Fast-growing is a distinctive feature of Paulownia. Good varieties are selected and managed well, and they can be grown in five or six years. There are obvious differences in the growth rate of Paulownia under the same site conditions. The tallest Paulownia tree in my country that we have seen in Sichuan is 75 years old, with a height of 44 meters, a total volume of 22.48 cubic meters, and an average annual volume growth of 0.3 cubic meters. Therefore, the growth of Paulownia is difficult to compare with other tree species.
Paulownia is a deep-rooted tree species with well-developed lateral roots. The distribution of Paulownia roots is closely related to soil texture, fertility and moisture. The distribution of roots of 3-year-old Paulownia is relatively shallow. Paulownia has a well-developed root system, with thick rhizomes, thin root ends, and large taper.
The tips are mostly distributed in clusters or bifurcated branches. In the thicker diameter of the transducing root or base, the root system is feathery, clustered, and sometimes juxtaposed. Another characteristic of the paulownia root system is that the absorbing roots are very thick, generally 1-5 mm thick, and some absorbing roots can be extended to 60 cm. The root hairs are cotton-like, with soil particles attached to them, and the development and distribution of the root system are greatly affected by the groundwater level, soil physical properties and nutrients.
The crown growth of Paulownia is continued by the accumulation of branches formed every year. Studies on the crown structure of Paulownia and its influence on the growth of the main stem have shown that there is a close correlation between the crown width of paulownia and the growth of diameter at breast height. Have a greater impact. In the Guanzhong area of Shaanxi, the crown width of Paulownia trees generally grows about 1 meter in the year after planting.
Where the site conditions are good, the branches can be branched more than 1.5 meters, and the poor ones are only 0.5-0.6 meters. From the second year to the third year, the crown width expanded rapidly, and the annual growth was about 1.5-2.0 meters. In 3-4 years, extra long branches are drawn from the middle and lower parts of the big branches to extend the main trunk to form a two-layer crown. After 5-6 years, the crown growth slowed down year by year.
A large number of analyses on the growth process of paulownia trunks show that the speed of growth at breast height and volume, the arrival of peak growth and the length of the duration depend on the type of Paulownia and the site conditions for growth. The stem-type development of Paulownia is divided into three types, namely, continuous dry type, intermittent dry type and no dry type. Under the climatic conditions of the natural distribution area of Paulownia, the annual growth law and monthly growth law of diameter at breast height are generally single-peak curves.