Advertisement

The dynamics of carbon accumulation in Eucalyptus and Acacia plantations in the Pearl River delta region

  • Hui Zhang
  • HuaBo Duan
  • MingWei SongEmail author
  • DongSheng GuanEmail author
Original Paper

Abstract

Key message

Plantation type and age strongly influence the quantity of carbon stored in forest ecosystems. The marked increase in total ecosystem carbon stock achieved over time by the Eucalyptus and Acacia plantations has confirmed that the afforestation of degraded soils can contribute positively to carbon sequestration.

Context

Reforestation has been widely conducted to restore and protect the eroded red soil in south China in recent decades. The question as to whether the content of soil organic carbon (SOC) can be boosted by establishing plantations of fast-growing tree species remains unresolved.

Aims

We addressed whether the afforestation of degraded soils can contribute positively to carbon sequestration, and whether the accumulation of SOC is more effective under a nitrogen fixing species such as Acacia than under Eucalyptus.

Methods

Here, a study was undertaken to measure the quantity of total ecosystem carbon (TEC) accumulated by plantations of both Eucalyptus and Acacia spp. in the Pearl River Delta region of southern China.

Results

The quantity of TEC increased significantly with stand age in both plantation types (P < 0.05). The largest single component of TEC was SOC, with stand age having a considerable effect on both SOC and overall biomass. The accumulation of SOC in the top 100 cm of the soil profile was higher under Acacia than under Eucalyptus (P < 0.05).

Conclusion

In terms of carbon sequestration, the afforestation of Eucalyptus and Acacia represent an effective forest management practice. The accumulation of SOC is more effective under Acacia than under Eucalyptus.

Keywords

Total ecosystem carbon Forest type Stand age Biomass Soil organic carbon 

1 Introduction

Forest ecosystems store globally about 80% of the aboveground carbon and over 50% of soil organic carbon (SOC) (Batjes 1996), and so make an important contribution to the regulation of the global carbon balance and to the mitigation of climate change. Although there is a continuing decline in the area of natural forest, afforestation/reforestation is on the increase, thereby promoting carbon sequestration and restoring the quality of degraded land (Kelty 2006; Wei, Li et al. 2013; Xie, Guo et al. 2013). Both plantation species composition and stand age are major determinants of the carbon budget (Chen, Zhang et al. 2011; Tang and Li 2013; Wei, Li et al. 2013; Xie, Guo et al. 2013). Rapidly growing plantation species fix considerable quantities of carbon over the short term (Laclau 2003; Peichl and Arain 2006; Chen, Zhang et al. 2011; Xie, Guo et al. 2013): Eucalyptus and Acacia plantations have been estimated to accumulate around 2 kg m−2 SOC over a 17-year period, while over a 29-year growing period, Norway spruce (Picea abies) and oak (Quercus sp.) managed only 0.9 and 0.2 kg m−2, respectively (Bhattacharya, Kim et al. 2016). Tree species native to the subtropics are typically rather intolerant of degraded soil, so species belonging to the genera Eucalyptus and Acacia, which are both tolerant and fast growing, are favored for reforestation (Yang, Liu et al. 2009; Chen, Zhang et al. 2011).

A rational assessment of the size of the carbon pool in a plantation requires the whole ecosystem to be considered. It has been suggested that most of the carbon accumulated in forest ecosystems is due to their high accumulation of biomass (Dou, Deng et al. 2013; Cheng, Lee et al. 2015), and that SOC should increase naturally with stand age following the reforestation of degraded soil (Xie et al., 2013). The dependency of SOC on plantation age is not universally acknowledged, since there are examples in which it has been shown to decrease somewhat during the establishment phase, before gradually increasing with stand age (Kasel, Singh et al. 2011; Assefa, Rewald et al. 2017). Since Acacia spp., unlike Eucalyptus spp., are able to fix atmospheric nitrogen, their growth results in an improvement to soil fertility; as a result, the accumulation of SOC under Acacia dominated plantations has been found to be generally superior to that achievable under Eucalyptus (Kasel, Singh et al. 2011). Some authors have argued that the high productivity of Eucalyptus and Acacia plantations results in a substantial export of nutrients in forest products such as nitrogen and phosphorus, and thus a slight decrease or no change in SOC was observed over time (Santana, Knicker et al. 2015; Cook, Binkley et al. 2016). Eucalyptus and Acacia plantations used for wood production are typically maintained for less than 10 years (Attiwill 1994; Inagaki, Kamo et al. 2010), so there is little evidence regarding the extent of their longer term capacity to store carbon. Furthermore, little attention has been given to the amount of SOC stored deeper in the soil profile in these two plantation types (Kasel, Singh et al. 2011; Souza-Alonso, Guisande-Collazo et al. 2015; Cook, Binkley et al. 2016), even though it has been claimed that, globally, the proportion of soil carbon present in the top 30 cm of the soils accounts for only around 30% or so of the carbon present in the top 100 cm (Batjes 2014).

The working hypotheses of the present research were threefold: (a) SOC can be boosted significantly as a result of afforestation, and especially, the accumulation of SOC is more effective under a nitrogen fixing species such as Acacia than under Eucalyptus; (b) a significant proportion of the SOC is held at depth in the soil profile; and (c) the two tree species are both effective in sequestering carbon. To test these hypotheses, the objectives of the study were to characterize the accumulation and allocation of total ecosystem carbon (TEC) in a sample of Eucalyptus (E. urophylla) and Acacia (A. mangium) plantations located in the Pearl River Delta (PRD) region of southern China, and establish the effect of species, stand age, and biomass on the SOC level in the top 100 cm of the soil. The wider purpose of the research was to provide a baseline for forest management, in particular with a view to enhancing the carbon sequestration capacity of forest ecosystems and identifying the species best suited for afforestation in the PRD.

