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Carbon stock and allocation of five restoration ecosystems in subalpine coniferous forest zone in Western Sichuan Province, Southwest China
Acta Ecologica Sinica 29 (2009) 51–55
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Carbon stock and allocation of five restoration ecosystems in subalpine coniferous forest zone in Western Sichuan Province, Southwest China Xian Junren a,d, Zhang Yuanbin b, Hu Tingxing c,*, Wang Kaiyun d, Yang Hua c a
College of Resource and Environment, Sichuan Agricultural University, Ya’an 625014, China Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China c College of Forestry and Horticulture, Sichuan Agricultural University, Ya’an 625014, China d Shanghai Key Laboratory of Urbanization Processes and Ecological Restoration, East China Normal University, Shanghai 200062, China b
a r t i c l e
i n f o
Keywords: Carbon stock Ecosystem Vegetation restoration Subalpine
a b s t r a c t As the largest carbon pool of the terrestrial ecosystem, forest plays a key role in sequestrating and reserving greenhouse gases. With the method of replacing space with time, the typical restoration ecosystems of herb (dominated by Deyeuxia scabrescens, P1), shrub (dominated by Salix paraqplesia, P2), broadleaf (dominated by Betula platyphylla, P3), mixed forest (dominated by Betula spp. and Abies faxoniana, P4), and climax (dominated by Abies faxoniana, P5) were selected to quantify the carbon stock and allocation in the subalpine coniferous forest in Western Sichuan (SCFS). The results indicated that the soil organism carbon (SOC) stock decreased with the depth of soil layer, and the SOC per layer and the total SOC increased largely with the vegetation restoration. The contribution of SOC to the carbon stock of ecosystems decreased with the vegetation restoration from 89.45% to 27.06%, while the quantity was from 94.00 to 223.00 t C hm 2. The carbon stock in ground cover increased with the vegetation restoration, and its contribution to the carbon stock of ecosystems was similar (3–4% of the total). Following the vegetation restoration, the plant carbon stock multiplied and reached to 430.86 ± 49.49 t C hm 2 at the climax phase. During the restoration, the carbon stock of different layers increased, and the contribution of belowground to the carbon stock of ecosystems decreased sharply. The carbon stock on ecosystem scale of the climax phase was 5.89 times that of the herb phase. Our results highlighted that the vegetation restoration in SCFS was a large carbon sink. Ó 2009 Ecological Society of China. Published by Elsevier B.V. All rights reserved.
1. Introduction The carbon circle of the terrestrial ecosystem plays a key role in regulating greenhouse gas such as CO2 [1–3]. Therefore, increasing the capacity of carbon sequestration and stock in the terrestrial ecosystem is essential for the budget of CO2. During the past two decades, the carbon stock on regional or national scale had been assessed in many countries [4], and that on provincial scale had also been assessed [5]. To reduce greenhouse effect, operate on the Kyoto protocol, and implement clear development mechanism (CDM) afforestation and reforestation, it becomes urgent to assess forest carbon stock capacity accurately. If the primary forest had been destroyed by disturbance, the new succession would be started. In the process of secondary forest restoration, the carbon stock of ecosystems will increase with the plant community biomass, especially the aboveground biomass largely. Some studies have assessed the aboveground plant carbon stock in the process * Corresponding author. E-mail address: [email protected] (H. Tingxing).
of the secondary forest restoration [6–9], while the carbon stocks of soil and root have also been assessed [10]. However, few carbon stock data of forest on ecosystem scale are available, and the carbon stock of subalpine coniferous forest in Western Sichuan (SCFS) of Southwest China is especially limited. The SCFS, as the absolutely major secondary forest in China, plays an important role in the terrestrial ecosystem of China. However, great demand and excessive utilization of human beings on forest resources have made it susceptible to a rapid degradation in ecosystem properties and ecosystem carbon levels. Therefore, the carbon stock data of the following secondary forest restoration of the SCFS are essential for forest carbon assessment and management in China, which will offer helpful data for the interlocution between countries or regions. Many forestry scholars and ecologists have paid much attention to the SCFS since the beginning of the 20th century, and much more distinguished achievements have been obtained [11–19]. However, the forest carbon stock on ecosystem scale has been rarely studied. Therefore, we studied the carbon stock and allocation in the vegetation restoration process of the SCFS zone with the field survey method of replacing
1872-2032/$ - see front matter Ó 2009 Ecological Society of China. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.chnaes.2009.04.007
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X. Junren et al. / Acta Ecologica Sinica 29 (2009) 51–55
space with time. The objectives of this study were: (1) to quantify the carbon stock at the ecosystem level in the SCFS region, (2) to quantify the carbon stock allocation in the vegetation restoration process of the SCFS region, and (3) to quantify the carbon stock capacity potential of ecosystem restoration in the SCFS.
This study was carried out in the Wanglang National Nature Reserve (WNNR) in Pingwu County, Sichuan Province, Southwest China. Today, the vertical distribution of vegetation in WNNR is mixed forest of conifers and broadleaf, deciduous broadleaf forest (2300– 2600 m), fir forest (dominated by Abies faxoniana), spruce-cypress forest (dominated by Picea purpurea and Sabina saltuaria, 2600– 3500 m), subalpine shrub and meadow (3500–4400 m), and rock vegetation (4400–4900 m), which have been well described [20,21]. Most restoration vegetations of the WNNR were shifted from the deforestation of 1950s. Consequently, in the WNNR the whole secondary succession series are distributed, which are herb phase (dominated by Deyeuxia scabrescens and Festuca spp.), shrub phase (dominated by Salix paraqplesia and Lonicera spp.), deciduous broadleaf forest phase (dominated by Betula platyphylla), mixed forest phase (dominated by Betula spp. and Abies faxoniana) and climax phase (dominated by A. faxoniana).
