Sri Lankan Forest Monks' Tradition claims a long history. As the oldest Theravada Buddhist country in the world, several forest traditions and lineages had been existed, disappeared and re-emerged circularly in Sri Lanka. The current forest traditions and lineages in Sri Lanka have been influenced by the Thai and Burmese traditions which descend from the ancient jambudeepa (Indian) and Seehaladeepa (Sri Lankan) traditions.
After the era of great Indian Emperor Asoka, India lost her place as the Theravada Buddhist center of the world. It is said that emperor Asoka and his advisor monks predicted this would happen and organized a Theravada Buddhist Mission to nine countries in Asia. As a result of this mission, the great arahant Mahinda who was the son of emperor Asoka was sent to Sri Lanka in order to establish Buddha Sasana (message of the Lord Buddha) with a group consists with six arahants called Ittiya, Uttiya, Sambala, Bhaddasala, Novice Sumana (Sumana Samanera) and anagami layman Bhanduka (Bhanduka Upasaka).
The King Devanampiya Tissa who was the king of Sri Lanka at that period met this group and accepted Buddhism and declare Buddhism as the state religion of Sri Lanka. The vice king Arittha who was the cousin of king Devanampiya Tissa was the first Buddhist monk of Sri Lanka who was called as arahant Upatissa.
One year Later the emperor Asoka decided to send another group to Sri Lanka in order to establish Buddhist Nuns' order (Bhikkhuni order) in Sri Lanka. The leader of this group was the daughter of the emperor Asoka who was the great arahant nun Sanghmitta. In addition to that eighteen groups of technical people which were dedicated for Buddhist cultural works were sent with arahant Sanghamitta in order to strengthen the established Buddhist Lineage in Sri Lanka.
Since the day of first establishment of Buddhist Lineage in Sri Lanka, it was managed to secure the Theravada tradition as the main Buddhist tradition until now. After the era of the great Indian emperor Asoka, Sri Lanka was the center of Theravada tradition in the world. The Pali Canon (Theravada Tipitaka) which was continued by memorizing was first written in Sri Lanka at the Aluvihara in Matale. Almost all the early commentaries of Dhamma (Attha Katha) were written in Sri Lanka. The popular commentary writer Bhiikku Buddhaghosa was able to translate Sri Lankan commentaries which had been written in Sinhala Language, in to Pali Language during the Anuradhapura era.
When other Theravada countries such as Siam (Thailand) and Ramanna (Part of Burma/Myanmar) lost their monks' lineage, Sri Lankan monks were sent to re-establish the Upasampada monks' lineage there during the period of Polonnaru Kingdom in Sri Lanka. Later in the 17th century BC, the Upasampada Lineage is disappeared in Sri Lanka due to the attacks and domination of Western intruders. The novice monk Weliwita Saranamkara was able to re-establish Upasampada in Sri Lanka which was brought from Siam (Thailand). During the 18th century Several monks were able to bring new Upasampada lineages again from Amarapura (a part of Burma/Myanmar) and Ramanna (a part of Burma/Myanmar).
In modern days three main Theravada Nikayas (Lineages) named as Siam Niakaya, Amarapura Nikaya, Ramanna Nikaya are dominant in Sri Lanka. Siyam Nikaya is the lineage brought from Siam, Amarapura Nikaya is the lineage brought from Amarapura and the Ramanna Nikaya is the lineage brought from Ramanna.
Early days the forest traditions were affiliated with the ancient monasteries such as Mihintale monastery, Ritigala monastery, Dimbulagala Monastery .. etc. Many ruins of ancient forest monasteries can be seen in the large forest areas of Anuradhapura, Polonnaruwa, Matale, Tissamaharama, Situlpawwa and Ruhuna. In that days Sri Lanka was the center of both Theravada village and forest traditions in the world. Currently the largest forest sect in Sri Lanka is the Sri Kalyani Yogashrama Samstha (Galduva Sect) of Ramanna Nikaya. In addition to that Vaturuvila Vanavasa sect of Siam Nikaya and several monasteries of all the three Nikayas continue to have forest monasteries.
Matara Nanarama Maha Thera who is considered to be the father of the Sri Lankan modern forest meditation tradition had developed a new meditation system which is balanced in both Vipassana and Samatha by researching through old Sri Lankan meditation methods and by learning Burmese Mahasi Vipassana Method. Some of his best student monks are listed below.
A student of late venerable Kadavedduve Jinavamsa Maha Thera who was the founder of the Sri Kalyani Yogashrama Samstha as well as Sayadaw U Acinna who was the founder of Pa Awk Tawya Monastery. He had an exceptional Mindfulness (Sati-memory and awareness) and control in the physical actions (Kaya Samvara) and day-to-day activities. It is said that he was a Bhodhisatva who was hoping to reach the Buddhahood in a future life.
A famous book author who published "The Magic of the Mind" and many other books. When he was residing in Mitirigala Nisssarana Vanaya, his teacher, the most venerable Matara Nanarama Maha Thera was the person to invite him to conduct the set of sermons on controversial topic 'Nibbana - The Mind Stilled'. 
A wellknown Vipassana meditation master who put emphasis on the value of Mindfulness (Sati) in meditation practice. He was influenced by Sri Lankan meditation method through Matara Nyanarama Maha Thera as well as by Burmese Mahasi method through Sayadaw U Pandita. He was a student of both of these great meditation masters. 
There are many forest monasteries scattered throughout Sri Lanka. Some of the main monasteries are listed below. 
Mitirigala Nissarana Vanaya is Located in the Western Province close to Colombo. First Abbot was late venerable Matara Nanarama Maha Thera. Affiliated to Kalyani Yogashrama Samstha. A branch monastery is established in Ritigala in North Central Province. Meditation method practiced here is related to both Sri Lankan tradition of most venerable Matara Nanarama Maha Thera and Burmese Mahasi Vipassana Method. Current abbot is the popular meditation master venerable Udairiyagama Dhammajiva Thera.
Na Uyana Aranya is situated in the North Western Province. This is a monastery currently following the Pa Auk method of meditation and related with Pa Auk Tawya Monastery in Burma (Myanmar). The late most venerable Nauyane Ariyadhamma Maha Thera was an abbot of Na Uyana Aranya.
A group of three wall kutis in the Laggala forest close to knuckles mountains in the north Central province. Independent solitary meditation practice is done by monks with daily alms round and fortnightly Patimokkha chanting. The famous ascetic monk Danish Nanadipa lived in the cottages of the Laggala forest for several decades. American Bhikkhu Kovida was another famous character in 1980s at Laggala.
A group of kutis (caves and huts) situated at Balangoda forest areas in which both local and foreign monks reside in.
There are plenty of single cottages and cave scattered all over the country which used by monks to dwell in. Some of them are Bundala Kut, Moragaha Ulpatha Kuti, Sangharaja Gallena ...etc.i