Sacred Forests of Eastern India Prove to Be Powerful Engines of Nutrient Cycling

Deep in the western districts of Odisha, India, small patches of forest have been protected for generations not by fences or legislation, but by faith. These sacred forests, guarded by local communities through religious beliefs and cultural traditions, are among the oldest forms of in situ biodiversity conservation on the subcontinent. A new year-long study has now revealed that these culturally protected woodlands are not merely spiritual refuges; they are also remarkably efficient nutrient-recycling machines, churning through leaf litter at speeds that rival or exceed those of better-studied tropical forests.

Researchers from Sambalpur University, Terracon Ecotech, and the Government of Odisha set out to quantify litterfall production, standing litter biomass, decomposition rates, and nutrient fluxes in four sacred forests across the region: Andhari, Dedungri, Medha, and Papanga. Three of the sites are dominated by sal (Shorea robusta), while Papanga is dominated by Cleistanthus collinus. The forests lie within a tropical savanna climate zone, where annual rainfall ranges from 900 to 1,400 millimeters, almost all of it delivered during the June-to-September monsoon, and where pre-monsoon temperatures can exceed 45 degrees Celsius. That pronounced seasonality shapes nearly everything that happens on the forest floor.

Between January and December 2023, the team measured litter inputs monthly using one-square-meter collection pits established at least ten meters inside each forest boundary to avoid edge effects. The collected material was separated into leaves, twigs, branches, and miscellaneous fragments, then oven-dried and weighed. Annual litterfall ranged from 8.59 megagrams per hectare per year at Andhari to 11.32 megagrams per hectare per year at Medha, figures that sit comfortably within the global range for tropical forests and actually exceed values reported for several other tropical dry deciduous forests in India. Leaves dominated the mix, contributing between 80.65 and 83.35 percent of total litterfall, followed by twigs, branches, and other material.

The seasonal signal was unmistakable. Litter production peaked in March at all four sites, coinciding with the height of the dry season, when water stress triggers leaf senescence and abscission in deciduous trees. Statistical analysis confirmed that month-to-month variation within sites was highly significant, while differences among the four forests were not. In other words, climate and phenology, not site identity, are the primary engines driving litterfall in these ecosystems. Standing litter biomass followed the same rhythm, accumulating to a maximum in March and dwindling to a minimum during the rainy and post-rainy months of August through November, with annual means ranging from 2.39 megagrams per hectare at Andhari to 2.68 at Medha.

The speed at which that litter disappeared was the study’s most striking finding. Using the classic litterbag technique, the researchers placed 20-gram samples of mixed-species fresh leaf litter, collected during the February-March peak litterfall period, into 20-by-20-centimeter nylon bags with one-millimeter mesh and laid them on the forest floor in a completely randomized design. Six bags were retrieved from each site every month. Roughly 95 percent of the initial litter mass had vanished within six months at every site. The fitted decay constants ranged from 5.75 to 6.65 per year, corresponding to half-lives of just 38 to 44 days. Model-based extrapolation suggested that 99 percent decomposition would be achieved within 274 to 318 days, although the authors caution that these figures extend beyond the six-month observation window.

Litter turnover rates told a similar story. The ratio of annual litterfall to standing litter biomass, a standard index of how quickly organic matter cycles through the forest floor, ranged from 3.59 to 4.22 per year, equivalent to residence times of only 87 to 102 days. Those turnover rates are higher than values reported for tropical semi-deciduous, tropical dry evergreen, and tropical evergreen forests, indicating that these small sacred groves process organic matter unusually fast. The researchers attribute the rapid decay to favorable temperature and moisture conditions during the decomposition period, which stimulate microbial activity, possibly combined with relatively high litter nutrient quality.

That quality question was addressed through chemical analysis of the mixed-species litter. Initial concentrations of nitrogen, phosphorus, and potassium differed significantly among the four forests, with Papanga showing the highest nutrient levels and the most favorable stoichiometric profile. Correlation analyses revealed that initial nitrogen and phosphorus concentrations were significantly associated with decomposition rates, while carbon content was not. The authors note an important caveat: lignin and cellulose, structural compounds that strongly regulate decomposability, were not measured, so the full biochemical picture of litter quality in these forests remains incomplete.

Nutrient release during decomposition followed a clear hierarchy: potassium was lost fastest, followed by nitrogen, then phosphorus. Potassium, highly soluble and prone to leaching, declined rapidly throughout the experiment, with release reaching 98.72 to 99.20 percent across the sites. Nitrogen loss ranged from 92.26 to 95.08 percent, and phosphorus from 80.54 to 95.34 percent after six months. Papanga recorded the highest total nutrient loss at 96.57 percent. Meanwhile, nitrogen and phosphorus concentrations actually increased in the residual litter, a pattern the researchers attribute to microbial immobilization, in which decomposer organisms accumulate these nutrients in their own biomass before releasing them back to the soil. Carbon concentrations remained relatively stable at Andhari and Medha but declined at Dedungri and Papanga.

The study’s authors are candid about its limitations. There were no non-sacred control forests for direct comparison, so the work characterizes variation within sacred forests rather than testing the effects of sacred-forest protection itself. Repeated temporal observations were not analyzed with mixed-effects models, and the correlation results should be read as associations rather than causal claims. Still, the baseline data fill a genuine gap: while litterfall and nutrient cycling have been extensively documented in tropical evergreen forests and, to a lesser degree, in sacred groves elsewhere in India, comparable information for the dry deciduous sacred forests of Western Odisha had been essentially absent.

The implications extend beyond ecology into conservation policy. Sacred forests persist as biodiversity hotspots and providers of ecosystem services, including carbon sequestration, water regulation, and soil conservation, precisely because community restrictions limit timber extraction, grazing, and fuelwood collection. Yet pressures such as fuelwood harvesting, livestock grazing, and non-timber forest product extraction persist to varying degrees, with Andhari and Dedungri showing signs of moderate degradation while Medha and Papanga remain relatively well preserved. By demonstrating that these culturally protected patches sustain high litter production, rapid decomposition, and substantial nutrient turnover, the study provides quantitative evidence that sacred forests function as localized reservoirs of soil fertility in human-dominated landscapes. As land-use intensification continues across tropical India, the researchers argue, protecting these living laboratories of biocultural conservation may be one of the most cost-effective strategies for maintaining nutrient cycling and ecological resilience in dry deciduous landscapes.

Subject of Research: Litterfall production, decomposition rates, and nutrient cycling in tropical dry deciduous sacred forests of Western Odisha, India

Article Title: Litterfall dynamics and decomposition-driven nutrient cycling in sacred forests of Eastern India

Article References: Pradhan, A., Mansingh, A., Gopinath, J. S., & Ekka, N. J. (2026). Litterfall dynamics and decomposition-driven nutrient cycling in sacred forests of Eastern India. Discover Plants, 3(1), Article 412. https://doi.org/10.1007/s44372-026-00892-7

Image Credits: AI Generated

DOI: 10.1007/s44372-026-00892-7

Keywords: litterfall, decomposition, nutrient cycling, sacred forests, tropical dry deciduous forest, Odisha, Shorea robusta, litterbags, soil fertility, ecosystem functioning, biocultural conservation, leaf litter