Sikang-Yunnan Vegetation - Terrestrial Biozones

Plant Formations in the Sikang-Yunnan BioProvince 

Copyright © 2010 Peter Martin Rhind 

Peter Martin Rhind 

Sikang-Yunnan Tropical Seasonal Rain Forest 

Concentrated on the lower slopes and in the wet valleys these forests occur on both 

laterite and limestone soils with only minor changes in floristic composition. They usually 

have three or four indistinct tree layers with a top canopy of emergent trees reaching 

heights of up to 45 m. Below this the main canopy layer reaches about 30 m and can have 

almost complete crown coverage and is rarely less than about 80%. The third layer (5-18 

m tall), usually has a crown coverage of less than 40%. Buttresses and cauliflory are 

common and both lianas and epiphytes are abundant. The suite of dominant trees vary 

according to changes in local conditions but usually include various combinations of the 

following: Alphonea monogyna, Pometia tomentosa, and the endemic taxa Celtis 

philippensis var. wightii (Ulmaceae) and Lasiococca comberi var. pseudoverticillata 

(Euphorbiaceae). Typical sub canopy species include Canarium pimela Cleidion 

spiciflorum, Debregeasia squamata, Diospyros hasselly, Ficus altissima, Glycosmis 

ferruginea, Pseudovaria indochinensis and a variety of endemic species like Aglaia 

testicularis, Amoora tetrapetala, Dysoxylum lenticellatum (Meliaceae), Aporosa 

yunnanensis (Phyllanthaceae), Beilschmeidia yunnanensis (Lauraceae), Bombax insignis 

(Bomacaceae), Cryptocarya acutifolia, Litsea dilleniaefolia (Lauraceae), Ehretia tsangii 

(Boraginaceae), Elaeocarpus austroyunnanensis (Elaeocarpaceae), Garcinia bracteata 

(Hypericaceae), Horsfieldia pandurifolia, Knema furfuracea (Myristicaeae), Mitrephora 

maingayi (Annonaceae), Murraya tetramera (Rutaceae), Sumbaviopsis albicans 

(Euphorbiaceae), Tapiscia yunnanensis (Staphyleaceae), Tetrameles nudiflora 

(Tetramelaceae), Walsura yunnanensis (Meliaceae) and the endemic palm Caryota urens 

(Arecaceae). Loeseneriella lenticellata and the endemic Ventilago calyculata var. 

trichoclada (Rhamnaceae) are two of the common lianas, and eiphytes are typified by 

Pothos chinensis and the endemic Rhaphidophora hongkongensis (Araceae). Shrubs are 

usually sparse on the ground but among the most common are Miliusa tenuistipitata, 

Sauropus macranthus and the endemic Psychotria siamica (Rubiaceae). The herb layer is 

not particularly well developed and mainly consists of seedlings and creeping lianas such 

as the endemic Derris caudatilinba (Fabaceae) and Loeseneriella yunnanensis 

(Celastraceae). 

Sikang-Yunnan Tropical Seasonal Moist Forest 

These forests are largely confined to middle and upper slopes from about 650 – 1300 m 

altitude on limestone as seen, for example, in Xishunangbanna in southern Yunnan. Two 

distinct tree layers are usually distinguished with the upper canopy reaching heights of 20- 

25 m. Buttresses and cauliflory are relatively scarce, but woody lianas and epiphytes are 

common. Many of the latter have small, thick leaves. However, these forests display a 

somewhat diverse physiognomy and floristic composition due to the great diversity of 

microhabitats. Additionally, the upper slope forests are largely evergreen whereas on the 

much dryer lower slopes they tend to be semi-evergreen. In the evergreen zone the 

dominant tree species are either Dracaena cochinchinensis and Osmanthus polyneurus or 

the two endemic taxa Cleistanthus sumatranus and Lasiococcus comberi var. 

pseudoverticillata (both of the Euphorbiaceae). Associated trees include Aglaia parviridus, 

Garruga floribunda var. gamblei, Mallotus paniculata, Salacia polysperma and several 

endemic taxa like Amoora calcicola (Meliaceae), Beilschmeidia yunnanensis (Lauraceae), 

Calona floribunda (Tiliaceae), Diospyros yunnanensis (Ebenaceae), Ficus orthoneura 

(Moraceae), Laportea urentissima (Urticaceae), Mitrephora thorellii (Annonaceae), 

Myrsine semiserrata (Myrsinaceae) and Stercula villosa (Malvaceae). The under storey

consists of many saplings and creeping lianas such as Hiptage benhalensis and the 

endemic Loeseneriella yunnanensis (Celastraceae), and many herbaceous elements 

particularly members of the family Urticaceae such as species of Elatostema and Pilea, 

and the endemic Procris crenata (Urticaceae). In the semi-evergreen zones the upper 

canopy is usually deciduous and typically dominated by endemic taxa like Bombax insignis 

(Bombacaceae), Calona floribunda (Tiliaceae), Garcinia bracteata (Hypericaceae) and 

Tetrameles nudiflora (Tetramelaceae), while the second layer is largely evergreen. Other 

associated trees include Eriolaena kwangsiensis, Erythrina lithosperma, Hymenodictyon 

excelsum, Kydia calycina, Lagerstroemia venusta, Radermachera microcalyx, Spondias 

pinnata and several endemic taxa such as Millettia tetraptera (Fabaceae) and Pistacia 

weinmannifolia (Anacardiaceae). The under storey consists of shrubs such as the endemic 

Colebrookea oppositifolia (Lamiaceae) and Murraya koenigii (Rutaceae), and creeping 

lianas like the endemic Amalocalyx yunnanensis (Apocynaceae), but epiphytes are 

infrequent. 

