Global palaeovegetation data for climate-biosphere model evaluation

A project to develop global biome data sets for 6000 and 18000 14C-yr BP from pollen and plant macrofossil records


Report of a joint IGBP-DIS/GAIM/ GCTE/ PAGES workshop, "BIOME 6000: Towards a global palaeovegetation data set"
11-13 May 1994
Horby, Sweden
Edited by
I. Colin Prentice, University of Lund, Sweden
Thompson Webb III, Brown University, Providence, Rhode Island, USA

Contents

Summary
Introduction and background
Biome reconstruction
Available palaeoecological data: current status
Plant functional types

Project implementation plan
Acknowledgments
References
Appendix 1: Project organization
Appendix 2: List of participants
Acronyms and abbreviations

Summary

"Climate-vegetation interactions: a 6000 yr BP experiment" is a current focus of GAIM. The experiment aims to quantify the importance of biogeophysical feedbacks in the climate system by comparing the performance of coupled and uncoupled climate-biosphere models, driven by the Earth's orbitally-induced change in seasonal insolation from 6000 yr BP to present. The existing, extensive coverage of palaeodata describing the state of the terrestrial biosphere at 6000 yr BP should provide a decisive standard against which to evaluate the model results.

The experiment thus has two major components. The modelling component relies on biome models and on coupling such models asynchronously to atmospheric general circulation models. The modelling component is well under way. There is therefore concern to stimulate the data synthesis component. A global data set describing the actual distribution of biomes during the centuries around 6000 yr BP, based on pollen and plant macrofossil records, is urgently required

Another planned GAIM experiment aims to account for changes in atmospheric trace-gas composition from the last glacial maximum (LGM, = 1800 14C-yr BP) to the Holocene through coupling models of physical climate, atmospheric chemistry and terrestrial biosphere trace-gas sources and sinks. Both 6000 yr BP and the LGM have become accepted "key times", both for palaeoclimate modelling (as in the Palaeoclimate Model Intercomparison Project, PMIP) and for palaeodata synthesis. Data for the LGM are more sparse, but they show large changes. A global data set describing biome distributions around the LGM is therefore also required.

Such development of data sets has community-wide support among palaeoecologists, on the understanding that the value and integrity of the primary data is respected. Major data synthesis activities for key times (including 6000 yr and the LGM) are already under way in every continent. In such syntheses, the primary data must be accessible and documented. Also for the development of global data sets, biome reconstruction should follow an objective procedure based on plant functional types (PFTs). A suitable procedure has now been developed, and tested with spatial networks of surface pollen-sample data from Europe, east Africa and eastern North America. The development of the required palaeovegetation data sets thus appears feasible with existing techniques, and builds on a firm collaborative basis.

With this background, the "BIOME 6000" project was initiated as a community-wide collaboration at an inaugural workshop, held in Horby, Sweden in May 1994 under the joint auspices of GAIM, IGBP-DIS, PAGES and GCTE. The aim of BIOME 6000 is to develop state-of-the-art global data sets of past vegetation for 6000 and 18000 14C-yr BP based on pollen and plant macrofossil records. First priority is given to 6000 yr BP, in the context of the current GAIM focus on climate-vegetation interactions. The workshop also recognized the usefulness of both the 6000 yr BP and LGM efforts for other current projects such as PMIP. The data sets will be strictly for past vegetation, and will therefore be complementary to PAGES data sets for other aspects of the palaeoenvironment.

The workshop made significant progress in assessing the current coverage of palaeovegetation data in each region. In some tropical regions, especially, the coverage of pollen data for 6000 yr BP has improved dramatically, both in terms of numbers of sites and in terms of "plugging" spatial gaps, since the last published synthesis. Regional working groups also produced lists of frequently identified pollen taxa with provisional assignments to PFTs. This attempt provides an important starting point for the biome reconstruction work and may lead to refinements of global PFT concepts used both in the BIOME 6000 project and in ecosystem modelling.

The project organization, as decided at the workshop, will consist of a general co-ordinator (I.C. Prentice, Lund University), a data co-ordinator (T. Webb III, Brown University), an international seven-person steering committee and eight "contact persons" each responsible for a region. Biome reconstructions will be carried out using a standard methodology, based on primary data compiled and documented at Brown, with co-operation and feedback from the regional contact persons. Several regional data workshops are proposed to facilitate the effort. The project's products are expected to become available for comparison with global model results in 1997.

Introduction and background

The project outlined here fills a need which arises from the increasing maturity of two, hitherto only tenously connected disciplines within global change science.

* Earth system modelling aims to elucidate the dynamic interactions between the physical climate system and the biosphere. Whereas climate modelling until recently was solely concerned with modelling the physical dynamics of atmosphere and oceans, earth system modelling attempts to include the major biogeochemical cycles and their contribution to the state of the climate and the biosphere. This modelling activity reflects the recent recognition that climate-biosphere interactions are important in the regulation of planetary metabolism, and that successful prediction of the consequences of human modification of climate and the biosphere on the time scales of "global change" is unlikely to be achieved unless such interactions are explicitly included. The emergence of earth system modelling has been made possible partly by recent developments in physical climate modelling and, especially, by rapid developments in large-scale modelling of ecosystem structure and function.

* Quaternary palaeoecology aims at an understanding of the nature and causes of changes in ecosystems during the past 2-3 million years of earth history, based on analysis of geological proxy records of ecosystems and the physical environment. From its roots as a descriptive historical science, Quaternary palaeoecology during the past 10-20 years has evolved a predictive agenda based on advances in our understanding both of the causes of natural environmental change and the mechanisms by which organisms, species and ecosystems respond to their environment. Analyses of large-scale spatial and temporal patterns in ecosystem composition have been made possible by (a) the continuing accumulation of proxy records, dated by radiocarbon and other means, by palaeoecologists around the world, and (b) synthesis activities carried out by a smaller number of individuals for the purposes of mapping, analysis and comparison with palaeoclimate model simulations.

