【作者】 肖兴翠；

【导师】 李志辉；

【作者基本信息】 中南林业科技大学 ， 森林培育， 2013， 博士

【摘要】 湿地松(Pinus elliottii)自引种到我国已有80多年历史,是一种优良的脂材两用树种,因其适应性强、分布广,早期生长快,树干通直,材质好,已经成为我国南方丘陵区最主要的造林树种之一。本文以湖南省泪罗市湿地松人工林为研究对象,对不同密度林分的林木生长量、生物量、根系状况、养分变化状况进行了研究,并就施肥、修枝对湿地松中龄林生长等方面的影响状况进行了观测与分析,为制定湘北区域湿地松人工林营林措施提供理论依据。研究结果表明：1.林分密度对除树高外的各生长指标均有显著或极显著影响。胸径、树高和单株材积均从8a生、林分蓄积从4a生开始随林分密度的增大而增大。不同密度以高密度林分高径比大、冠高比小、树干相对饱满。到11a生时,低密度林分中≥14cm的中径阶木所占比例大,高密度林分中8-12cm的小径阶木所占比例大。综合成本效益分析,培育湿地松中大径材及脂材两用林宜选用1667、2000株.hm-2两种密度,培育中小径材宜选用2400株·hm-2作为初植密度。2.林分密度对单株、林分生物量及其分配均有极显著影响。9a生及11a生乔木层单株生物量均随林分密度的增大明显减小,乔木层、凋落物生物量及林分总生物量均随林分密度的增大而增大,地被物生物量总体随林分密度的增大而减小；林分各组分中以乔木层生物量所占比例最大,分别占林分总量的81.6%-88.1%和83.0%-87.6%；乔木层各器官中均以树干生物量比例最大,分别占其总量的37.7%-43.7%和41.4%-45.8%；建立的各器官生物量模型精度较高,可用于估测湿地松各器官生长量；不同密度林分平均生产力分别为8.9t·hm-2a-1和9.1t·hm-2a-1,以2400株.hm-2林分结构较为合理,适宜作为湘北湿地松纸浆材造林密度。3.林分密度对单株、林分根系生物量均有显著或极显著影响。随着林分密度的增大,9a及11a生单株根系生物量减小,林分根系生物量总体增大,其中根桩和大根合计分别占总根量的60.7%-70.9%和63.9%-75.2%；不同密度根系生物量均随土层深度的增加而明显减小,11a生时有63.1%以上的根系集中分布在0-40cm土层内,有81.4%以上的根系集中分布在距树干0-50cm范围内,因此对湿地松施肥的位置应该设在距树干50cm、深度20cm左右为宜,以确保肥料最大限度的被根系吸收。利用建立的湿地松单株各级根系生物量模型,可以估测单株各径级根系生物量及总根量,为根系的开发利用提供依据。4.林分密度对湿地松单株及林分营养元素积累量均有显著影响,随着林分密度的增大,9a及11a生乔木层单株营养元素积累量减小,乔木层、凋落物营养元素积累量及林分总量总体增大；林分各组分以乔木层为主,分别占林分营养元素积累总量67.7%-79.2%和69.3%-76.5%,乔木层以林冠枝叶和干材营养元素积累为主,11a生时分别占其总量的44.1%-50.1%和39.1%-44.9%。随着林分密度增大,林分吸收量和存留量显著增大,归还量略微减小,周转期总体变长,养分循环速率略微减小,养分利用效率增大；综上分析,以1667、2000株.hm-2作为湿地松人工林适宜经营密度,对林地进行选择性除杂,并将凋落物及采伐时剩余的枝叶保留在林地,适当增施P、N、K肥,以维持湿地松人工林的地力。5.施肥对湿地松生长及土壤等均有明显影响。施肥3a后,胸径、单株材积生长量比对照显著提高,以700g·株-1的施肥量各指标生长量最大。施肥2a后的土壤养分与施肥前相比,不同土层pH值及速效P均有所减小,有机质、速效K含量均有所增加,速效N含量大幅增加。施肥7个月后,豆马勃子实体个数在施肥量100-800g·株-1范围内总体随施肥量的增加而增加,是对照的2.0-24.0倍,施肥量过多可能会抑制豆马勃菌的生长。综合分析,对湿地松中龄林追肥,以追施N、P、K配方肥700g·株-1最佳。6.修枝对湿地松中龄林除冠幅外的各指标生长量均有不利影响,高强度修枝2a后,不同密度湿地松胸径、单株材积和蓄积生长量显著低于对照,冠幅生长量显著高于对照,中低强度和留桩的方式修枝对生长量的不利影响相对较小。对高密度湿地松进行修枝对干形影响更大,中高强度及留桩方式修枝使高径比变大,冠高比变小,干形更为饱满。修枝3-4个月,流脂松节数量总体随修枝强度的增加而增加,采用低强度、留桩的方式修枝可以减少松节流脂。综合修枝2a的成本效益,对6a及7a生湿地松以不修枝为宜。综合以上研究结果,1667、2000株·hm-2两种密度投入产出较好,养分周转期较短,循环速率较高,可作为培育湿地松中大径材首选造林密度,而2400株.hm-2林分结构较好,生物量相对较高,可作为培育中小径材的初植密度。在培育过程中对湿地松中龄林进行选择性除杂,追施700g·株-1的P、N、K肥配方肥,注意将凋落物保留在林地,采伐时将枝叶保留在林地,有利于维持地力,提高湿地松林分生产力。更多还原

【Abstract】 Pinus elliottii is an excellent dual-use species for producing rosin and lumber with more than80years history since introduced to China, and has become one of the most important afforestation species in hilly area of southern China as its strong adaptability, wide distribution, quick growth in early period, straight trunk and good timber quality. In this paper, different densities of slash pine forest planted in MiLuo city, Hunan province were studied on its growth, biomass, root development and nutrient cycling, and the influence of fertilization and pruning on the growth of middle-aged slash pine forest was studied and analyzed so as to provide the theoretical basis for developing silvicultural measures of slash pine plantations in northern Hunan. The results showed that:1. Densities had significantly or extremely significant influence on each growth index except height. The DBH, height and individual volume all decreased since8years old, the stand volume increased since4years old. The higher density, the higher H/D and the lower C/H with better developed trunk. For11years old plantations, the proportion of