In botany, an evergreen plant is a plant that keeps leaves all year round . Here, the single leaf of evergreen plants lasts for more than one vegetation period . However, a functionally evergreen plant can replace the leaves several times a year in a constant process (alternating evergreen), although the tree retains abundant, evenly green leaves at all times. If the leaves are more durable and last longer than one to two years, these plants are referred to as overwintering evergreen or year-round evergreen and permanent evergreen , permanent green .
The counterpart are deciduous or rain - and spring , summer , or evergreen plants that lose all of their leaves for part of the year .
A transitional form are semi-evergreen , semi, some evergreen and semi-deciduous plants, here they can be,. B. shed their leaves for a short time in late winter and rejuvenate relatively quickly or be completely bare only in very severe winters. Plants can also be considered semi-evergreen if they lose most, but not all, of their leaves for part of the year. Sometimes they are called semi-evergreen because of certain situations that may arise. For example in the event of droughts, certain weather and climatic conditions and because of certain insects. They can therefore be designated as facultative deciduous plants.
Semi -evergreen plants are sometimes also referred to as those that shed their leaves after the winter when they sprout, i.e. overwintering evergreens . These are then, as in principle also the permanently green plants, called wintergreen .
Different types of evergreen and semi-evergreen plants can also be distinguished based on the amount of rainfall: wet, moist or dry, arid.
The shelf life of evergreen plants varies from several months to a maximum of 45 years for the long-lived pine ( Pinus longaeva ). Species with a leaf shelf life of over five years are rare.
Welwitschia , an African bare-seeded plant that has only two leaves, is a special case . However, these grow continuously over the entire lifetime of the plant. The end of the leaf dies and weathers. The shelf life of a piece of leaf is between 20 and 40 years.
In warm tropical regions, most of the plants in the rainforest are evergreen. They replace their leaves piece by piece over the year, depending on how the leaves age and fall off. Plants in dry spell climates can be evergreen or deciduous. In warm temperate climates , most of the plants are evergreen. Fewer evergreen plants are found in cold temperate climates, as few evergreen plants can withstand temperatures below −25 ° C. The most common evergreen plants in these areas are the conifers .
In areas where there is a reason for plants to be deciduous, be it because of a cold season or a dry season, being evergreen is mostly an adaptation to low nutrient levels. Deciduous trees lose nutrients each time they shed their leaves, which they have to pull out of the ground when the new leaves are formed. When only few nutrients are available, evergreen plants have an advantage, even if their leaves or needles have to withstand cold or drought and even if they cannot photosynthesize as efficiently. In warm climates, species such as the pine or cypress can get by with poor soils. In the taiga or in boreal forests , organic material decomposes slowly due to the cold. The nutrients from the shed leaves are therefore not available again quickly. This also gives preference to evergreen plants.
In temperate climates, evergreen plants favor themselves: the shed needles (or possibly leaves) of evergreen plants have a higher carbon-nitrogen ratio than those of deciduous trees. This leads to a more acidic soil and a lower nitrogen content. This makes it harder for deciduous trees to survive.
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