The southern mountainous areas in Ningxia are representative regions of the Loess Plateau, with extremely fragile ecological environment. Large area of pure plantations established during the project of Grain for Green has suffered from poor nutrient availability and biodiversity loss, while planting mixed plantations is commonly consi-dered as an effective way to improve the ecological benefits. We selected Robinia pseudoacacia + Picea asperata mixed plantation, R. pseudoacacia + Armeniaca sibirica mixed plantation, A. sibirica pure plantation and R. pseudoa-cacia pure plantation located ina Ningnan mountainous area as test objects. Based on the theory and method of ecological stoichiometry, we measured the C, N and P contents of leaves, litter and fine roots to understand nutrient cycling characteristics of different plantations. The results showed that there was significant difference in foliar stoichiometry of each tree species within the four plantations. P. asperata leaves had the highest C content in the R. pseudoacacia + P. asperata mixed plantation, and R. pseudoacacia leaves had the highest N and P contents in the R. pseudoacacia + A. sibirica mixed plantation. N content of R. pseudoacacia and A. sibirica leaves was significantly higher in mixed plantation compared with that in pure plantation. There was no significant difference in litter biomass, litter C, N, P contents and stoichiometric ratios between the pure and mixed plantations of R. pseudoacacia. Litter biomass in A. sibirica pure plantation was significantly higher than that in R. pseudoacacia + A. sibirica mixed plantation, while litter C content was significantly lower than that in the mixed plantation. Fine root biomass decreased with increasing soil depth in the four plantations, with total fine root biomass being the highest in the R. pseudoacacia + A. sibirica mixed plantation. N content and N:P of fine roots in the R. pseudoacacia + A. sibirica mixed plantation were higher than those in R. pseudoacacia and A. sibirica pure plantations. There was significant negative correlation between N content in leaves and fine roots of R. pseudoacacia + A. sibirica mixed plantation. There were significant negative correlations between the N content of leaves and litter, as well as between the P content of leaves and fine roots in the R. pseudoacacia + P. asperata mixed plantation. P content between litter and fine roots in A. sibirica pure plantation was significantly negatively correlated. Nutrient status of mixed plantations was better than pure plantations in the Ningnan mountainous area, with the mixed plantation of R. pseudoacacia and A. sibirica being the best. Mixed planting reduced nutrient limitation on plant growth to a certain extent.

Erigeron annuus (L.) Pers. (annual, daisy or tall fleabane) is an annual herb native to North America but has been introduced and naturalized worldwide. In this study, its complete chloroplast (cp) genome was assembled from Illumina sequencing reads. The cp genome is 153,177 bp long with an A + T-biased base composition. It encodes a panel of 113 genes, including 80 protein-coding, 29 tRNA, and four rRNA genes. Nineteen genes are completely or partially duplicated, while 17 genes possess one or two introns. Phylogenetic analysis suggested E. annuus is mostly closely related to Erigeron canadensis L. and that the two genera Conyza and Erigeron are not mutually monophyletic.

We studied the effects of stand age on allocation and equation fitting of aboveground and below-ground biomass in four Quercus acutissima stands (14, 31, 46, and 63 years old) in the Central Loess Plateau of China. The stem wood, stem bark, branch, foliage, and belowground biomass of each of the 20 destructive harvesting trees were quantified. The mean total biomass of each tree was 28.8, 106.8, 380.6, and 603.4 kg/tree in the 14-, 31-, 46-, and 63-year-old stands, respectively. Aboveground biomass accounted for 72.25%, 73.05%, 76.14%, and 80.37% of the total tree biomass in the 14-, 31-, 46-, and 63-year-old stands, respectively, and stem wood was the major component of tree biomass. The proportion of stem (with bark) biomass to total tree biomass increased with stand age while the proportions of branch, foliage, and belowground biomass to total tree biomass decreased with stand age. The ratio of belowground biomass to aboveground biomass decreased from 0.39 in the 14-year-old stand to 0.37, 0.31, and 0.24 in the 31-, 46-, and 63-year-old stands, respectively. Age-specific biomass equations in each stand were developed for stem wood, stem bark, aboveground, and total tree. The inclusion of tree height as a second variable improved the total tree biomass equation fitting for middle-aged (31-year-old and 46-year-old) stands but not young (14 years old) and mature (63 years old) stands. Moreover, biomass conversion and expansion factors (BCEFs) varied with stand age, showing a decreasing trend with increasing stand age. These results indicate that stand age alters the biomass allocation of Q. acutissima and results in age-specific allometric biomass equations and BCEFs. Therefore, to obtain accurate estimates of Q. acutissima forest biomass and carbon stocks, age-specific changes need to be considered.

