Minglin WANG

Tibet Linsheng Forest Industry Co., Ltd., Nyingchi 860000, China

Abstract [Objectives] As the desertification of river valleys in Nyingchi City, Tibet is relatively serious, and the area of river valley desertification continues to expand, the effect of different afforestation treatments on Salix microstachya cuttings is discussed. [Methods] The effect of different afforestation treatments on the survival rate and preservation rate of S. microstachya cuttings were investigated. [Results] Different afforestation treatments all improved the survival rate and preservation rate of S. microstachya cuttings to a certain extent, and among all the treatments, mulching treatment showed the most obvious improving effect. [Conclusions] This study provides a direction for the research of afforestation measures in river valleys in Nyingchi.

Key words Afforestation treatment, Salix microstachya, Cutting, Research

1 Introduction

The desertification of river valleys in Nyingchi City, Tibet is relatively serious. Desertified land is distributed in five counties (districts) of Bayi, Mainling, Nang County, Bome, and Zayu. The types of desertified land mainly include mobile sandy land, semi-mobile sandy land, bare gravel, semi-bare gravel, fixed sandy land, sandy shrub grassland, and desertified cultivated land. In terms of time distribution, as the Yarlung Zangbo River has great changes in water level during high and low water periods, the point bars and central bars formed by sediment deposition in summer are widely exposed to the water surface in winter and spring. In addition, the weather is dry and windy in spring, constituting the most active source of sand during the dry season. As a result, it shows significant seasonal changes. What’s more, subject to changes in terrain, wind environment and vegetation, under the influence of river water changes and other factors, it shows the overall distribution along the river valley and both sides of the river valley in a belt shape, spot-like discontinuous distribution in some areas, and diversity of landforms. Sandy areas are mostly distributed on the point bars, central bars, terraces, alluvial fans, and mountain slopes on both sides of the river valleys of Yarlung Zangbo River, Niyang River, and Nujiang River.

According to the desertification monitoring data of the Tibet Autonomous Region in 2012, the total area of desertified land in Nyingchi City is 62 453 ha, mainly located in the basins of Yarlung Zangbo River, Niyang River and Nujiang River. The areas of lightly (open sandy land, desertified cultivated land), moderately (fixed sandy land), heavily (semi-fixed sandy land) and extremely heavily (mobile sandy land) desertified land are 39 667, 9 462, 8 685 and 4 640 ha, respectively. The area of lightly and moderately desertified land accounted for 79%, and the area of heavily and extremely heavily desertified land accounted for 21% of the total.

Salix

microstachya

is a deciduous shrub of the Salicaceae family, naturally distributed in Tibet, Xinjiang, Ningxia, Qinghai and other provinces of China. It is photophilous and intolerant to shade, and grows poorly in shade. The root system of

S.

microstachya

is well-developed. It is resistant to dryness and water logging, and has strong wind resistance. It is resistant to saline-alkaline soil and can grow normally on saline-alkaline soil with a salt content of 1.2%.

2 Overview of the test site

The test site is located in the nursery in Bayi District, with altitude of 3 000 m, annual highest temperature of 29.3 ℃, annual lowest temperature of -14.5 ℃, annual average temperature of 8.6 ℃, effective accumulated temperature of 1 800-2 200 ℃, number of days with average temperature ≥10 ℃ of about 160 d, frost-free period of 160-180 d, annual rainfall of 650 mm (concentrated in June to September), and annual average relative humidity of 60%. It belongs to a warm and semi-humid climate. The test soil was sandy loam with low fertility.

3 Methods

3.1 Treatment of test materials

The test materials were 2-3-year-old well-grown

S.

microstachya

seedlings collected from the nursery of Bayi District, Nyingchi City, Tibet. In March, 2019, afforestation test was carried out in Bayi District, Nyingchi City. The

S.

microstachya

seedlings were planted in holes (80 cm×80 cm). The following treatments were designed: mulching with stone (covering the surface of the tree pits with stones with a diameter of about 3 cm), mulching with film (covering agricultural film over the tree pits), mulching with straw (covering the surface of tree pits with barley straw), applying water-retaining agent (mixing water-retaining agent with soil and using as subsoil) and control (untreated).

3.2 Investigation method

The survival rate of afforestation and the preservation rate after one year were investigated. In each plot, 20 plants were selected randomly. The means were calculated for statistics and analysis. The survival rate was investigated at the end of the fourth month after the afforestation, and the preservation rate was investigated one year after the afforestation.

