When we consider the main object of forestry, the tree, it immediately becomes clear why experimental population geneticists have been so hesitant in making this object a primary concern of their research. Trees are very long-living organisms with generation intervals frequently exceeding those of their investigators by multiples. They virtually exclude, therefore, application of the classical methods of population genetics since these are based on observing genetic structures over generations. This situation, where the limits set to observation are so severe, particularly requires close cooperation between theory and experiment. It also requires careful consideration of results obtained for organisms other than trees, in order to gain additional insights by comparing the results for trees with those for other organisms. Yet, the greatest challenge to population and ecological genetics probably originates from the fact that forests are very likely to be the most complex ecosystems of all, even in some cases where they are subject to intense management. This complexity, which equally comprises biotic and abiotic factors varying both in time and space, makes extremely high demands on the adaptational capacity and thus flexibility of the carriers of such an ecosystem. Longevity combined with immobility during the vegetative phase, however, appears to contradict the obvious necessity of adaptational flexibility in forest tree populations when compared with short lived and/or mobile organisms.

Inhalt
I Tree Breeding.- invited guest lecture: The Population Genetic Basis of Breeding Theory.- Hybridisation and Cytogenetics of European Birches.- II Mating Systems.- invited guest lecture: Mating System Estimation in Forest Trees: Models, Methods and Meanings.- invited guest lecture: Understanding the Genetic Structure of Plant Populations: Some Old Problems and a New Approach.- invited guest lecture: Inbreeding and Selection in Natural Populations.- Polymorphic Equilibria Under Inbreeding Effects and Selection on Components of Reproduction.- Mating System Dynamics in a Scots Pine Seed Orchard.- Reproductive Success of Genotypes of Pinus sylves-tris L. in Different Environments.- Multilocus Analysis of External Pollen Contamination of a Scots Pine (Pinus sylvestris L.) Seed Orchard.- Gene Dispersion and Selfing Frequency in a Seed-Tree Stand of Pinus sylvestris (L.) 1.- invited guest lecture: Genetic Constraints on the Evolution of Plant Reproductive Systems.- invited guest lecture: Evolution of Outbreeding Systems.- III Genetic Differentiation Within and Between Populations.- The Effects of Forest Management on the Genetic Variability of Plant Species in the Herb Layer.- Studies on Breeding Structure in Two Tropical Tree Species.- A Multilocus Study of Natural Populations of Pinus sylvestris.- Genetic Effects of Scots Pine (Pinus sylvestris L.) Domestication.- Genetic Differentiation Among Scots Pine Populations From the Lowlands and the Mountains in Poland.- Effects of Selection Pressure by SO2 Pollution on Genetic Structures of Norway Spruce (Picea abies).- Measurement of Genetic Differentiation in Plant Populations.- List of contributors.