Type conversion from native California sage scrub to non-native grassland accelerates decomposition processes.
Predicting how plant invasions influence decomposition processes is difficult, as multiple factors change with plant community alteration. Here, we examined the importance of various abiotic and biotic factors (litter quality (C:N), UV radiation, and macroinvertebrate access) in driving early decomposition processes in native California sage scrub (CSS) and in adjacent non-native grassland habitats. Many findings from our experiment were consistent with studies from semi-arid regions (e.g., UV radiation drove decomposition processes and high quality litter decayed more rapidly). However, the acceleration of litter decomposition in the non-native grassland relative to native California sage scrub (CSS) was unexpected and contrasts with studies of partially invaded CSS systems. Our results highlight that studies of invaded systems that still retain native species diversity should not be extrapolated to type-converted systems. We hypothesize that high grass cover in the type-converted grassland created conditions that enhanced soil moisture, bacterial abundance, and macroinvertebrate influence relative to the CSS, accelerating decomposition and reducing regional C storage.