林木分化对兴安落叶松异速生长方程和生物量分配的影响

林木因对资源竞争而产生分化,从而影响林木的异速生长方程和生物量分配,但其影响程度还不清楚。采用林木相对直径法将38株兴安落叶松(Larix gmelinii)样木在林分中的分化等级分为优势木、中等木和被压木,量化林木分化对林木异速生长方程和生物量分配的影响。结果显示:生物量组分异速生长方程多以胸径(DBH)为自变量为好,但以枝下高处的树干直径为自变量估测其枝、叶生物量时更精确。在一定的胸径范围内,同一胸径下不同林木分化等级的地下部分各组分生物量没有显著差异(P0.05),但优势木分配更多的生物量给枝和叶,中等木比优势木分配更多的生物量给树干,中等木比被压木分配更多的生物量给地上部分,而且被压木和中等木的树高显著高于优势木。除根茎生物量之外,不同林木分化等级的生物量组分(包括枝、叶、树干和根系)的相对分配比例无显著差异(P0.05),根冠比保持相对稳定。这些结果表明,主要由竞争而引起的林木分化改变了兴安落叶松地上生物量组分的异速生长和分配,但其相对分配格局较为保守。     

兴安落叶松天然林生物量及生产力的研究

 依据生物量标准木237株、解析木814株以及355块标准地实测材料对内蒙古大兴安岭林区三个气候区兴安落叶松天然幼、中龄林的生物量和净初级生产力进行了分析比较。结果表明,兴安落叶松天然林的生物产量明显受热量带的影响。残差分析证实了VAR模型lnW =lna+blnD+cD或lnW=lna+bln D2H+CD2H在估测兴安落叶松天然林生物量方面的应用价值,该模型对相对生长率随D或D2H呈线性变化的情况更为适合。本文还给出了各气候区适宜的林分密度和叶面积指数范围。     

祁连山青海云杉树干液流密度的优势度差异

以祁连山排露沟小流域青海云杉林为研究对象,选取有代表性的优势木、亚优势木、中等木和被压木各3—5株,2015年6月16日至10月14日应用热扩散技术对不同优势度青海云杉树干液流密度进行测定,并同步测定相关的林外气象因子。结果表明:(1)青海云杉液流密度呈昼高夜低趋势,晴天液流密度变化幅度较大,而阴雨天变化幅度较小。(2)晴天树木优势度越大,其液流在日内的启动越早,结束越晚,峰值也越大;优势木的平均液流密度为(0.0758±0.0475)m L cm~(-2)min~(-1),是亚优势木的1.5倍,是中等木和被压木的1.68倍。(3)青海云杉平均液流密度基本呈现6月份最大,其次是8月份,9、10月份明显减小,且优势木亚优势木中等木被压木。(4)相关性分析和逐步回归表明,青海云杉日均液流密度与太阳辐射强度、饱和水气压差和空气温度呈正相关关系,与空气相对湿度和降雨量呈负相关关系。影响优势木、亚优势木和中等木液流密度的主要气象因子是太阳辐射强度,被压木液流密度主要受空气相对湿度的影响。     

不同年龄杜香-兴安落叶松林粗木质残体贮量及特征

以大兴安岭杜香-兴安落叶松林为对象,采用2类标准分析不同年龄林分粗木质残体(CWD)的物种组成、径级结构及腐烂等级,揭示CWD特征及贮量的变化。结果表明:Harmon标准计算的密度、体积和生物量为350～659株·hm-2、2.64～38.27m3·hm-2和1.13～8.52t·hm-2,分别比LTER标准高出52.07%～92.38%、17.44%～63.13%和16.88%～22.11%。随着林分年龄的增加,Harmon标准计算的CWD密度呈"U"型分布,体积和生物量均呈近似正态分布;LTER标准计算的CWD密度从中龄林开始逐渐上升,体积和生物量则逐渐降低。随着林分年龄的增加,2类标准计算的腐烂等级高的CWD密度、体积和生物量比例均逐渐增加,其中幼中龄林以Ⅰ-Ⅱ级腐烂为主,近成熟林以Ⅱ-Ⅲ级为主。群落由兴安落叶松和白桦构成,兴安落叶松CWD在数量、体积和生物量上均占76%以上。     

