Patterns of variation among forests of tropical Asian mountains, with some explanatory hypotheses

Figures & data

Table 1. The global characteristics of forest zones by elevation in the equatorial and oceanic tropics, as observed in Asia (after Whitmore 1984; Ashton 2014).

	Lowland forest	Lower montane forest	Upper montane forest	Subalpine thicket and shrubland
Maximum canopy height	25–70 m	15–35 m	1.5–6 (-20 in N.G.) m	1–5 m
Emergent trees	Present to 70 m, or absent	Mostly absent, <50 m	Rare, <20 m	Rare, <5 m
Pinnate leaves	Frequent	Less frequent, a few species common	Uncommon	Absent
Dominant leaf size	Mesophyll or notophyll	Notophyll (microphyll)	Microphyll	Microphyll and smaller, cupped, shiny
Buttresses	Usually frequent, large	Uncommon, small	Absent	Absent
Cauliflory	Frequent	Uncommon	Absent	Absent
Big woody vines	Uncommon to abundant	Rare to common	Absent	Absent
Bole climbers	Locally common	Locally common	Rare	Absent
Vascular epiphytes	Usually uncommon	Abundant, species-rich, arboreal	Abundant, less species-rich, descending to ground	Few
Non-vascular epiphytes	Local, species-poor	Frequent, increasing with elevation, species- rich	Abundant in equatorial regions and coastal, less so in seasonal forests, less species-rich, especially where seasonal	Sparse

Figure 1. The five immigration tracks of the Tropical Asian flowering plant flora, numbered in large font size: 1, tropical, from the late Cretaceous/Paleocene from North America and Europe; 2, tropical, from the late Cretaceous into Indian Gondwana, and from thence to the Far East from the late Eocene; 3, warm temperate, at first from North America via Europe, but mostly probably from the lower Miocene and East Asia; 4, initially warm temperate, from the lower Miocene, Australasia; 5, tropical arid, from the mid-Miocene, Africa through the middle East. Tracks 2, 3 and 4 make the major contributions to the mountain flora. Place names that are referred to in the text are numbered by in small font size individual localities with black numbering and indicated with a dot, wider areas with blue numbering:

1, Thar Desert; 2, Mt. Abu; 3, Arravalli Range; 4, Western Ghats; 5, Mahableshwar Plateau; 6, Goa; 7, Mt. Nilgiries; 8, Deccan Plateau; 9, Mt. Pachmarhi; 10, Eastern Ghats; 11, Sri Lanka; 12, Mt. Knuckles; 13, Adam’s Peak; 14, Horton Plains; 15, Bengal Bay; 16, Andaman Islands; 17, Himalayas; 18, Ganges Valley; 19, Nepal; 20, Mt. Similipal; 21, Mt. Parasnath; 22, Tibet; 23, Bhutan; 24, Khasi Hills; 25, Meghalaya; 26, Mt. Victoria; 27, Chin Hills; 28, Sandoway; 29, Burma (Myanmar); 30, Indo-Burma; 31, Mt. Doi Chang Dao; 32, Mt. Doi Inthanon; 33, Yunnan; 34, Mt. Kao Yai; 35, Thailand; 36, Mt. Kamchay; 37, Cambodia; 38, Laos; 39, Annamite Range; 40, Vietnam; 41, Mt. Phu Bea; 41, Western Ghats; 42, Hainan; 43, Guangxi; 44, Qin Ling Shan; 45, Honshu; 46, Kangar; 47, Pattani; 48, Peninsular Malaysia; 49, Sumatra; 50, Sundalands; 51, Mt. Santubong; 52, Borneo; 53, Brunei; 54, Mt. Kinabalu; 55, Mt. Silam; 56, Luzon; 57, Philippines; 58, Makassar Strait; 59, Sulawesi; 60, Bali; 61, Lesser Sunda Islands; 62, Timor; 63, New Guinea; 64, Mt. Trikora; 65, Mt. Hagen; 66, Mt. Wilhelm; 67, Mt. Kerigomna; 68, Australasia; 69, Louisiades Archipelago.

Table 2. Summary of elevational zonal changes in climate, soils and forests in the humid tropics. The motor to habitat change with elevation is temperature decline, ca. 6.5 K km^-1 ascent on tropical mountains, and its interaction with atmospheric humidity to produce cloud (fog) and consequent precipitation. These factors of climate, with substrate, determine soil formation in interaction with forest cover and litter production. Absence or presence of cloud/fog seasonality results in differing soil and forest zonation, indicated in the paired columns. Temperatures are mean monthly values.

Elevation(m)	Climate						Soil				Forest formation
	Summertemperature (°C)	Perhumid/summer rain		Winter temperature (°C)	Dry months >2		Perhumid/summer rain		Dry months >2		Perhumid/summer rain		Dry months >2
4000	0	Annual frost		0	Winter cloud base		Skeletal soils, mires				Treeline		Treeline
		Occasional frost									Gradient to subalpine thicket
3000	8	Intermittent cloud Daily diurnal canopy fog			Summer air frost Winter annual frost		Ferric podsols		Increasingly acidic humicmulls				Warm temperate frost (>20 N); gradual transition to upper montane species/structure (New Guinea rainshadow)
2000- 1500	14	Isolation and elevation bring increasing diurnal canopy fog	Fog free Diurnal shadow	Lowest valley frost	Increasing seasonal diurnal canopyfog	Fog free Diurnal shadow	Humic podsols(siliceoussubstrates)	Humic mulls	Humic mulls	Humic ultisols/latosols	Upper montane forest	Lower montane forest	Lowermontane forest	Deciduous forest/pine savanna
1200- 1000	21	Daily inland cloud base			Summer cloud base			Ecotone		Ecotone		Ecotone		Ecotone
750 0	27			15			Tropical lowland udult/humult ultisols/podsols		Tropical lowland udult/humult ultisols/latosols		Lowland forest		Lowland forest

Whitmore TC. 1984. Tropical rain forests of the far east. 2nd ed. Oxford: Clarendon Press.

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Ashton PS. 2014. On the Forests of tropical Asia, lest the memory fade. Royal Botanic Gardens, Kew and Arnold Arboretum, Harvard University.

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