The effect of canopy position on growth and mortality in mixed sapling communities during self-thinning

This research investigates how species in the sapling phase differ in growth and survival depending on light availability (as estimated by canopy position) by means of tree-ring analysis and modelling mortality. We harvested 120 live and 158 dead saplings in self-thinning communities consisting of Silver birch (Betula pendula Roth.), Scots pine (Pinus sylvestris L.), Japanese larch (Larix kaempferi Carr.) and Douglas fir (Pseudotsuga menziesii Mirb. Franco) in the Netherlands. Results are evaluated within the framework of a trade-off between high-light growth and low-growth survival. Radial growth, measured at ground level, generally declined over time. In addition, a decreasing light availability further reduced growth in all species except Douglas fir. Trees died when radial growth was reduced to about 0.5 mm year¿1. Mortality in all species except Scots pine was significantly related to recent growth, but mortality curves were not different. The light-demanding Silver birch and Japanese larch differed from the shade-tolerant Douglas fir in both high-light growth and low-growth mortality, in line with a growth-survival trade-off. The light-demanding Scots pine did not fit this pattern as it was unable to transfer high radial growth into height gain, leaving it in suppressed canopy positions. This indicates the importance of height growth in the growth-survival trade-off. Differences in mortality probabilities affect the potential for coexistence, however, in all species also fast-growing individuals died suggesting additional factors causing mortality during self-thinning, other than direct competition for ligh

Cable Design for FAIR SIS 300

GSI, Darmstadt is preparing to build FAIR (Facility for Antiproton and Ion Research) which include SIS 300, a 300T - m fast-ramping heavy ion synchrotron. Dipoles for this ring will be 2.9 m long, producing 6 T over a 100 mm coil aperture and ramped at 1 T/s. The cable for these dipoles must have low losses and produce acceptable field distortions during the fast ramp. We plan to achieve this objective by using fine (~ 3 mum) filaments of NbTi in a wire with an interfilamentary matrix of CuMn to reduce proximity coupling and increase the transverse resistivity. The Rutherford cable have a thin stainless steel core and the wires will be coated with SnAg solder which has been oxidized, using a recipe similar to that developed at CERN, to increase the adjacent strand resistance Ra. Measurements of crossover strand resistance Re and Ra in cored cable with oxidized SnAg coating will be presented, together with data on critical current, persistent current magnetization and eddy current coupling in a wire with ultra fine filaments and a CuMn matrix in the interfilamentary region of the wire. These data will be used to predict losses and field distortion in the SIS 300 dipole and optimize the final design of cable for FAIR

Inhoud en functionaliteit Koepelvisie Bos : een verkenning naar een hernieuwde benadering voor het verbinden van doelstellingen aan terreinbeheer van bossen

De koepvisie van Staatsbosbeheer geeft algemene handvatten aan het beheer door doelstellingen te koppelen aan maatregelen die in het terreinbeheer mogelijk, wenselijk of noodzakelijk zij

The role of bracken (Pteridium aquilinum) in forest dynamics = [De rol van adelaarsvaren (Pteridium aquilinum) in de bosdynamiek]

Bracken fern ( Pteridium aquilinum ) causes stagnation in forest succession in many parts of the world. The mechanisms by which bracken affects the establishment and growth of plant species are studied, focusing on the regeneration of tree species in forest habitats.Bracken is well adapted to the forest environment. Data show that productivity is maintained under low light levels. When the tree canopy is opened up or removed, above-ground production increases sharply to produce dense swards. Under most tree species ( Pinus , Quercus , Larix , Betula ), the translucent canopies allow for the long term persistence of bracken clones. On the dry sandy soils of The Netherlands, beech ( Fagus sylvatica ) is the only tree species that can completely inhibit bracken growth. The relationship between bracken and ancient forests is mainly historical, and due to the lack of sporal regeneration and low survival of bracken outside the tree canopy cover.Under favourable conditions, bracken builds a physical structure that strongly reduces light levels available to plants growing under its canopy and smothers plants under collapsing and dead fronds. A field experiment indicated that below-ground competition by bracken is negligible. Species diversity of the forest understorey was negatively correlated with frond biomass.The slowly decaying litter builds a thick ectorganic soil layer that impedes establishment of light-seeded species. An experiment demonstrated how, besides bulk density and thickness, also the horizontal layering of the organic particles contributes to reduced species establishment on deep ectorganic soil layers. Despite numerous claims that the bracken plant produces substances that are toxic to other plants, experimental evidence did not confirm this allelopathic nature of bracken. A review of the literature suggested that the potential phytotoxicity of bracken is due to the release of compounds that protect the plant against herbivory.Field experiments showed that voles and mice make preferential use of the protective bracken cover. The increased abundance of rodents resulted in a high seed predation under bracken. The hoarding behaviour of wood mice ( Apodemus sylvaticus ) caused a directed dispersal of seeds towards the bracken structure. Bracken impinges on all causes of successional change in the vegetation. Tree establishment is blocked unless the clones are physically disturbed. Some implications for forest management are discussed.Key-words: allelopathy, bracken, competition, litter, Pteridium aquilinum, seed dispersal, seed predation, stagnation, succession.</p

De linde terug in het bos : verslag veldwerkplaats Droog zandlandschap Doorwerth, 9 mei 2008

Verslag van de veldwerkdag Droog zandlandschap in Doorwerth op 9 mei 2008. Tijdens deze veldwerkdag is in de bossen bij kasteel Doorwerth gekeken naar de 0strooisellaag van verschillende bostypen. Aanplant van lindes in een eikenbeukenbos op een relatief arme bodem geeft een zichtbare verbetering van de strooisellaag. De verzuring die in bossen plaatsvindt kan op deze manier plaatselijk worden bestreden. De aanplant van linde en andere boomsoorten met goed verterend strooisel kan dus een bijdrage leveren aan het oplossen van het verzuringsprobleem. Daarbij leidt de verbeterde strooiselkwaliteit tot een verhoging van biodiversiteit en bloemenpracht in het voorjaar

A conduction-cooled, 680-mm-long warm bore, 3-T Nb3Sn solenoid for a Cerenkov free electron laser

A compact, cryocooler cooled Nb3Sn superconducting magnet system for a Cerenkov free electron laser has been designed, fabricated and tested. The magnet is positioned directly behind the electron gun of the laser system. The solenoidal field compresses and guides a tube-shaped 100 A, 500 kV electron beam. A two-stage GM cryocooler, equipped with a first generation ErNi5 regenerator, cools the epoxy impregnated solenoid down to the operating temperature of about 7.5 K. This leaves a conservative operational margin for the MJR type of Nb3Sn conductor of about 350% (I c) at 3T. Current leads with HTS sections between the first and second stage of the cryocooler effectively reduce the conductive heat leak. In the warm bore, 60 mm in diameter and 680 mm long, an operational magnetic field of 2 T has been achieved during laser operation without any quench. The field homogeneity is better than 99.5% over 450 mm axial length. Design details and test results of this magnet system are presented

Clusters of Quercus robur and Q. petraea at the Veluwe (the Netherlands)

In this report three main questions were studied: (1) are oak clusters genetically identical, (2) can leaf morphology be used to identify clonal structures of oak and (3) what is the origin of oak clusters. The study sites were situated in a drift sand area (Maanschoten) as well as in an area with pre-glacial material (Wilde Kamp)