北京松山自然保护区蒙古栎林的空间结构特征

以松山自然保护区面积为0.6 hm²样地的调查数据为基础,利用角尺度、大小比数和混交度3个林分空间结构参数,分析了蒙古栎天然林的空间结构特征.结果表明：蒙古栎林乔木层共有10个种群,蒙古栎种群密度和断面积占有明显优势,是乔木层的优势种和建群种;蒙古栎林平均混交度为0.299,林分混交程度低,优势种以零度混交和弱度混交为主,伴生种的混交状况普遍较好;蒙古栎和油松种群在空间结构单元中以优势木、亚优势木和中庸木为主,分别占种群总株数的68%和58%,其他种群的树种优势度不明显,多为被压木;该林分的空间分布格局为聚集分布,但林木聚集程度和聚集规模较低.     

黑龙江省市县林区落叶松人工林碳储量成熟的研究

基于42株碳密度测定样木和黑龙江省各市县落叶松人工林固定样地（2006~2007年）生物量及含碳量调查数据,构建落叶松人工林单木碳储量相容性模型及林分碳储量预估模型,探讨落叶松人工林在不同立地下碳储量变化规律,确定碳储量成熟龄。结果表明：以碳储量直接作为因变量建立的单木碳储量相容性模型,拟合效果较好。在Ⅰ、Ⅱ、Ⅲ级立地条件下落叶松人工林碳储量成熟龄分别为37.8、39.2、42.5 a。研究认为,相同年龄落叶松人工林林分的碳储量随立地条件质量的提高而增加。相同立地条件下落叶松人工林林分的碳储量随年龄的增大而增加,林分平均碳积累量与连年碳积累量呈现先增大后减小的趋势,这表明林分的碳储量增长过程并不是一成不变的,其达到一定年龄后增长的幅度随年龄的增加而逐渐减少。     

黑龙江省落叶松人工林碳储量动态研究

基于36株碳密度测定样木和5期黑龙江省森林资清查数据（1986~2005）,利用非线性度量误差模型来估计黑龙江省落叶松人工林的碳储量动态变化。结果表明：黑龙江省人工落叶松不同器官碳密度在456.7~479.0 mg·g^-1之间,不同器官碳密度差异显著,各器官碳密度由高到低为：树叶>树枝>树干>树根。不同林龄落叶松人工林树干、树根树枝和树叶的碳储量分配比例分别稳定在：66.75%~68.92%、21.59%~22.62%、5.99%~8.16%和2.47%~3.50%。其中,树根和树枝含碳量比重随林分年龄增加而增加,树干和树叶含碳量比重随林分年龄增大而减小。1986~2005年黑龙江省落叶松人工林碳储量总体呈增长趋势,2000年时达最大,为30.38 t·hm^-2,在此期间,平均每年以1.21 t·hm^-2的速度增加。2005年黑龙江省不同区域落叶松人工林碳储量在25.43~34.35 t·hm^-2之间,各区域碳储量由高到低依次为：小兴安岭南坡>完达山地区>张广才岭东坡>张广才岭西坡>小兴安岭北坡。     

基于BP人工神经网络的兴安落叶松天然林全林分生长模型的研究

以大兴安岭地区兴安落叶松天然林为研究对象,基于688块固定标准地数据,采用MATLAB中log-sigmoid型函数(logsig)和线性函数(purelin)为神经元的作用函数,依据全林分生长模型的概念,以年龄（A）、地位级指数（SCI）和林分密度指数（SDI）作为输入变量,以林分每公顷蓄积量（M）作为输出变量,构建和训练了全林分生长的BP人工神经网络模型,并与常规建模方法进行了对比研究。结果表明,BP人工神经网络模型的拟合精度高达99.6%,检验精度为98.9%,说明与其它建模方法相比人工神经网络建模具有较高的拟合精度和适应性,对林分生长具有更好的预测能力。     

