Included here is most of Szechwan (west of the Szechwan Basin) including the Szechwan Alps and the Yunnan Plateau together with mountains bordering northeastern Burma, northern Laos and northwest Tonkin. The forests have been divided into seasonal rain and seasonal moist forests.

Sikang-Yunnan Tropical Seasonal Rainforest

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. 


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