Effects of liming on health and growth of young Schima superba trees under canopy of a Pinus massoniana stand damaged by soil acidification in Chongqing, China

In the past decades the decline of Masson pine (Pinus massoniana) forest caused by soil acidification due to excess sulphur (S) and nitrogen (N) input has become common in Chongqing, China. Schima superba, an excellent shade-tolerant and fire-resistant species, is believed to be more resistant to soil acidification than Masson pine. Accordingly, its saplings were often grown in acidified and declining Masson pine stands to transform them and enhance prevention and control of forest fires and, in fact, cultivating S. superba saplings under canopies of Masson pine stands growing on acidified soil may be an important measure of forest transformation in the future. But on the other hand, liming is an effective practice to alleviate damage of soil acidification to Masson pine forests. In 2004, we established permanent plots limed with 0 (unlimed control), 1, 2, 3, and 4 t ha(-1) limestone powder in an acid-damaged (> 25 % defoliation) Masson pine stand mixed with S. superba saplings in Chongqing, and observed positive responses of Masson pine growth 8 years after liming. In 2015 we conducted an investigation to assess the effects of liming on the health and growth of young S. superba trees under the canopy of this stand. The results showed that compared to the unlimed control, liming increased pH, exchangeable calcium (Ca), and Ca/Al molar ratio, but decreased exchangeable aluminum (Al) in the 0-20 cm mineral soil layer. As a result, length densites of living fine roots of the young S. superba trees increased, while their defoliation decreased. Over 11 years, mean height increment of the S. superba trees increased from 3.7 m in the unlimed control to 3.8, 4.0, 4.7, and 5.9 m in the 1, 2, 3, and 4 t ha(-1) lime treatments, and their mean basal diameter (5 cm above the ground) increment increased from 2.4 to 2.7, 3.2, 3.9, and 4.9 cm, respectively. Liming favored the transformation of the Masson pine stand. These effects rose with increasing dose.