Tropical Mixed Deciduous Forest Research Articles

Late Holocene vegetation history and monsoonal climate change from the Core Monsoon Zone of India

To understand the vegetation response to climate change and the Indian Summer Monsoon rainfall (ISMR) variability during the Late Holocene (approx. 2.5 ka), pollen analysis was conducted on a 1.2-m-long lacustrine sediment profile from the Korba District of Chhattisgarh, central India, within the core monsoon zone (CMZ). The pollen evidence suggest that between approx. 2500 and 1950 cal yr BP, open tropical deciduous forest vegetation occupied the landscape under a warm and relatively less humid climate, coupled with decreased ISMR. Between approx. 1950 and 1035 cal yr BP, a warm and relatively more humid climate prevailed, along with moderate ISMR, leading to the transition of the existing vegetation to an open mixed tropical deciduous forest. Between approx.1035 and 220 cal yr BP (CE 915–1730), the mixed tropical deciduous forest became established under a warm and humid climate with increased ISMR, coinciding globally with the Medieval Climatic Anomaly (MCA). Mixed tropical deciduous forest expanded and transformed into a dense mixed tropical deciduous forest between approx. 220 cal yr BP to the present (CE 1730 onwards). This transformation occurred under a warm and relatively more humid climate, accompanied by intensified ISMR, aligning with the Current Warm Period (CWP). Gradual forest transformation from open vegetation to dense mixed tropical deciduous forests, as well as in the ISMR has been observed since the last approx. 2.5 ka in central India. Cereal-based agricultural practices and other anthropogenic activities have been documented in the study area since approx. 2.5 ka, with an accelerated pace observed from 1035 cal yr BP to the present.

Dust captured by a canopy and individual leaves of trees in the tropical mixed deciduous forest: Magnitude and influencing factors

Forest tree leaves play a significant role in air purification, but forest fires could offset the dust sink role. This study aims to assess the functions of the forest in atmospheric dust sink and source and assess the dust capturing capacity of individual leaves of various tree species in the tropical mixed deciduous forest in the dry season (November 21, 2021, to January 23, 2022), along with its influencing factors—climatic variables, environmental variables, and leaf morphology. The result shows that the downward flux or the forest dust sink role was predominant midday when air–mass turbulence played a role. Nonetheless, net mass PM1 and PM10 concentration trapped by the forest canopy was low, 0.79 and 2.24 µg m−3, respectively. For PM2.5, forest fires could outrun the PM2.5 sink role for the entire dry season. Considering the individual tree leave, maximum dust capturing capacities for the forest trees ranged from 0.95 to 5.197 g m−2. Leaf dust capturing capacity was enhanced under cold and dry weather, strong winds, and for trees with defoliated or irregular shape. Leaf/leaflet enhancing the dust capturing capacity exhibited large size; either thick and leathery texture (Coriaceous) or thin, semi-translucent, membrane-like texture (Membranaceous); indumentum top being short, stiff trichomes (Scabrous); or indumentum bottom surface being densely short, soft trichomes (Tomentose). The various dust capturing dynamics among tree species could benefit dust capturing by the forests in the dry season.

Modern pollen–vegetation relationship from the Mahasamund District (Chhattisgarh), central India: implications for palaeoecological reconstruction

The study of modern pollen–vegetation relationship is crucial for the proper interpretation of fossil pollen records. In the present study, a total of 29 surface samples, collected from the edge of the forested areas of the Mahasamund District, Chhattisgarh State, central India, were palynologically analysed with the principal aims of evaluating the modern pollen assemblages and understanding the modern pollen and extant vegetation relationship. The study reveals the dominance of non-arboreal pollen (NAP) taxa over the arboreal pollen (AP) taxa, suggesting open mixed tropical deciduous forest type vegetation in and around the study area. The tree taxa, on the whole, constitute an average sum of 19.78% pollen of the total pollen sum, whereas the contribution of herbs is 43.58% pollen (average sum). The major non-arboreal taxa are Cerealia/Cereal Poaceae (average value; 5.45% pollen) and Poaceae (average value; 4.34%), whereas the cultural plant pollen taxa, such as Amaranthaceae, Caryophyllaceae, Brassicaceae, Cannabis sativa, Alternanthera, and Borreria contribute with an average sum of 11.69% pollen to the total pollen sum. Most of the common forest elements are not recorded because they are insect-pollinated or have low pollen preservation potential, and, hence, the modern pollen assemblages do not directly reflect the actual extant vegetation occupying the landscape of the study area. This bias would also be expected in late Quaternary pollen records of central India and, hence, can provide information of the actual vegetation when analysing fossil pollen samples.

