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The hypothetico-deductive modelling framework introduced in Chap. 2 is applied to examining the evolutionary aspects of the annual cycle in boreal and temperate trees. For use of growth resources and competition (capacity adaptation), early onset and late cessation of growth are selected for. However, due to the risk of spring and autumn frost damage (survival adaptation), they are simultaneously selected against. This trade-off is examined by means of computer simulations with models representing various regulation principles of the annual cycle. Considerable differences among the principles are reported. When the principles are equally constrained for avoidance of frost damage, some of them allow the trees to use the growing season more comprehensively than others. Next, differences among the provenances of the tree species are examined within the framework of the modelling approach. The annual cycle of each provenance is adapted to its native climate, and this adaptation is manifested in several traits associated with the environmental regulation of the annual cycle. In the models of the annual cycle, this genetic differentiation is readily addressed via the values of the model parameters, such as critical night length of growth cessation or the chilling requirement of rest break. The possibilities of addressing the effects of the maternal environment on the annual cycle traits of the offspring are also discussed, and so is the emerging approach of combining genetic and ecophysiological modelling of the annual cycle.

Boreal and temperate trees grow under climatic conditions in which the ambient air temperature displays pronounced seasonal variation. Unlike herbs and grasses, trees overwinter without a sheltering snow cover, so that they are exposed to all the harsh climatic conditions. That is why their climatic adaptation is based on their annual cycle of development, whereby the frost-hardy dormant phase and the susceptible growth phase are synchronised with the seasonality of the climate. The main aspects of this adaptive strategy of trees are briefly discussed, emphasising both the geographical and the year-to-year variation of the seasonal air temperature conditions. Many boreal and temperate tree species have large ranges of geographical distribution, so that their different provenances have adapted to the particular local climate prevailing at their native growing site. The extent of the geographical variation in air temperature crucial for this adaptation is highlighted by examining the climatic records of four locations within the European distribution range of Pinus sylvestris. The extent of the year-to-year variation is similarly highlighted by examining a 92-year climatic record from Jyvaskyla, central Finland. In the coolest summer, the temperature sum in Jyvaskyla was similar to the average temperature sum 600 km north of Jyvaskyla; and in the warmest summer it was similar to the average temperature sum 600 km south of Jyvaskyla. This limited analysis suffices to reveal the extent of the climatic year-to-year variation that trees need to acclimate to at their native growing site.

An intensive field program was conducted in the subtropical Lower Rio Grande Valley of Texas (LRGV) to evaluate the establishment of the imported para- sitoids of B. tabaci. Thirty populations/species of Eretmocerus and Encarsia para- sitoids were mass reared for field release in multiple agricultural crops and garden plantings. Small releases of the Eretmocerus spp. were also made in the Texas Wintergarden to the northwest of the LRGV. Field tests were conducted on the major crops to determine which species showed the best potential. Banker plants (parasitoid inoculated seedling transplants) were used to facilitate early season augmentative releases of parasitoids in commercial imidacloprid treated cantaloupe melons and watermelons. Following the initial releases, several species showed initial establishment, but only Eret. hayati overwintered and dispersed. This result was confirmed by using RAPD-PCR which was used to distinguish the morpho- logically similar Eretmocerus spp. By 1997, Eret. hayati was established across the entire LRGV and northeastern Mexico. Eretmocerus hayati was predicted to do well in the LRGV because of the high attack rate it exhibited in pre-release quarantine studies and its climatic adaptation to the subtropical LRGV, which is similar to its native range in Pakistan.

