Palaeovegetation of China: a pollen data-based synthesis for the mid-Holocene and last glacial maximum

Pollen data from China for 6000 and 18,000 ¹⁴C yr bp were compiled and used to reconstruct palaeovegetation patterns, using complete taxon lists where possible and a biomization procedure that entailed the assignment of 645 pollen taxa to plant functional types. A set of 658 modern pollen samples spanning all biomes and regions provided a comprehensive test for this procedure and showed convincing agreement between reconstructed biomes and present natural vegetation types, both geographically and in terms of the elevation gradients in mountain regions of north‐eastern and south‐western China. The 6000 ¹⁴C yr bp map confirms earlier studies in showing that the forest biomes in eastern China were systematically shifted northwards and extended westwards during the mid‐Holocene. Tropical rain forest occurred on mainland China at sites characterized today by either tropical seasonal or broadleaved evergreen/warm mixed forest. Broadleaved evergreen/warm mixed forest occurred further north than today, and at higher elevation sites within the modern latitudinal range of this biome. The northern limit of temperate deciduous forest was shifted c. 800 km north relative to today. The 18,000 ¹⁴C yr bp map shows that steppe and even desert vegetation extended to the modern coast of eastern China at the last glacial maximum, replacing today’s temperate deciduous forest. Tropical forests were excluded from China and broadleaved evergreen/warm mixed forest had retreated to tropical latitudes, while taiga extended southwards to c. 43°N.     

Last glacial maximum biomes reconstructed from pollen and plant macrofossil data from northern Eurasia

Pollen and plant macrofossil data from northern Eurasia were used to reconstruct the vegetation of the last glacial maximum (LGM: 18,000 ± 2000 ¹⁴C yr bp ) using an objective quantitative method for interpreting pollen data in terms of the biomes they represent ( Prentice et al., 1996 ). The results confirm previous qualitative vegetation reconstructions at the LGM but provide a more comprehensive analysis of the data. Tundra dominated a large area of northern Eurasia (north of 57°N) to the west, south and east of the Scandinavian ice sheet at the LGM. Steppe‐like vegetation was reconstructed in the latitudinal band from western Ukraine, where temperate deciduous forests grow today, to western Siberia, where taiga and cold deciduous forests grow today. The reconstruction shows that steppe graded into tundra in Siberia, which is not the case today. Taiga grew on the northern coast of the Sea of Azov, about 1500 km south of its present limit in European Russia. In contrast, taiga was reconstructed only slightly south of its southern limit today in south‐western Siberia. Broadleaved trees were confined to small refuges, e.g. on the eastern coast of the Black Sea, where cool mixed forest was reconstructed from the LGM data. Cool conifer forests in western Georgia were reconstructed as growing more than 1000 m lower than they grow today. The few scattered sites with LGM data from the Tien‐Shan Mountains and from northern Mongolia yielded biome reconstructions of steppe and taiga, which are the biomes growing there today.     

Biomes of western North America at 18,000, 6000 and 0 14C yr bp reconstructed from pollen and packrat midden data

A new compilation of pollen and packrat midden data from western North America provides a refined reconstruction of the composition and distribution of biomes in western North America for today and for 6000 and 18,000 radiocarbon years before present (¹⁴C yr bp ). Modern biomes in western North America are adequately portrayed by pollen assemblages from lakes and bogs. Forest biomes in western North America share many taxa in their pollen spectra and it can be difficult to discriminate among these biomes. Plant macrofossils from packrat middens provide reliable identification of modern biomes from arid and semiarid regions, and this may also be true in similar environments in other parts of the world. However, a weighting factor for trees and shrubs must be used to reliably reconstruct modern biomes from plant macrofossils. A new biome, open conifer woodland, which includes eurythermic conifers and steppe plants, was defined to categorize much of the current and past vegetation of the semiarid interior of western North America. At 6000 ¹⁴C yr bp , the forest biomes of the coastal Pacific North‐west and the desert biomes of the South‐west were in near‐modern positions. Biomes in the interior Pacific North‐west differed from those of today in that taiga prevailed in modern cool/cold mixed forests. Steppe was present in areas occupied today by open conifer woodland in the northern Great Basin, while in the central and southern Rocky Mountains forests grew where steppe grows today. During the mid‐Holocene, cool conifer forests were expanded in the Rocky Mountains (relative to today) but contracted in the Sierra Nevada. These differences from the forests of today imply different climatic histories in these two regions between 6000 ¹⁴C yr bp and today. At 18,000 ¹⁴C yr bp , deserts were absent from the South‐west and the coverage of open conifer woodland was greatly expanded relative to today. Steppe and tundra were present in much of the region now covered by forests in the Pacific North‐west.     

