4th, December
Winbourne, J. B., Smith, I. A., Stoynova, H., Kohler, C., Gately, C. K., Logan, B. A., ... & Hutyra, L. R. Quantification of urban forest and grassland carbon fluxes using field measurements and a satellite‐based model in Washington DC/Baltimore area. Journal of Geophysical Research: Biogeosciences, e2021JG006568.
Urban areas emit about 70% of the world's fossil fuels. This paper reported that most of the CO2 emitted from fossil fuel use is absorbed by urban vegetation by using a vegetative photosynthesis and respiration model that is in good agreement with the total ecosystem exchange observed in the Baltimore area, Washington DC.
3rd, December
Liu, W., Atherton, J., Mõttus, M., Gastellu-Etchegorry, J. P., Malenovský, Z., Raumonen, P., ... & Porcar-Castell, A. (2019). Simulating solar-induced chlorophyll fluorescence in a boreal forest stand reconstructed from terrestrial laser scanning measurements. Remote Sensing of Environment, 232, 111274.
By using the Discrete Anisotropic Radiative Transfer (DART) model, this paper reported that compared to the planophile leaf angle distribution the spherical and vertical leaf angle distribution decreased SIF by about 25% and 60%, respectively.
2nd, December
Samuelsson, K., Chen, T. H. K., Antonsen, S., Brandt, S. A., Sabel, C., & Barthel, S. (2020). Residential environments across Denmark have become both denser and greener over 20 years. Environmental Research Letters, 16(1), 014022.
The NDVI greening trend in Denmark cities was driven by the increasing temperatures and by urban planning policies, which double the forest area and restore the wetland.
1st, December
Chuai, X., Yuan, Y., Zhang, X., Guo, X., Zhang, X., Xie, F., ... & Li, J. (2019). Multiangle land use-linked carbon balance examination in Nanjing City, China. Land Use Policy, 84, 305-315.
As expected, the main cause of land-use change in Nanjing was the expansion of the built-up land cover. However, a small proportion of the built-up area showed a greening trend, and most of the greening trend was caused by cropland management. The increase and decrease of NDVI also showed good agreement with the increase and decrease of net ecosystem productivity.
4th, November
Xiao, J., & Moody, A. (2004). Trends in vegetation activity and their climatic correlates: China 1982 to 1998. International Journal of Remote Sensing, 25(24), 5669-5689.
The cropland, which occupies 36% of China showed 37% greening trends over the 17 years. The reason was mainly due to crop management, such as chemical fertilizer, irrigation, and crop variety.
3rd, November
Kong, J., Ryu, Y., Huang, Y., Dechant, B., Houborg, R., Guan, K., & Zhu, X. (2021). Evaluation of four image fusion NDVI products against in-situ spectral-measurements over a heterogeneous rice paddy landscape. Agricultural and Forest Meteorology, 297, 108255.
Very high spatial resolution satellite data could be useful for capturing small changes in urban land cover types.
2nd, November
Persson, Å., Eriksson, C., & Lõhmus, M. (2018). Inverse associations between neighborhood socioeconomic factors and green structure in urban and suburban municipalities of Stockholm County. Landscape and urban Planning, 179, 103-106.
The NDVI trend in Stockholm was around 0.002 year-1, which was due to the increasing size and age of the street trees. The NDVI trend and the greening reason were similar to the Seoul city result.
1st, November
Gregg, J. W., Jones, C. G., & Dawson, T. E. (2003). Urbanization effects on tree growth in the vicinity of New York City. Nature, 424(6945), 183-187.
The planted trees in urban had twice as faster growth rates compared to trees planted in the rural areas. It is widely known urban areas have a higher temperature, CO2, and nitrogen deposition than rural areas. This paper, however, identified that the rural areas' trees growth rate could be reduced caused by the higher ozone (O3) exposures.
