大兴安岭兴安落叶松(Larix gmelinii)天然林分级木转换特征

通过调查样地,作树干解析,分析了不同结构兴安落叶松天然林分级木（优势木、平均木和被压木）转换特征。研究表明：（1）不同结构的兴安落叶松天然林分级木转换年龄、方向和转换率均不同。兴安落叶松分级木转换率29.4%。分级木中,优势木、平均木和被压木转换率分别35.3%、41.2%、11.8%。分级木转换中,优势木与平均木相互转换比例较高,优势木转平均木占83.3%,平均木转优势木占85.7%;优势木向被压木转换比例仅为16.7%;被压木不能转换成优势木,只能转换成平均木,被压木中无转换占88.2%,在森林经营和抚育采伐中应考虑伐除这些被压木。（2）在林分年龄36～65a范围内,随着林分年龄增大,其转换率呈增加趋势。林分年龄30～39a、50～59a和60～69a时,其转换率分别0、33.3%和46.7%。（3）随着林分密度增加,分级木转换率呈增高趋势。当林分密度小于2500株.hm^-2时,主要于优势木与平均木间转换。当林分密度大于2500株.hm^-2时,才出现其它分级木与被压木相互转换现象。（4）不同林型分级木转换率和转换方向不同。草类-落叶松和杜香-落叶松林分级木转换率分别50%和9.5%。（5）不同水平格局林分分级木转换率不同。聚集分布和随机分布时,其转换率分别61.1%和13.3%。

Analysis on classified stem transformation characteristic of Larix gmelinii natural forest at Daxingan Mountains

On the basis of setting sample plots and making trunk analysis, this study analyzed the transformation characteristics in different classified stems structures (dominant stem, average stem and overtopped stem) of Larix gmelinii natural forest. The results show : (1) each different structure of L.gmelinii classified stems has different transformation age, direction and transformation rate. The transformation rate of L.gmelinii classified stems is 29.4%, where dominant stem, average stem and overtopped stem are 35.3%, 41.2% and 11.8%. In the transformation rates of classified stems, the interconversion proportion between dominant stem and average stem is high, from dominant stem to average stem is 83.3% and from average stem to dominant stem is 85.7%; from dominant stem to overtopped stem is only 16.7%, the transformation from overtopped stem to dominant stem is not observed, while the transformation from overtopped stem to average stem is observed, 88.2% of overtopped stem has no transformation to other classified stems, considering management and tending of forests those overtopped trees should be removed. (2) The stand age is within 36-65a, the transformation rate tends to increase, as the stand gets old. When the ages are within 30-39a, 50-59a and 60-69a, the transformation rates are 0, 33.3% and 46.7%. (3) The transformation rate of classified stems tends to increase with the stand density increment. When the stand density is up to 2,500 trees·hm-2, the main transformation appears between dominant stems and average stems. When the stand density is over 2,500 trees·hm-2, transformed phenomenon between overtopped stem and other classified stems appears. (4) According to forest types, the transformation rate and direction are different. The transformation rates of Herbage-Larix gmelinii and Ledum-Larix gmelinii are 50% and 9.5%. (5)The horizontal stands patterns show that the transformation rate of classified stems is different. The transformation rates of clustered distribution and random distribution are 61.1% and 13.3%.