the woods . The dry forest soil leads to lower water intake for the trees to extract when the rains arrive
floods in the country
2011 Thailand floods
Khun Tan Range