Asilver fir shoot showing three successive years of retained leaves.Cupressus sempervirens (Mediterranean cypress), an evergreen tree.
Inbotany, anevergreen is a plant which hasfoliage that remains green and functional throughout the year.[1] This contrasts withdeciduous plants, which lose their foliage completely during the winter or dry season. Consisting of many different species, the unique feature of evergreen plants lends itself to various environments and purposes.
The longevity of individual leaves in evergreen plants varies from a few months to several decades, up to a maximum of 45 years in theGreat Basin bristlecone pinePinus longaeva.[4]
Evergreen and deciduous species vary in a range of morphological and physiological characters. Generally, broad-leaved evergreen species have thicker leaves than deciduous species, with a larger volume ofparenchyma and air spaces per unit leaf area.[5] They have larger leaf biomass per unit leaf area, and hence a lowerspecific leaf area. Construction costs do not differ between the groups.[citation needed] Evergreens have generally a larger fraction of total plant biomass present as leaves (LMF),[6] but they often have a lower rate of photosynthesis.
Asouthern live oak inSouth Carolina during winterEcuadorian Amazon rainforest. This humid tropical forest has warm temperatures and receives rainfall year round. Vegetation consists of a majority of broadleaf evergreen species.[7]
Deciduous trees shed their leaves usually as an adaptation to a cold or dry/wet season. Evergreen trees also lose leaves, but each tree loses its leaves gradually and not all at once. Mosttropical rainforest plants are considered to be evergreens, replacing their leaves gradually throughout the year as the leaves age and fall, whereas species growing in seasonally arid climates may be either evergreen or deciduous. Most warmtemperate climate plants are also evergreen.[citation needed] In cool temperate climates, fewer plants are evergreen. In such climates, there is a predominance ofconifers because few evergreenbroadleaf plants cantolerate severe cold below about −26 °C (−15 °F).[clarification needed][citation needed] In addition, evergreen foliage experiences significant leaf damage in these cold, dry climates. Root systems are the most vulnerable aspect of many plants. Even though roots are insulated by soil, which tends to be warmer than average air temperatures, soil temperatures that drop too low can kill the plant. The exact temperature which evergreen roots can handle depends on the species, for example,Picea glauca (White Spruce) roots are killed at −10 °F (−23 °C).[8]
In areas where there is a reason for being deciduous, e.g. a cold season or dry season, evergreen plants are usually an adaptation of low nutrient levels. Additionally, they usually havehard leaves and have an excellent water economy due to scarce resources in the area in which they reside.[9] The excellent water economy within the evergreen species is due to high abundance when compared to deciduous species,[9] whereas deciduous trees lose nutrients whenever they lose their leaves. In warmer areas, species such as somepines andcypresses grow on poor soils anddisturbed ground.[citation needed] InRhododendron, a genus with many broadleaf evergreens, several species grow in mature forests but are usually found on highly acidic soil where the nutrients are less available to plants.[citation needed] Intaiga orboreal forests, it is too cold for theorganic matter in the soil to decay rapidly,[10] so the nutrients in the soil are less easily available to plants, thus favoring evergreens.[11]
In temperate climates, evergreens can reinforce their own survival; evergreen leaf and needle litter has a higher carbon–nitrogen ratio than deciduousleaf litter, contributing to a higher soil acidity and lower soil nitrogen content. This is the case with Mediterranean evergreen seedlings, which have unique C and N storages that allow stored resources to determine fast growth within the species, limiting competition and bolstering survival.[12] These conditions favor the growth of more evergreens and make it more difficult for deciduous plants to persist. In addition, the shelter provided by existing evergreen plants can make it easier for younger evergreen plants to survive cold and/or drought.[11][13][14]
Evergreen plants can have decorative as well as functional uses. In months where most other plants are dormant, evergreens with their sturdy structure, and vibrant foliage are popular choices to beautify a landscape. Additionally, evergreens can serve as awindbreak, stopping heat loss from buildings during cold months when placed on the (latitude/hemisphere specific) side of a structure. e.g. the northwest in Virginia, USA.[8]
Evergreens have long heldcultural significance across many societies. they are commonly used as symbols oflife,endurance, and renewal, because they remain green through winter.[15]
^Villar, Rafael; Ruiz-Robleto, Jeannete; Ubera, José Luis; Poorter, Hendrik (October 2013). "Exploring variation in leaf mass per area (LMA) from leaf to cell: An anatomical analysis of 26 woody species".American Journal of Botany.100 (10):1969–1980.doi:10.3732/ajb.1200562.PMID24107583.
^Woodward, Dr. Susan L."Amazon Rainforest".Department of Geospatial Science, Radford University. Archived fromthe original on 2024-12-11. Retrieved2024-11-16.
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