防护林阶段定向经营研究I.理论基础

基于多年防护林经营研究与实践，在分析防护林经营目的的基础上，提出了防护林阶段定向经营理论基础，以防护林的防护成熟为核心，将防护林经营阶段划分为成熟前期，即从栽植后形成相对稳定的幼林到初始防护成熟龄；防护成熟期，防护成熟状态持续的时期，即从初始防护成熟龄到终止防护成熟龄；更新期，林木接近自然成熟开始更新直到更新结束并形成相对稳定的幼林，防护林经营的定向是指在任何经营阶段内，一切经营技术与措施都是为了使防护林向着成熟的状态发展，即防护成熟是防护林经营的方向，是最终目的，为尽量维持防护林的成熟状态并使防护效益不间断，针对发育正常与低质衰退的林分，在各个经营阶段内采取相应的系列经营管理与改造措施。

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.