Pollen-based reconstructions of Japanese biomes at 0, 6000 and 18,000 14C yr bp

A biomization method, which objectively assigns individual pollen assemblages to biomes ( Prentice et al., 1996 ), was tested using modern pollen data from Japan and applied to fossil pollen data to reconstruct palaeovegetation patterns 6000 and 18,000 ¹⁴C yr bp Biomization started with the assignment of 135 pollen taxa to plant functional types (PFTs), and nine possible biomes were defined by specific combinations of PFTs. Biomes were correctly assigned to 54% of the 94 modern sites. Incorrect assignments occur near the altitudinal limits of individual biomes, where pollen transport from lower altitudes blurs the local pollen signals or continuous changes in species composition characterizes the range limits of biomes. As a result, the reconstructed changes in the altitudinal limits of biomes at 6000 and 18,000 ¹⁴C yr bp are likely to be conservative estimates of the actual changes. The biome distribution at 6000 ¹⁴C yr bp was rather similar to today, suggesting that changes in the bioclimate of Japan have been small since the mid‐Holocene. At 18,000 ¹⁴C yr bp the Japanese lowlands were covered by taiga and cool mixed forests. The southward expansion of these forests and the absence of broadleaved evergreen/warm mixed forests reflect a pronounced year‐round cooling.     

Late Quaternary biomes of Canada and the eastern United States

Pollen data have been used to construct biome maps for today, 6000 ¹⁴C yr bp and 18,000 ¹⁴C yr bp for Canada and the eastern United States. The inferred modern biome distributions agree well with independent reconstructions of North American vegetation prior to European settlement. Some discrepancies between the pollen data and the modern potential vegetation are caused by post‐settlement clearing of the landscape and the consequent increase of herbaceous types in the recent pollen record. Biome distributions at 6000 ¹⁴C yr bp reflected the warmer and drier conditions then prevalent in the continental interior, but the overall position of biomes was similar to that of today. The boreal treeline in North America was not significantly north of its present position, in contrast to the 100–200 km shift reported for Siberia. At the last glacial maximum (18,000 ¹⁴C yr bp ), steppe and tundra were prevalent in the Midwest and north‐western Canada, and coniferous forests and woodlands grew in eastern North America. The open vegetation at 18,000 ¹⁴C yr bp was probably due to drier conditions and/or lower concentrations of atmospheric CO₂. The composition and physical structure of biomes is not constant over time. Mid‐Holocene biomes were similar in structure to those of today, but shifts in the relative importance of individual plant functional types are large enough that the physical properties of biomes, such as albedo, canopy conductance and surface roughness, are likely to have varied even during the Holocene. Last glacial maximum biomes were structurally different from their modern counterparts. The biome maps therefore may obscure significant vegetational changes in space and time during the late Quaternary. The difference between the highest and next highest affinity scores for each sample measures how strongly affinity scores discriminate among biomes. For many biomes, the difference is not large, and affinity score ties are not uncommon, highlighting the importance of tie‐break procedures when using the biomization method.     