Sikang-Yunnan Montane Dwarf Forest 

Occurring on limestone hill and mountaintops of Xishuangbanna in southern Yunnan 

between 900-1600 m these stunted forests grow to no more than about 15 m in height. 

They usually have just one tree layer but may form both evergreen and semi-evergreen 

stands depending on moisture levels. The dominant or co-dominant trees include 

Dracaena cochichinensis and Ficus neriifolia in the semi-evergreen zones and the 

endemic Myrsine semiserrata (Myrsinaceae) and Pistacia weinmannifolia (Anacardiaceae) 

in the evergreen zones. Other characteristic tree species include the endemic 

Pterospermum proteus (Malvaceae). Epiphytes are very common with many orchids such 

as Bulbophyllum nigrescesns and Eria hainanensis, and a variety of bryophytes and 

lichens. Among the typical under storey species is the strange endemic Agapetes 

burmanica (Ericaceae) with its distinctive swollen, water storage roots. Less common 

species are Clematis kerrii, Fagopyrum tataricum, Kalanchoe laciniata and several 

endemics such as Bauhinia carcinophylla (Fabaceae), Peperomia heyneana (Piperaceae), 

Pilea platanifolia (Urticaceae) and Tetrastigma delavayi (Vitaceae). 

Sikang-Yunnan Montane Evergreen Oak Forest 

Forest dominated by the evergreen oak Quercus longispica typically occur below the Abies 

forest of Yunnan and range in altitude from about 2400 – 3200 m. The canopy is usually 

quite low (about 8 m) but very dense with crowns of tree closely touching. Associated trees 

may include Acer wardii, Cyclobalanus glauca, Magnolia globosa, Pasania leucostachya, 

Quercus griffithii, Q. serrata, Q. variabilis and Sloana forrestii. The trees are often crooked 

and festooned with beard lichens such as Usnea longissima. Other epiphytes are common 

especially the epiphytic fern Drynaria delavayi that adorns virtually every tree, and 

climbers such as Akebia trifoliate and Ampelopsis heterophylla may also be encountered. 

The rich shrub layer is often dominated by Pittosporum heterophyllum var. ledoides, but 

many other species like Euptelea franchetii, Lonicera koehneana, Prunus pilosiuscula, 

Ribes tenue and Stachyurus chinensis occur. Despite the fact that the forest floors are 

often covered in a thick layer of fallen leaves the ground layer flora is very rich. Other 

endemic taxa associated with these forests include Cercis yunnanensis (Fabaceae), 

Machilus yunnanensis var. duclouxiana (Lauraceae) and Michelia yunnanensis 

(Magnoliaceae). 

Sikang-Yunnan Montane Coniferous Forest 

Montane forests dominated by conifers can be found in eastern Sikang and northwestern 

Yunnan. In the latter they are chiefly dominated by the endemic Abies delavayi (Pinaceae), 

whereas in Sikang Abies squamata and the endemic Picea likiangensis (Pinaceae) usually 

Copyright © 2010 Peter Martin Rhind

dominate. In other respects they are similar and among the less common conifers are 

various endemic species such as Abies forrestii (Pinaceae), Pinus yunnanensis 

(Pinaceae) and Tsuga yunnanensis (Pinaceae). Of considerable geobotanical interest is 

the presence of the ancient relict conifers Metasequoia glyptostroboides (Cupressaceae) 

and Taiwania cryptomerioides (Cupressaceae). Originally Taiwania was thought to be 

confined to Taiwan, but relict stands were discovered along the sheltered sides of valleys 

above 2000 m in the upper Chiu-Kiang, Nu-Kiang and other places. It is a forest giant 

towering above the forest canopy. Trees of Metasequoia (dawn redwood) are thought to 

be the remnants of an extensive ancient forest of giant conifers contemporaneous with the 

giant redwoods of the New World. Many of these often isolated conifer forests are in a 

completely natural state stocked with many old and mature trees. The tree are often 

covered in a thick layer of bryophytes and draped with beard lichen (Usnea longissima) 

giving the canopy a grayish appearance. At ground level the vegetation is varied and 

maybe completely absent in some of the denser stands where there are thick layers of 

fallen needles. In other places scattered shrubs of Cotoneaster, Rubus or Spiraea may be 

present or herbaceous species like Beesia calthaefolia, Bergenia purpuracens, Berneuzia 

thibetica, Cardamine macrophy, Circaeaster agrestis, Clintonia udensislla, Corydalis 

cheirifolia, Hemiphragma heterophyllum and Tiarella polyphylla. 

Copyright © 2010 Peter Martin Rhind 

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Copyright © 2010 Peter Martin Rhind

Sikang-Yunnan Vegetation - Terrestrial Biozones

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