Phytolith analysis reveals the intensity of past land use change in the Western Ghats biodiversity hotspot

Abstract

25This paper presents a study of phytoliths (opal silica bodies from plants) from sediment sequences 26 obtained from two tropical forest patches in the Western Ghats of India: a sacred grove (sequence 27 covers last 550 cal years BP) and a forest patch in a plantation (sequence covers last 7500 cal years 28 BP). The sites are located at mid-elevation (c. 650-1400 m above sea level) in a mosaic landscape 29 showing anthropogenic open habitats as well as some evergreen forests. The aim of this paper is to 30 evaluate the landscape composition of grassland and forest over time in the region, grassland being 31 invariably shaped by anthropogenic activities, particularly fire for cultivation. We identified and 32 classified phytoliths into 34 morphotypes from five taxonomic groups: Poaceae (grasses), 33Cyperaceae (sedges), Arecaceae (palms), Pteridopsida (ferns) and woody dicotyledons (broad-leaved 34 trees and shrubs). We also calculated the humidity-aridity index (Iph). First, our results show that 35 grasses are the most represented phytolith types in both sites, followed by broad-leaved trees and 36 shrubs, palms, sedges, and ferns. Second, the highly variable climatic index Iph over the last 1000 37 years suggest that changes in phytolith percentage (e.g. broad-leaved trees) might be caused by 38 human agro-pastoral activities, such as clearing through fires and irrigation. Prior to these human 39 activities, the phytolith signal for early Holocene climate is congruent with the existing literature. 40Finally, this study compares new phytolith results with previous pollen data from the same sites. We 41 find good agreement between these two botanical proxies throughout, thus validating our findings. 42We provide important evidence regarding the history of environmental change due to 43 anthropogenic activities in the Western Ghats. This has important implications because it provides 44 insights into how tropical forest will respond to increased intensity of human activities. 45

The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity: insights from climate chamber and climate transect calibrations

“…In grasses, which are well known silica accumulators, silica accounts for several % of dry weight (d.w.) and is mainly located in the stem and leaf epidermis. Phytolith morphological assemblages from soils and sediments are commonly used as past vegetation and hydrous stress indicators (e.g., Aleman et al, 2012;Backwell et al, 2014;Bremond et al, 2005a, b;Contreras et al, 2014;Nogué et al, 2017;Piperno, 2006). The potential of the δ 18 O signature of phytoliths (δ 18 O Phyto ) from grasses for paleoclimate reconstruction has been investigated through growth chamber and North American Great Plains calibrations.…”

Effects of leaf length and development stage on the triple oxygen isotope signature of grass leaf water and phytoliths: insights for a proxy of continental atmospheric humidity

“…Phytoliths can take the shape of the cells they form in, which gives them morphological taxonomic properties. Hence, phytolith morphological assemblages extracted from buried soils, loess and sediments are commonly used for palaeoenvironmental reconstructions (Miyabuchi and Sugiyama, 2015;Nogué et al, 2017;Woodburn et al, 2017). In grasses, silica, that represents several percent of the dry weight (d.w.), polymerises mainly in the leaf epidermis from where the plant water evaporates during transpiration (Alexandre et al, 2011;Kumar et al, 2016), and to a much lesser extent in the stem (Webb and Longstaffe, 2000).…”

Dissolution does not affect grass phytolith assemblages

“…Phytoliths are extensively used in paleobotany (e.g., Piperno and Pearsall, 1998;Prasad et al, 2011), archaeobotany (e.g., Ball et al, 2016;Lu et al, 2009Lu et al, , 2016, paleoenvironmental and paleoclimatic studies (e.g., Arrá iz et al, 2017;Issaharou-Matchi et al, 2016;Nogué et al, 2017;Yost et al, 2021;Zhang et al, 2020). They are produced in stems and leaves of many plants (Hodson et al, 2005), and are particularly abundant, taxonomically diagnostic, and precisely classified within grasses (Poaceae) (Piperno, 2006).…”

“…Grass phytolith assemblages can provide detailed information about the composition of past grass flora (e.g., Bremond et al, 2008;Cordova et al, 2011;Fredlund and Tieszen, 1994). Phytolith ratios, particularly those including grass silica short cells (GSSCs), have been used as climatic proxies to track paleoclimate changes (e.g., Aleman et al, 2014;Nogué et al, 2017;Zhang et al, 2020).…”