4th, October
Lee, D. K., & Lee, Y. K. (2005). Roles of Saemaul Undong in reforestation and NGO activities for sustainable forest management in Korea. Journal of Sustainable Forestry, 20(4), 1-16.
After the Korean War, most forest areas were destroyed and left as barren land cover. Thus, During the 1960s and 1670s, the Korean Government implemented afforestation using certain fast-growing trees. Forest in Korea is therefore mostly human-made.
3rd, October
Cao, J., An, Q., Zhang, X., Xu, S., Si, T., & Niyogi, D. (2021). Is satellite Sun-Induced Chlorophyll Fluorescence more indicative than vegetation indices under drought condition?. Science of The Total Environment, 148396.
Compared to vegetation indices (e.g., NDVI and EVI), SiF yield was the most sensitive indicator of drought stress in the US cornfield region. Also, SiF and GPP showed a strong correlation. However, in figure 13, SiF does not appear to decrease consistently with drought in the cornfield sites.
2nd, October
Qian, Y., Zhou, W., Yu, W., & Pickett, S. T. (2015). Quantifying spatiotemporal pattern of urban greenspace: new insights from high resolution data. Landscape ecology, 30(7), 1165-1173.
Urban land cover is highly heterogeneous. Diverse land covers exist even in a block, such as impervious, vegetation, and barren surface. Urban vegetation land covers (i.e., greenspace) are distributed in even small patches. Thus, to quantify/monitor urban vegetation land covers, this paper emphasizes the importance of using high-resolution satellite data in urban areas.
1st, October
Yuan, F., Sawaya, K. E., Loeffelholz, B. C., & Bauer, M. E. (2005). Land cover classification and change analysis of the Twin Cities (Minnesota) Metropolitan Area by multitemporal Landsat remote sensing. Remote sensing of Environment, 98(2-3), 317-328.
When quantifying NDVI by land cover types in Seoul, we have experienced that some urban street trees were classified as impervious land cover types. At first, we expected a misclassification error by the CCDC method. According to this study, however, errors appear to be related to omission and commission errors. In this study, trees nearby streets and highways were generally classified as urban, but as tree canopy grew, it was classified as forest.
4th, September
Jin, S., Homer, C., Yang, L., Xian, G., Fry, J., Danielson, P., & Townsend, P. A. (2013). Automated cloud and shadow detection and filling using two-date Landsat imagery in the USA. International Journal of Remote Sensing, 34(5), 1540-1560.
To fill the gap from cloud mask and Landsat line error, I used the neighbourhood pixel interpolation method, which was listed in this paper. This method interpolates the missing data by predicting the values from nearest neighbour pixels. However, the limitation of this method was, when the data gap size is large, it predicts poorly, and missing data could exist.
3rd, September
Pretzsch, H., Biber, P., Uhl, E., Dahlhausen, J., Schütze, G., Perkins, D., ... & Lefer, B. (2017). Climate change accelerates growth of urban trees in metropolises worldwide. Scientific Reports, 7(1), 1-10.
By analyzing the urban tree rings, this paper identified that urban trees growth was 21% and 14% affected by global climate change and urban heat island, respectively. Total of 1,383 urban trees were sampled in ten metropolises in diverse ecosystems.
2nd, September
Berner, L. T., Massey, R., Jantz, P., Forbes, B. C., Macias-Fauria, M., Myers-Smith, I., ... & Goetz, S. J. (2020). Summer warming explains widespread but not uniform greening in the Arctic tundra biome. Nature communications, 11(1), 1-12.
To estimate the maximum NDVI, this paper generated the annual Landsat NDVI time series by using the phenology curve model. This method could work well on the large scale (i.e., city) study, however, it seems to be complicated in the pixel-scale study. Also, to use the phenology curve model, it could not fully use the fine-resolution Landsat data (30 m) as it needs to be buffer by 50 m (radius).
