A Study of the Artificial Vegetation Restoration Technology in the Wenchuan Earthquake Area

Yu WANG，Xingliang LIU，Anm in M IN，LiWANG*，Wenbao MA，Hongli PAN，Hongxia LI，Li ZHANG

1．Sichuan Academy of Forestry Sciences，Chengdu 610081，China；2．Aba Academy of Science and Technology，Wenchuan 62300，China

The＂5·12＂Wenchuan earthquake triggered the landslides in varying degrees with the amount initially estimated to be as many as tens of thousands．A large number of mountain landslides changed the appearance of mountains and rivers，causing broken mottled mountain，damaged roads，and blockage of rivers．In the rainy season，it is easy to form new landslides and generate mudslides，so the ecological reconstruction of the disaster area and acceleration of the vegetation restoration are strategic and practical issues to be urgently solved，playing a particularly urgent and important role in promoting the rapid and healthy development of the area［1－3］．As of May 2011，the reconstruction projects completed accounted for 95%of the planned projects，which means that the Wenchuan earthquake area basically completes the reconstruction task，and is about to enter the phase of rapid development［4－7］．

However，the follow-up study on the vegetation restoration after the end of the relevant ecological project of vegetation restoration is rarely reported，so based on the damaged slope characteristics in the Wenchuan earthquake area，we choose the representative vegetation restoration mode in this study to research the vegetation community structure and ecological situation after 2 years of artificial vegetation restoration，in order to provide a theoretical basis for the future ecological restoration and reconstruction of plant community in the earthquake-stricken area．

1 Experimental materials

1．1 Overview of the study area The experimental site is located in Laohuzui of Yinxiu Town in Wenchuan County，featuring a humid climate．It is influenced by the southeast and southwest monsoons in summer，and due to the location at the windward slope，the temperature is high and there is a lot of rain．It is affected by the northwest monsoons in winter，with an average annual temperature of14．1 oC．The frost-free period is 247－269 d，the rainfall is 528．7－1332．2 mm，and the sunshine hours are 1693．9－1042．2 h，suitable for the growth of all kinds of plants and animals．

The mountains are severely damaged by the earthquake in the study area，and through the field survey of the earthquake-stricken area，it is found that the soil degradation mainly occurs in the surface of wound and debris arising from the earthquake-induced landslides，and the original surface soil and the vegetation are destroyed and covered，with poor land occupation conditions，so the natural soil repair and natural vegetation restoration are very difficult．

1．2 Design of vegetation restoration mode

1．2．1 The horizontal structure configuration and integrated measures．On the basis of site type investigation，we follow the principle of matching species with the site and establish the ecology－economy type vegetation pattern．The community configuration is mainly based on the mountain site，gradient and biological and ecological characteristics of all plants tested．In order to effectively play the soil and water conservation benefit，the vegetation takes the horizontal ribbon mixed configuration along the contour．Arbor and shrubs（or vine）are planted along the contour in the shape of horizontal strip，and the herbaceous plants are planted along the contour in the shape of strip．According to the site conditions，we conduct the combination of economic and ecological types，and adopt corresponding different management measures．

（i）The upper ring of slopes（slope distance of about40m）．The upper ring soil is the slid mountain surface soil with abundant organic matter，so there is no need to take too many engineering measures in this region．We adopt conventional manual operation，to terrace the slope land along the horizontal contour，and the slope distance is4m．The width of the transformed terraced land is 1 m，and in order to maintain soil and water，the outer edge of terraced land is10 cm higher than the inner edge．

（ii）The middle ring of slopes．The soil layer is thin，and the gravel content is high．After simply changing the belt，it is easily collapsed again，so the bamboo basket is used to load the gravel and soil，and it is buried 30cm deep in the ground，and laid along the horizontal line of contour．The slope distance is6－8m．A total of10 slope protection belts are set．The seedlings are planted inside the bamboo basket．The grass and flower seeds are sown on the protection edge of bamboo basket to form a ribbon vegetation belt．

