In forest ecosystems, the rapid turnover of fine roots (≤2 mm in diameter) is a major pathway of carbon and nutrient flow from plants to the soil. This study was conducted to determine how fine root biomass (FRB), productivity (FRP) and turnover (FRT) are affected by site characteristics, seasonal variation, soil depth and tree girth size in sub‐tropical sal forest ecosystem. Four sites (S1, S2, S3 and S4) were established in the Bhabhar region of Nainital istrict, Uttarakhand, India within an elevational range of 405 and 580 m, and at each site, sal trees were categorized into five girth classes. Fine roots were sampled seasonally up to a depth of 60 cm and divided into three layers (0–20, 20–40 and 40–60 cm). FRB was significantly affected by tree girth size and decreased with increasing girth size, while the effect of tree girth on FRP and FRT was observed to be insignificant. Seasonal variation of FRB in all girth sizes showed a keen resemblance as the standing FRB reached its pinnacle during the rainy season and the bottom line in the winter season. Maximum FRB was reported for the uppermost, organo‐mineral‐rich soil depth (0–20 cm) at 1.0 m distance from the tree bole and decreased with increasing soil depth and distance from the tree bole while FRT showed a reverse trend. The present study provided a holistic outlook on variations in FRB, FRP and FRT and the impact of edaphic characteristics and tree girth on fine root dynamics in the sal forest ecosystem of Central Himalaya, India.

The belowground systems of trees have a major role in forest functioning through absorption of water and nutrient cycling. This study deals with the fine root dynamics including fine root biomass, necromass, production, turnover, and nutrient return in transitional Sal (Shorea robusta Gaertn. f.) dominated sub-tropical forest ecosystems of Central Himalaya, India. Four sites namely, Site-1 (Kaladhungi), Site-2 (Fatehpur), Site-3 (Ranibagh), Site-4 (Amritpur) were selected in Sal forest within an elevational range between 405 and 580 m above sea level. The dominant and associated co-dominant species were selected from each site for the estimation of fine root dynamics by using sequential core and ingrowth core methods. The results revealed that the fine root biomass, necromass, and production were significantly (p < 0.05) affected by location, seasons, and soil properties. The fine root biomass and production decreased with increasing soil depth and also influenced by stand characteristics including tree density and basal area. The rainy season was most productive with maximum fine root biomass (507.37 kg ha–1) as well as fine root production (600.26 kg ha–1 season–1) in the dominant tree species S. robusta. Among the associated co-dominant tree species highest fine root biomass (330.48 kg ha–1) and fine root production (410.04 kg ha–1 season–1) was reported for Tectona grandis L. during the rainy season, while lowest fine root biomass (126.72 kg ha–1) and fine root production (195.59 kg ha–1 season–1) in the Glochidion velutinum Wight tree species during the winter season. Annual fine root production ranged from 460.26 to 1583.55 kg ha–1 yr –1, while turnover rate varied from 1.37 to 4.45 yr–1 across all the studied sites. The fine roots added carbon input of 154.38 to 564.20 kg ha–1 yr–1 and nitrogen input of 6.58 to 24.34 kg ha–1 yr–1 to the soil through annual flux. The study improves our understanding on fine root parameters under the influence of sites, soils and seasonal and spatial variation. The return of nutrients to the soil through fluxes from the roots illustrates the role of fine roots in carbon and nitrogen cycling of the forests and this potential can be harnessed to assess the long-term carbon and nitrogen pool estimations in forests and to plan and manage the forest ecosystems.

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