Time to pick the fruits of propeller trees
Propeller trees, Dipterocarpus spp (Dipterocarpaceae), are important for the Southeast Asian forest ecosystems. Many species have a hard and durable timber, leaves for roof thatching or food packing, source of resin, excellent bark for epiphytic orchids and they are ectomycorrhizal hosts of many edible (and poisonous) mushrooms. What are the common tree species here in the Chiang Mai valley, and how do I get them?
A positive trend is that around Dokmai Garden, which develops at a tremendous speed, new land owners tend to save the native dipterocarps. The most common species in the lowlands, and in all of the province, is Dipterocarpus tuberculatus. Yesterday’s wind blew down a few fruits which I collected like a troll finding gold. The fruits are not available every year, and last time we planted many seedlings was in 2010, the worst drought in 50 years, so they all succumbed. This year we shall be prepared and even babysit (irrigate) if the drought is too severe. I love to eat mushrooms and I find this particular tree handsome, so I need to boost it in the garden. An established tree can stand droughts and fire, while seedlings are sensitive.
Another common lowland dipterocarp is Dipterocarpus obtusifolius, also growing naturally nearby Dokmai Garden. I collected a nice heap of seeds of this species too. The aim is to create an educational lowland monsoon forest.
Left: Dipterocarpus tuberculatus leaf and fruits. Note the leaf’s heart-shaped base and fanning veins. Right: Dipterocarpus obtusifolius leaf and fruits. Note the leaf’s blunt (obtuse) tip and base, and the veins being parallel to each other.
A close-up picture of the D. tuberculatus fruits. They have two prominent wings for wind dispersal, and three remnants of wings looking like mouse ears. Between these five wings, the fruits have five ridge-like ‘tubercles’. The wings are fused and completely wrap the seed, a nut.
Another common dipterocarp planted in the Chiang Mai valley is Dipterocarpus alatus, the tall tree you see along the old road between Chiang Mai and Lamphun. That species has fruits with ridges from top to bottom and such fruits should also be collected now. Many governmental forest nurseries provide D. alatus seedlings, but I have never seen the other two dipterocarps offered. Based on our experience here at Dokmai Garden I think that is due to the amazing growth speed of D. alatus, even when left without water. The timber of D. obtusifolius is considered inferior to that of the other two species, but for leaf litter designers its coppery and densely corrugated leaves are a delight.
At higher elevations there are other dipterocarp species, and in wetter habitats such as Borneo is the heart of Dipterocarpus biodiversity with 40 of the world’s ca 70 species. The name was coined by Karl Friedrich von Gärtner (1772-1850) in 1805. He was a German physician and botanist focused on plant reproduction and published ‘Dipterocarpus‘ in a supplement (Supplementum carpologiae) to his father Joseph Gärtner’s magnum opus De Fructibus et Seminibus Plantarum, first volume published in 1788.
Text & Photo: Eric Danell
(Precipitation report: thunder and clouds, a few drops of rain, but nothing measurable (i.e. over 0.5 mm) so keep watering demanding plants!).