（iii）The lower ring of slopes（slope distance of about 30m）．The lower ring is the gravel accumulation zone arising from landslides occasioned by earthquake，and there is a need to collect a portion of gravel into the wire cage during this control，and use the wire cage as the retaining wall．The seedlings are planted inside the retaining wall．The slope distance is 8－10m，and the belt width is 1．8－2．0m．The specification of wire cage is2．0×1．0m×1．0m，and three retaining walls are set．The soil is embedded in the retaining wall，and the grass and flower seeds are sown to form a unique biological retaining wall．

1．2．2 Vegetation restoration measures．According to the natural site conditions in the restoration area and the principle of matching species with the site，it is dominated by the native trees，and the specific vegetation restoration measures are as follows：

（i）The upper ring of slopes（slope distance of about40m）．The plants within the horizontal terraces are mixed bushes and trees，and the grass seeds are sown on the outer slope terraces．

Plant species are chosen as follows：

Arbor species：Eucalyptus camaldulensis Dehnh．，Liquidambar formosana Hance，and Ligustrum lucidum Ait．

Shrub species：Pyracantha fortuneana（Maxim．）Li．

Herbaceous species：Poa annua L．，F(xiàn)estuca rubra L．，and Cynodondactylon（Linn．）Pers．

（ii）The middle ring of slopes．The plants within the horizontal belt are mixed arbor and shrub，and the grass seeds are sown in the bamboo basket．

Plant species are chosen as follows：

Arbor species：Eucalyptus camaldulensis Dehnh．，Liquidambar formosana Hance，and Ligustrum lucidum Ait．

Shrub species：Pyracantha fortuneana（Maxim．）Li．

Herbaceous species：Poa annua L．，F(xiàn)estuca rubra L．，Cynodondactylon（Linn．）Pers．，Tagetes patula L．，and Medicago sativa L．

（iii）The lower ring of slopes（slope distance of about 30m）．The plants within the horizontal belt are mixed arbor and shrub，and the grass and flower seeds are sown in the wire cage retaining wall．

Plant species are chosen as follows：

Arbor species：Argentina willows，Litsea cubeba（Lour）Pers．，and Ligustrum lucidum Ait．

Shrub species：Armeniaca sibirica（L．）Lam．

Herbaceousspecies：Poa annua L．，F(xiàn)estuca rubra L．，Cynodondactylon（Linn．）Pers．，Tagetespatula L．，and Medicago sativa L．

2 Research methods

2．1 Sample plot setting and survey The stratified sampling method and systematic samplingmethod are used for the entire artificial restoration slope．According to the difference in the artificial slope gradient，the artificial vegetation restoration slope is roughly divided into three parts：upper slope，middle slope and lower slope．Then in each part，the systematic sampling is conducted in accordance with a certain distance．The plot size is1×1 m2，and there are a total of 30 plots on the entire slope．Some indicators are recorded within the plots，such as the composition and structure of plant communities，plant diversity，and vegetation cover［8］．

2．2 Data processing The species diversity of community refers to the number of all species in the community and the number of each species．It has two meanings：the number or richness of species refers to the amount of species in one community or habitat；the evenness of species refers to the distribution of number of individuals of all species in one community or habitat，which reflects the evenness of distribution of number of individuals of all species［9］．

To compare the differences in the diversity between the relevant plants in the community，we use richness index，Simpson index，Shannon－Weiner index，Pielou index and other indices．

The index is calculated according to the following formula：

where s is the total number of plant species in the community；n is the total number of individuals of species in the community；Piis the proportion of the number of individuals of plant species i to the total number of individuals of plants in the community．

