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Journal of Resources and Ecology >

2022 , Vol. 13 >Issue 1: 113 - 119

DOI: https://doi.org/10.5814/j.issn.1674-764x.2022.01.013

Restoration Ecology and Ecological Engineering

The Ecological Water Demand of Different Vegetation Types in the Bashang Area, Northwest Hebei Province

  • XU Zhongqi , 1, †, * ,
  • ZHANG Naixuan , 1, † ,
  • WANG Ran 1 ,
  • YANG Xin 1 ,
  • SUN Shoujia 2 ,
  • YAN Tengfei 3
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  • 1. College of Forestry, Agricultural University of Hebei, Baoding, Hebei 071000, China
  • 2. Chinese Academy of Forestry, Beijing 100091, China
  • 3. Forestry Bureau of Zhangbei County, Zhangbei, Hebei 076450, China
* XU Zhongqi, E-mail:

† means that they have the same contribution to this paper.

XU Zhongqi, E-mail:

ZHANG Naixuan, E-mail:

Received date: 2021-07-21

  Accepted date: 2021-10-18

  Online published: 2022-01-08

Supported by

The Forestry Industry Public Welfare Project(201404206-02)

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Abstract

In order to construct stable vegetation for reducing wind and sand disasters and soil erosion in the Bashang Area of Northwest Hebei Province in China, it is very important to understand the ecological water demand of different vegetation types in this area. Based on observed data and the Irmak-Allen formula, we investigated the ecological water demand and ecological water shortage of arbor, shrub and grassland in Bashang Area of northwestern Hebei province. The results showed that the actual evapotranspiration values of the three vegetation types in the growing seasons in the study area from high to low were arbor forest (401.81 mm), shrub (358.78 mm) and grassland (346.02 mm). The minimum ecological water requirements of arbor forest, shrub and grassland in the growing season were 243.96 mm, 218.35 mm and 211.36 mm, respectively, and the optimal ecological water requirements were 472.99 mm, 423.34 mm and 409.77 mm, respectively. In addition, the optimal ecological water shortage values were 198.56 mm for arbor forest, 148.91 mm for shrub and 135.34 mm for grassland. The ecological water shortage of vegetation has obvious seasonality, with the largest water shortage in May and June, and a lower and steady water surplus in July to October. Therefore, an artificial water supplementation in May and June would alleviate the drought stress of the vegetation. The rainfall in Bashang Area of Northwest Hebei Province can meet the requirements of minimum ecological water demand for arbor forest, but the gap between the rainfall and the optimal ecological water requirement is too large to support good growth of an arbor forest, which could explain why the degradation of poplar protective forests has occurred in Bashang Area.

Key words： Bashang Area; Northwest Hebei; vegetation; actual evapotranspiration; ecological water demand

Cite this article

XU Zhongqi , ZHANG Naixuan , WANG Ran , YANG Xin , SUN Shoujia , YAN Tengfei . The Ecological Water Demand of Different Vegetation Types in the Bashang Area, Northwest Hebei Province[J]. Journal of Resources and Ecology, 2022 , 13(1) : 113 -119 . DOI: 10.5814/j.issn.1674-764x.2022.01.013

1 Introduction

The water condition is the main factor determining vegetation type and growth conditions in an area (Wang, 2000). If the water conditions cannot meet the needs of vegetation, whether due to anthropogenic or natural factors, then the vegetation tends to degenerate or needs to be replaced by other vegetation types. Therefore, understanding the water demand of different vegetation options is the basis for vegetation construction. Vegetation ecological water demand represents the amount of water that must be supplied to ensure the healthy growth of vegetation and the normal functioning of ecological services. It is generally evaluated by vegetation evapotranspiration (He et al., 2004). According to the different living conditions of vegetation types, the ecological water demand of vegetation can be divided into different grades (Zhang and Yang, 2002). Compared with other measures, the minimum water requirement of vegetation and the optimal water requirement of vegetation growth are studied more often. The former refers to the amount of water required for vegetation to maintain the minimum survival state, and the latter refers to the amount of water required for vegetation to maintain a good growth state (Min et al., 2004). Bashang Area in Northwest Hebei is located in the southern edge of the Inner Mongolia Plateau, with arid, low temperature and windy climatic characteristics. Therefore, the wind-sand hazard in this region is serious. In order to control wind and sand, prevent soil erosion and maintain the stable development of local agriculture and animal husbandry, a large number of poplar-based shelter forests have been constructed since the 1960s (Xing, 2015). However, in recent years, there has been large-scale degradation of the poplar shelterbelts in the region, and the degradation area of poplar shelterbelts has reached 81000 ha, accounting for 79.5% of the total area of constructed poplar shelterbelts (Guo, 2013). Some studies suggest that the dry climate of the region could not meet the water demand of the poplar shelterbelts, leading to serious drought stress and the deaths of the poplars (Sun et al., 2018; Zheng et al., 2018; Liu et al., 2021). However, the water consumption of the local shelterbelt and the gap between the local precipitation and the shelterbelt water demand are not clear, and from the viewpoint of vegetation water demand, determining what kind of vegetation, such as arbor forest, shrub or grassland, would be most suitable for the dry climate in the area remains to be studied. Hence, through the combination of actual observation data and model simulation, this paper studied the actual ecological water consumption, ecological water demand, ecological water shortage and their differences for arbor forest, shrub and grassland in Bashang Area, aiming to provide a scientific basis for understanding the causes of poplar shelterbelt degradation and future decision making regarding vegetation construction in the Bashang Area of northwestern Hebei Province.