1st, September
Wei, S., Chen, Q., Wu, W., & Ma, J. (2021). Quantifying the indirect effects of urbanization on urban vegetation carbon uptake in the megacity of Shanghai, China. Environmental Research Letters, 16(6), 064088.
It was interesting that urbanization can promote vegetation carbon uptake by vegetation landscape pattern fragmentation in Shanghai. Such as Seoul 1998 Olympic Games, Shanghai green space was improved during the 2010 World Expo caused by the city government policy.
4th, August
Chalkley, B., & Essex, S. (1999). Urban development through hosting international events: a history of the Olympic Games. Planning perspectives, 14(4), 369-394.
The 1988 Olympic Games have changed Seoul's environment such as the street scene and the Han River riverfront. This paper was useful in introducing the history of land use and land cover in Seoul in the 1980s.
3rd, August
Zhu, Z., Fu, Y., Woodcock, C. E., Olofsson, P., Vogelmann, J. E., Holden, C., ... & Yu, Y. (2016). Including land cover change in analysis of greenness trends using all available Landsat 5, 7, and 8 images: A case study from Guangzhou, China (2000–2014). Remote Sensing of Environment, 185, 243-257.
Guangzhou had a gradual greening trend over the past 15 years. This paper also confirmed that the Landsat 8 NDVI values had a large bias compared to the EVI. Also, emphasized the importance of considering land cover changes when analyzing the greening trends in regions where land cover changes occur frequently, such as urban regions.
2nd, August
Hong, S. K., Song, I. J., & Wu, J. (2007). Fengshui theory in urban landscape planning. Urban ecosystems, 10(3), 221-237.
This paper well-organized Seoul's land use and land cover change since the 1920s.
1st, August
Hong, S. H., Kim, J. S., Ki, K. S., Park, S. G., & Kurosawa, K. (2013). Woodpeckers appearance and forest vegetation type in urban forests of Seoul area, Korea. J. Fac. Agric. Kyushu Univ., 58, 253-258.
We could know that most of the Korean forest vegetation that existed now is the result of afforestation by reading this paper. The Korean War (1950 - 1953) was the cause of the forest vegetation loss. The afforestation was carried out in the 1960 and 1970s.
4th, July
Liu, M., Liu, S., Ning, Y., Zhu, Y., Valbuena, R., Guo, R., ... & Hu, W. (2020). Co-Evolution of Emerging Multi-Cities: Rates, Patterns and Driving Policies Revealed by Continuous Change Detection and Classification of Landsat Data. Remote Sensing, 12(18), 2905.
The expansion of impervious surface explains the browning trend in urban areas. For example, Liu et al. (2020) reported the impervious surface of CZTUA, a typical urban agglomeration in China, increased by 2.25% per year and most of the land cover transformations were made in cropland and forest land cover.
3rd, July
Nguyen, T. T., Barber, P., Harper, R., Linh, T. V. K., & Dell, B. (2020). Vegetation trends associated with urban development: The role of golf courses. PloS one, 15(2), e0228090.
Golf courses are sometimes considered to reduce biodiversity. However, in urban area golf courses seems to play a role in maintaining vegetation cover.
2nd, July
Zhu, M., Zhang, J., & Zhu, L. (2021). Variations in growing season NDVI and its sensitivity to climate change responses to Green development in Mountainous areas. Frontiers in Environmental Science, 9, 179.
Mountainous areas, which is a stable area, NDVI showed an increasing trend with a rate of 0.027 per decade (p < 0.05). Some degraded vegetation was mostly affected by urbanization. In addition, the increase in NDVI had a greater effect on temperature than precipitation in mountainous areas.
1st, July
Zhang, Y., Odeh, I. O., & Han, C. (2009). Bi-temporal characterization of land surface temperature in relation to impervious surface area, NDVI and NDBI, using a sub-pixel image analysis. International Journal of Applied Earth Observation and Geoinformation, 11(4), 256-264.