Typical sampling method was conducted to select typical forest gaps of different size, each typical forest gap contained 3 repeats, and the Pinus tabulaeformis seedlings from different size gaps in artificial P.tabulaeformis plantation of Huanglong mountain in Shaanxi province were selected as the research objects.The research was aimed at surveying the effects of forest gap size on branch architecture, leaves characteristics and their vertical distribution, and exploring the adaptation and architecture of P.tabulaeformis seedlings to different size forest.The results showed significant differences in the aboveground architecture and growth of P.tabulaeformis seedlings in different size gaps.(1)Gap size was positively related to caliper, seedling height, crown length and crown area.(2)With the increase of forest gap size, the stepwise bifurcation and interval between branch, while the total bifurcation ratio was declined.(3) The gap size was contrary correlated with needle length and width, but with the increased with needle length-width ratio, total needle area and average needle number.(4)The needles in CK were mostly distributed in below middle part of seedlings, whereas the seedlings in forest gap were mostly distributed in above middle part of seedlings.(5) With the increase of forest gap size, the needle number and relative total needle number of whorled branch in same year increased.In order to promote the regeneration of P.tabulaeformis seedlings, cultivate high quality wood, and improve the stand quality, we should adopted appropriate thinning techniques in the future.

The capacity of plants to occupy different habitats is made possible by the plastic responses of their presenting in heterogeneous habitats. Light directly influences the plastic responses of plant architectural traits. We measured five years-old saplings of Chinese cork oak growing in different light intensity habitats (forest edge, forest gap and understory). A suite of architectural and leaf morphological attributes indicated a pronounced ability of Chinese cork oak to adapt to shade. Under low light intensity habitats, Chinese cork oak had a significant tendency to invest more in crown growth, characterized by the highest crown area, the lowest crown length ratio and the largest angle of the inclination of the main stem to the vertical. It expressed marked plagiotropic growth in shade indicating a horizontal light-foraging strategy. In addition, Chinese cork oak significantly exhibited the highest specific leaf area and the lowest total leaf area under low light intensity habitats. In shade, they showed some plasticity in displaying most of their leaf area at the top of the crown to minimize self-shading and to enhance light interception. This differentiation can be defined as a plastic phenomenon, likely related to the higher efficiency of light interception and absorption by saplings.

Objective]The purpose of this paper is to explore carbon density and its allocation in young plantation of Platycladus orientalis at different ages using hilly loess in Ning County of Gansu Province as the study area,with an expectation to provide the theoretical basis for evaluation on the ecological benefit of artificial forest in the hilly Loess Plateau.[Method]P. orientalis plantation at different ages of 7,10,12 and 14 years were used for this study. Three sample-plots were set up for every stand age,then samples were individually taken from tree,shrub,herb and litter layers,and soil was sampled at a depth of 0 -100 cm in each plot. The carbon contents of plant and soil samples were determined by using elemental analyzer Liqui TOCⅡ,the carbon density and its allocation were analyzed in young plantations of P. orientalis in the hilly Loess Plateau in Gansu Province. [Result]The results showed that the carbon content in different organs of P. orientalis ranged from 447. 51 to 513. 93 g·kg -1 ,with an order of cone> leaf> stem>thick-branch> fine-branch > fine-root > stump > bark > thick-root > large-root > medium-root > small-root. The carbon content of root was the lowest in shrub and herb layers,and the carbon content of un-decomposed layer in litter was higher than that of semi-decomposed layer. Significant difference in carbon content was observed among different layers of the ecology system of P. orientalis plantation at different ages. The carbon content in the soil layer (0 -100 cm) ranged from 23. 31 to 96. 08 g·kg -1 ,and increased with the increase of stand age but decreased with the increase of soil depth. The carbon density of the tree layer in the vegetation was higher than that of shrub,herb and litter layers. The carbon density in 0 -100 cm soil layer was the largest in the ecosystem,showing significant difference with the increase of age. The carbon densities in the ecosystem of P. orientalis plantation at ages of 7,10,12 and 14 years were 37. 56,44. 67, 50. 87 and 56. 34 t·hm -2 ,respectively. All the carbon densities in tree,shrub,herb,humus ,and soil layer increased with the increase of stand age.[Conclusion]The carbon content of tree layer of P. orientalis plantation showed significant (P<0. 05)difference among organs of the trees,but no significant difference was observed for the same organ at different ages(P>0. 05). Carbon stocks in different layers of the P. orientalis plantation ecosystems were found in the order of soil>tree> herb > litter > shrub. The carbon density of different layers of P. orientalis plantation increased with the increase of age,and the proportion of carbon distribution of tree,shrub,herb,and litter layers increased while that of soil layer decreased with increase of stand ages.

