Response of runoff and soil erosion to erosive rainstorm events and vegetation restoration on abandoned slope farmland in the Loess Plateau region, China

Journal Pre-proofs Research papers Response of runoff and soil erosion to erosive rainstorm events and vegetation restoration on abandoned slope farmland in the Loess Plateau region, China Liang Yue, Jiao Juying, Tang Bingzhe, Cao Binting, Li hang PII: DOI: Reference:

S0022-1694(20)30154-2 https://doi.org/10.1016/j.jhydrol.2020.124694 HYDROL 124694

To appear in:

Journal of Hydrology

Received Date: Revised Date: Accepted Date:

26 November 2019 11 February 2020 13 February 2020

Please cite this article as: Yue, L., Juying, J., Bingzhe, T., Binting, C., hang, L., Response of runoff and soil erosion to erosive rainstorm events and vegetation restoration on abandoned slope farmland in the Loess Plateau region, China, Journal of Hydrology (2020), doi: https://doi.org/10.1016/j.jhydrol.2020.124694

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

© 2020 Published by Elsevier B.V.

Response of runoff and soil erosion to erosive rainstorm events and vegetation restoration on abandoned slope farmland in the Loess Plateau region, China Liang Yuea,c, Jiao Juyinga,b,*, Tang Bingzheb, Cao Bintingb, Li hangb a

State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Academy

of Sciences and Ministry of Water Resources, 26 Xinong Road, Yangling, Shaanxi Province 712100, PR China b

Institute of Soil and Water Conservation, Northwest A&F University, 26 Xinong Road, Yangling, Shaanxi Province 712100, PR

China c

University of Chinese Academy of Sciences, 100049, Beijing, PR China

Abstract It has been widely known that vegetation restoration plays a vital importance in controlling surface runoff and soil erosion. The most of soil erosion were caused by erosive rainstorm events. Yet, the response of surface runoff and soil erosion to erosive rainstorm events and vegetation types has not been fully understood. In this study, we monitored the vegetation, rainfall, runoff and soil erosion on ten runoff plots under field conditions from 2015 to 2019 and examined the impact of erosive rainstorm events on runoff and soil erosion among different vegetation types (Artemisia scoparia→Stipa bungeana→Lespedeza davurica (Asc→Sb→Ld), Stipa bungeana→Artemisia gmelinii (Sb→Agm), Bothriochloa ischaemum (Bi), Artemisia gmelinii + Stipa bungeana (Agm + Sb), Artemisia gmelinii + Stipa grandis (Agm + Sg), Sophora viciifolia (Sv), Artemisia gmelinii + Artemisia giraldii (Agm + Agi)) and bare land on abandoned land slopes. The results showed that vegetation restoration could decrease 68.0% to 97.4% of runoff and 98.0% to 99.9% of soil erosion compared to the bare land and there were no significant differences of surface runoff and soil loss among different vegetation types under the 11 erosive rainstorm events. The average soil loss of erosive rainstorm events among vegetation types could be 2.1 to 15.6 times as those of ordinary erosive rainfall events. The erosive rainstorm events caused a significant variance of surface runoff and soil erosion because of variant 1

antecedent soil moisture and rainfall intensity. In practice, the natural vegetation restoration should be recommended in semi-arid environment and, the erosive rainstorm events should be paid enough attention in causing intense soil erosion in the rainy reasons. Keywords: Soil erosion, Surface runoff, Vegetation restoration, Erosive rainstorm event, Abandoned slope

1.Introduction Soil erosion is regarded as a serious eco-environmental problem which led to land degradation and natural ecosystem destruction (Dlamini et al., 2011; Lal, 2001). It can mainly influenced by a combination of climatic changes and anthropogenic activities (Fu et al., 2017; Raclot et al., 2018). Vegetation restoration has been widely considered to conserve soil and water across the world (Buttle and Farnsworth, 2012; Fattet et al., 2011; García-Ruiz, 2010; Molina et al., 2012; Puigdefábregas, 2005; Zhang et al., 2015). Vegetation type, vegetation coverage and plant trait could impact the hydrological and erosive processes of restoration land substantially. There are discrepancies among vegetation types of their effects in controlling the surface runoff and soil erosion. Some assessments across a wide range of vegetation types concluded that the forestland and shrubland yielded the lower soil erosion, while the farmland and orchard showed the higher soil erosion (Cerdan et al., 2010; García-Ruiz et al., 2015; Guo et al., 2015; Xiong et al., 2019). In semi-arid environment, grassland and woodland could also be considered to reduce more gully erosion compared to orchards (Wang et al., 2016). However, other researches showed that the shrubland could also reduce more runoff and soil erosion than forestland or grassland (García-Ruiz, 2010; Zhou et al., 2016; Zhou et al., 2019). Some scholars demonstrated that a mixed structure of forests and shrubs would be more beneficial for combating water and soil loss (Mohammad and Adam, 2010; Burylo et al., 2011; Buttle and Farnsworth, 2012). The vegetation coverage was negatively correlated with sediment generation among vaious vegetation types (Wang et al., 2016; Zhou et

2

al., 2016) because that the canopy can dramatically intercept raindrops and absorb their kinetic energies (Bochet et al., 2006; Geißler et al., 2012; Ghimire et al., 2012; Liu, 1998; Wang, 2012). Besides, the ground cover, including the biological crust and litter layer, can also exert considerable effects on decreasing the suface runoff and soil loss (Chen et al., 2018; Hosseini et al., 2016; Wang et al., 2016). The biological soil crusts protected the soil against erosion by increasing the threshold friction velocity (Bowker et al., 2008) and causing higher soil surface roughness (Rodríguez-Caballero et al., 2012), which would reduce the shear effect and the transport capacity of water flow (Helming et al., 1998; Gaur and Mathur, 2003), ultimately control the surface runoff and soil loss. The litter layer could decrease the erosive force of raindrop and overland flow (Wang et al., 2019). Besides, the plant litter could be incorporated into topsoil layer (Brown et al., 1990; Pannkuk and Robichaud, 2003) and the incorporated plant litter could effectively decrease the soil detachment capacity, rill erodibility and critical shear stress (Sun et al., 2016). Most of soil erosion was induced by a small number of intense rainstorms with short duration and high rainfall intenstiy (Fu, 1989; Zheng et al., 2008; Jiao et al., 1999). Even one of these individual intense rainfall events could cause serious flood and severe soil erosion (Bookhagen, 2010; Bryndal et al., 2017; Martı́nez-Casasnovas et al., 2002; Wang et al., 2016; Wei et al., 2009). There were abundant existing studies regarding the impact of rainfall characteristics or single rainfall event on the runoff and soil erosion of restoration vegetation (Cerda et al., 2017; Chen et al., 2018; Dos Santos et al., 2017; Peng and Wang, 2012; Wang et al., 2016; Wei et al., 2007; Wei et al., 2009; Xu et al., 2013), whereas few efforts have been made to examine the response of water and soil loss among various vegetation communities to erosive rainstorm events. Additionally, the long-term monitoring of water and soil loss by field plots were scarce in previous researches (Cerdan et al., 2010).

3

The Loess Plateau of China is well known as the region suffering from severe soil erosion in the world (Douglas, 1989; Fu, 1989; Shi and Shao, 2000; Tang et al., 1993;). Nowadays, the “Grain for Green” project has been conducted in the Loess Plateau for 20 years and massive sloping farmland has been converted into forest, shrub and grassland (Jiao et al., 2008; Tang et al., 2004; Wang et al., 2016). The afforestation and vegetation restoration have improved the vegetation cover tremendously, which consequently decreased the surface runoff and soil erosion remarkably (Sun et al., 2006; Zheng, 2006; Zhou et al., 2016). In the Loess Plateau, the rainstorm events caused most of runoff and soil erosion (Fu, 1989; Jiao et al., 1999; Zheng et al., 2008). Hence, the runoff and soil erosion on present underlying conditions under rainstorm events should be examined to fully understand the impact mechanism of vegetation restoration on reducing the runoff and soil erosion. The current study analyzed the data of vegetation, runoff and soil loss under ten field runoff plots conducted on abandoned slope farmland in the Loess Plateau, and quantified the surface runoff and soil erosion of vegetation communites with different abandoned ages (5-43 years) and restoration types under erosive rainstorm events. The specific objectives of the study were to: (1) investigate the characteristics of erosive rainstorm events and vegetation on abandoned slope; (2) compare the surface runoff and soil erosion among different vegetation types; (3) examine the response of surface runoff and soil erosion to erosive rainstorm events among different vegetation types. The results would provide reference for the selection of vegetation types and the evaluation of soil and water conservation benefits of ecological restoration in semi-arid areas.

2. Material and methods 2.1 Site description The study was conducted in Fangta (36°48’E, 109°15’E, 10.5 km2), a small watershed located in the Ansai County, North Shaanxi Province, China (Fig.1). The small watershed belongs 4

to the hilly-gullied region of the Loess Plateau. The altitude ranges from 1040 to 1395 m. The climate of this region is a temperate semi-arid and the average annual precipitation is 505 mm, which primarily occurs from July to September. The soil type is mainly loessal soil with silt loam texture (USDA soil taxonomy). The soil is prone to water erosion because of the loose soil particles and poor corrosion resistance (Ren et al., 2016; Shi and Shao, 2000). In Fangta watershed, most of sloping farmlands has been transformed into artificial vegetation and natural vegetation because of the “Grain for Green” project which has been carried out for 20 years. Nowadays, the natural vegetation species in Fangta watershed are mainly Artemisia gmelinii, Stipa bungeana, Stipa grandis, Bothriochloa ischaemum, Periploca sepium, Sophora viciifolia, etc. The artifical vegetation species are Robinia pseudoacacia, Hippophae rhamnoides and Caragana intermedia etc (Tang et al., 2019).

