Stephen A.
As a Botanist - with a Doctorate in Palynology and Functional Ecology, his domains of expertise are in: a) Palynology, Systematic Botany, b) Forest Ecology and Seed Ecology.
As a Researcher, he has authored several articles.
As a Researcher, he has authored several articles.
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Papers by Stephen A.
the nutritive and therapeutic uses of 86 vegetables present in the markets of Chennai, Tamil Nadu, India.
the nutritive and therapeutic uses of 86 vegetables present in the markets of Chennai, Tamil Nadu, India.
The size of the pollen grains varied from 13.8micron (Aerva lanata) to 205.6micron (Stachytarpheta jamaicensis). Pollen shape ranges from Spherical (Aerva lanata, Sorghum vulghare, Hibiscus vitifolius), Spheroidal (Vernonia albicans), Spheroidal or Prolate Spheroidal(Hyptis suaveolens, Waltheria indica), Oblate Spheroidal (Stachytaarpheta jamaicensis), Prolate Spheroidal (Cleome viscosa), Prolate (Crotalaria juncea), Oblate ( Cardiospermum halicacabum). The type of pollen with reference to aperture was Monoporate( Sorghum vulghare), 3 Colporate (Cleome viscosa, Crotalaria juncea), 4 Colporate (Waltheria indica), 3 -4 Porate (Vernonia albicans), 3 colpate (Stachytarpheta jamaicensis), 6 Colpate (Hyptis suaveolens), 3 porate with streaks (Cardiospermum halicacabum), Polyporate (Aerva lanata, Hibiscus vitifolius).
The present study is significant in the preparation of pollen data for the future studies in the field of Agriculture, Taxonomy, Ecology, Palynology and human health.
For some time now, serious international efforts promoted by the International Geosphere Biosphere Programme – Global Climate and Terrestrial Ecosystem (IGBP-GCTE) programme are underway to measure for a large number of species and shortlist significant plant traits that would underlie such functional plant classification systems. The fundamental idea here is to assess vegetation responses to environmental changes and vice versa.
Understanding of leaf trait relationships across multiple species and habitats and their patterning with respect to climate can provide information about major dimensions of variation among plant species and their habitat preferences.
In this paper, various leaf traits and their patterning with respect to climate and diversity of vegetational assemblages based on the similarities between leaf trait characters are presented from selected sites of Eastern and Western Ghats.
The present instrumental record of the monsoon candidly demonstrates that in South India it is characterized by a complexity and spatial variability that has an antiquity that probably goes back to the LGM (18000 BP) or at least early Holocene (11000 BP). This underlines the need for a spatially well distributed set of palaeovegetation reconstruction in this region in order to effectively understand its past performance at the regional scale of South India. Using the novel multidisciplinary approach, incorporating remote sensing we short-listed a number of potential sites in mainland South India. Here, we present the preliminary results of one of these sites, Rusulcheruvu, a rainfed reservoir (tank) at the foothills of the Achampet plateau, near the NSTR (Nagarjunasagar Srisailam Tiger Reserve), Central Andhra Pradesh. This tank currently supports an ayacut of ~ 300 acres. Two cores were taken from this tank at different locations nearly 50 to 100 m apart. The first, at the centre of the tank yielded a core of ~1.5 m before reaching the rock bottom while the second core more towards the periphery was only around 80 cm after which a weathered layer was encountered. Two radiocarbon dates indicate that the site is around 1400 BP. Although the cores have been subsampled at 2 cm intervals, we present here only the broad pollen spectrum all along the cores at 5 to 8 cm intervals.
Some of the most significant pollen taxa encountered in the cores include deciduous tree taxa such as Melastomataceae/ Combretaceae, Haldina, Ixora, Trema and Grewia in addition to some evergreen elements such as Syzygium, Elaeocarpus and Gnetum. Poaceae and Cyperaceae are among the dominant herbaceous taxa, with other herbs such as Chenopodiaceae/ Amaranthaceae and Compositae echinate also being encountered. The paucity of human impact markers such as Casuarina, Polygonum plebeium, and Eucalyptus indicates that the site has remained relatively undisturbed. The spectrum as a whole reflects a decrease in the total tree pollen influx from the surrounding deciduous forests since the past 1400 years. The pollen percentage diagram as well as the quantitative diagram of pollen influx (pollen per gram of sediment) are presented and described in detail vis-a-vis the present day vegetation on the slopes providing the run off input to the tank.
It is essential therefore, to ensure that the final residue is relatively free from extraneous materials, especially microdebris, which influences both the quantitative and microscopic analyses.
In this paper, we focus our attention on a refinement of the laboratory procedure in order to get rid of or at least minimize microdebris that often hinder lucid observation of the pollen grains for identification and counting under the microscope. It is important that the final residue mounted on the slide is at least a faithful subset of the initial samples. To achieve this, a sieving method is described for concentrating pollen from sediments and surface samples using a membrane filter. The effectiveness of this method was also tested in comparison with standard ultrasonic sieving process where two steps – filtration and ultrasonic treatment - are coupled together (Caratini 1980). In our new method, these steps are decoupled and we mainly use filtration, by a membrane filter using vacuum suction – the ultrasound treatment is preliminary and mainly to break down aggregates and disperse the suspension prior to filtration. In the paper we discuss the adverse effects of coupling these two steps and the advantages and disadvantages of the different methods.
In this method, currently being tested in our laboratory, we aim to ensure that there is minimal pollen escape or loss. We recommend this laboratory processing method for a wider use in most pollen laboratories, as the process is inexpensive, can be easily added on to the existing method and requires only simple, easily available equipment.