The link between these endeavours is the fact that Quaternary palaeodata, properly analysed, can test various aspects of the performance of earth system models under conditions different from today.

The best-established examples of the application of Quaternary palaeodata to test models come from the period around and after the last glacial maximum (LGM), ca 18000 14C-yr BP (corresponding to ca 21000 astronomical years before present, according to the U-Th calibration of the 14C clock), and especially the Holocene epoch, starting at 10000 14C-yr BP and extending through the so-called "climatic optimum" ca 6000 yr BP (see Box) to the present. There are vastly more terrestrial palaeodata for these intervals than for any earlier time in geological history. Although there is still much that is not understood about higher-frequency climate variations since the LGM, the broad outlines of the transition from LGM to 6000 yr BP to present have an accepted explanation in terms of changes in the Earth's orbital configuration: direct (radiative forcing) effects of orbital variations combined with consequent (but lagged) changes in continental ice-sheets, atmospheric composition and sea-surface conditions produce the low-frequency "envelope" of climate change since the LGM (COHMAP Members 1988; Mitchell et al. 1988; Harrison et al 1992; Wright et al. 1993). This explanation is convincing because even simple "snapshot" experiments with atmospheric general circulation models (AGCMs), forced by these changing boundary conditions, correctly predict the large-scale qualitative aspects of palaeoenvironmental patterns at different times since the LGM (Wright et al. 1993).


SIX THOUSAND YEARS BP AND THE "CLIMATIC OPTIMUM"

The term "climatic optimum" is a shorthand expression based on the fact that during some part of the early or mid-Holocene many warmth-requiring species of plants and animals extended further north in the northern high latitudes, and moisture-requiring vegetation and associated fauna extended further into what are now arid regions of the northern-hemisphere tropics, than was the case either before (during the glacial period) or after (during the later Holocene). However, the continued use of this term is potentially misleading, for several reasons:

* The timing of "optimal" conditions was not the same everywhere, leading to varying notions of what time interval is meant.

* Different condtions are "optimal" for different types of plants, animals and ecosystems.

* Conditions were not "optimal" everywhere, by any definition. Extensive regions were drier around 6000 yr BP than today (e.g. much of North America), and not all regions were warmer than today.

* Some northern-hemisphere mid-latitude regions experienced a more seasonal climate, in which summers warmer than today were accompanied by winters colder than today. By no means all "warmth-requiring" species in these regions had ranges extending further north than present.

These diverse aspects of the early/mid-Holocene climate are now thought to be consequences of variations in the Earth's orbit (COHMAP Members, 1988; Wright et al., 1993). Higher than present insolation in northern-hemisphere summer was offset by lower than present insolation in northern-hemisphere winter. The increased tilt of the Earth's axis also meant higher than present total annual insolation in the high latitudes of both hemispheres. The increased seasonality of insolation in the northern hemisphere increased the land-sea contrast that powers the northern monsoons (Kutzbach & Street-Perrott, 1985; Kutzbach, 1987). The maximum orbital anomaly occurred around the beginning of the Holocene, but the melting of the Laurentide ice sheet was not complete until ca 6000 yr BP. Before that time, the climates of regions "downstream" of this ice sheet (including much of North America and northern Eurasia) were modified due to its continuing effect on the Westerly circulation (COHMAP Members, 1988; Mitchell et al., 1988; Harrison et al., 1992).

The period around 6000 yr BP offers the simplest case to analyse because by that time the large continental ice sheets had gone and atmospheric CO2 and other trace gases has reached their more-or-less stable late-Holocene (pre-industrial) levels, leaving only the still very different-from present orbital configuration. Snapshot experiments for 6000 yr BP have, for example, consistently and correctly predicted higher than present temperatures in the high latitudes and higher than present precipitation in today's arid northern subtropics, as well as many more specific regional patterns (Wright et al. 1993). The realism of these predictions has been evaluated with palaeodata of various kinds, with palaeoecological data and lake-level records playing a primary role.

There are differences among the predictions of different AGCMs, just as there are for high-CO2 scenarios. There also remain data-model discrepancies, especially in the magnitudes of simulated climate anomalies. These differences and discrepancies presumably are due to inexact or incomplete formulations of processes, and/or to omission of significant processes. So far the comparisons of palaeodata and palaeoclimate simulations have been mostly general and qualitative, and the discrepancies have not usually been analysed in detail. However as models develop, the palaeodata will be used increasingly as a standard against which model performance in palaeoclimate simulations is assessed.

The most specific and quantitative comparisons of palaeoclimate simulations and palaeoclimate that have been performed to date rely on statistical inverse modelling procedures (e.g. transfer functions, analog methods) to reconstruct climate variables from palaeodata. However, there are good reasons to rely more on "forward modelling" procedures in which the comparisons are made in terms of properties closer to the data. For example, pollen assemblages are translated into biomes rather than climate. Then modelling the biome distribution as a function of climate can be done more mechanistically, using biome models (Prentice et al., 1992; VEMAP Participants, in press).

A systematic data-model comparison approach, using biome modelling as the tool to facilitate comparisons with palaeoecological data, is already being planned for the Palaeoclimate Model Intercomparison Project (PMIP). Over fifteen climate modelling groups participate in PMIP and are producing LGM and 6000 yr BP simulations under a standard protocol. More ambitiously, it should be possible to compare model results obtained with and without the inclusion of further processes, not normally included in AGCMs, including the reciprocal interactions between vegetation and climate.

