A preliminary mapped summary of holocene pollen data for northeast China

Quaternary Science Reviews, Vol. 17, pp. 669—688, 1998 ( 1998 Elsevier Science Ltd. Printed in Great Britain. All rights reserved. PII: S0277-3791(98)00017–1 0277—3791/98, $19.00

A PRELIMINARY MAPPED SUMMARY OF HOLOCENE POLLEN DATA FOR NORTHEAST CHINA GUOYU REN* and LANSHENG ZHANG*National Climate Center, No. 46 Baishiqiao Road, Beijing 100081, Peoples+ Republic of China -Beijing Normal University, Xinjiekouwai Street, Beijing, 100871, Peoples+ Republic of China Abstract—Maps of pollen data have long been unavailable for continental Asia despite their importance for paleoecological and paleoclimatic studies. Pollen data from 65 Holocene sites have allowed the mapping of eight pollen taxa and seven time slices for Northeast China. These pollen maps show significant vegetation changes during the last 10,000 years in the current forest regions of Northeast China, with the early Holocene characterized by widely distributed Betula trees, the mid-Holocene by the development of temperate deciduous forest mainly consisting of Quercus and ºlmus trees, and the late Holocene by the marked increase in the abundance of Pinus trees and the development of temperate mixed conifer and deciduous forest. An unexpected finding from the pollen mapping research is the south-to-north propagation of the mid-to-late-Holocene forest decline, which may have been caused by the persistent human activities and the gradually northward expansion of agriculture during the last 5000 years. It is thus evident that caution has to be taken when reconstructing the mid-to-late-Holocene climates from pollen records in some regions of Northeast China. The classic paleoclimate reconstruction for the southern part of the study area and possibly for North and Northwest China needs to be re-evaluated. ( Elsevier Science Ltd. All rights reserved

Here we present the preliminary research results for the Holocene pollen maps from northeast China and describe the methods used to produce contours whether isopolls or isochrones. The maps are then used to interpret the past vegetation. The underlying causes for the vegetation changes are discussed and a few conclusions are drawn.

INTRODUCTION Isopoll and isochrone maps have been widely used in the studies of late Quaternary paleoecology and paleoclimatology (Bernabo and Webb, 1977; Huntley and Birks, 1983; Huntley, 1990; Webb, 1985; Anderson et al., 1994; Ren, 1994). These maps illustrate the changing patterns of past vegetation (Bernabo and Webb, 1977), show how major ecotones have moved (Webb, 1983; Bernabo and Webb, 1977), and aid interpretations of past climates (Bartlein et al., 1984; Huntley, 1990; COHMAP Members, 1988). Furthermore, this acquired paleoecological and paleoclimatological knowledge aids researchers in testing and calibrating ecological and climatic models (Huntley, 1990; COHMAP Members, 1988; IGBP, 1994), in estimating past variations in the terrestrial carbon reserves (Prentice and Sarnthein, 1993), and in assessing effects of human activities on Holocene vegetation and environment (Ren, 1994). Time series of maps summarize late Quaternary pollen data for North America and Europe (Webb, 1983; Anderson and Brubaker, 1994; Huntley and Birks, 1983; Huntley, 1990). In the continental East Asia, however, pollen-mapping has not been done before 1994, largely due to the low density of sites with well-dated records. Ren (1994) made a first attempt to summarize the Holocene vegetation and climatic changes of Northeast China through mapping of the available fossil pollen data. The maps revealed some interesting patterns in vegetation change that are hard to identify from analysis of pollen data at single sites.

MODERN ENVIRONMENT OF THE STUDY AREA Physiography The study area extends from 37° to 59°N and 110 to 135°E and includes: Heilongjiang, Jilin Liaoning provinces, the Northern part of Hebei Province (including Beijing Municipality) and Inner Mongolia Autonomous Region east of 110°E (Figs 1 and 2). Major topographical features of the area are the extensive Northeast Plain surrounded by a series of mountains and hills. The Northeast China Plain consists of the Sanjiang Plain, Songnen Plain and Liaohe Plain, each of which is no more than 400 m above sea level. Two series of the northeast-southwest-trending mountains, the Daxingan Mts. and the Changbai Mts., run parallel along the western and eastern sides of the Songnen Plain and Liaohe Plain, while the Xiaoxingan Range with a northwest—southeast orientation lies to the north of the Songnen Plain. Both the Liaohe River and the Songhuajiang River originate in the Daxingan Mts., but the former flows eastward and then southward into the Bohai Sea, 669

670

Quaternary Science Reviews: Volume 17

and the latter runs up to the northeastern corner of the study area, where it combines with the other two large rivers, the Heilongjing River and the Wusulijiang River, forming a low-lying Sanjiang Plain character-

ized by widely scattered bogs and swamps, which can also be found in the other regions, though to a less extent. Climate Nearly every part of Northeast China is strongly influenced by temperate east Asian monsoon. Mean January temperatures range from !6°C in the south to !30°C in northern Daxingan Mts. The mean July temperatures have a much more homogeneous distribution, with the highest temperatures occurring in the south and the inland plains (Fig. 2). Annual precipitation decreases from more than 1000 mm in northern Hebei Province and southeastern Liaoning Province to less than 300 mm in some stations west of Daxingan Mts. (Fig. 3). Eighty to ninety percent of the total annual precipitation falls in the three summer months (June—August). Little snow or rain falls in winter and spring, and most regions are normally dry during the beginning stage of plant growth, a unique climatic phenomenon not characteristic of the same latitude areas of Europe and North America. The climates are most like those in Kansas, Minnesota, and Alberta in North America. Vegetation

FIG. 1. Physiographic regions of Northeast China.

Modern vegetation cover consists of the temperate types, including temperate moist forest, temperate forest steppe and temperate steppe (Fig. 4). Forest is found in mountain and hill regions, and steppe dominates the major fluvial plains and the Inner Mongolia Plateau west of the Daxingan Mts. A mixed plant belt called forest steppe between the forest of the Changbai Mts. and the steppe in the Songnen and Liaohe Plains.

FIG. 2. Mean January and July temperature (°C) in northeast China.

G. Ren and L. Zhang: Summary of Holocene Pollen Data

FIG. 3. Annual precipitation (mm) in northeast China.

