Palynomorph quantitative representation and interpretation in vegetation studies.
Palynology is a multi-disciplinary field of science that deals with the study and application of extinct, [fossilised] and extant palynomorphs (pollen and spore) and other related microscopic biological entities in the environment. It is divided into palaeo- and actuo-palynology, and provides substantial proxies to understanding past and present vegetation dynamics respectively. With reference to the two geological principles of uniformitarianism and of the evolution of fauna/flora, the distribution of plant indicators across ecological zones, palynomorph morphology and pollen analysis, palynology can be used to identify the change in past and present local and regional vegetation and climate and humans impact on the environment. Other supportive areas of endeavour like radiocarbon dating, sedimentology, taphonomic processes and geomorphology can be used to triangulate inferences drawn from palynological data. Palynomorphs are made of outer cell walls embedded with an inert, complex and resistant biopolymeric signature (called sporopollenin) which helps to facilitate long term preservation in different environmental matrices under favourable conditions, hence its widespread applicability. Palynology have proven to very reliable in reconstructing past vegetation, decrypting essential honeybee plants and understanding the impact of climate on plant population using pollen analysis, for which is the basis for the application of palynology in environmental studies. The application of palynology in climate, vegetation and anthropogenic studies begins with the selection of matrix (sediments from lake, river, ocean, excavation, relatively intact soil profile, bee products), coring or collection of samples, subjection to a series of chemically aided digestion, separation, physical filtration, decanting, accumulating of palynomorphs, microscopic study and ends with the interpretation of recovered information. Literature review on the application of palynology for understanding vegetation and climate interactions is presented in this paper.
- vegetation dynamics
- pollen analysis
- environmental reconstruction
In this review, vegetation dynamics is the succession pattern, spatial distribution, diversity and interaction of plants with humans traceable by pollen footprints in terrestrial ecosystems. Kim  opined that vegetation dynamics is greatly influenced by climatic factors and patterns of land use by humans. The changes in vegetation pattern occur rapidly or gradually, and palynology can be used to study these changes. Palynology provides fair playing ground for participatory and collaborative research bordering on understanding past and recent changes in the vegetation of an area. By virtue of the principles of palynology and of pollen analysis, pollen grains and spores are best applied to resolving environmental puzzles especially those related to vegetation change. It is important to emphasise that palynology is highly preferred and considered rich in providing indices on the change in vegetation in a place for several reasons; the chemically resistant compound embedded in the outer walls of pollen and spores facilitating preservation, the ubiquitous nature of pollen and spore, high pollen productivity, distinctiveness in the morphology of pollen types helping in identification of parent flora among others. The organic compound in the pollen is resistant to microbial attack, temperature regimes and pressure when buried in the soil and lastly because palynomorphs are produced in abundance, transported by wind, human, insects (and other animals) or water to different environments and ubiquitous in nature. The ubiquitous characteristic nature of pollen is a function of its productivity and there is currently very limited data on it. Unpublished data with Sowunmi  and Obigba  has revealed that the pollen productivity for
1.1 Palynology and its applications
The term palynology was first introduced in 1944 . The word palynology was derived from two Greek words “
Sowunmi  defined palynology as
It is primarily divided into two (past – palaeopalynology and present - actuopalynology), and has become highly applicable in several other emerging fields but only those involving vegetation dynamics will be discussed here. Palaeovegetation (or palaeoecology), petrolipalynology, palynostratigraphy, archaeopalynology, forensic palynology, pharmaceutical palynology, melissopalynology, paleobotany, palynotaxonomy or systematic palynology, and aeropalynology are some of the areas of research in palynology. There are several other emerging fields of interdisciplinary research in palynology which has spanned into plant systematics, apiculture, public health, earth sciences, climatology, environmental reconstruction and archaeology, however, other supportive mechanisms like radiocarbon dating, sedimentology, taphonomic processes and geomorphology can be used to triangulate inferences drawn from recovered palynomorphs.