5

Fig.1.(a) The location of Fangta watershed on the Loess Plateau in China, (b) The location of runoff plots in the Fangta watershed, (c) The layout of ten field runoff plots, (d) Bare land and vegetation types in field runoff plots, (e) The runoff-plot system.

2. 2 Data collection

6

Ten runoff plots were conducted in the Fangta watershed in 2015 (Fig.1b). The shape of runoff plot was approximately a rectangle with 2.5 m in width and 10 m in length combined with a triangle (0.625 m2) at the bottom for closing up the runoff plot. Hence, the area of each runoff plot is 25.625 m2. The runoff plots were delimited by impervious PVC sheets (2 mm thickness) inserted perpendicularly into the soils. At the outlet of each runoff plot, a PVC pipe and volumetric barrel were installed to collect the surface runoff and soil loss under each erosive event (Fig.1d,e). To compare the response of water and soil loss to different vegetation types, we monitored nine main vegetation types and a bare land as the control (Table 1). The Artemisia scoparia→ Stipa bungeana→Lespedeza davurica (Asc→Sb→Ld), Stipa bungeana→Artemisia gmelinii (Sb →Agm), Bothriochloa ischaemum (Bi), Artemisia gmelinii + Stipa bungeana (Agm + Sb), Artemisia gmelinii + Stipa grandis (Agm + Sg), Sophora viciifolia (Sv) and Artemisia gmelinii + Artemisia giraldii (Agm + Agi) were selected as the locally natural vegetation restoration types, with abandoned years ranging from 5 to 44 years. The Caragana korshinskii (Ck) and Robinia pseudoacacia (Rp) represented the artifical planted vegetation types with abandoned years of 20 to 34, respectively. The bare land plot was weeded periodically to keep it as a bare land. Table 1 Basic characteristics of runoff plots. Abandoned Plot

Average Vegetation type (abbreviation)

No.

Vegetation

Litter

Biotic crust

coverage

coverage

coverage

years (2015Slope/° 2019)

1

Bare land（Bl）

21

-

-

-

-

35

5-9

20.5 ± 5.6

9.4 ± 2.8

64.7 ± 10.9

Artemisia scoparia→Stipa 2

bungeana→Lespedeza davurica （Asc→Sb→Ld）

7

Stipa bungeana→Artemisia 3

21

10-14

36.5 ± 6.5

19.1 ± 5.7

45.7 ± 6.8

23

15-19

56.0 ± 3.3

23.7 ± 5.6

25.1 ± 7.7

25

25-29

51.5 ± 6.7

18.9 ± 5.4

56.5 ± 10.1

29

40-44

61.0 ± 4.8

32.2 ± 13.0

26.8 ± 8.1

35

40-44

50.5 ± 8.5

24.7 ± 5.7

17.5 ± 7.2

32

40-44

65.5 ± 4.6

23.4 ± 6.0

20.4 ± 6.6

gmelinii（Sb→Agm） 4

Bothriochloa ischaemum（Bi） Artemisia gmelinii + Stipa

5

bungeana（Agm + Sb） Artemisia gmelinii + Stipa

6

7

grandis（Agm + Sg） Sophora viciifolia（Sv） Artemisia gmelinii + Artemisia

8

giraldii（Agm + Agi）

9

Caragana korshinskii（Ck）

43

20-24

67.8 ± 3.9

58.9 ± 12.8

20.9 ± 13.6

10

Robinia pseudoacacia（Rp）

23

30-34

58.6 ± 6.9

92.8 ± 3.0

1.0 ± 1.0

Note: The coverages were measured in the August; Data of the coverage are given as means ± standard error of means.

Runoff and soil loss of each runoff plot were collected from 2015 to 2019 if there was runoff generated after a rainfall event. Firstly, the volume of runoff in volumetric barrel was measured, then we stirred and mixed the sediment and water homogeneously in the volumetric barrel and runoff samples were collected into bottles with a volume of 1850 ml. If the volume of sample was less than 1850 ml, we collected all the sample. All volumetric barrels were emptied and cleaned out after the measurement and sampling for the next erosive event. Whereafter, the runoff sample of each runoff plot was settled for 8 h and the sediment was separated. Subsequently, the sediment was dried in oven over 24 h at 105 ℃ and weighed to obtain the sediment concentration. Lastly, the soil loss amount of each plot was determined by the sediment concentration multiplies the total runoff volume in volumetric barrel. Rainfall process data were obtained by two self-recording rain gauges (machine type: TPJ32) near the runoff plots with the measurement accuracy of 0.2 mm. The rainfall amount, duration, average intensity and maximum intensities of 15-minute, 30-minute and 45-minute were

8

extracted from the rainfall process data. If the rainfall interval exceeded 6 h, the successive rainfall events were regarded as two rainfall events (Renard et al., 1997; Wischmeier and Smith, 1958). The vegetation, litter and soil biotic crust coverage of each vegetation plot were also measured after every erosive event in August from 2015 to 2019. The vegetation coverage of Rp refers to the total coverage of trees, shrubs and herb species, that of Ck and Sv types refer to the coverage of shrubs and herb species, that of other communties refer to the the coverage of herb species. The abundance, height, coverage of each species in each plot were recorded in three quadrats (1 m × 1 m) in August from 2015 to 2019.

2.3 Statistical analyses In current study, we analyzed the runoff and soil erosion data based on event scale in five consecutive years (2015–2019). The surface runoff depth (H) and soil erosion modulus (SM) were respectively presented as follows: H = (R/AP) × 103

(1)

where H, R and AP means surface runoff depth (mm), the runoff volume (m3) generated by a erosive event and area of runoff plot (m2), respectively. SM = SL/AP

(2)

where SM, SL, AP refers to soil erosion modulus (t•km-2), soil loss amount (t) generated by a erosive event and area of runoff plot (km2), respectively. Species importance value (IV) was used as the index for expressing the importance of species (Qu et al, 1983). IV was calculated as follows: IV= (RC + RF + RD) /3

9

(3)

where IV is the species importance value for each species, RC means the percentage of coverage for each species to the sampling quadrat, RF refers to the percentage of frequencies of each species appearing in sampling quadrats to the total numbers of sample quadrats, RD refers to the percentage of density for each species to the total density of all species in the sampling quadrat. Ultimately, we averaged the IV values of each species in three quadrats to get the IV values of each species in every runoff plot. The erosive rainstorm selection was based on erosive rainstorm criterion of rainfall amount within different rainfall duration on the Loess Plateau presented by Wang and Jiao (2018). Namely, if the rainfall amount of certain rainfall duration in a rainfall event was higher than the values in Table 2, the rainfall event was recognized as erosive rainstorm event. Table 2 Erosive rainstorm criterion of different rainfall durations in the Loess Plateau (Wang and Jiao, 2018). Rainfall duration (min)

5

10

15

30

60

120

180

240

360

720

1440

Rainfall amount (mm)

5.8

7.1

8.0

9.7

11.9

14.6

17.8

20.5

25.0

35.1

50.0

One-way analysis of variance (ANOVA) and Tukey method test were used to evaluate the differences in runoff and soil erosion (significant differences were set as 95% level).

3. Results 3.1 Vegetation characteristics The main species (with maximum importance value) of nine vegetation types varied from year to year (Table 3). The main species of Asc→Sb→Ld transformed from Artemisia scoparia to Stipa bungeana in 2016 and Lespedeza davurica in 2018. Regarding the Sb→Agm, the main species became Artemisia gmelinii since 2017 while it was Stipa bungeana in 2015 and 2016. With respect to other vegetation types, the main species did not show dramatically change in the

10

study period. Notablely, Artemisia gmelinii was the most common main species among these vegetation types. Table 3 Main species of vegetation plots from 2015 to 2019. Plot No.

2015

2016

2017

2018

2019

2

Asc

Sb

Sb

Ld

Ld

3

Sb

Sb

Agm

Agm

Agm

4

Bi

Bi

Bi

Bi

Bi

5

Agm

Agm

Agm

Agm

Agm

6

Agm

Agm

Agm

Agm

Agm

7

Sv

Sv

Sv

Sv

Sv

8

Ps

Agm

Ps

Ps

Ps

9

Ck

Ck

Ck

Ck

Ck

10

Rp

Rp

Rp

Rp

Rp

Note: Asc: Artemisia scoparia, Sb: Stipa bungeana, Ld: Lespedeza davurica, Agm: Artemisia gmelinii, Bi: Bothriochloa ischaemum, Sv: Sophora viciifolia, Ps: Patrinia scabiosaefolia, Ck: Caragana korshinskii, Rp: Robinia pseudoacacia.

In general, the vegetation coverage rises with the abandoned age increases. Ck type showed the highest vegetation coverage (67.8%), followed by Agm + Agi type (65.5%) and Agm + Sg type (61.0%) (Table 1). While Asc→Sb→Ld community with the least abandoned age (5-9 years) showed the smallest vegetation coverage (20.5%). In terms of the biotic crust coverage, the Asc→ Sb→Ld community showed the highest value (64.7%), followed by Agm + Sb community (56.5%). Besides, the biotic crust coverage of Rp community (1.0%) was least among vegetation types. With regard to litter coverage, the Rp community had the highest litter coverage (92.8%), followed by Ck community (58.9%). Meanwhile, the litter coverage of Asc→Sb→Ld community (9.4%) was the smallest among all vegetation types (Table 1).