Climate-vegetation interactions and the GAIM 6000 yr BP experiment

GAIM is concerned with promoting and facilitating interdisciplinary studies involving data synthesis and data-model comparisons as well as modelling. The emphasis is on quantifying interactions among different components of the earth system through the biogeochemical and hydrological cycles. GAIM has so far identified four foci that represent timely opportunities to combine data-based and various kinds of modelling activities. Each GAIM focus relies on techniques and data that exist today, or that are actively under development. The new challenges posed by GAIM are in coupling different types of model, meshing different sources of data, and devising ways to make the data and the model results commensurate.

One area of interest for GAIM is "climate-vegetation interactions". Sensitivity studies with AGCMs have suggested that large-scale changes to the contemporary vegetation may have important consequences for the global climate

(e.g. Charney et al. 1975; Bonan et al. 1992; Chalita & le Treut 1994). Other AGCM studies with a specifically palaeoclimatological focus have been carried out recently. These studies have shown that the known greater extension of shrub- or grasslands in what is now the Sahara during the early to mid-Holocene, up to around 6000 yr BP, would have amplified the direct effect of orbital forcing on the monsoons (Street-Perrott et al. 1991); and that the poleward extension of taiga in Canada and Siberia during the same interval would have amplified the effect of orbital forcing on growing-season temperatures in the north (Foley et al. 1994). These are examples of "biogeophysical feedbacks", which arise because vegetation mediates the exchange of water and energy between the land surface and the atmosphere. Changes in vegetation characteristics such as albedo, height, foliage cover and phenology exert a strong influence on these exchanges. So when external factors (such as the Earth's orbital configuration) change in such a way as to produce a change in climate, the response of vegetation patterns is not just a passive reaction, but may have further feedback effects on the climate.

The GAIM focus "Climate-Vegetation Interactions: A 6000 yr BP experiment" aims to characterize and quantify these biogeophysical feedbacks, using palaeodata for 6000 yr BP as the standard. The experiment has two major components: coupled climate-vegetation modelling, and palaeoecological data synthesis.

The modelling component relies on the existence of mechanistic models (biome models) that predict the distributions of broad-scale ecosystem types (biomes) as a function of the physical environment. The BIOME model of Prentice et al. (1992) has been used in this way to translate the results of AGCM experiments (e.g. for the LGM, 6000 yr BP, and future high-CO2 climates) into global vegetation maps (Claussen and Esch 1993, Prentice et al. 1993). Such a model can also be asynchronously linked to an AGCM, allowing simulation of the equilibrium state of the coupled system (Claussen 1994, Henderson-Sellers & McGuffie 1995, Ciret and Henderson-Sellers in press). Coupled model studies of this kind are underway in several climate modelling groups, focusing initially on 6000 yr BP.

Another GAIM experiment, not yet designed in as much detail as the 6000 yr BP experiment, aims to account for natural changes in atmospheric trace-gas composition after the LGM as shown by ice-core palaeorecords, through coupling models of physical climate, atmospheric chemistry and terrestrial biosphere trace-gas sources and sinks. Future model-coupling experiments envisaged might also explore the causes of natural changes in atmospheric CO2 and terrestrial carbon storage after the LGM.

The data synthesis component relies on the existence of a very large body of pollen and plant macrofossil records from the past twenty thousand years, from sediments dated (usually by 14C) with a precision of a few hundred years. In order to make full use of these data for global change research, a community-wide effort is required (a) to assemble the data for all of the continents, and (b) to represent them in some compact and globally consistent form.

It has been clear for some time that such an effort would be strongly supported by the palaeoecological community. Discussions began at the International Palynological Conference (Aix-en-Provence, France, September 1992) and were continued at the NATO Advanced Research Workshop on Forward and Inverse Modelling in Palaeoclimatology (Aussois, September 1993). The direction of current modelling efforts argues for the initial focus of such a project being 6000 yr BP, but the LGM is regarded as an important second focus. There are fewer data available for the LGM, probably only about 20% of the number of data points available for 6000 yr BP, but the changes they show are generally very large, so the signal-to-noise ration is also large.

These considerations led the GAIM Task Force to propose the data synthesis task that has become known as BIOME 6000. BIOME 6000 is jointly sponsored by GAIM, the IGBP Data and Information System (IGBP-DIS) and the two IGBP core projects Global Change and Terrestrial Ecosystems (GCTE) and Past Global Changes (PAGES). Its aim is to generate global palaeovegetation data sets, with first priority to the time interval around 6000 yr BP and second priority to the LGM, based on existing pollen and plant macrofossil records.

TheHorby workshop in May 1994 formally initiated BIOME 6000 as a global, community-wide collaborative project. Almost all of the scientists who attended the workshop (Appendix 2) are palaeoecologists who combine active field research programmes with large-scale mapping and data analysis interests. Each continent was represented by a cross-section of the relevant research leaders. Those present included many who have worked over a long period with the Co-operative Holocene Mapping Project (COHMAP), and several of those directly involved in the collection of new data especially in the tropics, semi-arid and remote northern regions.

Biome reconstruction

The global nature of this new palaeovegetation mapping enterprise means that the palaeoecological data must not simply be left in the form of abundances of taxa, so one of the challenges for BIOME 6000 is to find a way to translate the taxon information into a common language. It is necessary to use the concept of "plant functional types" (PFTs) as advocated by the GCTE project (Steffen et al. 1992). Plant taxa must be assigned to PFTs and the data must be interpreted in terms of biomes, which are defined as combinations of PFTs.

