Carbon dioxide emissions: Spatiotemporal variation in a young and mature riparian forest

Forested riparian zones in agricultural landscapes provide multiple ecological services including nutrient abatement and carbon (C) sequestration. However, limited information exists on CO2 emissions from rehabilitated riparian forests, which could negate their C sequestration potential. The objective of this study was to evaluate temporal and spatial variation of CO2 emissions, and its relationship to soil and vegetation characteristics, in a 30-year old riparian zone rehabilitated with trees (RH) compared to a 150-year old undisturbed natural (UNF) riparian forest. Soil moisture, temperature, C, total nitrogen (TN) and vegetation characteristics (light intensity, distance to the nearest tree) were significantly (p < 0.05) different between RH and UNF sites. Soil CO2 emissions were significantly greater (p < 0.05) in the RH (27 mg CO2-C m(-2)h(-1)) than in the UNF (18 mg CO2-C m(-2)h(-1)) riparian forest. Both riparian forests exhibited strong seasonal patterns of CO2 emissions with significantly greater (p < 0.05) emissions during the summer. Carbon dioxide emissions were significantly different (p < 0.05) with respect to location (perpendicular and parallel) from the stream. For example, emissions were significantly different (p < 0.05) among perpendicular locations in the RH site, but among parallel locations in the UNF site. Emissions of CO2 were significantly correlated (p < 0.05) to soil moisture and temperature in the RH site, and significantly correlated (p < 0.05) to temperature, SOC and TN content in the UNF site. Carbon dioxide emissions were not significantly correlated (p < 0.05) to vegetation characteristics. We concluded that the younger RH site generated contrasting soil and vegetation characteristics that influenced spatial CO2 emissions differently compared to a mature riparian forest. However, our study also found that seasonal changes had a stronger influence on CO2 emissions than spatial variability in both riparian forests.