Holocene vegetation and climate history at Haligu on the Jade Dragon Snow Mountain, Yunnan, SW China

Transcription

1 Climatic Change (2012) 113: DOI /s Holocene vegetation and climate history at Haligu on the Jade Dragon Snow Mountain, Yunnan, SW China Xiao-Yan Song & Yi-Feng Yao & A. H. Wortley & K. N. Paudayal & Shao-Hua Yang & Cheng-Sen Li & S. Blackmore Received: 28 August 2010 / Accepted: 16 November 2011 / Published online: 10 December 2011 # Springer Science+Business Media B.V Abstract This paper uses pollen analysis to investigate and document the changing climate and vegetation during the Holocene based on a 400 cm core in depth obtained at a wetland site at Haligu (3,277 m a. s. l.) on the Jade Dragon Snow Mountain in Yunnan, China. By applying the Coexistence Approach to pollen data from this core, a quantitative reconstruction of climate over the last 9,300 years was made based on each pollen zone and individual core sample, which reveals the temperature and precipitation change frequently during that time. The qualitative analyses show that from 9300 to 8700 cal. yr BP, the vegetation was dominated by needle-leaved forest (mainly Pinus and Abies), indicating a slightly cool and moderately humid climate. Between 8700 and 7000 cal. yr BP, evergreen broad-leaved forest, dominated by Quercus, became the predominant vegetation type, replacing needleleaved forest at this elevation, implying a warmer and more humid climate. During the period 7000 to 4000 cal. yr BP, the vegetation changed to mixed needle-leaved and evergreen broad-leaved forest, indicating a warm and moderately humid climate, but somewhat cooler than the preceding stage. From 4000 to 2400 cal. yr BP, the vegetation was again dominated by evergreen broad-leaved forest, but coniferous trees (mainly Pinus) Xiao-Yan Song and Yi-Feng Yao contributed equally. X.-Y. Song: Y.-F. Yao : C.-S. Li (*) State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Xiangshan, Beijing, People s Republic of China lics@ibcas.ac.cn X.-Y. Song Shanxi Agricultural University, Taigu , People s Republic of China A. H. Wortley : S. Blackmore Royal Botanic Garden Edinburgh, 20a Inverleith Row, Edinburgh EH3 5LR, UK K. N. Paudayal Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal S.-H. Yang The Research Institute of Alpine Economic Plant, Yunnan Academy of Agricultural Sciences, Lijiang , People s Republic of China

2 842 Climatic Change (2012) 113: began to increase, especially relative to a decline in Quercus. This implies that the climate remained warm and humid but slight drier than previously. The evergreen Quercus phase ( yr BP) was designated as the Holocene climatic optimum in the Haligu core sediments. It is correlated with a markedly greater abundance and diversity of pteridophytes spores than was recorded before or after this period. From 2400 cal. yr BP to present, the vegetation was dominated by needle-leaved forest, of which Pinus formed the predominant component, accompanied by Abies and Tsuga. This reflects a slightly cooler, humid climate but also correlates with a period of increasing human settlement on the lower slopes of the mountain. At this elevated site, several hundred metres above the highest present day settlements, direct palynological evidence of anthropogenic activity is uncertain but we discuss ways in which the marked decline in Quercus pollen during this period may reflect the impact of ways in which natural resources of the mountain have been utilised. 1 Introduction Pollen analysis has been used extensively to reconstruct the past history of vegetation and climate in a range of ecosystems during the Quaternary (e.g. Webb and Bryson 1972;Birks and Birks 1980; Huntley1990, 1992; Tonkovetal.2002; Xiaoetal.2004; Tonkov and Marinova 2005;Antόnetal.2006;Fengetal.2006a;Liewetal.2006;Yietal.2006;Zhaoetal.2007)but relatively few such studies have been undertaken in the Hengduan Mountains, a key location as a global hotspot of biodiversity in China (Li and Walker 1986; Sun et al. 1986; Walker 1986;for one exception see Zhou et al. 2003). Furthermore, whilst palynological evidence is often used to draw inferences about the influence of anthropogenic factors on vegetation during the Holocene, the vast majority of such studies have focused upon Europe (e.g. Mudie et al. 2007; Rubiales et al. 2007; Gonzalez-Samperiz et al. 2008) or the Americas (e.g. Brown and Hebda 2003; Periman2005; Niemann and Behling 2008). A few studies have ventured further afield into Africa (Brncic et al. 2007), the Near East (Neumann et al. 2007),Southeast Asia(Dam et al. 2001;Maxwell 2004) and the Loess Plateau of China (He et al. 2002), but little such work has yet been undertaken in Southwest China. The presence of a number of natural wetlands yielding abundant, well-preserved palynomorphs, at a range of altitudes makes the Jade Dragon Snow Mountain or Yulong Xue Shan, one of the highest peaks (5,596 m a. s. l.) in the Hengduan Mountain region, particularly appropriate for studying the relationships between climate, people and vegetation. The rich and diverse nature of the regional flora, in which palynomorphs can sometimes be identified below generic level, occasionally even to species (see for example, Fujiki et al. 2005), should ultimately enable an estimation of the changes in both floristic composition and diversity over time. With this objective in mind, we have undertaken SEM studies of single pollen grains isolated from the cores. The strong altitudinal zonation of vegetation in the Hengduan Mountains also offers the potential, as more studies are undertaken, to compare between sites and build up an understanding how this zonation arose and how it responds, through time, to climate change and human impacts. We therefore make comparisons with other studies close to our study area in NW Yunnan (Lin et al. 1986; Jiang et al. 1998; Shen et al. 2006). It is also possible to make interesting comparisons with recent investigations of palaeoecology in nearby Tibet (e.g. Kaiser et al. 2007, 2008; Miehe et al. 2006, 2008) aswellasotherpartsofchinaandthe Himalayan region. In order to draw inferences about past climate we have applied the Coexistence Approach of Mosbrugger and Utescher (1997). Future work will focus on