2 Study area

This study was conducted at Ertai Forest Farm of Zhangbei County (41°19'N, 114°52'E) in Northwest Hebei Province, China. It is adjacent to Guyuan County and Chabei Management Area, 30 km from Zhangbei County and 280 km from Beijing. The forest farm is located in the Bashang Area, the southern edge of Inner Mongolia Plateau The terrain is flat and the altitude is 1300 m. Located in the alpine, arid and semi-arid Bashang Area on the southern edge of Inner Mongolia, the regional climate is a Northern temperate continental monsoon climate with an average annual temperature of 3.2 ℃. The extreme low temperature and extreme high temperature are -43.0 ℃ and 30.0 ℃, respectively. The annual average precipitation is about 300 mm, mainly concentrated in July to August. The average annual evaporation is about 1772 mm. The annual average sunshine duration is nearly 3000 h. The frost-free period of the whole year is between 90 and 110 days. The overall climatic characteristics are mainly diurnal temperature difference, low temperature, windy, less rain, drought, and a short frost-free period. The forest vegetation in this area includes poplar plantations, Pinus sylvestris var. mongolica and elm (Ulmus pumila) plantations, with a coverage of 21.3%. At the same time, and there are shrubs mainly composed of seabuckthorn (Hippophae rhamnoides) and korshinskii (Caragana intermedia). The grassland is mainly composed of Leymus chinensis, Cleistogenes caespitosa, Carex rigescens, Medicago falcata and others.

3 The data sources and research methods

3.1 The data sources

Meteorological data of 2017 came from Zhangbei Meteorological Bureau, and the soil moisture data for the same period were measured by a soil moisture neutron instrument installed in Ertai Forest Farm.

3.2 Calculation of ecological water requirements of the vegetation types

3.2.1 Calculation of vegetation evapotranspiration

The evapotranspiration of vegetation was obtained from the potential evapotranspiration, vegetation coefficient and soil moisture correction coefficient in the region. The calculation formula is as follows (He et al., 2004; Min et al., 2004; Chu, 2009).
ETi=Ks×Kc×ET0
where ETi is the actual evapotranspiration of vegetation type i; ET0 is the potential evapotranspiration of a reference crop determined by local climatic conditions; Ks is the correction coefficient of soil moisture, which is related to soil texture and soil moisture; and Kc is the vegetation coefficient, which is related to vegetation types and growth conditions.

3.2.2 Calculation of potential evapotranspiration

The monthly potential evapotranspiration ET0 of Zhangbei County was calculated by the Irmak-Allen formula. This formula is derived from the Penman-Monteith method, a standard potential evapotranspiration estimation method recommended by the Food and Agriculture Organization of the United Nations (FAO). Several studies have proven that the monthly potential evapotranspiration calculated by this formula is the closest to the calculation results of the Penman-Monteith method recommended by FAO, which is superior to other evapotranspiration calculation methods (Qin et al., 2016; Li et al., 2017).
ET0=0.489+0.28Rn+0.023T
where Rn is the net evapotranspiration of crops, and T is the average temperature.

