Source: Water Conservancy Engineering Network Author: Wang Zheng Date: [2009- 1 1-27]

With the increase of landscaping area and the diversification of plant configuration in recent years, the shaping and pruning of garden trees has become an important topic. Because of the different kinds of trees, the methods of shaping and pruning vary widely. The author believes that no matter which method is adopted, landscape workers must follow the following five principles.

1. Follow the principle of biological characteristics of trees.

Different garden tree species have different growth habits, such as branching mode, dryness, stratification, apical dominance, germination ability, branching ability and so on. The biological characteristics of different tree species must be respected and adapted when pruning.

2. Follow the principle of tree life cycle growth and development.

In its life cycle, any garden tree always follows the growth process of centrifugal growth-centrifugal nudity-centripetal renewal. The purpose of pruning is to adapt to and control all kinds of growth and change laws in the life cycle of trees of different ages, prolong the life cycle of centrifugal growth, control the premature appearance of centrifugal nudity, maintain and create a new crown by using the centripetal renewal law, and maintain the roundness of its crown and the life cycle of the whole tree.

3. Follow the principle of correlation between the integrity of trees and the growth and development of various organs.

A tree is a living system, and different organs have their own functions, which are closely linked, mutually promoted and restricted. Tree pruning must follow the principle of adapting to the integrity of trees and the correlation between the growth and development of various organs, and coordinate and balance these relationships.

4. Follow the niche principle of each tree species in the plant community

Artificial ornamental trees are only a cluster in the early stage of planting. Only through long-term growth and cultivation and the role of the external environment can a plant community with a certain species composition and a certain appearance be gradually formed. All kinds of trees tend to form their niches in plant communities. In the process of pruning, we must pay attention to the plant community structure, and carry out rich and diverse treatments in appearance, color and lines, which is artistic and ornamental. According to the requirements of the overall structure of the community, reasonable shaping and pruning are carried out.

5. Follow the principle of the pruning reaction law of garden trees.

The pruning methods of garden trees in winter mainly include short cutting, shrinking cutting, thinning and slow release. Because the growth potential, growth position, growth posture and pruning intensity of branches are different, their pruning reactions are also very different. When pruning, we must deeply observe and study the above comprehensive factors, follow the law of tree pruning reaction, and prune carefully to achieve the ideal pruning purpose. In addition, the influence of site conditions and surrounding environment on tree pruning reaction must be considered.

In a word, it is necessary to promote the growth of trees as a whole and restrain the growth of trees locally through reasonable pruning, so as to improve the ecological effect of individual and group garden trees.

Generally speaking, the pruning of garden trees can be divided into winter pruning and summer pruning.

1, winter pruning. Also known as dormant pruning (generally 65438+February to February of the following year). It is best to plant trees with poor cold tolerance in early spring to avoid cold wounds. Deciduous trees generally shed their leaves in winter and germinate in the next spring. Pruning in winter has great influence on crown formation, new shoot growth and flower and fruit branch formation of ornamental trees.

2, summer pruning. Also called growth pruning (usually from April to 10). From bud germination to defoliation, that is, before the new bud stops growing. The specific pruning date should also be different according to the local climatic conditions and tree species characteristics. For example, when pruning flowering fruit trees, it is necessary to cut off inner branches, upright branches, useless branches, excessively dense cross branches, weak drooping branches, pests and diseases, etc. , so that nutrition is concentrated on the backbone branches, which is conducive to flowering and fruiting. Hedge pruning in summer mainly keeps it clean and beautiful. Other garden trees are trimmed into different shapes according to functional requirements.

Third, different seasons have different requirements for pruning garden plants.

The growth and development of garden trees change with the seasons. Only by correctly grasping the pruning period can we ensure the smooth realization of the purpose of management and protection. The pruning method was described in the previous work, which mainly combined the techniques of brushing teeth, coring, pruning and tillering to carry out large-scale pruning during the dormant period of flowers and trees to avoid excessive juice loss and affect the growth potential.

Spring is the growth period or flowering period of flowers and trees, trees store less nutrients, and flowers and trees themselves are in a period of consuming nutrients. At this time, pruning is prone to premature aging, but it will inhibit the growth of trees. For example, the flower buds on the branches of varieties that bloom in early spring were differentiated last year, so it is not advisable to cut them short in spring, and they should be pruned behind the flowers, which is harmful to umbrella, moss-core umbrella, peptone umbrella and other foliage trees. /2 The terminal buds are tender and the concentrated buds are thinner. Trees with strong germination ability and many adventitious buds should be peeled in time, such as winter jasmine and hibiscus in the snow.