11

3.2 Rainfall and erosive rainstorm characteristics There is high variability in the rainfall amount in rainy seasons (from May to October per year) among different years. The highest rainfall amount of rainy seasons was 466.2 mm in 2016, while the smallest rainfall amount was 181.8 mm in 2015 (Table 4). The total number of rainfall events in rainy seasons of study period (from 2015 to 2019) was 145 in which there were 51 erosive events. In a rainy season, there were only 25.6% to 66.7% of the total rainfall events leading to soil loss. Table 4 Rainfall characteristics of rainy season from 2015 to 2019. Erosive Number of Rainfall

Number

rainfall

Year

Erosive rainstorm

Number of erosive

amount (mm)

rainstorm events

erosive amount (mm)

of events

amount events (mm)

2015

181.8

36

137.1

11

0

0

2016

466.2

21

410.5

14

226.8

5

2017

437.0

11

204.0

6

48.9

1

2018

388.6

38

286.8

10

91.4

3

2019

459.8

39

324.0

10

139.5

2

Note: The erosive events refer to the rainfall events which generate runoff at least in one vegetation plot.

Eleven erosive rainstorm events were selected from rainfall events during 2015 to 2019 based on the erosive rainstorm criterion on the Loess Plateau (Table 2). Erosive rainstorm events occurred five, one, four and two times in 2016, 2017, 2018 and 2019, respectively (Table 5). While there were no erosive rainstorm events in 2015. The rainfall amounts of erosive rainstorm events varied from 14.7 to 72.1 mm and the average value was 46.1 mm. The duration of the 11 events ranged from 1.5 to 20.0 h with an average value of 10.3 h. Additionally, the maximum intensities of 15-minute, 30-minute and 45-minute was in the range of 14.0 to 90.4 mm•h-1, 12.0 to 62.2 mm•h-1 and 10.7 to 37.3 mm•h-1, respectively. The erosive rainstorm event with 12

maximum rainfall amount took place in 2019/07/24, raining for 15 hours and 45 minutes, and the amount occupied 16.8% of the total rainfall amount of rainy season in 2019, while the erosive rainstorm events with highest maximum intensities of 15-minute, 30-minute and 45-minute occurred in 2018/06/30. The results indicated that not only heavy rainfall events with high rainfall amount and intensities, but also some events with smaller amounts and shorter durations can be considered as erosive rainstorm events. Table 5 Characteristics of erosive rainstorm events from 2015 to 2019. Date

P (mm)

T (h)

I15 (mm•h-1)

I30 (mm•h-1)

I60 (mm•h-1)

The erosive rainstorm criterion met

2016/06/10

46.6

2.5

38.4

25.2

18.9

P (15 min) >8.0 mm

2016/06/22

27.8

3.0

37.2

33.2

27.4

P (15 min) >8.0 mm

2016/07/06

34.0

1.5

52.8

41

21.9

P (15 min) >8.0 mm

2016/07/19

58.5

15.0

14

12

10.7

P (720 min) >35.1 mm

2016/08/16

60.0

15.3

63.6

38.4

19.7

P (15 min) >8.0 mm

2017/05/24

48.9

19.5

26.4

22.2

18.1

P (30 min) >9.7 mm

2018/06/30

54.6

10.0

90.4

62.2

37.3

P (5 min) >5.8 mm

2018/08/07

14.7

2.0

17.9

17.9

13.4

P (60 min) >11.9 mm

2018/09/06

22.1

9.2

20.2

14.6

12.2

P (60 min) >11.9 mm

2019/07/24

72.1

15.8

31.2

21.6

16.6

P (30 min) >9.7 mm

2019/08/7

67.4

20.0

29.2

26.2

21.1

P (30 min) >9.7 mm

Note: Note: P, rainfall amount (mm); T, rainfall duration (h); I15, maximum 15-minute intensity (mm•h-1); I30, maximum 30-minute intensity (mm•h-1); I60, maximum 60-minute intensity (mm•h-1).

3.3 Runoff and soil erosion under erosive rainstorms The runoff depth and soil erosion modulus of bare land under erosive rainstorm events were much higher than those of vegetation types (p<0.05). These vegetation types could reduce 68.0% to 97.4% of runoff depth and 98.0% to 99.9% of soil loss compared to bare land under erosive rainstorm events (Fig.2). Among vegetation types, Sb→Agm and Bi led to more runoff with mean

13

depth of 2.19 and 1.83 mm under the 11 erosive rainstorm events (Fig.2). However, the Rp and Ck exhibited little runoff depths which were not higher than 1 mm under all erosive rainstorm events. Regarding the soil loss among vegetation types, Sb→Agm caused most soil erosion with mean soil erosion modulus of 9.4 t•km-2 under erosive rainstorm events, while the Ck and Rp produced smaller soil erosion with average soil erosion modulus of 0.27 and 0.46 t•km-2, respectively. Nevertheless, there are no significant difference of runoff and soil loss among different vegetation types under erosive rainstorm events.

Fig.2. Runoff and soil erosion of ten runoff plots under erosive rainstorm events. Note: Solid transverse lines and dots in this figure present the median and mean value, respectively. The box boundaries show the 75% and 25% quartiles, the whisker caps above and under the boxes show the 90% and 10% quartiles, and the hollow circles above and under the boxes indicate the maximum and minimum quartiles. The number of erosive rainstorm events is showed above each boxplot. Within each panel, the different letters means significantly different according to a one way ANOVA (p < 0.05).

14

There are significant variation of surface runoff and soil erosion under vegetation types among different rainstorm events (Fig.3). The highest surface runoff of vegetation types mostly occurred in 2016/08/16 (3.7 mm of As→Sb→Ld, 8.1 mm of Bi, 4.1 mm of Agm + Sb, 5.2 mm of Sv, 2.3 mm of Agm + Agi and 0.8 mm of Ck) and 2018/06/30 (4.0 mm of Agm + Sg and 0.6 mm of Rp). These two rainstorm events were both characterized by higher rainfall amount and maximum 30-minute intensity. Additionally, there were significant differences in soil erosion of vegetation types among different rainstorm events (Fig.3). The highest soil erosion events mostly happened in 2016/06/22 (83.1 t•km-2 of Sb→Agm, 31.0 t•km-2 of Bi, 8.3 t•km-2 of Agm + Sg and 10.9 t•km-2 of Agm + Agi) and 2016/08/16 (7.1 t•km-2 of Asc→Sb→Ld, 23.4 t•km-2 of Sv and 2.0 t•km-2 of Rp). The results showed that the soil erosion under rainstorm events enlarged as the maximum 30-minute intensity increased. However, the 2016/07/19, 2019/07/24 and 2019/08/07 rainstorm events with higher rainfall amount and lower maximum 30-minute intensity led to lower soil erosion. This indicated that the maximum 30-minute intensity, instead of rainfall amount, is the controlling factor of soil erosion.

15

Fig.3. Runoff and soil erosion of bare land and vegetation communities under erosive rainstorm events. Note: The bars of vegetation communities mean the average values of vegetation plots in each rainstorm event, the different letters means significantly difference of vegetation plots between rainstorm events according to a one way ANOVA (p < 0.05).

4. Discussion 4.1 The effects of vegetation types on runoff and soil erosion It has been demonstrated worldwide that vegetation restoration can effectively reduce surface runoff and soil loss under erosive rainstorm events (Cerdan et al., 2002; Kang et al., 2001; Wang et al., 2016; Wei et al., 2009). Previous studies also proved that the vegetation types in later succession stages had relatively high community functional diversity which would generate smaller soil erosion (Zhu et al., 2015). The soil physical properties gradually improved with more

16

soil organic matter, water stable aggregates and enhanced soil infiltration capacity as the abandoned ages increased, which ultimately decreased runoff and erosion (Zhang et al., 2015; Chen et al., 2017a; Chen et al., 2017b). Besides, the vegetation coverage constantly increased as abandoned ages advanced in current study (Table 4) and the vegetation coverage correlated negatively with surface runoff and soil erosion significantly (Zhou et al., 2016). In this study, the vegetation coverage and litter coverage of vegetation types with abandoned ages longer than 20 years (plot 5-10) were higher than those of vegetation types with abandoned ages shorter than 20 years (plot 2-4). The average vegetation coverage and litter coverage in study period were 37.7% and 17.4% of plot 2-4 and 59.2% and 41.8% of plot 5-10, respectively (Table 1). As a consequence, the average runoff and soil loss of plot 2-4 were 1.9 and 3.2 times higher than those of plot 5-10 under 11 rainstorm events (Fig.2). Notably, the Ck and Rp community generated much smaller surface runoff and soil erosion than those of other vegetation types under erosive rainstorm events (Fig.2). The Robinia pseudoacacia was the only arbor species in all vegetation types of current study, and the canopy of arbor was considered to protect soil from erosion effectively by intercepting rainfall (Bochet et al., 2006; Liu, 1998; Zhao et al., 2001). Furthermore, average coverage of litter layers for the Robinia pseudoacacia was 92.8% from 2015 to 2019, which was higher than other vegetation types (Table 1). The litter layer under the vegetation types led to higher surface roughness and enhanced infiltration capacity (Boer and Puigdefábregas, 2005; Woods and Balfour, 2010). Moreover, the soil non-capillary porosity and soil particle fractal dimension of Robinia pseudoacacia community have been directly improved, consequently enhancing the soil infiltration capacity (Tang et al., 2019). The high soil infiltration capacity decreased the flow velocity and runoff depth effectively (Bodí et al., 2012; Cerdà and Doerr, 2008) and accordingly led to little runoff and soil loss (Fig.2). Besides, the Ck type had the average vegetation coverage of 67.8%, which was the highest among all vegetation types. Moreover, the litter coverage of Ck

17

type was 58.9%, which was just lower than that of the Rp among all types (Table 1). Vegetation cover and litter layers which were close to ground can also protect surface soil against raindrop splash and control surface runoff and soil erosion, effectively (Chen et al., 2018; Liu et al., 2017; Wang et al., 2001). In current study, the average runoff of Ck and Rp types under 11 erosive rainstorm events were 0.20 and 0.17 mm, and the soil erosion of the two vegetation types were 0.26 and 0.45 t•km-2. The surface runoff and soil erosion of Ck and Rp types were smaller compared with other vegetation types with a reduction of 86.7% and 87.6% in average runoff depth, 92.7% and 87.5% in average soil erosion, respectively.

