首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到18条相似文献,搜索用时 0 毫秒
1.
With the book publication “Forest and Nature Governance — A practice based approach” (Arts et al., 2013, Eds.) the Forest and Nature Conservation Policy Group of Wageningen University, The Netherlands demonstrates its high aspirations of developing a new research approach. This article aims at discussing the methodological and conceptual contributions of the book to the field of forest and environmental policy research and proposes perspectives for further developing this methodological approach. It finds the “practice based approach” being an innovative, theoretically sound concept, which is able to produce valuable and “thick” empirical results. The approach is also found offering a plethora of possibilities to link up to analytical policy research. Yet, the approach will require further elaboration, especially on questions regarding the role of definitions, its contribution towards explaining social phenomena, and concerning the use of normative orientations in some of the empirical cases. The future challenges of the approach lie in either moulding a niche for further developing it independent from other schools, or in influencing mainstream approaches through theoretical innovations or surprising empirical results.  相似文献   

2.
3.
Telomeres are the structures that locate at the terminals of linear eukaryotic chromosomes. They can play essential roles in many cellular processes. The terminal location of Arabidopsis-type TTTAGGG tandem repeats were thought to be highly conserved. The terminal location of Ginkgo biloba L. consisting of TTTAGGG tandem repeats, were confirmed by Bal31 exonuclease degradation and Southern blotting. By comparing telomeric restriction fragment (TRF) lengths at different developmental stages from embryos to seedlings, a fluctuant tendency towards variation was found in these samples. The TRF length of embryos was also compared with that of embryonal calli and an upward trend was discovered in callus culture. The results suggest that there should be a telomerase mechanism or/and ALT mechanism for the maintenance of telomere length.  相似文献   

4.
ThemiteofthegenusLeptusisworld-widedistributedandectoparasitedoninsectsandonspiders.InJapan,ninespeciesofthisgenushavebeenrec...  相似文献   

5.
We combine historical maps and satellite derived data to reconstruct the development of a Swedish boreal landscape over the past 300 years. The aim is to understand legacies from past use patterns in present-day forest composition and consequences for conservation objectives from a landscape perspective. We analyze landscape development in cross-tabulation matrixes, building change trajectories. These trajectories are tested in linear models to explain the distribution of present-day landscape composition of coniferous, mixed, and deciduous forests >110 years. Of 49 tested change trajectories, 11 showed a significant association. Associations for mixed and coniferous forests were similar and linked to characteristics such as forest continuity, which characterized the studied landscape. Deciduous older forests did not show any association to forest continuity but were more likely to occur on areas that specifically shifted from forests with grazing in the 1720s to open impediment (likely indicating low tree coverage) in the 1850s. There were large shifts and spatial redistribution in ownerships over time. Use patterns and legacies varied between small- and large-scale ownership categories as well as within small-scale categories. The legacies found in the study indicate a complex origin of heterogeneous landscape elements such as older deciduous forests. Additionally, the origin of the legacies indicates a potential need to diversify conservation management based on the influence of past use patterns. Despite large inconsistencies in historical and contemporary data we argue that this type of analysis could be used to further understand the distribution of landscape elements important for conservation objectives.  相似文献   

6.
Wood Science and Technology - In order to study the detailed water extract of wood components in birch under hydrothermal treatment, xylem sap obtained by mechanical...  相似文献   

7.
8.
9.
In Bulgaria near Marikostino, in a forest ofPinus nigra Arn. 239 egg batches were sampled over four generations ofThaumetopoea pityocampa (Den. &; Schiff.) (Lep., Thaumetopoeidae) in various seasons. Directly after collection the batches were singled in test tubes, closed with cotton stoppers and stored under laboratory conditions at 20–22°C. Oviposition always started from the base towards the tip of the needles. The emergence of egg parasitoids was observed daily, and the parasitoids were counted and identified. The eggs from which parasitoids emerged were marked for further studies. After removing the adults and opening the eggs, the impact of the species of parasitoids was evaluated by identifying the meconia and other rests (left overs). Ooencyrtus pityocampae (Mercet) was the most abundant egg parasitoid, followed byAnastatus bifasciatus (Fonsc.). Only few individuals ofBaryscapus servadeii (Dom.) were collected. The hyperparasitoidBaryscapus servadeii (Dom.) were collected. The hyperparasitoidBaryscapus transversalis Graham, was found at low densities. Only a few eggs were parasitised byTrichogramma embryophagum Htg. Total mortality of the host eggs varied from 34.7 to 79.7% depending on the period of parasitism and on the numbers of sterile eggs. The impact of the parasitoids was calculated to be 9.3–38.9%, depending on the period when parasitism had taken place. The mean number of eggs per batch varied from 203 to 253. The rate of parasitism was reduced by early sampling of the egg batches. In some cases, a very high percentage (up to 29.2%) of undeveloped eggs was found. In all samples a small percentage of empty eggs was always observed.  相似文献   