671

Warm temperate deciduous forest grows in the south of the study area, where varied species of Quercus are common, and species of ºlmus, Juglans, ¹ilia, Carpinus, Corylus, Pinus and Betula are also important components of the forest. Between the coldtemperate conifer forest and the warm-temperate deciduous forest is temperate mixed conifer and deciduous forest, in which Pinus koraiensis is the dominant species. Other important species include Abies holophylla, Carpinus cordota, Acer mono, Quercus mongolica, ºlmus propinqua, Fraxinus mand shurica, Juglans mand shurica, ¹ilia amurensis and Betula platyphylla. As a representative type for Northeast China, the mixed forest covers the Changbai Mts., Xiaoxingan Range and the western pediment belts facing the Songnen Plain (Wu, 1980). Temperate steppe mainly develops on the central plains and the Inner Mongolia Plateau. Its floristic components mainly include the families of Gramineae, Chenopodiaceae, Compositae and Cyperaceae. One genus most commonly found in the steppe is Artemisia (Wu, 1980; Academic Sinica, 1985). The best developed forest steppe appears on the eastern fringe of the Songnen and Liaohe Plains, where trees and herbs grow alternately in the different topographical units. Of the trees, those corresponding to the deciduous components of the mixed forest to the east are usually the most common. At present, however, nearly the whole forest steppe belt and part of the steppe close to it are farmed (Fig. 4).

DATA AND METHODS Data

FIG. 4. Modern vegetation types in Northeast China. Revised from Wu 1980.

In the northern end of the Daxingan Mts., cold temperate forest appears, with ¸arix dahurica as its dominant species. This forest is a southwards extension of the Siberian conifer forest along the mountains.

Pollen data are mainly taken from the published research reports for single sites, with the exception of a few sites that came from unpublished dissertations. Considerable variation exists among the data in such aspects as the topographic position of the sampling sites, sediment type of the samples, sampling interval, radiocarbon-dating control, laboratory analysis procedure, and percentage calculation method. These problems have to be taken into consideration before confidence is given to the data. Topographic position: Pollen studies have been done in varied topographic positions. The sites for pollen mapping were selected for the regions to minimize differences in elevation. When the data in mountainous regions were used, only those from the basal belt of the vertical floristic distributions were chosen. The upper limit of the basal belt is approximately 900 m in the Changbai Mts., and it declines to about 600 m in the Xiaoxingan Range. Few sites were used from the other mountainous regions. Sediment type: Continuous lacustrine and peat sediments are most favorable for paleoecological studies that use fossil pollen data (Birks and Birks, 1980). Often the pollen deposition in peat can be more

672

Quaternary Science Reviews: Volume 17 TABLE 1. Fossil pollen sites selected from the published research reports for Northeast China

No.

Site

Location

1

Gushantun

2

Dadianzi

3

Sandaomiao

4

Harbaling

5

Liangsuixiang

Huinan, Jilin Huinan, Jilin Changbai Mts., Jilin Dunhua, Jilin Luohe, Jilin

6

Chuangye

7

Qindeli

8

Bielahonghe

9

Yangmuxiang

10

Qinghe

11

Shenjiadian

12

Jiajihe

13

Tanghongling

14

Qianjing

15 16

Harbin 853farmland

17

Laodaomiao

18

Hailangxiang

19

Gonghelai

20 21

Bolahu Maili

22

Seling

23

Zhoujiayoufang2

24

Daluoshu

25 26

Zhoujiayoufang1 Shaolanghe

27

Dongwenggen

28

Resuitang

29

Wudan

30

Wulanaodu

31

Dadianzi

32

Hongshengxiang

33

Kaitong

34

Xiaonan

Time range used (ka BP)

Radiocarbon Dates

Authors

0—10

4

Liu (1989)

0—10

4

0—10

3

0—10

3

Sun and Yuan (1990) Yuan and Sun (1990) Peat Group (1983) Wang and Xia (1990) Xia (1988)

0—10

5

Xia (1988)

0.8—6 0—2

3 1

Xia (1988) Xia (1988)

0—2

1

Xia (1988)

0— 4

3

Xia (1988)

0— 4

2

Yin (1984)

0.8—6

3

Yin (1984)

0.8—4 2 4—6

1 2 1

Yin (1984) Liu (1989) Ye et al. (1983)

2—4

1

0—4

1

Houqi, Inner Mongolia Qianqi, Jilin Houqi, Inner Mongolia Suangyang, Jilin Yushu, Jilin

0.8—6

3

Xiao and Sun (1987) Xiao and Sun (1987) Xia et al. (1993)

2—6 0—4

5 7

Xia (1993) Ren (1994)

0—0.8

1

Qiu et al. (1981)

4—10

1

Naiman, Inner Mongolia Yushu, Jilin Wudan, Inner Mongolia Tailai, Heilongjiang Chifeng, Inner Mongolia Chifeng, Inner Mongolia Chifeng, Inner Mongolia Aohan, Inner Mongolia Tailai, Heilongjiang Tongyu, Heilongjiang Changcun, Jilin

0, 2, 10

6

Wang and Xia (1988) Han (1992)

6 2

4 1

Sun et al. (1985) Wu et al. (1992)

0, 4

4

Ye et al. (1989)

6

2

Jiang (1992)

2

1

Jiang (1992)

8

2

Wu et al. (1992)

4

2

Kong et al. (1991)

0, 4, 6

2

Qiu et al. (1992)

0, 8

1

Qiu et al. (1992)

6

1

Wang and Xia, (1988)

Fuyuan, Heilongjiang Sanjiang, Heilongjiang Sanjiang, Heilongjiang Mishan, Heilongjiang Baoqin, Heilongjiang Huachuan, Heilongjiang Xiaoxingan, Heilongjiang Xiaoxingan, Heilongjiang Xiaoxingan, Heilongjiang Heilongjiang Baoqin, Heilongjiang Hailin, Heilongjiang Ningan, Heilongjiang

0.8—2

2

0, 8

2

673

G. Ren and L. Zhang: Summary of Holocene Pollen Data TABLE 1. (Continued) No.

Site

Location

35

Hetun

36

Mangshigou

37 38 39

Xingbarhudongqi Dalainuor Pulandian

40

Dagushan

41

Qianyang

42

Qianwatun

43

Paoya

44

Lianhuashan

45

Bachagou

46 47

Ewenkeqi Sanxianpu

48

Hailarbeishan

49

Yangerzhuang

50

Maohebei

Naiman, Inner Mongolia Naiman, Inner Mongolia Inner Mongolia Inner Mongolia Dalian, Liaoning Donggou, Liaoning Donggou, Liaoning Zhuanghe, Liaoning Fuxian, Liaoning Fuxian, Liaoning Changxing, Liaoning Inner Mongolia Changling, Jilin Hailar, Inner Mongolia Huanghua, Hebei Hebei