2 Materials and methods

2.1 Local climate and soils

The PRD lies in the Chinese province of Guangdong (21° 31′–23° 10′ N, 112° 45′–113° 50′ E). Its climate is subtropical and monsoonal, characterized by hot, humid summers and mild winters. The region has a mean annual rainfall of 1600 mm, with the main rainy season occurring during July and August. The mean annual temperature is approximately 21 °C, while the daytime temperature exceeds 30 °C on around 120 days per year. The chosen sites, at which 10 were planted exclusively with Acacia and 11 exclusively with Eucalyptus, with both tree species adjacent to each other, lie in hilly land in the neighborhood of the cities Guangzhou, Zhuhai, and Heshan. The Eucalyptus plantations were measured in the period November–December 2010 and the Acacia ones between December 2010 and January 2011. The local red soils were, prior to the establishment of the plantations, covered with a combination of small shrubs and grass. A full description of the soils’ physicochemical characteristics are given in Table 1. The plantations fell into three age groups: young (less than 6 years), middle-aged (6–15 years), and mature (over 16 years). Further descriptive details of the sites are given by Zhang et al. (2012) and are reproduced in Table 1.
Table 1

A summary description of the study Eucalyptus and Acacia plantations

Type

Period

DBH (cm)

Height (cm)

Stand density (n/hm−2)

Aspect

Gradient

Total nitrogen (mg kg−1)

pH value

Bulk density (g cm−3)

Eucalyptus

Young

7.13 ± 1.35Aa

8.55 ± 3.06 Aa

2761 ± 102Aa

SW

25–60°

329.48 ± 180.50Aa

4.57 ± 0.29A

1.53 ± 0.09a

Middle-aged

12.38 ± 0.94Bb

14.65 ± 0.31 Bb

1719 ± 122Bb

SW

22–52°

408.90 ± 206.86Aa

4.24 ± 0.16Ba

1.52 ± 0.16a

Mature

15.07 ± 2.80Bb

18.58 ± 4.74Bc

1367 ± 445Bb

SW

18–65°

693.82 ± 325.50B

4.08 ± 0.16Bb

1.45 ± 0.15a

Acacia

Young

8.70 ± 0.53Aa

7.07 ± 0.06Aa

1541 ± 17A

SW

23–51°

497.94 ± 257.27Aa

4.19 ± 0.19A

1.58 ± 0.17Aa

Middle-aged

12.43 ± 1.84Ab

9.83 ± 1.54 Ab

1244 ± 142B

SW

27–48°

636.48 ± 350.84Aa

4.39 ± 0.09B

1.60 ± 0.10Aa

Mature

18.73 ± 1.70B

14.90 ± 1.25Bc

830 ± 12C

SW

20–63°

949.16 ± 587.95Bb

4.05 ± 0.11C

1.38 ± 0.19B

Forest type

ns

ns

**

*

*

ns

Values shown as mean ± standard deviation; different lowercase (P < 0.05) and uppercase (P < 0.01) letters within a column indicate a significant difference between the various ages of a given forest type

DBH diameter at breast height (1.3 m), ns not significant

*Significant difference (P < 0.05); **significant difference (P < 0.01) between the Eucalyptus and Acacia plantations

2.2 Biomass and soil sampling

At each site, the canopy biomass captured within a 30 m × 30 m quadrat was measured. The understorey biomass (shrubs, ferns and grasses) was estimated from a destructive harvest of the central 1 m2 of each of five 2 m × 2 m quadrats. The contribution of the litter layer was obtained from a set of five 1 m × 1 m quadrats arranged along the diagonal of the main 30 m × 30 m quadrat. Felled dead wood and standing dead trees of trunk diameter > 2.5 cm and height > 1 m were included within the coarse woody debris (CWD) fraction. The Zhang et al. (2012) estimate of the relative contribution to the overall biomass of the various fractions (trees, shrubs, herbaceous species, litter, and CWD) was adopted. Estimates of the SOC, total nitrogen content (TN), and hydrolyzable nitrogen (HN) in the top 100 cm of the soil profile were obtained from samples taken from each of an upper, mid, and lower slope location: an equal number of 500 g soil aliquots was taken from the top 10 cm of the profile, from the next 10 cm (10–20 cm), from 20–30, 30–40, 40–50, 50–75, and 75–100 cm, producing a total of 231 soil samples (11 sites × three locations × seven soil depths) from the Eucalyptus plantations and 210 (10 × 3 × 7) from the Acacia plantations. Samples of undisturbed soil from each of the various layers were also collected using a soil sample ring kit (100 cm3), and the cutting ring method was used to measure soil bulk density (Lu 1999).

2.3 Laboratory analyses

SOC contents were obtained from air-dried (at room temperature) soil samples after the removal of surface organic matter and fine roots. Samples from each layer within a site were mixed in equal proportion and passed through a 0.149-mm sieve. The carbon content of the soil and biomass components was determined using a wet oxidation method (Forestry Standards of the People’s Republic of China method LY/T1237-1999). Soil pH was measured using a Toledo Five Easy pH meter (Mettler, Giessen, Germany). Three replicates of the surface soil (0–10 cm) were assessed for their TN content using a Foss 2300 Kjeltec Analyzer Unit (Foss Analytical AB, Höganäs, Sweden). A 0.0050–1.0000 g sample of either soil or biomass was digested in 5 mL 0.8 M K2Cr2O7 and 5 mL 18 M H2SO4, held at 170–180 °C for 5 min, and titrated with 0.2 M FeSO4·7H2O. An estimate for the quantity of biomass carbon was obtained by multiplying the weighed biomass by its derived proportion of carbon. The quantity of carbon present in the canopy was estimated by assuming that 50% of the biomass was carbon (Lieth and Whittaker 1975; Razakamanarivo, Grinand et al. 2011), while the quantity stored in the various soil layers was calculated by multiplying soil bulk density by both the depth of the layer and the concentration of carbon present. The TEC was obtained by summing the quantities of carbon stored in the biomass and in the soil.