phases on ecosystem scale with the field survey method of replacing space with time. Five similar altitude and slope communities of herb (dominated by Deyeuxia scabrescens, P1), shrub (dominated by S. paraqplesia, P2), broadleaf (dominated by B. platyphylla, P3), mixed forest (dominated by B. spp. and A. faxoniana, P4), and climax (dominated by A. faxoniana, P5), which were representatives of different vegetation restoration phases, and selected to quantify carbon stock and allocation. Eight replicated square plots were sampled in each community (Table 1). The quadrate plots of forest, shrub and herb were 20 20 m, 2 2 m and 1 1 m, respectively. All plants at each plot were surveyed and sorted into three layers of trees (tree diameter at breast height DBH P 5 cm), understory (DBH < 5 cm, including smaller trees and shrubs), and herb. The carbon stock of tree layers in different communities was surveyed by mean tree in these communities, which meant to measure biomass and carbon stock of 5–7 new up-root trees. According to the biomass model of height and DBH [22], and the age of trees obtained by using the method of Chen et al. [23], we made a biomass and carbon stock model. Biomasses of understory, herb and ground cover (including litter, lichen and some coarse woody debris with diameter < 2 cm) were measured by destroying samples. The soils were sampled from the layers of 0–20 cm (I), 20–40 cm (II) and 40–60 cm (III, the soil was counted as 60 cm if the soil depth was less than 60 cm). All samples of plants and soil were brought to laboratory to measure the carbon concentration [24]. All data were counted with Microsoft Excel 2000 (Microsoft office 2000, USA).
2.2. Sampling methods
3. Results
We selected the herb (dominated by D. scabrescens), shrub (dominated by S. paraqplesia), deciduous broadleaf (dominated by B. platyphylla), mixed forest (dominated by B. spp. and A. faxoniana) and fir forest (dominated by A. faxoniana) as the restoration series, and studied carbon stock and allocation in the five restoration
3.1. Soil organism carbon (SOC)
2. Materials and methods 2.1. Research site
The concentration and stock of SOC decreased sharply with the soil depth (Table 2). From P1 to P5, the SOC concentration in layer II was 47.52%, 49.00%, 62.49%, 57.66% and 48.36% that in layer I,
Table 1 General characteristics of the studied communities. No.
Community
Altitude (m)
Soil type
P1
Herb community Willow shrub Birch forest Mixed forest Fir forest
2730
Brown soil
2680 2605 2704 2854
Brown soil Brown soil Dark brown soil Dark brown soil
P2 P3 P4 P5
Average DBH (cm)
Average Age (a)
–
–
– 12.4 22.5 28.3
– 48.4 83.1 143.7
Wood plant density (tree hm 2) – 57500 1975 740 210
Average height (m)
Coverage (%)
0.8
90
1.5 13.5 27.0 35.0
80 60 75 70
Table 2 SOC stock and allocation in the studied communities. Community types P1
P2
P3
P4
P5
Soil layer
SOC concentration (g C kg 1)
SOC stock (t C hm 2)
Average SOC concentration of community (g C kg 1)
SOC stock of community (t C hm
I II III
43.10 ± 4.50 20.48 ± 2.09 4.34 ± 1.10
42.01 ± 4.05 38.41 ± 7.76 13.62 ± 3.26
15.63 ± 1.17
94.04 ± 7.73
I II III
46.35 ± 4.89 22.71 ± 4.60 5.72 ± 0.72
62.57 ± 4.46 50.78 ± 6.14 19.07 ± 4.36
19.22 ± 2.46
132.43 ± 9.58
I II III
46.42 ± 4.76 29.01 ± 3.06 7.55 ± 2.10
76.64 ± 10.94 63.20 ± 4.32 26.05 ± 6.33
22.64 ± 1.12
165.89 ± 11.60
I II III
73.35 ± 5.69 42.29 ± 7.89 25.31 ± 3.71
101.75 ± 12.18 73.47 ± 13.16 46.99 ± 7.90
44.52 ± 3.93
222.20 ± 18.44
I II III
65.43 ± 6.86 31.64 ± 6.78 21.09 ± 3.05
85.94 ± 7.82 47.07 ± 9.27 33.65 ± 6.05
37.71 ± 2.42
166.65 ± 10.57
2
)
Total Root
1.70 ± 0.15 8.33 ± 1.01 11.20 ± 1.50 18.97 ± 1.30 63.74 ± 7.12 5.67 ± 0.52 26.54 ± 3.23 62.54 ± 8.52 100.93 ± 6.88 367.12 ± 42.37
Total (t C hm
2
) Aboveground
7.37 ± 0.67 34.87 ± 4.24 73.74 ± 10.02 119.90 ± 8.18 430.86 ± 49.49
X. Junren et al. / Acta Ecologica Sinica 29 (2009) 51–55
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that in layer III was only 10.07%, 12.34%, 16.26%, 34.51% and 32.23% that in layer I, and that in layer III was 21.19%, 25.19%, 26.03%, 59.85% and 66.66% that in layer II, respectively. Therefore, the SOC in different layers increased along the restoration, and the SOC stock had the same trend, too. The SOC stock increased largely with the restoration, which was presented as forest phase > shrub phase > herb phase. The SOC concentration of P1 was 81.29%, 69.02%, 35.10% and 41.44% that of P2–P5, while the SOC stock of P1 was 71.01%, 56.69%, 42.32% and 56.48% that of P2–P5, respectively. The SOC concentration of P2 was 84.91%, 43.18% and 50.98% that of P3–P5, while the SOC stock of P2 was 79.83%, 59.60% and 79.54% that of P3–P5, respectively. The difference of SOC concentration and stock between P3 and P5 was not significant, and P4 had the highest SOC concentration and stock.