51 52

Baiyangdian Fenzhuang

53

Xinlitun

54

Xinlitun2

55

Gaolizhang

56

Taoshan

57 58 59

Dawuangzhuang Wuliying Daziying

60

Nanzhuangtou

61 62

Summer Palace Mengchun

63

Donggaochun

64

Huangshan

65

Jiangnancun

Hebei Fangshan, Beijing Haidian, Beijing Haidian, Beijing Haidian, Beijing Huairou, Beijing Yanqing, Beijing Yanqing, Beijing Hebei Xusui, Hebei Beijing Changzhou, Hebei Pinggu, Beijing Harbin, Heilongjiang Yongji, Jilin

heterogeneous and indicate the past local and extralocal plant changes better than these data from lake sediments, because the data from peat are generally free of the effects of pollen focusing and pollen redeposition inherent in the lake basins (Jacobos and Bradshaw, 1981). The high carbon content of peat can also make radiocarbon dating in peat more reliable than dating in lacustrine sediments, though root pen-

Time range used (ka BP) 8—10

Radiocarbon Dates

Authors

1

Wang (1991)

1

Qui (1991)

2—4 2—10 4—10

2 4 4

Xia (1991) Li et al. (1990) Chen et al. (1977)

4—8

3

Chen et al. (1977)

0.8—8

2

Chen et al. (1977)

0.8—6

2

Chen et al. (1977)

10

2—10

11

Zhao (1989)

6—10

9

Zhao (1989)

2

1

Chen et al. (1977)

0.8—2 0.8—4

1 2

4

3

Xia (1993) Wang and Xia (1988) Xia (1993)

2—10

3

Xu et al. (1993)

4—10

4

2—10 10

3 5

2

1

0.8—2

1

Li and Liang, (1985) Xu et al. (1988) Zhang et al. (1981) Zhang et al. (1981) Zhou (1984)

10

7

Zhang et al. (1981) Zhang et al. (1981) Kong (1982) Kong (1982) Li and Liang, (1985) Yuan et al. (1989)

2

4 2

Zhou et al. (1993) Xu et al. (1993)

2

1

Wang (1991)

10

3

8

1

Wang and Xia, (1988) Sun et al. (1980)

8—10

2

4—6

2

6—8 2—6 8—10

3 3 2

6—8

etration from plants growing on the mire surface can sometimes make peat dates too young. Most pollen samples in the study area were prepared from peat, in both the developing bogs and swamps and in the buried peat. Some come from other sediment layers, and precaution was taken when the data from the non-peat layers were used. Generally, only data obtained from the lake sediment samples are

674

Quaternary Science Reviews: Volume 17

chosen, and the data values occurring in the fluvial sediment, loess and paleosols were compiled merely as reference data rather than being used as the basis for preparing pollen maps. Sampling interval: Data reliability depends to a large extent on the time resolution of pollen time series, which in turn is determined by the sampling intervals within a given core or section. Wide sampling intervals are common for the fossil pollen studies made before 1985, and it naturally weakens our confidence in them. In spite of this, certain constraints can be set in selecting data in order to ensure high precision. Only those pollen sites with the sampling intervals finer than 1 sample per 600 yr were put into the data set. In a few areas in which the data are very rare, sites were included with a time resolution that was more coarse than 1 sample per 600 yr. Dating control: Before 1982, many pollen studies were published with no radiocarbon dates. All of them are omitted, and no dating procedure based on pollenstratigraphic correlation was permitted. When a core or section did not have enough radiocarbon dates (e.g. fewer than three in the whole Holocene period), only the pollen percentage values at the fixed mapping levels most close to the carbon dates were selected. If more than three radiocarbon dates exist in a pollen time series, age assignments for the fixed mapping levels were performed based on a graph of the age—depth relationship. Such a method was not applied, however, if the sediment from which the samples were taken was heterogeneous, and a simple linear interpolation between the carbon dates was used instead. All of the dates used in the present paper are in uncalibrated radiocarbon time. A total of 65 fossil pollen sites were used after the above considerations were applied (Table 1 and Fig. 5). The regions with good data coverage include the Liaodong Peninsula, Changbai Mts., Sanjiang Plain,

FIG. 5. Distribution of the fossil pollen sites used in this study.

Xiaoxingan Range, Songnen Plain, upper Liaohe Plain and the northern part of Hebei Province. The Daxingan Mts. and Inner Mongolia Plateau are poorly represented. Methods The procedure for preparing pollen maps approximately follows that of Webb et al. (1983) and Webb (1985), though some revisions have been made that are better suited to the specific conditions of the study area. Pollen taxa and time level: A few of the most common families or genera in Northeast China were selected for mapping. They include Picea/Abies, Pinus, Quercus, ºlmus, Betula, Artemisia, and Chenopodiaceae pollen. Total arboreal pollen was also mapped. The percentages of Picea and Abies are combined because they are usually not given separately in the published reports. Six time slices in 2000-yr intervals were chosen from 10,000 yr B.P. (10 ka) to 0 yr B.P. (0 ka), and 800 yr B.P. (0.8 ka) was also chosen as a mapping time slice in order to investigate the vegetation change in the Medieval Warm Period. The number of sites with data differ among the time slices with 21 at 10 ka, 24 at 8 ka, 30 at 6 ka, 34 at 4 ka, 37 at 2 ka, 22 at 0.8 ka, and 27 at 0 ka. Coverage is best after 6 ka because peat accumulated mostly during the last 6000 years in Northeast China (Ma et al., 1989; Ren, 1994). For modern percentage values, ten extra sites with surface pollen data were also included. Data extraction: Original percentage values for all of the fossil pollen sites were read from the pollen diagrams given in the references quoted in Table 1. Smoothing for the percentage curves was performed by hand before digitizing in order to buffer against the influences of extreme values. Standardization: Because Chinese palynologists used different sums for calculating pollen percentages, a standardization was needed to make the data comparable. This required recalculation of the percentage values using a sum of total pollen grains from terrestrial plants excluding Cyperaceae. The most frequently published sums include: (1) the total pollen and spore grains counted; (2) the total pollen and spore grains from terrestrial plants; and (3) the total pollen grains from trees. In a few cases, two sums, the total pollen grains from trees and the total pollen and spore grains from other plants, were used. Map construction: Isopolls were drawn by hand for the selected taxa and time slices. Base maps with a scale of 1 : 9 million were used. The interval between the contours of pollen percentages is prescribed as 5% except for that of Arboreal pollen and Artemisia, for which the interval is 10%. Specific isopolls were chosen before isochrones were drawn by overlapping on to one base map the isopolls of the same taxon from different time slices. The isochrones represent 30% for Artemisia, 20% for Pinus, 10% for Betual, and 5% for Picea/Abies, ºlmus, Quercus and Chenopodiaceae

G. Ren and L. Zhang: Summary of Holocene Pollen Data

pollen. The 40% isopoll for Arboreal pollen today corresponds well to the central axis of the forest steppe in the east of the Songnen Plain, and this isopoll was therefore chosen for mapping.