3 Results and analysis

3．1 The species composition of the community on slope It is found from the survey that the plants grow well on the artificial restored slope，and the total coverage is up to98．35%．The major plants are Ligustrum lucidum Ait．，eucalyptus，Liquidambar formosana Hance，walnut，Argentina willow，Ligustrum lucidum Ait．，Clematis florida Thunb．，Akebia trifoliata，Poa annua L．，thyme，Coix lacroyma－jobi L．var．ma－yuen（Roman．）Stapf，F(xiàn)allopia multiflora（Thunb．）Harald，Polygonum chinense L．，etc．There are 27 plant species found in the plots，belonging to26 genera and 18 families，including 16 herbaceous plant species，accounting for 59．26%of the total number of species，and 3 shrub species and 5 arbor species，accounting for 10．7%and 18．52%of the total number of species，respectively．The composition of plant families on the slope is dispersed．In terms of the community structure，the herbaceous plant is the dominant group，and it is dominated by leguminous plants and gramineous plants．The leguminous plants and Gramineae plants play an important role in the early period of soil and water conservation and community succession on the artificial restored slope．

As can be seen from Table1，there are obvious differences in the composition of plant communities in different slope positions．The lower slope has the most abundant plant families，genera and species；the middle slope is slightly different from the lower slope；the upper slope has few families，genera and species than the lower slope．

3．2 Analysis of vegetation diversity From Table 1 and Table 2，it can be found that after two years of artificial vegetation restoration，the form and structure of communities on the restored slope have been basically formed，and the indices related to the species diversity have been well improved；the density matching of herbaceous and shrub plants is more reasonable，it has formed a lot of grass and shrub communities on the slope，and the community function is relatively stable．

As for the composition of species on the slope，the number of species is increased from initial 12 to current 27，and the increased 15 invading plants are shrubs and herbs（Table 2），and the invasion by arbor is not found．

Table 1 The composition of plant communities on the restored slope

Table 2 New plants on the slope

The herbaceous plants on the slope are still the previously artificially sown Poa annua L．，F(xiàn)estuca rubra L．，and Cynodondactylon（Linn．）Pers．，but they have degenerated to some extent，and there are a variety of surrounding local grasses invading and gradually getting stable．The major invading plants are Poa annua L．，thyme，Coix lacroyma－jobi L．var．ma－yuen（Roman．）Stapf，F(xiàn)allopia multiflora（Thunb．）Harald and Polygonum chinense L．

Table3 The vegetation diversity index in different slope positions

As can be seen from Table 3，the indices related to the diversity of plant community species are also affected by the slope position．The Marglef richness index，Simpson dominance index and Shannon diversity of plant community show the feature of lower slope＞middle slope＞upper slope，while the Pielou evenness index shows the feature of upper slope＞middle slope＞lower slope．As for the diversity index，there are no significant differences between the middle slope and lower slope，while there are great differences between the middle slope and upper slope，possibly because the soil conditions on the upper slope are poorer than the soil conditions on the middle and lower slopes．There are no dense shrubs and trees covering the top of the slope，and there is one gutter，so the top of the slope is seriously eroded when there is heavy rain．The emphasis on upper slope is not enough during the artificialmaintenance．

3．3 Characteristics of community structure After 2 years of vegetation restoration，it is no longer the herb community dominated by herbaceous plants on the slope，and the herbaceous layer is gradually changed from a even state to a mosaic state．All kinds of communities cluster，the proportion of shrubs is increased significantly，and the shrub and grass community is formed on the slope．The herbaceous layer is mainly occupied by Setaria viridis（L．）Beauv．，Cynodondactylon（Linn．）Pers．，Poa annua L．，F(xiàn)estuca rubra L．，thyme，Coix lacroyma－jobi L．var．ma－yuen（Roman．）Stapf，F(xiàn)allopia multiflora（Thunb．）Harald，Polygonum chinense L．And Cynodondactylon（Linn．）Pers．，Poa annua L．，Coix lacroyma－jobi L．var．ma－yuen（Roman．）Stapf，F(xiàn)estuca rubra L．a(chǎn)re the main species，and the average height of herb layer is about45 cm．The dominant species of shrub layer is Ligustrum lucidum Ait．，D．Orientalis，and Akebia trifoliata．Ligustrum lucidum Ait．is the main species，and the height of shrub layer is about120cm．The arbor layer is mainly occupied by Ligustrum lucidum Ait．，Liquidambar formosana Hance，walnut，and eucalyptus，which are all artificially planted trees．The survival rate of artificially planted arbor is high，and the average height of arbor is150 cm．

