[Phase-directional management of protective plantations. I. Fundamentals]

In order to ensure the higher effectiveness, more stability and sustainability of Protective plantations, the definition of phase-directional management (PDM) of protective plantations was brought forward on the basis of management researches and practices for protective plantations. The basics of PDM is protective maturity, which is defined as the time when the protective plantations attain to the state that the protective plantations can provide effective and complete protection to the objects needed to be protected. Protective maturity has two points, initial protective maturity age (IPMA), the age of protective maturity started, and terminal protective maturity age (TPMA), the age of protective maturity ended. Three management phases of protective plantation, i.e., prematurity phase, the period from sapling or establishment to initial protective maturity, protective maturity phase, the period of protective maturity lasting, and regeneration phase, the period during regeneration and before the establishment, are divided based on the fundamental of protective maturity. Directional management of protective plantation means that all of the management techniques in each phase are directed at the aim of protective maturity, i.e., protective maturity is the direction of management of protective forests, and protective maturity is the final objective for the management of protective forests. In order to sustain the protective maturity state, corresponding measures should be conducted in each phase, according to the classification of protective plantations. In pre-maturity phase, the purpose of managing is to accelerate the protective maturity, therefore, the measures such as weed clearing, soil cultivation, irrigation, fertilization, intercropping and branch cutting etc. should be conducted in protective plantations. In maturity phase, the aim of managing is to sustain the protective maturity, i.e., the techniques (tending and thinning) of controlling the structure of protective plantations should be paid emphases. In the period of regeneration, the objective of managing is to recover the protective maturity, accordingly, the regeneration patterns and ways should be determined reasonably. Additionally, the methods of determining protective maturity, i.e., the core of the phase-directional management, are also given corresponding to farmland shelterbelt, sand-fixation forest and water and soil conservation forest. For farmland shelterbelt, IPMA can be determined according to the growth pattern of tree height under the suitable structure (porosity). For sand-fixation forest, it can be determined by the cover degree of the forest, i.e., the age when cover degree gets to pi/4 can be considered as IPMA. In the case of water and soil conservation forest, IPMA is determined by the canopy closure at the height of 1m above forest ground, which can be obtained from the hemispherical silhouettes in vertical direction. As for the TPMA, it can be described by the natural age of trees for all of above-mentioned three kinds of protective plantations, but the concrete methods for estimating the natural age of trees in each kind of forests are different.