Numerous studies interpret urban heat islands with vegetation cover and emphasize the benefit of urban trees. However, this paper identified land surface temperature had a stronger correlation between normalized difference built-up index (percent of impervious surface area) than the NDVI.
4th, June
Sun, J., Wang, X., Chen, A., Ma, Y., Cui, M., & Piao, S. (2011). NDVI indicated characteristics of vegetation cover change in China’s metropolises over the last three decades. Environmental monitoring and assessment, 179(1), 1-14.
By monitoring AVHRR NDVI over three decades in Chinese cities, this paper identified 40 of the 54 cities showed significant browning trend with an average slope of -1.32 x 10-3 per year. Intrestingly, this paper showed the opposite result from Dallimer et al. (2011). The NDVI showed an inverted U-shape.
3rd, June
Dallimer, M., Tang, Z., Bibby, P. R., Brindley, P., Gaston, K. J., & Davies, Z. G. (2011). Temporal changes in greenspace in a highly urbanized region. Biology Letters, 7(5), 763-766.
In UK's urbanized area, green space showed an U-shape over time. The green space increased between 1991 and 2006 in 12 cities. However, most of the greenspace gain occurred after 2001, which was caused by the policy reforms.
2nd, June
Du, J., Fu, Q., Fang, S., Wu, J., He, P., & Quan, Z. (2019). Effects of rapid urbanization on vegetation cover in the metropolises of China over the last four decades. Ecological Indicators, 107, 105458.
Interestingly, this paper monitored NDVI for 40 years in an urbanized area of China and identified that NDVI changes showed a U-shape. This indicates long-term observation is needed when determining whether urban areas are greening or browning.
1st, June
Kaspersen, P. S., Fensholt, R., & Drews, M. (2015). Using Landsat vegetation indices to estimate impervious surface fractions for European cities. Remote Sensing, 7(6), 8224-8249.
This paper reported that NDVI tends to decrease as the impervious cover increases in eight European cities. NDVI is used as one of the tools to estimate urban impervious surface fraction. However, there were limitations when extracting impermeable surface maps using NDVI. Misclassification of bare soil is an example.
4th, May
Lü, Y., Zhang, L., Feng, X., Zeng, Y., Fu, B., Yao, X., ... & Wu, B. (2015). Recent ecological transitions in China: Greening, browning and influential factors. Scientific reports, 5(1), 1-8.
China has experienced both greening and browning. They have identified that most of the browning took place in urban areas. The increased population could be one of the driving factors of the urban area's browning trend.
3rd, May
Li, H., Li, Y., Gao, Y., Zou, C., Yan, S., & Gao, J. (2016). Human impact on vegetation dynamics around Lhasa, southern Tibetan plateau, China. Sustainability, 8(11), 1146.
The urbanization of Lhasa has resulted in the browning of vegetation due to road construction. This paper discussed that it is difficult to separate the factors of human activity and climate change.
2nd, May
Yuan, W., Zheng, Y., Piao, S., Ciais, P., Lombardozzi, D., Wang, Y., ... & Yang, S. (2019). Increased atmospheric vapor pressure deficit reduces global vegetation growth. Science advances, 5(8), eaax1396.
The increase of VPD influences the vegetation index. Globally, since 1999, a browning trend has been detected with the increasing VPD.
1st, May
Strohbach, M. W., Döring, A. O., Möck, M., Sedrez, M., Mumm, O., Schneider, A. K., ... & Schröder, B. (2019). The “hidden urbanization”: Trends of impervious surface in low-density housing developments and resulting impacts on the water balance. Frontiers in Environmental Science, 7, 29.
Found out that impervious surface is an important issue in urban areas caused by the water balance. With the increase of impervious surface (8 to 56% in German city), the infiltration rates decreased by 4 to 19% and runoff increased by 4 to 18%. This paper also identified most of the 'hidden impervious surfaces' are in housing areas.
