水蒸气处理法制作压缩整形木的研究(Ⅰ)-构造变化和尺寸稳定性   总被引：10，自引：0，他引：10  

刘一星  李坚  刘君良  沈隽 《东北林业大学学报》2000,28(4):9-9,12

应用自行设计、制造的木材高温水蒸气处理成型设备和模肯,实验制作了截面为正方形的压缩整形木,并对整形木材的构造变化和尺寸稳定性进行了分析和评价。其结果为：压缩整形木的某些部位的解剖分子可发生向内溃陷,细胞腔变小,纹孔膜破裂,但细胞壁没有破坏;压缩整形木的变形回复率很低。吸湿、吸水膨胀率均明显低于素材,具有良好的稳定性。  相似文献   

北部湾经济区外来植物入侵风险评估   总被引：1，自引：0，他引：1  

林建勇  温远光  韦洁  赵金龙 《现代农业科技》2011,(8):130-131,133

基于风险评估理论,并结合北部湾经济区的地域特点和外来植物入侵的现状,提出了北部湾经济区外来植物入侵风险评估指标体系。该指标体系由6个1级指标、32个2级指标构成。并对区内已确定的87种入侵植物的入侵风险进行评估,得出每种植物的入侵风险值。该结果可为入侵植物的引种管理与危害防治提供参考。  相似文献   

北部湾划界后广西北部湾渔区渔民转产转业问题研究     

陈禄青  周明钧 《安徽农业科学》2010,38(29):16628-16630

在阐述北部湾划界的内容与划界对渔民生产生活面临的新形势的基础上,剖析了北部湾划界后广西北部湾渔区渔民转产转业面临的问题,并提出了相应的对策建议,以期促进广西北部湾渔区渔民转产转业。  相似文献   

环北部湾渔民对休渔制度认知程度的调查分析     

卢伙胜  郑国钦  冯波 《渔业经济研究》2009,(5):7-11

通过问卷的方式，对环北部湾地区的渔民进行了休渔制度认知程度的调查，结果表明，渔民对休渔制度普遍持认可的态度，但是对休渔制度的具体实践提出了不同的看法。在分析渔民对休渔制度持不同态度的深层次原因的基础上，提出了改进休渔制度的建议。  相似文献   

广西北部湾滨海地区公园植物多样性调查研究     

苏凤秀 《中国农学通报》2022,38(22):79-83

为摸清广西北部湾滨海城市公园植物绿化资源现状及特点,用典型随机抽样法对广西北部湾地区的北海市、钦州市、防城港市的10个公园52个标准样地进行植物群落调查研究。统计结果表明,该区域植物资源丰富,共有183种,隶属于60科140属,其中蕨类植物1科1属1种,裸子植物5科7属7种,被子植物54科132属175种。乔木层树种最为丰富,达100种,占总数的55%;其次为灌木层,为56种,占总数的30%;草本层种类最少,仅为27种,占总数的15%。植物构成体现热带亚热带及滨海特色,大多数种类具有地域性景观特色,主要以王棕(Roystonea regia)、假槟榔(Archontophoenix alexandrae)、木麻黄(Casuarina equisetifolia)等为主,建议增加滨海乡土植物的筛选及应用,为北部湾地区及滨海地区的绿化建设提供参考。  相似文献   

Regional differences in patterns of fish species loss with changing land use     

Ryan M. Utz  Robert H. Hilderbrand 《Biological conservation》2010,143(3):688-699

Human-centered land use causes ecosystem degradation and loss of biodiversity in streams, yet such processes may be highly heterogeneous among species and regions. We quantified fish species sensitivity to several classes of land use and determined if trends varied among three geoclimatic regions of Maryland, USA. Our approach compares the cumulative frequency distribution (CFD) of sites where a species was expected to occur to the CFD of those where it was collected to estimate the species-specific maximum degree of land use tolerated and the minimal amount that may induce an impact. Fishes were most vulnerable to urban land use gradients, though trends were region-specific with heightened sensitivity in the Piedmont (64-72% of species negatively affected) relative to the Coastal Plain (45-52% negatively affected). Species found in both regions exhibited greater vulnerability to urbanization in the Piedmont. Responses to agricultural land use were less severe though trends were region-specific as well with the least sensitive in the Piedmont and the greatest negative impact in the Highlands region. In many cases, reduced population abundances were detected at lower levels of land use relative to the range where the species was apparently extirpated. Our results demonstrate that population reduction and species loss due to land use change differs substantially among regions, even within a single species. Greater sensitivity observed in abundance-weighted analyses implies that further loss of fish diversity may be impending in impacted streams. Our results have direct application to prioritize conservation resources and forecast future declines in species distributions and biodiversity.  相似文献   

厦门湾海水养殖鱼类常见疾病与防治     

郑惠东 《福建水产》2007,(2):19-23

本文通过对厦门湾及其沿岸的海水养殖鱼类疾病种类、病原、流行情况和防治方法进行调查,总结出常见疾病15种,其中病毒性疾病3种,细菌性疾病4种,寄生虫性疾病6种,其它疾病2种.对疾病的发生原因和防治对策加以重点阐述.  相似文献   