In summer, with the increase of rain, the illumination and ventilation are poor, which makes nurseries, bushes and flowers dense and humid, and easy to rot. It is necessary to remove dead branches and rotten leaves in time, prune too slender branches and flowering branches, and improve the growing environment.

Autumn is the storage period of plant nutrients and the active period of root growth, so we should try our best to avoid pruning woody plants, because the knife edge is easy to cause decay and cannot enter dormancy, which leads to the weakening of trees.

Winter is the season of large-scale pruning of plants, and deciduous flowers and fruits are generally pruned after defoliation. Evergreen flowers and fruits are pruned before germination. Pruning in winter has an important influence on crown composition, new shoot growth and flower and fruit branch formation. Young trees are mainly shaped, and shaped foliage trees are mainly used to control the growth of lateral branches and promote the vigorous growth of main branches. Shape the ornamental fruit trees, and focus on cultivating the trunk and main branches of the trees to make them shape and bloom as soon as possible.

According to the growth law of evergreen trees, April-10 is the active period, and pruning is appropriate at this time to avoid pruning in winter; And 165438+ vertical year10-March is the dormant period. If the branches and leaves are cut off, there is a danger of freezing injury. It is expected that cuttings can be obtained from June to July for cutting propagation.

For flowers and trees, fruit trees, garden trees and street trees, competitive branches should be controlled and pruned at any time regardless of season, such as internal branches, long branches, upright branches, branchlets, pests and diseases, drooping branches, etc.

The periodic changes of external environmental conditions are not exactly the same every year. Fluctuation of meteorological factors (such as temperature and rainfall). The process of tree phenology can be changed in a certain range in different seasons and using different cultivation techniques every year. Different trees and varieties have different phenology, especially deciduous trees and evergreen trees.

(1) Annual Cycle of Deciduous Trees

Because of the climate in temperate regions, there are four seasons in a year, so the seasonal change of phenology of deciduous trees in temperate regions is particularly obvious. The annual cycle of deciduous trees can be clearly divided into growth period and dormancy period. That is, it begins to sprout and grow in spring and grows before defoliation in autumn. The growth period of adult trees is characterized by vegetative growth and reproductive growth.

Trees are dormant after defoliation until the next year to adapt to unfavorable environmental conditions such as low temperature in winter. There is a transition period between growth period and dormancy period. That is, from growth to dormancy and from dormancy to growth. Although these two transitional periods are short, they are very important.

In these two periods, some trees often do not adapt to cold and drought resistance and changes in external conditions, which often lead to harm. This is particularly evident in continental climate areas. The four periods of phenology of deciduous trees are described as follows.

① dormant period to growing period

This period is before the trees germinate, that is, the average temperature of the day is stable above 3℃, and the germination stops when the buds expand. The release of tree dormancy is usually marked by bud germination. And physical activity is earlier.

Trees need certain temperature, moisture and nutrients to change from dormancy to growth. When there is suitable temperature and humidity, after a certain period of time, the sap begins to flow, and some tree species (such as walnuts and grapes) will have obvious "bleeding".

The temperature required for bud expansion of northern tree species is relatively low. When the average temperature of the day is stable above 3℃, it can reach a certain accumulated temperature after a certain period of time. Trees growing in warm areas need higher accumulated temperature for bud expansion. The accumulated temperature required for flower bud expansion is lower than that for leaf bud. When the tree stores enough nutrients, the buds expand early and orderly, and quickly enter the growth period. During this period, the cold resistance of trees is reduced, and when the temperature drops suddenly, the budding flower buds and southwest branches are vulnerable to freezing injury. Dry areas are also prone to dead branches. ② Growth period. From tree germination to defoliation, including the whole growing season. This period occupies a long time in a year. During this period, the trees will change obviously with the seasons. Such as budding, spreading leaves, flowering and fruiting, forming many new organs (such as leaf buds or flower buds). Germination is usually used as a sign that trees begin to grow. In fact, roots grow before germination. Different trees experience a series of life activities every year according to their fixed phenological order under different conditions during the growing period. Different tree species experience different phenology in different order. Some sprout flower buds first, and then unfold leaves; Others germinate leaf buds first, unfold the leaves separately, and then form flower buds and bloom. The beginning, end and duration of each phenological period of trees also vary with species and varieties, environmental conditions and cultivation techniques.

③ Growth turns into dormancy. The natural shedding of leaves in autumn is an important sign that trees enter dormancy. Before normal defoliation, new shoots must undergo tissue maturation process to survive the winter smoothly.

As early as the new shoots began to thicken from bottom to top, they gradually began to lignify and stored nutrients in tissues (mostly carbohydrates such as starch and soluble sugar and a few nitrogen compounds). This accumulation process continues to strengthen after the new shoots stop growing, which is beneficial to the differentiation of flower buds and the thickening of branches.

