**2. Characteristics of vegetation and soil system of** *H. ammodendron* **plantation**

#### **2.1 Basal characteristic of** *H. ammodendron* **plantations in study site**

In Mosuowan Reclamation Area, Corps 150, southern edge of the Gurbantunggut Desert, *H. ammodendron* plantations were chosen for this study, *Characteristic on the Stability of* Haloxylon ammodendron *Plantation… DOI: http://dx.doi.org/10.5772/intechopen.99050*

which are constructed on moving sandy land within an area of about 57.61 km<sup>2</sup> . Thus soil and climate is similar among these plantations. All plantations were established by transplanting 1-yr-old *H. ammodendron* seedlings in regular spacing (**Table 1**). Thus *H. ammodendron* individuals could be classified into two main storeys, i.e. transplanted individuals (canopy storey) and seedlings including those naturally regenerated between transplanted ones (regeneration storey). None of the plantations were subjected to irrigation, pruning, thinning or any other silvicultural practices after transplantation. In addition, no incident of insect, rodents and fire was recorded since 1981. Except *H. ammodendron* seedlings, understory plants were dominated by *Ceratocarpus arenarius* and *Salsola ruthenica*, with a low total cover less than 8% (**Table 1**, **Figure 1**).

In August, when soil water content of the study site was relatively stable and close to the average level in a year [21], vegetation survey was carried out in nine *H. ammodendron* plantations. In each plantation, three 20 m � 30 m sample plots were established, with each at least 100 m away from the others. Within each sample plots, the numbers of survived and dead individuals for canopy storey was recorded (**Table 1**). Meanwhile, height, basal stem diameter and crown width (north–south and east–west) of survived individuals were measured one by one. Then the crown projected area, above-ground biomass and canopy density of major storey were calculated according to Phillips and Macmahon's ellipse formula [22] and Song's Eq. [23], respectively.

#### **2.2 Characteristics of canopy storey in six** *H. ammodendron* **plantations at different Chronosequence stage**

Vegetation survey was carried out in six *H. ammodendron* plantations, which having capacity of normal natural regeneration. According to Rundel's method [24], combining with the characteristic of slow growth and false ring of H. ammodendron [25], the structure of canopy storey was analyzed by quantity and size dynamic of tree height and basal stem diameter. Tree height class was divided into 0 � 0.5 m, 0.5 � 1.0 m, 1.0 � 1.5 m, 1.5 � 2.0 m, 2.0 � 2.5 m, 2.5 � 3.0 m, 3.0 � 3.5 m, 3.5 � 4.0 m, 4.0 � 4.5 m, 4.5 � 5.0 m, 5.0 � 5.5 m and 5.5 � 6.0 m. Basal stem diameter was divided into 0 � 1 cm, 1 � 2 cm, 2 � 4 cm, 4 � 6 cm, 6 � 8 cm, 8 � 10 cm, 10 � 12 cm, 12 � 14 cm, 14 � 16 cm, 16 � 18 cm and 18 � 22 cm. Structural characteristics of main layer were analyzed by quantity and size.

As shown in **Figures 2** and **3**, in the growth process of *H. ammodendron*, the distribution centers of height class and basal stem diameter class of the canopy storey


**Table 1.**

*The sample plots information of* H. ammodendron *plantations at different chronosequence stage.*

#### **Figure 1.**

*The original appearance (A), land preparation (B), the* H. ammodendron *plantation with age of 7 (C), 17 (D), 28 (E), 42 (F).*

moved to a higher section gradually, and the structure of size class showed a trend of continuous differentiation first and then concentration. It indicated that the intraspecific competition among individuals was intensifying, and the population structure tended to be more and more complex, which was conducive to the rational use of spatial resources. The tree height and basal stem diameter class of canopy storey showed obvious differentiation in the plantations with the age of 17 and 20. It indicated that, after the competition and self-thinning, some individuals having competitive advantage had entered in the rapid growth stage, and most individuals could grow to the canopy storey (HT 2.5–3.0 m, BSD 8-10 cm). After the age of 28, *H. ammodendron* plantation would start to decline, when branch aging and withering appeared, and the natural death rate of *H. ammodendron* in canopy storey would reach 5% 8%.
