1 Xishuangbanna Tropical Botanical Garden, Chinese Academy of SciencesTropical Asia: an overview (Part 2) Richard T Corlett Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences
2 The Vegetation of Tropical AsiaThe eastern half – tropical East Asia – was, until recently, almost entirely covered in forests. The western half – confusingly called ‘South Asia’! – includes the full range of tropical ecosystems, from tropical rainforest to desert. I will focus on the forested (and now half-deforested) east for the rest of this lecture.
3 This map shows the historicaldistribution of tropical rainforest in tropical Asia: mostly in Sundaland, but with large areas also in Indochina, and outliers in India and Sri Lanka.
4 Tropical rain forests = the tall, dense, evergreen forests in areas of the lowland tropics where it is hot and wet all year.
5 Tropical montane rain forestsIncreasing altitude Tropical lowland rain forests Tropical seasonal forests Extreme edaphic conditions Increasing seasonality Forests on extreme soil types
6 Tropical montane rain forestsIncreasing altitude Tropical lowland rain forests Tropical seasonal forests Extreme edaphic conditions Increasing seasonality Forests on extreme soil types
7 Tropical montane rain forestsIncreasing altitude Tropical lowland rain forests Tropical seasonal forests Extreme edaphic conditions Increasing seasonality Forests on extreme soil types
8 Tropical montane rain forestsIncreasing altitude Tropical lowland rain forests Tropical seasonal forests Extreme edaphic conditions Increasing seasonality Forests on extreme soil types
9 Patterns of diversity In general, the eastern half of the region supports the most species. Within Tropical East Asia, however, patterns of diversity vary between taxa. In Africa and the Neotropics (South and Central America), diversity in almost all taxa peaks in the equatorial region – the vast Congo and Amazon basins, respectively. In East Asia, however, there is more land in the north and the equatorial region consists of islands and a narrow peninsula.
10 Within the tropics, regional patterns of plant species richness are strongly correlated with the number of wet days per year (or, inversely, with dry season length). [Kreft & Jetz, 2007, PNAS]. As this map shows, northern Borneo (arrowed) is the richest areas in Asia and one of the richest in the world, despite being an island. Copyright ©2007 by the National Academy of Sciences
11 Lambir Lambir, in Sarawak, Borneo, has the most species-rich (known) rainforest in tropical Asia: a 52 hectare (= c. half a square kilometer) plot supports 1175 tree species, compared with 1166 species in the entire temperate forest of the northern hemisphere – Asia, Europe, and North America!
12 But animal species richness does not necessarily follow the same pattern. The best data is for birds: Bird species richness in East Asia in 100 X 100 km quadrats (Ding et al. 2006) – breeding birds only Note that Borneo is NOT the highest for birds.
13 But animal species richness does not necessarily follow the same pattern. The best data is for birds: Instead, the richest area for birds is on the northern margins of the tropics, in the topographically complex region where India, Myanmar (Burma) and China meet.