7.37 ± 0.67 0.61 ± 0.10 0.91 ± 0.20 1.18 ± 0.11 1.03 ± 0.08 1.70 ± 0.15 0.14 ± 0.02 0.21 ± 0.05 0.27 ± 0.03 0.24 ± 0.02 5.67 ± 0.52 0.47 ± 0.08 0.70 ± 0.15 0.91 ± 0.08 0.79 ± 0.06 – 8.19 ± 1.02 1.09 ± 0.14 2.68 ± 0.25 4.05 ± 0.17 – 26.07 ± 3.25 3.46 ± 0.45 8.54 ± 0.80 12.90 ± 0.55
– 34.26 ± 4.26 4.55 ± 0.59 11.22 ± 1.06 16.95 ± 0.72
Aboveground Root
– – 68.28 ± 9.17 107.50 ± 7.32 412.88 ± 49.59 – – 9.90 ± 1.33 16.02 ± 0.92 59.46 ± 6.72 P1 P2 P3 P4 P5
Aboveground
– – 58.38 ± 7.84 91.48 ± 5.26 353.43 ± 39.94
Total Root )
2
Tree (t C hm Community type
Table 3 Plant carbon stock in different layers of the studied communities.
Shrub (t C hm
2
) Aboveground
Total
Herb (t C hm
2
)
Root
Total
3.2. Plant carbon stock The tree contributed absolute majority to plant carbon (Table 3). In P3, P4 and P5, the contribution of trees to plant carbon was 92.55%, 89.65% and 95.78%, while that of shrubs was 6.21%, 9.36% and 3.98%, and that of herbs was 1.24%, 0.99% and 0.24%, respectively. In P2, the contribution of shrubs to plant carbon was 98.21%, and that of herbs was only 1.79%. This indicated that the community structure changed largely for the taller trees that dominated following the restoration, and the tree capacity of sequestrating carbon increased greatly. In the same way, the belowground carbon increased largely, too. The root carbon stock changed from 1.70 ± 0.15 t C hm 2 of P1 to 63.74 ± 7.12 t C hm 2 of P5 (37.49 times of P1), and the contribution of roots to belowground carbon stock was 93.29%, while that of P4 and P3 was 88.39% and 84.44%, respectively. This also showed that the function of roots in reformation of soil was gradually strengthened following the vegetation restoration. The contribution of roots to plant carbon stock from P1 to P5 was 23.08%, 23.89%, 15.19%, 15.82% and 14.79%, respectively, which indicated that the carbon stock assessment on ecosystem scale should pay much attention to the root. In a word, the plant carbon stock had been multiplied following the vegetation restoration. For example, plant carbon stock of P5 was 430.86 ± 49.49 t C hm 2, which was 58.42 times that of P1 (7.37 ± 0.67 t C hm 2), and was also higher than those of P3 and P4. 3.3. Carbon stock of ground cover The carbon stock of ground cover increased largely following the vegetation restoration (Table 4). The carbon stock of ground cover of P1 was 53.84%, 44.66%, 30.92% and 17.06% that of P2– P5, that of P2 was 82.96%, 57.44% and 31.70% that of P3–P5, that of P3 was 69.24% and 38.21% that of P4 and P5, and that of P4 was 55.19%. It showed that carbon stock of ground cover was similar between the neighboring restoration phases. In different restoration phases, the carbon stock of ground cover varied from 3.64 ± 0.67 to 21.35 ± 3.64 t C hm 2. However, the contribution of ground cover to the whole plant carbon stock on ecosystem scale was from 3% to 4%. 3.4. Carbon allocation The carbon stock in different layers per studied ecosystem increased largely along with the process of vegetation restoration (Table 4). The carbon stock of P1 on ecosystem scale was 105.06 ± 7.39 t C hm 2. The carbon contribution sequence in different layers of P1 was soil > plant > ground cover, which was similar to that of P2, P3 and P4 (Table 4), while that of P5 was plant > soil > ground cover. The absolute majority to carbon stock of P1– P4 was the belowground, while that of P5 was the aboveground. Along with the process of vegetation restoration, the carbon stock
X. Junren et al. / Acta Ecologica Sinica 29 (2009) 51–55
91.08 ± 1.33 80.85 ± 1.45 71.51 ± 2.38 68.10 ± 1.97 37.34 ± 2.04
105.06 ± 7.39 174.06 ± 10.46 247.79 ± 17.15 353.88 ± 21.76 618.86 ± 53.97
of the plant, the soil and the ground cover increased largely. However, their contributions to carbon stock of ecosystems varied greatly, i.e., the contribution of plants increased largely, the contribution of ground cover was between 3% and 4%, and the contribution of soil decreased gradually. 4. Discussions and conclusions
95.74 ± 7.67 140.76 ± 9.45 177.09 ± 12.03 241.17 ± 18.86 230.40 ± 14.11
4.1. SOC
Note: Aboveground carbon stock included that of litter, lichen and plant canopy; underground carbon stock included that of soil and root.
8.92 ± 1.33 19.15 ± 1.45 28.49 ± 2.38 31.90 ± 1.97 62.66 ± 2.04 89.45 ± 1.53 76.05 ± 2.02 67.00 ± 2.81 62.74 ± 2.27 27.06 ± 2.36 P1 P2 P3 P4 P5
3.64 ± 0.67 6.77 ± 1.42 8.16 ± 1.34 11.78 ± 1.21 21.35 ± 3.64
3.49 ± 0.71 3.88 ± 0.72 3.30 ± 0.56 3.35 ± 0.45 3.46 ± 0.53
7.37 ± 0.67 34.87 ± 4.24 73.74 ± 10.02 119.90 ± 8.18 430.86 ± 49.49
7.06 ± 0.92 20.07 ± 2.50 29.69 ± 2.95 33.92 ± 1.94 69.48 ± 2.41
94.04 ± 7.73 132.43 ± 9.58 165.89 ± 11.60 222.20 ± 18.44 166.65 ± 10.57
9.32 ± 1.09 33.31 ± 2.79 70.70 ± 8.54 112.71 ± 7.32 388.46 ± 43.53
Underground Aboveground
Carbon stock (t C hm 2) Percentage (%)
Soil Plant
Carbon stock (t C hm 2) Percentage (%)
Ground cover
Carbon stock (t C hm 2)
Community type
Table 4 Carbon allocation in different layers in the studied ecosystems.
