dataesr/scientific-paragraphs-categorization huggingface dataset:
This project aimed to use palaeoecological data from the mid-Holocene as a benchmark to evaluate simulations with coupled climate-biosphere models and thus to assess the extent of biogeophysical (vegetation-atmosphere) feedbacks in the global climate system  (Prentice et al. 2000). After the validation of the modern pollen dataset  (Gajewski et al. 2002; Jolly et al. 1998) , the biomization method was successfully applied to reconstruct modern  (Lézine et al. 2009; Vincens et al. 2006 ) and past biomes for selected time periods, typically the Last Glacial Maximum (LGM) and the Holocene  (Jolly et al. 1998; Elenga et al. 2000). Past biome reconstructions have also been performed for the Plio-Pleistocene  (Bonnefille et al. 2004; Novello et al. 2015)  and more recent time periods such as the last glacial-interglacial cycle and the Holocene  (Amaral et al.
Quantitative reconstructions of climate variables from pollen data Modern-analogue, regression, and model-inversion techniques have been developed to reconstruct past climates from pollen assemblages or pollen-based reconstructed biomes worldwide. Using the APD modern pollen dataset,  Peyron et al. (2007)  provided the first quantitative pollen-based reconstruction of precipitation for all of Africa at 6000 yr BP based on the Modern Analogues Technique (MAT) and the Plant-Functional Types (PFT) climate relationships. Results were then compared with atmospheric general circulation model output and coupled ocean atmosphere-vegetation models developed in the frame of the Paleoclimate Model Intercomparison Project (PMIP) international project (Joussaume and Taylor 1995). More recently,  Wu et al.
Vegetation reconstructions from pollen data Palaeoecological data from the APD led to a series of reconstructions of vegetation at a continental scale. Site-based global biome maps for Africa for the mid-Holocene and LGM were first completed within the framework of the 'BIOME 6000' project  (Prentice et al. 2000). More recently, APD palaeoecological data was included in a global synthesis of changes in composition and structure of past vegetation since the LGM performed by  Nolan et al. (2018). This study provided a baseline for evaluation of the magnitudes of ecosystem transformations under future emission scenarios. At a regional scale, APD data were used to reconstruct the Green Sahara and evaluate plant migration rates during the African Humid Period  (Hély et al. 2014; Watrin et al. 2009).
2019; Miller and Gosling 2014; Scott 2016) , and therefore long-term vegetation changes are mostly derived from marine cores (e. g. ,  Dupont and Kuhlmann 2017; Hessler et al. 2010). Thanks to a recent funding from the Belmont Forum for Science-driven e-infrastructure innovation for the project 'Abrupt Change in Climate and Ecosystems: Where are the Tipping points?', the APD is now being relaunched and developing further collaborations with international databases ('NEOTOMA', 'PANGAEA') and the French Institute Pierre Simon Laplace (IPSL). One of the priorities is to gather and validate data published since 2007, the date of the closure of the French data centre Medias-France where APD was stored. Today, 67 new late Quaternary, 17 Plio-Pleistocene and 20 marine new pollen series have been collated.
Strong links are being developed with NEOTOMA (https://www. neotomadb. org/) and PANGAEA (https://pangaea. de/) databases. These new datasets benefit from improved dating techniques and age modelling methods. The result of which is that newly acquired pollen series have reduced temporal uncertainty and improved resolution, allowing to more precision in interpretation of local and regional ecosystem dynamics and climate-vegetation interactions. All this allows to envisage new scientific developments of which one can cite three examples here:.
CONCLUSION The African Pollen Database aims at providing the scientific community, students and teachers with scientific and educational tools (pollen grain determination tools, modern and fossil data duly validated and dated, publications) to address key issues for understanding the vulnerability of ecosystems facing climate change. It ensures interoperability with international databases for multi-proxy reconstructions of the past environment. Beyond these activities, the African Pollen Database is a scientific network to develop the sharing of data and knowledge between researchers in different countries.
Statistical analysis and data presentation To assess the robustness of the palaeoecological datasets 95% confidence intervals were calculated (following Maher 1981). Bayesian Change Point (BCP) analysis (Barry and Hartigan 1993), which determines if there is a significant change in the mean of the variable at a given point in a time series, was used on: (i) Sporormiella (herbivore) concentration, and (ii) micro-charcoal (fire) concentration data. The posterior probabilities of the BCP analysis indicated the likelihood of significant change of those variables at each time step sampled  (Barry and Hartigan 1993; Blois et al. 2011). Where the posterior probability of the BCP analysis exceeded 0. 8 for Sporormiella or charcoal, a zone boundary was defined, indicating a significant change in herbivory or fire activity.
