Aim of study: We compared the decomposition rate of the accumulated litter, the stock, and the return of nutrients to the soil, between an area dominated by bamboos in the understory and an area where this dominance does not occur. Area of study: Fontes do Ipiranga State Park, an Urban Fragment of Atlantic Forest at the Municipality of São Paulo, Southeastern Brazil. Materials and methods: The decomposition rates were measured over one year (0, 3, 6, 9, and 12 months), avoiding litter addition through nylon nets over the soil. The collected material was separated into the following fractions: bamboo leaves and branches (bamboo material); other leaves and branches (other material); very decomposed material not identifiable (unidentifiable). The content of macro (N, P, K, Ca, Mg, and S) and micronutrients (B, Cu, Fe, Mn, and Zn) were determined. Main results: The litter accumulated was significantly higher in the mature area than in the bamboo area. The decomposition rates did not differ significantly between the two areas. Except for K and Mn, the concentrations of macro and micronutrients were equal to or greater in the mature forest. Research highlights: Unlike reported in other areas, there is no greater litter accumulation in the bamboo-dominated understory nor a slower decomposition rate. The nutrient content is lower in the bamboo-dominated disturbed area.