3 Climatic Change (2012) 113: extending the number of sites that can be compared both at different altitudes on the Jade Dragon Snow Mountain and elsewhere in the Hengduan Mountains. 2 Study area: geography, climate and local vegetation The study area, Haligu ( N, E), is located at the southern end of the Jade Dragon Snow Mountain in Yulong County of Lijiang City, Yunnan, SW China (Fig. 1). Due to the exceptional floristic diversity of this region and its conservation value, the site is now protected within the wider landscape of the Lijiang Alpine Botanic Garden. It comprises a natural wetland, now expanded into a small lake retained by a man-made dam, lying in an intermontane basin at 3,277 m a. s. l., surrounded by a north-south mountain range rising at its peak to 5,596 m a. s. l.. Currently there has no human settlement in the study area. At 3,080 m a. s. l., about 2 km far from Haligu, the Naxi ethnic minority settlement can be found in Wenhai village. The study area is located within a vegetation sub-domain characterised by Pinus yunnanensis forest and Picea-Abies forest typical of northwesterncentral Yunnan (Fig. 1) (Writing Group of Yunnan Vegetation 1987). The vegetation of the immediate area comprises mixed forest dominated by coniferous trees (Pinus yunnanensis) and evergreen oak (Quercus aquifolioides) along with deciduous broad-leaved trees such as Populus davidiana, Acer davidii and Rhododendron spp.. At higher elevations important tree species include Abies delavayi, Picea likiangensis and Tsuga dumosa. The area is strongly influenced by the southwest monsoon arising from the Indian Ocean. Thus the summers are warm and humid and the winters cool and dry. The mean annual temperature and precipitation measured at Lijiang (situated below the study site at about 2,200 m a. s. l.), are 12.8 C and 935 mm, respectively. About 90% of the annual precipitation falls in the summer, between June and October. The warmest month is July, with a mean temperature of 17.9 C, and the coldest month is January, with a mean temperature of 5.9 C (Feng et al. 2006b). Fig. 1 A. The location and vegetation types of Haligu Lake and its adjacent study sites in NW Yunnan. IIAii-1: domain of semi-humid evergreen broad-leaved forest and Pinus yunnanensis forest of central and eastern Yunnan; IIAii-1a: subdomain of Cyclobalanopsis glaucoides forest, Castanopsis orthacantha forest and Pinus yunnanensis forest of central Yunnan; IIAii-1b: subdomain of mid-domain Pinus yunnanensis forest and sclerophyllous evergreen Quercus forest of central and northern Yunnan; IIAii-1c: subdomain Pinus yunnanensis forest and Picea-Abies forest of northwestern central Yunnan (Writing Group of Yunnan Province 1987; Xu et al.2004). B. The position of core, moss and surface soil samples. C. Panoramic view of Haligu Lake in January 2005

4 844 Climatic Change (2012) 113: Materials and methods 3.1 Core and lithology In January 2005, a sediment core 400 cm in length was obtained using a Russian corer which comprises a 40 cm long steel chamber (diameter 10 cm) and of 1 m long steel rods. The corer was pressed into the sediment and pulled up when reaching the desired depth. Coring was made in 40 cm overlapping steps (0 40 cm, cm, cm, etc.). To avoid contamination, the chamber was cleaned before a new round of coring starts. The core was documented in the field, and wrapped in plastic foil and placed in halved PVC tubes. The upper 120 cm of the core consists of black-brown clay; the lower 280 cm is interspersed with a few coarse sand laminae and pebbles. Sub-aerial exposure of the sediments is indicated by the presence of yellow clay layers at varying intervals (Fig. 2). 3.2 Pollen analysis Forty samples were extracted at 10 cm intervals for palynological investigation. In addition, five surface soil samples from the surrounding mountain area and three moss samples from the proximity of the core (Fig. 1) were collected for comparison with the fossil pollen assemblage. Fig. 2 Lithology of the Haligu core and depth-age curve showing the rate of sedimentation

5 Climatic Change (2012) 113: Thirty grams of each sample were treated by heavy liquid separation (Peck 1974; Moore and Webb 1978; Moore et al. 1991; Li and Du 1999) followed by acetolysis (Erdtman 1960). In order to calculate the pollen concentration, a tracer of Lycopodium spores was added to each sample at the beginning of treatment (Stockmarr 1971). Identification of spores and pollen was performed by comparison with modern pollen slides, palynological literature and monographs (IBCAS 1976; IBSCIBCAS 1982; Wang et al. 1995; Wei 2003; Fujiki et al. 2005). All samples from the core yielded abundant, well-preserved palynomorphs: more than 300 spores and pollen grains were counted in most samples using a Leica DM 2500 light microscope. The SEM studies of single pollen grain were undertaken using the model of SUPRA 55VP at Royal Botanic Garden Edinburgh. Spores and pollen grains were summed into four categories: tree and shrub, herb, pteridophyte and aquatic taxa. Pollen percentages and concentration calculations and pollen diagram plotting were carried out with Tilia and Tilia Graph (Grimm 1997). Taxa present at very low frequencies are not shown on the pollen diagram. However, it should be noted that future studies will focus more closely on these as potential indicators of species diversity within taxa and of anthropogenic impacts. 3.3 Radiocarbon dating Four AMS radiocarbon dates of humic acid from the sediments were obtained by the Scottish Universities Environmental Research Centre (SUERC) in Glasgow, Scotland. The 14 C age is quoted in conventional years BP (before 1950 AD). Bulk samples from the cores were used because fragments of plant material suitable for analysis were not present. Age calibration has been established using the calibration curve in Reimer et al by means of the OxCal v3.10 calibration programme (Bronk 2005). Date ranges are cited in calibrated years AD/BC at 95% probability with end points rounded out to 10 years (Mook 1986; Foster et al. 2008). The results of radiocarbon dating are presented in Table Climate analysis The Coexsitence Approach (CA) (Mosbrugger and Utescher 1997) was used to reconstruct the Holocene climate at Haligu. This method is appropriate for quantitative terrestrial climate reconstructions in the Cenozoic using plant fossils, including leaves, fruits and seeds, pollen and wood. Based on the assumption that the climatic tolerance of a fossil taxon is similar to that of its Nearest Living Relative (NLR), the aim of the CA is to find the climatic ranges in which a maximum number of NLRs of a given fossil flora can coexist. The coexistence interval is considered as the best estimate of the climatic conditions under which the past flora lived. The detailed procedure for obtaining the climatic tolerance of a NLR follows Yao et al. (2009). Table 1 Results of radiocarbon dating Lab. code Depth (cm) Materials δ 13 C (VPDB) 14 C yr BP Cal. yr BP Cal. yr AD/BC SUERC Humic acid ± AD SUERC Humic acid ± BC SUERC Humic acid ± BC SUERC Humic acid ± BC

