Distribution patterns of the subtropical evergreen broad-leaved forests of southwestern China , as compared with those of the eastern Chinese subtropical regions C

Distribution patterns of the subtropical evergreen broaD-leaveD forests of southwestern china, as compareD with those of the eastern chinese subtropical regions.— This paper analyzes the geographic distribution patterns of the subtropical evergreen broad-leaved forests of southwestern China, and compares with other subtropical regions in the east of China in terms of forest types, pertinent species, and spatial distribution along latitudinal, longitudinal and altitudinal gradients. In general, for both the western and the eastern subtropical regions, the evergreen broad-leaved forests are dominated by species of Castanopsis, Lithocarpus, Cyclobalanopsis (Fagaceae), Machilus, Cinnamomum (Lauraceae), Schima (Theaceae), Manglietia, and Michelia, (Magnoliaceae), while in southwestern China there are more diverse forest types including semi-humid, monsoon, mid-montane moist and humid evergreen broad-leaved forests, but only monsoon and humid forests in the east. The Yunnan area has more varied species of Lithocarpus or Cyclobalanopsis or Castanopsis as dominants than does eastern China, where the chief dominant genus is Castanopsis. The upper limits of the evergreen broad-leaved forests are mainly 2400–2800 m in western Yunnan and western Sichuan, much higher than in eastern China (600–1500, but 2500 m in Taiwan). Also discussed are the environmental effects on plant diversity of the evergreen broad-leaved forest ecosystems exemplified by Yunnan and Taiwan.

Primary EBLFs once covered most of the subtropical areas of East Asia, but are now greatly diminished as a result of human activities. A recent study found only 5% of China's total land area to be covered by natural EBLFs (Chen, 1995). In the subtropical regions of China, extensive secondary forests have recently been grown on land used for agriculture or firewood production from the 19th to the middle 20th century, but remnants of the natural EBLFs are still found in remote isolated areas, on steep slopes, in nearly inaccessible or protected areas in nature reserves, and around temples. China, especially Yunnan, is home to the most diversified subtropical EBLFs to be found in East Asia (Tang & Ohsawa, 2009;Tang, 2010;.
In this paper the aim is to present an overview of the distribution patterns of the subtropical EBLFs across SW China as compared with all the Chinese subtropical regions to the east.

