Influence of restored riparian forest structure and age on channel morphology and health of neotropical streams

Natural regeneration of riparian forest is vital for stream ecosystem health. However, there is limited evidence on the impact of passive restoration on key processes that sustain the functionality of small-order tropical streams. The objective of this study was to evaluate the ecological effectiveness of riparian forest restoration at enhancing the health of degraded agricultural streams in the neotropics. The study was conducted in 15 catchments in southeastern Brazil, using the space-for-time substitution design, where the 15 catchments were divided into three classes according to the age of their naturally regenerating riparian forests. We assessed the riparian forest structure, canopy cover, as well as stream channel attributes such as channel morphology, hydro-chemical conditions, and biological characteristics. Our results demonstrated that the structural complexity of riparian forests had a significantly higher forest structure and canopy cover compared to younger riparian areas. The large woody debris volume and abundance in the stream displayed an increase trend with the age of riparian forest and had important influence in channel morphology and, consequently, on the water quality, and primary production. We concluded that age of passive restoration was strongly linked to the riparian forest structure demonstrating that mature restored areas was responsible to improve physical, chemical and biological conditions of degraded streams. The results of this study can be used to guide and assist in the selection of strategies that ensure improvements in the health of degraded streams in the neotropics.