The park encompasses the highest mountain in Thailand, Doi Inthanon, as well as several lesser summits. The doi (mountain) is largely a granite batholith intruding a southerly extension of the Shan Hills range and forming the divide between the Nam Mae Ping river to the east and the Nam Mae Chaem river to the west. Lower elevations in the most easterly part of the park are limestone formations and contain a number of caves.
Formerly known as Doi Angka, the mountain now bears (since 1899) a shortened version of the name of Chiang Mai's last sovereign, King Inthawichayanon. During his reign, he had, with great foresight, expressed his concern for the forests of the northern hill country as the watershed for all of central Thailand. The modern study of rain forest hydrology has borne out his early convictions and given substance to Thai folklore which describes this hill region as the home of the Phiphannam, the 'spirit who shares water'. Before the King died, he commanded that his remains be placed at the top of this mountain: his ashes at the summit stupa are visited by thousands of people each year.
The park covers an area of 48,240 ha. Its lowlands, below 800 m in elevation, are warm and very dry during the dry season, but the summit of Doi Inthanon at 2565 m has a climate more like Canada than Thailand. The temperature has been known to drop as low as -8 degrees centigrade and frosts are not unusual during the cool, dry season. January is the coldest month: an average nighttime temperature is 5.5 degrees centigrade. At any season, Doi Inthanon is a comfortable reprieve from the heat of the lowlands. At altitudes above 1000 m, rainfall exceeds 2500 mm, considerably more than at nearby Chiangmai. Even in the dry season, November to April, there is occasional rain or the summit may be shrouded in cloud for a part of the day; persistent mist is an important factor in the maintenance of moist forest there.
The various submontane forest formations at higher elevations are a unique asset of the park. They have dominant species belonging to temperate climate families rather than tropical. The summit area supports the only red rhododendron in Thailand (R. delavayi), which blooms from December through February. There are also two white-blossomed species abundant on Doi Inthanon, which are restricted to only a few other sites. Epiphytes, plants which live on tree trunks and branches but do not receive their moisture and nutrients from the host tree as do true parasitic plants are common. They rely upon the accumulation of dust particles and humus around their 'root' area and the moisture retained there, augmented by frequent bathing in cloud and mist. Epiphytic orchids are also abundant, along with lichens, lianas and ferns. At mid-elevations, 800-1500 m, two species of pine are present, Pinus merkusii mixed with dipterocarp in the lower range, and P. kesiya with oak and laurel on drier slopes in the upper range. The pines are thought to be a relic from a prehistoric cooler climatic period when flora from the Sino-Himalayan region migrated southward. At the mid-elevations of the park, much of the forest has been removed by the activities of swidden cultivators and the slopes converted to fire climax grasslands.
Formerly known as Mae Sa Botanic Garden, the QSBG was established in 1992 as the first botanical garden of the country under the Prime Minister's Office. In October 2002, it was transferred to the Ministry of Natural Resources and Environment. The QSBG is located 27 km NW of Chiang Mai at the edge of Doi Suthep - Pui National Park. It covers an area of 960 ha, with about 80% designated as a conservation zone. This mountainous area is drained by three major streams, the Nawai, Phunsi and Mae Sa Noi.
Biologists in the Technical and Research Department carry out major scientific activities related to biodiversity conservation. This Department is responsible for various activities concerning botanical research, conservation and education, and is now expanding to include entomology. There are three sections in the Department:
The Herbarium. This is the third largest herbarium in the country with its collection of more than 20,000 specimens, consisting of native and exotic species emphasising plants of Southeast Asia. The Sanga Sabhasri Library is also located within the Herbarium building.
The Natural Science Museum. The Museum was opened to the public on 10 April 1999. It is undergoing construction to develop permanent and temporary exhibitions that will explore the world of plants, insects and animals. The Darwin Initiative National Insect Depository will be housed in this Museum.
The Laboratory Centre. This centre is responsible for various activities concerning biodiversity conservation of plants and, now, insects. Botanical work includes in vitro conservation and molecular genetic studies of native orchids, seeds of wild species and extraction of essential oils. Curation of insect specimens collected under the Darwin Initiative is carried out in this centre.
Administrative Centre, Queen Sirikit Botanic Garden