ANALYSIS OF POLLEN MAPS The isopolls for given time slices are shown in Figs 6—12, and the isochrones for different taxa are presented in Fig. 13. Several major features of the spatial distribution and temporal variation of pollen taxa are evident on these maps. Early Holocene (10— 7 ka) At 10 ka, the beginning time of Holocene, tree pollen was rare everywhere compared to later dates (Fig. 6). It was about 70% in the Changbai Mts., 40—60% on the Liaodong Peninsula, and 10—40% in the Songnen and Liaohe Plains. The most abundant arboreal taxon was Betula pollen, which reached 25—30% in the Changbai Mts. and the Sanjiang Plain and 20—25% in the Liaodong Peninsula. Picea/Abies percentages are generally 5—10% in the Changbai Mts., 1—5% on the Sanjiang Plain, and around 1% on the Liaodong Peninsula. Pinus pollen abundance was at its lowest for the Holocene. Quercus and Artemisia pollen occurred in relatively high abundance where Picea/Abies pollen was low on the Liadong Peninsula. Otherwise the pollen for deciduous trees such as ºlmus and Quercus was in low abundance and was not usually higher than 10% in the eastern forest regions. Tree pollen percentages increased in the east at 8 ka (Fig. 7 and Fig. 13), with ºlmus and Quercus pollen accounting for the largest portion of the increase. ºlmus percentages increased up to 15 to 20% on the Sanjiang Plain and in the Changbai Mts., while Quercus pollen percentages exceeded 20% in the Changbai Mts. and on the Liaodong Peninsula. The abundance of Betula pollen had declined by this time and was below 10% on the Sanjiang Plain, between 15% and 20% in the Changbai Mts., and 10—15% on the Liaodong Peninsula. Little change is recorded for the other tree taxa. Mid-Holocene (7 to 3 ka) This period witnessed some remarkable changes in the fossil pollen record of Northeast China. Most noticeable were the rise of Pinus percentages almost everywhere and the decline of tree pollen percentages in the southern regions. Tree percentages continued to increase in the first half of the mid-Holocene. They rose to 90% or higher at some sites in the Changbai Mts. and on the Liaodong Peninsula by 6 ka (Fig. 8 and Fig. 13). The increase in tree pollen percentages mainly resulted from the further increase in Quercus and ºlmus pollen percentages. Isopolls of 20% Quercus and 20% ºlmus

675

pollen appear in the Changbai Mts., and Quercus pollen percentages were even higher than 30% at a few places on the Liaodong Peninsula. In the eastern part of the Songnen and Liaohe Plains, increased percentages of the deciduous tree pollen were noticeable as well. The trends in pollen abundance changes that started at the beginning of Holocene seem to have persisted until about 6 ka. From 6 to 4 ka, tree pollen percentages continued to rise slightly in the study area except at sites on the Liaodong Peninsula and in Hebei Province, where tree pollen percentages declined markedly (Fig. 9 and Fig. 13). Betula percentages decreased on the Liaodong Peninsula, but Betula percentages rose slightly at sites on the Sanjiang Plain and in the Xiaoxingan Range. The most remarkable event at this time was the rapid increase of Pinus pollen percentages in almost every part of the study area. The appearance of the 20% isopoll for Pinus pollen records this event on the map for 4 ka. This isopoll surrounds an extensive area from the Liaodong Peninsula to the Xiaoxingan Range and Sanjiang Plain. In the meantime, Picea/Abies percentages rose in the central and northern forest regions, though not so strongly as Pinus pollen percentages. Pollen percentages from deciduous trees, ºlmus in particular, generally decreased from 6 to 4 ka, which, at least in the central and northern regions, may be resulted from the big increase in Pinus pollen percentages. Late Holocene (3—0 ka) The pollen change trends starting from 4 ka BP have lasted throughout the late Holocene. Tree percentages continue to decline in Liaodong Peninsula and Hebei Province, as seen from the isopolls for 2 ka BP (Fig. 10) and isochrones (Fig. 13). Moreover, they begin to decrease as well in the southeastern part of Horqin Sandland, to the far north of Liaodong Peninsula. In the central and northern regions, however, tree percentages remain unchanged or even a continuous rising in some sites, which still may be induced by the steady increase of Pinus pollen during the last 3000 years. By 2 ka BP, Pinus percentages reaches more than 30% in a few sites of Changbai Mts. and Xiaoxingan Range, though they start to decrease in Liaodong Peninsula. Further declination of deciduous tree pollen occurs in almost every forest region. VEGETATION RECONSTRUCTION The pollen maps and their interpretation can be used to reconstruct vegetation change through different stages of the Holocene. For this discussion, the whole Holocene is divided into three periods, and the vegetation condition during each of them is described. Early Holocene birch period Represented by the time slice of 10 ka, this stage may last from as early as 12 to 8 ka, if the records for 12 ka

676

Quaternary Science Reviews: Volume 17

FIG. 6. Isopolls for 10,000 yr B.P. in Northeast China. The values shown on the map represent the pollen percentages. Regions with sparse data are indicated by dash lines.

G. Ren and L. Zhang: Summary of Holocene Pollen Data

677

FIG. 7. Isopolls for 8000 yr B.P. The values shown on the map represent the pollen percentages. Regions with sparse data are indicated by dash lines.

678

Quaternary Science Reviews: Volume 17

FIG. 8. Isopolls for 6000 yr B.P. The values shown on the map represent the pollen percentages. Regions with sparse data are indicated by dash lines.

G. Ren and L. Zhang: Summary of Holocene Pollen Data

679

FIG. 9. Isopolls for 4000 yr B.P. The values shown on the map represent the pollen percentages. Regions with sparse data are indicated by dash lines.

680

Quaternary Science Reviews: Volume 17

FIG. 10. Isopolls for 2000 yr B.P. The values shown on the map represent the pollen percentages. Regions with sparse data are indicated by dash lines.

G. Ren and L. Zhang: Summary of Holocene Pollen Data

681

FIG. 11. Isopolls for 800 yr B.P. The values shown on the map represent the pollen percentages. Regions with sparse data are indicated by dash lines.

682

Quaternary Science Reviews: Volume 17

FIG. 12. Isopolls for 0 yr B.P. The values shown on the map represent the pollen percentages. Regions with sparse data are indicated by dash lines.

G. Ren and L. Zhang: Summary of Holocene Pollen Data

683

FIG. 13. Isochrones for the selected pollen taxa in Northeast China. The values shown on the map represent thousands years before present. Specific isopolls are set at 40% for Arboreal pollen, 30% for Artemisia, 20% for Pinus, 10% for Betula, and 5% for the other mapped taxa.