6 846 Climatic Change (2012) 113: In this study, seven climatic parameters have been estimated for climate analysis, i.e. mean annual temperature (MAT), mean temperature of the warmest month (WMT), mean temperature of the coldest month (CMT), mean annual range of temperature between summer and winter (MART 0 WMT-CMT), mean annual precipitation (MAP), mean maximum monthly precipitation (MMaP) and mean minimum monthly precipitation (MMiP). 4 Results 4.1 Radiocarbon chronology Radiocarbon dates provide a reliable basis for establishing a chronological context for the observed changes in pollen stratigraphy and inferred vegetation development at Haligu during the Holocene. A depth-age curve was constructed for the Haligu core (Fig. 2). The model shows sediment-accumulation rates of c mm/year, 0.24 mm/year, 0.52 mm/year and 0.51 mm/year for the time intervals cal. yr BP, cal. yr BP, cal. yr BP, cal. yr BP, respectively. This shows that throughout the lower part of the core, from 8820 cal. yr BP until 5130 cal. yr BP, the rate of sediment accumulation was more or less constant but that it reduced considerably between 5130 cal. yr BP and 1330 cal. yr BP. 4.2 Pollen analysis Surface samples Thirty different palynomorphs were identified from five soil samples collected from the surrounding mountain, comprising 19 angiosperms, three gymnosperms and eight pteridophytes (Table 2). The pollen assemblage is dominated by trees and shrubs, which provide between 84.9% and 98.8% of the total pollen. Pinus pollen ( %) dominates in all five soil samples, followed by Abies ( %) and Quercus ( %). Herb pollen is present at low percentages ( %), and comprises Artemisia, other Compositae, Polygonaceae and Rubiaceae among others. Pteridophyte spores are particularly diverse and include examples from Athyriaceae, Gleicheniaceae, Gymnogrammaceae, Hymenophyllaceae, Ophioglossaceae, Polypodiaceae, Pteris and Sinopteridaceae. This pollen assemblage is consistent with the local vegetation of the lake basin and the surrounding mountains, reflecting a needleleaved forest dominated by Pinus and accompanied by some broad-leaved components, e.g. Quercus and Ericaceae. In total, 22 palynomorphs were recovered from the three moss samples, including 15 angiosperms, three gymnosperms and four pteridophytes (Table 2). In this assemblage, tree and shrub pollen accounts for 89.5% of sample HaM1, 80.7% of HaM2 and 83.2% of HaM3. Pinus pollen dominates in each sample with percentages 60.8%, 50.6% and 65%, respectively. Abies pollen reaches 22.4% in HaM1, and Alnus pollen reaches 20.5% in HaM2. Herb pollen ranges from 9.5% to 15.0% and is dominated by Artemisia, Cyperaceae and Polygonaceae. The percentage of fern spores is 0 1.8% and only four fern taxa were recorded: Pteris, Athyriaceae, Gymnogrammaceae and Polypodiaceae. This assemblage also reflects the dominance of needle-leaved trees (Pinus and Abies) and one broad-leaved taxon (Alnus) in the local vegetation.

7 Climatic Change (2012) 113: Table 2 List of palynomorphs recovered from the surface samples and Haligu core sediments Palynomorph taxa Surface samples Core sediments Soil Moss Algae Zygnema + Pteridophytes Ophioglossaceae + + Sinopteridaceae + + Hymenophyllaceae + + Athyriaceae Gymnogrammaceae Polypodiaceae Pteris Gleicheniaceae + Lygodiaceae + Loxogrammaceae + Cyatheaceae + Osmundaceae + Selaginellaceae + Gymnosperms Pinus Abies Tsuga Ephedra + Angiosperms Alnus Betula Quercus + + Castanea + Castanopsis + Carya + Corylus + + Tilia + Ulmus + Salix + Euphorbiaceae Malvaceae Anacardiaceae + + Oleaceae + + Aquifoliaceae + Ericaceae Araliaceae + Palmae + + Verbenaceae + + Pterocarya + Thymelaeaceae + + Juglandaceae + + Rosaceae + +

8 848 Climatic Change (2012) 113: Table 2 (continued) Palynomorph taxa Surface samples Core sediments Soil Moss Rubiaceae + Magnoliaceae + Combretaceae + Flacourtiaceae + Guttiferae + Hamamelidaceae + Leguminosae + Loganiaceae + Loranthaceae + Meliaceae + Myrsinaceae + Rhoipteleaceae + Rutaceae + Sapindaceae + Sterculiaceae + Theaceae + Piperaceae + Polygonaceae Lobeliaceae + Onagraceae + + Gesneriaceae + + Nepenthaceae + Capparidaceae + Caprifoliaceae + Chenopodiaceae + Acanthaceae + + Ranunculaceae + Cyperaceae + + Dipsacaceae + Gentianaceae + Compositae + + Artemisia Menispermaceae + Mimosaceae + + Melastomaceae + Amaranthaceae + Caryophyllaceae + Convolvulaceae + Cruciferae + Labiatae + Poaceae + Umbelliferae + Myriophyllum + Total : present

9 Climatic Change (2012) 113: Sediment core zonation, description and pollen diagram The pollen grains and spores extracted from the core samples showed a high degree of taxonomic diversity. The palynoflora consists of 78 palynomorphs, which can be assigned to 48 angiosperm families and 13 genera, four genera of gymnosperms, 11 families and one genus of pteridophytes and one genus of algae (Table 2). Some selected spores and pollen recovered from the Haligu core are shown in Figs. 3, 4, 5, and6. The pollen diagram was divided into Fig. 3 A selection of palynomorphs recovered from Haligu core sediments Pinus L Tsuga Carr Betula L Araliaceae (1, 2, 4, 5, 7, 8. Polar view; 10, 11. Equatorial view; 3, 6, 9, 12. Close-up of the exine ornamentation)

10 850 Climatic Change (2012) 113: Fig. 4 A selection of palynomorphs recovered from Haligu core sediments (continued) Magnoliaceae Alnus Mill Ericaceae Caryophyllaceae (19, 20. Polar view; 13, 14, 16, 17. Equatorial view; 15, 18, 21, 24. Close-up of the exine ornamentation) three distinct zones based primarily on significant changes in the pollen frequencies of the major taxa (Fig. 7). Brief descriptions of the three pollen zones are as follows. Pollen Zone 1: Pinus-Abies ( cm; 9300 to 8700 cal. yr BP) Pollen Zone 1 is characterized by a high percentage of tree and shrub pollen (90.2%), with Pinus being relatively dominant, reaching 57.8% and