Observed and modelled distributions of channel and gully heads—with examples from SE Spain and Belgium     

M. J. Kirkby  L. J. Bull  J. Poesen  J. Nachtergaele  L. Vandekerckhove 《CATENA》2003,50(2-4):415-434

In soil erosion by overland flow, sediment discharge is driven by discharge and gradient against the resistance of the soil and vegetation. The form of the relationship, which is taken as a sum of power law terms, may then be inferred from several data sources: (1) ephemeral gully head location, (2) permanent channel head location, (3) slope profile form, (4) consistency with evolutionary models and (5) erosion plot data. The paper focuses on (1) to (4), in order to understand how far these data constrain the form of the dependence on discharge and gradient. Field data from mapping a set of ephemeral gully heads after storms show a weak inverse relationship between channel head gradient and catchment area, which flattens towards an upper threshold gradient of about 25%. These relationships are compared with those theoretically obtained for a range of sediment transport laws which have been previously used, and which are analysed to forecast both overall slope profile form and the location of stream heads. The theory predicts that the location of ephemeral gully heads produced in a single storm will differ from the long-term average stream head location. There is a fairly good relationship between theoretical and observed locations, associated with the form of the sediment transport law. For a single event, the location depends on storm magnitude which cannot be well defined from the data sets, creating a spread of data with an envelope curve defined for the largest events. The empirically acceptable sediment transport equations have also been used to analyse families of slope profiles in a small area, and used within a landscape evolution model to generate landscapes which are compatible with those observed in the field, and provide confirmation of the long-term viability of the expressions obtained to forecast the direction, style and rates of landscape evolution in response to land use or climate drivers.  相似文献   

Long-term recovery of stream habitat structure and benthic invertebrate communities from in-stream restoration     

Timo Muotka  Riku PaavolaAntti Haapala  Milan NovikmecPekka Laasonen 《Biological conservation》2002,105(2):243-253

Headwater streams channelized for water transport of timber in Finland are being restored to their pre-channelization state. The primary motivation is the enhancement of sport fisheries, but restoration probably has profound impacts also on other stream organisms. We assessed how such “single-goal” restorations affect benthic macroinvertebrate communities. We revisited the streams sampled by Laasonen et al. [Aquatic Conservation: Marine and Freshwater Ecosystems 8 (1998)] in the early 1990s when the streams had been recently restored. In 1997, the recovery period of these streams ranged from 4 to 8 years. Habitat structure among the stream types represented a distinct recovery gradient, with streams restored 1 month before sampling and natural streams being the endpoints of a gradient in moss cover (highest in natural, lowest in recently restored streams). Channelized streams supported a characteristic set of indicator species, whereas shifts in species composition between restored and natural streams were more gradual. Macroinvertebrate communities in unmodified streams changed little between the two surveys, whereas communities in restored streams had undergone considerable changes. In-stream restoration is an unpredictable disturbance, to which stream biota cannot have any evolved responses. Therefore, the relatively rapid recovery of habitat structure and macroinvertebrate communities in restored streams is encouraging. However, long-term monitoring of benthic communities in both restored and natural streams is needed to assess whether restoring rivers by these techniques will enhance the recovery of benthic biodiversity in boreal streams.  相似文献   

Annotated checklist and fisheries interactions of cetaceans in Togo,with evidence of Antarctic minke whale in the Gulf of Guinea     

Gabriel H. SEGNIAGBETO  Koen VAN WAEREBEEK  Joseph E. BOWESSIDJAOU  Koffivi KETOH  Takouda K. KPATCHA  Kotchikpa OKOUMASSOU  Kossi AHOEDO 《Integrative zoology》2014,9(1):1-13

Based on strandings and captures, 9 cetacean species, including 6 odontocetes and 3 mysticetes, are documented (photos and specimens) in Togo's coastal waters (newly‐recorded species marked with an asterisk): Antarctic minke whale (Balaenoptera bonaerensis*), Bryde's whale (Balaenoptera brydei or B. edeni), humpback whale (Megaptera novaeangliae), sperm whale (Physeter macrocephalus), pygmy sperm whale (Kogia breviceps*), short‐finned pilot whale (Globicephala macrorhynchus*), pantropical spotted dolphin (Stenella attenuata*), common bottlenose dolphin (Tursiops truncatus) and common dolphin Delphinus sp. An anecdotal sighting record for killer whale (Orcinus orca) is considered reliable. The lack of Sousa teuszii records in Togo is consistent with its apparent contemporaneous absence in Ghana. The B. bonaerensis specimen, entangled in a purse seine set on small pelagics, is a first record for the Gulf of Guinea. The occurrence of this Southern Ocean species north of the equator underscores the severe gaps in our understanding of cetacean distribution off western Africa. The majority of artisanal fishermen operating in Togolese coastal waters are of Ghanaian origin and are thought to promote trade and consumption of cetacean bushmeat. Because captures are illegal, enforced with some success in the main fishing centers, covert landings of cetaceans are exceedingly difficult to monitor, quantify or sample. Concern is expressed about pollution of Togo's coastal waters with heavy metals due to phosphorite mining and export from the coastal basin near Hahotoé and Kpogamé.  相似文献