长白落叶松人工林乔木层生物量分布特征及其固碳能力研究

基于8~56 a长白落叶松人工林样地生物量调查数据,建立了长白落叶松林各器官生物量模型,探讨了不同林龄长白落叶松人工林干材、树皮、树枝、树叶、树根的生物量分布与变化规律及单木与林分乔木层的固碳能力。结果表明:随着林龄的增大,长白落叶松人工林林木及各器官生物量均呈现不同程度的增加趋势,单株木生物量由8 a时的0.174 kg增加至56 a时的328.196 kg,林分乔木层生物量由8 a时的0.519 t·hm-2增加至56 a时的251.39 t·hm-2,其中树干所占比例最大,且增幅最大。长白落叶松人工林单木平均碳储量为74.822 kg,56 a林分乔木层碳密度为130.455 t·hm-2,平均碳密度达63.113 t·hm-2,各器官碳储量变化规律明显。长白落叶松人工林幼龄林、中龄林、近熟林、成熟林林分乔木层的年平均固碳量分别为0.087、1.193、1.703、2.124 t·hm-2,固碳量年平均增长率排序为中龄林幼龄林成熟林近熟林。研究认为,长白落叶松人工林单株木及林分各器官生物量随林龄增加具有明显的变化规律,成熟林分固碳水平最高,中龄林分后期固碳潜力最大。     

水杉人工林建植50年后的分化特征

通过种群统计学、格局分析和树干解析等对50 a生水杉人工林林分的分化特征进行了研究.结果表明:小个体林木占有相对多数(>50.4%);林木分化现象显著,特别是树高与材积的分化十分突出,林分已出现一定强度的自然稀疏;基于TSTRAT程式的林木分级结果表明,亚优势木占绝对优势(45.7%),其树冠构成该林分的主林冠;竞争指数依次为优势木级<亚优势木级<中庸木级<被压木级,各级的基尼系数基本上低于全林总计;优势木绝对生长率和相对生长率在林分成熟期以前均大于标准木,且胸径速生期持续时问较标准木长;林分高度生长受压抑程度低于胸径生长;林木分布格局总体呈均匀型,与造林初始基本一致;优势木和被压木为聚集分布,中庸木和枯死木为随机散布,亚优势木的分布型则介于随机和聚集之间.林木种群分化既表现在个体大小的不均等性上,也表现在空间分布的非匀质性上.目前林分结构特征的主要成因可以归结为密度压力下的种内竞争.     

东灵山辽东栎林主要树种种群11年动态变化

 该研究在北京东灵山区一个30 m×40 m的纯辽东栎(Quercus liaotungensis)林永久性样地内进行,林龄为80年左右。样地中高于2 m的成树密度在1991、1997和2002年3次调查中呈逐年递减趋势,这种降低主要是由辽东栎个体的死亡引起的;而树木总胸径面积呈逐年增加趋势,主要是存活个体生长的结果。从1991年到2002年,辽东栎种群的优势度变化不大,且种群径级结构为单峰曲线,差异不显著。为了探讨这种径级分布格局形成的机制,应用离散模型对辽东栎种群的胸径年平均生长率G(t, x)、年平均死亡率M(t, x)及年平均生长率方差D(t, x)进行了计算,发现辽东栎种群的死亡率曲线呈倒J-型,个体的年平均生长率与胸径呈显著的线性正相关（p<0.01）。离散模型的系数分析和G(t, x)-D(t, x)的关系曲线分析均表明辽东栎种群内存在非对称种内竞争,即大胸径个体对小胸径个体的生长有抑制作用,这种作用主要是由相对较高的种群密度引起的对光资源的竞争。非对称种内竞争有利于维持辽东栎种群和整个群落的稳定状态。     