2.4 Statistical analysis

The means and associated standard deviations of the proportion of carbon and quantity of carbon stored in the biomass and soil, as well as the TN contents were calculated. A two-way analysis of variance was used to test for the effect of tree type and stand age on the proportion or the quantity of carbon stored in the biomass and in the soil, as well as the distribution of SOC and TN content within the top 100 cm of the soil. Regression analyses were performed between TEC content and stand age, SOC content, and the amount of biomass represented in the CWD and litter layer. All calculations and analyses were carried out using the software package SPSS v17.0 (SPSS Inc., Chicago, IL, USA).

Data availability

Data presented are available at https://doi.org/10.6084/m9.figshare.5853420.v3 (Song et al. 2018).”

3 Results

3.1 TEC stock

The stock of TEC increased with stand age in both plantation types (Fig. 1): the associated coefficients of determination (R2) were 0.87 for the Eucalyptus and 0.93 for the Acacia plantations. The quantity of TEC was significantly greater in the mature than in the middle-aged or the young plantations, ranging from 79.8 to 204.9 t ha−1 under Eucalyptus and from 117.4 to 226.8 t ha−1 under Acacia.
Fig. 1

The relationship between total ecosystem carbon and stand age in both a Eucalyptus and an Acacia plantation

3.2 Biomass carbon stock

Both stand age and plantation type had a major impact on the accumulation of carbon and on its distribution between the various components (Table 2). The middle-aged and mature plantations both produced significantly more total biomass carbon than the young ones (P < 0.01). The contribution of the understorey layer, litter layer, and CWD were all nonnegligible. This was especially the case for the Acacia stands, in which the proportion was 8% in both the middle-aged and mature plantations, compared to, respectively, 5 and 4% for the Eucalyptus stands.
Table 2

Variation in the size of the TEC stock and its components in the plantations (Mg ha−1)

Type

Period

Canopy tree layer biomass carbon

Secondary biomass carbon

Total biomass carbon

SOC

TEC

Eucalyptus

Young

27.31 ± 16.46Aa

2.14 ± 0.85A

29.45 ± 17.28 Aa

50.31 ± 32.10a

79.76 ± 31.93Aa

Middle-aged

68.47 ± 11.81Bb

6.35 ± 1.00B

74.82 ± 12.54 Bb

60.31 ± 15.84a

135.13 ± 27.33Ab

Mature

93.21 ± 3.15Bc

9.03 ± 0.89C

102.24 ± 3.59 Bc

102.66 ± 13.90b

204.90 ± 15.70Bc

Acacia

Young

38.72 ± 2.95 Aa

4.53 ± 0.36Aa

43.24 ± 2.79Aa

74.13 ± 20.63a

117.38 ± 21.70Aa

Middle-aged

56.46 ± 11.68 a

13.55 ± 2.42Bb

70.01 ± 12.93b

101.07 ± 13.73a

171.08 ± 21.20b

Mature

76.83 ± 11.69Bb

17.31 ± 1.07Bc

94.14 ± 12.05Bc

132.70 ± 34.94b

226.84 ± 43.38Bc

Forest type

ns

**

ns

*

ns

Total biomass carbon included canopy tree layer biomass carbon and the secondary biomass and its various components (shrubs, herbaceous species, litter layer and CWD). Values are means ± standard deviation. Different lowercase and uppercase letters in the same column indicate significant differences among different ages for same forests type according to LSD (least significant difference) test at P < 0.05 and P < 0.01 level, respectively

ns not significant

*Significant difference (P < 0.05); **significant difference (P < 0.01) between the Eucalyptus and Acacia plantations

3.3 Correlations between biomass and SOC

In this study, significant positive correlations were established between SOC storage and total biomass (Fig. 2), between SOC storage and litter biomass (Fig. 3), and between SOC storage and the CWD biomass (Fig. 4); the relationships were particularly strong for the Acacia-based plantations. The accumulation of litter and CWD biomass was more effective in the Acacia plantations (respectively, 4.0–15.5 and 0.9–13.4 t ha−1) than in the Eucalyptus ones (respectively, 2.0–9.6 and 0–2.6 t ha−1), which implies that the volume of raw material contributing to SOC is greater in the former plantation type.
Fig. 2

The relationship between soil organic carbon and total biomass in both a Eucalyptus and an Acacia plantation

Fig. 3

The relationship between soil organic carbon and the biomass stored in the litter in both a Eucalyptus and an Acacia plantation

Fig. 4

The relationship between soil organic carbon and the biomass stored in the coarse woody debris in both a Eucalyptus and an Acacia plantation

3.4 SOC stock

SOC stock increased with stand age (Fig. 5), with associated R2 values of 0.57 for the Eucalyptus stands and 0.75 for the Acacia stands. A significant positive correlation existed between the SOC storage in the top 100 cm of the soil and both stand age and forest type (P < 0.05, Table 2). The Acacia trees were more effective accumulators of SOC than the Eucalyptus ones: SOC storage under the former ranged from 74.1 to 132.7 t ha−1, while under the latter, the range was only 50.3–102.7 t ha−1. The overall contribution of SOC to TEC was highly significant: 60% in the case of Acacia and 53% in the case of Eucalyptus.
Fig. 5

The relationship between soil organic carbon and stand age in both a Eucalyptus and an Acacia plantation

