# A Review on Carbon Source and Sink in Arabic Land Ecosystems
## 4 Main Factors Affecting the Dynamics of Carbon Sources and Sinks in Arable Land Ecosystems
### Impact of Human Management Measures on Arable Land Carbon
#### 4.2.4 Land Use Change  
Land use change is considered to be the second largest cause of carbon emissions after fuel consumption [117]. [PERSON] et al. [118] concluded that 156 Pg C was released into the atmosphere globally due to land use change and management during 1850-2000. The growing population's demand for food, fiber and fuel had accelerated the transformation of natural land into managed land, such as from forest or natural grassland to pasture or arable land [119]. The transformation from natural ecosystems to agricultural ecosystems would consume organic carbon pool, mainly due to: (I) low return of biomass carbon, (II) large loss of organic carbon caused by erosion, mineralization and leaching, and (III) large changes in soil temperature and water status [14]. Some studies had also focused on changes in carbon stocks between specific ecosystems. [PERSON] et al. [120] found that the conversion from virgin forest to arable land resulted in 25% to 30% SOC loss by a meta-analysis using 385 existing studies in tropical land. [PERSON] et al. [121] found that the replacement of existing forest land by rape field would lead to net emissions, while the replacement of existing arable land by perennial miscanthus and short rotation shrub would produce significant net greenhouse gas benefits. In a study on the black soil area in Northeast China, [PERSON] et al. [84] found that the conversion of grassland to arable land would lead to the loss of C and N in 0-30 cm soil layer to a certain extent. [PERSON] et al. [122] concluded that 25-30% of the carbon in the topsoil would be released into the atmosphere when the forest was transformed into permanent arable land. It could be seen that the mutual transformation of forest and arable land will strengthen or reduce the carbon sequestration capacity of soil to a certain extent. [PERSON] and [PERSON] [123] used land use change rate and carbon density data to compare the interaction between different ecosystems, considering five land use types: Arable land, pasture, plantation, industrial wood and fuelwood. The results showed that the net carbon flux of land use change from 1850 to 2015 was 145 \(\pm\) 16 Pg C. Most of the emissions came from tropical regions (10\({}^{2}\)\(\pm\) 5.8 Pg C). The average global net emissions in the last decade (2006-2015) were 1.11 (\(\pm\)0.35) Pg C yr\({}^{-1}\), including the net carbon source in tropical regions (1.41 \(\pm\) 0.17 Pg C yr\({}^{-1}\)), the net carbon sink in northern mid-latitudes regions (\(-\)0.28 \(\pm\) 0.21 Pg C yr\({}^{-1}\)), and the neutrality in southern mid-latitudes regions.  
Recently, some studies combined RS and GIS to obtain land use change information and then estimate carbon emissions. [PERSON] et al. [124] combined remote sensing, GIS and IPCC method to quantify changes in vegetation carbon storage and SOC storage resulting from land use change during 1970-2010 in Zhejiang province of China. The result showed that land use change has resulted in huge amounts of carbon emissions, mainly caused by decrease of farmland with high SOC content, attributing to urban expansion. [PERSON] et al. [125] used the land use change data from 2000-2020 of Anhui province in China, evaluated the net carbon emissions and clarified the carbon emission effect from three aspects of carbon footprint, ecological carrying capacity and ecological deficit. They found that forestland is the main carbon source, also the carbon footprint of increases rapidly, the ecological carrying capacity changes slowly, and the ecological deficit becomes larger and larger, indicated that with economic development, carbon emissions from construction land will become more and more significant, and the low-carbon development will face great pressure. The improvement of the availability and quality of multi-spatial and multi-temporal remote sensing data and the emergence of new analysis technologies have deepened the understanding of impact of land use change on carbon emissions [124].