Vegetative litter decomposition along urban ephemeral streams in Southeastern Arizona

Riparian areas provide a wide range of ecosystem services. Population growth in Arizona has led to the urban encroachment of riparian areas. Urbanization alters microclimatic conditions that can affect ecosystems processes. This study investigated the impacts of urbanization levels on ecosystems processes (decomposition rates) of riparian areas along ephemeral streams. Nine sites were selected within Marana, Arizona with three housing density levels: high (7–8 houses ha⁻¹), moderate (2.5–4.5 houses ha⁻¹) and low (<1.5 houses ha⁻¹). The litter bag method was used for the three dominant woody species: Parkinsonia microphylla, Larrea tridentata, and Acacia constricta. Litter bags were collected prior to and after the winter rainy and summer monsoon seasons. The variables studied were carbon, nitrogen and lignin content, carbon to nitrogen ratio and mass loss. Soil temperature and moisture, air temperature, relative humidity and precipitation were also recorded. The litter variables mostly were not affected by housing density. The regression analysis for mass loss on the litter and microclimate variables indicated lignin content and carbon to nitrogen ratio as the most important factors. Most other studies indicate moisture availability as the most limiting factor. The moisture in these areas could have been sufficient because of the proximity to the ephemeral stream thus leading to different results. Overall, the decomposition processes along ephemeral streams in this region are resilient to changes related to these urbanization levels. Setting aside small riparian areas along ephemeral streams appears to aid in their preservation and is recommended for future urban developments.