There are some differences in the structure of vegetation community，and the middle slope is similar to the lower slope，but both of them are significantly different from the upper slope（Table 4）．The height of herbaceous layer on the upper slope is similar to that on the middle slope and lower slope，but its coverage is significantly higher than that of other two slopes，and the main herbaceous plant is also simple．The height of shrub layer on the upper slope is slightly lower than that on the middle and lower slopes，and its coverage is significantly low．The main shrub is also simple．The main arbor plants on the upper slope are the same as those on other slopes，but its height and coverage are lower than those of the middle and lower slopes．

3．4 Analysis of vegetation slope protection in different slope positions After the implementation of vegetation restoration project on the damaged slope，the slope is well protected due to good vegetation effect．There are differences in the vegetation slope protection between different slope positions（Table 5），and there are no significant differences in the slope protection effect between the middle and lower slopes，but the slope protection effect is better than on the upper slope．The whole slope has high vegetation coverage，mostly close to100%．The vegetation coverage on the middle slope is 99．42%，and the vegetation coverage on the lower slope is 99．88%，slightly higher than the vegetation coverage on the upper slope（98．54%）．In terms of the plant diversity，the middle and lower slopes are also better than the upper slope．

Table 5 Analysis of vegetation slope protection in different slope positions

The soil moisture of slope is in the range suitable for plant growth，but the middle slope occupies 18．98%and the lower slope occupies17．87%，significantly higher than the soil moisture of the upper slope（15．68%）．The soil bulk density on the slope is also suitable for plant growth．The soil bulk density on the middle and lower slopes is1．18g／cm3and 1．20 g／cm3，respectively，lower than the soil bulk density on the upper slope（1．28 g／cm3）．The vegetation on the slope plays a good role in soil and water conservation．The thickness of the middle and lower slopes is17．01 cm and 16．98cm，respectively，significantly better than the thickness of the upper slope（15．01cm）．

As can be seen from Table 5，the vegetation coverage，diversity，soil moisture，bulk density and thickness are closely related to each other．On the slope with good soil conditions，the vegetation restoration effect is also good，and such difference is greatly correlated with the gradient．

Due to differences in gradient，there are significant differences in the water and fertilizer conditions between different slope positions，and there are also differences in the vegetation growth and soil thickness．

4 Conclusions

After the artificial vegetation restoration on the damaged slope in the earthquake disaster area，all the initial artificially planted species have shown adaptation to the climate and environment of the Wenchuan earthquake area；the richness，dominance and diversity indices of community have increased and the community structure is increasingly stable．The artificially sown Poa annua L．，F(xiàn)estuca rubra L．a(chǎn)nd Cynodondactylon（Linn．）Pers．can grow rapidly on the slope，play a good role in soil and water conservation，and provide an environment for future vegetation succession．The sur-vival rate of artificially planted Ligustrum lucidum Ait．，Liquidambar formosana Hance and Ligustrum lucidum Ait．is high，and they can quickly grow，playing an important role in promoting the vertical development and stability of community．

The major invading plant is herb，and it is based on Asteraceae and Gramineae．The invading shrub species are Clematis florida Thunb．，Akebia trifoliata and D．orientalis，and the arbor is difficult to invade，possibly because the herb density is too large on the slope，and the indigenous shrub and arbor species are poorly tolerant of poor，acid soils．The artificial planting of seedlings can be used to introduce indigenous shrub and arbor species．The gradient plays an important role in promoting the artificial vegetation restoration．When the gradient is about 45°，in order to ensure the soil thickness of the slope and provide better conditions for the future vegetation restoration，it is necessary to take some additional process to stabilize the slope，and conserve soil and water．

There are no obvious differences in the indicators related to vegetation and soil between the middle and lower slopes，but better than on the upper slope，so it is necessary to artificially plant more seedlings on the upper slope，increase more inputs to the upper slope conservation，and plant more trees and shrubs at top of upper slope to resist rain and other natural disasters，or when conditions permit，appropriately reduce the gradient of the upper slope．

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