11 Climatic Change (2012) 113: Fig. 5 A selection of palynomorphs recovered from Haligu core sediments (continued) Compositae Cyperaceae Polypodiaceae Zygnema (28, 29. Equatorial view; 27, 30, 33, 36. Close-up of the exine ornamentation) 19,400 grains/g, accompanied by significant percentages of Abies (23.9%) and Quercus (4.1%). Pollen of the tree genus Carya was also present in minute quantities, but was not present in the Pollen Zones 2 and 3. Herb

12 852 Climatic Change (2012) 113: Fig. 6 A selection of palynomorphs recovered from Haligu core sediments (continued). 37. Acanthaceae 38. Polygonaceae 39. Palmae 40. Anacardiaceae 41. Combretaceae 42. Carya Nutt. 43. Quercus L. 44. Poaceae 45. Piperaceae 46. Castanopsis Spach. 47. Melastomataceae 48. Umbelliferae 49. Pteris L. 50. Gymnogrammaceae 51. Hymenophyllaceae 52. Athyriaceae Scale bar 0 20 μm for 37 46; 0 10 μm for 47; 0 50 μm for Pollen Zone 2: pollen accounted for 9.6% and included Artemisia, other Compositae, Cyperaceae and Polygonaceae. Two taxa of pteridophytes were recorded, Athyriaceae (5.0%) and Polypodiaceae (1.9%). Aquatic plants were also present, but at a very low percentage (0.1%). Pinus Quercus Athyriaceae ( cm; 8700 to 2400 cal. yr BP) In this zone, the percentage of tree and shrub pollen showed a marked decrease, reaching the lowest value seen in the entire profile (67.2%) and reflecting a marked increase in Pteridophyte spores. Based on variations in

13 Climatic Change (2012) 113: Fig. 7 Pollen percentage and concentration diagram of Haligu sediment core, Yunnan Subzone 2a: Subzone 2b: Subzone 2c: Pollen Zone 3: the percentage and concentration of the main taxa (Abies, Pinus, Quercus, Athyriaceae and Polypodiaceae), three subzones were distinguished and are described below. Athyriaceae Quercus ( cm; 8700 to 7000 cal. yr BP) Pollen concentration decreased very sharply in this section of the core and most taxa display their lowest values for the entire pollen diagram. Tree pollen declined to 54.7%, with Pinus declining to 17.9% (280 grains/g) and Abies to 1.6% (the lowest percentage in the pollen zone). Quercus pollen climbed to 27.3%, the highest level in the pollen zone, but its concentration was 470 grains/g, the lowest value in the pollen diagram. The percentage of herbs (44.9%) increased markedly. The fern taxa Athyriaceae and Polypodiaceae spores reached 25.8% and 7.6%, respectively. Pinus Quercus ( cm; 7000 to 4000 cal. yr BP) In this subzone, tree and shrub pollen increased up to 74.7% and their concentration reached 7,440 grains/g. Pinus pollen increased to 33.2%, but its concentration remained relatively low (3,550 grains/g). Abies pollen reached 8.6%. Fagaceae pollen (mostly Quercus, 19.6%) fluctuated slightly, and its pollen concentration was 2,340 grains/g. In some slides, Acanthaceae, Anacardiaceae and Palmae pollen grains were recorded for the first time. Athyriaceae declined to 7.7% and Polypodiaceae was present at 8.3%. Quercus Polypodiaceae ( cm; 4000 to 2400 cal. yr BP) In this subzone, there was a sharp increase in the percentage of fern spores (up to 38.5%) with a major increase in Polypodiaceae (17.6%), Athyriaceae (8.4%) and Hymenophyllaceae (7.6%), but the concentration of spores was not high. Pinus pollen declined to 14.9%, with a concentration of 3,440 grains/g. Fagaceae pollen increased noticeably to 23.6% (with Quercus at 20.4% and a concentration of 2,040 grains/g). Araliaceae pollen appeared for the first time. Pinus Abies Tsuga (120 0 cm; 2400 cal. yr BP to present) In Zone 3 a sharp increase in tree and shrub pollen percentage and concentration (average 90.6% and 81,700 grains/g) was recorded, consisting

14 854 Climatic Change (2012) 113: mainly of Pinus (66.4%), Abies (11.4%) and Tsuga (7.1%). The concentration of Pinus was 57,800 grains/g, the highest value in the entire pollen diagram. The concentration of Quercus was 3,130 grains/g, higher than in the other zones. Pollen of some species representative of tropical and subtropical vegetation was encountered in this pollen zone, including Melastomataceae, Combretaceae, Myrsinaceae and Piperaceae, although only in small quantities. Herbs accounted for 8.7%, with the most abundant pollen type being Cyperaceae (5.2%). All spore percentages were very low in this zone, a marked contrast with Zone Climate analysis In total, 63 palynotaxa belonging to seed plants recovered from core samples are used in CA for climate analysis (Table 3). The coexistence intervals for each pollen zone and individual core sample are shown in Tables 4, 5 and Figs. 8, 9. From pollen zones 1 to 3, the mean value of MAT shows a decrease from 17 C to C, while the mean value of MAP sharply increases from mm in pollen zone 1 to mm of pollen zones 2 and 3 (Fig. 8). The curves of climate changes at Haligu based on the individual core sample show frequent fluctuations of temperature and precipitation during the past 9,300 years (Fig. 9). The MAT is characterized by a slightly decreasing trend, which coincides with the coexistence results for each pollen zone. Table 3 Palynotaxa used in CA for core samples together with their nearest living relatives (NLRs) No. Palynotaxa & NLRs No. Palynotaxa & NLRs No. Palynotaxa & NLRs 1 Pinus 22 Myriophyllum 43 Dipsacaceae 2 Abies 23 Myrsinaceae 44 Gentianaceae 3 Tsuga 24 Oleaceae 45 Labiatae 4 Ephedra 25 Palmae 46 Menispermaceae 5 Quercus 26 Pterocarya 47 Melastomaceae 6 Castanea 27 Rutaceae 48 Onagraceae 7 Castanopsis 28 Ranunculaceae 49 Leguminosae 8 Carya 29 Salix 50 Piperaceae 9 Acanthaceae 30 Sapindaceae 51 Poaceae 10 Alnus 31 Sterculiaceae 52 Polygonaceae 11 Corylus 32 Theaceae 53 Rosaceae 12 Anacardiaceae 33 Thymelaeaceae 54 Umbelliferae 13 Aquifoliaceae 34 Tilia 55 Malvaceae 14 Araliaceae 35 Ulmus 56 Meliaceae 15 Betula 36 Euphorbiaceae 57 Loranthaceae 16 Caprifoliaceae 37 Verbenaceae 58 Magnoliaceae 17 Combretaceae 38 Gesneriaceae 59 Compositae 18 Ericaceae 39 Amaranthaceae 60 Convolvulaceae 19 Flacourtiaceae 40 Artemisia 61 Cruciferae 20 Juglandaceae 41 Caryophyllaceae 62 Cyperaceae 21 Hamamelidaceae 42 Chenopodiaceae 63 Rhoipteleaceae

