Objective This paper aims to reveal the influencing rule of liberation cutting intensity on the medium and long term carbon sink of Korean pine forests by planting conifer and reserving broadleaved trees (PCRBT), and to provide basis for the restoration of zonal climax vegetation broadleaved Korean pine forest.
Method The carbon storage (vegetation and soil), net primary productivity (NPP) and net annual carbon sequestration (ANCS) of the mid-term (35 years) Korean pine forests by PCRBT under different liberation cutting (LC) intensities (control(C), low-intensity LC(L)-1/7, moderate-intensity LC(M)-1/5, and high-intensity LC(H)-1/4 (volume ratio)) were measured simultaneously by the relative growth equation and carbon/nitrogen analysis method in temperate Xiaoxing’an Mountains of northeastern China, to reveal the law and mechanism of the effect of liberation cutting on carbon sink of Korean pine forest.
Result (1) The vegetation carbon storage ((81.15 ± 3.63) − (85.48 ± 2.30) t/ha) of the Korean pine forests by PCRBT was significantly lower than that of control ((100.24 ± 1.10) t/ha) by 14.7%−19.0% (P < 0.05) after liberation cutting 30 years, but the difference of vegetation carbon reserves was not significant among the low-, medium-, and high-intensity liberation cutting (because the carbon reserves of upper canopy broadleaf trees decreased with liberation cutting intensity (21.1%−31.2%), while the carbon reserves of Korean pine under canopy increased by 39.0%−107.4%). (2) The soil carbon storage ((108.32 ± 6.27) − (121.42 ± 11.75) t/ha) of the Korean pine forests by PCRBT was similar to that of control (−8.4%−2.7%, P > 0.05), however, the spatial distribution patterns of soil carbon storage were changed by the liberation cutting (on the horizontal distribution, the soil surface carbon storage decreased with increasing of liberation cutting intensity; on the vertical distribution, low-intensity and moderate-intensity liberation cutting made its vertical distribution changed from upper soil layer > middle soil layer ≈ lower soil layer in control forest to upper soil layer > middle soil layer > lower soil layer, or upper soil layer ≈ middle soil layer > lower soil layer). (3) The carbon storage of ecosystem ((189.47 ± 5.16) − (218.44 ± 10.65) t/ha) of the Korean pine forest by PCRBT had been recovered under low intensity LC (−5.3%, P > 0.05), but moderate-intensity and high-intensity LC still made them significantly lower than that of control by 9.3% and 13.3% (P < 0.05), and the carbon storage distribution ratio of the ecosystem was slightly changed by all the three intensity LC treatments (the carbon storage ratio of vegetation was reduced by 3.06% − 4.57%). (4) The NPP ((8.02 ± 0.79) − (9.51 ± 0.79) t/ha) and ANCS ((3.72 ± 0.37) − (4.42 ± 0.37) t/ha) of the Korean pine forest under low intensity liberation cutting treatment had been restored (−11.5% and −9.7%, P > 0.05), while moderate-intensity and high-intensity liberation cutting still made them significantly lower than that of control by 15.4%−15.7% and 14.0%−15.8% (P < 0.05), but there was no significant difference among the different liberation cutting intensity treatments (which because the net primary productivity and the annual net carbon sequestration of upper canopy broadleaf trees decreased by 20.8%−25.6% and 19.3%−24.5%, however, those of Korean pine under canopy increased by 0.90−1.12 t/ha and 0.43−0.52 t/ha, with the liberation cutting intensities increasing).
Conclusion Low-intensity liberation cutting has made the ecosystem carbon storage and annual net carbon sequestration amount of the Korean pine forests by planting conifer and reserving broadleaved tree restored after 30 years, while moderate-intensity and high-intensity liberation cutting made them significantly reduce by 9.1%−14.3% and 14.3%−16.7% in the Xiaoxing’an Mountains. Therefore, from the perspective of maintaining forest carbon sink, it is more appropriate to adopt low intensity liberation cutting in the management practice of the secondary forest restoring zonal climax vegetation.
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