【Objective】This study aimed to research the effects of thinning intensity on fruiting quantity and quality of Quercus variabilis forest on the south slope of Qinling Mountains.【Method】Q.variabilis half-mature and pure forests under close-to-natural management in Shangluo,the south slope of Qinling Mountains were selected as the object in July 2011.Based on different thinning intensities(30%,20%,10%and 0(CK)),the individual fruiting status,the total number of stand fruits,seeds spatial distributions,seeds characteristics and seeds germination rates of Q.variabilis forests 5years after thinning were analyzed.【Result】The average fruiting number of individual plant increased with the increasing intensity,and the order of different treatments was 30%20%10%0(CK).The total number of stand fruits of 30%thinning intensity increased the most by 8.4% compared to the control group.The upper fruiting number of the average single plant accounted for 73.8%,while the lower part accounted for 26.2%.The sunny side of canopy layer set the most fruits with the ratio of 62.2%.The seed size,1 000-seed mass,and seed germi-nation of Q.variabilis were different under different thinning intensities,and seed quality and heated indoor germination rate were the best when the thinning intensity was 30%.【Conclusion】The thinning intensity of 30%(canopy density keep 0.6)was most conducive to the improvement of fruiting and seed quality of Q.variabilis half-mature forest,and it could promote the sustainable development of Q.variabilis natural forest.

Objective]Xanthoceras sorbifolia is naturally distributed in the northwest of China,strongly tolerant to cold, drought and poor site conditions. It is an important species for oil production and erosion control in north China. Moreover,it is an ideal tree species for land conversion of cropland to forest and for management of barren hills in the northern Loess Plateau of China.[Method]In order to understand the characteristics of seed germination,seedling development and their influencing factors,24 sampling plots were established in 3 habitats ( sunny slope,semi-sunny slope and semi-shady slope) of X. sorbifolia forests on the Loess Plateau where is the central distribution of the species.[Result]One-year-old seedlings were found at all habitats,but the average number varied among habitats. A larger number of 632 individual·hm -2 at the sunny slope,48 individual·hm -2 at the semi-shady slope. The conversion rates of seeds to seedlings were low at all 3 habitats,and manifested as semi-shady slope (0. 57%) > semi-sunny slope (0. 43%) > sunny slope (0. 25%). The total number of seedlings was small at all 3 habitats,and gradually decreasing with the age of seedlings. For different ages from 1-5 years,the number of seedlings showed the following order: sunny slope> semi-sunny slope > semi-shady slope. Due to the differences of sunlight intensity and moisture content among the 3 habitats,X. sorbifolia seedlings has evolved different adaptive strategies,the height,basal diameter,and crown width of 1-5 year seedlings showed the order of sunny slope > semi-sunny slope > semi-shady slope. The sunny slope was more beneficial to the growth of X. sorbifolia seedlings. The underground biomass of 1-5 year seedlings were greater than above-ground biomass at all 3 habitats,and above-ground biomass and underground biomass showed the order of sunny slope >semi-sunny slope > semi-shady slope. Due to environmental heterogeneity, the age of maximum biomass ratio of underground to aboveground ( R:S) differed among the 3 habitats,at sunny and semi-shady slopes the R:S value peaked at the age of 2 years,whereas t the semi-sunny slope,the value peaked at the age of 4 years. The stem dry mass,leaf dry mass,and root dry mass of 1-5 years seedlings were greater at the sunny slope than the semi-sunny and semi-shady slopes, and the difference tendency to increase with age. With the increase of age,the biomass ratios of stem,leaf and root at sunny slope respectively to those at semi-sunny and semi-shady slopes will be increasingly different. Environment factors had significant influence on the number,height,and biomass of seedlings. The number of seedlings was significantly positively correlated with light intensity,and significantly negatively correlated with the total plant coverage. The height of seedlings was significantly negatively correlated with soil moisture. The biomass of seedlings was significantly positively correlated with light intensity.[Conclusion]At the sunny slope,seed germination rate was lower. However,it was beneficial for establishment of the seedlings compared to the semi-sunny and semi-shady slopes. The growth performance of seedlings was superior at the sunny slope to at the semi-sunny and semi-shady slopes,indicating that at this habitat the seedlings could make full use of growing conditions to shorten the time for entering the main forest storey. Therefore,the sunny slope should be selected for growing plantations of Xanthoceras sorbifolia.