4.2 Response of runoff and soil erosion to erosive rainstorm events The erosive rainstorm events could generate several times surface runoff and soil erosion higher than ordinary erosive events which should be paid attention to prevent (Table 6,7). The max runoff event of bare land had the runoff depth of 12.4 mm, which was 15.5 times higher than average runoff depth in ordinary events. In addition, the highest runoff depth among vegetation types was 8.1 mm of Bi, which was 77.1 times as average runoff depth of ordinary events in the vegetation type. The runoff ratio of max event to average ordinary events under vegetation types were higher than the ratio of bare land because of the slight runoff depth under ordinary events of vegetation types. The max soil loss event of bare land had the soil erosion modulus of 2883 t•km2,

which equaled 101.2 times of average soil erosion modulus in ordinary events. Besides, the

highest soil erosion modulus among vegetation types was 83.1 t•km-2 of Sb→Agm, which was 141.3 times as average soil erosion modulus of ordinary events in the type. The results highlighted the devastating impact of erosive rainstorm events on surface runoff and soil erosion, which generally agreed with those of previously published studies (Bull et al., 2000; Jiao et al., 2017; Li et al., 2019; Mueller and Pfister, 2011; Wang et al., 2016). The phenomenon may be on account of the synthetic function of high soil moisture and intense rainfall intensity. In the Loess Plateau, rainfall events mostly occurred between June to September on the Loess Plateau (Fu, 18

1989) and the frequent rainfall events caused the high soil moisture content and maintained the soil saturation (Fang et al., 2017; Li et al., 2019; Ponce and Hawkins, 1996). The subsequent erosive rainstorm events with high rainfall intensity (Fig.3), therefore, could generate runoff easily and consequently bring on more soil loss because of high pre-soil moisture and rainfall intensity (Li et al., 2019). Additionally, the rainfall amount and intensity exhibited high temporal variability in the rainy season (Table 5), thus the surface runoff and soil erosion under different rainstorm events were different significantly with each other (Fig.3), which is to blame for the changeable pre-soil moisture and rainfall intensity. For instance, although the erosive rainstorm events happened in 2016/06/22 was only 27.8 mm, it led to max soil loss in bare land and vegetation types of Sb→ Agm, Bi and Agm + Agi. That might be partly due to the erosive rainstorm event occurred in 2016/06/10 with rainfall amount of 46.6 mm and rainfall event happened in 2016/06/11 with rainfall amount of 12.7 mm which jointly contributed to the high antecedent soil moisture content. In the 2016/06/22 erosive rainstorm event, the soil erosion modulus of bare land, Sb→ Agm and Bi types were 101.2, 141.3 and 75.9 times as soil erosion modulus of ordinary erosive events in these types, respectively. On the contrary, the erosive rainstorm of 2019/07/24 was characterized by highest rainfall amount (72.1 mm) and lower runoff and soil erosion. That may be on account of the lower maximum 30-minute intensity and little antecedent rainfall of this erosive rainstorm event. Table 6 The runoff of erosive rainstorm events and their comparison to ordinary rainfall events. Average

Runoff ratio

Runoff ratio

of max event

of average

to average

erosive

ordinary

rainstorm

events

events to

Average runoff depth Max runoff Runoff plot

runoff depth of erosive

depth (mm)

of ordinary rainstorm events (mm) evetns (mm)

19

average ordinary events Bl

12.41

6.67

0.80

15.5

8.3

Asc→Sb→Ld

3.67

0.93

0.11

33.9

8.6

Sb→Agm

7.39

1.79

0.11

66.6

16.1

Bi

8.08

2.14

0.10

77.1

20.4

Agm + Sb

4.14

1.34

0.29

14.3

4.6

Agm + Sg

4.01

1.41

0.09

46.2

16.3

Sv

5.16

1.36

0.22

23.2

6.1

Agm + Agi

2.32

0.74

0.04

55.8

17.9

Ck

0.85

0.18

0.02

36.9

8.0

Rp

0.58

0.17

0.02

25.2

7.5

Note: The ordinary events (38) are erosive events (49) but not erosive rainstorm events (11).

Table 7 The soil erosion of erosive rainstorm events and their comparison to ordinary rainfall events. Soil erosion ratio of Average soil

Soil erosion Average soil

Max soil

erosion of

erosion

erosive

modulus

rainstorm

(t•km-2)

evetns (t•km-

average ratio of max

erosion of

erosive event to

Runoff plot

ordinary

rainstorm average

events (t•km-

events to ordinary

2) 2)

average events ordinary events

Bl

2883.02

451.89

28.48

101.2

15.9

Asc→Sb→Ld

7.14

1.56

0.37

19.4

4.2

Sb→Agm

83.09

9.15

0.59

141.3

15.6

Bi

30.97

4.97

0.41

75.9

12.2

20

Agm + Sb

3.18

0.79

0.29

11

2.7

Agm + Sg

10.99

2.57

0.52

21.1

4.9

Sv

23.36

3.42

0.25

93.7

13.7

Agm + Agi

10.87

2.47

0.36

30.1

6.8

Ck

0.77

0.24

0.11

7

2.1

Rp

1.99

0.45

0.06

33.7

7.5

4.3 Implications Planted shrubs and trees can significantly reduce water and soil loss (Cerda et al., 2017; Chen et al., 2018a; Zhou et al., 2016). In current study, the artifical planted shrub (Ck) and forest (Rp) types had lower average runoff (0.20 and 0.17 mm) and soil erosion (0.26 and 0.45 t•km-2) compared to bare land with a reduction of 97.24%, 97.42% in surface runoff and 99.94%, 99.90% in soil erosion modulus under 11 erosive rainstorm events, respectively. However, large-scale artificial afforestation probably consumed soil water content rapidly and led to the deficits of soil moisture (Fu et al., 2017; Jia et al., 2020; Liu et al., 2018; Zhao et al., 2019). The planted shrubs and trees may form ‘dried soil layer’, which could consequently inhibit the growth and natural succession of vegetation (Chen et al., 2018; Fu et al., 2017; Wang et al., 2011; Shao et al., 2016), ultimately hampering the sustainable development of vegetation restoration and decreasing the soil and water conservation benefits (Chen et al., 2018; Wang et al., 2011). The unsustainability of many ecological restoration projects all over the world, such as the Great Plains Shelterbelt initiated by Roosevelt in 1934, the Great Plan for the Transformation of Nature launched by Stalin in 1940s, the Algerian Green Dam began in 1970s and the Three-North Shelter Forest Program in China started since 1970s (Li and Zhai, 2002) have also proved the rule. Additionally, naturally restored herbaceous vegetation can also effectively control the runoff and soil erosion on abandoned farmland slopes (Chen et al., 2018; Fattet et al., 2011; Wei et al., 2007). And there were no significant differences of surface runoff and soil erosion between planted types and natural vegetation types (Fig.2). Moreover, the natural vegetation succession 21

hardly not require economic and human input and consumed less soil moisture compared to those of exotic trees and shrubs (Chen et al., 2018; Fu et al., 2017; Yang et al., 2017). Hence, the natural vegetation succession could be chosen primarily as a suitable strategy of ecological restoration projects on the semiarid hilly areas. In practice, the trees and shrubs could be planted in areas with abundant soil moisture such as shady slopes or lower part of slopes to fully prevent the runoff and erosion. In the Loess Plateau, the “Grain for Green” Project adopted the natural restoration and artificial afforestation simultaneously and effectively reduced the runoff and sediment (Fu et al., 2011; Fu et al., 2017). Nevertheless, more attention must be paid to the sustainable development of the “Grain for Green” Project in the future.

5. Conclusion The vegetation coverage of different vegetation types would rise with the abandoned age increased and there was high variability in the rainfall characteristics of erosive rainstorm events. The vegetation restoration on abandoned slopes could effectively decrease the surface runoff and soil erosion under the 11 erosive rainstorm events during 2015 to 2019. The vegetation types could reduce 68.0% to 97.4% of surface runoff depth and 98.0% to 99.9% of soil loss compared to bare land under erosive rainstorm events. However, the differences of surface runoff and soil erosion under erosive rainstorm events among vegetation types were not significant. The erosive rainstorm events resulted in much more runoff and soil loss than those of ordinary events and there were significant variances of surface runoff and soil erosion among different erosive rainstorm events. The relatively high soil erosion could happen in certain erosive rainstorm events because of the high rainfall intensity and antecedent soil moisture content. In summary, the erosive rainstorm events should be paid enough attention in probably triggering high runoff and soil erosion in the rainy reasons.

Acknowledgements 22

This work was supported by the National Natural Science Foundation of China (no.41771319) and the National Key Research and Development Program of China (No.2016YFC0501604). We also thank our colleagues Yifeng Zhang, Na Deng, Xiqin Yan, Chunjing Zhao, Tongde Chen, Xue Cao, Yulan Chen, Qian Xu, Xiaotian Zong, Haolin Wang and Jianjun Li for their assistance with fieldwork.