Pollen-based biome reconstruction for southern Europe and Africa 18,000 yr bp

Pollen data from 18,000 ¹⁴C yr bp were compiled in order to reconstruct biome distributions at the last glacial maximum in southern Europe and Africa. Biome reconstructions were made using the objective biomization method applied to pollen counts using a complete list of dryland taxa wherever possible. Consistent and major differences from present‐day biomes are shown. Forest and xerophytic woods/scrub were replaced by steppe, both in the Mediterranean region and in southern Africa, except in south‐western Cape Province where fynbos (xerophytic scrub) persisted. Sites in the tropical highlands, characterized today by evergreen forest, were dominated by steppe and/or xerophytic vegetation (cf. today’s Ericaceous belt and Afroalpine grassland) at the last glacial maximum. Available data from the tropical lowlands are sparse but suggest that the modern tropical rain forest was largely replaced by tropical seasonal forest while the modern seasonal or dry forests were encroached on by savanna or steppe. Montane forest elements descended to lower elevations than today.     

Pollen-based reconstructions of biome distributions for Australia, Southeast Asia and the Pacific (SEAPAC region) at 0, 6000 and 18,000 14C yr BP

Aim This paper documents reconstructions of the vegetation patterns in Australia, Southeast Asia and the Pacific (SEAPAC region) in the mid‐Holocene and at the last glacial maximum (LGM). Methods Vegetation patterns were reconstructed from pollen data using an objective biomization scheme based on plant functional types. The biomization scheme was first tested using 535 modern pollen samples from 377 sites, and then applied unchanged to fossil pollen samples dating to 6000 ± 500 or 18,000 ± 1000 ¹⁴C yr bp . Results 1. Tests using surface pollen sample sites showed that the biomization scheme is capable of reproducing the modern broad‐scale patterns of vegetation distribution. The north–south gradient in temperature, reflected in transitions from cool evergreen needleleaf forest in the extreme south through temperate rain forest or wet sclerophyll forest (WSFW) and into tropical forests, is well reconstructed. The transitions from xerophytic through sclerophyll woodlands and open forests to closed‐canopy forests, which reflect the gradient in plant available moisture from the continental interior towards the coast, are reconstructed with less geographical precision but nevertheless the broad‐scale pattern emerges. 2. Differences between the modern and mid‐Holocene vegetation patterns in mainland Australia are comparatively small and reflect changes in moisture availability rather than temperature. In south‐eastern Australia some sites show a shift towards more moisture‐stressed vegetation in the mid‐Holocene with xerophytic woods/scrub and temperate sclerophyll woodland and shrubland at sites characterized today by WSFW or warm‐temperate rain forest (WTRF). However, sites in the Snowy Mountains, on the Southern Tablelands and east of the Great Dividing Range have more moisture‐demanding vegetation in the mid‐Holocene than today. South‐western Australia was slightly drier than today. The single site in north‐western Australia also shows conditions drier than today in the mid‐Holocene. Changes in the tropics are also comparatively small, but the presence of WTRF and tropical deciduous broadleaf forest and woodland in the mid‐Holocene, in sites occupied today by cool‐temperate rain forest, indicate warmer conditions. 3. Expansion of xerophytic vegetation in the south and tropical deciduous broadleaf forest and woodland in the north indicate drier conditions across mainland Australia at the LGM. None of these changes are informative about the degree of cooling. However the evidence from the tropics, showing lowering of the treeline and forest belts, indicates that conditions were between 1 and 9 °C (depending on elevation) colder. The encroachment of tropical deciduous broadleaf forest and woodland into lowland evergreen broadleaf forest implies greater aridity. Main conclusions This study provides the first continental‐scale reconstruction of mid‐Holocene and LGM vegetation patterns from Australia, Southeast Asia and the Pacific (SEAPAC region) using an objective biomization scheme. These data will provide a benchmark for evaluation of palaeoclimate simulations within the framework of the Palaeoclimate Modelling Intercomparison Project.     

