格木是我国华南主要的乡土珍贵用材树种之一,掌握其人工林生长分化过程并合理选择间伐时间,对于格木大径材培育技术具有重要意义。以广西凭祥的10个格木中龄林样地为研究对象,将林木分为优势木、平均木和被压木3个等级,并依据各等级林木的竞争响应与生长动态,分析林分的分化过程和管理策略。结果表明:1)林分中个体生长分化显著,处于竞争劣势地位的个体通常具有较高的树干形数、高径比、冠径比和较低的冠长比,竞争反应主要表现为树高增加,胸径和树冠下降。2)胸径在前5 a生长缓慢,6~25 a为速生期,在第7 a出现明显的等级间分化;树高在3 a和7 a各有一次分化,速生期自3a起延续至第15 a左右,其分化起始时间及速生期结束时间均早于胸径的对应时间;胸径与树高的连年生长量和平均生长量的交叉时间分别在22~24 a和10~12 a;单株材积在15 a以后进入速生期,其平均生长量和连年生长量在35 a未交叉,即未达到数量成熟期;在25~35 a,优势木材积占单位面积材积的50%左右,表明林分竞争较强,不利于目标树的生长发育。3)格木早期分枝多,导致成材的分枝高度低,节子多,影响后期出材率和木材质量,因此其大径材培育宜采取分段式管理,中幼林期以干形和质量培育为主,后期主要进行目标树产量培育;在第7 a时进行目标树初选,在第15 a、25 a、35 a左右可各进行一次目标树选择和干扰树间伐。

Erythrophleum fordii is one of the main native precious timber species in southern China.Understanding the tree growth characteristics and stand differentiation process of plantations,and accordingly determining appropriate thinning timings are crucial for optimizing large-size timber cultivation techniques for the E.fordii.From 10 sample-plot investigation in E.fordii middle-aged plantations,the trees were divided into three social classes involving dominant,average,and suppressed trees.With the competitive responses and growth dynamics of trees across different social classes,the differentiation processes within the stand and proposed corresponding management strategies were analyzed.The results showed that:1) Significant growth differentiation is among individuals within the stands.Trees at competitive disadvantage typically exhibit higher stem form factors,height-to-diameter ratios,and crown-to-diameter ratios,but lower crown length-to-height ratios.The competitive responses were primarily manifested by increased tree height,while Diameter at breast height(DBH) and crown dimensions showed relative declines in E.fordii plantations.2) DBH increased slowly in the first 5 years,entered a rapid growth phase from Year 6 to 25,and significant class differentiation emerging at Year 7,while height differentiation occurred earlier with two distinct divergences at Year 3 and 7,respectively,and its rapid growth phase initiated at Year 3 and persisted until approximately Year 15.The intersection points of current annual increment(CAI) and mean annual increment(MAI) occurred at Year 22 to 24 for DBH and Year 10-12 for height.Individual tree volume entered rapid growth phase after Year 15,its CAI and MAI not intersecting by Year 35,indicating unattained quantitative maturity.During Year 25 to 35,tree volume of dominant trees consistently accounted for approximately 50% of stand volume per unit area,reflecting intense competition unfavorable for target tree development.3) Through comprehensive analysis of the tree species characteristics and stand differentiation process,especially the early branching of E.fordii could result in low branch height and numerous knots after forest formation,which adversely affects the later timber yield and wood quality,therefore,the large-size timber cultivation of E.fordii could take phased management strategy,emphasizing stem form and quality improvement during the young and middle stages of plantations,followed by yield optimization in the later stage,and initial target tree selection could be at Year 7,but not need thinning;the first thinning would be around Year 15;and the second and the third thinning would be around Year 25 and 35,respectively.