References: Bochet, E., Poesen, J., Rubio, J.L., 2006. Runoff and soil loss under individual plants of a semi-arid Mediterranean shrubland: influence of plant morphology and rainfall intensity. Earth Surf. Processes Landforms. 31(5), 536–549. https://doi.org/10.1002/esp.1351. Bodí, M.B., Doerr, S.H., Cerdà, A., Mataix-Solera, J., 2012. Hydrological effects of a layer of vegetation ash on underlying wettable and water repellent soil. Geoderma. 191, 14–23. https://doi.org/10.1016/j.geoderma.2012.01.006. Boer, M., Puigdefábregas, J., 2005. Effects of spatially structured vegetation patterns on hillslope erosion in a semiarid Mediterranean environment: a simulation study. Earth Surf. Processes Landforms. 30(2), 149–167. https://doi.org/10.1002/esp.1180. Bookhagen, B., 2010. Appearance of extreme monsoonal rainfall events and their impact on erosion in the Himalaya. Geomat. Nat. Hazards Risk. 1(1), 37–50. https://doi.org/10.1080/19475701003625737. Bowker, M.A., Belnap, J., Bala, C.V., Johnson, N.C., 2008. Revisiting classic water erosion models in drylands: The strong impact of biological soil crusts. Soil Biol. Biochem. 40(9), 2309–2316. https://doi.org/10.1016/j.soilbio.2008.05.008. Brown, L.C., West, L.T., Beasley, D.B., Foster, G.R., 1990. Rill erosion one year after incorporation of crop residue. Transactions of the ASAE. 33(5), 1531–1540. https://doi.org/10.13031/2013.31505. Bryndal, T., Franczak, P., Kroczak, R., Cabaj, W., Kołodziej, A., 2017. The impact of extreme rainfall and flash floods on the flood risk management process and geomorphological changes in small Carpathian

23

catchments: a case study of the Kasiniczanka river (Outer Carpathians, Poland). Nat. Hazards. 88(1), 95–120. https://doi.org/10.1007/s11069-017-2858-7. Bull, L.J., Kirkby, M.J., Shannon, J., Hooke, J.M., 2000. The impact of rainstorms on floods in ephemeral channels in southeast Spain. Catena. 38(3), 191–209. https://doi.org/10.1016/S0341-8162(99)00071-5. Burylo, M., Hudek, C., Rey, F., 2011. Soil reinforcement by the roots of six dominant species on eroded mountainous marly slopes (Southern Alps, France). Catena. 84(1–2), 70–78. https://doi.org/10.1016/j.catena.2010.09.007. Buttle, J.M., Farnsworth, A.G., 2012. Measurement and modeling of canopy water partitioning in a reforested landscape: The Ganaraska Forest, southern Ontario, Canada. J. Hydrol. 466–467, 103–114. https://doi.org/10.1016/j.jhydrol.2012.08.021. Cerdà, A., Doerr, S.H., 2008. The effect of ash and needle cover on surface runoff and erosion in the immediate post-fire period. Catena. 74(3), 256–263. https://doi.org/10.1016/j.catena.2008.03.010. Cerda, A., Lucas, B.M.E., Ubeda, X., Francisco, M.J., Keesstra, S., 2017. Pinus halepensis M. versus Quercus ilex subsp Rotundifolia L. runoff and soil erosion at pedon scale under natural rainfall in Eastern Spain three decades after a forest fire. For. Ecol. Manage. 400, 447–456. https://doi.org/10.1016/j.foreco.2017.06.038. Cerdan, O., Govers, G., Le Bissonnais, Y., Van Oost, K., Poesen, J., Saby, N., Gobin, A., Vacca, A., Quinton, J., Auerswald, K., Klik, A., Kwaad, F.J.P.M., Raclot, D. Ionita, I., Rejman, J., Rousseva, S., Muxart, T., Roxo, M.J., Dostal, T., 2010. Rates and spatial variations of soil erosion in Europe: A study based on erosion plot data. Geomorphology. 122(1–2), 167–177. https://doi.org/10.1016/j.geomorph.2010.06.011. Cerdan, O., Le, B.Y., Couturier, A., Bourennane, H., Souchère, V., 2002. Rill erosion on cultivated hillslopes during two extreme rainfall events in Normandy, France. Soil Tillage Res. 67(1), 99–108. https://doi.org/10.1016/S0167-1987(02)00045-4.

24

Chen, H., Zhang, X.P., Abla, M., Lü, D., Yan, R., Ren, Q.F., Ren, Z.Y., Yang, Y.H., Zhao, W.H., Lin, P.F., Liu, B.Y., Yang, X.H., 2018. Effects of vegetation and rainfall types on surface runoff and soil erosion on steep slopes on the Loess Plateau, China. Catena. 170, 141–149. https://doi.org/10.1016/j.catena.2018.06.006. Chen, W.Y., Xu, X.X., Hua, R., Ding, K., Shahmir, A.K., Du, F., 2017a. Effects of forestlands and grasslands on soil aggregates under different vegetation restoration ages in loess hilly region. Acta Sci. Circumst. 37(4), 1486–1492 (in Chinese). https://doi.org/10.13671/j.hjkxxb.2016.0256. Chen, W.Y., Zhang, S.N., Hua, R., Xu, X.X., 2017b. Effects of forestlands and grassland restoration process on soil infiltration characteristics in loess hilly region. J. Beijing For. Univ. (Chin. Ed.) 39(1), 62–69 (in Chinese). https://doi.org/10.13332/j.1000-1522.20160156. Dlamini, P., Orchard, C., Jewitt, G., Lorentz, S., Titshall, L., Chaplot, V., 2011. Controlling factors of sheet erosion under degraded grasslands in the sloping lands of KwaZulu-Natal, South Africa. Agric. Water Manage. 98(11), 1711–1718. https://doi.org/10.1016/j.agwat.2010.07.016. Dos Santos, J.C.N., de Andrade, E.M., Medeiros, P.H.A., Guerreiro, M.J.S. de Queiroz Palácio, H.A., 2017. Effect of Rainfall Characteristics on Runoff and Water Erosion for Different Land Uses in a Tropical Semiarid Region. Water Resour. Manag. 31(1), 173–185. https://doi.org/10.1007/s11269016-1517-1. Douglas, I., 1989. Land degration, soil conservation and the sediment load of the Yellow River, China: Review and assessment. Land Degrad. Dev. 1(2), 141–151. Fang, N.F., Wang, L., Shi, Z.H., 2017. Runoff and soil erosion of field plots in a subtropical mountainous region of China. J. Hydrol. 552, 387–395. https://doi.org/10.1016/j.jhydrol.2017.06.048. Fattet, M., Fu, Y., Ghestem, M., Ma, W., Foulonneau, M., Nespoulous, J., Le Bissonnais, Y., Stokes, A., 2011. Effects of vegetation type on soil resistance to erosion: Relationship between aggregate stability and shear strength. Catena. 87(1), 60–69. https://doi.org/10.1016/j.catena.2011.05.006.

25

Fu, B.J., Liu, Y., Lu, Y.H., He, C.S., Zeng, Y., Wu, B.F., 2011. Assessing the soil erosion control service of ecosystems change in the Loess Plateau of China. Ecol. Complex. 8(4), 284–293. https://doi.org/10.1016/j.ecocom.2011.07.003. Fu, B.J., Wang, S., Liu, Y., Liu, J.B., Liang, W., Miao, C.Y., 2017. Hydrogeomorphic Ecosystem Responses to Natural and Anthropogenic Changes in the Loess Plateau of China. Annu. Rev. Earth Planet. Sci. 45(1), 223–243. https://doi.org/10.1146/annurev-earth-063016-020552. Fu, B.J., 1989. Soil erosion and its control in the loess plateau of China. Soil Use Manage. 5(2), 76–82. https://doi.org/10.1111/j.1475-2743.1989.tb00765.x. García-Ruiz, J.M., 2010. The effects of land uses on soil erosion in Spain: A review. Catena, 81(1), 1–11. https://doi.org/10.1016/j.catena.2010.01.001. García-Ruiz, J.M., Beguería, S., Nadal-Romero, E., González-Hidalgo, J.C., Lana-Renault, N., Sanjuán, Y., 2015. A meta-analysis of soil erosion rates across the world. Geomorphology. 239, 160–173. https://doi.org/10.1016/j.geomorph.2015.03.008. Gaur, M.L., Mathur, B.S., 2003. Modeling event-based temporal variability of flow resistance coefficient. J. Hydrol. 8(5), 266–277. https://doi.org/10.1061/(ASCE)1084-0699(2003)8:5(266). Geißler, C., Kühn, P., Böhnke, M., Bruelheide, H., Shi, X., Scholten, T., 2012. Splash erosion potential under tree canopies in subtropical SE China. Catena. 91, 85–93. https://doi.org/10.1016/j.catena.2010.10.009. Ghimire, C.P., Bruijnzeel, L.A., Lubczynski, M.W., Bonell, M., 2012. Rainfall interception by natural and planted forests in the Middle Mountains of Central Nepal. J. Hydrol. 475, 270–280. https://doi.org/10.1016/j.jhydrol.2012.09.051. Guo, Q.K., Hao, Y.F., Liu, B.Y., 2015. Rates of soil erosion in China: A study based on runoff plot data. Catena. 124, 68–76. https://doi.org/10.1016/j.catena.2014.08.013.