Modelling the vegetation of China using the process-based equilibrium terrestrial biosphere model BIOME3

1 We model the potential vegetation and annual net primary production (NPP) of China on a 10′ grid under the present climate using the processed‐based equilibrium terrestrial biosphere model BIOME3. The simulated distribution of the vegetation was in general in good agreement with the potential natural vegetation based on a numerical comparison between the two maps using the ΔV statistic (ΔV = 0.23). Predicted and measured NPP were also similar, especially in terms of biome‐averages. 2 A coupled ocean–atmosphere general circulation model including sulphate aerosols was used to drive a double greenhouse gas scenario for 2070–2099. Simulated vegetation maps from two different CO₂ scenarios (340 and 500 p.p.m.v.) were compared to the baseline biome map using ΔV. Climate change alone produced a large reduction in desert, alpine tundra and ice/polar desert, and a general pole‐ward shift of the boreal, temperate deciduous, warm–temperate evergreen and tropical forest belts, a decline in boreal deciduous forest and the appearance of tropical deciduous forest. The inclusion of CO₂ physiological effects led to a marked decrease in moist savannas and desert, a general decrease for grasslands and steppe, and disappearance of xeric woodland/scrub. Temperate deciduous broadleaved forest, however, shifted north to occupy nearly half the area of previously temperate mixed forest. 3 The impact of climate change and increasing CO₂ is not only on biogeography, but also on potential NPP. The NPP values for most of the biomes in the scenarios with CO₂ set at 340 p.p.m.v. and 500 p.p.m.v. are greater than those under the current climate, except for the temperate deciduous forest, temperate evergreen broadleaved forest, tropical rain forest, tropical seasonal forest, and xeric woodland/scrub biomes. Total vegetation and total carbon is simulated to increase significantly in the future climate scenario, both with and without the CO₂ direct physiological effect. 4 Our results show that the global process‐based equilibrium terrestrial biosphere model BIOME3 can be used successfully at a regional scale.     

利用孢粉记录定量重建大尺度古植被格局

 古植被定量重建是过去全球变化研究的重点之一, 生物群区化(Biomisation)方法以特征植物功能型来定义生物群区, 通过一种标准化数量方法计算孢粉谱的相似得分, 以此把孢粉谱转变为生物群区类型, 是进行古植被定量重建的一种有效方法。该文在前人综述文章的基础上, 简述了生物群区化方法定量重建古植被格局的发展历史、具体步骤及存在问题, 重点描述了以此方法为基础重建的全新世中期(MH)和末次盛冰期(LGM)的全球古植被分布格局, 以及中国的古植被定量重建工作和古植被格局变化。目前的研究表明, 全新世中期北极森林界线在某些地区有轻微的北移迹象, 北部的温带森林带通常向北远距离迁移, 欧洲的温带落叶林也大范围向地中海地区(向南)和向北扩展, 在北美内陆, 草原侵入到森林生物群区, 但中亚地区却没有此现象, 中国大陆的森林生物群区扩张, 典型撒哈尔植被(如干草原、干旱疏林灌丛和热带干旱森林)进入撒哈拉地区, 而非洲热带雨林却呈减少趋势; 末次盛冰期苔原和草原扩张, 在欧亚大陆北部逐渐混合, 北半球的森林生物群区向南迁移, 北方常绿森林(泰加林)和温带落叶林呈碎片状, 而欧洲和东亚的草原却大范围扩张, 非洲的热带湿润森林(比如热带雨林和热带季雨林)有所减少, 在北美洲的西南地区, 荒漠和草原被开阔针叶疏林所取代。     

Climate and CO2 controls on global vegetation distribution at the last glacial maximum: analysis based on palaeovegetation data, biome modelling and palaeoclimate simulations