3.2.3 Determination of vegetation coefficients (Kc)

The area was covered by snow from November to March, during which the vegetation stopped growing. The germination of trees begins in April and ends in October (Xu and Singh, 2005). The vegetation coefficients from April to June were determined according to the research results of Chu (2009) and Chen and Wang (2001), as shown in Table 1.
Table 1 Vegetation coefficients (Kc) of different vegetation types
Month Forest Shrub Grassland
April 0.5 0.4 0.3
May 0.7 0.6 0.6
June 0.9 0.8 0.8
July 1.1 0.9 0.9
August 0.8 0.8 0.8
September 0.6 0.6 0.6
October 0.5 0.5 0.4

3.2.4 Determination of soil amendment coefficient

Ks is the soil correction coefficient, which is the ratio of vegetation evapotranspiration under soil moisture stress to vegetation evapotranspiration under a sufficient soil moisture supply. It is calculated by the Jensen formula (Jensen, 1982; He et al., 2004; Min et al., 2004).
When Sw ≤ S ≤ S*,
${{\text{K}}_{\text{s}}}\text{=}\ln \left( \frac{\text{S}-{{\text{S}}_{\text{w}}}}{{{\text{S}}^{\text{*}}}-{{\text{S}}_{\text{w}}}}\times 100\text{+}1 \right)/\ln 101$
In this formula, S represents the actual soil moisture content; Sw represents soil wilting water content; and S* represents the critical soil water content.
The actual soil water content S is obtained from the actual soil water content data measured by a cosmic ray neutron instrument. The soil wilting water content and soil temporary wilting water content were calculated with reference to the relevant literature, through the poplar plantation sandy land soil moisture characteristic curve formula studied by Liu (2007) and the water potential parameters of soil moisture content studied by He et al. (2004). The growth retardation water content and soil critical water content were calculated from field capacity. The growth retardation water content was 60% of the field capacity (Wang et al., 2017), and the soil critical water content was generally 70%-80% of the field capacity (Zhang and Yang, 2002). The monthly soil moisture correction coefficients Ks were obtained (Table 2).
Table 2 Soil moisture correction factor for each month
Month Monthly average soil moisture (%) Modified soil moisture coefficient KS
April 6.58 0.87
May 4.81 0.79
June 3.08 0.68
July 7.25 0.89
August 3.69 0.73
September 7.10 0.89
October 8.66 0.93
The soil temporary wilting water content (Sr) is represented by the lower limit of the minimum water requirement for vegetation growth, and the growth retardation water content (St) is represented by the lower limit of the optimal water requirement for vegetation growth. From these two values, the soil moisture correction coefficient of the minimum ecological water requirement and the optimal ecological water requirement can be obtained, and the soil moisture correction factors are 0.49 for minimum ecological water demand and 0.95 for optimal ecological water demand.

3.2.5 Determination of vegetation ecological water shortage

Vegetation ecological water shortage represents the difference between vegetation ecological water demand and effective rainfall in the study area (Liu, 2014; Zhou, 2017). The formula is as follows:
△E=Ei-PI
PI=β×P
where △E is the monthly ecological water shortage of vegetation (mm); Ei is the monthly ecological water requirement quota (mm) for different vegetation types; PI is the effective rainfall (mm); and P represents the monthly actual rainfall (mm), which is the amount of water that can be directly or indirectly used for vegetation growth and other necessary water consumption in the total rainfall. β is the rainfall infiltration coefficient, related to P: when P< 5 mm, β =0; when 5 < P < 50 mm, β =1; and when P> 50 mm, 0.7 < β < 0.8.

4 Results and analysis

4.1 Actual evapotranspiration values of different vegetation types

The actual evapotranspiration values of different vegetation types are shown in Table 3. The vegetation evapotranspiration from high to low for the whole growing season from April to October was arbor forest, grassland and shrub, and the actual evapotranspiration amounts were 401.81 mm, 358.78 mm and 346.02 mm, respectively. On the time scale, evapotranspiration of the three vegetation types increased at first and then decreased from April to October. Evapotranspiration mainly occurred from May to August, and the highest level was in July. Evapotranspiration in July accounted for 27.16% (forest), 24.89% (shrub) and 25.80% (grassland) of the amounts for the whole year.
Table 3 The monthly actual evapotranspiration of different vegetation types
Month Forest Shrub Grassland
Actual
evapotranspiration (mm)		 Proportion (%) Actual
evapotranspiration (mm)		 Proportion (%) Actual
evapotranspiration (mm)		 Proportion (%)
April 37.71 9.39 30.17 8.41 22.63 6.54
May 58.55 14.57 50.19 13.99 50.19 14.50
June 65.57 16.32 58.28 16.24 58.28 16.84
July 109.13 27.16 89.29 24.89 89.29 25.80
August 63.39 15.78 63.39 17.67 63.39 18.32
September 41.38 10.30 41.38 11.53 41.38 11.96
October 26.07 6.49 26.07 7.27 20.86 6.03
Whole growing season 401.81 100.00 358.78 100.00 346.02 100.00