Future perspectives To determine the relative importance of herbivory and fire as consumers of vegetation, and how this changes through time, at Lake Bosumtwi further research is required. Firstly, a robust internal chronology should be established through detailed examination of the nature and frequency of the laminations, and secondly further details should be extracted from the palaeoecological and palaeoclimatic record. Specifically, detailed pollen and phytolith analyses are required at a higher temporal resolution to characterize trajectories of vegetation change. These vegetation data need to be supported by: (i) further charcoal analyses (micro-and macro-charcoal and charcoal chemistry) to reveal the biomass consumption and temperature of burning  (Gosling et al. 2019; Whitlock and Larsen 2001) , (ii) examination of a full suite of coprophilous fungal spores (not just Sporormiella) to provide insights into changing animal assemblages  (Loughlin et al.
1998; Vandergoes and Prior 2003; Piotrowska et al. 2004 ) with the following preparation steps: (1) Treatment with ∼10% HCl (heated), (2) Treatment with ∼10% KOH (heated), (3) Dense-media separation with sodium-polytungstate (SPT; ∼2. 1 g/cm 3 ),  (4)  Treatment with 12 M H 2 SO 4 for 2 h, with 1. 2 M H 2 SO 4 for 3 h (heated),  (5)  Microscopic analysis of the residues to decide on the next steps for the processing procedure,  (6)  Density separation (1. 6-1. 2 g/cm 3 ) with CsCl or repeated with 2. 1 g/cm 3 SPT, with microscopic control of the potential different phases,  (7)  Sieving (<6 µm). Pollen slides were analysed using a transmitted light microscope (Leica DMRB) with 400-1000× magnification. Pollens were identified by using the reference collection of the DAI (Deutsches Archäologisches Institut, Berlin, Germany), electronic photographs of the African Pollen Database (downloaded in 2012, www://medias.
The Bayesian approach, adapted to scattered data, resulted in an age-depth model indicating a deposition of lake sediments between c. 9650 and 5500 cal yr BP. Based on the published data in  Lézine et al. (2011b)  and complemented by 14 C-dates published in  Jäkel and Geyh (1982) , an extended dataset of published 14 C-dates for the Tibesti mountains was compiled. Following a modified classification scheme by  Lézine et al. (2011b) , the dates were assigned to the categories lacustrine, fluviatile terraces, playas, palustrine, arid and cultural and summed per millennium (Figure  6 ). The frequency distribution of dates of lacustrine contexts peaks during the Early Holocene, as do dates from fluviatile terraces. Considering only 14 C-datings other than calcareous crusts, which are possibly susceptible to the hard water effect and volcanic CO 2 -gazing, sharpens the peak to the Early Holocene.
ACKNOWLEDGEMENTS This study is supported by a grant from the DFG priority program SPP 1234 'Entangled Africa'. DEM data were provided by the DLR (Deutsches Zentrum für Luft-und Raumfahrt/German Aerospace Center). Fieldwork was supported by DFG project 57444011-SFB806. We are grateful to Dr. Baba Mallaye, Director of the Centre National de la Recherche pour le Développement (CNRD) in N'Djaména, for his comprehensive support of the missions. We also thank our team members Jan Kuper and Mahadi Chaha for their help with the sampling. We thank an anonymous reviewer and Jean Maley for their most fruitful reviews and suggestions which most significantly improved the manuscript.
Maley (1970) ,  APLF (1974) ,  Ybert (1979)  and  Bonnefille and Riollet (1980). Pollen nomenclature, which follows the standard defined by the African Pollen Database  (Vincens et al. 2007) , was based on  Lebrun and Stork (1991-2015). The pollen spectra was composed of 105 taxa among which 57 trees, shrubs, lianas and palms, 21 herbs, 16 undifferentiated (trees, shrubs or herbs), 7 aquatics and 4 ferns (Table  1 ). Pollen taxa have been grouped according to the phytogeographical affinity of the parent plants following  Trochain (1940)  and  White (1983)  (Table  1 ). Vincens et al. (2007)  a "type" is added to the name of the taxon (1) to the genus when several plant genera display similar pollen morphology. The species name can be added in case of monospecificity or when the species is dominant or characteristic in the study area (2) to the species when, the genus being clearly identified, several species can be concerned.