Percentage (%)
Carbon stock (t C hm 2)
Percentage (%)
Carbon stock (t C hm 2)
Percentage (%)
Total (t C hm
2
)
54
In our study, the SOC stock of P3 and P4 was nearly the same as most of the recent studies (10.03–21.27 kg C m 2) [25], which was obviously higher than that of the grassland recovery and reconstruction in the northern Loess Plateau [26]. In different restoration phases, SOC decreased with the soil depth. Following the vegetation restoration, the concentrations and stocks of SOC increased [10], and those in each soil layer increased, too. In the restoration process, the SOC stock and concentration sequence of different vegetation types were: forest phase > shrub phase > herb phase. The SOC of P1 decreased sharply with the soil depth. The SOC of P2 also decreased with the soil depth, and the decreasing extent was far less than that of P1, which could be due to the root actions of inserting, dying and secreting. In forest, the root actions were more effective, which led to higher SOC in different layers. The SOC of P5 was significantly less than that of P4, which was higher than that of P3 because the increased root actions of the deciduous broadleaf species, e.g. birch, could stimulate litter decomposition and activate soil microorganism. This showed that the effect of vegetation to soil was strengthened with the vegetation restoration, which increased the SOC largely. Our study also showed that the deciduous broadleaf species could increase SOC and activate the soil ecological process. Therefore, the SOC on small scale (e.g. similar soil and climate) depended on vegetation, and that on large scale depended on soil, climate and so on [25]. 4.2. Plant carbon stock In the SCFS, the plant carbon stock on community scale increased significantly with the vegetation restoration, and the contributions of different layers to the community plant carbon stock shifted from the herb to the shrub, and then to the tree. In our study, the plant carbon concentration was far higher than that in other forests [4,27], while that of P3 was lower than that of Dongling Mt. in Beijing [22], which could be due to different methods, scales and community ages. In this study, the plant carbon stock of P5 multiplied following the restoration, and reached to 430.86 ± 49.49 t C hm 2. The plant carbon stocks of P3, P4 and P5 were 10.00, 6.26 and 58.42 times higher than that of P1, and 2.11, 3.44 and 12.36 times higher than that of P2, respectively. Different communities had different dominating species, which was due to different plant carbon stocks. For example, plant carbon stock of P5 was 5.84 times higher than that of P3, and 3.59 times higher than that of P4, that of P4 was 1.63 times higher than that of P3, and that of P2 was 4.73 times higher than that of P1, respectively. These data were obviously higher than those in the study by Hu et al. [28], and this difference was due to different methods and communities. In our study, the contribution of roots to plant carbon stock ranged from 14% to 24%, which indicated that carbon stock assessment on the roots on ecosystem scale should be paid much attention to though there were some troubles in the measurement of root carbon stock and concentration. In the five studied communities, the contribution sequence of roots to plant carbon stock was P5 (10.30%) > P3 (5.36%) > P2 (4.78%) > P3 (4.52%) > P1 (1.62%). Therefore, the vegetation restoration in the SCFS zone has great carbon sequestrating potential, which rests on proper wood species ratio, and the model of afforestation and reforestation.
X. Junren et al. / Acta Ecologica Sinica 29 (2009) 51–55
4.3. Carbon stock During the vegetation restoration in the SCFS, the carbon stocks in different layers increased significantly, and were higher than those of some other similar recent studies [4,7,28–32]. This was mainly because the disturbance of human beings was removed in WNNR. Of course, the community type and age, method, and scale were other reasons. Contribution of different layers to ecosystem carbon stock varied largely in different restoration phases (Table 4). The major contributor to ecosystem carbon stock was the plant in climax phase (P5), while that in other phases was the soil. Following the vegetation restoration, the carbon stock percentage of the belowground decreased, while that of the aboveground increased largely, and then became the absolute majority to the ecosystem carbon stock in the climax phase. This study showed that the carbon stock heterogeneity existed in different ecosystems and different layers. For example, the carbon stock in herb phase (P1) was 105.06 ± 7.39 t C hm 2, and that in climax phase (P5) was 618.86 ± 53.97 t C hm 2 (5.89 times that of P1). Although we studied the carbon stock in different layers such as litter, tree, herb, understory, root and soil. However, the coarse woody debris with diameter P2 cm, soil microorganism and animal, carbon turnover, and the dynamics of community structure have yet been studied, thus leading to some uncertainty in this study. On the other hand, our study was conducted in a national nature reserve, which meant that the samples were limited to some extent, which became another obstacle for assessing. Therefore, precise carbon stock assessment on the above-mentioned factors, in particular the dynamics of the community, in the vegetation restoration in the future should be paid much attention to. Our results highlighted that the vegetation restoration in the SCFS zone could bring tremendous carbon sequestration. If the vegetation reached to the climax phase, the SCFS zone would be a large carbon sink, which could offer more important data to the national negotiation of greenhouse gas budget. The study by Zhang et al. [4] indicated that the vegetation restoration aimed to carbon stock in Zhejiang Province needed more time, i.e., about 50 years. The vegetation restoration in the SCFS zone would need more time because of lower temperature, heavier heterogeneity of microenvironment, shorter growth season and slower growing rate. Hence, proper trees, afforestation model and management strategies should be selected for vegetation restoration. The study on the secondary forest carbon pool indicated that the secondary forest restoration would be a large potential sink of carbon sequestration, but the destroying disturbance should be removed [33]. Therefore, proper trees and appropriate arrangement in pairs or groups, afforestation model, and ecosystem management strategies were the key factors to promote and enlarge the carbons sink in the SCFS zone. Acknowledgements This project was jointly supported by the National Natural Science Foundation of China (Nos. 90511008 and 90202010), the Provincial Project of Science and Technology of Sichuan, China (No. 05SG023–009), and the Open Foundation of Shanghai Key Laboratory of Urbanization Process and Ecological Restoration (Nos. 20070010 and 20070005). The authors would like to thank the Wanglang National Nature Reserve for its help in field investigation. References [1] B. Moore III., B.H. Braswell, Earth metabolism: understanding carbon cycling, AMBIO 23 (1994) 4–12.