4.2 Actual evapotranspiration water shortage of different vegetation types

According to the monthly actual evaporation and rainfall of different vegetation types, the monthly ecological water shortages are shown in Table 4. The ecological water shortages were positive in arbor forest from April to July, shrub forest from April to May and grassland from April to June. In addition, the peak of ecological water shortage appeared in May for all types, and the water shortage reached levels of 52.75 mm, 44.39 mm and 44.39 mm, respectively. On the one hand, this indicates that the water output was greater than the input in the spring, which would lead to the decrease of soil water content in the spring. On the other hand, it also shows that all three plantation types were affected by insufficient water in spring, especially in arbor forests.
Table 4 Actual ecological water deficit of the different vegetation types in the growing season (Unit: mm)
Month Rainfall Forest Shrub Grassland
April 0 37.71 30.17 22.63
May 5.8 52.75 44.39 44.39
June 36.7 28.87 21.58 21.58
July 96.85 12.28 -7.56 -7.56
August 64.78 -1.39 -1.39 -1.39
September 37.8 3.58 3.58 3.58
October 32.5 -6.43 -6.43 -11.64
Whole growing season 274.43 127.38 84.35 71.59

4.3 Minimum and optimal ecological water demand quotas of different vegetation types

As shown in Table 5, there are differences in the minimum and the optimal ecological water demand quotas of the three plantings in the growing season. The minimum and optimal ecological water demand quotas in the growing season were in a sequence of arbor forest > shrub > grassland. The minimum ecological water demand quotas of arbor forest, shrub and grassland were 243.96 mm, 218.35 mm and 211.36 mm, respectively; while the optimal ecological water demand quotas were 472.99 mm, 423.34 mm and 409.77 mm, respectively. The values of arbor forest were 1.12 times and 1.15 times those of shrub and grassland, respectively.
Table 5 Minimum and optimal ecological water requirements of the different vegetation types during the growing season (Unit: mm)
Month Forest Shrub Grassland
Minimum Optimal Minimum Optimal Minimum Optimal
April 21.24 41.18 16.99 32.94 12.74 24.71
May 36.32 70.41 31.13 60.35 31.13 60.35
June 47.25 91.60 42.00 81.43 42.00 81.43
July 60.08 116.49 49.16 95.31 49.16 95.31
August 42.55 82.50 42.55 82.50 42.55 82.50
September 22.78 44.17 22.78 44.17 22.78 44.17
October 13.74 26.63 13.74 26.63 10.99 21.31
Whole growing season 243.96 472.99 218.35 423.34 211.36 409.77

4.4 Minimum and optimal ecological water shortage values of different vegetation types

In the growing season, the minimum and optimal ecological water shortage values of arbor forests were ‒30.47 mm and 198.56 mm (Table 6), respectively, indicating that the effective rainfall in the growing season was greater than the minimum ecological water demand quota, but lower than the optimal ecological water demand quota. This means that precipitation in the growing season can only maintain a low-level growth state of the trees, but it cannot meet the better growth condition. Also note that the water shortage amount is relatively large, close to 200 mm, and largest in May and June.
Table 6 Minimum and optimal ecological water deficits of the different vegetation types in the growing season (Unit: mm)
Month Forest Shrub Grassland
Minimum Optimal Minimum Optimal Minimum Optimal
April 21.24 41.18 16.99 32.94 12.74 24.71
May 30.52 64.61 25.33 54.55 25.33 54.55
June 10.55 54.90 5.30 44.73 5.30 44.73
July -36.77 19.64 -47.69 -1.54 -47.69 -1.54
August -22.23 17.72 -22.23 17.72 -22.23 17.72
September -15.02 6.37 -15.02 6.37 -15.02 6.37
October -18.76 -5.87 -18.76 -5.87 -21.51 -11.19
Whole growing season -30.47 198.56 -56.08 148.91 -63.07 135.34
For shrub and grassland, the optimal ecological water shortage values were 148.91 mm and 135.34 mm, respectively. There were also large gaps, but the water shortage amounts were lower than that of arbor forest. At the same time, precipitation in July, when plants grow best, is higher than the optimal ecological water demand levels of shrub and grassland, which is beneficial to the growth of shrub and grassland vegetation.