1.2 Palaeovegetation and environmental reconstruction
This area of research is centred on understanding past ecological dynamics in view to elucidating the past and present legacies of humans, the changes in the regional and local ecosystems, the impact of climate variability and how these information can be used in predicting future changes or current patterns. Palynology has been used for decades for understanding palaeovegetation dynamics and changes from analysing different substrates like guano deposits [8, 9], climate changes in forests , rock shelters , lakes sediments  or surface sediments . The word ‘palaeo’ means ‘past, ancient, old or prehistoric’, so, it will be acceptable to say palaeovegetation is vegetation of the past or prehistoric vegetation. One of the way in understanding change in vegetation is by studying palynomorph abundance and variability in undisturbed stratified sediments. Two geological principles are used to support palaeovegetation studies. The first is the Principle of Uniformitarianism which proposes that the natural geologic laws or processes that exist in the present day are same or at one time were observed in the universe in the past, and these changes apply to every other area on earth. The inference is that, the earth has always had uniform changes and that the present changes can be used to uncover changes that occurred in the past and vice versa. Therefore, the changes that occurred in past in terms of vegetation are almost same as at today. The second law is the ‘Evolution of fauna and flora’ which says that in a vertically stratified sedimentary soil profile, the stratum on top is younger in age and formation than the one below. What this means is that, the farther the stratum down the earth, the older the soil and the closer the stratum to the surface, the younger it will be. This also implies that these strata are embedded with fossilised plant and animal remains preserved over time. In recent times, the law has been referred to as the ‘principle of fauna/flora succession’ [14, 15] where fossilised materials succeed themselves in the vertical strata. That is, the fossilised fauna and flora beneath evolved to the next stratum just next to it (on top) and so on till it gets to the earth surface or top soil. This order occurs in a reliable format except for disturbed and distorted soil profile. This principle is applied to paleo-vegetation up to what I called ‘actuo-vegetation’ using pollen analysis of each stratum referred to as sub sample. Since inception several studies have been conducted on this. Novello et al.  described how palynology was used to decipher last glacial (115,000 years before present) to Holocene (about 12,000 years before present) vegetation and environmental change in South America using cave deposits. Using certain pollen types, the palaeovegetation changes with respect to pollen abundance in sediments through routine pollen analysis are presented below. These reviews provide clues to the vegetation dynamics based on the presence or absence of pollen grains in the sediments and possible factors influencing their abundance in the sampled regions.
1.3 Melissopalynology and conservation of bee flora
Melissopalynology is the branch of palynology that deals with the study of palynomorphs in honey and other honeybee products like propolis, beewax and bee breed. The aim is to find out the botanical and geographical origin of the honey . Honey is produced by the action of eusocial honeybees foraging for proteins and carbohydrates. They visit ‘nectariferous’ and ‘polliniferous’ flowers (Figure 1, No 6 & 8) for pollen and nectar and sweet fruits like pineapple, mango, water melon and others (Figure 1, No. 1–5 & 7) for natural sugars. Honeybees are regular visitors of very colourfully scented flowers for nectar or pollen because their larval and adult dietary requirements depend on it . Pollen is the bee’s major source of protein, fat, minerals and vitamins, while nectar is the major source of carbohydrates from which honeybees source for energy. In the course these foraging expedition, the honeybees collects pollen and other non-pollen materials (honeydew elements) co-incidentally for the production of honey in their hives. The pollen is the focus for this aspect of palynology and its usefulness for vegetation dynamics of the present day. Preliminarily, pollen grains are the male microgametophyte of either unicellular or multicellular form that is produced in the flowers with the primary responsibility of pollination and fertilisation. This invariably means they can be used to track flowering patterns for honeybee plants. Honey bees are major pollinators among flying insects and are so essential in conserving plant diversity.
Apiculture is the aspect of agriculture that covers this part of biological sciences. Melissopalynology thus deals the representation of pollen types (that is flowering plants visited by honeybees) in honeys collected and marketed for humans. Depending on the rate of foraging and seasonality of flowering in honeybees plants, honeybee farmers can collect or extract honey from honeycombs or artificially manufactured hives on a weekly or monthly basis. The taste, colour, texture and fragrance of the honey are dependent on the type of flora visited. If the honey is derived from a single flora, it is called unifloral and if it is from several floras, it is referred to as multifloral or polyfloral honey. In understanding flora dynamics, mulitfloral honeys are best for analysis. This can reflect the yearly pollen calendar for a locality where plants are cultivated or grown in the wild. Several studies have been carried out in this aspect by many researchers. Vegetation dynamics
The atmosphere is made of several airborne particulate matter of which pollen and spores are part of. Wind dispersed pollen and spores are released from lower green and flowering plants respectively at different times in the year and can be used to trace seasonality and presence of pollen in the atmosphere for public health reasons. Aeropalynology as the name implies is the study of airborne palynomorphs sampled through a pollen trap. This study is important if deleterious allergy triggers must be identified. One of the founding fathers of palynology, Erdtman, defined aeropalynology as the study of pollen and spores in the atmosphere . In Ezike
This area of research is in environmental archaeology where the interaction of humans with their environment (particularly the plants) in antiquity is deciphered by detail analysis of pit excavations. The archaeological materials alongside with the palynomorphs recovered are used to interpret past interactions of humans with their flora. There are anthropological studies available on this aspect involving the use of palynology e.g. farming history and prehistoric weapon production and furnace use [11, 23]. Johnston  mentioned that archaeologists in the course of their study find fossilised pollen and spores of different shapes in excavations; hence, archaeopalynology is the study of palynomorphs in archaeological sites in an attempt to reconstruct the ancient lifestyle (diets, farming practices, raw material sourcing), food sources, physical landscape, domestication attempts and the understanding the impact of humans on earth. The methods in the analysing archaeopalynological samples are outlined in the paper by Dontella and Federico . It includes removal of organic and inorganic matter, microscopy, identification and counting. Based on the pollen types found, the vegetation types and interaction of humans with the flora can be elucidated. The law of geologic laws of uniformitarianism and flora/fauna succession is also applied here. It is important to succinctly note that pollen analysis remains the basis for the application of palynology in vegetation studies. Some important archaeopalynological works has been carried out in Nigeria like those of Orijemie [11, 23].
