Litter dynamics, leaf area index and forest floor respiration as indicators for understanding the role of Nepalese alder in white oak forests in central Himalaya, India

The present study is an attempt to understand the role of Nepalese alder (Alnus nepalensis D. Don) in litter production, leaf litter decomposition, leaf area index (LAI) and rate of forest floor respiration as indicators of carbon flux in white oak (Quercus leucotrichophora A. Camus) forests. Five forest stands of oak mixed alder (OMA) and five oak without alder (OWA) were selected along a basal area gradient under similar ecological conditions in Indian central Himalaya. We estimated monthly variations in litterfall, leaf litter decomposition and leaf area index (LAI) in Q. leucotrichophora and A. nepalensis in OMA and OWA stands. Soil and litter CO₂ effluxes were estimated seasonally using the soda-lime absorption method. The seasonal pattern of litterfall showed a bimodal trend in OMA and unimodal trend in OWA forest stands. Forest floor biomass (leaf, twig, reproductive parts, herbaceous and miscellaneous litter) was highest in summer (707–1080 g/m²) followed by winter (414–678 g/m²) and rainy (281–541 g/m²) seasons in OMA stands. In OWA stands, forest floor biomass was highest in summer (463–646 g/m²) followed by rainy (321–411 g/m²) and winter (149–279 g/m²) seasons. Total litter production, leaf litter decomposition rates, change in LAI and soil respiration were significantly higher (p < 0.01) for OMA stands than OWA stands. The maximum annual LAI ₘₐₓ ranged from 4.10 to 6.78 m² m⁻² in OMA stands and from 1.9 to 3.06 m² m⁻² in OWA stands. Total soil respiration (TSR), litter-free soil respiration (LFSR) and litter respiration (LR) were also higher (p < 0.01) in OMA compared to OWA stands. Mean rate of TSR, LFSR, and LR was 280.18 mg m⁻²h⁻¹, 180.45 mg m⁻²h⁻¹, and 46.40 mg m⁻²h⁻¹ in OMA and 188.46 mg m⁻²h⁻¹, 150.1 mg m⁻²h⁻¹, 38.35 mg m⁻²h⁻¹, respectively, in OWA stands and for both recorded highest in monsoon season. The results indicate that A. nepalensis enhances litter production, LAI, leaf litter decomposition, and forest floor respiration in the oak forests, which in turn would result in increased carbon flux.