15 Climatic Change (2012) 113: Table 4 Coexistence intervals of each of the three pollen zones (Mean value in parentheses) Pollen zone MAT ( C) Cal. MAT ( C) WMT ( C) CMT ( C) MART ( C) MAP (mm) MMaP (mm) MMiP (mm) (13.65) (20.3) (6.1) (18.7) (1259.1) (258.65) 2 54 (28) (15.2) (22.6) (7.35) (18.7) (1259.1) (262.6) 2 54 (28) (17) (24.3) (5.8) ) (865.6) (204.8) (10.5)

16 856 Climatic Change (2012) 113: Table 5 Coexistence intervals for individual core sample (Mean value in parentheses) Sample No. Depth (cm) MAT ( C) Cal. MAT ( C) WMT ( C) CMT ( C) MART ( C) MAP (mm) MMaP (mm) MMiP (mm) (11.3) (19.65) (3.15) (22.65) ( ) (236.45) (34.7) (11.3) (19.65) (3.15) (22.65) ( ) (235.85) (27.6) (13.1) (19.65) (6.3) (18.15) (1257.1) (236.45) (34.9) (13.05) (20.25) (5.7) (18.7) (1259.1) (235.85) (35.1) (11.3) (19.3) (3.15) (22.65) ( ) (232.55) (34.15) (11.3) (19.65) (3.15) (22.65) ( ) (232.55) (34.15) (11.3) (19.3) (3.15) (22.65) ( ) (232.55) (34.15) (11.25) (20.25) (2.55) (23.2) ( ) (235.85) (34.7) (13.7) (20.25) (6.7) (18.15) ( ) (258.65) (27.6) (13.65) (20.25) (6.1) (18.7) ( ) (258.65) (27.6) (13.35) (20.25) (4.7) (18.7) ( ) (248.25) (34.7) (15.6) (22.6) (8.15) (18.15) ( ) (240.45) (27.45) (15.2) (22.6) (7.35) (18.15) (1257.1) (248.85) (34.9) (13.1) (19.65) (6.3) (18.15) ( ) (236.45) (34.7) (14.05) (21) (3.15) (22.65) ( ) (241.05) (34.7) (18.45) (25.55) (9.8) (16.45) ( ) (273.8) (33.35) (15.6) (22.6) (8.15) (18.15) ( ) (240.45) (27.6) (11.3) (19.65) (3.15) (22.65) ( ) (231.95) (27.05) (13.05) (20.25) (5.7) (18.7) (1259.1) (235.85) 2 54 (28) (11.3) (19.65) (3.25) (18.15) ( ) (235.85) (27.6) (13.1) (19.65) (6.3) (18.15) (1257.1) (235.85) (27.8) (15.6) (22.6) (8.15) (18.15) ( ) (240.45) (27.6) (14.15) (21.65) (5.5) (18.7) (1227.1) (250.35) (27.95) (15.55) (22.6) (7.55) (18.7) (1259.1) (258.65) 2 54 (28) (10.9) (19.65) (2.35) (22.65) (1109.4) (231.95) (27.2)

17 Climatic Change (2012) 113: Table 5 (continued) Sample No. Depth (cm) MAT ( C) Cal. MAT ( C) WMT ( C) CMT ( C) MART ( C) MAP (mm) MMaP (mm) MMiP (mm) (11.3) (19.65) (3.15) (22.65) ( ) (235.85) (27.6) (13.05) (20.25) (5.7) (18.7) (1257.1) (235.85) (34.9) (11.25) (20.25) (2.55) (23.2) ( ) (235.85) (27.6) (11.3) (19.65) (3.15) (22.65) ( ) (236.45) (34.7) (15.2) (22.6) (7.35) (18.15) (1259.1) (258.65) 2 54 (28) (11.3) (19.65) (3.15) (22.65) ( ) (235.85) (27.6) (15.55) (22.6) (7.55) (18.7) (1259.1) (240.45) 2 54 (28) (15.6) (22.6) (8.15) (18.15) ( ) (241.05) (34.7) (10.9) (19.65) (2.35) (22.65) (1109.4) (231.95) (27.2) (15.2) (22.95) (7.35) (18.7) (1259.1) (258.65) (35.1) (13.8) (21.65) (5.9) (18.15) (1259.1) (258.65) 2 54 (28) (11.3) (19.65) (2.6) (22.65) ( ) (235.85) (27.6) (13.1) (19.65) (6.3) (18.15) (1257.1) (236.45) (29.15) (13.1) (19.65) (6.3) (18.15) ( ) (235.85) (27.6) (17) (24.3) (5.8) (19.05) (865.6) (204.8) (10.5)

18 858 Climatic Change (2012) 113: Fig. 8 Coexistence intervals of each of the three pollen zones. 1: zone 1, 2: zone 2, 3: zone 3 In view of no climate record from Haligu (3,277 m a. s. l.), so we attempt to use the climate data from Lijiang meteorological station to make a calibration for the quantitative data of mean annual temperature (MAT) at Haligu. The MAT measured at Lijiang (2,200 m a. s. l.) is 12.8 C (Feng et al. 2006b), but Haligu is about 1,000 m higher than Lijiang. According to a C decrease in temperature for a 100 m increase, the present MAT of Haligu would be C (mean value 7.3 C). Although the estimated MAT for the first core sample (11.3 C) is quite close to the mean value of five surface soil samples (12.4 C) (Table 6), there exists a correction coefficient of about 4 C between the estimated MAT and the present one. So we attempt to calibrate the MAT values of each pollen zone and individual core sample by subtracting 4 C, and the calibrated MAT values are listed in Tables 4 and 5. 5 Discussion and conclusions 5.1 Holocene vegetation and climate history at Haligu Today Pinus is mainly distributed below 3,200 m a. s. l. elevation in SW China. Usually, it is found in slightly warm and moderately dry habitats. In the Lijiang Alpine Botanic Garden area surrounding Haligu, three species: Pinus armandii (Elevation: 2,600 3,200 m a. s. l.), P. densata (Elevation: 2,600 3,170 m a. s. l.) and P. yunnanensis (Elevation: 3,000 3,200 m a. s. l.) are recorded (Wang et al. 2007). Tsuga is a hygrophilous and Fig. 9 Climate changes at Haligu during the Holocene based on the coexistence analysis of individual core sample (Holocene optimum is marked by grey rectangle)

