用潜在疏密度评价林分长势

目的林分长势是林分活力的直接体现，疏密度是反映林分密度和长势的重要指标之一。计算疏密度的关键是对标准断面积的准确求算，但在实际应用中标准林分难以判定，标准断面积的可获得性较差，削弱了其可应用性，探求新的指标是解决这一问题的有效途径，因此本研究旨在探究可以替代疏密度的新指标。方法一定的立地条件下，林地生产力是有限的，基于最终产量恒定法则，本研究以长期连续监测且经营数表齐全的杉木试验林分为材料，1989年编制的全国分区杉木标准表为参照，以林分内不同比例较大林木个体的平均断面积与全部林木株数的乘积表示林分生长能够达到的潜在最大断面积，即在50% ~ 80%林木株数比例范围内，以5%为梯度，依次比较不同比例较大林木个体所得潜在最大断面积与标准断面积的差值，求使潜在最大断面积与标准断面积偏差率最小时所对应林木株数比例，并以此为基础，分析天然林中林分断面积与潜在最大断面积的关系，检验潜在最大断面积的计算方法在天然林中的适用性。结果当较大林木株数占总株数比例为70%时，所有试验样地的潜在最大断面积与标准断面积的偏差最小，均在 ± 10%左右，此时，潜在疏密度与疏密度的差值最小；天然林中70%较大林木个体断面积之和与林分断面积呈显著线性关系，故可用70%较大个体的平均断面积与总株数乘积作为潜在最大断面积，来求算潜在疏密度。结论林分潜在最大断面积可以70%较大林木个体平均断面积与林木总株数的乘积表示，所求潜在疏密度可替代疏密度来表征林分长势。 

Evaluating stand growth state by potential density of stocking

ObjectiveStand growth is a direct reflection of stand vitality, density of stocking is one of the most commonly used indices to reflect the degree of closeness and its growth status in a stand. Accurate calculation of standard basal area is the key to calculate density of stocking, but it has poor availability and applicability because of the difficulty to distinguish standard stand among all stands of an area. exploring an alternative index is an effective way to solve this problem. Therefore, the purpose of this study is to find the new index.MethodThe potential productivity of a forest is finite under certain site conditions. Based on the Law of Constant Ultimate Capacity, in this study, we analyzed Cunninghamia lanceolata plantations under continuous monitoring with its growth process data all in readiness, with Cunninghamia lanceolata standard tables, which compiled in 1989 as cross reference. The potential maximum basal area of the stand was expressed by the product of the average basal area of a certain percentage of larger individuals and the total number of trees in the stand. Comparing the proportion from 50%?80% at 5% interval, we seek to find the ratio when the deviation rate between the potential maximum basal area and standard basal area was at its minimal value, and analyzed the applicability of potential maximum basal area in natural forests on this basis.Resultthe results suggested when the proportion was 70%, the deviation rate between the potential maximum basal area and the standard basal area of all test plots was about ± 10%, and the difference between the potential density of stocking and the density of stocking was at its minimal value. Furthermore, in order to test the applicability to natural forests, statistical analysis indicated that there was a significant linear relationship between the basal area with 70% as the larger trees and the stand basal area in the natural forest. The results showed that the potential density of stocking of a stand could be calculated by the product of the average basal area with 70% as the larger trees and the total number of trees.ConclusionThe potential maximum stand basal area could be expressed as the product of the average basal area with 70% as the larger trees and the total number of trees. The potential density of stocking, as an alternative index, can replace the density of stocking to characterize density and growth status of a stand.