| Urban forest is an important part of urban ecosystem. It is the most direct and effective means to mitigate urban carbon(C) emissions. China is in the rapid progess of urbanization, which will influence the structure and function of urban forest ecosystem. This research combined remote sensing technology, geographic information system technology and field survey to study the characteristics and carbon storage of urban forest in Changchun. The main objectives of this study were to:(1) Quantify the C storage of urban forests in Changchun, Northeast China;(2) Understand the effects of forest type and urbanization on landscape pattern, species biodiversity and C storage of urban forests;(3) Understand the change of the landscape pattern and C storage of urban forests in different scales;(4) Build the correlation model between Normalized Difference Vegetation Index(NDVI) and carbon of urban forests to estimate the C storage change in different time series of urban forests;(5) Quantify the growth rate and sequestrate rate of different species of urban forest and consequently estimate the average amount of carbon sequestration among different types of urban forest, and among different gradients of urbanization of urban forests. The results can provide insights for decision-makers and urban planners to better understand the effects of forest type and urbanization on C storage of urban forests in Changchun, and make better management plans for urban forests. The main conclusion are as follows:(1) There were obvious differences for landscape pattern among different types of urban forests. The attached forest(AF) and road forest(RF) had higher patch number and patch density than the production and management forest(PF), landscape and relaxation forest(LF) and ecological and welfare forest(EF). Howerer, the patch COHESION and aggregation indices(AI) were smaller for the AF and the RF. There were also obvious differences for landscape pattern among different gradients of urbanization of urban forests. The patch connection gradually increased and the patch aggregation gradually decreased from the first ring to the fourth ring.(2) Mid-mature forest and young forest were the main forest types, while mature forest was rare. The community structure were different for types of urban forests, the RF had the largest average diameter at breast height(DBH), followed by the EF, and the PF had the smallest average DBH. The health condition was not going well. The RF and AF had poorer health conditions which were poorer. In different urbanization gradients, the average DBH of urban forest was decreased from the first ring to the fourth ring,then slightly increased in the fifth ring. The health condition of urban forests in urban center was better than that in the suburb. Management and maintenance were urgently needed for the trees with poor condition.(3) The species richness of urban forests in Changchun was low. This may have a closely related to the cold climate and geography characteristics. The six species Salix matsudana, Populus davidiana, Pinus sylvestris var. mongolica, Picea asperata, Armeniaca mandshurica, and Pinus tabulaefomis var. mukdensis were the most important in the city. In addition, the urban forests were dominated by native species in the urban setting. There were obvious differences among different types of urban forests. AF had the highest species richness and diversity, followed by LF, RF, EF, and PF. As for RF, an appropriate and diverse mix of large size tree and small size tree or shrub species should be selected to increase the diversity. For EF and PF, based on the 10/20/30 rule of thumb, the diversity must be urgently inreased in the species, genus, and family. Compared with different types of urban forest, species distribution for different urbanization gradients were less uneven. The species richness and diversity increased from the first ring to the third ring and then decreased from the third ring to the fifth ring. Based on the 10/20/30 rule of thumb, the diversity should be increased at the species level in the first ring and the fifth ring, and should be increased at the family level in the second ring and the fifth ring.(4) The mean C density was 4.41 kg/m2 in Changchun. The total C storage was 4.74×108 kg. The total estimated economic value of C storage was about 129.54 million RMB. In addition, the differences in C density and C storage among different types of urban forests indicated that DBH and forest cover area were the most factors that affected the C density and C storage. This suggests that reasonable planning and management of urban forests can improve the urban C storage. The significant differences in C density and C storage along the urbanization gradient indicate the vital role of urbanization effects on the urban forest C storage. The lower forest cover and C density between the fourth ring and the fifth ring suggested that there is huge potential to increase C storage.(5) Urban forest landscape pattern and C storage were dependent on the scale. Under different landscape scales, there were significant relationship between landscape pattern indices and C storage of urban forests. The C storage can be increased through increasing the patch TA and COHESION and decreasing the ENN-MN and PARA-AM.(6) Urban forest area was gradually increased during the year of 1984-2014. Increment of urban forest area was small during the year of 1995-2005, and the patches were isolated. However, the increment in urban forest area was obvious from 2005 to 2014, which was mainly attributed to the internal filling and increased the patch aggregation. There was significant correlationship between NDVI and C storage.(7) The annual amount of C sequestration of urban forests in Changchun was about 3.9604×107 kg. AF had the largest annual amount of C sequestration. The rate was 1.62, 2.66, and 3.72 times as that of RF, EF, LF, respectively. For different urbanization gradients, the fourth ring had the largest annual amount of C sequestration, which were 1.20, 2.13, 3.31, and 13.32 times as that for the third ring, the fifth ring, the second ring and the first ring. Populus alba var. pyramidalis, Populus alba, Padus racemosa, Quercus mongolica, Acer negundo, Picea asperata, Prunus ussuriensis and Malus baccata were the best fitted species to increase the urban forest C storage. |
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