Effect of tree canopy on species composition, diversity and biomass of herbaceous vegetation and soil characteristics in semi-arid forests of the Aravalli hills

Abstract

Background: Herbaceous vegetation is of great ecological importance and responds quickly to environmental changes. Present study was aimed to understand the variation in herbaceous species composition, diversity, biomass and soil physicochemical properties in canopy gaps and under the canopy of semi-arid forests in the Aravalli hills. Methods: Four permanent plots consisting of canopy gaps and under canopy were established. To study herbs phytosociological attributes and biomass, 10 quadrats of 0.5 x 0.5 m size were laid in each plot. For soil physico-chemical properties, 5 soil samples were collected randomly at 0-10 cm depth from each plot. Relationship between biodiversity indices, herbs biomass and soil physicochemical properties was determined using Redundancy Analysis (RDA) and correlation analyses. Results: The sites differed in terms of herbaceous species composition, diversity, biomass and soil physico-chemical properties. Canopy gaps were dominated by grasses while forbs were higher under the canopy. Across the sites, poaceae was the dominant family. All species showed contagious distribution pattern. Oplismenus burmannii reported highest IVI (138.0; 230.5) under the canopy while Achyranthes aspera (56.15) and Eragrostis ciliaris (53.1) had highest IVI in canopy gaps. Diversity indices were higher in canopy gaps. Herbaceous community biomass in canopy gaps ranged from 700-900 gm-2 while under the canopy it ranged from 30-70 gm-2. Cenchrus ciliaris (597.97 gm-2) and Chrysopogon sp. (391.2 gm-2) constituted major proportion of biomass in canopy gaps. The soil of under canopy regions had lower pH and bulk density, but higher soil moisture (%), electrical conductivity, soil organic carbon (SOC), soil total nitrogen (TN), SOC stock and soil TN stock than the canopy gaps. Linear positive relationship between species diversity and biomass; negative relationship between soil chemical properties and herbaceous biomass was found in study area. Even though canopy had positive effects on soil physico-chemical properties, overall negative effect on herbaceous diversity and biomass was seen. Conclusions: Reduced light for photosynthesis and tree root competition for soil resources may be the major factors negatively affecting herbaceous diversity and biomass. Canopy had a significant impact and herbs species composition, diversity, biomass and soil physico-chemical properties showed distinct differences in relation to it.