[Phase-directional management of protective plantations. II. Typical protective plantation: farmland shelterbelt]

This paper is the second part of the series reports on phase-directional management of protective plantations. Based on the fundamentals of phase-directional management for protective plantations in paper I, discussions on protective maturity, management phase, and regeneration patterns and methods for shelterbelt or windbreak were conducted. Firstly, the two points of protective maturity of Populus spp. i.e., initial protective maturity age (IPMA) and terminal protective maturity age (TPMA), were determined. According to the growth pattern of shelterbelt, the IPMA was 16 years and 24 years for local poplar and hybrid poplar shelterbelts, respectively, and TPMA was the natural age for both local and hybrid poplar shelterbelts, which was determined on the basis of change pattern of porosity. Secondly, the three management phases of shelterbelts were divided quantitatively based on the analyses of discrete degrees of diameter, IPMA and TPMA. Thirdly, the corresponding measures for phase-directional management in each phase were also developed. In pre-maturity phase, i.e., the period from establishment of shelterbelt to IPMA, the measures such as soil cultivation, irrigation, fertilization, weed clearing, intercropping and branch cutting etc. should be conducted. In maturity phase, i.e., the period from IPMA to TPMA in theory, but the period from IPMA to regeneration age in practice, the techniques of managing the shelterbelt porosity around 0.25 (the best porosity value for wind protection) should be developed. In this phase, the porosity model was constructed according to the distribution pattern of base area for the poplar shelterbelt. The classification of shelterbelt trees, i.e., 4-grade classification, was established by considering the contribution of trees to the shelterbelt structure, which can provide the standard for thinning and tending of shelterbelt. Additionally, the density controlling techniques were also discussed. In the period of regeneration, i.e., from the regeneration age to the establishment of next generation shelterbelt, the techniques of regeneration such as determination of regeneration age, arrangement of regeneration patterns should be paid great emphasis. The influences of regeneration patterns and methods on regeneration period were specially discussed, and the changes of three management phases were illustrated by different regeneration patterns in the end of this paper. These results were obtained from poplar shelterbelt, but the fundamentals could be applied in any other shelterbelts.