Chlorophytum sikkimense (Agavoideae; Asparagaceae): a new species from Sikkim Himalaya

A new species of Chlorophytum is described from Sikkim. The new species is distinct from other closely related species (C. assamicum and C. breviscapum) by its scape with sterile bracts, pedicel articulation above middle, longitudinal anther dehiscence and white ovary. It grows in similar habitat as aforementioned species i.e., floor of tropical mixed deciduous forest at an elevation of 600–700 m and currently known only from Sirisay forest of Sikkim Himalaya. Detailed description and color plates of the new species are provided.

Is bat guano a potential pollen trap? A comparative assessment from conventional soil and moss substrates from Eraaning Cave of Meghalaya, India

This study examines the pattern of preservation of pollen and non-pollen palynomorphs on bat guano samples in Eraaning Cave in relation to the current vegetation of the surrounding Garo hills of Meghalaya. It is observed that, the recorded pollen data does reflect the tropical mixed deciduous forest with an admixture of riparian and evergreen plant taxa from the local and regional vegetation. The presence of evergreen and riparian taxa namely, Mesua, Schima, Duabanga, and Syzygium in the pollen assemblage is strongly indicative of the high rainfall in the region. The recovery of fern and fungal spores in the pollen assemblage also reflects the warm and humid climatic condition in this region. The forestland and open-land samples from the vicinity of the cave were also studied to understand the nature of pollen preservation in relation to the bat guano samples. The presence of cereal, Areca, Psidium, and Citrus along with Melastoma pollen in both bat guano and open-land samples is indicative of the anthropogenic activities in and around the study area. Multivariate principal component analysis (PCA) and box plot were applied to the quantified data obtained from pollen frequency analyses which clearly revealed a significant variation and similarity in vegetation types among the surface samples collected in and around Eraaning Cave. The generated pollen data from the bat guano, forestland, and open-land samples reveals that, bat guano in cave sediments provides a reliable substrate to understand the modern pollen and vegetation relationship and can fruitfully be utilized as a baseline for the reconstruction of the palaeoecology in the Garo hills of Meghalaya. The study also suggested that the bat species utilized the mixed vegetation composition and different landforms as their preferred habitats as demonstrated by the pollen data from the bat guano samples.

Monsoonal climatic reconstruction from Central India during the last ca. 3600 cal yr: signatures of global climatic events, based on lacustrine sediment pollen records

Pollen analyses of a 90 cm deep lacustrine sediment profile from the Mahasamund District of Chhattisgarh State, central India demonstrated that between ca. 3600 and 2500 cal yr BP (Neoglacial climate interval), open forest vegetation occupied the landscape in the region under a dry climate, probably indicating reduced monsoon (the Indian Summer Monsoon: ISM) rainfall. Further, the open forest vegetation was succeeded by a mixed tropical deciduous forest between ca. 2500 and 1650 cal yr BP (∼550 BC to AD ∼300) under a warm and humid climate with increased monsoon rainfall. The warming period and an amelioration of climate (strong ISM condition) is comparable to the Roman Warm Period (RWP), recorded globally between 2500–1600 cal yr BP (∼550 BC to AD ∼350), and also known as the ‘Golden Age of India’ owing to increased agricultural output, trade commerce and socio-economic prosperity in India. Subsequently, between ca. 1650 and 950 cal yr BP (AD ∼300–1000), the existing mixed tropical deciduous forest transformed into an open mixed tropical deciduous forest under a warm and relatively less humid climate with reduced monsoon rainfall, correlatable with the Dark Ages Cold Period (DACP). Finally, between ca. 950 cal yr BP to the present (AD 1000 onwards), mixed tropical deciduous forest again came into existence and occupied the landscape around the study area under a warm and relatively more humid climate with intensification of the monsoon rainfall, corresponds with the Medieval Warm Period (MWP), which is known between AD 740 and 1150 worldwide.

Vegetation response to the Indian Summer Monsoon (ISM) variability during the Late-Holocene from the central Indian core monsoon zone

Pollen analysis and radiocarbon dating of a 1.4 m deep lacustrine sediment profile from Chhattisgarh State, central India, in the core monsoon zone (CMZ), has revealed the vegetation history, associated climate change and the Indian Summer Monsoon (ISM) rainfall variability during the Late-Holocene. The pollen evidence suggests that between ca. 3000 and 2600 cal year BP, tree-savannah vegetation occurred in the region having a comparatively lesser monsoon rainfall. The forest expanded and culminated into an open-mixed tropical deciduous forest between ca. 2600 and 2200 cal year BP under a warm and moderately humid climate with an increase in monsoon rainfall. Subsequently, between ca. 2200 and 2000 cal year BP, the existing open-mixed tropical deciduous forest transformed into a mixed tropical deciduous forest under a warm and humid climate with further increase in monsoon rainfall. Finally, between ca. 2000 and 1800 cal year BP, a dense mixed tropical deciduous forest occupied the landscape under a regime of a warm and relatively more humid climate with further strengthening of the ISM. The gradual warming, and the climatic amelioration with the intensification of the ISM, during the Late-Holocene (ca. 2600–1800 cal year BP; ~650 BC to AD150) corresponds to the Roman Warm Period (RWP), recorded globally between 2500 and1600 cal year BP (~550 BC to AD ~350). Human activities were present around the study area, which varied according to the ISM variations. The present study provides insights into the gradual intensification of the monsoon since the last ca. 2600 cal year BP (between ca. 2600 and1800 cal year BP), and an increase in the ISM strength in the CMZ of India, against the generally weakening trend during the Late-Holocene.

Pollen records of vegetation dynamics, climate change and ISM variability since the LGM from Chhattisgarh State, central India

Pollen records of a lacustrine sedimentary profile from the Chhattisgarh State, central India revealed that between ~22,200 and 18,658 cal yr BP, open vegetation occupied the landscape under a cool and dry climate, probably indicating a reduced monsoon precipitation. This cool and dry climate, influenced by weakening of the Indian Summer Monsoon (ISM), globally matches with the Last Glacial Maximum (LGM). Between ~18,658 and 7340 cal yr BP, under the influence of a warm and moderately humid climate with increased monsoon precipitation, the open vegetation was succeeded by open, mixed tropical deciduous forest. This open, mixed tropical deciduous forest continued to grow in the region, with an increase in the frequency of some of the tree taxa especially, between ~7340 and 1961cal yr BP under a warm and relatively more humid climate with increased monsoon precipitation, correlatable with the Holocene Climatic Optimum (HCO)/Holocene Thermal Maximum (HTM). Between ~1961 cal yr BP and the Present, dense, mixed tropical deciduous forest came into existence under a warm and relatively more humid climate with further increase in monsoon precipitation. The present study provides an unprecedented record of the vegetation dynamics, climate change and the ISM variability since the LGM from one of the poorly understood areas of the tropics where rainfall is essentially controlled by the monsoon (ISM) variability.

Prolonged warming over the last ca. 11,700 cal years from the central Indian Core Monsoon Zone: Pollen evidence and a synoptic overview

Paleopalynological records of 1.1 m deep lacustrine sediment profile from the central Indian Core Monsoon Zone (CMZ) have provided a prolonged warming trend over the last ca. 11,700 years. Palynological evidence suggests that between ca. 11,700 and 8500 cal yr BP, a mixed tropical deciduous forest occurred in the region under a warm and humid climate with good monsoon precipitation. The forest expanded into a dense mixed tropical deciduous forest since ca. 8500 cal yr BP to the present, under warm and relatively more humid climatic conditions with further increase in monsoon precipitation. This warm climatic phase represents the Holocene Climate Optimum (HCO) or Holocene Thermal Maximum (HTM). Prior to the initiation of the long warm period, an open vegetation occurred in the region between ca.14,100 and 11,700 cal yr BP, under a cool and dry climate, probably indicating reduced monsoon precipitation, and partially matching with the Older Dryas stadial. The present study provides insights into the vegetation dynamics and associated climatic changes in response to the Indian Summer Monsoon (ISM) variability over the last ~14.1 ka from a poorly understood area of the tropics in South Asia, where rainfall is essentially controlled by the ISM. In addition, an account of the asynchronous warming during the Holocene from the central Indian CMZ, as well as other tropical regions of the Indian sub-continent, has been presented here. Global contextualization of the Holocene warming has also been summarized in this communication.

A comparative assessment of pollen in modern vegetation and bat guano in Pipulbari Cave of Meghalaya, India

This study presents a palynological examination of modern bat guano to understand the quality of pollen preservation in relation to the extant vegetation in and around the vicinity of the Pipulbari Cave. Surface soil samples from the nearby forest, cropland and wetland areas were also studied for the comparison of pollen rain in relation to the current vegetation and landscape in the region. The pollen data recovered from the forest are indicative of tropical mixed deciduous forest composed of Shorea, Salmalia, Mesua, and Duabanga which exactly conforms to the extant vegetation in the region. The wetland vegetation was characterized by the consistent recovery of marshy and aquatic taxa including Cyperaceae, Polygonum, and Nymphaea in the pollen assemblage. The pollen preserved in cropland was characterized by the presence of cereal and Brassica. The pollen data from the modern bat guano samples display a relative dominance of the forest constituents as compared to wetland and cropland vegetation which reflects the preferential foraging of bats in dense forest areas. A multivariate principal component analysis (PCA) was applied to quantify data obtained from pollen frequency analyses of different areas inside Pipulbari Cave, which clearly revealed a significant group variation in vegetation type on the basis of dispersal and deposition of pollen in surface soil and bat guano samples. The pollen data from the modern bat guano samples are shown to provide a reliable basis for paleoecological reconstructions if they were to be based on the modern pollen analog method.

Floristic and climatic reconstruction in the Indo-Burma region for the last 13,000 cal. yr: A palynological interpretation from the endangered wetlands of Assam, northeast India

The present study deals with pollen analyses from two sedimentary sequences (280 and 150 cm deep) cored from wetlands in Deepor (Kamrup district) and Hasila (Goalpara district) in the western Brahmaputra flood plain of Assam. This region is a part of the Indo-Burma region and documents changes in vegetation, climate and alterations in the wetland level as well as of anthropogenic impacts as related to the fluctuating orientation of the southwest monsoon during the past 13,040 cal. yr. The presence of cool taxa, both trees and ferns, Schima, Ilex, Gleichenia dichotoma and Pteris pentaphylla, though present in small amounts, indicate cool and dry climatic conditions from 13,040 to 11,700 cal. BP. This is followed by a shift to warmer and moderately humid climate between about 8390–3450 cal. BP which coincides with the Holocene thermal maximum (8000–7000 yr BP) and could be attributed to an intensified southwest monsoon. A palynozone depicting less warm and humid climate was observed between 3450 and 2250 cal. BP because of the occurrence of low frequencies of Shorea and Terminalia along with marshy taxa. Climatic conditions were again improved from 2250 cal. BP onwards under warm and moderately humid climate owing to the proliferation of Sal and its associates and thereafter, between 1500 and 710 cal. BP, an increased humid climate is indicated by relatively high percentages of Shorea, Syzygium, Impatiens, Onagraceae and Myriophyllum indicating strong monsoonal conditions corresponding to Medieval Warm Period (MWP). Deterioration of the tropical mixed deciduous forest under a warm and relatively dry climatic regime has occurred since 710 cal. BP accompanied by accelerated human settlement, as shown by an abrupt increase in Poaceae > 45 µm along with typical ruderal pollen taxa.

Using a tree-based approach to evaluate logging damage in a tropical mixed deciduous forest of Myanmar: comparison with cases in Cambodia

ABSTRACTLogging damage to residual trees is an important parameter when considering the sustainability of selective logging in tropical natural forests. Here, we applied a proposed tree-based approach to evaluate logging damage in a tropical mixed deciduous forest in Bago Yoma, Myanmar and compared the cases with semi-evergreen forests of Cambodia. The logging damage was assessed in twenty 0.1-ha plots, each of which contained the stump and crown of one felled tree, and multinomial logistic regression was used to quantify the probability of the felled tree causing severe, slight, or no damage to residual trees. In both cases of Myanmar and Cambodia, severe damage was dependent on the size of the residual and felled trees, while slight damage was independent of the size of felled trees. There was no slight damage of residual trees with ≥50 cm diameter at breast height (DBH) in Myanmar, whereas slight damage increased with residual tree size in Cambodia and in tropical rain forests of other countries. This difference could be attributed to the sparseness of standing trees (98 trees ha−1) in our study site in Myanmar, which made it easier to control the felling direction to avoid damage to larger residual trees. Additionally, the probability of increasingly severe damage with increasing DBH of the felled trees was higher in Myanmar than in Cambodia; one of the reasons may be the steeper terrain at the Myanmar site.

Mid-Holocene pollen records from southwestern Madhya Pradesh, central India, and their palaeoclimatic significance

ABSTRACTA new pollen record from south western Madhya Pradesh, central India provides a palaeoenvironmental record for the core monsoon zone (CMZ) of India. The 2m deep lacustrine sediment profile demonstrates that between ∼5679 and ∼4939 cal yr BP, open vegetation occurred in the region, indicative of a dry climate with reduced monsoonal precipitation. This was replaced by a mixed tropical deciduous forest under a warm and humid climate with increased monsoonal precipitation between ∼4939 to ∼3762 cal yr BP. From ∼3762 cal yr BP to the present day, a dense mixed tropical deciduous forest has existed under a warm and relatively more humid climate indicating a further increase in monsoonal precipitation. Cereal-based agricultural practice is evident during the most recent two phases.

Effects of directional felling, elephant skidding and road construction on damage to residual trees and soil in Myanmar selection system

SUMMARY Reduced-impact logging (RIL) is widely expected to maximize conservation values of selectively logged tropical forests; however, there remains a lack of supporting data to confirm the effectiveness of individual RIL practices. This study evaluates the extent of damage to residual stands and soil caused by directional felling, elephant skidding, and road construction in a tropical mixed deciduous forest under the Myanmar Selection System (MSS). The felling damage number was consistently larger for bamboo clumps than for trees over the range of felled tree size and felling intensity. Soil disturbed by road construction made up 4.6% of the 9-ha study area, but no visible damage to residual trees and soil from elephant skidding was found three months after the operation. Directional felling toward bamboos and elephant skidding of MSS are effective as RIL practices, producing the lowest level of damage to residual trees and soil as compared with other RIL studies.

Pollen records related to vegetation and climate change from northern Chhattisgarh, central India during the late Quaternary

Pollen records from a 1.8-m deep sediment profile from Lakadandh Swamp, Baikunthpur Forest Range of Koriya District, Chhattisgarh (C'garh, central India), show the late Quaternary vegetation and climate history. Lakadandh Swamp occurs in the core monsoon zone of India. The study revealed that between ∼12,785 and ∼9035 cal. yrs BP, tree savannah vegetation, – composed of Poaceae, Amaranthaceae, Tubuliflorae along with the tree taxa Holoptelea sp. and Sapotaceae; sparsely distributed Acacia sp., Emblica officinalis, Lagerstroemia sp., Madhuca indica and Syzygium sp., thickets of Ricinus and Zizyphus sp. – occurred in the region under a cool and dry climate probably indicative of reduced monsoon precipitation. The early part of this phase is comparable with the Younger Dryas (YD) cold event which occurred between ∼12,800 and ∼11,500 yrs BP. Between ∼9035 and ∼4535 cal. yrs BP, the expansion of existing taxa Holoptelea sp., Sapotaceae, Madhuca indica, Ailanthus excelsa and Lagerstroemia sp. as well as the appearance of Acacia, and Shorea robusta, Acanthaceae, Rungia sp., and Ricinus sp., shows the tree savannah vegetation was replaced by open mixed tropical deciduous forest under a regime of warm and moderately humid climate with increased monsoon precipitation. Since ∼4535 cal. yrs BP to Present, owing to the improvement of most of the forest constituents, particularly Madhuca indica, Holoptelea sp., Sapotaceae and Lannea coromandelica, and also with immigration of Terminalia sp., Diospyros sp., Butea sp. and Maytenus sp., mixed tropical deciduous forest has taken over the space covered by open mixed tropical deciduous forest under a warm and relatively more humid climate, with further increase in monsoon precipitation. The existing cereal-based agricultural practice increased during the latter two phases, which could be attributed to increased monsoon precipitation.

Modern pollen–vegetation relationship in the tropical mixed deciduous forest of the Koriya District in Chhattisgarh, India

The present paper analyses the pollen deposition pattern in a swampy area of tropical mixed deciduous forest at the Baikunthpur Forest Range in the Koriya District of Chhattisgarh, India, based on the palynological investigation of surface samples. The palynological assemblages revealed the dominance of non-arboreal pollen taxa (NAPs: herbs) over the arboreal pollen taxa (APs: trees and shrubs). Among the arboreal taxa, trees constitute on average 41.92% of the pollen in the total pollen rain, whereas the average contribution of shrubs is only 2.19%. Among the herbaceous taxa, Poaceae (grasses) has a relatively high frequency (average 38.20%). The NAPs, on the whole, constitute on average 53.51% of the pollen in the total pollen rain. Cerealia, Chenopodiaceae/Amaranthaceae, Caryophyllaceae, Brassicaceae, Artemisia and Alternanthera reflect the agrarian activities in the study area. Cyperaceae and other marshy taxa represent boggy places around the sampling site and Typha, Lemna, Potamogeton and Nymphoides the aquatic vegetation. Pinus, Cedrus, Picea and Alnus occur in low frequencies and are exclusively wind transported from the Himalayas. Trilete fern spores and lycopods are indicative of humid climatic condition.

Vegetation and climate change during mid and late Holocene in northern Chhattisgarh (central India) inferred from pollen records

Pollen analysis of a 1.8 m deep sediment core from Matijharia Lake, Baikunthpur Forest Range of Koriya District in Chhattisgarh state (C'garh), central India, has been carried out with the principal aim of investigating the vegetation and climate history from mid- to late-Holocene. The study has demonstrated that between 6410 and 4250 cal. BP, tree savannah vegetation, which is largely constituted of grasses, Cerealia, Chenopodiaceae/Amaranthaceae, Tubuliflorae, together with sparsely distributed tree taxa Madhuca indica, Sapotaceae, and Lannea coromandelica occupied the region under a cool and dry climate with reduced monsoon precipitation. Between 4250 and 1000 cal. BP, with the enhancement of M. indica, Sapotaceae, L. coromandelica, Acacia, Holoptelea as well as the incursion of Diospyros melanoxylon, Emblica officinalis, Shorea robusta, Syzygium, Grewia, Ailanthus excelsa and others along with shrubby Rungia, the tree savannah vegetation was transformed into a mixed tropical deciduous forest. The overall enrichment in the vegetation mosaic, particularly arboreals, indicates that the region experienced a warm and humid climate with increased monsoon precipitation. Since 1000 cal. BP to Present, dense mixed tropical deciduous forest succeeded the mixed tropical deciduous forest with forest constituents particularly M. indica, Sapotaceae, L. coromandelica, S. robusta, E. officinalis, D. melanoxylon, Syzygium, and also with the immigration of some more arboreal taxa such as Terminalia, Grewia, Annona, Lagerstroemia, and others (though meagerly). From this proliferation of forest elements, it is surmised that a warm and relatively more humid climate prevailed in the region with further increase in monsoon precipitation. The region was under cereal-based agricultural practice, accelerated during the second phase (between 4250 and 1000 cal. BP) due to prevalence of the active SW monsoon.

Modern pollen assemblages from teak (Tectona grandis Linn. F.) dominated tropical deciduous forest in southwestern Madhya Pradesh, India

This paper gives an account on the modern pollen rain–vegetation relationships, based on the pollen analysis of 12 surface samples, 2 samples each collected from the southern, northern, eastern and western flanks of Amjhera Swamp as well as 4 from the mixed tropical deciduous forests dominated by teak (Tectona grandis) in Hoshangabad District, southwestern Madhya Pradesh, India. The pollen assemblages demonstrate the dominance of arboreals (trees and shrubs) over non–arboreals (herbs). Among the tree taxa, Madhuca indica is constantly represented with average pollen frequency of 37.36% in most of the samples which could be attributed to the good preservation of its pollen in the sediments coupled with its high pollen dispersal efficiency. Terminalia (av. 5.1%) is also retrieved steadily. However, Tectona grandis is untraced in the samples despite being an enormous pollen producer and dominant forest component, which could be due to its low pollen dispersal efficiency and differential pollen preservation. Besides, Adina cordifolia, Mitragyna parvifolia, Schleichera oleosa and Emblica officinalis are present with average pollen frequencies of 8.1%, 7.8%, 6.69% and 1.126%, respectively, but only in a few samples. Syzygium, Maytenus, Lagerstroemia, Lannea coromandelica, etc. are also intermittently recovered in almost all the samples, but in varying frequencies (< 0.5%–7.91%) despite their frequent presence in the forest. This erratic display of all these taxa could be inferred to their low pollen productivity, since majority of the tropical trees portray a strong tendency of entomophily. The partial preservation of their pollen in the sediments cannot also be denied. The relatively meagre representation of grasses, sedges, Malvaceae, Xanthium except Tubuliflorae and culture pollen taxa such as Cheno/Am, Caryophyllaceae, Brassicaceae and Cannabis sativa are suggestive of poor herbaceous cover around the swamp and also in the mixed tropical deciduous forest. However, the record of Cerealia and other culture pollen taxa stamps the proximity of cultivated land and human habitation in and around the investigation site. The abundance of trilete fern spore as well as Ceratopteris, monolete fern spore and trilete with perine, though in relatively low values envisages their origin from the local sources as ferns and their allies flourish well in moist and shady habitats.