3.5 The soils’ organic carbon and nitrogen content, carbon/nitrogen ratio, and bulk density

The variation in SOC content between the various soil layers in the two plantation types is summarized in Table 3. The SOC content in the top 100 cm of the soil increased markedly with stand age, ranging from 3.7 to 8.5 g kg−1 under Eucalyptus, and from 5.6 to 11.7 g kg−1 under Acacia. SOC content decreased gradually with increasing soil depth. At all of the sites, significantly (P < 0.01) more SOC was concentrated in the upper 20 cm of the soil than was found deeper in the profile. The SOC content of the top 10 cm was 3.6–5.3 (Eucalyptus) and 3.2–4.8 (Acacia) times higher than that present in the lowest 25 cm (75–100 cm), while the respective increases in the 10–20 cm layer were in the range 2.0–2.8 and 2.6–3.0. The TN content and carbon/nitrogen ratio both rose gradually with stand age, ranging from, respectively, 329.5–693.8 t kg−1 and from 10.4–11.7 (Eucalyptus), and from 497.9–949.2 t kg−1 and 11.2–12.4 (Acacia). In both plantation types, the TN content and the carbon/nitrogen ratio decreased gradually with soil depth, independently of stand age: both variables were at their highest in the surface soil layer, ranging from 1346.2–211.4 t kg−1 and from 14.1–8.9 (Eucalyptus) and from 1857.2–259.4 t kg−1 and 15.1–9.7 (Acacia) (Table 4, Fig. 6). The soils’ bulk density changed in the opposite sense with both stand age and soil depth. Independently of stand age, the bulk density of the upper (0–20 cm) layer was significantly lower than that of the lower (50–100 cm) layer: the range was 1.2–1.6 g cm−3 under Eucalyptus, and 1.2–1.8 g cm−3 under Acacia (Fig. 7).
Table 3

The effect of stand age and tree species on the accumulation of SOC (g kg−1)

Type

Period

0~10 cm

10~20 cm

20~30 cm

30~40 cm

40~50 cm

50~75 cm

75~100 cm

Eucalyptus

Young

8.21 ± 3.42Aa

4.51 ± 2.91Aa

3.10 ± 2.14a

2.88 ± 2.00a

2.89 ± 1.91a

2.37 ± 1.87a

2.25 ± 1.82a

Middle-aged

11.65 ± 1.66Aa

5.73 ± 1.91Aa

4.62 ± 1.66ab

3.31 ± 1.12a

2.83 ± 1.20a

2.67 ± 1.18a

2.19 ± 0.71a

Mature

18.95 ± 2.56Bb

11.59 ± 1.38Bb

7.76 ± 1.83b

6.46 ± 0.69b

5.66 ± 0.82b

4.73 ± 0.65a

4.16 ± 0.90a

Acacia

Young

9.91 ± 1.50A

7.84 ± 2.79a

6.04 ± 2.33a

5.39 ± 1.83a

4.15 ± 1.80a

2.81 ± 1.06a

3.07 ± 1.62a

Middle-aged

17.43 ± 2.51B

10.98 ± 3.67a

7.39 ± 0.78a

5.42 ± 1.45a

4.56 ± 1.24a

3.93 ± 0.91a

3.68 ± 0.59a

Mature

25.73 ± 2.36C

15.93 ± 5.82b

11.69 ± 4.37b

9.22 ± 4.02a

8.12 ± 3.21a

6.07 ± 1.99b

5.33 ± 1.81a

Forest type

*

*

*

*

ns

ns

ns

Values shown as mean ± standard deviation. Different lowercase (P < 0.05) and uppercase (P < 0.01) letters within a line indicate a significant difference between the various ages of a given forest type. ns: not significant, *: significant difference (P < 0.05) between the Eucalyptus and Acacia plantations

ns not significant

*Significant difference (P < 0.05) between the Eucalyptus and Acacia plantations

Table 4

Variation in TN across the top 100 cm of the plantation soils (mg kg−1)

Soil depth (cm)

Eucalyptus

Acacia

Young

Middle-aged

Mature

Young

Middle-aged

Mature

0~10

581.99 ± 152.58Aa

829.53 ± 137.88A

1346.19 ± 135.02A

894.80 ± 66.23Aa

1300.16 ± 327.84A

1857.18 ± 696.77Aa

10~20

446.77 ± 190.27ABab

489.97 ± 85.11Ba

902.27 ± 110.79B

738.49 ± 258.03Aa

760.72 ± 255.60Ba

1256.52 ± 559.87Aab

20~30

309.36 ± 171.31Bb

423.46 ± 33.54Bab

669.38 ± 85.60Ca

499.50 ± 132.93Bb

680.34 ± 102.97Bab

1051.64 ± 475.61ABb

30~40

249.94 ± 103.67Bbd

315.74 ± 25.77Cb

601.75 ± 46.59CDa

494.46 ± 81.42Bab

504.71 ± 115.16Bbc

844.95 ± 396.08ABbd

40~50

262.51 ± 123.78Bbd

315.90 ± 62.02Cb

502.31 ± 37.36Dab

354.24 ± 115.34Bbd

487.84 ± 71.80 Bbc

671.62 ± 237.44Bbd

50~75

244.38 ± 125.62Bbd

263.78 ± 87.04Cbd

469.77 ± 65.86DEab

244.73 ± 99.47Bcd

386.73 ± 145.84Cd

485.84 ± 136.63ABd

75~100

211.43 ± 126.42 Bd

223.94 ± 62.54Cbd

365.08 ± 64.57DEb

259.36 ± 88.34Bcd

334.86 ± 131.05Cd

476.35 ± 128.41ABd

Values shown as mean ± standard deviation. Different lowercase (P < 0.05) and uppercase (P < 0.01) letters within a line indicate a significant difference between the various soil type of a given forest type and forest age

Fig. 6

The carbon/nitrogen ratio of soil of different depths for different aged Eucalyptus (a) and Acacia (b) stands

Fig. 7

The bulk density of soil at different soil depths under Eucalyptus (a) and Acacia (b) plantations