26

Helming, K., Römkens, M.J.M., Prasad, S.N., 1998. Surface roughness related processes of runoff and soil loss: a flume study. Soil Sci. Soc. Am. J. 62, 243–250. https://doi.org/10.2136/sssaj1998.03615995006200010031x. Hosseini, M., Keizer, J.J., Pelayo, O.G., Prats, S.A., Ritsema, C., Geissen, V., 2016. Effect of fire frequency on runoff, soil erosion, and loss of organic matter at the micro-plot scale in north-central Portugal. Geoderma. 269, 126–137. https://doi.org/10.1016/j.geoderma.2016.02.004. Jia, X.X., Zhao, C.L., Wang, Y.Q., Zhu, Y.J., Wei, X.R., Shao, M.A., 2020. Traditional dry soil layer index method overestimates soil desiccation severity following conversion of cropland into forest and grassland on China’s Loess Plateau. Agr. Ecosyst. Environ. 291, 106794. https://doi.org/10.1016/j.agee.2019.106794.Jiao, J.Y., Tzanopoulos, J., Xofis, P., Mitchley, J., 2008. Factors Affecting Distribution of Vegetation Types on Abandoned Cropland in the Hilly-Gullied Loess Plateau Region of China. Pedosphere. 18(1), 24–33. https://doi.org/10.1016/S10020160(07)60099-X. Jiao, J.Y., Wang, W.Z., Hao, X.P., 1999. Precipitation and erosion characteristics of rain-storm in different pattern on Loess Plateau. J Arid Land Resour Environ. 13(1), 38–42 (in Chinese). https://doi.org/10.1088/0256-307X/15/12/025. Jiao, J.Y., Wang, Z.J., Wei, Y.H., Su, Y., Cao, B.T., Li, Y.J., 2017. Characteristics of erosion sediment yield with extreme rainstorms in Yanhe Watershed based on field measurement. Trans. Chin. Soc. Agric. Eng. 33(13), 159–167 (in Chinese). https://doi.org/10.11975/j.issn.1002-6819.2017.13.021. Kang, S.Z., Zhang, L., Song, X.Y., Zhang, S.H., Liu, X.Z., Liang, Y.L., Zheng, S.Q., 2001. Runoff and sediment loss responses to rainfall and land use in two agricultural catchments on the Loess Plateau of China. Hydrol. Process. 15(6), 977–988. https://doi.org/10.1002/hyp.191. Lal, R., 2001. Soil degradation by erosion. Land Degrad. Dev. 12(6), 519–539. https://doi.org/10.1002/ldr.472. Li, P., Xu, G.C., Lu, K.X., Zhang, X.M., Shi, P., Bai, L.L., Ren, Z.P., Pang, G.W., Xiao, L., Gao, H.D., Pan, M.H., 2019. Runoff change and sediment source during rainstorms in an ecologically constructed 27

watershed on the Loess Plateau, China. Sci. Total Environ. 664, 968–974. https://doi.org/10.1016/j.scitotenv.2019.01.378. Li, S.D., Zhai, H.B., 2002. The comparison study on forestry ecological projects in the world. Acta Ecol. Sin. 22(11), 1976–1982 (in Chinese). https://doi.org/10.3321/j.issn:1000-0933.2002.11.025. Liu, W.J., Luo, Q.P., Lu, H.J., Wu, J.E., Duan, W.P., 2017. The effect of litter layer on controlling surface runoff and erosion in rubber plantations on tropical mountain slopes, sw china. Catena. 149, 167–175. https://doi.org/10.1016/j.catena.2016.09.013. Liu, Y., Miao, H.T., Huang, Z., Cui, Z., He, H.H., Zheng, J.Y., Han, F.P., Chang, X.F., Wu, G.L., 2018. Soil water depletion patterns of artificial forest species and ages on the Loess Plateau (China). For. Ecol. Manage. 417, 137–143. https://doi.org/10.1016/j.foreco.2018.03.005. Martı́nez-Casasnovas, J.A., Ramos, M.C., Ribes-Dasi, M., 2002. Soil erosion caused by extreme rainfall events: mapping and quantification in agricultural plots from very detailed digital elevation models. Geoderma, 105(1), 125–140. https://doi.org/10.1016/S0016-7061(01)00096-9. Mohammad, A.G., Adam, M.A., 2010. The impact of vegetative cover type on runoff and soil erosion under different land uses. Catena. 81(2), 97–103. https://doi.org/10.1016/j.catena.2010.01.008. Molina, A., Vanacker, V., Balthazar, V., Mora, D., Govers, G., 2012. Complex land cover change, water and sediment yield in a degraded Andean environment. J. Hydrol. 472–473, 25–35. https://doi.org/10.1016/j.jhydrol.2012.09.012.Mueller, E.N., Pfister, A., 2011. Increasing occurrence of high-intensity rainstorm events relevant for the generation of soil erosion in a temperate lowland region in Central Europe. J. Hydrol. 411(3–4), 266–278. https://doi.org/10.1016/j.jhydrol.2011.10.005. Pannkuk, C.D., Robichaud, P.R., 2003. Effectiveness of needle cast at reducing erosion after forest fires. Water Resour. Res. 39(12), 1333. https://doi.org/10.1029/2003WR002318. Peng, T., Wang, S., 2012. Effects of land use, land cover and rainfall regimes on the surface runoff and soil loss on karst slopes in southwest China. Catena, 90, 53–62. https://doi.org/10.1016/j.catena.2011.11.001.

28

Ponce, V.M., Hawkins, R.H., 1996. Runoff curve number: Has it reached maturity? J. Hydraul. Eng. 1, 11– 19. https://doi.org/10.1061/(ASCE)1084-0699(1996)1:1(11). Puigdefábregas, J., 2005. The role of vegetation patterns in structuring runoff and sediment fluxes in drylands. Earth Surf. Process. Landf. 30(2), 133–147. https://doi.org/10.1002/esp.1181. Qu, Z.X., Wu, Y.S., Wang, H.X., Jiang, H.Q., Tang, T.G., 1983. Plant ecology. Higher Education Press: Beijing. (in Chinese) Raclot, D., Le Bissonnais, Y., Annabi, M., Sabir, M., Smetanova, A., 2018. Main Issues for Preserving Mediterranean Soil Resources From Water Erosion Under Global Change. Land Degrad. Dev. 29(3), 789–799. https://doi.org/10.1002/ldr.2774. Ren, Z.P., Zhu, L.J., Wang, B., Cheng. S.D., 2016. Soil hydraulic conductivity as affected by vegetation restoration age on the Loess Plateau, China. J Arid Land. 8, 546–555. https://doi.org/10.1007/s40333016-0010-2. Renard, K.G., Foster, G.R., Weesies, G.A., McCool, D.K., Yoder, D.C., 1997. Predicting soil erosion by water: A guide to conservation planning with the revised universal soil loss equation (RUSLE). U.S. Department of Agriculture Agricultural Handbook. No. 703. US Department of Agriculture, Washington, DC. Rodríguez-Caballero, E., Cantón, Y., Chamizo, S., Afana, A., Solé-Benet, A., 2012. Effects of biological soil crusts on surface roughness and implications for runoff and erosion. Geomorphology, 145–146(1), 81–89. https://doi.org/10.1016/j.geomorph.2011.12.042. Shao, M.A., Jia, X.X., Wang, Y.Q., 2016. A review of studies on dried soil layers in the Loess Plateau. Adv. Earth Sci. 31(1), 14–22 (in Chinese). https://doi.org/10.11867/ j.issn.1001-8166.2016.01.0014. Shi, H., Shao, M.A., 2000. Soil and water loss from the Loess Plateau in China. J. Arid. Environ. 45(1), 9– 20. https://doi.org/10.1006/jare.1999.0618.

29

Liu, S.J., 1998. Estimation of rainfall storage capacity in the canopies of cypress wetlands and slash pine uplands in NorthCentral Florida. J. Hydrol. 207(1–2), 0–41. https://doi.org/10.1016/s00221694(98)00115-2. Sun, G., Zhou, G.Y., Zhang, Z.Q., Wei, X.H., McNulty, S.G., Vose, J.M., 2006. Potential water yield reduction due to forestation across China. J. Hydrol. 328(3–4), 548–558. https://doi.org/10.1016/j.jhydrol.2005.12.013. Sun, L., Zhang, G.H., Liu, F., Luan, L.L., 2016. Effects of incorporated plant litter on soil resistance to flowing water erosion in the Loess Plateau of China. Biosyst. Eng. 147, 238–247. https://doi.org/10.1016/j.biosystemseng.2016.04.017. Tang, B.Z., Jiao, J.Y., Yan, F.C., Li, H., 2019. Variations in soil infiltration capacity after vegetation restoration in the hilly and gully regions of the Loess Plateau, China. J. Soils Sediments. 19(3), 1456– 1466. https://doi.org/10.1007/s11368-018-2121-1. Tang, K.L., Xiong, G.S., Liang, J.Y., Jing, K., Zhang, S.L., Chen, Y.Z., Li, S.M., 1993. Varieties of Erosion and Runoff Sdeiment in Yellow River Bain. Chinese Sciences and Technique Press, Beijing (in Chinese). Tang, K.L., 2004. Soil and Water Conservation in China. Science China Press, Beijing (in Chinese). Wang, X.P., Zhang, Y.F., Hu, R., Pan, Y.X., Berndtsson, R., 2012. Canopy storage capacity of xerophytic shrubs in Northwestern China. J. Hydrol. 454–455, 152–159. https://doi.org/10.1016/j.jhydrol.2012.06.003. Wang, H.S., Liu, G.B., Wang, Q.N., 2001. Structural characteristics of effective vegetation for preventing soil erosion. Chin. J. Eco-Agric. 9(2), 58–60 (in Chinese). https://doi.org/CNKI:SUN:ZGTN.0.200102-018. Wang, L.J., Zhang, G.H., Wang, X., Zhu, P.Z., 2019. Soil loss: Effect of plant litter incorporation rate under simulated rainfall conditions. Land Degrad. Dev. 30(10), 1193–1203. https://doi.org/10.1002/ldr.3304.

