*2.5.4 Comprehensive evaluation of vegetation and soil system of* H. ammodendron *plantation*

Through principal component analysis, the overall information of the original 18 variables were replaced by the first 5 principal components, contribution rate was 90.91% (**Table 8**). Among them, the Eigen Value of the first principal component was 7.531, which accounted for 41.84% of the total variation and formed a correlation with above-ground biomass (0.900), crown projected area (0.874), basal stem diameter (0.831), and tree height (0.830) etc.. Therefore this principal component could represent the growth characteristic index of vegetation. The Eigen Value of the second principal component was 3.486, which accounted for 19.37% of the total variables. The chlorophyll mass fraction (0.918) had a greater positive effect on it, and the cell damage rate (0.858) had a strong negative correlation, so this

*Characteristic on the Stability of* Haloxylon ammodendron *Plantation… DOI: http://dx.doi.org/10.5772/intechopen.99050*


#### **Table 7.**

*The comprehensive evaluation on coupling coordination of vegetation and soil system of* H. ammodendron *plantations at different chronosequence stage.*

principal component mainly could reflect the physiological characteristics of the vegetation. The SMC (0.947) had the greatest positive effect on the third principal component, so the principal component could mainly reflect the physical characteristics of soil. The variable related to the fourth principal component was sHN (0.808), so this principal component could represented the nutrient characteristics of soil. The variable which had the greatest negative effect on the fifth principal component was potassium mass fraction of vegetation (0.805), so this principal component could represent the nutrient characteristics of vegetation. The extracted five principal components could represent the variables including the growth, physiological and nutrient characteristics of vegetation, physical and chemical characteristics of soil. So these five principal components could be used to replace the comprehensive evaluation score of the identification and evaluation index system of *H. ammodendron* plantation.

Through the comprehensive evaluation scores of *H. ammodendron* plantation in **Table 9**, it could be seen that the 42-yr-old one ranked the first, followed by plantation with the age order of 28, 20, 23, 12, 15, 17, 33 and 7. That is to say, during the process of sand fixation, the comprehensive score calculated based on the five principal component scores increased gradually, thus the comprehensive ranking was gradually higher than before (**Table 9**).

#### **2.6 Conclusions and discussion**

The constructive species could regenerate successfully, which is the basic premise of sustainable development of artificial forest. The 7-yr-old *H. ammodendron* plantation, in the southern fringe of Gurbantunggut Desert, had weak self-generation ability and it could maintain such ability until the age of 33. During the process of individuals growth in canopy storey, there were abundant regenerated individuals of the grade I seedlings under canopy, which indicated that


#### **Table 8.**

*The Eigen values and contribution rate of the principal constituent.*


#### **Table 9.**

*Comprehensive evaluation of* H. ammodendron *plantations.*

the *H. ammodendron* seeds can successfully germinated and grew into seedlings, as well as reflected the characteristics of high maturing rate, short seed dormancy period and high germination rate of the *H. ammodendron. W*hich was also the main reason

#### *Characteristic on the Stability of* Haloxylon ammodendron *Plantation… DOI: http://dx.doi.org/10.5772/intechopen.99050*

for abundance of grade I seedling (HT < 30 cm). The number of grade I seedlings accounted for the largest proportion in regeneration storey, and rich seedling bank could provide a strong guarantee for the regeneration and succession of the population [30]. However, the large seedling bank could not guarantee proper regeneration and ensure sufficient number of higher grade seedlings, and grade III seedlings (HT ≥ 50 cm) were the key for transferring from the regeneration storey to the canopy storey, and thus realizing natural regeneration and sustainable development of the *H. ammodendron* population. Therefore, moderate thinning and tending measures should be taken for *H. ammodendron* plantation to form a more stable structure. The SHN was the main influencing factor of seedling regeneration in *H. ammodendron* plantation. Therefore, avoiding destroy the shrub and grass with strong nitrogen fixation ability, and properly retaining withered litters on soil surface would increase the SHN content in soil, and at last would promote the growth of seedlings.

The *H. ammodendron* plantation system, at the south edge of Gurbantunggut Desert, had weak self-optimization ability, the interdependence and mutual restriction relationship between vegetation and soil. Along with the increase of the plantation age, the ratio of f(x)/g(y) gradually increased too. It showed that *H. ammodendron* population restoration measures had a strong ability to adapt to the environment, and the growth and development speed of population exceeded the development speed of soil, and this may indicate that such vegetation was able to adapt to the local environment, but had a limited ability to reconstruct the soil. When the plantation developed to the age of 42, the coupling degree (C) and coupling coordination degree (D) between vegetation and soil system, f(x)/g(y) were relatively larger, it could be inferred that the vegetation-soil system of the *H. ammodendron* plantation tended to transform from a declining type to a coordinated development type. It is concluded that the competition of vegetation growth would be more intense in the coming years. Therefore, artificial management measures, such as spring water collection, regular fertilization and tree pruning are needed to promote the healthy growth of *H. ammodendron* and the natural regeneration of seedlings, so as to improve the diversity and coverage of vegetation, in order to enhance the coordination degree of vegetation and soil, and finally realize the transformation to a high-level coupling state.
