Simulation of the long-term effects of different strategies for precommercial thinning in Pinus sylvestris     

Nils Fahlvik  Mattias Berglund  Hampus Holmström  Urban Nilsson 《Scandinavian Journal of Forest Research》2018,33(4):347-356

The influence of the intensity and timing of precommercial thinning (PCT) on stand development and financial return was studied in Scots pine stands. Functions describing the early development of the stand structure after PCT were developed. The functions were based on 195 plots within 41 PCT experiments in Sweden. The dimension distribution of the established stand was estimated and used as input to the decision support system Heureka, to simulate the stand development until final felling. The studied treatments included PCT to 1000, 2000 and 3000?stems?ha^?1 at mean heights of 2, 4 and 6 m. Separate simulations were carried out for different site fertilities. Mean annual volume increment increased with increasing number of stems after PCT whereas the timing of PCT had only a small effect. The land expectation value (LEV) generally decreased with increasing mean height at PCT, primarily because of the increased cost of PCT. LEV decreased with increasing number of stems after PCT at low fertility sites whereas only minor differences were found for PCT to 1000 and 2000?stems?ha^?1 at medium and high fertility sites. The general pattern persisted when different scenarios of future timber quality were simulated.  相似文献   

济南市发展现代都市农业的主要模式与对策建议   总被引：1，自引：0，他引：1  

济南市建设发展现代都市农业研究课题组  张崇顺  席玉坤 《山东农业科学》2010,(10):114-120

都市农业是发展现代农业的重要载体。本课题在研究国内外都市农业发展趋势、深入调查分析济南市发展都市农业的优势条件及制约因素的基础上,提出了加快农业结构调整步伐、建立济南特色都市农业体系的政策建议。  相似文献   

分子证据表明苏拉威西岛特有鸟种苏拉山鸫(Geomalia heinrichi)属于地鸫属(Zoothera)(鸫科,鸟纲)(英文)     

Urban OLSSON  Per ALSTR 《中国鸟类》2013,4(2):155-160

苏拉威西地区特有鸟种苏拉山鸫(Geomalia heinrichi)的分类地位,是属于画眉科还是鸫科,长期以来一直备受争议。基于线粒体细胞色素 b 基因、细胞核肌红蛋白内含子 2 以及鸟氨酸脱羧酶内含子 6–7 基因,我们估计了鸫科 43 个分类群的系统发育关系。结果表明,苏拉山鸫是地鸫属的一个分支,并具有较高的支持率。我们建议将 Geomalia 并入地鸫属(Zoothera),并命名为 Zoothera heinrichi。  相似文献   

Internationalization of SMEs in the Baltic Sea Region: Barriers of cross-national collaboration considering regional innovation strategies for smart specialization     

Susanne Mueller-Using  Wieslaw Urban  Jan Wedemeier 《Growth and change》2020,51(4):1471-1490

This paper provides new evidence on barriers that hamper small and medium-sized enterprises (SME) in the Baltic Sea Region (BSR) to establish international collaboration. Our analysis makes use of collected data concerning internationalization of SMEs in seven BSR countries. Our logistic multivariate regression model, which we applied after selecting relevant variables using the LASSO method, indicates a significant positive effect for the entities´ demand in support to acquire clients as well as the absence of foreign markets operations. A significant adverse effect is found for cooperation agreements as a support tool for internationalization as well as the interest to participate in an innovation and internationalization system. SMEs rather desire their internationalization capacity building than direct support in acquiring clients. Overall, our results support the hypothesis that strengthening cross-national collaborations and establishing appropriate support programs are important toward innovativeness and competitiveness among SMEs in the BSR. Smart Specialization Strategies (S3) could provide a framework for building cross-national collaborations.  相似文献   

Ergebnisse von Unterbodenuntersuchungen in den Bezirken Rostock,Schwerin und Neubrandenburg     

Harald Grosse  Urban Hammer 《Archives of Agronomy and Soil Science》2013,59(4):341-349

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The relevance of marine chemical ecology to plankton and ecosystem function: an emerging field     

Ianora A  Bentley MG  Caldwell GS  Casotti R  Cembella AD  Engström-Öst J  Halsband C  Sonnenschein E  Legrand C  Llewellyn CA  Paldavičienë A  Pilkaityte R  Pohnert G  Razinkovas A  Romano G  Tillmann U  Vaiciute D 《Marine drugs》2011,9(9):1625-1648