30

Wang, W.Z., Jiao, J.Y., 2018. Rainfall and Erosion Sediment Yield and Sediment Reduction of Soil and Water Conservation in the Loess Plateau. Science China Press, Beijing (in Chinese). Wang, Y.Q., Shao, M.A., Zhu, Y.J., Liu, Z.P., 2011. Impacts of land use and plant characteristics on dried soil layers in different climatic regions on the Loess Plateau of China. Agric. For. Meteorol. 151(4), 437–448. https://doi.org/10.1016/j.agrformet.2010.11.016. Wang, Z.J., Jiao, J.Y., Rayburg, S., Wang, Q.L., Su, Y., 2016. Soil erosion resistance of “Grain for Green ” vegetation types under extreme rainfall conditions on the Loess Plateau, China. Catena. 141, 109– 116. https://doi.org/10.1016/j.catena.2016.02.025. Wei, W., Chen, L.D., Fu, B.J., Huang, Z.L., Wu, D.P., Gui, L.D., 2007. The effect of land uses and rainfall regimes on runoff and soil erosion in the semi-arid loess hilly area, China. J. Hydrol. 335(3–4), 247– 258. https://doi.org/10.1016/j.jhydrol.2006.11.016. Wei, W., Chen, L.D., Fu, B.J., Lü, Y.H., Gong, J., 2009. Responses of water erosion to rainfall extremes and vegetation types in a loess semiarid hilly area, NW China. Hydrol. Process. 23(12), 1780–1791. https://doi.org/10.1002/hyp.7294. Wischmeier, W.H., Smith, D.D., 1958. Rainfall energy and its relationship to soil loss. Trans. American Geophysical Union. 39(2), 285–291. https://doi.org/10.1029/TR039i002p00285. Woods, S.W., Balfour, V.N., 2010. The effects of soil texture and ash thickness on the post-fire hydrological response from ash-covered soils. J. Hydrol. 393(3–4), 274–286. https://doi.org/10.1016/j.jhydrol.2010.08.025. Xiong, M.Q., Sun, R.H., Chen, L.D, 2019. A global comparison of soil erosion associated with land use and climate type. Geoderma. 343, 31–39. https://doi.org/10.1016/j.geoderma.2019.02.013. Xu, X.X., Jun, T.J, Zheng, S.Q., 2013. Sediment sources of Yan'gou watershed in the Loess Hilly region China under a certain rainstorm event. SpringerPlus. 2.Suppl 1: S2. Yang, Y., Dou, Y.X., Liu, D., An, S.S., 2017. Spatial pattern and heterogeneity of soil moisture along a transect in a small catchment on the Loess Plateau. J. Hydrol. 550, 466–477. 31

https://doi.org/10.1016/j.jhydrol.2017.05.026.Zhang, L., Wang, J.M., Bai., Z.K., Lü, C.J., 2015. Effects of vegetation on runoff and soil erosion on reclaimed land in an opencast coal-mine dump in a loess area. Catena. 128, 44–53. https://doi.org/10.1016/j.catena.2015.01.016. Zhao, C.L., Shao, M.A., Jia, X.X., Zhu, Y.J., 2019. Factors Affecting Soil Desiccation Spatial Variability in the Loess Plateau of China. Soil Sci. Soc. Am. J. 83(2), 266–275. https://doi:10.2136/sssaj2017.11.0391. Zhao, H.Y., Wu, Q.X., Liu, G.B., 2001. Mechanism on soil and water conservation of forest vegetation on the Loess Plateau. Sci. Silv. Sin. 37(5), 140–144 (in Chinese). https://doi.org/10.3321/j.issn:10017488.2001.05.024. Zheng, F. L., 2006. Effect of vegetation changes on soil erosion on the loess plateau. Pedosphere. 16(4), 420–427. https://doi.org/10.1016/s1002-0160(06)60071-4. Zheng, M.G., Cai, Q.G., Chen, Q.J., 2008. Modelling the runoff-sediment yield relationship using a proportional function in hilly areas of the Loess Plateau, North China. Geomorphology. 93(3–4), 288– 301. https://doi.org/10.1016/j.geomorph.2007.03.001. Zhou, J., Fu, B.J., Gao, G.Y., Lü, Y.H., Liu, Y., Lü, N., Wang, S., 2016. Effects of precipitation and restoration vegetation on soil erosion in a semi-arid environment in the Loess Plateau, China. Catena. 137, 1–11. https://doi.org/10.1016/j.catena.2015.08.015. Zhou, J., Fu, B.J., Yan, D.C., Lü, Y.H. Wang, S., Gao, G.Y., 2019. Assessing the integrity of soil erosion in different patch covers in semi-arid environment. J. Hydrol. 571, 71–86. https://doi.org/10.1016/j.jhydrol.2019.01.056. Zhu, H.X., Fu, B.J., Wang, S., Zhu, L.H., Zhang, L.W., Jiao, L., Wang, C., 2015. Reducing soil erosion by improving community functional diversity in semi-arid grasslands. J. Appl. Ecol. 52, 1063–1072. https://doi.org/10.1111/1365-2664.12442.

Ａppendix: Table A.1 Species composition of vegetation plots from 2015 to 2019. 32

Plot No.

2

3

4

5

6

7

Year

Species with the top 5 importance value

2015

Asc

Ld

Pb

Ha

Sb

2016

Sb

Pt

Ld

Pa

Ha

2017

Sb

Svi

Ld

Asc

Pb

2018

Ld

Ha

Pta

Pta

Svi

2019

Ld

Asc

Svi

Ls

Pb

2015

Sb

Ame

Ld

Agm

Asc

2016

Sb

Ld

Mo

Agm

Va

2017

Agm

Ph

Ma

Sg

Ld

2018

Agm

Va

Sb

Ps

Bi

2019

Agm

Ame

Sb

Ps

Ld

2015

Bi

Ld

Sb

Cs

Pta

2016

Bi

Ld

Sb

Cc

Pta

2017

Bi

Ld

Pta

Sb

Pb

2018

Bi

Pb

Ld

Ch

Asc

2019

Bi

Ld

Pta

Ha

Agm

2015

Agm

Sb

Ld

Ame

Va

2016

Agm

Sb

Msu

Pta

Ld

2017

Agm

Sb

Ld

Pta

Ma

2018

Agm

Sb

Ld

Lu

Va

2019

Agm

Ps

Ld

Lu

Mo

2015

Agm

Sb

Ld

Ha

Va

2016

Agm

Sb

Ha

Va

Sch

2017

Agm

Ld

Sb

Vd

Lm

2018

Agm

Sce

Sb

Ld

Iso

2019

Agm

Vd

Lu

Lu

St

2015

Sv

Agm

Ld

Sd

Sb

2016

Sv

Agm

Ld

Ha

Pta

2017

Sv

Agm

Ld

Sg

Pte

2018

Sv

Agm

Ld

Pta

Cf

2019

Sv

Agm

Ld

Pte

Pte

33

8

9

10

2015

Ps

Agm

Ame

Lm

Pch

2016

Agm

Pta

Ld

Pa

Ha

2017

Ps

Agm

Lm

Mo

Va

2018

Ps

Agi

Lm

Agm

Amo

2019

Ps

Pta

Agm

Ame

Bi

2015

Ck

Agm

Agi

Ld

Sb

2016

Ck

Agm

Sb

Ld

Agi

2017

Ck

Agm

Ld

Agi

Ck

2018

Ck

Agi

Agm

Wc

Wc

2019

Ck

Agm

Ld

Rc

Bi

2015

Rp

Svi

Pa

Ac

Sn

2016

Rp

Asp

Ah

Ca

Isi

2017

Rp

Svi

Agm

Msc

Rc

2018

Rp

Amo

Asc

St

Pce

2019

Rp

Svi

Agm

Amo

Rc

Note: Asc: Artemisia scoparia, Sb: Stipa bungeana, Ld: Lespedeza davurica, Agm: Artemisia gmelinii, Bi: Bothriochloa ischaemum, Sg: Stipa grandis, Sv: Sophora viciifolia, Agi: Artemisia giraldii, Ck: Caragana korshinskii, Rp: Robinia pseudoacacia, Pb: Potentilla bifurca, Ha: Heteropappus altaicus, Pta: Potentilla tanacetifolia, Pa: Poa annua, Svi: Setaria viridis, Ls: Lagedium sibiricum, Ame: Astragalus melilotoides, Mo: Melilotus officinalis, Va: Vicia amoena, Ph: Patrinia heterophylla, Ma: Melilotus albus, Ps: Patrinia scabiosaefolia, Cs: Cleistogenes squarrosa, Cc: Cleistogenes chinensis, Ch: Cleistogenes hancei, Msu: Melilotus suaveolens, Lu: Linum usitatissimum, Sch: Serratula chinensis, Vd: Viola dissecta, Lm: Lobularia maritima, Sce: Serratula centauroides, Iso: Ixeridium sonchifolium, St: Stemmacanthauniflora, Sd: Sophora davidii, Pte: Polygala tenuifolia, Cf: Clematis fruticosa, Pch: Pulsatilla chinensis, Amo: Artemisia mongolica, Wc: Wikstroemia chamaedaphne, Rc: Rubia cordifolia, Ac: Asparagus cochinchinensis, Sn: Solanum nigrum, Asp: Achnatherum splendens, Ah: Artemisia hedinii, Ca: Clematis aethusifolia, Isi: Incarvillea sinensis, Msc: Melica scabrosa, St: Speranskia tuberculata, Pce: Pennisetum centrasiaticum.

