Soil respiration following Chinese fir plantation clear-cut: Comparison of two forest regeneration approaches

Abstract

In response to ecological problems originating from long-term pure coniferous plantations, clear-cut, species mixing, and other forest regeneration practices have been proposed to develop into mixed conifer-broadleaved stand. However, the dynamic effects of these forest regeneration approaches on soil respiration have not been well investigated. In this study, we compared soil respiration for three continuous years from two completely different forest regeneration approaches in clear-cut areas with uncut as control in pure Chinese fir plantations in subtropical China. These two approaches were, I: ground vegetation cut and removal of slash in the first year followed by the second year's ground vegetation cut but retained on the site, and II: ground vegetation cut and slash burning in first year followed by second year's soil ploughing, replanting, ground vegetation cut but retained on the site. Soil respiration changed obviously as forest practices were applied in the both regeneration sites. Mean respiration rate for the first year was lower for the treatments of Approach I and Approach II than uncut control (−15.0% and −26.8%), indicating that soil respiration decreased with ground vegetation removal or slash burning after clear-cut. In contrast to the first year, mean respiration rate was higher for the treatments of Approach I and Approach II treatments than uncut control (+12.8% and +32.2% in the second year, 16.3% and 30.8% in the third year), indicating ground vegetation cut with retaining residuals or soil ploughing significantly increased soil respiration. These drastically changes were mainly due to the rapid growth of understory vegetation and new seedlings, the difference of species composition, the availability of respired organic matter and the intensity of soil disturbance induced by different specific forest practices of two regeneration approaches over time. In addition, the different species mixing and forest management practices enhance the uncertainty linked to the analyses of soil respiration. Our results suggest that high intensity forest regeneration approach has a higher soil CO2 emission and lower production of biomass. Forest regeneration approaches could decrease the temperature sensitivity of soil respiration. Our findings provide new insights into the effects of forest practices on soil CO2 flux following clear-cut.