14 But animal species richness does not necessarily follow the same pattern. The best data is for birds: Topographic complexity may allow more bird species to coexist. Also there is far more land at this latitude. By why don’t the same arguments apply to tree diversity? Maximum tree diversity
15 What’s so special about Tropical Asia?It supports about 25% of global terrestrial biodiversity, with most of these species not occurring outside the region. But at the family level it has many similarities with Africa, to which it has been connected by land for > 20 million years. For example, Africa and Asia both have elephants, apes, Old World monkeys, civets, hornbills, and bulbuls, but share no species in these groups. A Malay civet (Konstans Wells)
16 Scandentia - treeshrewsMAMMALS Only in Asia: Hylobatidae – gibbons Tarsiidae – tarsiers Scandentia - treeshrews Dermoptera – colugos (‘flying lemurs’) Billy Hau Wikipedia: Paul J Morris Wikipedia: Lip Kee Yap
17 MAMMALS Tropical Asia also has an extremely high diversity of squirrels, with a dozen or more species living together at some sites: on the ground, in the trees, and, at night, gliding between trees. Wikipedia: Pratik Jain Ecology Asia 2012 Wikipedia: Rakesh Kumar Dogra
18 MAMMALS And also a very high diversity of carnivores – vertebrates that eat other vertebrates. A single forest may have species, including: 15-25 species of mammalian carnivores (including < 6 species of cats, < 6 species of civets, < 3 mongooses etc.), plus 20 or more species of snakes, species of diurnal birds of prey, and up to 8 owls. Wikipedia: Bjørn Christian Tørrissen Wikipedia: Mariluna
19 BIRDS Birds are better at crossing geographical barriers than mammals, so most bird families and genera in tropical Asia are shared with Africa and/or Australia-New Guinea. The Oriental Region has only three small endemic bird families (including the leafbirds), but several others, including the highly diverse babblers (Timaliidae), as well as the pheasants and flowerpeckers, have most of their diversity in this region. Orange-bellied leafbird, Samson So Scarlet-backed flowerpecker, Henry Lui Black-capped babbler, Jon Hornbuckle
20 HONEYBEES There is one species of honey bee (Apis mellifera) in Africa and Europe, and this has been introduced all over the world, but tropical Asia is notable for the high diversity of honeybees – at least 11 species, with up to 5 in any one area. Usually, there is at least one small (workers 7–10 mm long), medium (10–14 mm, like A. mellifera) and large (17–20 mm) species in each habitat. Only the medium-sized species nest in tree-holes and other cavities: the small and large ones nest in the open. A nest of the giant honeybee, Apis dorsata. The outer ‘wall’ of the nest consists of living bees.
21 Major unique feature botanically is the dominance of the large trees by Dipterocarpaceae. This is a pantropical family, but only in tropical rainforest in Asia and New Guinea and most diverse in Asia.
22 Lambir The 52-hectare plot at Lambir, in Sarawak, Borneo supports 88 species of dipterocarp trees, including most of the largest individual trees. The single genus Shorea accounts for 53 species. These trees are valuable timber (and the many species can be grouped into a few categories for sale), so logging is both more profitable and more damaging in these forests than in tropical rainforests in other parts of the world.
23 The dry deciduous forests in areas with a 4-7 month dry season are also dominated by dipterocarps, although in this case there are only 4-6 species, all with thick, fire-resistant bark.
24 Asian rainforests are also the only ones with members of the Fagaceae (oaks, chestnuts etc.) and they reach their highest diversity here.
25 Summary: Tropical Asia – the Oriental Region – is separated from the Palearctic Region to the north by climate, and from the Australian Region to the south-east by the history of land connections. It can be divided internally into a southeastern Sundaland subregion, a north-eastern Indochina subregion, and a western Indian subregion, which are progressively drier and more seasonal in that order. Sundaland is largely covered in tropical rainforest, Indochina in various seasonal forests, and India has everything from rainforest to desert.
26 Summary: Tropical lowland rainforest is confined to areas that are hot and wet all year. A variety of +/- deciduous seasonal forests grow in areas where rainfall and/or temperature vary seasonally. Forests also change with increasing altitude and there are distinctive forest types on extreme soil types. Patterns of diversity differ strikingly among trees and birds in tropical Asia, with tree diversity highest in northern Borneo and bird diversity highest in northern Indochina. We are not sure why! Tropical Asia supports around 25% of global terrestrial biodiversity, but shares most families with Africa and many with New Guinea.
27 Summary: Gibbons, tarsiers, treeshrews, colugos, and leafbirds are confined to tropical Asia, and babblers, pheasants, flowerpeckers, and honeybees are most diverse here. The dominance of the large tree layer by the family Dipterocarpaceae is the most distinctive botanical feature of the rainforests and some seasonal forests. The diversity of Fagaceae is also notable. Thank you!
28 Reading: My own book, published by Oxford University Press in 2009, is the only one that covers the entire eastern half of tropical Asia. Chapters 1-3 cover the material in this lecture, but in far more detail. I wrote a brief summary for the open-access journal Current Science: Corlett RT What’s so special about Asian tropical forests. Current Science 93 (11):