4 Discussion

4.1 The effect of tree species and stand age on stored SOC

The soil’s carbon pool reflects a balance between its loss through decomposition and its gain through the decomposition of leaf litter and CWD (Dou, Deng et al. 2013; Chen, Yu et al. 2017), the growth of the understory and root expansion (Cheng, Lee et al. 2015). There are two considerations which could explain the positive effect of stand age on SOC storage: the first relates to the increasing size of the carbon input from the understory layer, the litter, and the CWD as the plantation ages (Zhang, Guan et al. 2012; Zhao, Kang et al. 2014); the second is a consequence of the very low level of SOC (25 t ha−1) present in the upper 30 cm of the soil prior to afforestation, giving the opportunity for a large increase as the trees aged (Chen, Yu et al. 2017). The ability of Acacia plants to biologically fix nitrogen through their symbiosis with Rhizobium spp. should favor SOC accumulation (Yang, Liu et al. 2009). A correlation of determination > 0.8 obtained between carbon and nitrogen storage in both plantation types (Fig. 8), and the fact that the level of nitrogen was higher under Acacia than under Eucalyptus (Table 1) supports the notion that increasing the nitrogen status of the soil enhances the storage of SOC. The outcome validates the superiority, in terms of SOC accumulation, of nitrogen fixing over nonfixing tree species (hypothesis a), and is consistent with related studies comparing the effect on SOC of nitrogen fixing trees and nonfixing ones (Resh, Binkley et al. 2002). Overall, assuming a similar land use history and a similar climate, the accumulation of SOC in a given soil type is mainly dependent on the nature of the long-term vegetation present (Yang and Wang 2005; Xian, Zhang et al. 2009): thus, tree species and tree age, both individually and in combination, are strong determinants of the size of the SOC stock.
Fig. 8

The relationship between soil organic carbon and total nitrogen content in both a Eucalyptus (a) and an Acacia (b) plantation

4.2 Effect of biomass on SOC storage

Early stand development in a poor soil requires as rapid as possible a buildup of SOC in order for the plants to thrive. One aim of reforestation is to generate a large volume of biomass over a long period, in order to boost SOC in the PRD (Xie, Guo et al. 2013). Our study has confirmed that SOC content is positively correlated with biomass, which agrees with related studies based on the performance of other plantation tree species used for reforestation purposes in southern China (Zhang 2009; Dou, Deng et al. 2013; Wang, Guan et al. 2014). For example, Dou et al. (2013) found that reforetation of P. massoniana under eroded red soil after 18–30 years significantly increased soil C levels; the C accumulation following the reforestation appeared to be due to a combination of large biomass input and low C decomposition (Dou, Deng et al. 2013). Wang et al. (2014) have shown that SOC in the top 100 cm of a variety of mangrove forest soils varied from 184 to 279 t ha−1, in line with the biomass of the canopy layer (60–385 t ha−1). Similarly, Zhang (2009) have demonstrated that the SOC content of the uppermost 100 cm of the soil profile under a stand of evergreen broad-leaved trees ranged from about 85 t ha−1 in a young forest to 151 t ha−1 in a mature one, again reflecting increases in the biomass represented in the litter and CWD.

4.3 The vertical distribution of SOC

The SOC content of the surface layer in the present mature plantations was comparable to that measured in 7-year-old plantations of either subtropical Eucalyptus (~ 20 g kg−1) or Acacia (~ 25 g kg−1) provided with a dressing of phosphate fertilizer before planting (Santana, Knicker et al. 2015). The vertical distribution of SOC in the soil is in line with that observed in similar studies based on either tropical or subtropical Eucalyptus (Mishra, Sharma et al. 2003; Cao, Fu et al. 2010) or Acacia (Lemma, Kleja et al. 2006; Laik, Kumar et al. 2009) plantations, as well as in other plantation types monitored in southern China (Dou, Deng et al. 2013). Other factors affecting SOC were the soil’s TN content, bulk density, and carbon to nitrogen ratio (Table 5); their vertical distribution also determined the significantly high SOC present in surface soil layer (P < 0.01). It is therefore clearly important to maintain the SOC at and immediately below the soil surface.
Table 5

Correlations between SOC content and soil properties in Eucalyptus and Acacia plantations of different stand age

Forest type

Bulk density

pH value

TN

C/N

Acacia

− 0.745**

−0.482**

0.912**

0.374**

Eucalyptus

− 0.582**

−0.631**

0.971**

0.680**

*Correlation is significant at the 0.05 level (two-tailed); **correlation is significant at the 0.01 level (two-tailed)

Most studies that estimated the SOC level focused on the organic layer and surface horizons in the upper 30 cm of the soil. However, the roots of plant and thus input of organic matter extend to deep subsoil horizons, and soil carbon level would be greatly underestimated if one does not include the amounts stored in subsoil (Rumpel and Kögel-Knabner 2011; Wiesmeier, Prietzel et al. 2013; Zhang, Wang et al. 2015). For instance, Zhang et al. (2015) claimed that the proportion of SOC in a cropping soil 30–200-cm depth can reach more than 70% of total SOC (Zhang, Wang et al. 2015). In this study, we found that the content of SOC at deeper horizons (30–100 cm) is still high, especially for mature forests (> 4 g kg−1). Subsoil SOC showed significant correlation with stand age and forest type (P < 0.05) (Table 3). Hypothesis (b) was confirmed: a substantial presence of SOC was detected up to 50 cm below the soil surface in the Eucalyptus plantations (P < 0.05), and the SOC content of mature plantation was significant higher than that of the middle-aged and young ones (P < 0.05), showing that carbon is able to accumulate at a deeper level than can readily be explained by the presence of a greater root biomass (Bauhus, Khanna et al. 2000). Meanwhile, under Acacia, the upper 75 cm of the soil profile also showed a significant SOC accumulation with stand age (P < 0.05), perhaps reflecting the activity of nitrogen fixing bacteria (Inagaki, Kamo et al. 2011), as is shown in Table 4. However, because in this study the soils were not sampled below a depth of 100 cm, it is not possible to conclude definitively that carbon sequestration was limited to the top 100 cm of the soil profile. Thus, future attempts to document soil carbon under tree plantations will need to monitor the status of the soil at depths below 100 cm.

