Singapore Flowering

Chemperai manillana (false olive, chemperai) is one of the first few species that flowered even before the end of the dry spell. This is a shrub or small trees commonly found in the understorey of forest. 

At about mid-March, visitors of the MacRitchie rainforests would have noticed its bright orange-red fruits along the trails, especially at the Chemperai Trail. The bright-red fruits should be attractive to birds, and we had observed bird feeding on the fruits.

It was said that its leaves and fruits can be eaten. I tasted the fruit, it had little flesh, and slightly bitter with a tinge of sweetness. Not recommended. >_<

The Dipterocarpus kunstleri trees have shed their flowers and all that remains on the trees now are the calyxes. 

Flowers were still adorning the tree two weeks ago.

The dry spell experienced in January and February 2014 has triggered mass (general) flowering in Singapore. This event has been reported on the news, e.g., here and here. However, the focus of those reports are mostly on flowering plants in the streetscapes and parks, which are mostly cultivated, exotic species. 

Flowering Tabebuia rosea, an exotic tree species in Singapore and Malaysia.

What is more exciting for us, students of botany, is the general flowering (GF) event in our lowland rainforest!!

Lowland rainforests in this part of the world (e.g. Peninsular Malaysia, Singapore, and Borneo) lack strong climatic seasonality. Hence, unlike the trees in seasonal forests which flower regularly or annually, many tree species in our lowland rainforest do not flower and fruit regularly. Some of the species only flower once every few years (supra-annual), and some have only been observed to flower during the GF period.

Irregular drought events In this region have now been identified to trigger GF. The prolonged dry spell of at least a month (or 40 mm of rainfall in 30 days) becomes a climatic cue for many tall tree species in the lowland rainforest to flower and fruit in the same period. The irregular drought is likely to occur every 6 to 7 years, coinciding with the natural El Niño Southern Oscillation (ENSO) cycle. The previous large general flowering event in Singapore was recorded in the year 2006.

During a GF event, one would expect many big forest trees to flower. This includes many species of the Dipterocarpaceae family (keruing family), which are dominant in our lowland primary rainforest. Other plant families that participate in GF include the Myrtaceae (nutmeg family), and Euphorbiaceae (rubber family). A list of such plant species can be found here. Not only do we see the flowering of supra-annual or GF-only species, plants that flower regularly are also expected to reach their reproductive maxima. 

Flowers of Dipterocarpus spp..

It has also been confirmed that different species of the Dipterocarpaceae family will flower sequentially. In Pasoh, Malaysia, it was observed that each species of Shorea flowered for about 20 days, and their flowering times were staggered. It has been hypothesized that sequential flowering allows for pollinators (e.g. bees) to not be satiated at any moment, thus allowing each tree species to take turn to be pollinated effectively. Shorea macroptera was the first to flower during this GF event in Pasoh, and this has already occurred in the general flowering event in Singapore!

Flowers of Shorea macroptera.

The flowering event is expected to last for another month, hence there is still time to enter the forest to look at the flowers. Some of the species flower profusely, and emit pleasant fragrances. Flowers of the big trees are harder to observe, but do look out for fallen flowers on the ground! What follows this is the mast fruiting event, which we will talk about next time.