How is mixed-species afforestation of poplar and Korean pine carried out?
The mountainous area of eastern Northeast China is the native home of Korean pine. Under natural conditions, many Korean pines have certain types of broadleaf tree species associated with them throughout their entire growth and development process, forming coniferous-broadleaf mixed forests. With the development and utilization of forest resources in the forest region, Korean pine forests have decreased over large areas, and the consumption of timber resources is very large. To restore forest resources as quickly as possible, the introduced larch and poplar varieties, although fast-growing and quick to form forests, are not conducive to the full utilization of forest land productivity and the restoration of ecological communities, and will also cause deterioration of forest soil conditions and reduce forest land productivity. Based on the characteristics and growth patterns of Korean pine, Ussuri poplar and David poplar, forming a fast-growing and high-yielding Korean pine-broadleaf mixed forest not only conforms to the current forestry development direction of advocating mixed forest establishment, but is also conducive to restoring the zonal climax community of the mountainous area of eastern Northeast China. Its main advantage is obtaining a reasonable stand structure that conforms to natural laws through human activity. In about 20 years, a large amount of poplar timber is obtained, and a Korean pine forest is formed.
I. Characteristics and growth patterns of Korean pine and Ussuri poplar
The biological characteristics and growth patterns of tree species are the main theoretical basis for our establishment of mixed forests. The main characteristics of the two tree species are briefly described as follows:
Korean pine is one of the main tree species in the mountainous area of eastern Northeast China and is the main component of the climax community in this region. It prefers well-drained, moist, fertile dark brown soil. In its juvenile stage it grows slowly and has strong shade tolerance, requiring a certain amount of shade. With increasing age, its shade tolerance gradually weakens, its demand for light gradually strengthens, and its growth rate accelerates. It grows best under a certain canopy density with appropriate regulation of its degree.
Ussuri poplar is a native tree species of the Northeast region. It is cold-tolerant and prefers moisture. It grows best on the lower and middle slopes of mountains in well-drained, deep and fertile soil. It is not shade-tolerant and requires sufficient light. The growth peak of Ussuri poplar comes relatively early. Height growth is fastest before 10 years, with the current annual increment reaching more than 1 m, and it begins to decline gradually after 10 years. Diameter at breast height grows fastest from 6-15 years, with the current annual increment reaching more than 1 cm, and then declines year by year. One rotation only requires about 25 years.
II. Theoretical analysis of mixed planting of Ussuri poplar and Korean pine
From the perspective of tree species characteristics, Ussuri poplar is an early fast-growing tree species and can become timber in 20-25 years, when its tree height, diameter at breast height and volume all reach their peak and it can be harvested and utilized. Korean pine grows slowly in its youth, and with increasing age its increment increases rapidly after 20 years. Mixed planting of the two can make up for each other's shortcomings and obtain greater benefits.
From the perspective of ecological conditions, both tree species like to grow in fertile, moist, well-drained soil and often grow in association. Ussuri poplar is light-demanding, while Korean pine needs shade in its youth. Therefore, forming a mixed forest in the initial stage of regeneration can both satisfy their respective ecological habits and avoid mutual competition. When the growth rate of Korean pine accelerates and its demand for light strengthens, it is exactly the harvesting period for Ussuri poplar, so harvesting can be carried out to regulate canopy density and release Korean pine. Because the fast-growing periods of the two tree species differ greatly, especially since Korean pine grows particularly slowly in the first 10 years and requires less nutrients, the two will not have adverse effects on each other in terms of nutrient demand.
According to production and management conditions, under the same site conditions, the growth of Ussuri poplar in pure forests and mixed forests is similar. Under the same site conditions, Korean pine in mixed forests is slightly lower in tree height, diameter at breast height and other aspects, but the difference is not great. It can thus be seen that if the density of Ussuri poplar is adjusted promptly and reasonably, it will not only not affect the growth of Korean pine, but can also achieve a double harvest of Korean pine and poplar.
In short, the mixed planting of Korean pine and poplar is feasible both in theory and in practice.
III. Mixed planting methods and density of poplar and Korean pine
Determining the mixed planting method and density should mainly consider the ecological habits of the tree species, growth patterns, silvicultural measures, rotation period, product specifications and other aspects. It is necessary both to create a good ecological environment to facilitate tree growth and to make full use of forest land productivity, while also facilitating the conduct and management of various production operations.
According to the ecological habits and growth patterns of the tree species, strip or clump mixed planting methods should not be used, because these two methods are not conducive to lateral shading of Korean pine, causing Korean pine to be under full light, and are also not conducive to the implementation of various management measures. The method of mixed planting between rows should be adopted, that is, planting Korean pine at the intersection points of the crossing lines of four adjacent poplars. To improve the preservation rate, the planting group method should be used, adopting the method of one-time planting and one-time final planting of large poplar seedlings and Korean pine. In this way, Korean pine is basically under lateral shade, while poplar, because of its rapid growth, quickly occupies the space and enters its fast-growing period.
According to the requirements for timber types and the characteristics of the tree species, poplar plantations should adopt a spacing of 3 m x 3 m or 6 m x 6 m. If too dense, the trees grow poorly, canopy closure occurs early, and the value of thinning timber is low; if too sparse, canopy closure does not occur for a long time, the standing volume per unit area within a certain period is also relatively low, and a large number of natural broadleaf trees will be mixed in, which is unfavorable for management.
IV. Analysis of management effects
In terms of wood quality, poplar grows rapidly, its trunk is straight, and its growth period is short. In about 20 years, about 200 cubic meters of timber per hectare can be obtained. At the same time, because of the role of poplar, it can change the phenomenon that Korean pine planted on bare land is prone to forking and improve the quality of Korean pine wood.
In terms of ecological benefits, while harvesting poplar, Korean pine that has grown for more than 20 years is retained, which is equivalent to shortening the cultivation period of Korean pine and giving full play to forest land productivity. At the same time, because of the vegetation cover, soil erosion is prevented, and the regional climax community of the mountainous area of eastern Northeast China, the Korean pine-broadleaf forest, can be formed.