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Carbon stock and allocation of five restoration ecosystems in subalpine coniferous forest zone in Western Sichuan Province, Southwest China Xian Junren a,d, Zhang Yuanbin b, Hu Tingxing c,*, Wang Kaiyun d, Yang Hua c a
College of Resource and Environment, Sichuan Agricultural University, Ya’an 625014, China Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China c College of Forestry and Horticulture, Sichuan Agricultural University, Ya’an 625014, China d Shanghai Key Laboratory of Urbanization Processes and Ecological Restoration, East China Normal University, Shanghai 200062, China b
a r t i c l e
i n f o
Keywords: Carbon stock Ecosystem Vegetation restoration Subalpine
a b s t r a c t As the largest carbon pool of the terrestrial ecosystem, forest plays a key role in sequestrating and reserving greenhouse gases. With the method of replacing space with time, the typical restoration ecosystems of herb (dominated by Deyeuxia scabrescens, P1), shrub (dominated by Salix paraqplesia, P2), broadleaf (dominated by Betula platyphylla, P3), mixed forest (dominated by Betula spp. and Abies faxoniana, P4), and climax (dominated by Abies faxoniana, P5) were selected to quantify the carbon stock and allocation in the subalpine coniferous forest in Western Sichuan (SCFS). The results indicated that the soil organism carbon (SOC) stock decreased with the depth of soil layer, and the SOC per layer and the total SOC increased largely with the vegetation restoration. The contribution of SOC to the carbon stock of ecosystems decreased with the vegetation restoration from 89.45% to 27.06%, while the quantity was from 94.00 to 223.00 t C hm 2. The carbon stock in ground cover increased with the vegetation restoration, and its contribution to the carbon stock of ecosystems was similar (3–4% of the total). Following the vegetation restoration, the plant carbon stock multiplied and reached to 430.86 ± 49.49 t C hm 2 at the climax phase. During the restoration, the carbon stock of different layers increased, and the contribution of belowground to the carbon stock of ecosystems decreased sharply. The carbon stock on ecosystem scale of the climax phase was 5.89 times that of the herb phase. Our results highlighted that the vegetation restoration in SCFS was a large carbon sink. Ó 2009 Ecological Society of China. Published by Elsevier B.V. All rights reserved.
1. Introduction The carbon circle of the terrestrial ecosystem plays a key role in regulating greenhouse gas such as CO2 [1–3]. Therefore, increasing the capacity of carbon sequestration and stock in the terrestrial ecosystem is essential for the budget of CO2. During the past two decades, the carbon stock on regional or national scale had been assessed in many countries [4], and that on provincial scale had also been assessed [5]. To reduce greenhouse effect, operate on the Kyoto protocol, and implement clear development mechanism (CDM) afforestation and reforestation, it becomes urgent to assess forest carbon stock capacity accurately. If the primary forest had been destroyed by disturbance, the new succession would be started. In the process of secondary forest restoration, the carbon stock of ecosystems will increase with the plant community biomass, especially the aboveground biomass largely. Some studies have assessed the aboveground plant carbon stock in the process * Corresponding author. E-mail address: [email protected] (H. Tingxing).
of the secondary forest restoration [6–9], while the carbon stocks of soil and root have also been assessed [10]. However, few carbon stock data of forest on ecosystem scale are available, and the carbon stock of subalpine coniferous forest in Western Sichuan (SCFS) of Southwest China is especially limited. The SCFS, as the absolutely major secondary forest in China, plays an important role in the terrestrial ecosystem of China. However, great demand and excessive utilization of human beings on forest resources have made it susceptible to a rapid degradation in ecosystem properties and ecosystem carbon levels. Therefore, the carbon stock data of the following secondary forest restoration of the SCFS are essential for forest carbon assessment and management in China, which will offer helpful data for the interlocution between countries or regions. Many forestry scholars and ecologists have paid much attention to the SCFS since the beginning of the 20th century, and much more distinguished achievements have been obtained [11–19]. However, the forest carbon stock on ecosystem scale has been rarely studied. Therefore, we studied the carbon stock and allocation in the vegetation restoration process of the SCFS zone with the field survey method of replacing
1872-2032/$ - see front matter Ó 2009 Ecological Society of China. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.chnaes.2009.04.007
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space with time. The objectives of this study were: (1) to quantify the carbon stock at the ecosystem level in the SCFS region, (2) to quantify the carbon stock allocation in the vegetation restoration process of the SCFS region, and (3) to quantify the carbon stock capacity potential of ecosystem restoration in the SCFS.
This study was carried out in the Wanglang National Nature Reserve (WNNR) in Pingwu County, Sichuan Province, Southwest China. Today, the vertical distribution of vegetation in WNNR is mixed forest of conifers and broadleaf, deciduous broadleaf forest (2300– 2600 m), fir forest (dominated by Abies faxoniana), spruce-cypress forest (dominated by Picea purpurea and Sabina saltuaria, 2600– 3500 m), subalpine shrub and meadow (3500–4400 m), and rock vegetation (4400–4900 m), which have been well described [20,21]. Most restoration vegetations of the WNNR were shifted from the deforestation of 1950s. Consequently, in the WNNR the whole secondary succession series are distributed, which are herb phase (dominated by Deyeuxia scabrescens and Festuca spp.), shrub phase (dominated by Salix paraqplesia and Lonicera spp.), deciduous broadleaf forest phase (dominated by Betula platyphylla), mixed forest phase (dominated by Betula spp. and Abies faxoniana) and climax phase (dominated by A. faxoniana).