19 Climatic Change (2012) 113: Table 6 Coexistence intervals of first core sample and surface soil samples (Mean value in parentheses) MAT ( C) WMT ( C) CMT ( C) MART ( C) MAP (mm) MMaP (mm) MMiP (mm) First core sample (11.3) (19.65) (3.15) (22.65) ( ) (236.45) (34.7) Soil sample (11.3) (19.3) (3.15) (22.65) ( ) (232.55) (34.15) Soil sample (13.1) (19.65) (3.15) (22.65) ( ) (231.95) (27.25) Soil sample (10.9) (19.65) (2.35) (22.65) ( ) (235.85) (27.6) Soil sample (11.3) (19.65) (3.15) (22.65) ( ) (231.95) (27.05) Soil sample (15.6) (22.6) (8.15) (18.15) ( ) (241.05) (34.55)

20 860 Climatic Change (2012) 113: cold-tolerant taxon, which requires mean annual temperatures of 8.4 to 10.5 C and mean annual precipitation of about 1,000 mm in Yunnan (Writing Group of Yunnan Vegetation 1987). Abies is also a cold-tolerant taxon with mean annual temperature requirements of 2 to 8 C and the mean annual precipitation requirements of about 600 mm in the mountains of SW China (CCCV 1980; Jarvis 1993). Evergreen sclerophyllous Quercus displays considerable ecological adaptability, and can grow in either dry or humid environments. This genus is widely distributed in the fog zone (with higher humidity, at about 3,100 m a. s. l.) on the Jade Dragon Snow Mountain where it forms a montane needle- and broad-leaved mixed forest along with Tsuga and Picea (Writing Group of Yunnan Vegetation 1987). At our personal observation, some small Quercus trees are present up to about 3,800 m a. s. l.. Betula is typically regarded as a cold and drought-tolerant taxon. Four species, Betula utilis, B. calcicola, B. delavayi, B. platyphylla, and one subspecies, B. delavayi var. polyneura are recorded in the Lijiang Alpine Botanic Garden (Wang et al. 2007). Cyperaceae species commonly grow in wetlands and surrounding areas, including the open, high altitude meadows of the Jade Dragon Snow Mountain. The high frequency of Cyperaceae pollen may imply humid conditions (Sun et al. 2003). Myriophyllum is very common in the lakes, rivers and ponds of Yunnan within the water depth of 4 m (Writing Group of Yunnan Vegetation 1987). Based on the ecological preferences of major taxa as described above, the palynological record of the Haligu core sediments spanning the last 9,300 years reveals a detailed history of vegetation and climate variation in this region during the Holocene (Fig. 10d). From 9300 to 8700 cal. yr BP (pollen zone 1), the vegetation was dominated by needle-leaved forest (composed mainly of Abies and Pinus) on the surrounding mountains. Broad-leaved components included Quercus and Ericaceae present at low proportions of the pollen sum. A few herbaceous and pteridophytic taxa, represented by low values, grew around the immediate area or under the coniferous or broad-leaved trees. This pollen assemblage indicates a slightly cool and moderately humid climate during this period. The period between 8700 and 7000 cal. yr BP (pollen zone 2a) was marked by a notable increase in the proportion of Quercus pollen and Athyriaceae spores, and a sharp decrease in Pinus and Abies pollen Fig. 10 Comparison of Late Pleistocene and Holocene vegetation succession in NW Yunnan

21 Climatic Change (2012) 113: values. In addition, some new broad-leaved taxa and herbaceous taxa appeared for the first time at this stage. This pollen assemblage indicates that, at 3,277 m a. s. l. (the elevation of the Haligu core), evergreen broad-leaved forest became the predominant vegetation type instead of needle-leaved forest at that time. The floristic diversity during this period was the highest encountered in the whole profile. The temperature and precipitation are inferred to have risen throughout the period, suggested by the increases in Quercus and other woody plants, which imply a warm and humid climate. It is assumed that Pinus and Abies were still abundant on the mountain, but at higher elevations than the core site. During the period 7000 to 4000 cal. yr BP (pollen zone 2b), Pinus and Abies showed a sharp increase, while Quercus also maintained a high value in this stage. Thus it can be inferred that the vegetation changed from the evergreen broad-leaved forest of the preceding stage to a mixed needle-leaved and evergreen broad-leaved forest at this time. The climate of this period was likely to have been warm and moderately humid, but somewhat cooler than the preceding stage and displayed apparent fluctuations in both temperature and humidity. Between 4000 and 2400 cal. yr BP (pollen zone 2c) the proportion of Pinus reached a minimum for the entire profile (at the beginning of the stage), then maintained a trend of slight increase to the end of the stage. Quercus showed a decreasing trend throughout this period. The vegetation of this stage may be characterised as a transition from evergreen broad-leaved forest to needle-leaved forest, with coniferous trees beginning to increase. This pollen assemblage reflects a slightly warm and moderately humid climate. From 2400 cal. yr BP to the present day (pollen zone 3), the assemblage was characterized by a striking increase in the proportion of conifers and a distinct decrease in Quercus. Pinus pollen displayed its highest percentage during this period. Another notable feature of this stage is the disappearance of almost all pteridophytic elements. The vegetation was dominated by needle-leaved forest, with Pinus as the predominant contributor, accompanied by Abies and Tsuga, which reflects a slight cool and humid climate during this period. 5.2 Comparison with other sites close to Haligu in NW Yunnan During the past two decades, several palynological studies from the Late Quaternary Period are available from NW Yunnan (e.g. Lin et al. 1986; Jiang et al. 1998; Shen et al. 2006). The previous study sites, i.e. Erhai Lake, Xihu and Heqing Basin, are close to our study area and located within the same domain of semi-humid evergreen broad-leaved forest and Pinus yunnanensis forest of central and eastern Yunnan (Fig. 1). So it enables us to compare them with the present palynoassemblage. The location of the study sites and a comparison of the results are shown in Figs. 1 and 10, respectively. At Erhai Lake (1,974 m a. s. l.), Shen et al. (2006) examined the roles of climate change and human impact on the development of the catchment system since cal. yr BP (Fig. 10a). From to cal. yr BP, the vegetation was characterized by the dominance of Betula and deciduous Quercus forests, indicating a relatively cold and wet winter climate during this period. From to cal. yr BP, a remarkable feature of the vegetation was the expansion of Tsuga and evergreen broad-leaved trees (Cyclobalanopsis, Lithocarpus and Castanopsis), reflecting a warming climate. From to 8400 cal. yr BP, an increase in evergreen oaks and dry-tolerant species (e.g. Eomecon, Caragana) suggested a greater seasonality in rainfall. Between 8400 and 6370 cal. yr BP, the expansion of evergreen broad-leaved oaks forest and Tsuga forest reflected a warm and wet climate condition, which was attributed to the Holocene optimum at Erhai Lake. After 6370 cal. yr BP, especially from ca yr BP, the vegetation was disturbed by human activities (e.g. increased population immigration and the expansion of irrigation farming), indicated by a marked decline in arboreal