Preliminary work with data from Europe (Prentice et al. in press), North America (T. Webb III unpublished results) and East Africa (D. Jolly unpublished results) has shown that it is indeed possible to translate pollen spectra into biomes, by means of a "fuzzy logic" algorithm. The key to the method is the idea that plant taxa identified in the palaeorecord can be assigned a priori to one or more PFTs. A taxon may potentially belong to more than one PFT if it includes several species that represent different PFTs, or individual species that can behave as a different PFT in different environments. Fuzzy logic enters the picture because the problem is neither a strictly statistical one, due to the past existence of plant assemblages that lack modern analogs, nor is it susceptible to ordinary Boolean logic, because it is rarely possible to be certain from the palaeorecord whether a given taxon was locally present or not (long-distance transport is a common complication). The method therefore relies on ranking "affinity scores" that represent the weight of infomation contained in each pollen spectrum that would support the assignment of that spectrum to a given biome.The steps in the method are as follows:

1. Each pollen taxon is initially assigned to one or more PFTs on the basis of the known biology of the species it represents.

2. The PFT assignments are checked by comparing the bioclimatic distribution of each taxon in turn with an expected bioclimatic distribution, based on its assignment to one or more PFTs. If discrepancies are found then the PFT assignments must be corrected. The product is a corrected PFT x taxon matrix .

3. Next, biomes must be defined in terms of their characteristic PFTs, yielding a biome x taxon matrix.

4. The two previous matrices are maipulated to yield a taxon x biome matrix, indicating which pollen taxa may occur in each biome.

5. Affinity scores for any given pollen spectrum and biome are calculated as the sum of pollen values for taxa that may occur in that biome. Prior to this calculation, the pollen values have to be transformed to increase the signal-to-noise ratio. Good results have been obtained using a square-root transformation after subtraction of a uniform "threshold" pollen percentage (1% or less).

6. The pollen spectrum is assigned to the biome with which it has the highest affinity, subject to a tie-breaking rule by which any biome whose list of characteristic taxa is a subset of another biome's list of characteristic taxa is given precedence.

Validation of this method has been provided by successful reconstructions of present-day biome distribution patterns from modern pollen assemblages in surface sediments. The method has numerous advantages for worldwide application, including its basis in PFTs (so that taxa with similar bioclimatic ranges in different biogeographic provinces can be treated as equivalent); an ability to produce well-founded biome reconstructions even when the pollen spectra have no known modern analogs; insensitivity to quantitative changes in taxon abundance due to human impacts on the landscape; and the lack of any requirement for comprehensive data sets on modern (surface-sample) pollen distribution. This last point is important because such data sets are lacking for most of the continents. Surface sample data, where available, can be reserved for validation.

To apply this approach globally requires active participation in the project by palaeoecologists with a knowledge of the flora and vegetation of their region. The key to the method's robustness lies in the application of the PFT concept, which in turn implies that taxa can be assigned to PFTs. This first step immediately overcomes what has been one of the major barriers to more widespread use of palaeoecological data in global change research, viz that the data are normally presented in the form of abundances of taxa whose ecological significance is only known to researchers who have specialized in the region in question. Such basic information is often not clear from floras, which have generally been written from a taxonomic rather than an ecological or biogeographical perspective.

Available palaeoeological data: current status

Palaeoecological data give information about past ecosystems. They are complementary to other terrestrial palaeodata sources (such as lake-level records, ice-core records, palaeosols, fossil dunes) that give information about other climatically influenced processes at the Earth's surface. The commonest sources of palaeoecological data are pollen and plant macrofossil records, which indicate the composition of past vegetation. There are already regional to continental-scale compilations of palaeoevegetation data covering most regions of the world, in the form of "time slices" including 6000 and 18000 yr BP among others. Several such compilations originated during the 1980's as part of or in association with the COHMAP project (Wright et al. 1993), and have subsequently been maintained and updated to a lesser or greater degree by the original investigators; other compilations have been started during the last few years.

Primary data repositories (pollen and plant macrofossil data bases) are a more recent development. Pollen data bases store all of the original pollen counts together with primary dating information, and are equipped with software that facilitates the extraction of secondary products (including time-slices). There are established pollen data bases in Europe (the European Pollen Data Base at Arles, France) and North America (the North American Pollen Data Base at Springfield, Illinois). There are also efforts under way to set up comparable pollen data bases for some other continents, including South America, and to set up a plant macrofossil data base for North America. Thus, somewhat different strategies have to be followed to compile the data from different continents, depending on the degree to which centralized data management has been developed.

The first specific task set to the workshop participants was to generate a provisional listing of sites, region by region, where palaeoecological data should be available with confident dating to either 6000 yr BP ?SYMBOL 177 \f "Symbol"? ca 500 yr, or 18000 yr BP ?SYMBOL 177 \f "Symbol"? ca 1000 yr (14C-years). For the most part the sites represent pollen records, but in the arid western USA pollen sites are few but many detailed, 14C-dated floristic records have been obtained from macrofossils in packrat middens. An initial site map was provided, based on archives of the COHMAP project at Brown University. It was found that in some tropical regions, especially, the coverage of palaeoecological data has improved dramatically during the past 5-10 years, both in terms of numbers of sites and in terms of "plugging" spatial gaps. Particularly important improvements were noted for tropical South America, China, SE Asia and central Siberia. Data provided after the meeting by several regional contact persons allowed the production of Figs 1-2, which give a first (necessarily incomplete) view of the data available.

