O. Gy. Dely szerk.: Vertebrata Hungarica 23. (Budapest, 1989)
Cao, van Sung: On the problem of zoogeographical division of the rodent fauna of Vietnam (Mammalia, Rodentia) 57-66. o.
The territory of Vietnam occupies the eastern part of the Indo-Chinese peninsula and it extends for a distance of 1650 km from south to north, from 8° 30' to 23° 22' . Maximum width of the country from west to east is 650 km from longitude 102° 10' to 109° 21*. The whole area of Vietnam covers 329. 600 km 2 (VU 19 79). According to the characteristics of relief and the types of vegetation the area of Vietnam can be divided into 8 geographical regions: north-eastern, north-western, North and South Truong-son, lowlands of Red River, Thanh-Nghe-Tinh, South Trung-bô and the delta of the Mekong. One of Vietnam's most characteristic features is her mountainous terrain. In Vietnam the mountains form three main ranges: the ranges of the North-East, the north-western mountains and the range of Truong-son. From these ranges emerge very high peaks such as the Phan Si Pan, 3143 a. s.l., the second highest one Ngoc linh, 2598 m and from the last one Chii dàng sin, 240 5 m. Truong-son runs parallel to the sea shore along the border between Laos, Cambodia and Vietnam, eastward it extends to the seashore and forms very high mountain ridgesNgang, Hái Van, Cà and others). There are some highlands in Vietnam' s mountains, sometimes lying above 1000 m. Highlands of the north are Taphinh, Môc châu, those of the south are Pleiku, Lam vien and Diiinh, Vietnam possesses huge river-systems with a number of tributaries which flow mostly from the west to the east immediately into the sea. These river-systems act as natural barriers to animal migration. The second most characteristic feature of Vietnam is the very humid tropical climate of the country. This is revealed by the temperature and rainfall parameters. Annual rainfall varies between 900 and 3500 mm. Also very high are these values for the mountain zones. The annual mean temperature is in many places higher than 20 °C. In the southern part of Vietnam the daily as well as the yearly fluctuations of temperature are moderate. On the other side, in the northern parts of the country, the fluctuation of temperature is very high (in winter the temperature may sink to +4 - +8°C, whereas in summer it raises to +36 - +38°C). Another characteristic feature of Vietnam's climate is the monsoon. The summer monsoon is saturated with humidity and it blows from the south from April till October. This type of monsoon is streaming in two directions. The western current streaming through the western slopes of Truong-son is losing a part of its humidity and reaches our country as a hot and drying wind ("wind from Laos"), On the contrary the other current is streaming from Southeast Asia, is saturated with humidity and brings abundant rainfalls. The winter monsoon blows from the north with cold air which is poor in humidity, it causes from October till March in the whole country a cold, dry weather. The above-mentioned system of monsoons causes a significant divergence between the northern and southern part of Vietnam. In summarizing the above-reported data we have to mention that the northern and southern parts of Vietnam's territory are differing significantly from each other. Let us analyse the zoogeographical division of the rodent fauna of Vietnam. Until now we have not any uniformly accepted theory about the zoogeographical division of Vietnam. The first attempt was made by BOURRET (1942) who outlined a zoogeographical division of the country based on the analysis of gibbons' distribution. The authors following him suggested the scheme of Vietnam's zoogeographical division according to different groups of animals: fishes (MAI 1963, 1973), birds (VO 1971), mammals (DAO et al. 1970), rodents (CAO 1978; DAO 1978). On the basis of all of these groups Vietnam's territory could clearly be divided into two provinces: a northern and a southern one, the boundary between them runs along the ridge Hái Van ("Cloud"). Setting out from rodent material DAO (1978) divides the territory of Vietnam into two zoogeographical provinces: into a no: hern one - with three districts: north-eastern, northwestern and northAnnamese - and into a southern one - with two districts: southAnnamese and southern district. For our zoogeographical analyses the above-mentioned schemes have been adopted, with some modifications, namely the delta of Bac bô, is ranked under the north-eastern district, whereas south-Annam with the Highland Tay nguyen under South Truong-son. By this way zoogeographically Vietnam can be divided into five natural units: north-eastern, northwestern, North Truong-son, South Truong-son and Nam Bo.