clImAte of the subtRopIcAl eblfs
China's subtropical regions are bounded to the north by a line running between the Huai River and the Qinling Mountains (35º N), with a southern limit 摘要 中国西南部亚热带常绿阔叶林分布格局，并与中国东部亚热带常绿阔叶林之比较。-本文分析了中国西南部 亚热带常绿阔叶林类型，植物群落及优势物种在经度、纬度、海拔梯度上的分布格局，并且与中国亚热带东 部(此文把中国西南部以东的中国亚热带均称为中国东部)的常绿阔叶林进行了深入比较。西南部及东部亚 热带常绿阔叶林一般是以栲属、石栎属、青冈属(壳斗科)，润楠属、樟属 (樟科)，木荷属(茶科)， 木莲属、含笑属(木兰科)的物种为优势种。西南部有更多样的森林类型，含半湿润，季风，中山湿性和湿 润亚热带常绿阔叶林，而东部只有季风和湿润亚热带常绿阔叶林。位于西南部的云南比中国东部有更多样的 石栎属、青冈属及栲属优势物种，而东部的主要优势属只有栲属。在滇西和川西，常绿阔叶林分布的海拔上 限主要是在2400-2800 m， 比中国东部常绿阔叶林分布的海拔上限(600-1500 m，台湾例外在2500 m)高很 多。本文还以云南与台湾为例，阐述了西南部及东部常绿阔叶林生态系统中植物多样性在环境及植物演替梯 度上的分布格局。 关键词：优势种；环境梯度；森林类型；植物多样性；空间分布；演替。 cómo citar este artículo / citation Tang, C. Q. 2015 (Ohsawa, 1995). The mountains located between 20º and 30º(33º) N show a transitional zonation pattern; the lower two zones are comparable to the lower two of the tropical zonation (tropical lowland and tropical lower montane), and the upper two zones are comparable to those of the temperate zonation (temperate lower montane and temperate upper montane). The tropical upper montane zone is not found north of 20º-30º(33º) N, while the tropical lower montane zone reaches down to sea level and so becomes also the temperate lowland zone. Thus the zonation between 20º and 30º(33º) N includes tropical lowland, tropical lower montane/temperate lowland, temperate lower montane, and temperate upper montane zones (Ohsawa, 1990(Ohsawa, , 1995. approaching the Tropic of Cancer. Eastward the subtropics extend to the coastlands and the islands of the East China Sea, the South China Sea and Taiwan; the westward limit is the Chinese national border, extending from the eastern slope of the Tibetan Plateau to southern Yunnan. The subtropical zone thus spans 11-12º from north to south, 28º from east to west (Wu, 1980). China's subtropical region is divided into three different zones: (1) the southern subtropics (transitional tropics), extending from latitude 22º to 24º or 25º N; (2) the middle subtropics, which lie between 24º or 25º N and 31º or 32º N; and (3) the northern subtropics (transitional subtropics) which cover from 31º or 32º N to 34º or 35º N (Hou, 1983). SW China is located at subtropical latitudes often distinguished as north, middle, and south subtropical (Fig. 3). A small part of southernmost Yunnan falls into the tropical zone. According to altitude, climates in SW China include tropical, subtropical, temperate, alpine and frigid. The climate is dominated by the Asian monsoon system, including the southwestern monsoon (the summer monsoon of India), the East Asian summer monsoon, and the East Asian winter monsoon, with dry continental winds in winter and moist oceanic winds in summer (Fig. 4). In China, generally the oceanic monsoon season begins earlier and ends later in the south than in the north, giving the south a longer rainy season and milder winter winds (Guo & Werger, 2010). In general, Chinese regions east of ca. 103º E are strongly influenced by the East Asian monsoon, while the regions to the west are affected by the Indian monsoon. Song (2013) offers the general information on the climate of the EBLFs. The annual temperature difference between the warmest and coldest months is smaller in the west (10-14ºC) than in the east (14-27ºC). In Holdridge's life zone system (1947), bio-temperature (the sum of temperatures >0ºC, if mean monthly temperature >30ºC is calculated as 30ºC) ranges from 12 to 24ºC for the EBLF. In the subtropical EBLF region of China, the bio-temperature is 15-22ºC.  Kira (1945) has proposed a warmth index (WI) and a coldness index (CI) for vegetation zones in East Asia, as follows: WI (ºC) = Ʃ(t − 5) • months; CI (ºC) = Ʃ(5 − t′) • months; t is the mean monthly temperature ≥5ºC and t′ is the mean monthly temperature ≤5ºC. In Japan, a WI of 85-180ºC • months and a CI of −10-0ºC • months correspond to the EBLF distribution, and a CI of −10ºC is a decisive northern limit for the EBLF (Kira, 1945;Hattori & Nakanishi, 1985). In China, a WI of 125ºC and a CI of −5ºC determine the northern limit of the EBLF distribution; a WI of 135ºC, and a CI of −2ºC correspond to the northern limit of the EBLF zone (Song, 2013).
In China, the annual precipitation for the EBLF in the eastern region ranges from 1100 to 1700 mm, and is between 800-1000 mm in most areas of the western region (such as central and northern Yunnan and northwestern Guizhou). However, due to the complexity of the topography and varying elevations, the annual rainfall is ca. 1500-1800 mm in southern Yunnan, though it reaches 1500-2800 mm (but 3673 mm in Bapo, Dulongjiang) in some lo-calities of western Yunnan, but in deep river valleys and on lee slopes it is just ca. 600-800 mm. In the western region, 80-90% of the annual precipitation falls from May to October, and the dry season is much more pronounced from November to April as compared with the east. The mean annual potential evapotranspiration for the subtropical EBLF region is ca. 800-1200 mm, and it is greater in the west than in the east. The Sichuan Basin area has the lowest evapotranspiration (Gao et al., 2006). Li (1997) divided the EBLF of East Asia into four regions: the Japanese, eastern Chinese, western Chinese, and western Chinese sclerophyllous distribution regions. The evergreen sclerophyllous forest should be considered apart from the subtropical EBLF, because the morphology, physiognomy, and structure of their leaves are different. The subtropics from 33º to 35º N constitute a transitional zone from EBLFs to deciduous broad-leaved forests.  Zhu (2013) considered a line at ca. 22º 30′ N to be the northern biogeographic boundary of the tropical zone in southern China. The evergreen broadleaved forest of southernmost Yunnan is considered to be a tropical montane evergreen broad-leaved forest (Zhu, 2007;Zhu & Yan, 2009). The subtropical EBLFs exclude northern tropical rain forests, which are basically tropical in nature but with some obvious transitional characteristics from tropical to subtropical floras, and are found at low altitudes in southernmost Yunnan (e.g. Xishuangbanna in S Yunnan, Xilongshan and Daweishan in SE Yunnan, Nangunhe in SW Yunnan). But here I do include the tropical montane evergreen broad-leaved forest of S, SE and SW Yunnan so as to take into account the altitudinal transition from the tropical rain forest to the subtropical EBLF. Song (2013) asserted that the subtropical EBLF of China corresponds to the region from 23º to 33º N and from 98º to 123º E. In fact, within Yunnan the forest extends west to ca. 97º 32′ E (e.g. Dulongjiang), and within Tibet it extends to 95º E (e.g. Chayu and Motuo in Yarlung Zangbo River). The most eastern longitude is 122º E in Taiwan. In sum, 95º-122º E is the longitudinal range of the EBLF within China. The distribution range of EBLFs in China is proposed in Fig. 5. A detrended correspondence analysis (DCA) (Fig. 6) for the plots of natural mature EBLFs of SW China, including Yunnan, Guizhou and the Sichuan Basin, that have been free of major disturbance during the past 60 years, indicates that along Axis 2 from the low to the upper side with increasing moisture, four forest types are roughly distinguished: the semi-humid EBLF (SH), the monsoon EBLF (MS), the humid EBLF (HE) and the mid-montane moist EBLF (MM). Axis 1 may indicate a gradient of topography or soil properties.

