Trees of the Dipterocarpaceae family include giants such as the great Dipterocarpus alatus ( Yang Na ยางนนา ) a tree not native to Chiang Mai, planted along the Chiang Mai Lamphun Rd.
A tree of similar appearance which once dominated the Ping River flood plain is D. turbinatus ( Yang Daeng ยางแดง ). Seed of Yang Daeng can be collected in May near the Queen Sirikit Botanical Garden, the Mok Fah Waterfall on the road to Pai and near the Cave at Chiang Dao.
The year 2011 was what is known as a mast year for these trees and also for the riverine Hopea odorata ( Takien ตะเคียน). In a mast year trees flower profusely together and produce vast amounts of seed. From one ancient Yang Na at Wat Chedi Luang 27,000 seeds were collected and around 10,000 seedlings produced.
This is not altogether good news however because it leads to over production and planting of an exotic species which, by excluding the planting of local trees, degrades the biodiversity of the region. Large quantities of Yang Na seedlings now stock nurseries as far afield as Nan province 350 km from where the seed was collected in Chiang Mai. Meanwhile areas which once had huge numbers of this tree spreading across the paddy fields from Tak to Ubon Ratchatani need large scale replanting of Yang Na.
Good news, however is that large numbers of Takien are available from government nurseries and if every village temple, school in the northern valleys were to plant a few, in time this would transform our landscapes. What we also may welcome is what appears to be a very poor year for Yang Na seed production while large amounts of seed of Shorea roxburghii are dropping from the many old trees in the grounds of Chiang Mai University.