台灣植物誌 第二版 Flora of Taiwan, 2nd edition Vol. 1
rate in this region is consistently lower than rainfall except in June and July. In contrast, the annual rainfall in the southwest amounts only to 1687-1810 mm, and only 11-12% of this amount falls from September to April of the following year. With a high rate of evaporation which often far exceeds the rainfall available during the same period, this region is subject to a winter drought. The Penghu Islands, west of the Western Coastal Plain of Taiwan, quite expectably, receive the least annual rainfall (977 mm) recorded in the Taiwan region.
The duration of sunlight in the various areas of Taiwan are similar to amounts of rainfall. Northern and northeastern Taiwan receive only 1403 and 1542 hours of annual sunshine respectively, making them the cloudiest area on the island. In contrast, western Taiwan and Hengchun in the far south are the sunniest places; they receive 2424 and 2469 hours of annual sunshine respectively. The annual means of relative humidity in various parts of the island are uniformly above 77%, with the highest being 85% at Ilan in the northeast and the lowest being 78% at Hengchun in the south. In the mountains, the highest humidity is found in the middle-elevation cloud zone; the annual mean at Alishan is 89%. Humidity begins to drop from 2500 m upward; it averages only 78% at Yushan.
On the basis of the conditions described above, various schemes of climatic subdivision have been proposed for Taiwan. Chen C-H (1957) had eight climatic regions in Taiwan according to Thornthwaite's system: northeastern Taiwan, northern Taiwan, southwestern Taiwan, western coast, southern Taiwan, eastern Taiwan, central mountains, and Penghu Islands. Su H-J (1985), based on annual precipitation and the ratio of winter precipitation to annual precipitation, recognized seven climatic regions: northeastern Taiwan, northwestern Taiwan, western-central Taiwan, southwestern Taiwan, southeastern Taiwan, eastern Taiwan, and Lanyu.
The soils of Taiwan were classified by Sheh & Wang (1991) into 15 types; among them lithosols, podozolic soils, colluvial soils, and alluvial soils are the major types. [The soil map of Taiwan published by Sheh & Wang (1991) was simplified as Figure 3 of this introductory series, on page 18-C of this book.]
Podzolic soils occur mainly on crests of ridges and spurs in the Backbone Range and Hsueshan Range. The soils are extremely acid, with pH values between 3.5-5.0 in water. In the cloud zone, a bleached white layer underlain by a thin placic horizon is often found.
In mountainous regions where the terrain is exceedingly broken and unstable, both lithosol and colluvial soil become much more extensive than do podozolic soils. They are derived from a broad array of parent materials and occur mainly on steep slopes and in gullies. Yellow soils cover the hilly regions below 1000 m. Commonly the soils are only weakly to moderately developed. Extensive cultivation and logging have, however, caused a serious loss of the surface layers of soils.
In the lowlands of northern and central Taiwan, riverine terraces of Pleistocene age are widespread. The surface soils there are highly-weathered to red and reddish-brown soils, which are strongly acidic in reaction. The coastal plains in the southwestern part of the island are mostly made up of alluvial soils of more recent origin. These soils show an intricate variability imposed by the inherently variable parent material. They are generally grayish to darkish in color, alkaline or neutral in reaction, and maintain a high mineral content. Along the coast, especially in the southwest, there are also areas of saline soils or alkaline soils; the high content of sodium chloride renders cultivation in those areas difficult or impossible.
NOTE Hsieh Chang-Fu is responsible for the sections of climate and soils as well as the preparation of Figures 1, 2 and 3; Shen Chung-Fu takes care of the section of geography and geology.
Introduction to the flora of Taiwan, 2:
geotectonic evolution, paleogeography, and the origin of the flora
1. GEOTECTONIC EVOLUTION OF THE TAIWAN ISLAND
I shall first make clear the geologic time scale and stratigraphy adopted in this paper in the beginning of this section. The Neogene geochronology used is that of Berggren et al. (1985), that is, the three concerned boundaries that segregate Oligocene, Miocene, Pliocene, and Pleistocene, respectively, are placed at 23.7 Ma, 5.3 Ma, and 1.67 Ma. The three subdivisions within the Pleistocene are delimited by 0.73 Ma and 0.13 Ma. Huang T-Y's (in Ho C-S, 1994; new tables 1-3, no paging) Neogene- Pleistocene biochronostratigraphy of Taiwan is followed.
It is now widely believed by geologists that the extensive region incorporating the southeastern coastal provinces of China (Zhejiang, Fujian, Guangdong, and Hainan) as well as the continental shelf of East China Sea had been a section of the Andestype continental margin along the eastern edge of China by the Late Cretaceous. During the Late Cretaceous-Eocene time this