Effects of thinning on tree growth and soil physiochemical properties in Cunninghamia lanceolata plantation

ABSTRACT Tree growth, along with soil properties, is greatly affected by forest management. We used a typical sampling to study the impact of four thinning intensities (T1: 0%, 2500 stems ha−1; T2: 20%, 2010 stems ha−1; T3: 30%, 1750 stems ha−1; T4: 40%, 1500 stems ha−1) on the tree growth and soil physicochemical properties and their correlation in Cunninghamia lanceolata plantations. The average annual increments in tree height, diameter at breast height (DBH), and volume increased with thinning intensity, and those of T4 differed significantly (P < 0.05) from those of T1. The average annual stand volume increments of T4 were significantly (P < 0.05) lower than that of T1, while the maximum value presented at T3. However, the effect of thinning in promoting the growth of Chinese fir diminished with time. As the thinning intensity increased, the diameter class distribution of the sample stands moved rightwards. Moreover, thinning improved soil physiochemical properties. The effects of thinning on soil properties in 0–20 cm soil layer were greater than those in 20–40 cm soil layer. There was a positive correlation between available nitrogen, available potassium and tree growth. The results of this study showed that thinning had a potential effect on tree growth and soil properties. The heavy thinning intensity (approximately 1500 stems ha−1) was the optimum for maintaining economic and ecological benefits. However, heavy thinning significantly reduced stand volume. From the perspective of improving stand volume and biomass, a moderate thinning intensity (approximately 1750 stems ha−1) could be considered for adoption.