4.4 Implications for carbon sequestration achieved by fast-growing plantation trees

Sequestering carbon in the soil, ultimately in the form of stable humus, may well prove to be a more productive method for mitigating the negative effects of climate warming than its more temporary storage in the form of biomass (Thuille and Schulze 2006; Farley 2007). The measured SOC content within the top 100 cm of soil under mature Eucalyptus (102.66 t ha−1) and Acacia (132.70 t ha−1) trees was rather lower than the estimated means derived from both national (193.6 t ha−1) (Zhou, Yu et al. 2000) and global (189.0 t ha−1) data (Dixon, Solomon et al. 1994). Even within the red soils typical of subtropical climates, the present estimates are considerably lower than what was derived from an analysis of a 20-year-old Mytilaria laosensis plantation (174.8 t ha−1) (Liu and Liu 2012). However, they are substantially higher than the reported levels in both a 24-year-old Pinus massoniana plantation (38.2 t ha−1) and a secondary forest (68.5 t ha−1) (Xie, Guo et al. 2013). The TEC contents of both the mature Eucalyptus (204.9 t ha−1) and Acacia (226.8 t ha−1) plantations were also below that of both nationally based (258.8 t ha−1) (Zhou, Yu et al. 2000) and globally based (275.0 t ha−1) means (Dixon, Solomon et al. 1994). Comparisons with other plantation types in the PRD suggest that, on the basis of TEC, both Eucalyptus and Acacia are less effective accumulators of carbon than certain native evergreen broad-leaved species (Sun and Guan 2014), but are more effective than Pinus massoniana (Zhang, Xu et al. 2011). Overall, Eucalyptus and Acacia are both able to sequester carbon with a satisfactory level of efficiency and so are well suited for afforestation purposes in the PRD. Given that stand age had a marked effect on TEC stock in both plantation types (Table 1; Fig. 1), the conclusion is that the use of a rapidly growing tree species for the afforestation of a poor soil should represent an effective forest management practice where the aim is to sequester carbon as fast as possible (hypothesis c).

The consideration of succession is important when estimating the size of a plantation’s carbon pool. As is shown in Table 6, the quantity of carbon accumulated in over the period 2000–2003 in PRD was 22.8 Mt., which corresponded to 26%–36% of the total carbon (1.29 × 108 t) emitted as a result of the burning of fossil fuels in Guangdong Province over the period 2000–2003 (China Statistics Press 2005; SFA 2005). Stands of mature Eucalyptus and Acacia account for just 24% of the total plantation area in the PRD: whereas they have accumulated some 8.0 Mt carbon, maintaining them for some additional years should further increase their contribution to carbon sequestration.
Table 6

Implications for carbon sequestration by Eucalyptus and Acacia plantations in Guangdong Province

Energy consumption (Carbon emissions)

Eucalyptus

Acacia

Total TEC

2000 (Mt C)

2001 (Mt C)

2002 (Mt C)

2003 (Mt C)

Young

Middle-aged

Mature

Young

Middle-aged

Mature

Area (× 104 ha)

TEC (Mt C)

Area (× 104 ha)

TEC (Mt C)

Area (×104 ha)

TEC (Mt C)

Area (×104 ha)

TEC (Mt C)

Area (×104 ha)

TEC (Mt C)

Area (×104 ha)

TEC (Mt C)

(Mt C)

63.30

68.20

76.08

87.76

3.987

3.180

4.059

5.485

2.866

5.872

1.569

1.842

2.523

4.316

0.917

2.080

22.776

Data on energy consumption is from China Statistics Press China Energy Statistical Yearbook 2004. (3/2005); unit is Mt (106 t) standard coal; according to the NDRC (National Development and Reform Commission), 1 Mt standard coal is equal to 0.67 Mt. C; resource: forest area during various periods is acquired by China Forestry Statistical Yearbook

5 Conclusions

The marked increase in TEC stock achieved over time by the Eucalyptus and Acacia plantations has confirmed that the afforestation of degraded soils can contribute positively to carbon sequestration. The largest single component of TEC was SOC. The major factors determining SOC accumulation in the top 100 cm of the soil profile were the species of tree, the stand age, and the biomass input. The accumulation of SOC under Acacia was more effective than under Eucalyptus. Protection of the SOC present in the surface layer of the soil is very important in the context of carbon sequestration, especially for Acacia plantations. The deeper soil layers (below 50 cm for Eucalyptus, and below 75 cm for Acacia) also represent a substantial carbon sink. The indications are that the afforestation of poor soils using rapid growing tree species should be an effective management practice for improving carbon budgets and compensating for the carbon emitted as a result of the burning of fossil fuel.

Notes

Acknowledgements

This research was supported by the National Natural Science Foundation of China (Grant numbers 51039007, 41101494, and 40971054). Experimental facilities were provided by Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, the School of Environmental Science and Engineering, Sun Yat-sen University.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

