Rodent impact on establishment of direct-seeded Fagus sylvatica,Quercus robur and Quercus petraea on forest land

Abstract

Seed predation by granivorous rodents constitutes a major problem during reforestation using direct seeding. Acorns or beech nuts were sown at 14 different sites in Denmark and southern Sweden, and seedling establishment was inventoried during the first three growing seasons. Around the time of sowing, rodents were either snap-trapped or live-trapped. At some sites, perches for raptors were installed, and at other sites, signs of predation were investigated or predation was monitored by camera surveillance. Granivorous rodents had a profound negative influence on sowings, and the removal of beech nuts occurred rapidly following sowing. Establishment of oak was better when surroundings consisted of mixed forests rather than broadleaved forests. Fewer rodents were caught, and establishment was better, in large reforestation areas. Rodent captures indicated that forest edges, slash piles and stone wall remains were suitable rodent microhabitats. Snap-trapping or raptor perches did not result in increased oak establishment. Neither sowing in summer nor increased seeding depth decreased predation by rodents on beech nuts. In conclusion, seeds need protection from rodents immediately at the time of sowing. Choosing large regeneration areas combined with removal of suitable rodent habitats seems to be a practical alternative for the development of successful strategies for direct seeding.     

Morphology and vegetation of a dune system in SE Denmark in relation to climate change and sea level rise

Recordings by the Danish Meteorological Institute show, that the mean temperature of Denmark has remained fairly constant and the mean precipitation in winter has increased very slightly during the last c. 100 years, and that the relative sea level rise in Danish waters amounted to between + 9 cm and -3 cm during the same period of time.For the W Baltic area a doubling of CO₂-level in the atmosphere is predicted to cause an increase in mean temperature by 3–4°C, an increase in length of growing season by c. 55 days, an increase in aridity, and a sea level rise of between 25 and 165 cm. Based on recent observations of morphology, soil and vegetation of a W Baltic dune system, possible effects of these changes upon vegetational composition, phytogeography, nutrient economy, stability, and ground water level of coastal dunes are discussed.     

Automatic Stem Mapping in Three Dimensions by Template Matching from Aerial Photographs

Recent developments in remote sensing have shown promising results for the detection and species classification of individual trees from high-resolution imagery of forests in leaf-on condition. Existing image-analysis algorithms produce a two-dimensional stem map in the observed imagery. This paper develops a new algorithm that generalizes existing template-matching algorithms to produce a stem map in the three dimensions of a forest in leaf-off condition. A self-contained algorithm to produce artificial template images is introduced. The image-analysis algorithm was applied to oak ( Quercus robur L.) grown under standard silvicultural treatment in Denmark. One analysis gave detection rates in the range 85-98% and root mean squared errors on the stem base coordinates below 8.1, 7.6 and 20.5 cm in the x -, y - and z -directions, respectively. It is concluded that it is indeed feasible to produce a quite accurate three-dimensional stem map.     

Molecular and morphometric study of metacercariae and adults of Pseudamphistomum truncatum (Opisthorchiidae) from roach (Rutilus rutilus) and wild American mink (Mustela vison)

The presence of metacercariae and adults of the trematode Pseudamphistomum truncatum in roach and mink, respectively, was recorded in Lake Fure North of Copenhagen, Denmark. This zoonotic digenean opisthorchiid represents a threat to humans due to its ability to infect the biliary system following ingestion of inadequately processed infected fish. Therefore precise species identification of infective metacercariae in fish used for human consumption is essential. Due to the relatively limited information on metacercarial identity obtained by morphometric studies a series of molecular techniques were used to link the larval parasite in fish with the un-equivocally diagnosed adults in the biliary system of the mink. By the use of carefully selected polymerase chain reaction (PCR) primers and subsequent sequencing of the ITS region from both metacercariae and adults full sequence identity of both metacercariae and adults were confirmed. The presence of this parasitosis in fish from a lake used for both commercial and recreational fisheries call for hygienic alerts in order to prevent accidental human infection with this opisthorchiid.     

Comparison of the Prevalence and Incidence of Infection with Bovine Virus Diarrhoea Virus (BVDV) in Denmark and Michigan and Association with Possible Risk Factors

Based on 2 previous surveys on the occurrence of infection with bovine virus diarrhoea virus (BVDV) in Danish and Michigan dairy herds, the prevalence and incidence of the infection were compared. The presence of certain possible risk factors for the occurrence of infection in the 2 areas were summarized and it was investigated if any of these risk factors had significant effect on the presence of animals persistently infected (PI) with BVDV in the dairy herds. Information on the cattle population density in the 2 areas was obtained from statistical yearbooks. Further information for the individual farms on age distribution, housing of animals, herd size, pasturing and purchasing policy was gathered. The prevalence of PI animals was more than 10 times higher in Denmark as compared to Michigan. In herds without PI animals, the annual incidence of seroconversion as calculated from the age specific prevalence of antibody carriers varied in most age groups between 20–25% in Denmark and between 5–10% in Michigan. All investigated risk factors except for herd size were in favour of a lower prevalence of infection in Michigan. The use of having animals on pasture and at the same time having purchased more than 40 animals within recent 31/2–4 years were significantly associated with presence of PI animals in the dairy herds (p = 0.01) when tested by the Mantel-Haenszel χ². Using mul-tivariable logistic regression, the occurrence of PI animals was found to be significantly related to the study area (Michigan and Denmark) as well as to herd size and purchase intensity.     

丹麦农业生产中的肥料使用及其对中国的启示

现代农业中大量使用的化肥在提高作物产量的同时,也带来了一些负面影响如土壤肥力下降、土壤板结等。文章综述了丹麦先进的肥料使用和管理方面的经验。丹麦政府通过根据作物需要制定N的允许施用量和P、K的推荐施用量、对肥料的施用季节和施肥方式进行规定、根据土壤检测的结果和作物产量调整营养元素施用量等措施较好地避免了化肥污染问题。这些先进的经验为中国解决化肥污染问题提供了借鉴。笔者提出中国在农业生产过程中应从限制化肥使用量、提高农民知识水平、提倡增施有机肥、改进施肥方式等方面避免对环境的污染。