| Dongting Lake is the second largest freshwater lake in China, and Dongting Lake region is one of the most important commodity grain production bases and the significant freshwater aquaculture products bases in the country as well. In order to maintain a sustainable high production in both agriculture and aquaculture in this region, a China-Germany collaboration afforestation project was started up in 1988 based on the initial establishment of protective forests. The objective of the project was to complete a total of 30,000 ha of afforestation area in eight counties in the region by five years with four major protective forest types:Preserved forests for soil and water conservation on hilly areas along the lake (PF), Replanting preserved forests for soil and water conservation on hilly areas along the lake (RPF), Protective forest bands on plain area (PFB), and Wave-break Forest bands along the shores of the lake (WFB). In the present study, physical and chemical properties of soils, vegetation composition, biomass productivity, nutrient element accumulation, and carbon storage were investigated in the four protective forest types in Li County within the Dongting Lake region. The results showed:1. The soils belonged to red soil, and were clay-textured and acidic with pH value of 4.54-5.27 in PF, RPF and PFB, but were lake-tide loam-textured and alkaline with pH value of 8.18 in WFB. Soil organic matter (SOM) ranged from 11.03 to 29.00 g.kg-1 in the study stands, in which SOM was significantly higher in PF than in other three forest types (p <0.05). In the study sites, available nitrogen (N) accounted only for 1.46% of total N in soils and phosphate (P) content level was low with the value of 0.16-0.67 g.kg-1. P content was the highest in WFB, which was significantly higher than those in other three forest types (p< 0.05). No statistic difference was found in terms of (potassium) K content (ranged 2.53-2.90 g.kg-1) among the four forest types (p< 0.05). Calcium (Ca) and Magnesium (Mg) contents in WFB (16.89 and 5.03 g.kg-1, respectively) were as high as 27-41 and 3-4 times of that in other forest types, respectively (p< 0.05). The concentrations of micronutrients in soils in the study sites ranged as:Fe:12555.40-15249.80 mg.kg-1, Cd:0.06-0.09 mg.kg-1, Mn:249.80-865.98 mg.kg-1, Zn:65.16-99.28 mg.kg-1, Cu: 31.57-44.16 mg·kg-1, Ni:36.59-56.26 mg.kg-1, Pb:22.08-29.99 mg·kg-1, and Co:3.79-6.67 mg.kg-1.2. It was found that species richness indexes in tree, shrub, and herbaceous layers in the four protective forest types were:9,17, and 8 in PF; 20,24, and 10 in RPF; 6,5, and 5 in PFB; and 1,2, and 33 in WFB. Shannon-Wiener diversity index was 0.893,2.432,0.996; 2.051,2.643, 1.455; 0.654,1.187,1.284; and 0.000,0.673,3.010 in tree, shrub and herbaceous in PF, RPF, PFB and WFB, respectively. Simpson diversity index in tree, shrub, and herbaceous was 0.393,0.882,0.456; 827,0.912, 0.701; 0.326,0.605,0.691; 0.000,0.480,0.947 in PF, RPF, PFB and WFB. Pielon evenness index were 0.406,0.858,479; 0.685,0.832,0.632; 0.406, 0.737,0.708; 0.000,0.971,0.860 in tree, shrub and herbaceous in PF, RPF, PFB, and WFB, respectively. The number of understory plant species was gradually increased with stand ages in the four forest sites, which would facilitate to soil and water conservation and maintains of soil fertility.3. Among the four protective forest types, average biomass of individual tree was 56.83 kg in 22-year old Masson pine forests in PF; 4.27 kg in 8-year old Masson pine and 3.62 kg in 8-year old Slash pine forests in RPF; 20.46 kg in 10-year old Slash pine and 5.07 kg in 6-year old Masson pine forests in PFB; and 193.79 kg in 10-year old Poplar forests in WFB. On average, biomass in over-storey was 109.97,4.51,28.57 and 116.27 t.hm-2 in PF, RPF, PFB and WFB, respectively. Annual productivity of the forest stands was 5.00,0.58,3.37 and 18.97 t.hm-2.a-1 in PF, RPF, PFB and WFB. Biomass in under-storey was 3.66,27.03,5.69 and 5.11 t.hm-2 in PF, RPF, PFB and WFB. Biomass in litter layer on the floor was 1.40,2.01,0.97 and 1.73 t.hm-2 in PF, RPF, PFB and WFB, respectively. The results indicated that the China-Germany afforestration project was successful with better stand vertical structures and relative high biomass production and site productivity in the four protective forest ecosystems. 4. The concentrations of macronutrient elements within plant organs ranged 4.05-39.04 g.kg-1(N),0.33-6.97g.kg-1(P),1.08-33.23 g.kg-1 (K), 1.50-21.00 g.kg-1 (Ca), and 0.67-4.86 g.kg-1 (Mg) in the four forest types. Besides a relative high concentration of Fe (> 160.00 mg.kg-1) in plant organs, the concentrations of other micronutrient elements (Ni, Pb, Cd, Mn, Zn and Cu) were all less than 15.00 mg.kg-1. It was found that the elements (N, P, C, Mg, Cu, Ni and Pb) were mostly accumulated in 10-year old Poplar forests highest, while the highest accumulation amount of K, Fe, Mn, Zn and Cd was appeared in 22-year old Masson pine forests. It was also found that three tree species(Cyclobalanopsis glauca, Symplocos caudate, and Ilexpurpurea) had the strongest capability to absorb and accumulate heavy metal element, Cd, with the biological absorption coefficient of 4666.7, 2800.0,1085.7, respectively. As a result, the three tree species can be chosen as ideal plant species for remediation and restoration of serious Cd-contaminated soils. The amount of macro-and micronutrients in the litter layer on the floor was 36.23 and 1650.18; 1.22 and 2357.96; 56.19 and 1936.83; and 33.62 kg.hm-2 and 879.65 g.hm-2 in PF, RPF, PFB, and WFB, respectively. It showed that soil fertility was better maintained in PF, RPF and PFB types.5. Concentration of carbon in soils ranged from 4.14 to 20.62g.kg-1 in the studied sites. The carbon storage was from 65.57 to 68.33 t.hm-2 and was declined with soil depth in the four protective forest types. Carbon storage was 15862.96-60730.86 kg.hm-2 in vegetation compartment and 618.74-1286.45 kg.hm-2 in litter layer compartment on the floor. On average, the carbon storage was 121.49,84.85,73.04, and 129.87 t.hm-2 in PF, RPF, PFB and WFB, respectively. The size of carbon pool in the studied forest ecosystems was in order soil> vegetation> litter layer.6. The direct economic benefits of timber production and indirectly benefits of ecological services of the protective forests, such as water resources conservation, preventing soil erosion, carbon sequestration, purification of air, landscape aesthetics, regulating local environment conditions were assessed and calculated. Our results showed that total annual value of the protective forests in the studied region was about 3.22 billion yuan (RMB), of which the ecological benefit was 3.1 billion yuan (RMB), accounting for 96.3% of the total values. The direct economic benefit (timber production) was 0.18 billion yuan (RMB) and accounting for only 3.7% of the total values. The results suggested that the China-Germany afforestration project in Dongting Lake region was successful and yielded a great deal of ecological, economic and social benefits. |
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