5 Discussion

In this study, based on the actual observation data and the Irmak-Allen formula, the ecological water demand of arbor forest, shrub and grassland were calculated in Bashang Area of Northwest Hebei Province, China. The ecological water demand values of the three vegetation types from large to small were arbor forest, shrub and grassland. During the growing season, the minimum, actual and optimal ecological water demand levels for arbor forest were 243.96 mm, 401.81 mm and 472.99 mm, respectively; for shrub they were 218.35 mm, 358.78 mm and 423.34 mm; and for grassland they were 211.36 mm, 346.02 mm and 409.77 mm, respectively. This suggests that the water demand of arbor forest is greater than those of shrub and grassland, and the drought stress in Bashang Area of Northwest Hebei Province is more serious. The shrub and grassland have better climate adaptability than arbor forest in this area.
The actual evapotranspiration water shortage and optimal ecological water shortage in the growing season of arbor forest reached 127.38 mm and 198.56 mm, respectively, which means that the effective rainfall in the growing season could not meet the requirement for maintaining a good growth state. This inadequacy can explain why poplar shelterbelts in Bashang Area have declined on a large scale. The actual evapotranspiration in the growing season of arbor forest in Bashang Area was 401.81 mm, which was much higher than the effective rainfall in the growing season (274.43 mm). The water output of arbor forest is much larger than the input, which will lead to a significant decrease in the soil moisture content of the forest (Bai et al, 2021). Therefore, poplar-dominated arbor forests will suffer from serious drought stress. Furthermore, drought stress can induce the occurrence of poplar decay (Yang et al., 1999), and eventually lead to poplar dehydration and death (Zheng et al., 2018).
In this study, the optimal ecological water quantity of arbor forest was close to that of a poplar forest in Beijing (432.58 mm) calculated by Dong et al. (2018), but the minimum ecological water quantity was quite different. The minimum ecological water requirement in Beijing was 179.00 mm, which is significantly lower than that in our study area. This difference is very likely due to the distinct climatic conditions in the two areas. In addition, according to the research results of Li et al. (2019) and Xiao et al. (2019), Zhangbei area has the highest potential evapotranspiration in Hebei Province, reaching 1265 mm, which is significantly higher than other areas in Hebei Province near Beijing, which is only about 1040 mm.
We found that the ecological water shortage of vegetation in Bashang region has obvious seasonality. The actual ecological water shortage and the optimal ecological water shortage were the largest in May and June, but they were relatively low from July to October, and even showed a surplus in some months. For example, in July, the actual water shortage of arbor forest was only 12.28 mm, and shrub forest and grassland water had surpluses (of 7.56 mm). In August, the three planting vegetation types had a surplus of 1.39 mm. Above all, the water shortage of plants in Bashang area mainly occurs at the transition of spring and summer (May and June). Artificial water supplementation in these two months will help to alleviate the drought stress of vegetation and promote the growth and development of the vegetation.

6 Conclusions

(1) The actual evapotranspiration of the three vegetation types in the growing season in the Bashang area of Northwest Hebei Province in China from high to low was arbor forest (401.81 mm), shrub (358.78 mm) and grassland (346.02 mm).
(2) The minimum ecological water requirements of arbor forest, shrub and grassland in the growing season in Bashang area of Northwest Hebei were 243.96 mm, 218.35 mm and 211.36 mm, respectively; and the optimal ecological water requirements were 472.99 mm, 423.34 mm and 409.77 mm, respectively. The rainfall in the Bashang region of Northwest Hebei can meet the minimum ecological water demand of the arbor forest, but the gap between the rainfall and the optimal ecological water demand is large. Therefore, the rainfall cannot maintain the good growth and survival of the arbor forest, which may be the main reason for the degradation of the poplar shelterbelt in the Bashang region.
(3) The ecological water shortage of vegetation in the Bashang area of Northwest Hebei has obvious seasonality. The water shortage is the largest in May and June, but relatively low from July to October, and even shows a surplus in some months. Artificial water supplementation in May and June will help to alleviate the drought stress of the vegetation.

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