The global vegetation response to climate and atmospheric CO₂ changes between the last glacial maximum and recent times is examined using an equilibrium vegetation model (BIOME4), driven by output from 17 climate simulations from the Palaeoclimate Modelling Intercomparison Project. Features common to all of the simulations include expansion of treeless vegetation in high northern latitudes; southward displacement and fragmentation of boreal and temperate forests; and expansion of drought‐tolerant biomes in the tropics. These features are broadly consistent with pollen‐based reconstructions of vegetation distribution at the last glacial maximum. Glacial vegetation in high latitudes reflects cold and dry conditions due to the low CO₂ concentration and the presence of large continental ice sheets. The extent of drought‐tolerant vegetation in tropical and subtropical latitudes reflects a generally drier low‐latitude climate. Comparisons of the observations with BIOME4 simulations, with and without consideration of the direct physiological effect of CO₂ concentration on C₃ photosynthesis, suggest an important additional role of low CO₂ concentration in restricting the extent of forests, especially in the tropics. Global forest cover was overestimated by all models when climate change alone was used to drive BIOME4, and estimated more accurately when physiological effects of CO₂ concentration were included. This result suggests that both CO₂ effects and climate effects were important in determining glacial‐interglacial changes in vegetation. More realistic simulations of glacial vegetation and climate will need to take into account the feedback effects of these structural and physiological changes on the climate.     

A new global biome reconstruction and data-model comparison for the Middle Pliocene

Aim To produce a robust, comprehensive global biome reconstruction for the Middle Pliocene (c. 3.6–2.6 Ma), which is based on an internally consistent palaeobotanical data set and a state‐of‐the‐art coupled climate–vegetation model. The reconstruction gives a more rigorous picture of climate and environmental change during the Middle Pliocene and provides a new boundary condition for future general circulation model (GCM) studies. Location Global. Methods Compilation of Middle Pliocene vegetation data from 202 marine and terrestrial sites into the comprehensive GIS data base TEVIS (Tertiary Environmental Information System). Translation into an internally consistent classification scheme using 28 biomes. Comparison and synthesis of vegetation reconstruction from palaeodata with the outputs of the mechanistically based BIOME4 model forced by climatology derived from the HadAM3 GCM. Results The model results compare favourably with available palaeodata and highlight the importance of employing vegetation–climate feedbacks and the anomaly method in biome models. Both the vegetation reconstruction from palaeobotanical data and the BIOME4 prediction indicate a general warmer and moister climate for the Middle Pliocene. Evergreen taiga as well as temperate forest and grassland shifted northward, resulting in much reduced tundra vegetation. Warm‐temperate forests (with subtropical taxa) spread in mid and eastern Europe and tropical savannas and woodland expanded in Africa and Australia at the expense of deserts. Discrepancies which occurred between data reconstruction and model simulation can be related to: (1) poor spatial model resolution and data coverage; (2) uncertainties in delimiting biomes using climate parameters; or (3) uncertainties in model physics and/or geological boundary conditions. Main conclusions The new global biome reconstruction combines vegetation reconstruction from palaeobotanical proxies with model simulations. It is an important contribution to the further understanding of climate and vegetation changes during the Middle Pliocene warm interval and will enhance our knowledge about how vegetation may change in the future.     

Sensitivity of African biomes to changes in the precipitation regime

Aim Africa is identified by the Inter‐governmental Panel on Climate Change (IPCC) as the least studied continent in terms of ecosystem dynamics and climate variability. The aim of this study was (1) to adapt the Lund‐Postdam‐Jena‐GUESS (LPJ‐GUESS) ecological modelling framework to Africa by providing new parameter values for tropical plant functional types (PFT), and (2) to assess the sensitivity of some African biomes to changes in precipitation regime. Location The study area was a representative transect (0–22° N and 7–18° E) through the transition from equatorial evergreen forests to savannas, steppes and desert northwards. The transect showed large latitudinal variation in precipitation (mean rainfall ranged from 50 to 2300 mm year^?1). Methods New PFT parameters used to calibrate LPJ‐GUESS were based on modern pollen PFTs and remote sensed leaf area index (LAI). The model was validated using independent modern pollen assemblages, LAI and through comparison with White's modern potential vegetation map. Several scenarios were developed by combining changes in total rainfall amount with variation in the length of the dry season in order to test the sensitivity of African biomes. Results Simulated vegetation compared well to observed data at local and regional scales, in terms of ecosystem functioning (LAI), and composition (pollen and White's vegetation map). The assessment of the sensitivity of biomes to changes in precipitation showed that none of the ecosystems would shift towards a new type under the range of precipitation increases suggested by the IPCC (increases from 5 to 20%). However, deciduous and semi‐deciduous forests may be very sensitive to small reductions in both the amount and seasonality of precipitation. Main conclusions This version of LPJ‐GUESS parameterized for Africa simulated correctly the vegetation present over a wide precipitation gradient. The biome sensitivity assessment showed that, compared with savannas and grasslands, closed canopy forests may be more sensitive to change in precipitation regime due to the synergetic effects of changed rainfall amounts and seasonality on vegetation functioning.     