References

  1. Assefa D, Rewald B, Sanden H, Rosinger C, Abiyu A, Yitaferu B, Godbold DL (2017) Deforestation and land use strongly effect soil organic carbon and nitrogen stock in Northwest Ethiopia. Catena 153:89–99CrossRefGoogle Scholar
  2. Attiwill PM (1994) Ecological disturbance and the conservative management of eucalypt forests in Australia. For Ecol Manag 63:301–346CrossRefGoogle Scholar
  3. Batjes NH (1996) Total carbon and nitrogen in the soils of the world. Eur J Soil Sci 47:151–163CrossRefGoogle Scholar
  4. Batjes NH (2014) Total carbon and nitrogen in the soils of the world. Eur J Soil Sci 65:10–21CrossRefGoogle Scholar
  5. Bauhus J, Khanna P, Menden N (2000) Aboveground and belowground interactions in mixed plantations of Eucalyptus globulus and Acacia mearnsii. Can J For Res 30:1886–1894CrossRefGoogle Scholar
  6. Bhattacharya SS, Kim K-H, Das S, Uchimiya M, Jeon BH, Kwon E, Szulejko JE (2016) A review on the role of organic inputs in maintaining the soil carbon pool of the terrestrial ecosystem. J Environ Manag 167:214–227CrossRefGoogle Scholar
  7. Cao Y, Fu S, Zou X, Cao H, Shao Y, Zhou L (2010) Soil microbial community composition under Eucalyptus plantations of different age in subtropical China. Eur J Soil Biol 46:128–135.  https://doi.org/10.1016/j.ejsobi.2009.12.006 CrossRefGoogle Scholar
  8. Chen D, C Zhang JW, Zhou L, Y Lin SF (2011) Subtropical plantations are large carbon sinks: evidence from two monoculture plantations in South China. Agric For Meteorol 151:1214–1225CrossRefGoogle Scholar
  9. Chen Y, Yu S, Liu S, Wang X, Zhang Y, Liu T, Zhou L, W Zhang SF (2017) Reforestation makes a minor contribution to soil carbon accumulation in the short term: evidence from four subtropical plantations. For Ecol Manag 384:400–405CrossRefGoogle Scholar
  10. Cheng J, Lee X, BK Theng LZ, Fang B, Li F (2015) Biomass accumulation and carbon sequestration in an age-sequence of Zanthoxylum bungeanum plantations under the Grain for Green Program in karst regions, Guizhou province. Agric For Meteorol 203:88–95CrossRefGoogle Scholar
  11. Press CS (2005) China energy statistical yearbook 2004. China Statistics Press. Access 3(/2005):2005Google Scholar
  12. Cook RL, Binkley D, Stape JL (2016) Eucalyptus plantation effects on soil carbon after 20years and three rotations in Brazil. For Ecol Manag 359:92–98CrossRefGoogle Scholar
  13. Dixon RK, Solomon A, Brown S, Houghton R, Trexier M, Wisniewski J (1994) Carbon pools and flux of global forest ecosystems. Science 263:185–190CrossRefPubMedGoogle Scholar
  14. Dou X, Deng Q, Li M, Wang W, Zhang Q, Cheng X (2013) Reforestation of Pinus massoniana alters soil organic carbon and nitrogen dynamics in eroded soil in south China. Ecol Eng 52:154–160CrossRefGoogle Scholar
  15. Farley KA (2007) Grasslands to tree plantations: forest transition in the Andes of Ecuador. Ann Assoc Am Geogr 97:755–771CrossRefGoogle Scholar
  16. Inagaki M, Kamo K, Miyamoto K, Titin J, Jamalung L, Lapongan J, Miura S (2011) Nitrogen and phosphorus retranslocation and N:P ratios of litterfall in three tropical plantations: luxurious N and efficient P use by Acacia mangium. Plant & Soil 341:295–307CrossRefGoogle Scholar
  17. Inagaki M, Kamo K, Titin J, Jamalung L, Lapongan J, Miura S (2010) Nutrient dynamics through fine litterfall in three plantations in Sabah, Malaysia, in relation to nutrient supply to surface soil. Nutr Cycl Agroecosys 88:381–395CrossRefGoogle Scholar
  18. Kasel S, Singh S, Sanders GJ, Bennett LT (2011) Species-specific effects of native trees on soil organic carbon in biodiverse plantings across north-central Victoria, Australia. Geoderma 161:95–106CrossRefGoogle Scholar
  19. Kelty MJ (2006) The role of species mixtures in plantation forestry. For Ecol Manag 233:195–204CrossRefGoogle Scholar
  20. Laclau P (2003) Biomass and carbon sequestration of ponderosa pine plantations and native cypress forests in northwest Patagonia. For Ecol Manag 180:317–333CrossRefGoogle Scholar
  21. Laik R, Kumar K, Das D, Chaturvedi O (2009) Labile soil organic matter pools in a calciorthent after 18 years of afforestation by different plantations. Appl Soil Ecol 42:71–78CrossRefGoogle Scholar
  22. Lemma B, Kleja DB, Nilsson I, Olsson M (2006) Soil carbon sequestration under different exotic tree species in the southwestern highlands of Ethiopia. Geoderma 136:886–898CrossRefGoogle Scholar
  23. Lieth H, Whittaker RH (1975) Primary productivity of the biosphere. Springer Verlag, New YorkCrossRefGoogle Scholar
  24. Liu E, Liu S (2012) The research of carbon storage and distribution feature of the Mytilaria laosensis plantation in south sub-tropical area. Acta Ecol Sin 32:5103–5109CrossRefGoogle Scholar
  25. Lu R (1999) Analytical methods of soil agricultural chemistry. Agriculture Science and Technology Press of China, Beijing, pp 15–20Google Scholar
  26. Mishra A, Sharma S, Khan G (2003) Improvement in physical and chemical properties of sodic soil by 3, 6 and 9 years old plantation of Eucalyptus tereticornis. Biorejuvenation Sodic Soil For Ecol Manage 184:115–124Google Scholar
  27. Peichl M, Arain MA (2006) Above-and belowground ecosystem biomass and carbon pools in an age-sequence of temperate pine plantation forests. Agric For Meteorol 140:51–63CrossRefGoogle Scholar
