Undeniably, exotic tree species have played an important role in enriching the diversity of landscaping tree species, urban greening landscape diversity and improving the ecological environment of urban green space. However, the potential dangers brought by these tree species should not be underestimated. How to correctly play the role of exotic tree species in landscaping construction and avoid its harm is a problem that practitioners need to think about.
Advantages of exotic tree species
1. Enrich the biodiversity of greening
Exotic tree species increase the species of introduced plants and enrich the diversity of urban greening tree species.
For example, in the past, there were few evergreen conifers and broad-leaved trees in the urban greening of Inner Mongolia Autonomous Region, and the effective study of introducing exotic tree species in many directions effectively eased the passive situation of long-term shortage of local greening tree species resources.
At the same time, exotic tree species can also be used as breeding germplasm resources to cross with local tree species, introducing useful genes into local tree species to be improved, and cultivating excellent varieties with strong adaptability and high ornamental value.
2. Enrich the landscape diversity of urban green space.
The unique ornamental value of exotic tree species can meet people's aesthetic psychological needs of "novelty, strangeness and strangeness" of garden plants, and it has rich landscape diversity.
For example, 1983 Ligustrum lucidum introduced from Germany has become an important color-leafed tree species in urban greening in China. Magnolia grandiflora, native to the eastern part of North China, has become a common excellent foliage and flower viewing tree species in. Of course, in this process, a large number of China plants also enriched the diversity of western landscapes.
3. Improve the urban ecological environment
Exotic tree species not only beautify the city, but also play an important ecological function.
For example, oleander, which is native to tropical and subtropical areas such as India and Iran, has become an excellent pollution-resistant and windproof tree species in the Yangtze River basin in China after years of planting.
Disadvantages of exotic tree species
1. Poor adaptability
Many exotic tree species can adapt well under normal climatic conditions, but once they encounter extreme weather, they are prone to large-scale disasters or deaths, and their resistance to natural disasters is far less than that of native tree species, which is one of the reasons why the greening industry has vigorously promoted native tree species in recent years.
2. It is easy to cause pests and diseases.
During the introduction of some exotic tree species, due to lax quarantine or other technical reasons, they often bring pathogenic bacteria or pests that are not found in China or the region, resulting in serious pests and diseases, and some native tree species are infected or injured and eventually die, which seriously threatens the local community structure and ecosystem.
3. Lead to biological invasion
Some exotic tree species are easy to spread into invasive tree species under suitable climate, soil, water and transmission conditions because of their strong ability of reproduction and transmission. Invasive tree species inhibit the survival of native tree species through competition, exclusion and hybridization, which leads to the gradual reduction of the species and quantity of native tree species, even endangered or extinct, seriously threatening the original natural ecosystem.
4. Intensify ecological damage
The invasion of exotic tree species will correspondingly change the ecological process of the green space system, such as the increase of water consumption and the intensification of soil impoverishment, which will eventually lead to the simplification and degradation of the ecosystem and reduce the stability of the green space system and its self-regulation ability to resist natural disasters.
How to introduce exotic tree species correctly?
First of all, in the planning of greening plant allocation, we should control the proportion of exotic species, so that native species are the main ones, supplemented by exotic species. In other words, exotic trees in the garden should always be in a secondary position, just as an ornament.
Secondly, some basic principles should be followed in planning exotic tree species.
1. Follow the law of plant introduction.
The introduction of exotic tree species must follow the law of plant introduction. Generally, suitable provenances should be selected according to the main environmental conditions such as geographical location, topography, landform, climate, soil and vegetation distribution. At the same time, the geographical distribution, origin center, habitat conditions and historical ecology of tree species are analyzed to understand the performance and introduction history of introduced exotic tree species in the local or nearby areas.
2. Assess the invasion risk of tree species
Through the analysis of various characteristics, environmental factors and human factors of exotic tree species, the influence of exotic tree species on introduced ecosystem is evaluated and predicted, so as to minimize or avoid the harm of exotic tree species to urban green space system.
3. Prevent diseases and insect pests caused by exotic tree species.
Exotic tree species are the main carriers of dangerous insects and microorganisms, and they are hidden. Therefore, before the introduction of tree species, the information of pests and diseases in their origin should be widely collected and the possible harm to the introduction of green space system should be analyzed. Even for exotic tree species with low risk of harm, quarantine, prevention and control and pest monitoring should be further strengthened during introduction.
Try planting
After determining the introduction object, a small amount of trial planting should be fixed at first, and attention should be paid to isolation and protection during the process. The contents of observation and identification mainly include growth adaptability, whether it is invasive, whether it carries or is susceptible to pests and diseases, etc.
At the same time, the trial planting must have enough observation and identification period to avoid ignoring some hidden symptoms. Generally speaking, the observation of annual plants should not be less than 1 growth period, and perennial plants should not be less than 2 years.