Life Family Taxon form SH SL SU GU   Data are presented as percentages and influx values (number of grains/cm 2 /year) and diagrams are drawn using Tilia and CONISS  (Grimm 1991). Pollen percentages were calculated against a sum excluding aquatics and ferns, the percentages of which were calculated separately against a sum including all the pollen grains and fern spores counted. Algae and fungi percentages were calculated against the sum of NPP. Correspondence statistical analyses (CA) were performed on the raw pollen counts using the Package 'Rcmdr/FactoMinR'  (Husson et al. 2020 ). ACANTHACEAE Hygrophila N x Justicia-type I x x Justicia-type flava N x x AMARANTHACEAE Achyranthes-type aspera N x x Aerva-type lanata N x x Alternanthera N x x Amaranthaceae undiff. I x x Celosia-type trigyna N x x Chenopodium-type N x x x Gomphrena N x x Suaeda I x x ANACARDIACEAE Anacardiaceae undiff.
DATA USED In this study, we use all the available Holocene pollen data from northern Africa stored in the African Pollen Database (APD) (Figure  1 ; Table  1 ). We focus on changes in landscape physiognomy, i. e. the shift from a C 3 plant dominated landscape to a C 4 plant dominated one at the end of the AHP. Therefore, pollen records from equatorial lowland forests (e. g. Elenga et al. 1994 Elenga et al. , 1996;; Reynaud-Farrera et al. 1996)  were excluded, since the impact of the environmental crisis, which occurred at the end of the AHP in the Congo Basin, was more a change in forest composition and density than the replacement of lowland forests by grasslands or wooded grasslands  (Vincens et al. 1999). The dataset consists of 36 sites among which seven continental (Bambili, Mbalang, Diogo, Mboro-Baobab, Kajemarum, Jikaryia, Yoa) and one marine (GeoB 9503-5) pollen records have been selected in order to characterize the evolution of the landscape in the    The chronology is given in calendar years BP (cal yr BP) after conversion of 14 C dates to calendar age according to  Stuiver et al.
POLLINATION SYNDROMES OF THE TROPICAL PLANTS The pollination syndromes of the families represented at the seven selected sites (Table  2 ) are derived from  Watson and Dallwitz (1992)  and the gymnosperm database (www. conifers. org). This reveals the major challenge of representing landscapes from pollen data in northern Africa. Most of the families present in our pollen records are entomophilous or zoophilous (mainly cheiropterophilous and ornithophilous), whereas 16% are anemophilous or entomophilous and only 5% are strictly anemophilous. Most of the entomophilous/zoophilous plants produce small amounts of pollen, which may be exceptionally large. As a result, they are under-represented (e. g. Adansonia) or rarely (e. g. Isoberlinia, Daniellia) represented in the pollen assemblages  (Watrin et al.
, 2006). In contrast, members of the Poaceae family, which is exclusively anemophilous, produce large quantities of pollen, and therefore largely dominate the pollen assemblages, particularly those derived from wooded grasslands and grasslands. Taking into account these specifications and the difficulties of measuring the quantity of pollen grains produced by the plants, the most widely used method for describing the pollen signature of the modern vegetation in terms of diversity, biomes or vegetation types is that of surface samples, either from soil, mosses or pollen traps. This method has been successfully developed in tropical Africa since  Hedberg (1954). Gajewski et al. (2002)  have validated the APD dataset, which covers all of sub-Saharan Africa.
A zonation was applied in order to facilitate the pollen data set interpretation. These pollen assemblage zones were done using a CONISS  (Grimm 1987)  cluster analysis. We calculated the Principal Curve (PrC) for our pollen assemblage to summarize the palynological compositional turnover along one ordination axis (De'ath 1999). Charcoal and pollen plots and numerical analyses were done using several R packages (R Core Team 2012). Full code, data and further details can be downloaded from Gil-Romera's GitHub repository shorturl. at/rxMW1 and from Neotoma database.