  28. Razakamanarivo RH, Grinand C, MA Razafindrakoto MB, Albrecht A (2011) Mapping organic carbon stocks in Eucalyptus plantations of the central highlands of Madagascar: a multiple regression approach. Geoderma 162:335–346CrossRefGoogle Scholar
  29. Resh SC, Binkley D, Parrotta JA (2002) Greater soil carbon sequestration under nitrogen-fixing trees compared with eucalyptus species. Ecosystems 5:217–231.  https://doi.org/10.1007/s10021-001-0067-3 CrossRefGoogle Scholar
  30. Rumpel C, Kögel-Knabner I (2011) Deep soil organic matter—a key but poorly understood component of terrestrial C cycle. Plant Soil 338:143–158CrossRefGoogle Scholar
  31. Santana GS, Knicker H, González-Vila FJ, González-Pérez JA, Dick DP (2015) The impact of exotic forest plantations on the chemical composition of soil organic matter in Southern Brazil as assessed by Py–GC/MS and lipid extracts study. Geoderma Regional 4:11–19CrossRefGoogle Scholar
  32. SFA (2005) The sixth National Forest Resources Inventory (1999-2003). State Forestry Administration (SFA)Google Scholar
  33. Song M, Duan H, Guan DS, Zhang H (2018) The dynamics of carbon accumulation in Eucalyptus and Acacia plantations in the Pearl River delta region. V3. FigShare [Dataset].  https://doi.org/10.6084/m9.figshare.5853420.v3
  34. Souza-Alonso P, Guisande-Collazo A, González L (2015) Gradualism in Acacia dealbata Link invasion: impact on soil chemistry and microbial community over a chronological sequence. Soil Biol Biochem 80:315–323CrossRefGoogle Scholar
  35. Sun L, Guan D (2014) Carbon stock of the ecosystem of lower subtropical broadleaved evergreen forests of different ages in Pearl River Delta, China. J Trop For Sci:249–258Google Scholar
  36. Tang G, Li K (2013) Tree species controls on soil carbon sequestration and carbon stability following 20years of afforestation in a valley-type savanna. For Ecol Manag 291:13–19CrossRefGoogle Scholar
  37. Thuille A, Schulze ED (2006) Carbon dynamics in successional and afforested spruce stands in Thuringia and the Alps. Glob Chang Biol 12:325–342CrossRefGoogle Scholar
  38. Wang G, Guan D, Zhang Q, MR Peart YC, Peng Y, Ling X (2014) Spatial patterns of biomass and soil attributes in an estuarine mangrove forest (Yingluo Bay, South China). Eur J Forest Res 133:993–1005.  https://doi.org/10.1007/s10342-014-0817-3 CrossRefGoogle Scholar
  39. Wei X, Li Q, Liu Y, Liu S, Guo X, Zhang L, Niu D, Zhang W (2013) Restoring ecosystem carbon sequestration through afforestation: a sub-tropic restoration case study. For Ecol Manag 300:60–67CrossRefGoogle Scholar
  40. Wiesmeier M, Prietzel J, Barthold F, Spörlein P, Geuß U, Hangen E, Reischl A, Schilling B, Lützow MV, Kögel-Knabner I (2013) Storage and drivers of organic carbon in forest soils of southeast Germany (Bavaria) – implications for carbon sequestration. For Ecol Manag 295:162–172CrossRefGoogle Scholar
  41. Xian J, Y Zhang TH, Wang K, Yang H (2009) Carbon stock and allocation of five restoration ecosystems in subalpine coniferous forest zone in Western Sichuan Province, Southwest China. Acta Ecol Sin 29:51–55CrossRefGoogle Scholar
  42. Xie J, Guo J, Yang Z, Huang Z, Chen G, Yang Y (2013) Rapid accumulation of carbon on severely eroded red soils through afforestation in subtropical China. For Ecol Manag 300:53–59CrossRefGoogle Scholar
  43. Yang J, Wang C (2005) Soil carbon storage and flux of temperate forest ecosystems in northeastern China. Acta Ecol Sin 25:2875–2882Google Scholar
  44. Yang L, Liu N, Ren H, Wang J (2009) Facilitation by two exotic Acacia: Acacia auriculiformis and Acacia mangium as nurse plants in South China. For Ecol Manag 257:1786–1793CrossRefGoogle Scholar
  45. Zhang F, Wang X, Guo T, Zhang P, Wang J (2015) Soil organic and inorganic carbon in the loess profiles of Lanzhou area: implications of deep soils. Catena 126:68–74.  https://doi.org/10.1016/j.catena.2014.10.031 CrossRefGoogle Scholar
  46. Zhang H, Guan D, Song M (2012) Biomass and carbon storage of Eucalyptus and Acacia plantations in the Pearl River Delta, South China. For Ecol Manag 277:90–97CrossRefGoogle Scholar
  47. Zhang X, Xu Z, Zeng F, Hu X, Han Q (2011) Carbon density distribution and storage dynamics of forest ecosystem in Pearl River Delta of low subtropical China. China Environ Sci 31:69–77CrossRefGoogle Scholar
  48. Zhang XY (2009) Allocation characteristics of three chief forest biomass and carbon stock in Guangzhou. Ph.D. Thesis., Sun Yat Sen University,ChinaGoogle Scholar
  49. Zhao J, Kang F, L Wang XY, Zhao W, Song X, Zhang Y, Chen F, Sun Y, He T (2014) Patterns of biomass and carbon distribution across a chronosequence of Chinese pine (Pinus tabulaeformis) forests. PLoS One 9:e94966CrossRefPubMedPubMedCentralGoogle Scholar
  50. Zhou Y, Yu Z, Zhao S (2000) Carbon storage and budget of major Chinese forest types. Chin J Plant Ecol 24:518–522Google Scholar

Copyright information

© INRA and Springer-Verlag France SAS, part of Springer Nature 2018

Authors and Affiliations

  1. 1.College of Civil Engineering, Shenzhen universityShenzhenChina
  2. 2.College of Resources and EnvironmentHuazhong Agricultural UniversityWuhanChina
  3. 3.Department of Environmental Science, School of Environmental Science and EngineeringSun Yat-sen UniversityGuangzhouChina
  4. 4.Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation TechnologySun Yat-sen UniversityGuangzhouChina

Personalised recommendations