10.
1三棘华枝SinophasmatrispinosumChenetChen,sp.nov.本新种与臀沟华枝SinophasmalatisectumChenetChen近似,但本种雄性臀节端部较窄,纵沟浅裂.背面具有3个排列成倒三角形的锥形突,第9节背板隆起成直角下垂等不同,可相区别.模式标本保存在中山大学.2单棘华枝SinophasmaunispinosumChenetChen,sp.nov.本新种与三棘华枝SinophasmatrispinosumChenetChen近似,但本种雄性臀节较狭长,两侧端叶扩展成瓣状;端部无纵沟,背面具有1个明显的锥形突,下生殖板形状以及第9节背板明显不同等,可相区别.模式标本保存在中山大学.3拟异尾华枝(雌性)SinophasmapseudomirabileChenetChen本种发表于1996年,当时仅报道其雄性,近在中山大学昆虫标本馆发现1对雌雄,其雌性与异尾华枝SionphasmamirabileGünther雌性相似.但本种头部形状,第7腹节腹板与腹瓣伸至的位置,以及尾须的形状等明显不同,可与之区别.模式标本保存在北京林业大学和中山大学.  相似文献   

11.
12.
Aldehydes play an important role in atmospheric chemistry and plant direct and indirect defense against environmental stresses.In this study,the emissions of saturated C6-C10 aldehydes from Populus simonii × P.pyramidalis 'Opera 8277' cuttings were examined by using a gas chromatography/mass spectrometry(GC/MS) technique at three levels of light intensity(400,800 and 1 200 μmol·m-2·s-1).A positive correlation between the emissions of these aldehydes and light intensity was found.Moreover,nordi-hydroguaiaret...  相似文献   

13.
A new species of the genus Rhynchina Guene′e, 1854, R. tongmaia Pan and Han, sp. n. is described from China. This species is compared with a supercially similar congener, R. rivuligera Butler, 1889 wit...  相似文献   

14.
A reliable,efficient anther culture system,the dominant technique for generating haploid plants in breeding programs,that can be used for generating transgenic poplar plants has been needed.In the present study,therefore,an anther culture system was developed using isolated mid-and late-uninucleate anthers of poplar(Populus simonii x P.nigra).From a combination of SSR and ploidy analyses,six double haploid and two haploid lines were characterized from 86 plants grown from 16 regenerated anther cultured lines.After 48 months of development,two plant lines from the regenerated plants maintained their haploid level in vitro for over 2 years.A number of haploid plants from the different lines weretransferred to soil.The leaves of these transplants were then used as explants for transformation with the APETALA1(AP1) gene using Agrobacterium tumefaciens.Overexpression of AP1 in haploid poplar induced early flowering with obvious petals when ectopically expressed.To our knowledge,this is the first report on changes in flowering time in AP1-trangenic poplar,which is important for elucidating the regulatory mechanism of tree flower development.  相似文献   

15.
16.
17.
Aldehydes play an important role in atmospheric chemistry and plant direct and indirect defense against environmental stresses.In this study,the emissions of saturated C6-C10 aldehydes from Populus simonii × P.pyramidalis ’Opera 8277’ cuttings were examined by using a gas chromatography/mass spectrometry(GC/MS) technique at three levels of light intensity(400,800 and 1 200 μmol·m-2·s-1).A positive correlation between the emissions of these aldehydes and light intensity was found.Moreover,nordi-hydroguaiaretic acid(NDGA),a special inhibitor of lipoxygenase(LOX),significantly inhibited the emissions of C6-C9 aldehydes at three levels of light intensity,but did not influence the emission of decanal(C10).The emissions of C6-C10 aldehydes in NDGA treated poplar cuttings,exhibited the same positive correlation with light intensity.The results indicated that LOX pathway contributes to the emissions of C6-C9 aldehydes,whereas some pathways regulated by light intensity might be a universal mechanism for emissions of C6-C10 aldehydes.  相似文献   

18.
•  Introduction  The simulation of diameter distributions is the basis for predicting volume in the so-called diameter distribution models. Combined with volume, volume ratio and taper equations, these models allow the prediction of volume assortments according to user needs. The simulation of diameter distributions is also essential in initialising individual tree models. It is also a useful aid for planning harvesting operations.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号