Palaeoecological records, primarily from fossil pollen, provide key insights into the natural history and origins of the modern ecosystems in Arabia, feedbacks between climate and vegetation, ecosystem resilience, anthropogenic influences, and disturbance. In other regions, dense networks of these palynological records even allow for spatially explicit mapping of past vegetation (e. g. Dawson et al. 2016; Huntley 1990; Webb and McAndrews 1976; Williams and Jackson 2007). In contrast, Arabia is very data poor. This results form a few linked problems: 1) due to aridity, there is a lack of traditional palaeoenvironmental archives like lakes that have existed continuously through multiple climatic cycles, 2) access to regions that have potential for palaeoenvironmental work has become increasingly difficult due to evolving global politics, 3) existing pollen data from the region were housed within the African Pollen Database (APD), which lapsed in 2007 due to lack of funding, making accessibility of data also difficult.
STATE OF RECORDS IN THE AFRICAN POLLEN DATABASE While Arabian palaeoecological records are quite few, their representation as a percentage of those in existence in data repositories such as the APD is also exceptionally low in comparison to other regions of Africa (Table  1 ). For this review, we consider only Arabian records south of the Levant for consideration, as Levantine and Near Eastern records have been contributed commonly to the European Pollen Database due to their Mediterranean affinity. The original data holdings of the APD dating to 2007 includes only 7 datasets. Within the framework of the relaunch of the APD, work has begun to inventory all Arabian records and encourage new data contributions. As a result, Table  1  shows that, of the 40 publications including pollen datasets, 9 new datasets have been contributed to date (total 16 Arabian records in APD).
Pre-Holocene Little palaeoecological information exists about the Cenozoic flora of Arabia prior to the Late Pleistocene, and none which falls under the convention of the African Pollen Database. The little that can be inferred is based on the ancient biogeographic connection of Arabia with Eastern Africa. Prior to the inception of the East Africa Rift system, the Arabian and African plates were joined, forming a continuous stretch of land from what is now Ethiopia into southwestern Arabia (Yemen, Oman, and Saudi Arabia;  Guba and Glennie 1998). This connection with Africa in the Eocene and Oligocene that sets the legacy of the modern floristic affinities with the African continent  (Kuerschner 1998). By c. 30 Ma ago, the Arabian plate separated from Africa which likely had important consequences for the climate and flora of the region.
2002; Ivory et al. , 2021). However, it is important to note, that as discussed above, much of southern as well as northern Arabia remained arid or semi-arid even at the peak in the monsoon, thus we suggest that these changes in vegetation composition are likely linked to the presence of increased surface water amidst persistent climatic aridity. Finally, the increase in biomass during the early to Mid-Holocene also appears to have resulted in a change in the dynamics of wildfires in some location in Arabia. Today throughout Arabia, wildfire is extremely uncommon due to lack of fuel and continuity of fuel on the landscape because of extreme aridity  (Cao et al. 2015). Charcoal and microcharcoal datasets are rarer even than other palaeoecological information; however, increased charcoal deposition in palaeolake deposits, hyrax middens, and even the appearance of burnt surfaces in fine-grained stream deposits is a testament to the increase in fuel locally, linked to higher rainfall seasonality  (Kimiaie and McCorriston 2014; McCorriston et al.
CONCLUSIONS The vegetation of Arabia is strongly imprinted by biogeographic and palaeoecological processes that unfolded over millions of years beginning with the separation from Africa during the Cenozoic. Although little empirical palaeoecological data exist, new efforts to relaunch the African Pollen Database including Arabia will galvanize new research efforts as well as syntheses by conforming to FAIR data standards that make existing data easier to find and work with  (Ivory et al. 2020; Wilkinson et al. 2016). This review attempts to summarize some of this work and inventory data holdings currently within the APD. Palaeoecological information from Arabia make it clear that while ecologically diverse and endemic, Arabian ecosystems have existed on the edge of extreme aridity for at least hundreds of thousands of years.
Pollen And Vegetation Data The collection of soil samples and vegetation surveys for the RPP study were performed in February 2010, October 2012, and April 2015. The pollen-vegetation dataset includes data from 4 sites in semi-deciduous forests, 10 sites in mountain forests, and 16 sites in savannahs (Figure  1 ; Table  S1 ). For further details on the methods used for collection of the pollen samples and vegetation surveys, pollen analysis, vegetation data handling, and on data access please see Supplementary Online Material, SOM-12. 1.