In addition to pollen and plant macrofossil data, 14C-dated megafossil remains have the potential to provide direct information about the presence of trees. This source of information is especially important in recording the former northward extent of forests in the present-day tundra regions of northern North America and Eurasia. A project of the Canadian Geological Survey has used tree megafossil data as a supplement to the relatively few available pollen diagrams from the Canadian Arctic, to map the palaeodistribution of forest types in Canada at 6000 yr BP.

Plant functional types

The workshop participants were also asked to produce a list of the most frequently identified pollen taxa in their region of study, and provisional assignments of each taxon to one or more PFTs. A preliminary list of PFTs was provided (Table 1), based on the types used by the BIOME model modified by experience so far. Although this classification is fairly standard, it is also extremely basic and may well not account for as much of the diversity of plant taxa that one might wish to make use of in interpreting palaeoecological records for biome mapping.

The results of this exercise are still being analysed. In summary, the following main points emerged:

* The tropical raingreen type could usefully be subdivided into at least two types, corresponding to different lengths of drought period tolerated (e.g. 2 months versus 5 months).

* The warm-temperate evergreen tree type is too broad, as it includes (for example) temperate rain forest species as well as drought-tolerant sclerophyllous species, palms and cycads with their distinctive life forms, and a very wide range of leaf sizes. Such distinctions have major environmental significance and are particularly important for temperate Southern Hemisphere vegetation changes.

* The term "heath" is ambiguous. Many tropical Ericaceae, Epacridaceae and Myrtaceae are warm-temperate evergreen trees or shrubs, characteristic of montane forests and shrub communities above the treeline. On the other hand there are species characteristic of magellanic moorland in temperate South America. A more strictly structural term would be preferred, e.g. "microphyllous shrub". More work is required to define the environmental space of different types of shrub.

The continuing analysis will contribute not to only to the specification of biome reconstruction procedures, but also to the continuing development of improved global biome models based on the PFT concept (e.g. Haxeltine et al. in press; Jolly & Prentice in prep.), and to the GCTE objective of developing a global key of PFTs. We hope that this highly pragmatic approach to the definition and application of PFTs will prove to be a useful complement to other approaches that are being developed by GCTE on a more explicit basis of physiological attributes and/or resource allocation theories.

Table 1. Initial list of plant functional types

Trees

Tropical evergreen (Te) Large-leaved evergreen trees characteristic of tropical rainforests. Intolerant of either frost or drought. Examples: Cecropia, Dipterocarpaceae, Bombax.

Tropical raingreen (Tr) Drought-deciduous trees characteristic of tropical dry forests and savannas. Intolerant of frost. Require a climate with strong seasonality of rainfall. Examples: Alchornea, Celtis spp.

Warm-temperate evergreen (wte) Evergreen trees, including sclerophyllous and mesophytic broad-leaved as well as needle-leaved taxa, characteristic of warm-temperate evergreen and mixed forests (e.g. temperate rainforests, Mediterranean forests, southern US pine forests, tropical montane forests). Frost tolerant, but intolerant of temperatures below ca -15C. Includes taxa tolerant of summer drought. Examples: southern Pinus, evergreen Quercus, Olea spp., Podocarpaceae, Sequoia, Eucalyptus.

Temperate summergreen (ts) Winter-deciduous broad-leaved trees characteristic of temperate deciduous forests. Frost tolerant but intolerant of temperatures below ca -40C. Require a climate with strong seasonality of temperature. Intolerant of summer drought. Examples: deciduous Quercus, Fagus, Castanea.

Cool-temperate conifer (ctc) Evergreen needle-leaved trees characteristic of cool conifer forests (e.g. Pacific Northwest USA forests, southern boreal conifer forests). Frost tolerant, but intolerant of temperatures below about -45C. Examples: Thuja, Pseudotsuga.

Boreal evergreen conifer (bec) Evergreen needle-leaved trees characteristic of taiga. Frost tolerant, but intolerant of temperatures below about -60C. Example: Picea spp.

Boreal summergreen (bs) Winter-deciduous broad- or needle-leaved trees characteristic of taiga. Usually shade-intolerant, extremely cold tolerant. Examples: Larix, Betula spp.

Shrubs

Sclerophyll shrubs (ss) Evergreen sclerophyllous broad-leaved shrubs characteristic of Mediterranean-type shrublands. Cold tolerance similar to warm-temperate evergreen trees, but tolerant of longer or more intense drought. Examples: Phillyrea, Proteaceae.

Others

Steppe forbs (sf) Examples: Artemisia, Chenopodiaceae

Desert forbs (df). Example: Ephedra

Arctic-alpine dwarf shrubs (aa). Example: Betula nana

Heaths (h). Examples: Ericaceae, Epacridaceae

Grasses (g): Poaceae

Sedges (s): Cyperaceae

Project implementation plan

The project organization, adopted at the meeting, is summarized in Appendix 1. The division of the globe into eight regions grew out of the working group structure that developed duiring the meeting. This division was done pragmatically, based on a combination of biogeographic and existing organizational considerations. It is emphasized that the lists of participants for each region is not intended to be definitive; it is hoped that more will join as the project develops.

In addition to deciding on this organization, the final discussions at the workshop led to a number of policy decisions, summarized below.

* Only data sources directly recording plants will be used as evidence for past vegetation. This is considered to be an important restriction because other systems (e.g. lakes, geomorphic systems) respond to different aspects of the physical environment. Apparent discrepancies between the response of different environmental systems can be informative. Thus, BIOME 6000 is strictly complementary to other palaeomapping activities based on lake levels, animal distributions, soils and landforms, including other data synthesis projects sponsored by PAGES.

