All organisms are fitted for the habitat in which they live. Some are sufficiently flexible in their requirements that they can withstand small shifts in their environment. Others are so well fitted that they cannot withstand habitat change and will eventually fail. The extent of seasonal changes varies with latitude. Plants in temperate and sub-arctic are fitted for changing weather patterns from hot and dry to cold and wet as the calendar moves from summer into winter. Deciduous plants start growing in spring with varying degrees of rapidity and move through flowering and fruiting in summer and early autumn. Finally, some produce a magnificent display of autumn colour, but all senesce and shut down with the return of winter. Evergreen plants frequently inhabit the higher latitudes and retain their foliage. This is an energy conservation measure as they can respond more quickly when winter ends and growth restarts.
Plants respond to seasonal change by sensing alterations in daylength, spectral composition and most importantly temperature. It is known as acclimatisation (acclimation in the American literature). Falling temperatures are the most potent triggers in preparation for winter dormancy. Cold and ultimately freezing weather will seriously damage plant growth where acclimatisation has not been completed. Without preparation freezing ruptures cell membranes in leaves and stems disrupting their normal functions. These effects are measurable and used as means of quantifying plant hardiness. Membrane leakiness correlates with increased ionic concentrations when damaged leaves are placed in water and the resultant pC measured. Changes in chlorophyll fluorescent indicated damaged photosynthetic apparatus and measurable. Similarly, in some species bonding in lipid molecules alters and can be traced by mass spectroscopy. Understanding these processes and their ultimate goal which is protective dormancy underpins more accurate understanding of the natural world. It also provides information useful for breeding cold tolerant crops and garden plants.
Cold Damaged Plant
The rapidity of climate change is such that the protective mechanisms of plants and other organisms cannot respond with sufficient speed. Autumn in cool temperate regions, for example, is now extending as an increasingly warm period. This means that plants are not receiving the triggers necessary for acclimatisation in preparation for severe cold. Buds are commencing growth earlier in spring and now frequently are badly damaged by short bursts of deep cold. These buds cannot be replaced and as a consequence deciduous trees and shrubs in particular are losing capacities for survival.