684

Quaternary Science Reviews: Volume 17

at a few sites are representative. The forest extent was small compared to any subsequent time, and steppe attained its maximum development in the plains and pediments. Forests were restricted to the eastern mountains and hills, in which Betula was the dominant component, followed in abundance by Picea, Abies, ºlmus and Quercus trees. Picea and Abies trees were more common in the north, while ºlmus and Quercus trees occurred more frequently in the south. Pinus trees probably grew in scattered patches, as suggested by Pinus pollen percentages that did not exceed 15% at any site. In the forests, trees were relatively sparse because the pollen accumulation rate remained low (Sun and Yuan, 1990; Yaun and Sun, 1990; Liu, 1989). Shrub Betula populations might have been large at least in the north (Xia, 1988; Xia, pers. comm.). At the beginning of Holocene, the southern hill regions and the lower Changbai Mts. were probably covered by an open forest, and an even more open forest environment prevailed on the Sanjiang Plain. At the end of this time period, ºlmus and Quercus populations were spreading at expense of Betula and Picea/Abies. Quercus mongolica was probably the dominant species of Quercus in the north, but it was probably less abundant than Quercus liaotongica in the south. The extensive central plains were still covered by steppe that mainly consisted of Artemisia, Chenopodiceae and Gramineae as prolific pollen producers. Mid-Holocene deciduous tree period The deciduous forest developed in the eastern wet regions around 6 ka. Some deciduous trees that are common today dominated the forests. Quercus and ºlmus, of course, were the most important tree taxa. They grew in large populations in the eastern regions and northern Hebei Province. Quercus populations were probably much more abundant than ºlmus populations in the south, especially on the Liaodong Peninsula, though the opposite was true on the Sanjiang Plain in the north. The other deciduous trees taxa also became more common. On the other hand, abundances of Betula, Picea and Abies populations decreased across much of the eastern forests. Pinus populations remained sparse, though some evidence that their abundance began to rise on the Liaodong Peninsula. In fact, Pinus populations were probably least common between 9 and 6 ka. In the east of the Songnen and Liaohe Plains, the ecotone between forest and steppe shift westwards (Fig. 13), and the extent of the central steppe shrank. However, much of the plains were still occupied by various herbs, not by an open forest or woodland. By 4 ka, two of the big changes had started. One was the large expansion of Pinus (Sun and Weng, 1992), and to a smaller degree, Picea/Abies, populations within the forest regions between 6 and 4 ka. In the Changbai Mts. and the regions to the north, populations of Pinus

koraiensis probably increased. But in the south, the main portion of the change may come from the increases of Pinus densiflora and Pinus tabuleaformis. The other big change was the decline of forests on the Liaodong Peninsula and in Hebei Province. Populations of major tree taxa started to decrease, though the most significant decline occurred for the deciduous tree populations including Quercus and ºlmus. Pollen data from representative sites indicate that the above two changes actually started around 5 ka, a little earlier than 4 ka, and they continued during the late Holocene. Late Holocene mixed forest period The decline in the southern forest that began between 6 and 4 ka persisted throughout the late Holocene. As a result, the abundance of major tree taxa decreased on the Liaodong Peninsula and in the northern part of Hebei Province, and the area of the forest decline expanded to the central regions, for instance, to the southeastern Horqin Sandland by 3 ka, and to a few sites in the Changbai Mts. by 2 to 1 ka. In the northern regions, including the Xiaoxingan Range, Sanjiang Plain, and some sites in the Changbai Mts., no long term forest decline ever occurred. The forests of these regions became denser than before, mainly because the population of Pinus koraiensis increased in abundance. The major deciduous trees may not have decreased as much as shown by the pollen percentages that, to a large extent, were affected by the increased pollen deposition from Pinus populations. The tree taxa that declined in the south included not merely deciduous taxa like Quercus and ºlmus, that had declined at 4 ka, but also Pinus and Betula. Herbs, especially Artemisia and Chenopodiceae, increased their abundance and coverage during the time of the forest decline and at some sites even dominated the landscapes that were originally forested. DISCUSSION The isopolls and isochrones prepared from the available pollen data summarize and organize many of the spatial and temporal variations evident in the interpretations of the data from single sites. The pollen maps have an exceptional advantage over the site analyses. The standardized data and maps allow correlation among different sites and investigation of the macro-spatial patterns in vegetational distribution and change. The mapped patterns are key to interpreting the potential causes of the past vegetation changes in Northeast China. Forest decline since 5 ka Interpretation of the fossil pollen maps produced an unexpected discovery that the forest declined and that the belt of decline shifted northwards during the last 5000 years. Around 5 ka, the forests on the Liaodong

G. Ren and L. Zhang: Summary of Holocene Pollen Data

Peninsula and in Hebei Province began to decline. After that, the forest decline in the southern regions continued, and the decline extended to many sites of the central regions during the last 3000 years. These include the southeast of the Horqin Sandland at about 3 ka and the western Changbai Mts. about 1 ka. In the northern regions, including the Xiaoxingan Range and Sanjiang Plain, no long-term trend in forest decline ever appeared. The spatial and temporal patterns of the forest change strongly resist the explanation of climate changes. Within such an area like Northeast China, no reliable evidence has ever been found to show that the climate change on the century to millennium time scale could propagate in any horizontal direction. Although the decrease in tree abundance mainly resulted from such deciduous trees as Quercus, ºlmus and Juglans on the Liaodong Peninsula around 4 ka, Pinus accounted for an increasing percentage of the decline soon after that. In the Changbai Mts., pollen accumulation rate data from a few sites indicate an almost simultaneous decrease in the abundance of the main trees during the last 3000 years. The unselectiveness of the decline of trees in the closed forests is rather difficult to explain by climate changes. According to the historic records and the archaeological evidence, on the other hand, human population density and agricultural activity intensity were larger in the southern regions than in the central and northern ones of the last 5000 years (Tan, 1982; Zhu, 1991; Tong, 1989; Tian, 1993; Ren, 1994). In fact, when agriculture was widely practiced by the early settlers on the Liaodong Peninsula and in Hebei Province at 5 ka, only a few groups of nomads and hunters cruised on the vast central and northern regions (Zhu, 1991; He, 1991; Jilin Archaeological Institute, 1991; Heilongjiang Archaeological Institute, 1991; Zhao and Xie, 1988). By 3 ka, however, the agriculture may have shifted north to the southeastern Horqin Sandland and the neighboring regions, where the earliest cultivation relics, named as ‘‘Gaotaishan Culture’’, were frequently discovered in the last decade (Xin, 1988; Tian, 1988; Zhang and Xu, 1991; Liaoning Archaeological Institute 1989). Afterwards, the ancient farmers might settled in the central plains and in some valleys of the western Changbai Mts. between 2 and 1 ka BP (Jilin Archaeological Institute, 1991; Heilongjiang Archaeological Institute, 1991). In the high north, including the Xiaoxingan Range and Sanjiang Plain, significant exploitation and settlement began only after the founding of the People’s Republic of China. Human activities instead of the climate changes may therefore have led to the late Holocene forest decline that the patterns on the pollen maps show. Early between 6 and 4 ka, the Liaodong Peninsula and Hebei Province were more densely populated, and agriculture there was well developed. Human deforestation, therefore, led to the forest decline in these regions (Goudie, 1981; Whitlow, 1987). After 4 ka, human population in the southern regions continued to in-