2. Pollen analysis, identification and vegetation-climate interaction
2.1 Pollen (or palynomorph) analysis
The application of palynology in any field is basically dependent on the use of pollen analysis for deducing inference on vegetation-climate-human interactions. Pollen analysis is relatively laborious, time consuming and expertise demanding. The purpose for pollen analysis is to disintegrate the palynomorphs from their matrices and concentrate them for proper identification. It is only the series of analytical procedures commencing with the collection of palynomoprh embedded substrates (honeybee products – pollen pellet, honey, propolis, terrestrial and aquatic sediments, air borne particulate matter, excavations, anther from flowers, faecal matter, drug samples and rocks) from the field to laboratory processing of the substrates (Figure 2). Microscopy which helps to determine relative abundance of one palynomorph type in comparison to other follows immediately after the laboratory processing. Depending on the type of matrix and the aim of the analysis, different laboratory procedures are employed. For example, the qualitative study of palynomorphs requires acetolytic (chemical removal of protosplamic content using 9:1 of acetic anhydride and concentrated hydrochloric acid) processing for elucidation of exine ornamentations or patterns. This may not be necessary for quantitative study of pollen and spores in honey or sediments. They type of matrix determines the number of treatments to be used. For soil matrices, the numbers of chemical processes are more than other matrices like honey, drugs samples, or pollen pellet. Erdtman  and Faegri and Iversen  gives full description of pollen analysis, however, the figure below shows a summarised procedure for pollen analysis of palynomorph embedded samples.
In the interpretation of results from pollen analysis, there are several limiting factors. These factors influence the representation of palynomorphs when recovered. Some of them are pollen dispersal mechanism, pollen productivity, and differential preservation capacity against environment induced deterioration. In interpreting of pollen analysis, microscopy, identification and counting are used as the quantification presented in Table 1. In counting and providing information about the abundance of a particular pollen type, Jones and Byrant  and Louveaux,
|Categorisation||Quantification (in %)||Interpretation based on dominance of the plant species|
|Predominant||more than 45||Overwhelmingly abundant flora in the vegetation|
|Secondary||16–45||Major vegetation coverage in the area that is complimenting the ‘predominant’ plant species|
|Important minor||3–15||Very useful flora present in the vegetation|
|Minor||between 1–3||Scanty and insignificant in number|
|Present||less than 1||Rarely noticed in the vegetation|
2.2 Pollen identification
The application of palynology on every other area of research is largely dependent on the accurate identification which is powered by the impeccable description of the morphological features of the pollen types recovered from the environmental matrix. Pollen grains are unicellular to multicellular units composed of a cell wall and protoplasm. The morphological features and their distinctiveness are found on the cell wall especially in the outer cell wall called the exine. The parameters used in describing pollen grains are polarity, symmetry, aperture types, pollen class, pollen size, and exine ornamentation (details in Figure 3). Expert experience is highly in identification since some pollen types may have close resemblance but represent different vegetation types e.g.