* The target dates for data extraction will be 6000 and 18000 14C-years BP, for consistency with previous data compilation efforts. For 6000 yr BP, this means accepting an age difference of a few hundred years between the target date and the insolation forcing for 6000 calendar yr BP which is conventionally used for palaeoclimate simulations (e.g. by PMIP). However, this difference is slight in terms of the insolation forcing and would be well below the noise level of the climate simulations. The advantage of avoiding a break with previous efforts was considered to greatly outweigh the advantage of an exact match with the nominal time represented by the simulations. Also, to choose a 14C-date close to 6000 astronomical years BP would introduce unwanted complications due to rapid (presumably non-orbitally forced: see e.g. Lamb et al., 1995) changes noted in many regions in the millenium around 5000 14C-yr BP. For the last glacial maximum, simulations now conventionally use insolation forcing for 21000 calendar yr BP, designed to match data from 18000 yr 14ÊC-yr BP.

* Primary data (counts of pollen grains or plant macrofossils) must to the greatest possible extent be the source of palaeovegetation information for these time periods. The data central in Brown University will therefore concentrate initially on incorporating these primary data, through the organizational network outlined in Appendix 1. At the same time, key information necessary for quality control will be solicited. For those regions with established data repositories, the process of extracting the required data will most naturally be done through the co-operation of the managers of these repositories, who will then be ex officio participants in the project. All of the data will be archived in such a way that the locations of the primary data points, the reliability of dating control on every point, and the logic used to reconstruct the biome, are transparent to users.

* The most appropriate technique to identify the sample or samples closest to each target date may vary with sedimentation conditions, and involves some investigator judgment (e.g. in certain cases where sedimentary hiatuses occur after 6000 yr BP, or more generally whenever there are large variations in sedimentation rate).

* Biome reconstructions, based on the primary data, will be carried out using a standard methodology, at Lund University or elsewhere according to agreement. An important task before this is done will be to decide on an operational PFT classification and to provide an assignment key that can be applied relatively easily by specialists from different continents. This task will be carried out a Lund University. The regional contact persons will provide the required information on the assignments of plant taxa to PFTs, and will make expert assessments of initial biome reconstructions as a check on the procedure. Reconstructions will be made separately for each region or subdivisions thereof, then consistency checks will be carried out before the global biome data set is compiled.

* A need was identified for three regional data workshops to be held in 1995: SE Asia/Oceania (already planned before the meeting), China (planned at the meeting and held in Beijing in May 1995), and Africa. Such a workshop for Africa is envisaged as a potential START activity, which could involve and bring together the dispersed community of palaeoecologists and vegetation ecologists working in African countries.

* The favoured form of primary publication would be a special issue of a Quaternary science journal, hierarchically structured with articles (each with a small number of authors) from each of 20-30 regions (covering the globe) and short summary articles for each continent. In addition, some form of multi-authored flagship publication is expected to be an eventual outcome of the planned collaboration between the BIOME 6000 data community and palaeoclimate modelling groups.

* The evolving products of the project will be accessible to active participants throughout the course of the project. An occasional newsletter, published from Brown University, will keep participants informed about the status of these products.

* A second "plenary" BIOME 6000 workshop should be held, preferably in 1996, to review progress, decide on the means to complete the project in a timely manner, determine policy regarding future access to and curation of the primary and derived data sets, and develop a detailed publication plan.

* Data sets are expected to become available for comparison with global model results in 1997.

Acknowledgments

We would like to thank the organizations who funded the workshop: the US National Oceanic and Atmospheric Administration National Geophysical Data Center (NOAA-NGDC), the Swedish Natural Science Research Council (NFR), PAGES, and IGBP-DIS. The initial planning was carried out by a small group including the editors of this report and Patrick Bartlein (University of Oregon), Raymonde Bonnefille (CNRS-Luminy), Berrien Moore III (University of New Hampshire and chair of GAIM), Jonathan Overpeck (NOAA-NGDC), and Ichtiaque Rasool (outgoing chair of IGBP-DIS). We are grateful to all these individuals for their enthusiastic participation in the planning process, and especially Ichtiaque Rasool who goaded the workshop into existence. Further active support at the planning stage was provided by Herman Zimmerman (PAGES), Brian Walker (GCTE) and Robin Webb (NOAA-NGDC). Dominique Jolly (Lund University) and Pavel Tarasov (Moscow State University) tirelessly ran the workshop day-to-day, and the staff ofHorby KursgŒrd provided always-friendly help with practical arrangements. Finally we thank all the participants for their extraordinary good will and hard work at the workshop and their evident enthusiasm to make the project a success.

Drafts of this report were critically read by Habiba Gitay (Australian National University) and Dominique Jolly (Lund University).

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Appendix 1: Project organization

Steering committee

Raymonde Bonnefille, Brian Huntley, Geoff Hope, Vera Markgraf, Colin Prentice (general co-ordinator), Thompson Webb III (data co-ordinator), Sun Xiangjun

Regional working groups

The following lists include people who were at the workshop, plus a few others who have agreed to participate in the project. It should be emphasized that the project is envisaged as an open collaboration; these lists are expected to expand somewhat as the project develops. Individuals who have agreed to act as regional "contact persons" with the project co-ordinators are shown in italics.