【目的】阐明栓皮栎（Quercus variabilis）产生干基萌苗的能力以及萌苗的产生和生长特性,以制定合理的人工促萌措施。【方法】2009-2010年,对陕西省周至县楼观台地区天然栓皮栎次生林中4个径级共40株栓皮栎个体进行环剥并跟踪观测2年,比较了不同径级栓皮栎产生干基萌苗的母树比例及萌苗的数量、枯死率、年龄结构和生长特征。【结果】1)栓皮栎母树均能在环剥后1个月产生愈伤组织以保护伤口,观测过程中没有母树死亡;2)78%的环剥母树能够产生干基萌苗,70%的母树能在环剥后2年内保存有活萌苗;3)胸径10~20cm（2和3径级）栓皮栎母树的萌发率最高,80.0%的母树在环剥后能产生干基萌苗,并在2个生长季均能保存活萌苗,萌苗枯死率为0.0%~24.7%,萌苗高度、冠幅和基径均大于1径级和4径级母树的萌苗;4)单株干基萌苗数量随着母树径级的增加而先增大后减小,4径级母树胸径最大,产生干基萌苗的时间最晚,萌苗数量最少;5)各径级母树在环剥后第2年仍然能产生当年生萌苗,但只有2径级母树的2年生萌苗所占比例远多于1年生萌苗,3径级母树则相反,4径级母树只有1年生萌苗。【结论】在栓皮栎次生林改造和经营中,可提前1~2年对胸径在10~20cm的间伐对象进行环剥,待其产生干基萌苗后再进行砍伐,这样有利于缩短间伐林地土壤的裸露时间,促进林地快速恢复。

为了揭示栓皮栎幼苗对干旱环境的适应能力,采用盆栽实验方法,设置对照、轻度、中度和重度干旱处理,研究了栓皮栎(Quercus variabilis Bl.)幼苗小细根(0.0＜D≤0.5mm)和大细根(0.5＜D≤2mm)的生长及生理生化指标对长期持续干旱胁迫的响应.结果显示:胁迫处理120d后,与对照相比,轻度胁迫促进细根数量、长度、表面积、体积和干物质量的增加,而中度和重度胁迫抑制细根生长;干旱胁迫下小细根数量和长度大于大细根,而大细根表面积、体积和干物质量显著大于小细根.干旱导致细根相对含水率、活力下降(P ＜0.001),丙二醛(MDA)含量增加(P ＜0.001);大细根相对含水率和活力高于小细根,但小细根中MDA含量显著高于大细根.与对照相比,轻度胁迫可以积累更多渗透调节物质(脯氨酸、可溶性糖和可溶性蛋白),并保持更高的抗氧化酶活性(超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)和抗坏血酸过氧化物酶(APX));中度胁迫则导致POD和APX活性的降低;而重度胁迫抑制了可溶性蛋白的积累和CAT、POD、APX活性的增加;与大细根相比,小细根渗透调节物质和抗氧化酶活性显著减少.当干旱强度超过中度胁迫时,栓皮栎幼苗细根生长和生理生化适应性降低;小细根对干旱环境的变化更敏感,寿命更短.实验中,即使在重度胁迫下也未发生根系严重脱水和幼苗死亡的现象,表明栓皮栎幼苗有较强的干旱忍受能力,适合在半干旱区植被恢复重建与造林工程中应用.