4th, April
Paschalis, A., Chakraborty, T. C., Fatichi, S., Meili, N., & Manoli, G. (2021). Urban forests as main regulator of the evaporative cooling effect in cities. AGU Advances, 2(2), e2020AV000303.
It was interesting to note that simply greening the city does not reduce the daytime surface urban heat island (SUHI). Heat reduction was mostly influenced by humid places through evaporation. However, the decrease in urban forests affected SUHI with a decrease in the leaf area index.
3rd, April
Dearborn, K. D., & Baltzer, J. L. (2021). Unexpected greening in a boreal permafrost peatland undergoing forest loss is partially attributable to tree species turnover. Global Change Biology.
This paper pointed out the importance of the field measurements in the boreal permafrost peatland zone. The forest loss due to permafrost thaw is driving an increase in NDVI values. However, when a negative NDVI trend was shown, the driving factor was the drought stress in the boreal conifer regions.
2nd, April
Zhou, X., & Wang, Y. C. (2011). Spatial–temporal dynamics of urban green space in response to rapid urbanization and greening policies. Landscape and urban planning, 100(3), 268-277.
Kunming greenspace also decreased by the rapid urbanization. The agriculture land cover type decreased and fragmented more compared to the forest land. Due to the policy, the grassland cover slowly increased in the 2000s, while it had decreased in the 1990s.
1st, April
Jia, W., Zhao, S., Zhang, X., Liu, S., Henebry, G. M., & Liu, L. (2021). Urbanization imprint on land surface phenology: The urban–rural gradient analysis for Chinese cities. Global Change Biology.
By analyzing more than 300 China urban regions, phenology showed an earlier start (SOS) and a later end (EOS) of the season. This paper identified for every 10% increased in urbanization intensity, SOS advanced 1.4 days on average and EOS delayed 0.21 days. However, this study had a limitation since the Land Surface Phenology product was used that cannot exclude the human-managed cropland.
4th, March
Edwards, R., & Treitz, P. (2017). Vegetation greening trends at two sites in the Canadian Arctic: 1984–2015. Arctic, Antarctic, and Alpine Research, 49(4), 601-619.
The mesic vegetation land cover types showed a significant greening trend in the Arctic region. Also, the greening trend was mainly affected by the July air temperature and the growing season length among the climate variables. This paper also mentioned the mixed pixel (within-pixel heterogeneity) issue in AVHRR data.
3rd, March
Raabe, K., Pisek, J., Sonnentag, O., & Annuk, K. (2015). Variations of leaf inclination angle distribution with height over the growing season and light exposure for eight broadleaf tree species. Agricultural and Forest Meteorology, 214, 2-11.
Monitored the seasonal and vertical variance of deciduous broadleaf tree leaf inclination angle using the digital camera. The leaf inclination angle distribution was variable in the spring season. Also, the seasonal change was greater at the top crown than the mid-, bottom crown.
2nd, March
Meroni, M., Rossini, M., Guanter, L., Alonso, L., Rascher, U., Colombo, R., & Moreno, J. (2009). Remote sensing of solar-induced chlorophyll fluorescence: Review of methods and applications. Remote Sensing of Environment, 113(10), 2037-2051.
Gave a great help in understanding how to estimate the sun-induced chlorophyll fluorescence using the Fraunhofer Line Depth (FLD) method.
1st, March
Jacobs, M., Rais, A., & Pretzsch, H. (2021). How drought stress becomes visible upon detecting tree shape using terrestrial laser scanning (TLS). Forest Ecology and Management, 489, 118975.
From the drought stress experiment, this study identified that the biggest influence was the change in crown size. This seems to be due to the increase in leaf angle. When the leaf angle increases the shape of the crown should decrease.
4th, February
Kolecka, N. (2021). Greening trends and their relationship with agricultural land abandonment across Poland. Remote Sensing of Environment, 257, 112340.