phases on ecosystem scale with the field survey method of replacing space with time. Five similar altitude and slope communities of herb (dominated by Deyeuxia scabrescens, P1), shrub (dominated by S. paraqplesia, P2), broadleaf (dominated by B. platyphylla, P3), mixed forest (dominated by B. spp. and A. faxoniana, P4), and climax (dominated by A. faxoniana, P5), which were representatives of different vegetation restoration phases, and selected to quantify carbon stock and allocation. Eight replicated square plots were sampled in each community (Table 1). The quadrate plots of forest, shrub and herb were 20 20 m, 2 2 m and 1 1 m, respectively. All plants at each plot were surveyed and sorted into three layers of trees (tree diameter at breast height DBH P 5 cm), understory (DBH < 5 cm, including smaller trees and shrubs), and herb. The carbon stock of tree layers in different communities was surveyed by mean tree in these communities, which meant to measure biomass and carbon stock of 5–7 new up-root trees. According to the biomass model of height and DBH [22], and the age of trees obtained by using the method of Chen et al. [23], we made a biomass and carbon stock model. Biomasses of understory, herb and ground cover (including litter, lichen and some coarse woody debris with diameter < 2 cm) were measured by destroying samples. The soils were sampled from the layers of 0–20 cm (I), 20–40 cm (II) and 40–60 cm (III, the soil was counted as 60 cm if the soil depth was less than 60 cm). All samples of plants and soil were brought to laboratory to measure the carbon concentration [24]. All data were counted with Microsoft Excel 2000 (Microsoft office 2000, USA).
2.2. Sampling methods
3. Results
We selected the herb (dominated by D. scabrescens), shrub (dominated by S. paraqplesia), deciduous broadleaf (dominated by B. platyphylla), mixed forest (dominated by B. spp. and A. faxoniana) and fir forest (dominated by A. faxoniana) as the restoration series, and studied carbon stock and allocation in the five restoration
3.1. Soil organism carbon (SOC)
2. Materials and methods 2.1. Research site
The concentration and stock of SOC decreased sharply with the soil depth (Table 2). From P1 to P5, the SOC concentration in layer II was 47.52%, 49.00%, 62.49%, 57.66% and 48.36% that in layer I,
Table 1 General characteristics of the studied communities. No.
Community
Altitude (m)
Soil type
P1
Herb community Willow shrub Birch forest Mixed forest Fir forest
2730
Brown soil
2680 2605 2704 2854
Brown soil Brown soil Dark brown soil Dark brown soil
P2 P3 P4 P5
Average DBH (cm)
Average Age (a)
–
–
– 12.4 22.5 28.3
– 48.4 83.1 143.7
Wood plant density (tree hm 2) – 57500 1975 740 210
Average height (m)
Coverage (%)
0.8
90
1.5 13.5 27.0 35.0
80 60 75 70
Table 2 SOC stock and allocation in the studied communities. Community types P1
P2
P3
P4
P5
Soil layer
SOC concentration (g C kg 1)
SOC stock (t C hm 2)
Average SOC concentration of community (g C kg 1)
SOC stock of community (t C hm
I II III
43.10 ± 4.50 20.48 ± 2.09 4.34 ± 1.10
42.01 ± 4.05 38.41 ± 7.76 13.62 ± 3.26
15.63 ± 1.17
94.04 ± 7.73
I II III
46.35 ± 4.89 22.71 ± 4.60 5.72 ± 0.72
62.57 ± 4.46 50.78 ± 6.14 19.07 ± 4.36
19.22 ± 2.46
132.43 ± 9.58
I II III
46.42 ± 4.76 29.01 ± 3.06 7.55 ± 2.10
76.64 ± 10.94 63.20 ± 4.32 26.05 ± 6.33
22.64 ± 1.12
165.89 ± 11.60
I II III
73.35 ± 5.69 42.29 ± 7.89 25.31 ± 3.71
101.75 ± 12.18 73.47 ± 13.16 46.99 ± 7.90
44.52 ± 3.93
222.20 ± 18.44
I II III
65.43 ± 6.86 31.64 ± 6.78 21.09 ± 3.05
85.94 ± 7.82 47.07 ± 9.27 33.65 ± 6.05
37.71 ± 2.42
166.65 ± 10.57
2
)
Total Root
1.70 ± 0.15 8.33 ± 1.01 11.20 ± 1.50 18.97 ± 1.30 63.74 ± 7.12 5.67 ± 0.52 26.54 ± 3.23 62.54 ± 8.52 100.93 ± 6.88 367.12 ± 42.37
Total (t C hm
2
) Aboveground
7.37 ± 0.67 34.87 ± 4.24 73.74 ± 10.02 119.90 ± 8.18 430.86 ± 49.49
X. Junren et al. / Acta Ecologica Sinica 29 (2009) 51–55
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that in layer III was only 10.07%, 12.34%, 16.26%, 34.51% and 32.23% that in layer I, and that in layer III was 21.19%, 25.19%, 26.03%, 59.85% and 66.66% that in layer II, respectively. Therefore, the SOC in different layers increased along the restoration, and the SOC stock had the same trend, too. The SOC stock increased largely with the restoration, which was presented as forest phase > shrub phase > herb phase. The SOC concentration of P1 was 81.29%, 69.02%, 35.10% and 41.44% that of P2–P5, while the SOC stock of P1 was 71.01%, 56.69%, 42.32% and 56.48% that of P2–P5, respectively. The SOC concentration of P2 was 84.91%, 43.18% and 50.98% that of P3–P5, while the SOC stock of P2 was 79.83%, 59.60% and 79.54% that of P3–P5, respectively. The difference of SOC concentration and stock between P3 and P5 was not significant, and P4 had the highest SOC concentration and stock.