川西亚高山次生桦木林恢复过程中的生物量、生产力与材积变化

采用空间代替时间的样地调查方法,利用异速生长方程和一元材积表计算不同林龄桦木林的生物量、生产力与材积,结果表明,桦木林乔木层及平均单株地上生物量均随林龄增加而增加,在50 a时达到最大;生产力则先增加而后逐渐减少,乔木层30 a时生产力为7.88 t.hm-.2a-1,到40 a和50 a时,分别下降到5.17 t.hm-.2a-1和1.19.thm-.2a-1;单株平均生产力在30 a时达到最大值1.13 kg.a-1,40 a时下降为0.96 kg.a-1,50 a时略有上升。林分蓄积量随林龄增加而增加,平均生长量在50 a达到最大值3.78 m.3hm-2,连年生长量在30 a时达到最大值6.07 m.3hm-2。平均单株材积增长速度随林龄增加而增加,50 a时平均生长量和连年生长量达到最大值。     

西双版纳热带人工雨林生物量及净第一性生产力的研究

通过标准木法和收获法研究分析了西双版纳热带人工模拟雨林的生物量及净第一性生产力。结果表明,林分总生物量约为390.4t·hm^-2,其中乔木层生物量达362.5t·hm^-2,占总生物量的92.8%,灌木层生物量为19.3t·hm^-2,占4.9%,层间植物9包括附生植物）的生物量为3.6t·hm^-2,草本层生物量为5.0t·hm^-2,分别占1.3%和0.9%。林分净第一性生产力为2227.3g.m^-2.年^-1,其中乔木层的净生产力为1553.5g·m^-2.年^-1,占整个林分净生产力的69.7%,灌木层、草本层及层间植物分别仅占26.9%、2.4%和1.0%,其器官分配比例以茎最高,0达42.0%;其次为叶,占30.2%;枝占13.5%。叶面积指数为7.061。同时建立了林分优势种及乔木层各器官生物量的优化回归模型。     

Biomechanical Plasticity Facilitates Invasion of Maritime Forests in the southern USA by Brazilian pepper (Schinus terebinthifolius)

Biomechanical plasticity and within-species growth form diversity are traits that can facilitate invasion by non-native plant species. We support this argument with evidence from the invasion of coastal habitats in northern Florida, USA, by Schinus terebinthifolius and describe some of the consequences of this invasion for overtopped saltmarsh plants. In crowded stands, Schinus grows more like a vine than a tree, with stem height : diameter ratios nearly twice than those observed in open-grown individuals but with no changes in wood density or the modulus of elasticity of stem material. When extracted from the surrounding vegetation, the formerly crowded Schinus stems buckle under their own weight. Schinus crowns also extend much further over adjacent saltmarsh than crowns of Juniperus virginiana, the only other tree species abundant in the study site. Along forest edges, the above-ground biomass of saltmarsh plants overtopped by Schinus crowns was reduced by more than an order of magnitude. The biomechanical plasticity of Schinus allows it to adapt its growth form to suit habitat conditions and can dominate the edges of salt marshes as a sprawling shrub and maritime forests as either a free-standing tree or a woody vine, depending on stand crowding     

Frequency of partial and missing rings in Acer saccharum in relation to canopy position and growth rate

Locally absent growth rings are known to occur in trees during periods of environmental stress, but little evidence has been available on their frequency in moist temperate forests or on their potential for causing problems in dendroecological studies. In this study, 95 stem disks of Acer saccharum cut from trees representing a wide range of size and age were examined for ring anomalies using three techniques – inspection of disks for partial rings, crossdating of each tree against regional master chronologies, and use of stand history evidence. The number of ring anomalies in Acer saccharum was inversely related to growth rate and vigor. Mean percentage of ring anomalies was 1.3% in dominant canopy trees, 4.6% in trees of the intermediate crown class, and 16.2% in overtopped trees. All of the overtopped trees had partial or missing rings, with a mean of 10 per tree and a range of 2 to 20. Use of crossdating to correct for ring anomalies appeared to be successful in 88% of the canopy trees. However, crossdating results were inconclusive in 32% of the overtopped trees because of low ring width variability, multiple missing rings, and short duration of trouble-free segments. Because overtopped trees are of limited value in reconstructing disturbance history and often cannot be crossdated reliably, we suggest that they normally be excluded from disturbance chronologies.     