Conceptualization, Yue Liang and Juying Jiao; Data curation, Yue Liang, Binting Cao, Hang Li and Bingzhe Tang; Formal analysis, Yue Liang; Funding acquisition, Juying Jiao; Investigation, Yue Liang, Binting Cao, Hang Li and Bingzhe Tang; Methodology, Yue Liang; Software, Yue 34

Liang; Supervision, Yue Liang and Bingzhe Tang; Validation, Juying Jiao; Visualization, Yue Liang; Roles/Writing - original draft, Yue Liang; Writing - review & editing, Yue Liang and Juying Jiao.

Fig.1.(a) The location of Fangta watershed on the Loess Plateau in China, (b) The location of runoff plots in the Fangta watershed, (c) The layout of ten field runoff plots, (d) Bare land and vegetation types in field runoff plots, (e) The runoff-plot system. 35

Fig.2. Runoff and soil erosion of ten runoff plots under erosive rainstorm events. Note: Solid transverse lines and dots in this figure present the median and mean value, respectively. The box boundaries show the 75% and 25% quartiles, the whisker caps above and under the boxes show the 90% and 10% quartiles, and the hollow circles above and under the boxes indicate the maximum and minimum quartiles. The number of erosive rainstorm events is showed above each boxplot. Within each panel, the different letters means significantly different according to a one way ANOVA (p < 0.05).

36

Fig.3. Runoff and soil erosion of bare land and vegetation communities under erosive rainstorm events. Note: The bars of vegetation communities mean the average values of vegetation plots in each rainstorm event, the different letters means significantly difference of vegetation plots between rainstorm events according to a one way ANOVA (p < 0.05).

Table 1 Basic characteristics of runoff plots. Abandoned Plot

Average Vegetation type (abbreviation)

No.

Vegetation

Litter

Biotic crust

coverage

coverage

coverage

-

-

-

years (2015Slope/° 2019)

1

Bare land（Bl）

21

-

37

Artemisia scoparia→Stipa 2

bungeana→Lespedeza davurica

35

5-9

20.5 ± 5.6

9.4 ± 2.8

64.7 ± 10.9

21

10-14

36.5 ± 6.5

19.1 ± 5.7

45.7 ± 6.8

23

15-19

56.0 ± 3.3

23.7 ± 5.6

25.1 ± 7.7

25

25-29

51.5 ± 6.7

18.9 ± 5.4

56.5 ± 10.1

29

40-44

61.0 ± 4.8

32.2 ± 13.0

26.8 ± 8.1

35

40-44

50.5 ± 8.5

24.7 ± 5.7

17.5 ± 7.2

32

40-44

65.5 ± 4.6

23.4 ± 6.0

20.4 ± 6.6

（Asc→Sb→Ld） Stipa bungeana→Artemisia 3

4

gmelinii（Sb→Agm） Bothriochloa ischaemum（Bi） Artemisia gmelinii + Stipa

5

bungeana（Agm + Sb） Artemisia gmelinii + Stipa

6

grandis（Agm + Sg） Sophora viciifolia（Sv）

7

Artemisia gmelinii + Artemisia 8

giraldii（Agm + Agi）

9

Caragana korshinskii（Ck）

43

20-24

67.8 ± 3.9

58.9 ± 12.8

20.9 ± 13.6

10

Robinia pseudoacacia（Rp）

23

30-34

58.6 ± 6.9

92.8 ± 3.0

1.0 ± 1.0

Note: The coverages were measured in the August; Data of the coverage are given as means ± standard error of means.

Table 2 Erosive rainstorm criterion of different rainfall durations in the Loess Plateau (Wang and Jiao, 2018). Rainfall duration (min)

5

10

15

30

60

120

180

240

360

720

1440

Rainfall amount (mm)

5.8

7.1

8.0

9.7

11.9

14.6

17.8

20.5

25.0

35.1

50.0

Table 3 Main species of vegetation plots from 2015 to 2019. Plot No.

2015

2016

2017

2018

2019

2

Asc

Sb

Sb

Ld

Ld

3

Sb

Sb

Agm

Agm

Agm

38

4

Bi

Bi

Bi

Bi

Bi

5

Agm

Agm

Agm

Agm

Agm

6

Agm

Agm

Agm

Agm

Agm

7

Sv

Sv

Sv

Sv

Sv

8

Ps

Agm

Ps

Ps

Ps

9

Ck

Ck

Ck

Ck

Ck

10

Rp

Rp

Rp

Rp

Rp

Note: Asc: Artemisia scoparia, Sb: Stipa bungeana, Ld: Lespedeza davurica, Agm: Artemisia gmelinii, Bi: Bothriochloa ischaemum, Sv: Sophora viciifolia, Ps: Patrinia scabiosaefolia, Ck: Caragana korshinski, Rp: Robinia pseudoacacia.

Table 4 Rainfall characteristics of rainy season from 2015 to 2019. Erosive Number of Rainfall

Number

rainfall

Year

Erosive rainstorm

Number of erosive

amount (mm)

rainstorm events

erosive amount (mm)

of events

amount events (mm)

2015

181.8

36

137.1

11

0

0

2016

466.2

21

410.5

14

226.8

5

2017

437.0

11

204.0

6

48.9

1

2018

388.6

38

286.8

10

91.4

3

2019

459.8

39

324.0

10

139.5

2

Note: The erosive events refer to the rainfall events which generate runoff at least in one vegetation plot.

Table 5 Characteristics of erosive rainstorm events from 2015 to 2019. Date

P (mm)

T (h)

I15 (mm•h-1)

I30 (mm•h-1)

I60 (mm•h-1)

The erosive rainstorm criterion met

2016/06/10

46.6

2.5

38.4

25.2

18.9

P (15 min) >8.0 mm

2016/06/22

27.8

3.0

37.2

33.2

27.4

P (15 min) >8.0 mm

2016/07/06

34.0

1.5

52.8

41

21.9

P (15 min) >8.0 mm

2016/07/19

58.5

15.0

14

12

10.7

P (720 min) >35.1 mm

2016/08/16

60.0

15.3

63.6

38.4

19.7

P (15 min) >8.0 mm

39

2017/05/24

48.9

19.5

26.4

22.2

18.1

P (30 min) >9.7 mm

2018/06/30

54.6

10.0

90.4

62.2

37.3

P (5 min) >5.8 mm

2018/08/07

14.7

2.0

17.9

17.9

13.4

P (60 min) >11.9 mm

2018/09/06

22.1

9.2

20.2

14.6

12.2

P (60 min) >11.9 mm

2019/07/24

72.1

15.8

31.2

21.6

16.6

P (30 min) >9.7 mm

2019/08/7

67.4

20.0

29.2

26.2

21.1

P (30 min) >9.7 mm

Note: Note: P, rainfall amount (mm); T, rainfall duration (h); I15, maximum 15-minute intensity (mm•h-1); I30, maximum 30-minute intensity (mm•h-1); I60, maximum 60-minute intensity (mm•h-1).

Table 6 The runoff of erosive rainstorm events and their comparison to ordinary rainfall events. Runoff ratio of average Average

Runoff ratio Average

runoff depth Max runoff Runoff plot

erosive of max event

runoff depth of erosive

rainstorm to average

depth (mm)

of ordinary rainstorm

events to ordinary

events (mm) evetns (mm)

average events ordinary events

Bl

12.41

6.67

0.80

15.5

8.3

Asc→Sb→Ld

3.67

0.93

0.11

33.9

8.6

Sb→Agm

7.39

1.79

0.11

66.6

16.1

Bi

8.08

2.14

0.10

77.1

20.4

Agm + Sb

4.14

1.34

0.29

14.3

4.6

Agm + Sg

4.01

1.41

0.09

46.2

16.3

Sv

5.16

1.36

0.22

23.2

6.1

Agm + Agi

2.32

0.74

0.04

55.8

17.9

Ck

0.85

0.18

0.02

36.9

8.0

Rp

0.58

0.17

0.02

25.2

7.5

40

Table 7 The soil erosion of erosive rainstorm events and their comparison to ordinary rainfall events. Soil erosion ratio of Average soil

Soil erosion Average soil

Max soil

erosion of

erosion

erosive

modulus

rainstorm

(t•km-2)

evetns (t•km-

average ratio of max

erosion of

erosive event to

Runoff plot

ordinary

rainstorm average

events (t•km-

events to ordinary

2) 2)

average events ordinary events

Bl

2883.02

451.89

28.48

101.2

15.9

Asc→Sb→Ld

7.14

1.56

0.37

19.4

4.2

Sb→Agm

83.09

9.15

0.59

141.3

15.6

Bi

30.97

4.97

0.41

75.9

12.2

Agm + Sb

3.18

0.79

0.29

11

2.7

Agm + Sg

10.99

2.57

0.52

21.1

4.9

Sv

23.36

3.42

0.25

93.7

13.7

Agm + Agi

10.87

2.47

0.36

30.1

6.8

Ck

0.77

0.24

0.11

7

2.1

Rp

1.99

0.45

0.06

33.7

7.5

(1) Vegetation restoration could significantly decrease surface runoff and soil erosion compared to the bare land. (2) There were no significant difference in surface runoff and soil loss between different vegetation types within the same erosive rainstorm event. 41

(3) The surface runoff and soil erosion had significant difference between different erosive rainstorm events in the same vegetation types.

42