Evergreen tree

Evergreen tree

This data is reviewed by the project of data compilation and application of Science Encyclopedia of science popularization in China.

Most of the pines and cypresses belong to evergreen trees (some belong to deciduous trees, such as Larch). Evergreen trees are evergreen all year round, but it does not mean that they will not lose leaves. The difference between evergreen trees and deciduous trees is that deciduous trees will lose most or all of their leaves in autumn and winter. Evergreen trees have fallen leaves in all seasons, but at the same time, they also have new leaves. Some leaves of pine and cypress families will stay on the trunk and will not fall when they are old or yellow (such as Chinese fir).

It is not only conifers and cypresses that can grow green, but also many broad-leaved trees are evergreen (such as coconut, black heart stone, green oak, dillentao, mulberry, banyan, Melaleuca, wax apple, etc.)

trim

There is no real dormancy period in evergreen trees. Roots, branches and leaves are active and metabolized all year round, and the nutrients produced by leaves are not completely used for storage. When the branches and leaves are cut off, the nutrients are also lost, which also has a great impact on the growth and nutritional status of trees. Therefore, the intensity of pruning should be controlled, the crown should be kept intact as far as possible, and only the dead branches, over dense branches and skirt branches on the trunk should be properly treated without excessive pruning.

Evergreen conifers are not resistant to heavy cutting, and usually only remove the main branches that are too dense, and remove or retract the main and side branches that disturb the tree shape. In addition to special plastic surgery, we should protect the central leadership from injury. For evergreen broad-leaved trees, the central leading trunk can be adopted, and the lateral branches can be removed if the lateral branches are too dense. The species with obvious rotation (e.g. Pinus thunbergii) have strong dryness. It is necessary to protect the top shoot, cut off the erect, overgrown and disturbed branches, and adopt the method of "thinning". For the species with no obvious rotation (such as Platycladus orientalis, Sabina vulgaris, Cedrus deodara, Sabina chinensis, etc.), it is necessary to deal with the main shoot competition branches (cutting or pinching) in time.

Root system

Here are five evergreen trees, including mango, guava, litchi, lime and loquat. The most interesting root system is guava.

Guava leaves begin to fall in early March and grow new leaves at the same time. It has been proved that it is the best plant to study the root system of plants. The light red roots grow strongly and can be easily distinguished from the gray alluvial soil (such as the soil in Pusa). It has a rich surface root system and a large number of branches that grow down to the permanent water level. At the beginning of hot weather, the whole root system of guava is active. The main area of root activity is in the fine sand layer 2.15-3.15 meters above the surface. When the hot weather comes completely, the absorbing roots near the surface of guava will dry up, and the root activity is limited to the deeper soil. On June 3, 1922, the monsoon climate began. On June 5, 48 hours after the rain, the surface roots were exposed. A large number of new roots were found 0.43-3.6 meters below the surface, and the longest roots could extend to 1 cm. As the early rain makes the soil moist, the areas where roots stop growing begin to produce new roots from top to bottom until the whole root system is active. After July, when the groundwater level rose, the situation changed. With the aggravation of water invasion, the deep roots began to enter a dormant state. By August 25, 2008, root activity was mainly confined to the area of 74 cm in the surface layer of soil, and basically lost below 1 m. In the late rainy season, active roots can avoid suffocation through strong aerotaxis. In October, with the decrease of subsoil water level and the improvement of subsoil aeration, the root system will have some interesting changes. In November, the underlying roots will become active again, which depends on the monsoon rainfall. By November 1921, due to less rainfall and little rise of groundwater level, the deep roots were active up to 4.6 meters. In the second November of 1922, the groundwater did not rise under the normal climate.

Although guava can grow through deep roots in hot season, it is more important to maintain the activity of surface roots by irrigation. For example, in the hot season of 1921, through surface irrigation, the leaf size increased from 9.1 cm × 4.0 cm to 11.6 cm × 5.0 cm, and the color also improved significantly. The root system and active root growth of mango, litchi, lime and loquat were similar to those of guava. These tree species can grow vertical roots from the surface of roots, but the roots of litchi and lime can not penetrate into the deep soil. The four tree species showed obvious aerotropism in the late rainy season.

compare

Requirements: evergreen and deciduous tree leaves have two kinds of leaves, one is evergreen, one is deciduous.

Operation: compare the leaves of evergreen tree and deciduous tree, touch and have a look, find out the difference between the two kinds of leaves.

Record: use symbols to record the characteristics of two different leaves. (thick, dark and glossy leaves).

Summary: no matter what tree we see, even if we don't know it, as long as its leaves are thick, dark and glossy, we can judge that it is an evergreen tree.

Phenological characteristics

The phenological dynamics of various organs of evergreen trees are very complex, which is characterized by no obvious leaf dormancy period. It is not that the leaves do not fall in the tree crown every year, but that the old leaves fall off year by year before and after the new leaves are drawn out in spring. Moreover, the leaf age of leaf fall off is different for different tree species, generally more than one year. On the whole, the crown is evergreen all the year round. This kind of defoliation is not to adapt to the changed environmental conditions, but the physiological phenomenon of the alternation of new and old leaves after the leaves aged and lost their normal functions. The phenological processes of different tree species, even the same tree species in different ages and different climatic regions are also very different. For example, in the southern zone of Pinus massoniana distribution, shoots are drawn two or three times a year, while in the northern zone, shoots are drawn only once a year; young Camellia oleifera can shoot in spring, summer and autumn, while adult Camellia oleifera only shoots in spring. Another example is the phenology of citrus, which is roughly divided into germination, flowering, branch growth, fruit development and maturity, flower bud differentiation, root growth, relative dormancy and other phenological periods. The phenological items of citrus are similar to those of deciduous trees, but the actual process is different. For example, the shoots can be sprouted many times in a year (spring, summer, autumn and winter), and there is a considerable interval between the shoots. Some tree species can blossom and bear fruit many times a year, such as lemon, tangerine, etc. Some tree species even take a shoot to bear a fruit, such as kumquat, while four season and month laurel can blossom all year round. Some species of the same tree at the same time flowering, shoot, fruiting, flower bud differentiation and other phenophase overlap phenomenon, such as Camellia oleifera. Some tree species have a long fruit growth period, such as Fuling summer orange, which blooms in spring and ripens at the end of the next spring; Cinnamomum cassia blossoms in autumn (September October) and ripens in the next spring. The fruit growth and maturity of Camellia oleifera is also over two years.

Chinese PinYin : Chang Lv Shu