middle class wood which diameter was≥14cm was higher in low density while the proportion of small class wood which diameter was8-12cm was higher in high density. As analyzing the cost and benefits comprehensively, we should select two densities of1667and2000tree·hm-2to cultivate middle-large diameter timber and dual-use species for producing rosin and lumber, and select2400tree-hm-2to cultivate middle-small diameter timber of slash pine.2. Stand density had extremely significant effect on biomass and its distribution of individuals and plantations. With the increase of stand density, the biomass of individual tree in arbor layer were significantly decreased, and the stand biomass of arbor layer, litter and the total biomass of stand increased, and the ground cover biomass generally decreased in9and11-year-old slash pine plantations. The biomass of arbor layer accounts for the largest proportion in different components of stand, which accounted for more than81.6%-88.1%and83.0%-87.6%of the total biomass of stand respectively. The stem biomass accounted for the largest proportion in different organs of arbor layer, which accounted for more than37.7%-43.7%and41.4%-45.8%of the stand biomass of arbor layer respectively. The biomass mathematical models of all organs had high accuracy, and various organs biomass and the total biomass can be estimated by the models. The average productivity of stands in different densities were8.9t-hm-2a-1and9.1t-hm-2a-1, and the stand structure with density of2400tree-hm-2was more reasonable which was suitable for slash pine pulpwood in the northern Hunan.3. Stand density had significantly or extremely significant effect on root biomass of individual tree and stand. With the increase of stand density, individual root biomass decreased, and stand root biomass generally increased in9and11-year-old slash pine plantations, among which the tap root and large-root accounted for more than60.7%-70.9%and63.9%-75.2%of the total root biomass respectively. The root biomass decreased significantly with increased soil depth in all stand densities, and more than63.1%the root biomass distributed in0-40cm depth soil and more than81.4%of the root biomass distributed around0-50cm from the trunk in the horizontal direction in11-year-old slash pine plantations. Therefore, to ensure that the fertilizer maximum absorbed by roots of slash pine, fertilization should be applied from the trunk50cm, depth20cm. The mathematical models of root biomasses of individual tree with different stem diameter had high accuracy, and root biomass of each class and the total root biomass can be estimated for the basis of the utilization and development of the root system.4. Stand density had significantly effect on nutrient accumulations of both individual tree and stand of slash pine. With the increase of the stand density, the nutrient accumulation of individual tree in arbor layer decreased, and that in stand of arbor layer, litter and the total quality of the stand increased in9and11-year-old slash pine plantations. The majority of all parts was arbor layer which accounted for more than67.7%-79.2%and69.3%-76.5%of the total nutrient accumulation respectively. The most nutrients accumulated in branch, leaves and timber