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Inventories of noble hardwoods genetic resources - Basic Requirements. EUFORGEN Noble Hardwoods Network, Turok J., Jensen J. Palmberg-Lerche Ch., Rusanen M., Russell K., de Vries S. and Lipman E., compilers, IPGRI, Rome, Report of the 3nd meeting, June 1998, Sagadi, Estonia: 92 – 97.
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An anthecological study of Tilia in the Great Plains and New England was undertaken for both native and introduced species. The floral bracts are postulated as being at least as important in pollinator attraction as they are in fruit dispersal. A characteristic sweet odor is always present, but becomes stronger at dusk. Flowers are protandrous with anthers opening for the first time late in the afternoon and releasing pollen abundantly for about 24 hr. Initial nectar production coincides with stigma receptivity which begins late in the afternoon, but on the second day a flower is open. Sixty-six species of insects in 29 families were collected. Bees and flies are the most common diurnal visitors and moths are the primary nocturnal visitors. Samples of pollen taken from the insects indicate a relatively high constancy. Experimental tests show that Tilia is not apomictic or self compatible. Anemophily plays a secondary role to entomophily in pollination. Nocturnal pollinators are slighly less effective than diurnal pollinators in effecting fruit set. Although nocturnal pollinators are favored by the syndrome of floral characteristics, it is concluded that Tilia is a generalist in regard to pollination. It is proposed that the lack of clear morphological differences between Tilia species leads to pollinator inconstancy and thus hybridization.
The capacity of recuperation of suppressed ashes - In the department of Chimay, Belgium, we have found a natural regeneration of ash with a mean age of 15 years and, however, a mean height of only 30 cm. The capacity of recuperation of this regeneration group has been researched. The suppressed regeneration is reacting very strongly during the second year after the liberation : the annual shoot = 14 cm. Different other facts prove the high capacity of recuperation of these ashes as well. These ashes react very good, and even better than nursery plants, when they are cut back. The results permit to conclude that with trying the natural regeneration of ash it isn't necessary at all to reject the preregeneration. A qualitative valuable preregeneration jus, needs a liberation; on the other side, a qualitative valueless one can be improved by cut back techniques.
Over the last decade, there has been an exponential growth in interest and investigation of the problem of how best to conserve populations of endangered species. As a result, there is now a very extensive and widely scattered literature on this subject. Among recent papers which cite a large number of references are those of Boyce (1992), Ellstrand and Elam (1993) and Nunney and Campbell (1993). Soulé’s (1987) book gives a valuable survey of the subject, in which the chapter by Lande and Barrowclough (1987) deals with the population genetics of the problem. Much of this literature is concerned with the conservation of species where ex situ conservation is not a realistic alternative. The demographic and population genetics theory on which discussion of this broader issue is based, however, is also relevant to the special case of those species where the conservation of material in gene banks is possible. The purpose of this chapter is to give a brief outline of the population genetics theory on which discussion of in situ conservation is based and to introduce some of the terms and concepts used in the literature. We also indicate the kinds of experimental investigation of populations which are necessary to produce better recommendations about minimum viable population size than are possible at present.
The genetic diversity that permits populations to evolve and respond to future stresses and selective pressures is the result of its past evolutionary history. Forces that affected its population size and changes in gene and genotypic frequencies have molded the levels and structure of its genetic variation and hence the future evolutionary capacities of its present populations. Therefore, the genetic diversity is both a cause and an effect of global change and is a measure of the dynamic changes underlying genetic variation that both permits and constrains the future evolution of temperate ecosystems. Neither the global climate nor the genetic variation in ecosystems are independent of the effects of the other, and the history of temperate ecosystems involves the joint evolution of genes and environment.
On the final day of the NATO Advanced Research Workshop, research priorities were discussed in four working groups, which dealt with:
The impact of global change on populations and species
The impact of global change on ecosystems and landscapes
The relationship between biodiversity and sustainability, and
International cooperation in research