Boreal and Temperate Trees in a Changing Climate
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.
Biometeorology