in arbor layer, which was more than44.1%-50.1%and39.1%-44.9%in11years old forest. With the increase of the stand density, the nutrient uptake and retention of the stand increased significantly, and the return slightly decreased, the turnover became longer, the nutrient cycling rate decreased a little, and the nutrient use efficiency increased. Therefore,1667and2000tree-hm"2were the suitable densities, and the cultivation measures including selectively removing other species, reserving the litter and residue of cutting, applying P-N-K fertilizer should be conducted to maintain the land capability of slash pine plantations.5. Fertilization had obvious effect on the growth and soil et al of slash pine. The DBH and the individual volume growth increased significantly compared with the control3years after fertilization, and the growth of each index was the highest treated by fertilization of700g-tree-1. The2years after fertilization, pH value and available P content in each soil layer decreased, and organic matter, available K content increased, and available N content increased in a large scale. The7months after fertilization, the number of Pisolithus fruiting body generally increased with the increase of the fertilizer, which was2.0-24.0times of the control, and excessive fertilizer maybe suppress the growth of Pisolithus tinctorius. By analyzing the effects of the fertilization on the growth and the cost and benefits, the rational measure was N-P-K fertilization of700g-tree-1for middle aged slash pine plantations.6. Pruning had adversely effected on the growth of each growth index except crown width in the middle aged slash pine. Two years after high intensity pruning, the growth of DBH, individual volume and stand volume in different density of slash pine were significantly lower than those of the control, while crown growth was significantly higher. The middle to light and stubble reserve method pruning showed less adverse effects on the growth. Pruning had bigger effect on stem form of the high density. Middle to heavy pruning and stubble method increased the H/D and decreased the C/H with well developed stem form. The number of rosin knot increased with the increase of the pruning intensity in the3rd-4th month. Lighter pruning and stubble method might decrease the loose knot resinosis. Comprehensively analyzing the cost and benefits of2years pruning, no pruning was suitable for6years old (2500tree-hm-2) and7years old (833tree-hm-2) slash pine plantations.In a conclusion, the invest-output of the forest which density was1667and2000tree-hm-2were better as their shorter nutrient turnover and higher cycling rate, which could be the rational afforestation density to cultivate middle-high diameter timber. While the forest with density of2400tree-hm-2had better stand structure and higher biomass, which could be the primary density to cultivate middle-low diameter timber. In the process of cultivating of slash pine, it were conducive to maintain the land capability and improve the productivity of middle-aged slash pine plantations through selectively removing weeds and bushes of the woodland, applying formula P-N-K fertilizer (700g-tree-1), reserving the litter and residue of cutting in the forest land.更多还原