4 Results and analysis

4.1 Effect of different treatments on the survival rate of

cuttings

In the treatment of mulching with stone, the survival rate of

S.

microstachya

was 79.9%, 28 percentage points higher than that of control; in the treatment of mulching with film. The survival rate of

S.

microstachya

was 87.8%, 35.9 percentage points higher than that of control; in the treatment of mulching with straw, the survival rate of

S.

microstachya

was 78.0%, increased by 26.1 percentage points in comparison to that of control; in the treatment of mulching with film+applying rooting powder, the survival rate of

S.

microstachya

was 94.5%, 42.6 percentage points higher than that of control; and in the treatment of applying water-retaining agent, the survival rate of

S.

microstachya

was 83%, 31.1 percentage points higher than that of control (Table 1). All the five afforestation treatments improved the survival rate of

S.

microstachya

well, and among them, mulching with film+applying rooting powder showed the best effect, of which the survival rate of

S.

microstachya

reached 94.5%.

Table 1 Effect of different afforestation treatments on survival rate of Salix microstachya cuttings %

4.2 Effect of different treatments on the preservation rate of

cuttings

In the treatment of mulching with stone, the preservation rate of

S.

microstachya

was 87.0%, 18.5 percentage points higher than that of control; in the treatment of mulching with film, the preservation rate of

S.

microstachya

was 91.0%, 22.5 percentage points higher than that of control; in the treatment of mulching with straw, the preservation rate of

S.

microstachya

was 81.1%, 12.6 percentage points higher in comparison to that of control; in the treatment of mulching with film+applying rooting powder, the preservation rate of

S.

microstachya

was up to 92.6%, 24.1 percentage points higher than that of control; and in the treatment of applying water-retaining agent, the preservation rate of

S.

microstachya

reached 82.5%, 14 percentage points higher that of control (Table 2). The five afforestation treatments all improved the preservation rate of

S.

microstachya

well, and among them, mulching with film+applying rooting powder had the best treatment effect, with the preservation rate reaching 92.6%.

Table 2 Effect of different afforestation treatments on preservation rate of Salix microstachya cuttings %

5 Conclusions

The low water content of sandy soil is the most important factor limiting the survival rate and preservation rate of plants. The main way to reduce desertification is to increase the water content of desertified soil. In this study, the effect of different afforestation treatments on

S.

microstachya

cuttings was investigated. The results show that different afforestation treatments all improved the survival rate and preservation rate of

S.

microstachya

to a certain extent; and among different treatments, the treatment of mulching with film improved the survival rate and preservation rate of

S.

microstachya

by 35.9 and 22.5 percentage points, respectively in comparison to control. This study provides a direction for future research on afforestation measures in river valleys of Nyingchi.

6 Measures to reduce soil and river valley desertification in Nyingchi City

6.1 Taking multiple measures to promote effective management of desertified land

We will conscientiously protect the forest and grass vegetation in sandy areas. For several years, the city has strengthened the protection of the Yani National Wetland Park and the Bome Galang National Forest Park in the sandy areas, and it is strictly forbidden to destroy the forest and grass vegetation in the protected areas. The protection of the national ecological public welfare forests in the sandy areas has been strengthened. The protection effect is linked to the wages of management and protection personnel. Forest logging and forest destruction are strictly prohibited. The fire prevention of vegetation and forest in the sandy areas is strengthened. Since 2016, the vegetation in the sandy areas has not been damaged by any forest fires.

6.2 Strengthening water resources management in sandy areas

The whole city fully implements the river chief system to strengthen water resources protection, shoreline management and protection, water pollution prevention, water environment governance and water ecological restoration work. The management of sand mining in the sandy areas is intensified comprehensively. All sand mining operations that do not meet the requirements are banned. Water-saving and efficiency-increasing activities are car-ried out actively. In agricultural construction, micro-sprinkler irrigation water-saving technology is promoted.

6.3 Earnestly implementing the environmental impact assessment system for development and construction projects in sandy areas

The city has always strengthened the supervision of project approval. Projects that do not comply with environmental protection laws and policies, serious pollution, high resource consumption, and serious environmental damage will not be approved. Environmental protection law enforcement is strengthened. Regarding to newly launched construction projects, the "three simultaneous" system of project construction, environmental impact assessment and environmental protection is implemented earnestly. In the work, the policy of paying equal attention to resource development and environmental protection is adhered to. We will conscientiously implement various environmental protection tasks such as comprehensive improvement of environmental protection and soil and water conservation.

6.4 Strengthening the construction of forestry ecological projects related to sandy areas

In addition to the special sand prevention and control work, the city’s forestry and grass departments have also implemented the protection and restoration project for the two national wetland parks, the "two-river four-stream" watershed afforestation project, Nyingchi-Lhasa Highway construction project, Bayi-Mainling Airport Highway green landscape corridor construction project and other key ecological construction projects related to the control of sandy areas, effectively promoting the sand prevention and control work in Nyingchi.