22 862 Climatic Change (2012) 113: taxa (e.g. Pinus) along with the increase in grass (e.g. Poaceae) and other disturbance taxa (e.g. Plantago, Chenopodiaceae). At Xihu, Eryuan (1,980 m a. s. l.), Lin et al. (1986) concluded that Pinus forests coupled with evergreen broad-leaved components (mainly Quercus) dominated all slopes since yr BP (Fig. 10b), indicating a subtropical monsoon climate, which is similar to the present condition. There had not been certain evidence of climatic change in this period. In Heqing Basin (2,200 m a. s. l.), Jiang et al. (1998) reconstructed the history of climatic and environmental changes in the past yr BP. Herein, the vegetation changes of Heqing Basin during the Holocene was shown in Fig. 10c. From to 8700 yr BP, the vegetation was dominated by conifer trees (mainly Abies, Picea and Pinus) and evergreen broad-leaved tree Quercus, indicating a slightly cold and wet climate. The phase between 8700 and 8200 yr BP is marked by the increase of Picea, Abies and evergreen Quercus and the decrease of Pinus, whichmayimplythe decline of temperature. From 8200 to 6000 yr BP, the vegetation was a needle- and broad-leaved mixed forest. This period was characterized by the sharp increase of pteridophytes and decrease of Picea, Abies and evergreen Quercus, reflecting a warm and dry condition. Between 6000 and 5600 yr BP, the increase of main components (e.g. Picea, Abies and evergreen Quercus) suggested the climate became cold and wet. During the period of 5600 to 3700 yr BP, the vegetation shifted to sparse forest and grassland, suggested by the sharp increase of Artemisia and Poaceae and decrease of conifer trees (e.g. Pinus, Abies and Picea) and evergreen broad-leaved tree (e.g. Quercus), indicating a warm and dry condition. From 3700 yr BP to present, the vegetation was dominated by Pinus forest along with evergreen Quercus, suggesting a cold and wet climate. At our study area, in pollen zone 1 ( cal. yr BP), the vegetation was dominated by needle-leaved forest (mainly Pinus and Abies), which corresponds to the slightly cold and wet condition as recorded in Heqing Basin between and 8700 yr BP. In pollen zone 2 ( cal. yr BP), it was a phase of evergreen Quercus, accompanied by abundant pteridophytes, which can be compared with the Holocene optimum recorded by the expansion of evergreen broad-leaved oaks forest and Tsuga forest at Erhai Lake between 8400 and 6370 cal. yr BP. In pollen zone 3 (2400 cal. yr BP to present), human activities may have impact on the local vegetation, leading to the increase of Pinus forest and decrease of Quercus tree at Haligu. Almost in the same period, the vegetation surrounding Erhai Lake was also disturbed by human activities since ca yr BP, causing a notable decline in arboreal taxa and increase in grass and other disturbance taxa. From pollen zones 1 to 2, the occurrence of abundant oak trees and pteridophytes in vegetation composition, together with the increasing of mean annual precipitation (MAP), mean maximum monthly precipitation (MMaP) and mean minimum monthly precipitation (MMiP) (Fig. 8), may reflect the strengthening of the summer monsoon and the weakening of the winter monsoon. From pollen zones 2 to 3, although the vegetation shows the decreasing of oak trees and pteridophytes, there need much more evidences to indicate the intensity change of the summer and winter monsoons. In summary, the patterns of Late Pleistocene and Holocene vegetation succession at Erhai Lake, Xihu, Heqing Basin and Haligu show different responses to the climate change and human activity. This may be attributed to different altitude and topography, causing different local climate. Moreover, human forcing may play an important role in the process of vegetation succession, e.g. it is notable at Erhai Lake.

23 Climatic Change (2012) 113: The Holocene optimum at Haligu The Holocene optimum has great significance, not only because it was an important recent climatic episode but also because it might serve as a valuable analogue for future climatic change (An et al. 2000; Xiao et al. 2004). There have been many definitions proposed for the Holocene optimum. Bates and Jackson (1987) defined it as the postglacial interval of most equable climate with warm temperatures and abundant rainfall. Shi and Kong (1992) treated it as the time of maximum Holocene warmth based on the preceding definition. Subsequently, Winkler and Wang (1993) and An et al. (2000) regarded the Holocene optimum as the time of maximum postglacial warmth and the time of peak Holocene monsoonal precipitation, respectively. However, the exact start and end dates of the Holocene optimum, and whether it was synchronous in different regions, have been the subject of much debate in China (An et al. 2000; He et al. 2004; Jung et al. 2004). Zhou et al. (2004, 2005) reported that a relatively warm and wet period occurred from to 6000 yr BP, based on studies of peaty sediments, Feng et al. (2005) concluded that a middle Holocene warm-humid period ranged from 9000 to C yr BP, from lacustrine and aeolian deposits on the Mongolian Plateau and Xiao et al. (2002) identified a warm phase between 7000 and 5500 yr BP in the desert/ loess transition of north-central China. Shen et al. (2006) pointed to the period of 8400 to 6370 cal. yr BP as the Holocene optimum dependent on the expansion of evergreen broadleaved oaks forest and Tsuga forest at Erhai, Northwest Yunnan. In the present study, as shown in Fig. 7, the pollen record from the Haligu core sediments indicates that the Holocene optimum, an episode marked by the expansion of evergreen Quercus, occurred in this region from 8700 to 2400 cal. yr BP. 5.4 Evidence of anthropogenic influences Whereas human influence on postglacial vegetation has been interpreted from palynological and other evidence in some detail for Europe and North America (e.g. Brugam 1978; Hirons and Edwards 1986; Smith and Cloutman 1988; Russell et al. 1993; Parker et al. 2002), a few studies regarding this aspect are available in China (e.g. An et al. 2002; He et al. 2002;Xuet al. 2002). In the Haligu core, several observations reported here may be interpreted in terms of increasing anthropogenic impact in the region. For example, in the period from 2400 cal. yr BP to the present day, evergreen Quercus pollen decreases steadily in the core. Whilst we cannot yet establish it with absolute certainty, this may be correlated with increased human settlement in the region, especially by the Naxi ethnic minority who are still the dominant people of the Jade Dragon Snow Mountain. The Naxi people today use large Quercus trees in construction, although such trees are now very rare in accessible parts of the mountain. However, they and other local people of the Yi ethnic minority, make heavy use of coppiced Quercus branches for fuelwood. Not only does this practice prevent Quercus trees from growing to mature size, it also greatly reduces the likelihood of flowering and therefore pollen production. In the forests around the study site, Quercus aquifolioides is one of the most abundant trees, but it is present in a heavily coppiced form, forming an understorey below Pinus yunnanensis. Thus the reduction in Quercus pollen observed from 2400 cal. yr BP to the present may be indicative of increasing human coppicing during this time. We hope, in the future, to be able to substantiate this idea by making comparisons with cores from areas elsewhere on the Jade Dragon Snow Mountain, more remote from human settlement were coppicing is not carried out.