7.37 ± 0.67 0.61 ± 0.10 0.91 ± 0.20 1.18 ± 0.11 1.03 ± 0.08 1.70 ± 0.15 0.14 ± 0.02 0.21 ± 0.05 0.27 ± 0.03 0.24 ± 0.02 5.67 ± 0.52 0.47 ± 0.08 0.70 ± 0.15 0.91 ± 0.08 0.79 ± 0.06 – 8.19 ± 1.02 1.09 ± 0.14 2.68 ± 0.25 4.05 ± 0.17 – 26.07 ± 3.25 3.46 ± 0.45 8.54 ± 0.80 12.90 ± 0.55
– 34.26 ± 4.26 4.55 ± 0.59 11.22 ± 1.06 16.95 ± 0.72
Aboveground Root
– – 68.28 ± 9.17 107.50 ± 7.32 412.88 ± 49.59 – – 9.90 ± 1.33 16.02 ± 0.92 59.46 ± 6.72 P1 P2 P3 P4 P5
Aboveground
– – 58.38 ± 7.84 91.48 ± 5.26 353.43 ± 39.94
Total Root )
2
Tree (t C hm Community type
Table 3 Plant carbon stock in different layers of the studied communities.
Shrub (t C hm
2
) Aboveground
Total
Herb (t C hm
2
)
Root
Total
3.2. Plant carbon stock The tree contributed absolute majority to plant carbon (Table 3). In P3, P4 and P5, the contribution of trees to plant carbon was 92.55%, 89.65% and 95.78%, while that of shrubs was 6.21%, 9.36% and 3.98%, and that of herbs was 1.24%, 0.99% and 0.24%, respectively. In P2, the contribution of shrubs to plant carbon was 98.21%, and that of herbs was only 1.79%. This indicated that the community structure changed largely for the taller trees that dominated following the restoration, and the tree capacity of sequestrating carbon increased greatly. In the same way, the belowground carbon increased largely, too. The root carbon stock changed from 1.70 ± 0.15 t C hm 2 of P1 to 63.74 ± 7.12 t C hm 2 of P5 (37.49 times of P1), and the contribution of roots to belowground carbon stock was 93.29%, while that of P4 and P3 was 88.39% and 84.44%, respectively. This also showed that the function of roots in reformation of soil was gradually strengthened following the vegetation restoration. The contribution of roots to plant carbon stock from P1 to P5 was 23.08%, 23.89%, 15.19%, 15.82% and 14.79%, respectively, which indicated that the carbon stock assessment on ecosystem scale should pay much attention to the root. In a word, the plant carbon stock had been multiplied following the vegetation restoration. For example, plant carbon stock of P5 was 430.86 ± 49.49 t C hm 2, which was 58.42 times that of P1 (7.37 ± 0.67 t C hm 2), and was also higher than those of P3 and P4. 3.3. Carbon stock of ground cover The carbon stock of ground cover increased largely following the vegetation restoration (Table 4). The carbon stock of ground cover of P1 was 53.84%, 44.66%, 30.92% and 17.06% that of P2– P5, that of P2 was 82.96%, 57.44% and 31.70% that of P3–P5, that of P3 was 69.24% and 38.21% that of P4 and P5, and that of P4 was 55.19%. It showed that carbon stock of ground cover was similar between the neighboring restoration phases. In different restoration phases, the carbon stock of ground cover varied from 3.64 ± 0.67 to 21.35 ± 3.64 t C hm 2. However, the contribution of ground cover to the whole plant carbon stock on ecosystem scale was from 3% to 4%. 3.4. Carbon allocation The carbon stock in different layers per studied ecosystem increased largely along with the process of vegetation restoration (Table 4). The carbon stock of P1 on ecosystem scale was 105.06 ± 7.39 t C hm 2. The carbon contribution sequence in different layers of P1 was soil > plant > ground cover, which was similar to that of P2, P3 and P4 (Table 4), while that of P5 was plant > soil > ground cover. The absolute majority to carbon stock of P1– P4 was the belowground, while that of P5 was the aboveground. Along with the process of vegetation restoration, the carbon stock
X. Junren et al. / Acta Ecologica Sinica 29 (2009) 51–55
91.08 ± 1.33 80.85 ± 1.45 71.51 ± 2.38 68.10 ± 1.97 37.34 ± 2.04
105.06 ± 7.39 174.06 ± 10.46 247.79 ± 17.15 353.88 ± 21.76 618.86 ± 53.97
of the plant, the soil and the ground cover increased largely. However, their contributions to carbon stock of ecosystems varied greatly, i.e., the contribution of plants increased largely, the contribution of ground cover was between 3% and 4%, and the contribution of soil decreased gradually. 4. Discussions and conclusions
95.74 ± 7.67 140.76 ± 9.45 177.09 ± 12.03 241.17 ± 18.86 230.40 ± 14.11
4.1. SOC
Note: Aboveground carbon stock included that of litter, lichen and plant canopy; underground carbon stock included that of soil and root.
8.92 ± 1.33 19.15 ± 1.45 28.49 ± 2.38 31.90 ± 1.97 62.66 ± 2.04 89.45 ± 1.53 76.05 ± 2.02 67.00 ± 2.81 62.74 ± 2.27 27.06 ± 2.36 P1 P2 P3 P4 P5
3.64 ± 0.67 6.77 ± 1.42 8.16 ± 1.34 11.78 ± 1.21 21.35 ± 3.64
3.49 ± 0.71 3.88 ± 0.72 3.30 ± 0.56 3.35 ± 0.45 3.46 ± 0.53
7.37 ± 0.67 34.87 ± 4.24 73.74 ± 10.02 119.90 ± 8.18 430.86 ± 49.49
7.06 ± 0.92 20.07 ± 2.50 29.69 ± 2.95 33.92 ± 1.94 69.48 ± 2.41
94.04 ± 7.73 132.43 ± 9.58 165.89 ± 11.60 222.20 ± 18.44 166.65 ± 10.57
9.32 ± 1.09 33.31 ± 2.79 70.70 ± 8.54 112.71 ± 7.32 388.46 ± 43.53
Underground Aboveground
Carbon stock (t C hm 2) Percentage (%)
Soil Plant
Carbon stock (t C hm 2) Percentage (%)
Ground cover
Carbon stock (t C hm 2)
Community type
Table 4 Carbon allocation in different layers in the studied ecosystems.