Climatic adaptation seems to be the most important component in the evolutionary process of boreal forest tree species. Recent evidence has been accumulating that this process may be less clear-cut than earlier assumed. In Picea abies, several independent tests have shown that the climate and weather conditions during sexual reproduction influence the adaptive properties of the progenies. The phenomenon is expressed in Norway spruce seed orchards established by moving parent trees, propagated as grafts, from north to south, from high to low elevation, or from outdoor to indoor greenhouse conditions. The progenies exhibit a changed phenology and a delayed development of frost hardiness in the autumn compared to their siblings reproduced in a colder environment. Observations on seedlings from seeds harvested in northern stands of provenances transferred from the south to the north, show that they have tuned their photoperiodic responses towards that the of the local provenances. Results with other conifer species indicate that they express similar effects. A possible explanation for the phenomenon is the existence of a regulatory mechanism, sensing the changes in temperature and/or photoperiod at some stages during the reproductive process in the female flower, and then modifying the expression of genes controlling adaptive traits in the progeny. Regardless of the type of mechanisms involved, these observations have changed our understanding of ecotype formation in Norway spruce, and given us some ideas why this species express strong clinal variation in combination with a large within population variation for the same adaptive traits. The maternal influence will often alter the phenotypic performance of the progenies in the ssame direction as natural selection. It may be one of the reasons why some conifer species under conditions seem so highly adaptable.

Common garden plantations have provided data for studies of the variability in quantitative adaptive traits among and within wild populations of forest tree species. The distribution of variability among and within populations, its patterns across the landscape and relationships to environmental variables have been used to interpret the ecological basis for genetic differentiation and evolution of the species (Rehfeldt 1988, 1989,1995; Campbell et al. 1989). The studies have shown that climatic adaptation seems to be the most important component in the evolutionary process of temperate and boreal conifers. Most species show substantial variability in adaptive traits both within and among populations, even at the climatic margin of their range (Savolainen 1997). The main evolutionary forces influencing the variability patterns are natural selection, genetic drill, gene flow, mutations and phenotypic plasticity (Eriksson 1998a). The marry types of variability patterns shown by different species and their degree of adaptedness to the sites suggest that species occupying the same environment may be influenced by different evolutionary forces, see examples discussed by Eriksson (1998b). Several selective forces may even operate on the same population, some simultaneously and some at different life stages or during different seasons of the year (Eriksson 1998a). The variability patterns are therefore most likely under the influence of several evolutionary forces interacting in rather complex ways. This conclusion is supported by the rather high levels of genetic variation in survival and annual growth rhythm traits maintained in the boreal forest (Savolainen 1997), in spite of a strong directional selection against the traits.

Plant lipids have a variety of industrial and nutritional uses and are central to plant membrane function and climatic adaptation. These lipids represent a vast array of chemical structures, and these structures determine the physiological and industrial properties of the lipid. Many of these structures result either directly or indirectly from metabolic processes that alter the degree of unsaturation of the lipid.

Long-term persistence and, hence, agronomic success as a pasture of the annual species subterranean clover depend primarily on seed yield and seed survival over seasons. In natural populations, plant characteristics influencing seed setting and formation of seed reserves in the soil are expected to be ‘adjusted’ to the prevailing environmental conditions of the sites of origin. Knowledge on plant/environment relationships may provide information on adaptive strategies of persistence, and guidelines for selecting adapted varieties to specific conditions. On pure lines from a number of populations such relationships were assessed for flowering time, seed yield, burr fertility, individual seed weight, initial hardseededness, and rate of hardseededness breakdown over summer. Flowering time decreased on decreasing annual rainfall, i.e., on shortening the growing season, as adaptive response to the need of producing adequate seed before the onset of the dry season. Individual seed weight decreased on decreasing rainfall, and increasing temperatures. Hard-seed maintenance over summer was higher in populations from hot and dry environments, where the marked effect of temperature on hardseededness breakdown exerts a strong selective pressure. Within-population variation, assessed on flowering time, was particularly wide, with early genotypes occurring even in populations from long-season environments. The adaptive relevance of maintaining high levels of within-population polymorphism to cope with unpredictable climatic fluctuations is discussed. Number of constituent lines as a measure of the population structure, and intra-population variation were both influenced by altitude and rainfall, tending to decrease as the climatic selective pressure becomes severe, under both low-rainfall, hot conditions and high-elevation, cold-prone environments.

Common garden testing of populations of different origin started with forest trees more than two hundred years ago. Since then, so-called provenance tests have been established with most commercially important species. Beyond the strictly silvicultural goals, the tests offer excellent opportunities to study intraspecific genetic variation patterns and represent probably the most powerful available tool for testing hypotheses of climatic adaptation in trees.