Taking the natural Quercus variabilis forest in Shangluo, south slope of Qinling Mountains as the object in May 2006 and August 2011, which was under close-to-natural management of different thinning intensities (30%, 20%, 10%), and the un-thinned forest as the control, changes of the stand growth situation before and after thinning, population regeneration, species diversity and soil fertility after 5 years of thinning were analyzed, and the effects of thinning on forestland revegetation and community development were evaluated comprehensively. The results showed that the number of 1-6 years old Q. variabilis seedlings increased with increasing thinning intensity, while no significant difference was found for above 6 years old seedlings. The regeneration potentials of population under 10%, 20% and 30% thinning were respectively increased by 10.8%, 28.5% and 32.9% compared with the control. Thinning promoted the DBH and crown of the trees and shrubs, as well as the height of shrubs, especially for light-loving plants, and the effect of promotion increased with increasing thinning intensity. The species diversity and soil fertility were improved after thinning, in order of 30% > 20% > 10% > control. The thinning intensity of 30% (canopy density 0.6) was more conducive to the continuable development of the natural Q. variabilis forest in which canopy density was above 0.85.

Investigation was carried out by surveying nearly 800 households of farmers in Qinba Mountains located in Hanzhong,Ankang,and Shangluo,by which edible and medicinal fungi were produced by using oak resources,such as Auricularia auricular,Gastrodia elata,and Polyporus umbellatus.Fixed costs,total costs,benefits,and resource use efficiency were analyzed and calculated in the procedures of resource feeding,production,and marketing.The results were reported as follows.1)Edible fungi that were produced by households of farmers mainly were consumed by the producers,the fungi were not the dominant income resource for them.In addition,traditionalbed-logproducing method was substituted by sawdust bags,which would results in less damage for oaks.2)High economic benefits could be obtained by producing medicinal fungi,such as G.elata,P.umbellatus,which were popular ways to use wood resources,and would be popularized in future.3)The imperfections of technique,the shortage of labor,the relative lack of funds,the poor transport conditions in mountainous,the unsound risk protection of investment and the rising prices of labor market were the major limited factors to bring about the unbalanced utilization of oak resources in the region.4)In order to raise the level of oak resource use efficiency,five aspects should be emphasized,such as technical training,scale intensive farming,market acquisitions unifying,fungi cultivation optimizing,and service level improving.

Sexual and asexual propagation of Xanthoceras sorbifolia natural populations in different habitats and their importance in population regeneration were studied. The results showed that X. sorbifolia populations were capable of the sexual and asexual propagation in 3 slope aspects, but a balance between the two propagation modes was observed. In sunny and semi-shady slope habitats, seedling amount and space-occupying competence were relatively high, suggesting that the sexual propagation was dominant. In semi-sunny slope habitat, the populations were superior in sexual sprout amount and space-occupying competence, suggesting that the predominant propagation mode was asexual. In the same habitats, asexual sprouts grew better than seedlings, while the growth of seedlings was in the order of sunny slope > semi-sunny slope > semi-shady slope on the basis of the same origin. The bottleneck stage appeared from seeds to seedlings for sexual propagation and from seedling to ramet for asexual propagation. X. sorbifolia invaded and settled in a way of sexual propagation in new habitats, and then rapidly occupied habitat space in a way of asexual propagation.

Aim of study: Quercus variabilis (Chinese cork oak) reproduces asexually and sexually. This study aimed to determine the status and growth of asexual and sexual recruits of Q. variabilis in different forest recovery stages. Area of study: Three selective logged stands and one unlogged stand in Q. variabilis forest, Shaanxi Province, China. Material and methods: Origin, number, basal diameter, height and size structure of Q. variabilis shoots (height ≤ 200 cm) were investigated in the plots of 5, 10, and 20-years post-logging stands and unlogged stand. Effects of recovery stage on the density and growth of the three original recruits (stump sprouts, stem base sprouts and true seedlings) were analysis by One-way ANOVA. Main results: Sprouts dominated logged stands, whereas true seedlings dominated unlogged stand, stem base sprouts only existed in 20-years post-logging and unlogged stands. Stump sprout density and sprout number per stump both declined with extended post-logging time. True seedlings density increased from 7 to 20 shoots/100 m 2 as the post-logging time extended, and peaked in unlogged stand (94 shoots/100 m 2 ). An ongoing size structure was observed in true seedlings in all stands. Stump sprouts were taller and greater than true seedlings. Research highlights: Stump sprouts contributed more to Q. variabilis forest recovery in the early stage after disturbance. The contribution of true seedlings was limited in the same stage, but they were beneficial for population long-term development. Stem base sprouts were most likely to be a survival strategy rather than a reproductive strategy.