24 864 Climatic Change (2012) 113: Acknowledgements The authors thank Prof. Nai-Qiu Du from the Institute of Botany, Chinese Academy of Sciences for her help with this study. We also wish to thank Dr. Ming-Mei Liang for assisting in a preliminary investigation of the potential of this study site, the staff of the Jade Dragon Field Station, especially David Paterson, for logistical support, and Frieda Christie for her guidance of SEM study. This study was supported by the National Basic Research Program of China (No. 2004CB070205), National Natural Science Foundation of China (No ), joint funding from the National Natural Science Foundation of China and Royal Society (No ), Science-Technology Foundation for Young Scientist of Shanxi Province (No ), Special founding for the Talents Introduction and Development of Shanxi Province, Scientific Research Staring Foundation for the Doctor and Postdoctoral Science Foundation of Shanxi Agricultural University. References An ZS, Porter SC, Kutzbach JE, Wu XH, Wang SM, Liu XD, Li XQ, Zhou WJ (2000) Asynchronous Holocene optimum of the East Asian monsoon. Quat Sci Rev 19: An CB, Chen FH, Feng ZD (2002) Study on the relationship between the vegetation change and the human activities in the Gangsu-Qinghai region during the period from mid- to late-holocene. Arid Land Geogr 25(2): (in Chinese with English abstract) Antόn MG, Romera GG, Pagés JL, Millán AA (2006) The Holocene pollen record in the Villaviciosa Estuary (Asturias, North Spain). Paleogeogr Paleoclimatol Paleoecol 237: Bates RL, Jackson JA (1987) Glossary of geology. American Geological Institute, Alexandria Birks HJB, Birks HH (1980) Quaternary palaeoecology. Edward Arnold, London Brncic TM, Willis KJ, Harris DJ, Washington R (2007) Culture or climate? The relative influences of past processes on the composition of the lowland Congo rainforest. Philos Trans R Soc London, Ser B Biol Sci 362: Bronk R (2005) OxCal Program v3.10. University of Oxford Radiocarbon Accelerator Unit Brown KJ, Hebda RJ (2003) Coastal rainforest connections disclosed through a Late Quaternary vegetation, climate, and fire history investigation from the Mountain Hemlock Zone on southern Vancouver Island, British Columbia, Canada. Rev Palaeobot Palynology 123: Brugam RB (1978) Pollen indicators of land-use change in southern Connecticut. Quat Res 9(3): CCCV (Compilation Committee of Chinese Vegetation) (1980) Vegetation of China. Science Press, Beijing (in Chinese) Dam RAC, Fluin J, Suparan P, van der Kaars S (2001) Palaeoenvironmental developments in the Lake Tondano area (N. Sulawesi, Indonesia) since yr BP. Paleogeogr Paleoclimatol Paleoecol 171:3 4 Erdtman G (1960) The acetolysis method. Svensk Botanisk Tidskrift 54: Feng ZD, Wang WG, Guo LL, Khosbayar P, Narantsetseg T, Jull AJT, An CB, Li XQ, Zhang HC, Ma YZ (2005) Lacustrine and eolian records of Holocene climate changes in the Mongolian Plateau: preliminary results. Quat Int 136(1):25 32 Feng ZD, Tang LY, Wang HB, Ma YZ, Liu KB (2006a) Holocene vegetation variations and the associated environmental changes in the western part of the Chinese Loess Plateau. Paleogeogr Paleoclimatol Paleoecol 241: Feng JM, Wang XP, Xu CD, Yang YH, Fang JY (2006b) Altitudinal patterns of plant species diversity and community structure on Yulong Mountains, Yunnan, China. J Mount Sci 24(1): (in Chinese with English abstract) Foster GC, Chiverrell RC, Harvey AM, Dearing JA, Dunsford H (2008) Catchment hydro-geomorphological responses to environmental change in the Southern Uplands of Scotland. Holocene 18: Fujiki T, Zhou ZK, Yasuda Y (2005) Asian environmental history 1-The pollen flora of Yunnan, China (Vol. 1). Lustre Press/Roli Books, New Delhi Gonzalez-Samperiz P, Valero-Garces BL, Moreno A, Morellon M, Navas A, Machin J, Delgado-Huertas A (2008) Vegetation changes and hydrological fluctuations in the Central Ebro Basin (NE Spain) since the Late Glacial period: Saline lake records. Paleogeogr Paleoclimatol Paleoecol 259: Grimm E (1997) TILIA version Illinois State Museum, Springfield He XB, Tang KL, Tian JL, Matthews JA (2002) Paleopedological investigation of three agricultural loess soils on the Loess Plateau of China. Soil Sci 167: He Y, Theakstone WH, Zhang Z, Zhang D, Yao T, Chen T, Shen Y, Pang H (2004) Asynchronous Holocene climatic change across China. Quat Sci Rev 61:52 63 Hirons KR, Edwards KJ (1986) Events at and around the first and second Ulmus declines: palaeoecological investigations in Co. Tyrone, Northern Ireland. New Phytol 104: