Modern pollen spectra from tropical South India and Sri Lanka: altitudinal distribution

Abstract

International audienceWe analysed the pollen content of 106 surface soil samples from evergreen and deciduous tropical forests distributed between 6 degrees and 13 degrees of latitude north in South India and Sri Lanka. The samples were collected along altitudinal gradients, ranging from 50 to 2420 m, in five regions that experience different rainfall regimes. Original pollen data from tropical vegetation subjected to seasonal monsoon rains are presented along altitude/temperature gradients. This paper includes a summarized description of the vegetation types mapped in the area. The pollen results are presented in the form of quantitative pollen diagrams and correspondence analyses. They show clear distinct pollen assemblages and markers for all types of vegetation in deciduous and evergreen vegetation. Forests are well identified by percentages of Arboreal Pollen greater than 50%, despite the fact that Dipterocarpaceae and Lauraceae are hardly recorded by pollen. The pollen distinction between low, medium and high elevation evergreen forests matches that established by ecologists. The botanical limits, respectively, placed at 900 m and 1500 m limits, correspond to the 20 degrees C and 15 degrees C-values of mean temperature of the coldest month. They appear clearly identified in the modern pollen record. This justifies further use of pollen data in Biome modelling

Indian monsoon variations during three contrasting climatic periods: The Holocene, Heinrich Stadial 2 and the last interglacial–glacial transition

“…with pollen percentages higher than 5%, is shown in Figure 3 Sutra et al (1996) show that Artemisia was a tracer for dry conditions during the last glacial in Nilgiri hills basin, SW India, covered at present by mountainous evergreen grasslands (Bonnefille et al, 1999;Gupta and Prasad, 1985). In contrast, in the North-Western part of the Indian peninsula, characterized by winter moisture in dry environments weakly affected by the summer monsoon, Artemisia is a marker of the influence of both summer and winter Indian monsoons (Demske et al, 2009;Van Campo et al, 1996).…”

“…In mountainous regions, vegetation distribution is also determined by temperature variations following the altitudinal gradient. However, below 900 m, the amount and seasonal distribution of annual rainfall are the most important factors on the vegetation distribution (Bonnefille et al, 1999). Most of the Godavari and Mahanadi river catchments are located in the CMZ and below 900 m (excluding the highest summits of the Eastern Ghats), and hence the vegetation responds to monsoon influence directly.…”

“…Poaceae, Cyperaceae and Amaranthaceae constitute the herbaceous vegetation that characterizes open environments. Nevertheless, Poaceae prefers dry areas (Bonnefille et al, 1999) and Cyperaceae moist conditions (Kraus et al, 2003). Suaeda sp.…”

“…The preparation technique for pollen analysis followed the protocol established at the Bonnefille et al, 1999;Gaussen et al, 1965;Hait and Belhing, 2009;Kraus et al, 2003;Legris, 1963;Selvam, 2003). In each sample, the percentages of different biomes are calculated as the sum of the percentages of the different morphotypes with the same ecological affinities.…”

Detrended correspondence analysis: A useful tool to quantify ecological changes from fossil data sets

“…Subsequently, pollen is submitted to differential preservation and degradation processes, causing further preservation bias. However, it has been demonstrated for diverse locations in the world that although imperfect, pollen spectra are feasible tools to identify vegetation patterns associated with biogeographic and environmental gradients at micro to macro scales, mostly depending on the particular environmental settings (Bush, 1991(Bush, , 1995Rodgers and Horn, 1996;Bonnefille et al, 1999;CorreaMetrio et al, 2011a;Urrego et al, 2011). Thus, pollen and spore signals offer proxies for vegetation diversity and reflect latitudinal, altitudinal, and other gradients associated with community composition and structure.…”