Africa: Raymonde Bonnefille, Hillaire Elenga, Dominique Jolly, Anne-Marie LŽzine, Jean Maley, J. Mworia-Maitima, Louis Scott

Tropical Asian monsoon region and Oceania: John Dodson, Geoff Hope, Matt McGlone, Raman Sukumar, Jean-Pierre Sutra

Central and South America: Mark Bush, Henry Hooghiemstra, Marie-Pierre Ledru, Vera Markgraf

North America: Patricia Anderson, Patrick Bartlein, Mary Edwards, Eric Grimm, Steve Jackson, Helne JettŽ, Glenn MacDonald, Pierre Richard, Robert Thompson, Thompson Webb III, Cathy Whitlock

Western and Central Europe, Mediterranean and Middle East: Sytze Bottema, Rachid Cheddadi, Jo‘l Guiot, Brian Huntley, Henry Lamb

Former Soviet Union and Mongolia: Patricia Anderson, Andrej Andreev, Konstantin Kremenetskii, Anatoly Lozhkin, Glenn MacDonald, Pavel Tarasov

China: Kam-bu Liu, Sun Xiangjun

Japan: Shinya Sugita, Hikaru Takahara

Appendix 2: List of participants

Patricia Anderson, Quaternary Research Centre AK-60, University of Washington, Seattle, WA 98195, USA. Tel: (+1-206) 543 0569, Fax: (+1-206) 543 3839

Andrej A. Andreev, Laboratory of Palaeogeography, Institute of Geography, Staromonetry 29, 109017 Moscow, RUSSIA. Tel: (+7-095) 238 0238, Fax: (+7-095) 230 2030

Patrick J. Bartlein, Department of Geography, University of Oregon, Eugene, OR 97403-1218, USA. Tel: (+1-503) 346 4967, Fax: (+1-503) 346 2067

Raymonde Bonnefille, CNRS, CEREGE BP80, F-13545 Aix-en-Provence, FRANCE. Tel: (+33) 42 97 15 88, Fax: (+33) 42 97 15 91

Mark Bush, Department of Botany, Duke University, Durham, NC 27708, USA. Tel: (+1-919) 684 3264

John Dodson, School of Geography, University of New South Wales, Sydney, NSW 2052, AUSTRALIA. Tel: (+61-2) 385 4390, Fax: (+61-2) 313 8884

Jo‘l Guiot, CNRS UA 1152, FacultŽ des Sciences de St JŽr™me, Box 451, Rue Henri PoincarŽ, F-13397 Marseille Cedex 13, FRANCE. Tel: (+33) 91 28 80 11, Fax: (+33) 42 32 33 90

Henry Hooghiemstra, Hugo de Vries Laboratorium, University of Amsterdam, Kruislaan 318, NL-1098 SM Amsterdam, THE NETHERLANDS. Tel: (+31-20) 525 7857, Fax: (+31-20) 525 7662

Geoff Hope, Department of Biogeography & Geomorphology, Research School of Pacific Studies, Australian National University, Canberra 0200, AUSTRALIA. Tel: (+61-6) 249 3283, Fax: (+61-6) 249 4917

Brian Huntley, Environmental Research Centre, Department of Biological Sciences, University of Durham, South Rd, Durham DH1 3LE, ENGLAND UK. (+44-191) 374 2432, Fax: (+44-191) 374 2432

Steve Jackson, Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86001-5640, USA. Tel: (+1-602) 523 9322, Fax: (+1-602) 523 7500

Dominique Jolly, Department of Ecology, Lund University, Ecology Building, Sšlvegatan 37, S-223 62 Lund, SWEDEN. Tel: (+46-46) 2223132, Fax: (+46-46) 2223742

Marie-Pierre Ledru, ORSTOM, 72 Route d'Aulnay, F-93143 Bondy, FRANCE. Tel: (+33-1) 48 47 30 88

Suzanne Leroy, PAGES/CPO, BŠrenplatz 2, CH-3011 Bern, SWITZERLAND. Tel: (+41-31) 3123133, Fax: (+41-31)3123168

Anne-Marie LŽzine, URA 1761-CNRS, Jussieu, Bo”te 106, F-75252 Paris cedex 5, FRANCE. Tel: (+33-1) 44 27 49 96, Fax: (+33-1) 44 27 49 92

Kam-bu Liu, Department of Geology and Anthropology, Louisiana State University, Baton Rouge, Louisiana 70803, USA. Tel: (+1-504) 388 6136, Fax: (+1-504) 388 2912

Anatoly Lozhkin, North East Research Institute, Russian Academy of Sciences, 16 Portovaya, Magadan 685000, RUSSIA. Tel: (+7-413) 003 0944

Jean Maley, DŽpartement de Palynologie, UniversitŽ de Montpellier II, F-34095 Montpellier cedex 5, FRANCE. Tel: (+33) 67 04 20 32, Fax: (+33) 67 54 08 28

Vera Markgraf, INSTAAR, University of Colorado, Boulder, CO 80309-0450, USA. Tel: (+1-303) 492 5117, Fax: (+1-303) 492 6388

Paige Newby, Department of Geological Sciences, Brown University, Providence, RI 02912-1846, USA. Tel: (+1-401) 863 2807, Fax: (+1-401) 863 2058

Colin Prentice, Department of Ecology, Lund University, Ecology Building, Sšlvegatan 37, S-223 62 Lund, SWEDEN. Tel: (+46-415) 22248, Fax: (+46-415) 22031

Pierre Richard, DŽpartement de GŽographie, UniversitŽ de MontrŽal, CP 6128, Centre Ville MontrŽal, QuŽbec H3C 3J7, CANADA. Tel: (+1-514) 343 8022, Fax: (+1-514) 343 8008

Louis Scott, Department of Botany and Genetics, University of the Orange Free State, P.O. Box 339, Bloemfontein 9300, SOUTH AFRICA. Tel: (+27-51) 401 2594, Fax: (+27-51) 488 772

Shinya Sugita, Department of Ecology, University of Minnesota, 100 Ecology, Minneapolis MN 55108, USA. Tel: (+1-612) 624 6240, Fax: (+1-612) 624 6777