Vegetation vis á vis climate change around Bhogdoi swamp in lower Brahmaputra flood plain of Assam, Northeast India since Late Holocene

Pollen records from 1.8 m deep sedimentary profile cored from Bhogdoi swamp, Kamrup District, lower Brahmaputra flood plain of Assam, Northeast India have revealed enrichment of tropical mixed deciduous forest elements including Shorea robusta, Syzygium cumini, Dillenia pentagyna and Acacia catechu indicating warm and humid climatic regime during 3,795–2,530 years BP. Subsequently during 2,530–680 years BP relative increment in proliferation of tropical mixed deciduous elements namely Lagerstroemia parviflora, Lannea coromandelica, Terminalia bellirica, Sapotaceae and Emblica officinalis occurred resulting into final settlement of tropical mixed deciduous forest under increased warm and humid climatic regime attributable to active Southwest Monsoon. However, from 680 years BP onward gradual deterioration of mixed deciduous forest occurred as evidenced by sudden decline in Sal and its associates under warm and relatively drier climate. Drastic increment in Melastoma, Ziziphus and Areca implying forest clearance at this phase. The occurrence of degraded pollen–spore along with adequate fungal remains especially Xylaria, Diplodia, Nigrospora and Microthyriaceous fruiting body is suggestive of aerobic microbial digenesis of rich organic debris during sedimentation.

Palaeovegetation and climate oscillation of western Odisha, India: A pollen data-based synthesis for the Mid-Late Holocene

The last 6000 years are of particular interest to the understanding of the Earth System because the boundary conditions of the climate system did not change dramatically (in comparison to larger glacial–interglacial changes), and because abundant, detailed regional palaeoclimatic proxy records cover this period. Here, we present fossil pollen data and examine their climatic interpretation based on a 200-cm-deep trenched sedimentary profile from Mahanadi river side, located near the Barpahar hillock of Bargarh District, Odisha, which is influenced by the South-west and North-east monsoon. The 5840 y chronology of the sediment core is based on three 14C dates on soil samples. During 5840–4380 BP, dense tropical mixed deciduous forest consisting of Madhuca, Syzygium and Acacia flourished in the region along with Rhizophora under a warm and humid climate governed by high monsoonal activity. This phase of climate is associated with the Holocene Climatic Optimum which falls within the temporal range of 8000–5000 BP. Subsequently, an increase in humidity was discerned between 4380 and 3230 BP, as evident by increase in forest elements, under warm and relatively humid climate in response to an increased monsoon. The climate during 3230–1860 BP was mild and in general less humid than today. This climate event was inevitably influenced by a notable global cold event 4200 years ago, which is synchronous with the collapse of the world's first human empire in Mesopotamia. After this event, there was a return of more humid climate from 1860 to 1300 BP, marked by high values of Potamogeton, Myriophyllum, Nymphoides, and fungal and trilete fern spores. This is further supported by the presence of Rhizophora and Sonneratia indicating high precipitation under the influence of coastal habitation. A striking signal of the Little Ice age (LIA) was observed since 1300 BP when the climate became relatively dry, as recognized in a sudden decline in major arboreals, along with high frequency of occurrence of dry herbs. This changing pattern of humidity was also reflected in the proportions of marshy/aquatic taxa, as well as ruderal taxa which is a result of human impact. The study will be helpful to display the palaeovegetation and climate in the region between Bengal and the Ganga plain.