Composition and structure of a chronosequence of young, mixed-species forests in southeastern Ohio, USA

Clearcutting, a commonly used silvicultural practice in southeastern Ohio, often results in a forest stand with a different species composition than the parent stand. The time frames during which shifts in species composition occur on different sites are unclear. While some studies have documented species composition at specific points in time, none have attempted to examine differences throughout the first decades of stand development. This study focused on the early successional dynamics of young, mixed-species forests of southeastern Ohio. Species compositions were examined across a chronosequence of sixteen stands that developed following clearcutting. Stand ages ranged from six to 26 years. The sample was limited to dry-mesic hardwood forests on southerly aspects and on soils derived from residuum or colluvium. Across the chronosequence, stand density ranged from 17 636 stems ha^-1 at age 6 to 2759 stems ha^-1 at age 26, and basal area ranged from 8.2 m² ha^-1 to 22.1 m² ha^-1. Clumps comprised a substantial portion of the total stand density and basal area. At age 6–8 years after clearcutting, clumped stems accounted for 35.1% of the density and 48.2% of the basal area. At age 26 years, these proportions were 25.7% and 29.4%, respectively. Clumped stems were significantly larger (p<0.05) than non-clumped stems at each age group except 26 years. Total Quercus spp. density was greatest at age 6–8 years (3386 stems ha^-1), and least at age 26 years (581 stems ha^-1). When considered as a proportion of the total stand, however, the proportion was relatively stable, averaging 21.3%. However, importance value (IV=[relative density + relative basal area]/2) of Quercus in the upper canopy (dominant and codominant crown classes) was twice as much (72%) at age 26 years compared to age 6–8 years (35%). Quercus prinus L. was the major species across the chronosequence. For all age groups except 18–20 years. Q. prinus IV was the highest of any individual species in the upper canopy, and it ranged from 27 in the youngest stands (6–8 years) to 69 in the oldest stand (26 years). Within the intermediate crown class, the IV of Q. prinus equaled or exceeded those of all other species, except for the 18–20 year age group where it was second to A. rubrum. Quercus alba L. and Quercus velutina Lam. were minor components at age 26 years, although they dominated a comparison sample of six mature stands of the same ecosystem type. Liriodendron tulipifera L. was abundant 6–8 years after clearcutting, but nearly absent at age 26 years. Acer rubrum L. was the major species in both the intermediate and overtopped crown classes throughout the chronosequence. As gaps in the canopy occur. A. rubrum may become a more common species within the dominant-codominant crown class.     

Potential density and basal area prediction equations for unthinned Eucalyptus hybrid plantations in the Gujarat state of India

The aim of this paper is to present equation for estimating potential stand density and basal area projection model for unthinned pure even-aged plantations of Eucalyptus hybrid in Gujarat State of India. Relationships between quadratic mean diameter and stems ha(-1) were developed, which was used to establish the limiting density line. Eight different stand level models, belonging to the path invariant algebraic difference form of a non-linear growth function, were compared for projecting basal area. They can be used to predict future basal area as a function of stand variables like dominant height and stem number per hectare and are crucial for evaluating different silvicultural treatment options. The performance of the models was evaluated using different statistical criteria. The model proposed by Pienaar and Shiver performed best and hence is recommended for projecting the basal area in E. hybrid stands.     

