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Genecology and the adaptations of forest trees

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  1. Introduction.
  2. Background.
    1. The recognition of genetic variation among populations of trees.
    2. What early botanists and foresters lacked.
    3. Investigations of provenance variation.
    4. The basic genecological experimental design used by Clausen, Keck, and Heisey.
  3. Evolutionary forces.
    1. The pattern of genetic variation.
    2. Species that show strong patterns of genetic variation.
  4. Genecological methods.
    1. Provenance trials.
    2. Short-term genecological experiments.
    3. Data analysis.
  5. Genecological trends.
    1. Local provenances in general.
    2. The steepness of genetic clines.
  6. Predicting response to climate change.
  7. Summary.

Genecology is the study of intraspeci?c genetic variation in relation to environmental conditions. It reveals patterns of adaptation of populations to their environments that result from differences in natural selection among locations. Genecological studies are conducted for the practical purposes of: (1) determining how far seed can be moved from the collection site to a reforestation site without risking maladaptation of the trees to the planting site; (2) delineating geographic breeding zones for which a single breeding program would suffice; (3) selecting optimal provenances within the native range for nonnative (introduced) species; and, more recently, (4) predicting the ability of populations of forest trees to adapt to rapidly changing climates. To meet these objectives, seed is collected from different provenances (geographic origins) throughout all or a portion of a species range and planted in one or more ?eld or nursery common-garden experiments. The survival and growth of trees of different provenances are observed under the same set of environmental conditions, allowing for the separation of genetic and environmental effects.

[...] A full century before both Darwin's theory of evolution was published in On the Origin of Species, and Johann Gregor Mendel determined the mechanics of heredity, Carl von Linne (also known as Carolus Linnaeus, the father of modern taxonomy), reported in 1759 that yew trees (Taxus baccata) from France were less cold-hardy than those from Sweden. Around the same time, Henri Louis Duhamel du Monceau, Inspector-General of the French navy and noted botanist, established the ?rst forest genetic trials on record. [...]

[...] In species with intraspeci?c taxonomic structure, genetic differentiation resulting from both isolation and past adaptation can overlay and complicate the interpretation of variation resulting from adaptation to current or recent environments in continuously distributed populations. Hybridization resulting from secondary geographic contact between previously separated species can also produce strong geographic patterns of adaptive variation, for example, in the introgression zone between Picea glauca and P. sitchensis in the coastal mountains of British Columbia and Alaska. Genecological Methods Provenance Trials Traditional provenance trials require ?ve steps: collection of seed; growing of seedlings; planting of a replicated experiment on multiple ?eld sites; measurement of traits; and analysis and interpretation of results. [...]

[...] Short-term genecological experiments can allow the separation of temperature- and moisture-related adaptation more easily than long-term provenance trials, where factors contributing to tree injury or death may be unclear; treatments controlling environmental factors allow detailed assessments of physiological responses to these treatments. Soil?temperature treatments have been successfully created through the use of soil heating cables, and such treatments have revealed provenance[?]treatment interaction in some species. Rather than develop experimental systems to grow seedlings under different temperature regimes, most investigators use arti?cial freeze-testing of shoots or other tissue samples collected from genecological experiments or provenance trials to assess genetic clines in cold-hardiness. [...]

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