types of the subtRopIcAl eblfs
In SW China, most significantly, four forest types are representative of the major subtropical EBLFs: (1) the semi-humid EBLF in Yunnan, western Sichuan, and western Guizhou.  (4) the humid EBLF in the Sichuan Basin (also including Chongqing) and eastern Guizhou, having no distinctive dry season throughout the year. The humid EBLF differs from the mid-montane moist EBLF in lacking rich epiphytes and lianas on tree trunks and branches. The humid EBLF in the Sichuan Basin and eastern Guizhou is considered as the same type as the typical humid EBLF of eastern China.
The montane mossy dwarf forest as classified by former researchers (e.g. Wu, 1980;Wu et al., 1987;Shi & Zhu, 2009), dominated by species of Rhododendron L. along with some dwarf trees of the Fagaceae, Vacciniaceae, Rosaceae, Aceraceae, grows in special topo-habitats such as near mountaintops. This is not considered a type of the subtropical EBLF in this paper.

effects of envIRonmentAl fActoRs on plAnt dIveRsIty pAtteRns In the subtRopIcAl eblfs
As an evidence of environmental effects on species diversity of the EBLF ecosystems,  provided species diversity models comparing the EBLF ecosystems of Yunnan and Taiwan (Fig. 11A,  B). In Yunnan, the monsoon EBLF in the mesic-humid sites tends to have higher species richness and diversity (Fig. 11A). Along the altitudinal gradients in Taiwan, higher diversity is found in the Machilus-Castanopsis zone at the middle altitudes (500-1500 m) and in the lower Cyclobalanopsis zone at the midhigh altitude (1500-2000 m) (Fig. 11B) (see Fig. 9 for the altitudinal distribution of dominant evergreen broad-leaved tree communities in Taiwan). Species diversity, as influenced by temperature and precipitation, varies with altitude. Thus, altitude in the EBLFs of Taiwan may be a proxy for temperature, because the annual rainfall is abundant (1800-3000 mm) throughout the EBLF zone. In short, site moisture is the best predictor of species composition and diversity in the EBLFs of Yunnan, while temperature along altitudes plays a decisive role in Taiwan. For forest ecosystems, various temporal trends in diversity have been observed during succession, including increases, decreases, and one or more peaks with passing time (e.g. Auclair & Goff, 1971;Peet, 1978;Halpern & Spies, 1995;Turner et al., 1997). Relationships between diversity and succession are complex and should be seen as system-specific. Secondary forests under varying degrees of human disturbance, such as coppice woods or those growing on abandoned farmland, exhibit a range of stages of plant succession in the EBLF zones of both the Yunnan and Taiwan areas. The peak in diversity in the stands at the middle successional stage of each study site in Yunnan and Taiwan (Fig. 11A, B) reflects the persistence of species with varying attributes, including fast growth, slow growth, light demands, limited or greater shade-tolerance, contributing to significantly higher species diversities as compared with the early successional stage. In general, as a forest develops, diversity in the late stage tends to decrease with the disappearance of short-lived light-demanding pioneer species (e.g. Pinus, Alnus Mill., Populus L., Carpinus L., Acacia Mill., Mallotus Lour., and Diospyros L.); however, in both Yunnan and Taiwan the differences in species diversity between the middle and late successional stages are not significant, which reflects the recruitment of shade-tolerant evergreen trees (e.g. Cyclobalanopsis, Castanopsis, Machilus, Ficus L., Manglietia, and Michelia) into the overstory.
This brief comparison clearly shows the effects of moisture, altitude, and disturbance/succession on plant species diversity patterns in the two EBLF ecosystems of Yunnan and Taiwan.