A biome classification of China based on plant functional types and the BIOME3 model

A biome classification for China was established based on plant functional types (PFTs) using the BIOME3 model to include 16 biomes. In the eastern part of China, the PFTs of trees determine mostly the physiognomy of landscape. Biomes range from boreal deciduous coniferous forest/woodland, boreal mixed forest/woodland, temperate mixed forest, temperate broad-leaved deciduous forest, warm-temperate broad-leaved evergreen/mixed forest, warm-temperate/cool-temperate evergreen coniferous forest, xeric woodland/scrub, to tropical seasonal and rain forest, and tropical deciduous forest from north to south. In the northern and western part of China, grass is the dominant PFT. From northeast to west and southwest the biomes range from moist savannas, tall grassland, short grassland, dry savannas, arid shrubland/steppe, desert, to alpine tundra/ice/polar desert. Comparisons between the classification introduced here and the four classifications which were established over the past two decades, i.e. the vegetation classification, the vegetation division, the physical ecoregion, and the initial biome classification have showed that the different aims of biome classifications have resulted in different biome schemes each with its own unique characteristics and disadvantages for global change study. The new biome classification relies not only on climatic variables, but also on soil factor, vegetation functional variables, ecophysiological parameters and competition among the PFTs. It is a comprehensive classification that using multivariables better expresses the vegetation distribution and can be compared with world biome classifications. It can be easily used in the response study of Chinese biomes to global change, regionally and globally.     

Pollen-based biome reconstructions for China at 0 and 6000 years

Biomization provides an objective and robust method of assigning pollen spectra to biomes so that pollen data can be mapped and compared directly with the output of biomgeographic models. We have tested the applicability of this procedure, originally developed for Europe, to assign modern surface samples from China to biomes. The procedure successfully delineated the major vegetation types of China. When the same procedure was applied to fossil pollen samples for 6000 years ago, the reconstructions showed systematic differences from present, consistent with previous interpretations of vegetation changes since the mid-Holocene. In eastern China, the forest zones were systematically shifted northwards, such that cool mixed forests displaced taiga in northeastern China, while broad-leaved evergreen forest extended c. 300 km and temperate deciduous forestc. 500–600 km beyond their present northern limits. In northwestern China, the area of desert and steppe vegetation was reduced compared to present. On the Tibetan Plateau, forest vegetation extended to higher elevations than today and the area of tundra was reduced. These shifts in biome distributions imply significant changes in climate since 6000 years ago that can be interpreted qualitatively as a response to orbital forcing and its secondary effects on the Asian monsoon.     

Short-term climate and vegetation dynamics in Lena River Delta (northern Yakutia,Eastern Siberia) during early Eocene

Early Eocene climate and vegetation evolution in northern Yakutia (Eastern Siberia) are quantitatively studied for the first time based on paleobotanical records, using the coexistence approach (CA) for paleoclimate, the plant functional type approach (PFT) and the integrated plant record method (IPR). Paleobotanical data of this time-interval were obtained from 18 palynofloras of the coal beds outcropping on the bank of the Bykovskaya Channel in the area of Bulunkan Bay (Lena River Delta). The results indicate the persistence of warm temperate and at times possibly nearly tropical, overall humid climate conditions throughout the early Eocene, and a relatively strong seasonality in precipitation. The vegetation reconstructed is in agreement with the climate conditions determined by the CA. Analyses of the PFT diversity spectra indicate the prevalence of mixed warm temperate evergreen-deciduous forests. Based on the IPR method, plant biomes varied from mixed mesophytic forests during warmer intervals to broadleaved deciduous forest/mixed mesophytic forest ecotone during cooler episodes. The presence of mangroves in our early Eocene records is possibly related to hyperthermal events such as the Paleocene–Eocene Thermal Maximum.     