Aim of study: Quercus variabilis (Chinese cork oak) reproduces asexually and sexually. This study aimed to determine the status and growth of asexual and sexual recruits of Q. variabilis in different forest recovery stages.Area of study: Three selective logged stands and one unlogged stand in Q. variabilis forest, Shaanxi Province, China.Material and Methods: Origin, number, basal diameter, height and size structure of Q. variabilis shoots (height ≤200 cm) were investigated in the plots of 5, 10, and 20-years post-logging stands and unlogged stand. Effects of recovery stage on the density and growth of the three original recruits (stump sprouts, stem base sprouts and true seedlings) were analysis by One-way ANOVA.Main results: Sprouts dominated logged stands, whereas true seedlings dominated unlogged stand, stem base sprouts only existed in 20-years post-logging and unlogged stands. Stump sprout density and sprout number per stump both declined with extended post-logging time. True seedlings density increased from 7 to 20 shoots/100 m2 as the postlogging time extended, and peaked in unlogged stand (94 shoots/100 m2). An ongoing size structure was observed in true seedlings in all stands. Stump sprouts were taller and greater than true seedlings.Research highlights: Stump sprouts contributed more to Q. variabilis forest recovery in the early stage after disturbance. The contribution of true seedlings was limited in the same stage, but they were beneficial for population long-term development. Stem base sprouts were most likely to be a survival strategy rather than a reproductive strategy.Key words: asexual reproduction; true seedling; post-logging time; Chinese cork oak.

The survival and development of Liaodong oak (Quercus liaotungensis Koidz) stump sprouts were studied for 6 years under leave-tree, as well as 60 and 75% crown closure uniform shelterwood in the Huanglong Mountains of China. Stump sprout survival rate, number of sprouts, and sprout height under the three partial harvests during the first year post-harvest did not differ. Six years post-harvest, 78.32% of the stumps had living sprouts. No variation in sprout survival was found among the treatments throughout the study period. The number of living sprouts per stump was 13.77 ± 0.50 in the first growing season after harvest, and dropped to 6.49 ± 0.22 after 6 years. This result indicated the occurrence of self-thinning within the sprout clumps. Moreover, the height of dominant sprout increased from 52.88 ± 1.62 cm (in the first year) to 132.82 ± 2.35 cm (in the sixth year) post-harvest. Sprout height in the leave-tree harvest type was higher than those in the two shelterwoods in the fifth and sixth years after logging. Annual height growth was approximately 8–96 cm during the first growing season, and then decreased at a rate of 1–44 cm per year in the following years. A negative relationship was found between sprout height and the number of sprouts per stump. This result indicated a trade-off between the number of sprouts and height growth. The number of sprouts per stump decreased by about 0.2 stem for each 1 m2/ha increased in residual basal area. Therefore, sprouting may play an important role in the restoration of the secondary forest after harvesting.

In August-November 2010 and August 2011, and taking the pure Quercus variabilis forests under close-to-natural management of different thinning intensity (30%, 20%, and 10%) in Shangluo district of south slope of Qinling Mountains as the object, an investigation was conducted on the seed amount of seed bank, the survival rate and growth status of seedlings, and their relationships with environmental factors 4-5 years after thinning. As compared with the control, the seed amount in the seed bank of 10%, 20%, and 30% thinning plots increased by 2.0%, 21.1%, and 34.8%, respectively in the fourth year after thinning, and the 1-year-old seedlings amount increased by 28.5%, 99.7%, and 122.2%, respectively in the next year. The survival rate of the seedlings in the 10%, 20%, and 30% thinning plots was increased by 25.5%, 235.7%, and 480.0%, respectively in the fifth year after thinning. Thinning improved the light, temperature, soil moisture, and soil nutrient conditions in the forests, which promoted the height- and new shoot growth and the leaf area index of each age seedlings. The three growth indices also increased with increasing thinning intensity. In the Q. variabilis forest with a canopy density of > or = 0.85, the thinning intensity 30% (canopy density 0.6) was most conducive to the seed germination and seedling growth.

