Effect of tree canopy on herbaceous vegetation and soil characteristics in semi-arid forests of the Aravalli hills

Herbaceous vegetation is of great ecological importance and responds quickly to environmental changes. The present study was aimed to understand the variation in herbaceous species composition, biomass and soil physico-chemical properties in the naturally formed gap and the understory of semi-arid forests in the Aravalli hills. Four permanent plots consisting of the gap as well as the understory were established. To study herbs phytosociological attributes and biomass, 10 quadrats of 0.5 × 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. Relationships among biodiversity indices, herbaceous biomass and soil physico-chemical properties were determined using Redundancy Analysis (RDA) and correlation analysis. Across the sites, Poaceae was the dominant family. All species showed a contagious distribution pattern. In the understory, Importance Value Index (IVI) was the recorded highest for Oplismenus burmannii, ranging from 138 to 230.5 while in the gap, it was the highest for Achyranthes aspera (56.15) followed by Eragrostis ciliaris (53.1). Both sites included, herbaceous community biomass in the gap ranging from 700 to 900 g m−2 while in the understory it ranged from 30 to 70 g m−2. Cenchrus ciliaris (597.97 g m−2) and Chrysopogon sp. (391.2 g m−2) contributed a major proportion of herbaceous community biomass in the gap. Oplismenus burmannii (52.2 g m−2), Dipteracanthus prostratus (16.6 g m−2) and Cynodon dactylon (9.6 g m−2) contributed a major proportion of herbaceous community biomass in the understory. The understory soil had significantly (p < 0.05) higher soil moisture (%), electrical conductivity (EC), soil organic carbon (SOC) and soil total nitrogen (TN) compared to the gap. Even though canopy had positive effects on soil physico-chemical properties, it has negatively influenced herbaceous species composition, diversity and biomass, due to significant reduction in solar radiation reaching the ground.