ERV analysis and RPP estimates Vegetation dispersion and mean plant cover over distance from the pollen sample points (Figure  3A ) based on the collected vegetation dataset (SOM-12. 1. 3) indicate that the ERV model's assumption of stationary vegetation is violated in the study region. Both vegetation dispersion and mean plant cover increase with distance until maximum values at c. 50-100 m and then decrease until c. 600 m instead of reaching an asymptote. The values of mean plant cover for Alchornea, Macaranga, Celtis, Moraceae and Poaceae indicate that these taxa have a more stable composition already from c. 200 m. The log likelihood curve shows a similar pattern as vegetation dispersion, although with a much less prominent 'overshoot' of the curve at 50 m. From 600 m, the values of mean plant cover remain relatively constant for all plant taxa.
Effects of violation of model assumptions and other factors The effects on RPPs of deviations from the ERV model assumptions and other factors have been discussed earlier in syntheses of RPP values in Europe  (Broström et al. 2008; Mazier et al. 2012) , temperate China  (Li et al. 2017 ) and the Northern hemisphere  (Wieczorek and Herzschuh 2020). The number of factors affecting RPPs and/or causing between-study variability in RPP values for a taxon are numerous. They span from between-study region differences in climate, land use, vegetation type/structure and plant species (including their pollination strategies), between-study variation in methods used to collect the pollen-vegetation dataset (including methods in field and laboratory, and data handling), to differences between models and/or model implementation (including dissimilarities in parameter setting, parameter values, and calculation procedures).
Gajewski et al. (2002)  analysed a database of all surface pollen data available in Africa and concluded that percentages of the three most abundant pollen taxa did not show any bias among sampling methods. However many studies have indicated biases of pollen assemblages in soil samples compared to, e. g. pollen traps due to poor preservation conditions (e. g. Zhang et al. 2015). We therefore assume that the most common pollen types in soils are those that are well preserved due to their species/taxon-specific wall structure, and that their amount corresponds to the pollen transported and deposited in the soil. To our knowledge, little is known on the number of years of pollen deposition in soil samples (e. g. Havinga 1984 ). Thus, we assume that they represent some years of pollen deposition.
LRA reconstructions of Holocene plant cover at regional and local spatial scales Although the 11 pollen taxa used in the LRA reconstructions generally represent > 60-70% of the total pollen sum of terrestrial pollen types in the four pollen records (Table  S3A ), it is essential to keep in mind that we are missing in many cases a third of the pollen record. Major taxa for which we would need RPP estimates to achieve more complete reconstructions of the plant cover are: Aerva-type, Antidesma-type, A. venosum, Ficus, Gnidia, Justicia, Maesa, and Rapanea (mountain woodlands), and Cussonia, Hymenocardia, Ixora, Olea, Tetrorchidium, and Uapaca (wooded grasslands). One RPP value  (19. 19  relative to Poaceae) is available for Justicia (Navya 2020). Based on a large database of surface pollen samples in Africa,  Gajewski et al.
2020; Tabares et al. 2021). In future work, the use of combined satellite and drone data might help to decrease the amount of field work and increase the consistency of vegetation datasets over large areas around each pollen sample site. The latter would probably improve the performance of models for estimation of RPPs. The LRA reconstructions in this study provide a first tentative quantification of changes in the Afromontane woodlands and wooded grasslands of Cameroon over the Holocene. The results suggest that the regional landscape in the mountain region was more open than pollen percentages suggest, and that the collapse of the high altitude forests around Bambili at 3 ka BP was faster and of larger magnitude than indicated by the pollen record. The latter will need to be confirmed by further studies involving a larger number of major taxa characteristic of the Holocene vegetation history of Cameroon.
The reconstructions also suggest that the woodlands' taxa composition, at both regional and local scales, is different once the pollen percentages are corrected using the RPP dataset and RPPs 2. 62 or 6. 38 for Podocarpus. The LRA reconstruction for Mbalang confirms the local occurrence of mountain woodland around the lake in Mid-Holocene. The correction of the pollen percentages indicate a larger cover of Prunus africana/Rubus pinnatus and Moraceae than their pollen percentages. Podocarpus and Moraceae are the most problematic taxa to model with the RPPs currently available. The reconstructions using high RPPs for Podocarpus are the most probable so far. It is not possible, based on this study, to assess the reliability of the available RPPs for Moraceae. U. Salzmann (University of Northumbria, Newcastle) and A.