Net primary production, carbon storage and climate change in Chinese biomes

Net primary production (NPP) and leaf area index (LAI) of Chinese biomes were simulated by BIOME3 under the present climate, and their responses to climate change and doubled CO₂ under a future climatic scenario using output from Hadley Center coupled ocean‐atmosphere general circulation model with CO₂ modelled at 340 and 500 ppmv. The model estimated annual mean NPP of the biomes in China to be between 0 and 1270.7 gC m^‐2 yr^‐1 at present. The highest productivity was found in tropical seasonal and rain forests while temperate forests had an intermediate NPP, which is higher than a lower NPP of temperate savannas, grasslands and steppes. The lowest NPP occurred in desert, alpine tundra and ice/polar desert in cold or arid regions, especially on the Tibetan Plateau. The lowest monthly NPP of each biome occurred generally in February and the highest monthly NPP occurred during the summer (June to August). The annual mean NPP and LAI of most of biomes at changed climate with CO₂ at 340 and 500 ppmv (direct effects on physiology) would be greater than present. The direct effects of carbon dioxide on plant physiology result in significant increase of LAI and NPP. The carbon storage of Chinese biomes at present and changed climates was calculated by the carbon density and vegetation area method. The present estimates of carbon storage are totally 175.83 × 10¹² gC (57.57 × 10¹² gC in vegetation and 118.28 × 10¹² gC in soils). Changed climate without and with the CO₂ direct physiological effects will result in an increase of carbon storage of 5.1 and 16.33 × 10¹², gC compared to present, respectively. The interaction between elevated CO₂ and climate change plays an important role in the overall responses of NPP and carbon to climate change.     

Present-day and mid-Holocene biomes reconstructed from pollen and plant macrofossil data from the former Soviet Union and Mongolia

Fossil pollen data supplemented by tree macrofossil records were used to reconstruct the vegetation of the Former Soviet Union and Mongolia at 6000 years. Pollen spectra were assigned to biomes using the plant-functional-type method developed by Prentice et al . (1996). Surface pollen data and a modern vegetation map provided a test of the method. This is the first time such a broad-scale vegetation reconstruction for the greater part of northern Eurasia has been attempted with objective techniques. The new results confirm previous regional palaeoenvironmental studies of the mid-Holocene while providing a comprehensive synopsis and firmer conclusions. West of the Ural Mountains temperate deciduous forest extended both northward and southward from its modern range. The northern limits of cool mixed and cool conifer forests were also further north than present. Taiga was reduced in European Russia, but was extended into Yakutia where now there is cold deciduous forest. The northern limit of taiga was extended (as shown by increased Picea pollen percentages, and by tree macrofossil records north of the present-day forest limit) but tundra was still present in north-eastern Siberia. The boundary between forest and steppe in the continental interior did not shift substantially, and dry conditions similar to present existed in western Mongolia and north of the Aral Sea.     

Pollen‐based biomes for Beringia 18,000, 6000 and 0 14C yr bp†

The objective biomization method developed by Prentice et al. (1996) for Europe was extended using modern pollen samples from Beringia and then applied to fossil pollen data to reconstruct palaeovegetation patterns at 6000 and 18,000 ¹⁴C yr bp . The predicted modern distribution of tundra, taiga and cool conifer forests in Alaska and north‐western Canada generally corresponds well to actual vegetation patterns, although sites in regions characterized today by a mosaic of forest and tundra vegetation tend to be preferentially assigned to tundra. Siberian larch forests are delimited less well, probably due to the extreme under‐representation of Larix in pollen spectra. The biome distribution across Beringia at 6000 ¹⁴C yr bp was broadly similar to today, with little change in the northern forest limit, except for a possible northward advance in the Mackenzie delta region. The western forest limit in Alaska was probably east of its modern position. At 18,000 ¹⁴C yr bp the whole of Beringia was covered by tundra. However, the importance of the various plant functional types varied from site to site, supporting the idea that the vegetation cover was a mosaic of different tundra types.     