685

crease (Ting, 1989, Zhao and Xie, 1988), leading to a further deforestation. At the same time, the area of settlement and agriculture moved slowly from south to north, causing the belt in which forests declined for first time to shift northwards as well. In the northern regions such as the Xiaoxingan Range and Sanjiang Plain, the arrival of agriculture was so late that the forest decline has not yet been identified in the coarsely sampled pollen records and resultant pollen maps. Climatic implications Fossil pollen indicate the natural changes in vegetation as well as climate, and the Holocene pollen records from the Liaodong Peninsula have been widely held as the classical ones for reconstructing the climate for the last 10,000 years (Chen et al., 1977; Zhou et al., 1984; Kong et al., 1982; Du et al., 1989; Li and Liang, 1985; Xia, 1988; Shi and Kong, 1992). According to the prevailing reconstruction, the Holocene climate of North China and Northeast China was broadly divided into three stages, which were designated as a cold-dry period (10—7.5 ka), a warm-wet period (7.5—2.5 ka) and cool-dry period (2.5—0 ka). These periods were correlated with the international classical Nordic climate periods (Birks and Birks, 1980; Bradley, 1985). During the last decade, another group of scientists argued, on the basis of some pollen and the other proxy data, that Holocene could be divided into warm-wet early stage and cool-dry late stage, with 5 ka as a dividing point (An and Liu, 1987; An et al., 1990, 1993; Wang and Feng, 1991). Although this suggestion is in agreement with the model simulations and the changes of earth’s orbital parameters (COHMAP Members, 1988; Kutzbach and Guetter, 1984; Kutzbach 1989), it is not supported by the lack of forest in the early Holocene in Northeast China, which may indicate drier conditions then than in the mid-to-late Holocene. It is also not supported by many of the mid-to-late Holocene pollen time series that show some asynchronous variations with each other and with those used as evidence by this group of Chinese scientists. One of the largest differences between the above two sets of climate reconstructions is for the beginning ages for the ‘cool-dry’ late Holocene, defined mainly on the basis of the decline of tree pollen. However, as mentioned above, because human activities may have been the main cause of the decline in tree abundance, the pollen data and the reconstructed vegetation are problematic for use in indicating climatic change after, e.g. 5 ka on the Liaodong Peninsula and in Hebei Province. The sharp divergence of the interpretations may be no more than an indirect reflection of the differences in the beginning dates for human modification of the natural environment. Some pollen records, however, were free of human disturbance and can be used to reconstruct the climate history for Northeast China. In the northern most part of the study area, a vast territory remained unsettled

686

Quaternary Science Reviews: Volume 17

before 1950. The fossil pollen data from the Xiaoxingan Range and the Shanjiang Plain, and also some sites in the western Changbai Mts., can be used to indicate climate changes not only for the early and middle Holocene, but also for the last few millennia. It is in these regions that the fossil pollen data support a largely different story about late Holocene climates. Between 10 and 5 ka, Quercus and ºlmus were the dominant components of the forests in Northeast China, and Pinus and Picea/Abies populations were much more sparse (Figs 6—8). Pinus and Picea/Abies today are more likely to be found in the regions with a cooler and wetter summer than that of regions with abundant populations of deciduous trees such as Quercus and ºlmus (Ren, 1994). The fossil pollen indicate that the summers of the early to mid Holocene were warmer and drier in the study area. After 5 ka, the percentages of Pinus and Picea/Abies pollen increased progressively, and the abundances of Quercus and ºlmus pollen decreased both relatively and absolutely. The pollen changes suggest that the summer climate in Northeast China has been becoming cooler and wetter since 5 ka BP. Evidence from peats, sand dunes, paleosols, and lake water levels also indicate an increasing wetness during the last 5000 years (Ren, 1994). The long-term cooling trend for summer has been found in many fossil pollen and peat records from middle and high latitude regions of the Northern Hemisphere (Webb and Bryson, 1972; Bartlein, 1984; Davis et al., 1980; Gajewski, 1988; Kelly and Huntley, 1991; MacDonald, 1989; Miller and Futyma, 1987; Ovenden, 1990; Zoltai and Vitt, 1990). Now the pollen data from Northeast China show that monsoon regions of Asia may have experienced exactly the same change in summer temperature, suggesting that it may occur over a much more extensive area of the Northern Hemisphere. This new finding supports a key climate interpretation derived from theory about the earth’s orbital changes. This theory indicates that the summer radiation of the north has been decreasing since its peak at about 9 ka and the summers in the Northern Hemisphere should have become cooler over this period and especially during the late Holocene (Kutzbach et al., 1989; COHMAP Members, 1988; An et al., 1990; Ren, 1991). Our interpretation of the pollen data from Northeast China, therefore, does not support the predictions from orbital theory for wetter conditions during the early Holocene, but supports the predictions for summer cooling in the late Holocene.

ACKNOWLEDGMENTS We thank Sun Xiangjun, Chen Shupeng, Cui Zhijiu, Yang Jingcun, Zheng Du, Kong Zhaochen, Zheng Shizhong, Li Wenhua, and Wu Jihua for their helpful suggestions. We also appreciate the help of Xiao Ping, Song Changqing, Han Guang, Lu Houyuan, Du Naiqiu, Wen Yan, Liu Yan, Niu Yuhong, Hu Weiya, Li

Caixing, Qin Yanfei, Bi Jun and Wang Jue. Special thanks are due to T. Webb for his invaluable comments and editing of the manuscript. This work is supported by the National Key Basic Research Programme of China, No. 27.