2.3 Late quaternary climate vegetation interaction in tropical West Africa
According to the geological time scale, the Late Quaternary is from 65,000 years BP (before present) to date. During the period, the plant communities were greatly influenced based on their response to climate change. Information on the fluctuation in mangrove and freshwater swamp forests, the relative dominance of other forms of forests and savanna is provided. As provided in details in Sowunmi  paper, the following were some of the vegetation-climate changes that had occurred basically in the expansion and contraction of forests and savanna and a wet-dry climate cycle. These changes were categorised into six time frames as presented in Table 2.
|Phases||Time frame||Climate||Savanna||Forest||Sea level|
|1||between 40,000 and 30,000 yrs. BP||Wet||Reduction of savanna||Extensive presence of freshwater swamp, distension of mangrove swamp farther south of the present day limits. Dry forests in the northern region became wetter (that is a gradual movement from drier to wetter type forest conditions)||Sea transgression which led to the re-establishment of the mangrove swamp (Inchirian transgression).|
|2||between 30,000 and 25,000 yrs. BP||Drier||Expansion of savanna southwards to cover forests. Deserted or Saharan landscape replaced by Sudanian vegetation farther north. Ergs formation in sahel and sudan||Destruction of forests or reduction of forests into pockets or refugia||Occurrence of the Ogolian regression, fall in sea levels|
|3||between 25,000–5,000 yrs. BP||Wetter||Forests re-established, became denser with increased species diversity, regrowth, expansion and extension of the Mangrove swamp||Nouakchottian transgression, rise in sea level|
|4||between 5,000 and 3,500 yrs. BP||Very wet and later dry||Expansion of savanna||Mangrove swamp forest disappeared (? 4000–3500 yrs. BP), forest reduction||Nouakchottian transgression continuation until 4000 yrs. BP from 5000 yrs. BP, later sea regression|
|5||between 3,500 and 3,000 yrs. BP||Wetter||Contraction of savannas||Expansion of forests|
|6||From 3,000 yrs. to present day||Warm and dry||Sudan and Sahel savannas depreciated in vegetation.||Northern axis of the forests was replaced by woodland savanna|
|increase in human inference in the natural vegetation (the Anthropocene), burning of vegetation, animal grazing and extensive farming|
3. Empirical studies
3.1 Palynomorphs, human-plant interactions and vegetation change
Anthropocentric (human cultural) and the anthropocene (climate/human induced) forces have altered ecosystems, plant growth response, habitat characteristics, and behaviour of plants in recent times. In West Africa, there are evident adaptive changes in certain plants including their survival and growth in diverse vegetation zones. Today, many savanna species are found growing favourably in residential areas in mangrove and fresh water swamp regions in West Africa. Although a few species are still considered useful in deciphering vegetation dynamics during pollen analysis as presented in Table 3. This is particularly noticed in the way savanna species thrive and survive in forest regions in southern Nigeria, although the survival of forest species in savanna has not been convincingly proven. Anthropogenic factors has led to the opening of forests canopies and planting of savanna (including ornamental) plants species and the guinea savanna region and deciduous low land rain forest is fast becoming a forest-savanna mosaic sometimes referred to as forest savanna transition. The availability of water, human interference through cultivation, burning, soil spatial variations, or herbivory pressure characterise this transition zone. Depending on the microclimate and anthropogenic impact, savanna and forest plant species co-exist, hence the presence of other vegetation-specific plant indicators are used to make decisions. Spores are usually used as bio-indicator for microclimates hence; the percentage of pollen and spore are good indices for understanding vegetation change and climate variability. Correct pollen identification is crucial to this application. Table 2 shows the plant or pollen indicators that can be used to different vegetation types if there abundance in sediments is measured on the basis of Table 1 above.
|Vegetation types||Pollen/flowering plants||Spores/lower plants|
|Open/disturbed forest/open vegetation||Asteraceae, Poaceae (grasses)||Amaranthaceae/Chenopodiaceae|
Freshwater swamp forest
|Residential and Ornamentals|
3.2 Understanding vegetation dynamics using percentage representation of palynomorphs recovered from environmental matrices
As earlier established in this review, pollen and spore percentage representation can be used to understand vegetation changes. This section will focus on changes in the abundance of certain pollen types (inferably, the plant species) in different environments across the globe and the possible factors influencing these changes. Some of these plants in
In Cameroun, Assi-kaudjhis  studied vegetational evolution in the Crater Lake Bambili which lies in the volcanic zone through the pollen analysis of sediments cored from two sites around the lake, a region located in the Guinean-Congolian forest belt. An inventory of the plant biodiversity was taken, and
In India’s Lonar Crater Lake, Riedel
3.3 Climate variability induced vegetation dynamism and interactions
The succession of one vegetation type by another is influenced by climatic, human or edaphic factors, or a combination of the triad. Across the globe, the phenomenal change and succession of vegetation in the past and present have been revealed through palynological studies. Few empirical studies are reported in this chapter for clearer understanding.