Marine chemical ecology comprises the study of the production and interaction of bioactive molecules affecting organism behavior and function. Here we focus on bioactive compounds and interactions associated with phytoplankton, particularly bloom-forming diatoms, prymnesiophytes and dinoflagellates. Planktonic bioactive metabolites are structurally and functionally diverse and some may have multiple simultaneous functions including roles in chemical defense (antipredator, allelopathic and antibacterial compounds), and/or cell-to-cell signaling (e.g., polyunsaturated aldehydes (PUAs) of diatoms). Among inducible chemical defenses in response to grazing, there is high species-specific variability in the effects on grazers, ranging from severe physical incapacitation and/or death to no apparent physiological response, depending on predator susceptibility and detoxification capability. Most bioactive compounds are present in very low concentrations, in both the producing organism and the surrounding aqueous medium. Furthermore, bioactivity may be subject to synergistic interactions with other natural and anthropogenic environmental toxicants. Most, if not all phycotoxins are classic secondary metabolites, but many other bioactive metabolites are simple molecules derived from primary metabolism (e.g., PUAs in diatoms, dimethylsulfoniopropionate (DMSP) in prymnesiophytes). Producing cells do not seem to suffer physiological impact due to their synthesis. Functional genome sequence data and gene expression analysis will provide insights into regulatory and metabolic pathways in producer organisms, as well as identification of mechanisms of action in target organisms. Understanding chemical ecological responses to environmental triggers and chemically-mediated species interactions will help define crucial chemical and molecular processes that help maintain biodiversity and ecosystem functionality.  相似文献   

Stand density and fertilization effects on aboveground allocation patterns and stem form of Pinus sylvestris in young stands     

Kristina Ahnlund Ulvcrona  Thomas Ulvcrona  Urban Nilsson  Tomas Lundmark 《Scandinavian Journal of Forest Research》2014,29(3):197-209

The increasing demand for forest biomass for energy generation could be partially met by growing denser stands and use of fertilizer. Before this is done at large scale, more knowledge of the effects of stand density and fertilization on aboveground allocation patterns and stem form is needed. Therefore, effects of pre-commercial thinning (PCT) to 3000 stems ha^?1, an unthinned dense control (C), and PCT combined with two levels of fertilization (100 kg ha^?1 of nitrogen applied either during the establishment of the field experiment (F1) or annually (F2)) were examined in 23- to 26-year-old Scots pine (Pinus sylvestris L.) stands six years after the establishment of the field experiment. In total, 114 sample trees were harvested using destructive biomass sampling. The growth allocation and stem form of trees with diameter at breast height (DBH; 1.3 m height) >5.0 cm were not affected by either the PCT or fertilization. Small trees (DBH < 5 cm) in denser, unthinned control plots had more slender stems (lower DBH/height ratios) and allocated less growth to branches and foliage than trees in PCT plots. Fertilization had little effect on the stem form and growth allocation of the smallest trees. Therefore, effects of stem density and fertilization on stem form and growth allocation to foliage were only found for small suppressed trees, and the treatments had very little influence on dominant and codominant trees.  相似文献   

Analysis of genetic variability in the Czech Dachshund population using microsatellite markers     

M. P&#;ibá&#;ová  P. Horák  D. Schröffelová  T. Urban  R. Bechy&#;ová  & L. Musilová 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2009,126(4):311-318

The primary goal of this study was to analyse genetic variation within and among six Dachshund varieties in the Czech Republic using 10 microsatellites from StockMarks^® Paternity Polymerase Chain Reaction (PCR) Typing kit. A total of 632 Dachshunds were sampled – 99 Standard Smooth-haired, 72 Standard Long-haired, 272 Standard Wire-haired, 42 Miniature Smooth-haired, 73 Miniature Long-haired and 74 Miniature Wire-haired. Average observed heterozygosity and polymorphic information content ranged in particular Dachshund varieties between 0.58–0.70 and 0.57–0.64, respectively. Subsequent analysis of the population structure ( F -statistics; Nei's genetic identity) showed that Standard Dachshunds shared allele frequencies most closely with their miniature equivalents, and smooth coat type is closer to Wire-haired coat type than to the Long-haired one. Analysis of molecular variance revealed that 11.81% of the total variance occured among varieties. The value of combined exclusion probability (0.9955) validated usefulness of this panel of microsatellites for parentage verification in all analysed populations. We carried out 234 parentage verifications with 1.28% cases where parentage did not match.  相似文献   

Research priorities. Shining light into black boxes     

Morin A  Urban J  Adams PD  Foster I  Sali A  Baker D  Sliz P 《Science (New York, N.Y.)》2012,336(6078):159-160

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Artificial dispersal of endangered epiphytic lichens: a tool for conservation in boreal forest landscapes     

Marlene Lidén  Monica Pettersson  Urban Bergsten  Tomas Lundmark 《Biological conservation》2004,118(4):431-442

Due to increasing fragmentation of the boreal forests of Fennoscandia, a number of epiphytic lichens are now becoming threatened. Since these species typically are limited by a poor ability of dispersal, one possible but largely unexplored strategy for conservation is to disperse lichen material artificially into suitable habitats. Therefore, the objective of this study was to evaluate survival and vitality in lichen fragments from Evernia divaricata (L.) Ach. and Ramalina dilacerata (Hoffm.) Hoffm. after transplantation into three different stand types situated in northern Sweden, using different fragment sizes and modes of transplantation. After one year, survival ranged between 85% and 97.5%, and new growth occurred at all transplantation sites. The study has shown that transplantations of small fragments might constitute a resource-efficient option for establishment of new populations of endangered lichen species, or for enlarging their populations at the present sites of occurrence. In addition, the mode of transplantation was of importance for fragment vitality.  相似文献