Chrysanthemoides monilifera ssp. rotundata invasion alters decomposition rates in coastal areas of south-eastern Australia

Weed invasion can disrupt ecological processes and the structure of ecosystems. One process potentially affected by weed invasion is leaf litter decomposition, which is important for supplying nutrients and organic matter to the soil. Leaf litter decomposition of the environmental weed Chrysanthemoides monilifera spp. rotundata was compared to that of the native coastal shrubs Acacia longifolia var. longifolia, Banksia integrifolia and Leptospermum laevigatum. This was undertaken in sand dunes heavily infested with C. monilifera and in native un-infested dunes. Coarse and fine mesh litterbags were used to determine the importance of soil microflora and litter invertebrates. C. monilifera decomposition was fitted to a double exponential decay model, whereas the native leaf decomposition was best explained by a single exponential decay model. The succulent C. monilifera leaves decomposed at a significantly higher rate than the sclerophyllous native leaf mix. Time to 99% leaf loss was estimated to be 0.9–1.3 years for C. monilifera and 3.1–4.4 years for the native species. This reflects the physical properties of the leaves and the lower leaf mass area of C. monilifera. C. monilifera leaves decayed faster in the coarse mesh bags compared to the fine, indicating leaf litter invertebrates positively influenced their decomposition. Mesh size had little affect on the native leaf decomposition rate. C. monilifera leaves generally decomposed faster within the weed infestations, partly due to invasion creating a protected environment with an altered microclimate. Replacement of native species with C. monilifera will alter nutrient cycling through changes in litter quality and decomposition rates. This may have implications for ecosystem resilience and stability.