Jean-Pierre Sutra, French Institute of Pondicherry, PB 33, 605001 Pondicherry, INDIA. Fax: (+91) 41339534

Pavel Tarasov, Department of Geography, Moscow State University, 119899 Leninskie Gory, Moscow, RUSSIA. Tel: (+7-095) 939 2830, Fax: (+7-095) 932 8836

Robert Thompson, US Geological Survey, Box 25046, MS 919, Denver Federal Center, Denver, Colorado 80225, USA. Tel: (+1-303) 236 0439, Fax: (+1-303) 236 5690

Robert S. Webb, Paleoclimatology Program, NOAA/NGDC, 325 Broadway, Boulder, Colorado 80303, USA. Tel: (+1-303) 497 6967, Fax: (+1-303) 497 6513

Thompson Webb III, Department of Geological Sciences, Brown University, Providence, RI 02912-1846, USA. Tel: (+1-401) 863 3128, Fax: (+1-401) 863 2058

Cathy Whitlock, Department of Geography, University of Oregon, Eugene, OR 97403-1218, USA. Tel: (+1-503) 346 4566, Fax: (+1-503) 346 2067

Sun Xiangjun, Institute of Botany, Academia Sinica Xiangshan, 141 Xizhimenwai Street, 100044 Beijing, CHINA. Tel: (+86-1) 259 1431

Referred to in Appendix 1 but not present at the meeting:

Sytze Bottema, Biologisch-Archaeologisch Institut, Rijksuniversiteit Groningen, Poststraat 6, NL-9712 ER Groningen, THE NETHERLANDS. Tel: (+31-50) 63 67 12, Fax: (+31-50) 63 69 92

Rachid Cheddadi, European Pollen Data Base, Centre Universitaire d'Arles, Espace van Gogh, F-13637 Arles, FRANCE. Tel: (+33) 90 96 18 18, Fax: (+33) 90 93 98 03

Mary Edwards, Department of Geology and Geophysics, University of Alaska, Fairbanks, Alaska 99775-0760, USA. Tel: (+1-907) 474 5014, Fax: (+1-907) 474 5163

Hillaire Elenga, CNRS, CEREGE BP80, F-13545 Aix-en-Provence, FRANCE. Tel: (+33) 42 97 15 88, Fax: (+33) 42 97 15 95

Eric Grimm, Illinois State Museum, Research and Collections Center, 1011 East Ash Street, Springfield, Illinois 62703, USA. Tel: (+1-217) 785 4848, Fax: (+1-217) 785 2857

Konstantin Kremenetskii, Laboratory of Palaeogeography, Institute of Geography, Staromonetry 29, 109017 Moscow, RUSSIA. Tel: (+7-095) 238 0298, Fax: (+7-095) 230 2090

Henry Lamb, Institute of Earth Studies, University of Wales, Aberystwyth SY23 3DB, WALES, UK. Tel: (+44-1970) 622597, Fax: (+44-1970) 622659

Glen MacDonald, Department of Geography, McMaster University, Hamilton, Ontario L8S 4K1, CANADA. Tel: (+1-905) 525 9140 x23217, Fax: (+1-905) 546 0463

Matt McGlone, Landcare Research, Nanaaki Whenua, PO Box 69, Lincoln, Canterbury, NEW ZEALAND. Tel: (+64-3) 325 3020, Fax: (+64-3) 325 2418

J. Mworia-Maitima, Palynology and Palaeobotany Department, National Museums of Kenya, P.O. Box 40658 Nairobi, KENYA. Tel: (+254) 742131/4, Fax: (+254) 741424

Jonathan Overpeck, Paleoclimatology Program, NOAA/NGDC, 325 Broadway E/GC, Boulder, Colorado 80303, USA. Tel: (+1-303) 497 6172, Fax: (+1-303) 497 6513

Raman Sukumar, Centre for Ecological Sciences, Indian Institute of Science, Bangalore 560012, INDIA. Tel: (+91-80) 334 3382 or 0985, Fax: (+91-80) 334 1683

Chhaya Sharma, Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow-226007, INDIA. Tel: (+91-0522) 74291 or 73206, Fax: (+91-0522) 74528

Hikaru Takahara, University Forest, Faculty of Agriculture, Kyoto Prefectural University, Nakaragi-cho, Shimogamo Sakyo-ku, Kyoto 606, JAPAN. Tel: (+81-75) 781 3131 x307

Acronyms and abbreviations

AGCM atmospheric general circulation model
CNRS Centre nationale de RŽcherche scientifique, France
COHMAP Co-operative Holocene Mapping Project (NSF/NOAA)
EPD European Pollen Data Base, France (EU)
EU European Union
GAIM Global Analysis, Interpretation and Modelling (IGBP)
GCTE Global Change and Terrestrial Ecosystems (IGBP)
IGBP International Geosphere-Biosphere Programme (ICSU)
IGBP-DIS IGBP Data and Information System (IGBP)
LGM last glacial maximum
NAPD North American Pollen Data Base, USA (NOAA)
NOAA National Oceanographic and Atmospheric Administration, USA
NFR Naturvetenskapliga forskningsrŒdet (Swedish Natural Science Research Council)
NSF National Science Foundation, USA
NGDC National Geophysical Data Center (NOAA)
ORSTOM Institut franais de Recherche scientifique pour le DŽveloppement en Cooperation, France
PFT plant functional type
PAGES Past Global Changes (IGBP)
PMIP Paleoclimate Modeling Intercomparison Project
RICE Regional Interactions of Climate and Ecosystems (GAIM)