Although the greening trend of the land surface is primarily attributed to climate change and CO2 concentration, human land use also has a large role. This study emphasized the effect of the abandoned agricultural land on the land surface greening in Poland. This may be possible in Poland but can not apply in Seoul due to the high density of population and construction.
3rd, February
Domke, G. M., Oswalt, S. N., Walters, B. F., & Morin, R. S. (2020). Tree planting has the potential to increase carbon sequestration capacity of forests in the United States. Proceedings of the National Academy of Sciences, 117(40), 24649-24651.
By using 1.4 trillion tree data this study evaluated the capacity of planting trees on mitigating CO2 emissions in the United States. The forest trees are already up taking 14% of the economy's CO2 emissions. Here, they have demonstrated the strategy of planting trees to mitigate climate change.
2nd, February
Wang, S., Bai, X., Zhang, X., Reis, S., Chen, D., Xu, J., & Gu, B. (2021). Urbanization can benefit agricultural production with large-scale farming in China. Nature Food, 1-9.
The study predicted that China's cropland would increase even as urbanization progresses. This result was the opposite of Seoul's cropland trend. However, I agree with the increasing crop yield since the technique has developed compared to the past agricultural techniques.
1st, February
Bhusal, N., Lee, M., Han, A. R., Han, A., & Kim, H. S. (2020). Responses to drought stress in Prunus sargentii and Larix kaempferi seedlings using morphological and physiological parameters. Forest Ecology and Management, 465, 118099.
Will be useful for my next water stress experiment. It would be a great reference when measuring the gas exchange rates (e.g., Amax, Vcmax, and Jmax). However, this experiment was held relatively longer than my future study. Also, I have learned about how to measure the leaf water potential through a PMS pressure chamber. The leaf water potential showed decreasing trend at both predawn and midday measurements under drought stress.
4th, January
Zhang, X., Liu, L., Wu, C., Chen, X., Gao, Y., Xie, S., & Zhang, B. (2020). Development of a global 30 m impervious surface map using multisource and multitemporal remote sensing datasets with the Google Earth Engine platform. Earth System Science Data, 12(3), 1625-1648.
The impervious surface from the multisource and multitemporal random forest (MSMT-RF) classification method had 14% more area than the impervious surface from the CCDC method in Seoul 2015. When overlaying the two results, the MSMT-RF classification method included barren land cover type and cropland greenhouses.
3rd, January
Piao, S., Wang, X., Park, T., Chen, C., Lian, X. U., He, Y., ... & Myneni, R. B. (2020). Characteristics, drivers and feedbacks of global greening. Nature Reviews Earth & Environment, 1(1), 14-27.
Monitored the global greening trend and identified the impact. The greening trend was mainly caused by global warming and the greening was concentrated in China and India due to land cover change (e.g., afforestation and agricultural intensification). This paper also assesses the impacts of greening on carbon, water, and energy balances.
2nd, January
Junttila, S., Hölttä, T., Puttonen, E., Katoh, M., Vastaranta, M., Kaartinen, H., ... & Hyyppä, H. (2020). Terrestrial laser scanning intensity captures diurnal variation in leaf water potential.
Identified the LiDAR scanner which operates at the 905 nm wavelength showed a relatively strong relationship (77%) with the leaf water potential than the 1550 nm wavelength LiDAR scanner. Interesting to see that the intensity could monitor the leaf function. This paper's idea will be informative for my water stress experiment in the near future.
1st, January
Hundertmark, W. J., Lee, M., Smith, I. A., Bang, A. H., Chen, V., Gately, C. K., ... & Hutyra, L. R. (2021). Influence of landscape management practices on urban greenhouse gas budgets. Carbon Balance and Management, 16(1), 1-12.
Although universities are well design to make a harmony of nature and buildings it was still a net biogenic carbon source. Soil respiration in lawn landcover type was a significant factor in this study area. By increasing the number of trees will able to offset the carbon emission in urban campuses.