In Maya region of southern Mexico and Central America, Franco-Gaviria
In south western region of Nigeria, Orijemie  investigated climate-vegetation dynamics using an 8 m-core drilled in Ikorigho with comparison with Ahanve to provided evidence of late Holocene mangrove dynamics and environmental changes. The vegetation was found to have changed from mangrove to low land rainforest. Mangrove swamp forest species were indicated by pollen and spore of
In central Gabon, Ngomanda
In Benin Republic in West Africa, Tossou
In Lake Chad region, Amaral
In Ghana, West Africa, Miller and Gosling  presented a fossil pollen record from sediment cores extracted from Lake Bosumtwi. The record covered the last c. 520,000 yrs. BP making it a apart of the Late Quaternary. The fossil pollen assemblages revealed that there was a dynamic vegetation change which can be broadly characterised as indicative of shifts between savanna and forest which also reflected the glacial – interglacial period. Savanna elements which heavily dominated the vegetation included Poaceae pollen (>55%) and was associated typically associated with Cyperaceae, Chenopodiaceaee/Amaranthaceae and Caryophyllaceae. Forest formations are were more diverse than the savanna, with the key taxa occurring in multiple forest zones being Moraceae,
In Cameroun, Lebamba
3.4 Honey, pollen and vegetation representation
Pollen analysis of honey samples started a long time ago dating back to late 1970 with Sowunmi  as foremost. Several reports are available on the melissopalynological analysis of honeys from different parts of Nigeria as reviewed as follows. One of the earliest studies was that of Agwu and Akanbi  in view to understanding the botanical origin of the honeys from Bichi, Edem-Ani, Nanka, Nimo Nsukka and Ogbomosho including Ohafia and Port Harcourt. They found out that 56 pollen types were identified in all belonging to 14 families, genera and tribes. Ogbomosho had the highest (29) number of pollen types. The study revealed that most of the honeys were rich in pollen apart from the Port-Harcourt and Ohafia honeys that were adulterated. The species that were dominant or most preferred by honeybees include
Melissopalynological analysis of four honey samples from four localities of Kogi State (Idah, Ajaka, Igalamela–Odolu and Inachalo-Oforachi) was carried out by Aina
Oyeyemi  collected three honey samples from an apiary for three months to determine the change in pollen content for the months of October to December in Ado Ekiti. The study revealed that pollen count ranged from 106,962 to 171,487. The honey samples were found to be multifloral in source and had abundant
Adekanmbi and Ogundipe  analysed three honey samples bought from open markets in Lagos, Nigeria. The proportion of pollen from each of the honey samples varied from 196 to 280. The most abundant taxa were
The genetically conscripted chemical signature called sporopollenin in the outer cell walls enhances the ability of palynomorphs to retain their shapes even after subjection to heat and pressure in sediment treatment with concentrated acid during routine palynological procedures. This enables clear identification of pollen types and in extension the vegetation dynamics. The identification of pollen flora in honey is currently been considered as good means of understanding economically and traditionally important plants for conservation and reforestation. The daily dispersal of pollen (including the allergenic ones) in the atmosphere sheds light on the seasonally of vegetation, their flowering, productivity of pollen and contamination of atmospheric quality. Studying cores from lakes, rivers and soil profiles provides evidence for the change in vegetation in relation to climate, plant response to stress and human interference in the past. This is applied based to vegetation science by virtue of the percentage representation pattern of palynomorphs. Although caution must be exercised in interpreting palynological data due to the moderating factors like differential preservation of pollen grains based inertness of the chemical compound in its outer wall, limited knowledge on pollen productivity of flowering plants, dispersal mechanisms which affects the quantity of grains recovered from soil and honey or atmospheric samples, issues of pollen morphological similarities. Describing and attributing vegetation characteristics to a locality or region, the modern behaviour of plants is to be considered.
The author’s special appreciation goes to Prof (Canon) M. Adebisi Sowunmi for laying the academic foundation for the understanding of palynology. Her academic, career-based and motherly advices were so helpful and she is so highly appreciated. Her contributions were highly transformative. The author is also grateful to Dr. E.A. Orijemie and Mr. P.C. Opara for their support, encouragement and support. To my parents Mr. and Mrs. Austin O. Kobi, I express my gratitude for the prayers and financial support.