Biophysical changes following landscape restoration : in Changting model restoration site in Fujian province, southern China

Sammanfattning: China has promised to tackle climate change by decreasing its emission and promote carbon sinks primarily by forest plantations and restorations. There is a growing debate about the impacts of large-scale restorations using few fast-growing species on the kind of ecosystem we are creating and its adaptation to the future environmental conditions. The aim of this thesis was to examine the recovery of both structural and functional attributes of ecosystem undergoing restoration using the Changting model restoration site as a case. Four sites were selected: a severely degrades site (DS), young mixed-species (YS) site where broadleaved species were planted on severely degraded land in 2008, old mixed-species (OS) with similar conditions and treatment as YS but planted in 1982 and secondary forest (SF) in Changting County, Fujian province, southeastern China. Trees and shrubs were inventoried in field and carbon stock was estimated with existing allometric equations. Understory vegetation and forest floor detritus were harvested and soil samples collected in the field for measuring carbon and nitrogen content using an elemental analyzer. General liner model analysis of variance (ANOVA) was preformed to determine significant differences between sites. The results show drastic increasing in tree species richness and good recovery of carbon and nitrogen stock. A total of 43 species, representing 21 families, were recorded in all the study sites; of which 2 species were recorded in the DS, 15 species in OS, 16 species in YS and 29 species in the SF. The species diversity (Shannon index) was the least in DS (0.08) and highest in the SF (2.78) while the mixed-species sites had moderate diversity values (1.92 for YS and 1.76 for OS). The total carbon stock was the highest in the secondary forest (275.1 ± 159.0 tC ha⁻¹) followed by old (181.3 ± 31.0 tC ha⁻¹) and young (62.1 ± 23.6 tC ha⁻¹) mixed-species stands and the lowest being in the degraded site (13.7 ± 8.3 tC ha⁻¹). The carbon stored in the woody biomass (both above- and below-ground) accounted for 67%, 60%, 10% and 8% of the total carbon storage in the SF, OS, YS and DS, respectively. The contributions of understory vegetation and forest floor detritus to the total carbon storage were 42% in the DS, 33% in the YS, 12% in OS and 9% SF. The total soil carbon stock decreased in the following order: SF (65 ± 12.3 tC ha⁻¹), OS (49.9 ± 21.3 tC ha⁻¹), YS (35.1 ± 21.1 tC ha⁻¹) and DS (6.6 ± 3 t C ha⁻¹). The rate of carbon accumulation was slightly higher in YS (6.1 ± 2.6 tC ha⁻¹ yr⁻¹) than in OS (5.1 ± 1.1 tC ha⁻¹ yr⁻¹). The rate of the carbon accumulation in the mixed-species stands is comparable (even more) to those of pure Pinus massoniana plantation but the former has a co-benefit of higher diversity than the monoculture. The soil nitrogen stock showed significant increase from degraded site to the other sites in the top soil. It can be concluded that the restoration projects in Changting are promising to successfully recover both structural (vegetation) and functional (nutrient cycling) attributes of the ecosystem while at the same time restoring some aspects of the biodiversity.