Twenty four fixed plots in three distribution regions of Quercus variabilis (Loess Plateau, marginal distribution zone; north slope of Qinling Mountains, semi-arid core area; and south slope of Qinling Mountains, moist core area) were installed, respectively, to investigate the age structure, growth status, and dry mass accumulation and allocation of 1-8 years old Q. variabilis seedlings, and path analysis was adopted to determine the key factors affecting the regeneration of the seedlings. In the distribution regions, the density of the seedlings decreased with their increasing age, and the density of the 1-8 years old seedlings all decreased in the order of south slope of Qin-ling Mountains > north slope of Qinling Mountains > Loess Plateau. The transformation rate of the seedlings with adjacent ages differed significantly among the three distribution regions. On Loess Plateau, the transformation rate of 7 years old to 8 years old seedlings was the lowest (30.2 +/- 2.9) %; on the north and south slopes of Qinling Mountains, the transformation rate of 4 years old to 5 years old seedlings was the lowest, being (53.9 +/- 3.7) % and (50.0 +/- 2.1) %, respectively. With the increasing age of the seedlings, their height and dry mass presented an increasing trend, with the order of south slope of Qinling Mountains > north slope of Qinling Mountains > Loess Plateau, the rate of root length to plant height tended to decline, and the rates of root breadth to canopy breadth and of root dry mass to shoot dry mass decreased after an initial increase. The rates of root length to plant height, root breadth to canopy breadth, and root dry mass to shoot dry mass were all the highest on Loess Plateau, and the lowest on south slope of Qinling Mountains. Air temperature, irradiance, canopy density and shrub coverage were the direct key factors affecting Q. variabilis seedling regeneration, among which, air temperature and irradiance were the positive factors, while canopy density and shrub coverage were the negative ones. Soil available nitrogen content and herb coverage were the indirect key factors affecting the Q. variabilis seedling regeneration positively and negatively, respectively.

In order to speed up the genetic improvement of Quercus variabilis,genomic DNAs of 24 materials of four types collected from the northern slope of Qinling Mountains were amplified by RAPD(random amplified polymorphic DNA) technology with 35 primers screened from 235 arbitrary primers.The total genetic diversity level of natural Q.variabilis population was high,the genetic differentiation of natural Q.variabilis population was great and its genetic variation was high.The natural population of Q.variabilis was divided into four variant types: thick-bark-deep-crack type,thick-bark-shallow-crack type,thin-bark-shallow-crack type,and thin-bark-deep-crack type.The genetic basis of the division was demonstrated by UPGMA cluster analysis,which coincided with its morphological taxonomy basically.Polymorphic loci,percentage of polymorphic loci,average observed number of alleles,Shannon information index and Nei's genetic diversity indicated that the changes of genetic diversity of all types were consistent:thick-bark-deep-crack typethin-bark-shallow-crack typethin-bark-deep-crack typethick-bark-shallow-crack type,and their genetic diversity was high.Genetic germplasm resources were extremely abundant and genetic improvement potentials were great in Q.variabilis.

栓皮栎是中国暖温带和亚热带林区的主要建群种和资源树种.为了明确林窗大小对栓皮栎实生幼苗生长发育的影响,通过设置固定样地,测定秦岭北坡5种不同面积林窗(面积分别为＜ 50,50 ～ 100,100 ～ 150,150 ～200,＞200 m2)中栓皮栎实生幼苗的存活数量、生长、干物质积累和分配等指标,分析栓皮栎实生幼苗的生长发育与环境因子之间的关系.结果表明:在幼苗期(1～5年生),随着年龄的增长,实生幼苗的数量呈现逐渐下降的趋势;在面积为150～ 200 m2的林窗中,栓皮栎实生幼苗在数量、生长指标和干物质积累量方面都优于其他林窗中的栓皮栎实生幼苗;林窗内的光照强度、灌木层盖度、草本层盖度、草本层高度、土壤温度、土壤养分条件与实生幼苗的存活呈正相关;空气湿度、枯枝落叶层厚度则与实生幼苗的生长呈负相关.在未来的经营过程中,抚育间伐创造面积为150 ～200 m2的林窗,林分郁闭度保持在0.75左右,能改善林地生境,促进种子萌芽和实生幼苗生长发育,为培育高质量的林木提供有利条件.