Deciduous leaves and evergreen leaves are two different ways of surviving unfavorable seasons, e.g. dark and cold winters. Deciduous trees are often connected to localities with high soil nitrogen level and low C/N ratios. They do not need to invest in protection against frost and herbivore damages during winter, but have to produce new leaves every spring. Evergreen trees and shrubs are often growing on localities with low nutrient level and because they keep their leaves during winter, they have to produce substances, often carbon-based, to protect against frost and insect attacks. They are also conservative and are often slow-growing dependent on competition from other plants about light, water and nutrients. One more advantage is that they are able to carry out photosynthesis during winter, although at a rather low rate. Some plants e.g. Vaccinium myrtillus, have green stems that can even carry out winter photosynthesis. 

The answer on the question is, however, that the evergreen leaves are not connected to the annual cycle like the deciduous leaves, and may therefore be able to be repleced also during the active period of the year, but like other woody species they go through winter dormancy to protect against witer damages.

Hi Adnan,

My answer is far less technical than those above, but there is still validity in its simplicity. Deciduous trees are by nature tied to a twelve month cycle, where as evergreen coniferous species are generally not. The tree species that really holds many secrets concerning this question is Cryptomeria Japonica, the leaves change colour from light green in the spring, dark green summer, brown winter and back to green again in the spring without loosing their leaves. You have to wonder at what bio-chemical strategies this species is using by changing the chlorophyll pigments according to season.

Deciduous leaves and evergreen leaves are two different ways of surviving unfavorable seasons, e.g. dark and cold winters. Deciduous trees are often connected to localities with high soil nitrogen level and low C/N ratios. They do not need to invest in protection against frost and herbivore damages during winter, but have to produce new leaves every spring. Evergreen trees and shrubs are often growing on localities with low nutrient level and because they keep their leaves during winter, they have to produce substances, often carbon-based, to protect against frost and insect attacks. They are also conservative and are often slow-growing dependent on competition from other plants about light, water and nutrients. One more advantage is that they are able to carry out photosynthesis during winter, although at a rather low rate. Some plants e.g. Vaccinium myrtillus, have green stems that can even carry out winter photosynthesis. 

The answer on the question is, however, that the evergreen leaves are not connected to the annual cycle like the deciduous leaves, and may therefore be able to be repleced also during the active period of the year, but like other woody species they go through winter dormancy to protect against witer damages.

Deciduous and evergreen trees in winter have not an identical strategy.Hardwood to deal with the cold of winter, their leaves are deciduous.Sugar in their broad leaves of the trees are injected.The sugar in winter acts like antifreeze.Throughout the year there are a few minor fall softwoods. Sugar back into the tree.

Je me permet d'ajouter sur la longevite des feuilles aux tropiques.

par exemple, chez Pholidota pallida, espèce d'orchidée d'Asie, les feuilles vivent facilement trois ans, et chez l'autre espèce du même genre(Pholidota chinensis) elle se chèche dans un an; alors que les conditions de vie sont très proches (comme si le sapin et le chene sont pas loin l'un de l'autre). 

Suite à votre question je propose d'indiqué toujours l'âge de la plante et de ces organes vegetativfs, car si vous étudier liane de vigne ou de Vanille, l'aproche à longitité n'est pas le même. Cordialement à tous.

Senescence is linked to adaptation and evergreen variants are often found. Leaf shedding occurs after a critical accumulation of signalsand several apoptotic effectors are involved. You should then specify a genus and a climate for giving value to leaf longevity. Continous growth versus seasonal is a matter of dominance but often evergreens are slow growing and late to repoduce by seeds but more invasive for their shade.