For trees with fruits, after picking mature fruits, the nutrient accumulation is more prominent until the leaves fall. Shortening of sunshine in autumn is the main factor that causes trees to fall into dormancy, followed by the decrease of temperature. Before defoliation, a series of changes occurred in leaves, such as the weakening of photosynthesis and respiration, the decomposition of chlorophyll, and the transfer of some nitrogen and potassium components to branches. Finally, the petiole base forms delamination and shedding. After defoliation, with the decrease of temperature, the contents of fat and tannin in tree cells increased. The increase of cell fluid concentration and protoplasm viscosity, the formation of plasma membrane lipid layer and the decrease of permeability are beneficial to the cold resistance and overwintering of trees.

The above shows that premature defoliation is not conducive to nutrient accumulation and tissue maturity. Drought, flood, disease, etc. It will cause early defoliation and even regrowth, which is very harmful. If the leaves don't fall, it means that the trees are not ready for wintering and are prone to freezing injury and dead branches. Sooner or later, different organs and tissues of trees will go into dormancy. Most temperate trees stop growing in late summer and early autumn and gradually enter dormancy. Some buds go to sleep long before the leaves fall. Generally, branchlets, thin and short branches and early buds enter the body early, and the buds at the lower part of long branches enter dormancy as early as the growing season. The inhibition can be relieved by cutting off the top of the new shoot and judging whether it is dormant by bud cutting reaction. Cutting buds do not germinate, indicating that they are in a dormant state. For example, cuttings germinate, but grow weakly.

And soon stopped growing, indicating that the degree of dormancy is still shallow. If the cut bud germinates easily and continues to prolong its growth, it means that it has not yet entered dormancy. The cortex and xylem enter dormancy early, and the cambium is the latest, so the cambium is easy to freeze when it encounters cold current in early winter. The main branches and trunks on the ground enter the dormant period late, and the root neck is the latest, which is vulnerable to freezing injury. Trees of different ages will go into dormancy sooner or later. Young trees enter dormancy later than adult trees. Trees that have just entered dormancy are in the initial dormancy (shallow dormancy) state, and their cold tolerance is not strong. When the temperature rises intermittently, their dormancy will be reversed, and when the temperature drops suddenly, they will often be frozen.

④ Relative dormancy period. The dormant period of deciduous trees is from normal defoliation in autumn to growth in the following spring (usually based on germination). Local bud dormancy appeared earlier.

During the dormant period of trees, although there is no growth phenomenon for a short time, various life activities are still going on in the body, such as respiration, transpiration, bud differentiation, root absorption, nutrient synthesis and transformation. These activities are only carried out weakly and slowly, so to be exact, dormancy is only a relative concept.

Deciduous dormancy is an adaptability of temperate trees to low temperature environment in winter during evolution. Without this characteristic, the growing young tissues will be damaged by early frost, which is very sad for winter.

(2) Annual cycle of evergreen trees

Evergreen trees do not shed their leaves all year round, but the life span of leaves is very long, mostly from one year to many years. Only some old leaves fall off every year can new leaves grow, so the whole tree has green leaves all year round.

Evergreen conifers: the needles of Pinus can live for 2 ~ 5 years, and the leaves of Cunninghamia lanceolata can live for 3 ~ 10 years. The leaves of Taxus chinensis can survive for 6 ~ 10 years. Most of their old leaves fall off in winter and spring, especially on windy days. Old leaves of evergreen broad-leaved trees often fall off gradually before and after germination and leaf spreading. The deciduous leaves of evergreen trees are mainly aged leaves that have lost their normal physiological functions, and there is a phenomenon of alternation between old and new. Evergreen conifers, tropical and subtropical evergreen broad-leaved trees growing in the north, have extremely complex phenological dynamics of their organs. The climate of various trees is very different, so it is difficult to generalize. Some trees can branch many times a year, such as: citrus can have spring shoots, summer shoots, autumn shoots and winter shoots; Some trees can blossom and bear fruit many times a year, or even bear fruit once a beat, such as kumquat; Some trees on the same plant can see several phenological overlaps and interlaces at the same time; The fruit of some trees has a long development period and often takes several years to mature. Trees near the equator have no four seasons, it rains all year round, and they can grow all year round, without dormancy, but they also have growth rhythms. In monsoon forest, which is a little far from the equator, because of the obvious dry and wet seasons, most trees grow and bloom in the rainy season and shed leaves in the dry season, and are forced to sleep due to high temperature and drought. Evergreen broad-leaved trees in tropical high altitude areas are also forced to sleep because of low temperature.