Percentage (%)
Carbon stock (t C hm 2)
Percentage (%)
Carbon stock (t C hm 2)
Percentage (%)
Total (t C hm
2
)
54
In our study, the SOC stock of P3 and P4 was nearly the same as most of the recent studies (10.03–21.27 kg C m 2) [25], which was obviously higher than that of the grassland recovery and reconstruction in the northern Loess Plateau [26]. In different restoration phases, SOC decreased with the soil depth. Following the vegetation restoration, the concentrations and stocks of SOC increased [10], and those in each soil layer increased, too. In the restoration process, the SOC stock and concentration sequence of different vegetation types were: forest phase > shrub phase > herb phase. The SOC of P1 decreased sharply with the soil depth. The SOC of P2 also decreased with the soil depth, and the decreasing extent was far less than that of P1, which could be due to the root actions of inserting, dying and secreting. In forest, the root actions were more effective, which led to higher SOC in different layers. The SOC of P5 was significantly less than that of P4, which was higher than that of P3 because the increased root actions of the deciduous broadleaf species, e.g. birch, could stimulate litter decomposition and activate soil microorganism. This showed that the effect of vegetation to soil was strengthened with the vegetation restoration, which increased the SOC largely. Our study also showed that the deciduous broadleaf species could increase SOC and activate the soil ecological process. Therefore, the SOC on small scale (e.g. similar soil and climate) depended on vegetation, and that on large scale depended on soil, climate and so on [25]. 4.2. Plant carbon stock In the SCFS, the plant carbon stock on community scale increased significantly with the vegetation restoration, and the contributions of different layers to the community plant carbon stock shifted from the herb to the shrub, and then to the tree. In our study, the plant carbon concentration was far higher than that in other forests [4,27], while that of P3 was lower than that of Dongling Mt. in Beijing [22], which could be due to different methods, scales and community ages. In this study, the plant carbon stock of P5 multiplied following the restoration, and reached to 430.86 ± 49.49 t C hm 2. The plant carbon stocks of P3, P4 and P5 were 10.00, 6.26 and 58.42 times higher than that of P1, and 2.11, 3.44 and 12.36 times higher than that of P2, respectively. Different communities had different dominating species, which was due to different plant carbon stocks. For example, plant carbon stock of P5 was 5.84 times higher than that of P3, and 3.59 times higher than that of P4, that of P4 was 1.63 times higher than that of P3, and that of P2 was 4.73 times higher than that of P1, respectively. These data were obviously higher than those in the study by Hu et al. [28], and this difference was due to different methods and communities. In our study, the contribution of roots to plant carbon stock ranged from 14% to 24%, which indicated that carbon stock assessment on the roots on ecosystem scale should be paid much attention to though there were some troubles in the measurement of root carbon stock and concentration. In the five studied communities, the contribution sequence of roots to plant carbon stock was P5 (10.30%) > P3 (5.36%) > P2 (4.78%) > P3 (4.52%) > P1 (1.62%). Therefore, the vegetation restoration in the SCFS zone has great carbon sequestrating potential, which rests on proper wood species ratio, and the model of afforestation and reforestation.
X. Junren et al. / Acta Ecologica Sinica 29 (2009) 51–55
4.3. Carbon stock During the vegetation restoration in the SCFS, the carbon stocks in different layers increased significantly, and were higher than those of some other similar recent studies [4,7,28–32]. This was mainly because the disturbance of human beings was removed in WNNR. Of course, the community type and age, method, and scale were other reasons. Contribution of different layers to ecosystem carbon stock varied largely in different restoration phases (Table 4). The major contributor to ecosystem carbon stock was the plant in climax phase (P5), while that in other phases was the soil. Following the vegetation restoration, the carbon stock percentage of the belowground decreased, while that of the aboveground increased largely, and then became the absolute majority to the ecosystem carbon stock in the climax phase. This study showed that the carbon stock heterogeneity existed in different ecosystems and different layers. For example, the carbon stock in herb phase (P1) was 105.06 ± 7.39 t C hm 2, and that in climax phase (P5) was 618.86 ± 53.97 t C hm 2 (5.89 times that of P1). Although we studied the carbon stock in different layers such as litter, tree, herb, understory, root and soil. However, the coarse woody debris with diameter P2 cm, soil microorganism and animal, carbon turnover, and the dynamics of community structure have yet been studied, thus leading to some uncertainty in this study. On the other hand, our study was conducted in a national nature reserve, which meant that the samples were limited to some extent, which became another obstacle for assessing. Therefore, precise carbon stock assessment on the above-mentioned factors, in particular the dynamics of the community, in the vegetation restoration in the future should be paid much attention to. Our results highlighted that the vegetation restoration in the SCFS zone could bring tremendous carbon sequestration. If the vegetation reached to the climax phase, the SCFS zone would be a large carbon sink, which could offer more important data to the national negotiation of greenhouse gas budget. The study by Zhang et al. [4] indicated that the vegetation restoration aimed to carbon stock in Zhejiang Province needed more time, i.e., about 50 years. The vegetation restoration in the SCFS zone would need more time because of lower temperature, heavier heterogeneity of microenvironment, shorter growth season and slower growing rate. Hence, proper trees, afforestation model and management strategies should be selected for vegetation restoration. The study on the secondary forest carbon pool indicated that the secondary forest restoration would be a large potential sink of carbon sequestration, but the destroying disturbance should be removed [33]. Therefore, proper trees and appropriate arrangement in pairs or groups, afforestation model, and ecosystem management strategies were the key factors to promote and enlarge the carbons sink in the SCFS zone. Acknowledgements This project was jointly supported by the National Natural Science Foundation of China (Nos. 90511008 and 90202010), the Provincial Project of Science and Technology of Sichuan, China (No. 05SG023–009), and the Open Foundation of Shanghai Key Laboratory of Urbanization Process and Ecological Restoration (Nos. 20070010 and 20070005). The authors would like to thank the Wanglang National Nature Reserve for its help in field investigation. References [1] B. Moore III., B.H. Braswell, Earth metabolism: understanding carbon cycling, AMBIO 23 (1994) 4–12.
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