The effect of charcoal production on carbon cycling in African biomes

Using biomass for charcoal production in sub-Saharan Africa (SSA) may change carbon stock dynamics and lead to irreversible changes in the carbon balance, yet we have little understanding of whether these dynamics vary by biome in this region. Currently, charcoal production contributes up to 7% of yearly deforestation in tropical regions, with carbon emissions corresponding to 71.2 million tonnes of CO₂ and 1.3 million tonnes of CH₄. With a projected increased demand for charcoal in the coming decades, even low harvest rates may throw the carbon budget off-balance due to legacy effects. Here, we parameterized the dynamic global vegetation model LPJ-GUESS for six SSA biomes and examined the effect of charcoal production on net ecosystem exchange (NEE), carbon stock sizes and recovery time for tropical rain forest, montane forest, moist savanna, dry savanna, temperate grassland and semi-desert. Under historical charcoal regimes, tropical rain forests and montane forests transitioned from net carbon sinks to net sources, that is, mean cumulative NEE from −3.56 ± 2.59 kg C/m² to 2.46 ± 3.43 kg C/m² and −2.73 ± 2.80 kg C/m² to 1.87 ± 4.94 kg C/m² respectively. Varying charcoal production intensities resulted in tropical rain forests showing at least two times higher carbon losses than the other biomes. Biome recovery time varied by carbon stock, with tropical and montane forests taking about 10 times longer than the fast recovery observed for semi-desert and temperate grasslands. Our findings show that high biomass biomes are disproportionately affected by biomass harvesting for charcoal, and even low harvesting rates strongly affect vegetation and litter carbon and their contribution to the carbon budget. Therefore, the prolonged biome recoveries imply that current charcoal production practices in SSA are not sustainable, especially in tropical rain forests and montane forests, where we observe longer recovery for vegetation and litter carbon stocks.     

论滇南西双版纳的森林植被分类

本文基于多年研究成果的总结,对西双版纳森林植被的分类、主要植被类型及其特征进行了系统归纳,并讨论了它们与世界类似热带森林植被的关系。以群落的生态外貌与结构、种类组成和生境特征相结合作为植被分类的原则和依据,可以将西双版纳的热带森林植被分类为热带雨林、热带季节性湿润林、热带季雨林和热带山地常绿阔叶林四个主要的植被型,包括有至少二十个群系。热带雨林包括热带季节雨林和热带山地(低山)雨林二个植被亚型。热带季节雨林具有与赤道低地热带雨林几乎一样的群落结构和生态外貌特征,是亚洲热带雨林的一个类型,但由于发生在季风热带北缘纬度和海拔的极限条件下,受到季节性干旱和热量不足的影响,在其林冠层中有一定比例的落叶树种存在,大高位芽植物和附生植物较逊色而藤本植物和在叶级谱上的小叶型植物更丰富,这些特征又有别于赤道低地的热带雨林。热带山地雨林是热带雨林的山地亚型,是该地区热带山地较湿润生境的一种森林类型,它在植物区系组成和生态外貌特征上类似于热带亚洲的低山雨林,隶属于广义热带雨林植被型下的低山雨林亚型。热带季节性湿润林分布在石灰岩山坡中、上部,在群落外貌上类似热带山地常绿阔叶林但在植物区系组成上与后者不同,它是石灰岩山地垂直带上的一种植被类型。热带季雨林是分布在该地区开阔河谷盆地及河岸受季风影响强烈的生境的一种热带落叶森林,是介于热带雨林与萨王纳之间的植被类型。热带山地常绿阔叶林(季风常绿阔叶林)是西双版纳的主要山地植被类型,它分布在热带季节雨林带之上偏干的山地生境。它在植物区系组成上不同于该地区的热带季节雨林,在生态外貌特征上亦不同于热带山地雨林,是发育在受地区性季风气候强烈影响的热带山地的一种森林植被类型。