Soil nitrogen turnover in proximal and distal stem areas of European beech trees

In European beech (Fagus sylvatica L.) forests, a large proportion of the water and ion input to the soil results from stemflow which creates a soil microsite of high element fluxes proximal to the tree trunk. The soil proximal to the stem is considered to have different rates of nitrogen turnover which might influence the estimation of N-turnover rates at the stand scale. In a previous study we reported high nitrate fluxes with seepage proximal to the stems in a forest dominated by European beech in Steigerwald, Germany. Here, we investigated the soil nitrogen turnover in the top 15 cm soil in proximal (defined as 1 m² around beech stems) and distal stem areas. Laboratory incubations and in situ sequential coring incubations were used to determine the net rates of ammonification, nitrification, and root uptake of mineral nitrogen. In the laboratory incubations higher rates of net nitrogen mineralization and nitrification were found in the forest floor proximal to the stem as compared to distal stem areas. No stem related differences were observed in case of mineral soil samples. In contrast, the in situ incubations revealed higher rates of nitrification in the mineral soil in proximal stem areas, while net nitrogen mineralization was equal in proximal and distal areas. In the in situ incubations the average ratio of nitrification/ammonification was 0.85 in proximal and 0.34 in distal stem areas. The net nitrogen mineralization was 4.4 g N m^-2 90 day^-1 in both areas. Mineralized nitrogen was almost completely taken up by tree roots with ammonium as the dominant nitrogen species. The average ratio of nitrate/ammonium uptake was 0.69 in proximal and 0.20 in distal areas. The higher water content of the soil in proximal stem areas is considered to be the major reason for the increased rates of nitrification. Different nitrogen turnover rates in proximal stem areas had no influence on the nitrogen turnover rates in soil at the stand scale. Consequently, the observed high nitrate fluxes with seepage proximal to stems are attributed to the high nitrogen input by stemflow rather than to soil nitrogen turnover. This revised version was published online in August 2006 with corrections to the Cover Date.     

哀牢山中山湿性常绿阔叶林林窗更新研究

对云南哀牢山中山湿性常绿阔叶林林窗更新状况的调查结果表明,林内优势树种在林窗阶段不占优势,其在林窗内的重要值显著低于成熟林分;林窗内外的乔木幼苗在组成上存在较大差异,林窗内的幼苗多样性(H=2．73,D=0．89)高于林冠下(H=2．25,D=0．82),二者的Jaccard相似系数只有0．6．许多树种的幼苗只出现在林窗内;林窗内的乔木幼苗密度(38636株·hm²)远远高于林冠下(17323株·hm²)．林窗内和林冠下的乔木幼苗(H≤50cm)均以高度为11～20cm幼苗的在数量上占优势,但林窗内高度超过20cm的幼苗比例明显高于林冠下;林窗大小对乔木幼苗更新有重要影响,不同树种的幼苗密度高峰出现在不同大小级别的林窗内．     

施氮量对不同肥力水平下夏玉米碳氮代谢及氮素利用率的影响

以郑单958为材料,在高产田和中产田两种地力水平下,利用15N标记法研究了施氮量对夏玉米氮素分配率、利用率和碳氮代谢的影响.结果表明:高产田适量施氮可以提高玉米产量,过量施氮没有表现出进一步增产效果,其氮肥利用率较低(29 04%).中产田随施氮量的增加产量提高,但氮素利用率却降低.各个器官15N积累量依次为籽粒>叶片>茎>根>叶鞘>穗轴.在高产田,当施氮量超过300kg·hm-2时,玉米籽粒和叶片中积累15N有所下降,而茎和根中积累15N的量随施N量的增加而增加;在中产田,随着施N量的增加,籽粒和穗轴积累15N量均相应增加.高产田叶片的硝酸还原酶活性、谷氨酰胺合成酶活性和蔗糖磷酸合成酶活性以及籽粒中蔗糖合成酶活性和酸性转化酶活性均是施氮300kg·hm-2时最大,施氮450 kg·hm-2则抑制了其活性的增强,而中产田的各个酶活性则随着施氮量的增加而增加.