Biophysical controls on surface fuel litterfall and decomposition in the northern Rocky Mountains, USA

Litterfall and decomposition rates of the organic matter that comprise forest fuels are important to fire management, because they define fuel treatment longevity and provide parameters to design, test, and validate ecosystem models. This study explores the environmental factors that control litterfall and decomposition in the context of fuel management for several major forest types in the northern Rocky Mountains (Idaho and Montana), USA. Litterfall was measured for more than 10 years using semiannual collections of six fine fuel components (fallen foliage, twigs, branches, large branches, logs, and all other canopy material) collected from a network of 1 m2 litterfall traps installed at 28 plots across seven sites. Decomposition of foliage, twigs, branches, and large branches were measured using litter bags installed on five of the seven sites. Measured litterfall and decomposition rates were correlated with major environmental and vegetation variables using regression analysis. Annual foliage litterfall rates ranged from 0.057 kg·m–2·year–1 for dry Pinus ponderosa Dougl. ex Laws. stands to 0.144 kg·m–2·year–1 on mesic Thuja plicata Donn ex D. Don stands and were correlated with the vegetation characteristics of leaf area index, basal area, and tree height (r > 0.5), whereas decomposition rates were correlated with the environmental gradients of temperature and relative humidity (r > 0.4).