REFERENCES Academic Sinica (1985) »egetation of Inner Mongolia. Science Press, Beijing. An, Z. and Liu, T. (1987) Long-term climate change in the LoessPlateau of China. In: ¹he Climate of China and Global Climate, pp. 3—12. China Ocean Press, Beijing. An, Z., Wu, C., Lu, Y., Zhang, D., Sun, X. and Dong, G. (1990) A preliminary study on paleoenvironment of the last 20,000 years in China. In: Liu, T. (ed.), ¸oess, Quaternary Geology and Global Change, Part 2, pp. 1—26. Science Press, Beijing. Anderson, P.M., Bartlein, P.J. and Brubaker, L.B. (1994) Late Quaternary history of tundra vegetation in northeastern Alaska. Quaternary Research, 41, 306—315. Anderson, P.M. and Brubaker, L.B. (1994) Vegetation history of north central Alaska: a mapped summary of late-Quaternary pollen data. Quaternary Science Review, 13, 71—92. Bartlein, P.J., Webb, T. III and Fleri, E. (1984) Holocene climate change in the northern Midwest; pollen-derived estimates. Quaternary Research 22, 361—374. Bernabo, J.C. and Webb, T. III (1977) Changing patterns in the Holocene pollen record of northeastern North America: a mapped summary. Quaternary Research, 8, 84—96. Birks, H.J.B. and Birks, H.H. (1980) Quaternary Paleoecology. Edward Arnold, London. Bradley, R.S. (1985) Quaternary Paleoclimatology. Allen and Unwin, Boston. Chen, C., Lu, Y. and Shen, C. (1977) Environmental changes in southern Liaoning Province during the last 10,000 years. Scientia Sinica, Series B, 22, 603—614. COHMAP Members (1988) Climate changes of the last 18,000 years: observations and model simulations. Science, 241, 1043—1052. Davis, M.B., Spear, R.W. and Shane, L. (1980) Holocene climate of New England. Quaternary Research, 14, 240—250. Du, N., Kong, Z. and Shan, F. (1989) A preliminary investigation on the vegetation and climatic changes since 11,000 yr BP in Qinghai Lake. Acta Botanica Sinica, 31, 803—814. Gajewski, K. (1988) Late Holocene climate changes in Eastern North America estimated from pollen data. Quaternary Research, 29, 255—262. Goudie, A. (1981) ¹he Human Impact: Man’s Role in Environmental Change. Basil Blackwell, Oxford. Han, G. (1992) The mechanism of desertification and its reversion in Horqin Sandy Steppe. PhD dissertation, Lanzhou Institute of Desert, CAS. Heilongjiang Archaeology Institute (1990) The major achievements of archaeological studies during the last decade. In: Archaeological Studies of the ¸ast Decade (1979—1989), pp. 84—90. China Archaeology Press, Beijing. Huntley, B. (1990) European vegetation history: palaeovegetation maps from pollen data—13,000 yr BP to present. Journal of Quaternary Science 5(2), 103—122. Huntley, B. and Birks, H.J.B. (1983) An atlas of past and present pollen maps for Europe, 0—13,000 years ago. Cambridge University Press, Cambridge. IGBP (1994) IGBP in action: work plan 1994—1998. IGBP Report, No. 28. 84-96. Jacobos, G.L. and Bradshaw, R.H.W. (1981) The selection of sites for paleovegetation studies. Quaternary Research, 16, 80—96. Jiang, T. (1992) Sporo-pollen vegetation discussion in the farmingpastoral belt of Inner Mongolia during Holocene. In: Zhou, T. and L. Zhang (eds), Environmental Change of Holocene and

G. Ren and L. Zhang: Summary of Holocene Pollen Data Future Prediction in the Farming Pastoral Belt of the Northern China, pp. 71—87. China Geology Press, Beijing. Jiang, T. (1988) The sporo-pollen of the Holocene and its environmental analysis in the Yangyuan County, Hebei Province. Journal of Beijing Normal ºniversity (Sup. 1), 152—158. Jilin Archaeological Institute (1990) Progress in archaeological studies in the last decade. In: Archaeological Studies of the ¸ast Decade (1979—1989), pp. 70—80. China Archaeology Press, Beijing. Kelly, M.G. and Huntley, B. (1991) An 11,000-year record of vegetation and environment from Lago di Marignano, Latium, Italy. Journal of Quaternary Science, 6, 209—224. Kong, Z., Du, N. and Zhang, Z. (1982) Vegetation development and climatic changes in the last 10,000 years in Beijing. Acta Botanica Sinica, 24(2), 172—181. Kutzbach, J.E. and Guetter, P.J. (1984) The sensitivity of monsoon climates to orbital parameter changes for 9,000 years BP. In: Berger, A.L., Imbrie, J., Hays, J., Kukla, G. and Saltzman, B. (eds), Milankovitch and Climate, Part 2, pp. 801—820. Reidel, Dordrecht, Holland. Kutzbach, J.E. (1989) Major perturbation of the hydrosphere-atmosphere-biosphere system. In: Bradley, R. (ed.) Global Change of the Past, pp. 43—60. OIES, UCAR, Boulder, CO. Li, R., Zheng, L. and Zhu, G. (1990) Lakes and environment in the inner Mongolia plateau, pp. 120—138. Beijing Normal University Press, Beijing. Li, W. and Liang, Y. (1985) Vegetation and environment of the hypsithermal interval of Holocene in eastern Hebei Plain. Acta Botanica Sinica, 27(6), 640—651. Liaoning Archaeological Institute (1989) Field excavating report of Pinganpu relics, Zhangwu county, Liaoning Province. Journal of ¸iaochai Archaeology, 1989(2), 99—109. Liu, J. (1989) Vegetation and climatic changes at Gushantun Bog in Jilin, NE China since 13,000 yr. BP. Acta Palaeontologica Sinica, 28, 495—509. Ma, X., Xia, Y. and Wang, R. (1987) A study on the peat formation periods of China. Geographical Research, 6, 31—41. MacDonald, G.M. (1989) Postglacial palaeoecology of the subalpine forest—grassland ecotone of southwestern Alberta. Palaeogeography, Palaeoclimatology, Palaeoecology, 73, 155—173. Miller, N.G. and Futyma, R.P. (1987) Paleohydrological implications of Holocene peat development in Northern Michigan. Quaternary Research, 27, 297—311. Ovenden, L. (1990) Peat accumulation in northern wetlands. Quaternary Research, 33, 377—386. Peat Study Group (1983) Peat resource in Jilin Province. Scientia Geographica Sinica, 3, 241—252. Prentice, I.C. and Sarnthein, M. (1993) Self-regulatory processes in the biosphere in the face of climate change. In: Eddy, J.A. and Oeschger, H. (eds), Global Changes in the Perspective of the Past, pp. 29—37. Wiley, New York. Qiu, S., Jiang, P., Li, F., Xia, Y. and Wang, P. (1981) The study of the environment change since the late Glacial Period in northeast China. Acta Geographica Sinica, 36, 315—327. Qiu, S., Li, Q. and Xia, Y. (1992) Paleosols of sandy lands and environmental changes in the western plain of Northeast China. Quaternary Science, 1992, 224—232. Ren, G. (1991) Solar radiation and climate changes. Advance in Earth Sciences, 6(6), 37—41. Ren, G. (1994) Climate, vegetation and human activities—environmental changes of northeast China during the last 10,000 years. Ph.D. dissertation, Beijing Normal University. Shi, Y. and Kong, Z. (1992) Climates and Environments of Holocene Megathermal in China. China Ocean Press, Beijing. Sun, J., Wang, S., Wang, Y., Zhou, Y., Lin, Z. Zhang, Q. and Chen, S. (1980) Paleoenvironment of the last glacial stage in Northeast China. Jilin Geology, 1980(4), 38—60. Sun, X. and Weng, C. (1992) Pollen records on the history of mixed conifer and hardwood forest in Northeast China. Acta Botanica Sinica, 34, 394—401. Sun, X. and Yuan, S. (1990) The pollen data and vegetation evolution during the 10,000 years in Jinchuan area, Jilin Province. In:

687

Quaternary Geology and Global Change, Part 2. Science Press, Beijing. Tan, Q. (1982) Historic Atlas of China, Vol. 1. China Cartography Press, Beijing. Tian, G. (1993) Distribution and interaction of the archaeological cultures with different origins near the Great Wall. In: Zhang, L. (ed.), Research on the Past ¸ife-supporting Environment Change of China, pp. 32—43. China Ocean Press, Beijing. Ting, Z. (1989) Studies on the Neolithic Age Archaeology in Northeast China. China Archaeology Press, Beijing. Wang, M. (1982) Sporo-pollen and algae assemblages and palaeoclimate of Holocene in Sanjiang Plain. In: Selected Papers from the First Symposium of the Palynological Society of China, pp. 13—21. Science Press, Beijing. Wang, P. and Xia, Y. (1988) Preliminary research of vegetation succession on the Songnen Plain since late Pleistocene. Bulletin of Botanical Research, 8, 87—96. Wang, P. and Xia, Y. (1990) Preliminary study on sporo-pollen society and its development process in T302 hole section, Liuhe, Jilin Province. Acta Phytoecologica et Geobotanica Sinica, 14, 287—292. Wang, S. and Feng, M. (1991) Environmental change of Daihai Lake, Inner Mongolia, and its relationship with the strength of the summer monsoon. Scientia Sinica, Series B, 36, 759—768. Webb, T. (1985) Holocene palynology and climate. In: Hecht, A.D. (ed.), Paleo-climate analysis and modeling, pp. 163—195. Wiley, New York. Webb, T. and Bryson, R.A. (1972) Late- and postglacial climate change in the northern Midwest, USA: Quantitative estimates derived from fossil pollen spectra by multivariate statistical analysis. Quaternary Research, 2, 70—115. Webb, T., Cushing, E.J. and Wright, H.E., Jr (1983) Holocene changes in the vegetation of the Midwest. In: Wright, H.E., Jr (ed.), ¸ate Quaternary environments of the ºnited States, Vol. 2, The Holocene, pp. 142—165. University of Minnesota Press, Minneapolis, MN. Whitlow, R. (1987) Man’s impact on vegetation: the African experience. In: Gregory, K.J. and Walling, D.E. (eds) Human Activity and Environmental Processes, pp. 353—375. Wiley, New York. Williams, L.D. and Wigley, T.M.L. (1983) A comparison of evidence for Late Holocene summer temperature variations in the northern hemisphere. Quaternary Research, 20, 286—307. Wu, Z. (1980) »egetation of China. Science Press, Beijing. Xia, Y. (1988) Preliminary study on vegetation development and climatic changes on the Sanjiang Plain in the last 12,000 years. Scientia Geographica Sinica, 8(3), 239—249. Xia, Y., Wang, P., Li, Q. and Jiang, G. (1993) The preliminary study on climate change of the warm period of Holocene in the Northeast China. In: Zhang, L.S. (ed.), Research on the past life-supporting environment change of China, pp. 296—315. China Ocean Press, Beijing. Xiao, J. and Sun, S. (1987) A discussion on sporo-pollen assemblages from the peat along Moudan and Mouling Rivers. Journal of Nanjing Normal ºniversity (Suppl), 100—106. Xu, Q., Wu, C., Wang, Z., Dong, G., Wu, S., Zhang, J., Du, N. and Kong, Z. (1993) Approach to palaeo-environment in the west coast of Bohai Bay since 25,000 a BP. Acta Phytoecologica et Geobotanica Sinica, 17, 20—32. Xu, Q., Chen, S. and Kong, Z. (1988) Preliminary discussion of vegetation succession and climate change during Holocene in the Baiyangdian Lake district. Acta Phytoecologica et Geobotanica Sinica, 12, 144—151. Ye, Y., Yan, F. and Mai, X. (1983) The sporo-pollen assemblages in three well formed bogs from Three-River Plain, Northeast China, and their geological significance. Scientia Geologica Sinica, 1983, 260—266. Yin, H. (1984) The problem on the bog formation in the eastern part of Xiao Hinggan Mountains. Acta Phytoecologica et Geobotanica Sinica, 8, 101—111. Yuan, S. and Sun, X. (1990) The vegetation and environmental history at the west foot of Changbai Mts., northeast China during the last 10,000 years. Acta Botanic Sinica, 32, 558—567.

688

Quaternary Science Reviews: Volume 17

Zhang, Z., Wang, D. and Ding, J. (1981) Environmental changes since 13,000 years ago in Beijing region. Scientia Geologica Sinica, 1981, 259—268. Zhao, F. (1989) Environmental change in the western part of southern Liaoning Province in the last 10,000 years. M.S. Thesis, Geology Institute, CAS. Zhao, W. and Xie, S. (1988) Population History of China. People’s Press, Beijing. Zhou, K., Chen, S., Chen, C., Ye, Y. and Liang, X. (1984) Holocene pollen analysis and paleoenvironment in the northern China. In:

Sporo-pollen Analyses of the Quaternary and Paleoenvironment, pp. 25—53. Science Press, Beijing. Zhou, X., Cai, S., Kong, Z. and Du, N. (1993) Preliminary research of vegetation and environment at Kunming Lake in the Summer Palace, Beijing. In: Research on the Past ¸ife-supporting Environment Change of China, pp. 32—43. China Ocean Press, Beijing. Zoltai, S.C. and Vitt, D.H. (1990) Holocene climate change and the distribution of peatland in western interior Canada. Quaternary Research, 33, 231—240.