Drivers of tree regeneration in coniferous monocultures during conversion to mixed forests in Central Europe – Implications for forest restoration management

In Central Europe,anthropogenic coniferous monocultures have been subject to conversion to more diverse mixed forests since the 1990s,however,they are still abundant across many forest landscapes.Artificial and natural tree regeneration both play a key role during conversion by determining the species composition and structure of the future forests.Many abiotic and biotic factors can potentially influence the regeneration process and its specific combinations or interactions may be different among tree species and its developmental stages.Here,we aimed to identify and quantify the effect of the most important drivers on the density of the most abundant regenerating tree species(i.e.,Norway spruce and European beech),as well as on species and structural diversity of the tree regeneration.We studied tree regeneration in four former monospecific coniferous stand types(i.e.,Norway spruce,Scots pine,European larch,and Douglas fir)in Southwest Germany that have been under conversion to mixed forests since the 1990s.We sampled tree regeneration in four growth height classes together with a variety of potentially influencing factors on 108 sampling plots and applied multivariate analyses.We identified light availability in the understorey,stand structural attributes,browsing pressure,and diaspore source abundance as the most important factors for the density and diversity of tree regeneration.Particularly,we revealed speciesspecific differences in drivers of regeneration density.While spruce profited from increasing light availability and decreasing stand basal area,beech benefited either from a minor reduction or more strikingly from an increase in overstorey density.Increasing diaspore source abundance positively and a high browsing pressure negatively affected both species equally.Our results suggest that humus and topsoil properties were modified during conversion,probably due to changes in tree species composition and silvicultural activities.The species and structural diversity of the tree regeneration benefitted from increasing light availability,decreasing stand basal area,and a low to moderate browsing pressure.We conclude that forest managers may carefully equilibrate among the regulation of overstorey cover,stand basal area,and browsing pressure to fulfil the objectives of forest conversion,i.e.,establishing and safeguarding a diverse tree regeneration to promote the development of mature mixed forests in the future.

Crown Morphology of Norway Spruce from Usual Tree Measurements

The crown morphology of Norway spruce (Picea abies Karst) was studied from 617 sample trees. In order to model branch and crown descriptors the linear and nonlinear regression methods were extensively used. Results show that the branch length can be fairly well predicted from the distance to the apex of the tree and that the branch spread has a high correlation with the branch length and the insertion angle. Models have been set up to predict the crown ratio, height to the base of the living crown, height to the first living branch and the height to the first dead branch from the usual whole-tree measurements, namely diameter at breast height total height and total age.

挪威云杉幼树韧皮部挥发性物质的测定

通过GC -MS测定挪威云杉幼树主干上部与下部韧皮主要挥发性物质的化学成分与含量 ,结果表明 :挪威云杉幼树的韧皮部挥发性物质的主要成分为α -蒎烯、茨烯、β-蒎烯、月桂烯、 3-蒈烯、柠檬烯、β -水芹烯 7种单萜化合物。α -蒎烯、β -蒎烯、月桂烯、 3-蒈烯、β -水芹烯的含量在上部韧皮与下部韧皮有明显差异 ,其中上部韧皮部α -蒎烯、β -蒎烯和 β -水芹烯的含量明显高于下部主干韧皮部 ,这为解释松树皮象的取食习性 ,打下了基础。

挪威云杉树脂的临界表面张力和临界Hamaker常数

应用一系列烷烃类液体和接触角技术 ,对挪威云杉 (PiceaabiesL .Karst .)树脂的一些表面特征作了研究。发现该树脂的临界表面张力约为 18.4 8mN/m ,根据Zisman的临界表面张力外推方法将液体的Hamaker常数与cosθ作图 ,发现该树脂有一个唯一的临界Hamaker常数约 4 .18× 10 2 0 J。

挪威云杉种源及家系苗期生长适应性的聚类分析

通过对引进的挪威云杉种源和窄冠垂枝型挪威云杉家系进行不同地点苗期试验,选取生长期、当年高和存活率等3个指标进行苗期生长适应性评价,研究结果表明,部分窄冠垂枝型挪威云杉家系具有良好的生长适应性,大部分存活率相对比较低,挪威云杉种源苗期生长普遍不能适应。

引种欧洲云杉自由授粉家系种实性状的多样性

为了揭示欧洲云杉种实性状的袁型变异程度及其变异规律，对欧洲云杉44个家系的25个种实性状进行调查，并对其多样性进行分析，结果表明：球果长、球果长／宽、鲜质量、干质量、种子长、种子宽家系间和家系内差异均达显著水平，其余种实性状家系间差异达显著水平；种实性状家系间的表型分化系数（Vs，t）为66．77％～99．27％。欧洲云杉家系平均千粒质量为（9．9046±1．5945）g，家系间变幅为5．40～13．60g；种实性状间，发芽势、发芽率与千粒质量呈极显著正相关，球果长／宽与千粒质量不相关，种子长／宽除与种子宽呈极显著负相关外，与其他种实性状不相关：其他种实性状间呈极显著或显著相关关系。欧洲云杉种实性状受强的家系遗传控制，家系间具有丰富的遗传变异，遗传改良潜力大，筛选出千粒质量≥11．05g的10个家系可用于种子园营建和多目标育种。

欧洲云杉优良无性系选择

2011年3月,选择378个欧洲云杉优良无性系3年生苗,在湖北宜昌国有樟村坪林场营造试验林,对欧洲云杉无性系进行再选择研究。结果表明:选择出的欧洲云杉36个优良无性系7年生(苗龄3年)时,其平均树高、当年抽梢长、地径、冠幅、保存率比其它342个无性系的分别提高了36.0%、47.0%、43.9%、23.7%、8.0%。

欧洲云杉扦插繁殖技术研究

为了快速有效地规模化扦插繁殖欧洲云杉,满足造林、绿化用苗的需要。采用全光照自动间歇喷雾装置,用河沙做基质。在林科院甘肃小陇山沙坝的实验基地做了ABT1、NAA、IBA、GGR不同激素,ABT1不同浓度和浸泡时间,5-10 cm、10-15 cm和〉15 cm三种不同插穗长度,5 a和23 a不同采穗母株年龄的嫩枝扦插试验及200 mg.kg^-1ABT1处理1 h的不同插穗类型（嫩枝带硬枝和嫩枝）的试验,用清水处理插穗做对照（CK）。试验数据采用spss12.0进行方差分析,结果表明：不同激素处理的插穗生根率差异显著。生根率大小顺序为：ABT〉GGR〉IBA〉NAA。而IBA处理的插穗生根数,根系总长和根系效果指数均大于其它处理,根系发达。ABT1不同浓度和浸泡时间处理的插穗生根率差异达极显著水平。以100.mg kg^-1和200 mg.kg^-1浸泡30 min和2 h生根率最好。50 mg.kg^-1浸泡1 h处理的插穗生根数、根系总长、根系效果指数大。嫩枝带硬枝和嫩枝生根率差异不显著,但生根数、根系总长和根系效果指数嫩枝带硬枝〉嫩枝。〉15 cm的插穗生根率和其它指标都高。采自23a生母株的插穗没有生根。