Spatio-temporal analysis of vegetation dynamics in derived savannah, Ogun State Nigeria from 2002 to 2023

Year 2025, Volume: 26 Issue: 2, 129 - 136, 30.06.2025

Oluseun Banjo , Daniel Abiodun Akintunde-alo , Peter Oluwagbemiga Ige

https://doi.org/10.18182/tjf.1473757

Abstract

Vegetation covers is a significant component of biogeochemical cycles. Derived savannah of Ogun State has been affected by vegetation loss and climate change in recent times. There is lack of information on the rate/extent of vegetation loss in the last two decades. This study assessed changes in vegetation cover in derived savanna ecosystem of Ogun State from 2002 to 2023. Landsat images were downloaded from the repository of the United States Geological Survey (USGS). Composites of red, green, blue and near-infra-red spectral bands of study period were obtained and classified using Maximum Likelihood (ML) algorithm into Land Use Land Cover (LULC) categories as follows: bare soil; built-up areas; forest; and grassland. Change in area extent and rate of change of area of classified images were determined for the study period. Confusion matrix of classified images were generated and compared with Google Earth satellite image with accuracy assessed using kappa coefficients. Overall accuracy of the classified images ranged between 79% and 88% with kappa coefficients of between 0.71 and 0.83. Results showed that built-up area increased from 10.3% cover in 2002 to 35.9% cover in 2023. However, there was a significant decline in forest cover from 31.5% to 13.7% for the same period. Significant increase at 4.2 km2 per year in area extent was observed for built-up LULC class while a decline of 2.0 km2 per year in forest cover was recorded for Forest LULC category from 2002 to 2023. The study revealed that urbanization increased as extent of initial forest cover were degraded and replaced with physical infrastructure. Therefore, there is urgent need for policies that promote conservation and sustainable management of forests and grasslands, as well as measures to promote green infrastructure and urban greening initiatives to address the decline in vegetation cover in the derived savanna ecosystem of Ogun State.

Keywords

Land use land cover (LULC) , Derived savannah ecosystem , Vegetation loss , Maximum likelihood classification

Ethical Statement

Not applicable

Bitki örtüsü dinamiklerinin 2002-2023 yılları arasında Ogun Eyaleti Nijerya'da seçilen savanada zamansal-mekansal analizi

Abstract

Bitki örtüsü biyojeokimyasal döngülerin önemli bir bileşenidir. Ogun Eyaleti'nin savanları, son zamanlarda bitki örtüsü kaybından ve iklim değişikliğinden etkilenmiştir. Son yirmi yılda bitki örtüsü kaybının oranı/derecesi hakkında bilgi eksikliği bulunmaktadır. Bu çalışma, 2002'den 2023'e kadar Ogun Eyaleti'nin savan ekosistemindeki bitki örtüsündeki değişiklikleri değerlendirmiştir. Landsat görüntüleri Amerika Birleşik Devletleri Jeolojik Araştırma Kurumu'nun (USGS) web sitesinden indirilmiştir. Çalışma dönemine ait kırmızı, yeşil, mavi ve kızıl ötesi spektral bantların kompozitleri elde edilmiş ve Maksimum Olasılık (ML) algoritması kullanılarak Arazi Kullanımı/Arazi Örtüsü (LULC) kategorilerine göre şu şekilde sınıflandırılmıştır: çıplak toprak, yerleşim alanları, orman ve otlak. Çalışma dönemi için sınıflandırılmış görüntülerin alan büyüklüğündeki değişim ve alan değişim oranları belirlenmiştir. Sınıflandırılmış görüntülerin hata matrisi oluşturulmuş ve kappa katsayıları kullanılarak değerlendirilen doğrulukla Google Earth uydu görüntüsüyle karşılaştırılmıştır. Sınıflandırılan görüntülerin genel doğruluğu, 0,71 ile 0,83 arasında, kappa katsayıları ise %79 ile %88 arasında değişmektedir. Sonuçlar, yerleşim alanının 2002'deki %10,3 kapalılıktan 2023'te %35,9'a yükseldiğini göstermiştir. Ancak aynı dönemde orman örtüsünde %31,5'ten %13,7'ye önemli bir düşüş göze çarpmaktadır. 2002'den 2023'e kadar, yerleşim LULC sınıfı için alan büyüklüğünde yılda 4,2 km2'lik önemli bir artış gözlemlenirken, orman LULC kategorisi için yılda 2,0 km2'lik bir azalma kaydedilmiştir. Çalışma, başlangıçtaki orman örtüsü azaldıkça ve yerini fiziksel altyapıya bıraktıkça kentleşmenin arttığını ortaya çıkarmıştır. Bu nedenle, ormanların ve otlakların korunmasını ve sürdürülebilir yönetimini destekleyen politikaların yanı sıra, Ogun Eyaleti'nin savan ekosistemindeki bitki örtüsündeki azalmayı ele almak için yeşil altyapıyı ve kentsel yeşillendirme girişimlerini teşvik edecek önlemlerin alınmasına acil ihtiyaç bulunmaktadır.

Keywords

Arazi kullanımı/arazi örtüsü (LULC) , Savana ekosistemi , Bitki örtüsü kaybı , Maksimum olasılık sınıflandırması

References

• Adetola, O., Solanke, A., 2013. Ecological significance and environmental problems of savanna ecosystems. Journal of Scientific Research and Reports, 2(2): 345-356.
• Afolayan, W. A., Akanbi, W. B., Afolayan, A. F., Adekunle, V. A., 2021. Ethnobotany and agro-ecological significance of savanna pockets in southern Nigeria. Journal of Applied Life Sciences International, 26(2): 27-40.doi: 10.9734/jalsi/2021/v26i230236.
• Afuye, G.A., Kalumba, A.M.,Orimoloye, I. R., 2021. Characterisation of vegetation response to climate change: A review. Sustainability, 13(13): 7265
• Anderson, J.R., 1976. A land use and land cover classification system for use with remote sensor data. US Government Printing Office.
• Areola, A. A.,Ikporukpo, C. O., 2020. Spatial analysis of urban spaces in an indigenous African city. International Journal of Development Research. 10(01): 33190-33203.
• Cao, J., Yeh, E. T., Holden, N. M., Qin, Y., Ren, Z., 2013. The roles of overgrazing, climate change and policy as drivers of degradation of China’s grasslands. Nomadic Peoples, 17(2):82 – 101.
• Cao, L., Yang, P., Li, Y.Y., Li, Z.L., Fang, H., 2018. Combining multiple remote sensing datasets to assess the spatiotemporal dynamics of vegetation in the northwest of China. Remote Sensing, 10(2):196.
• Cao, L., Xu, M., Liu, Y., Yu, Z., Sun, L., Tian, X., Zhang, W. 2023. Response of soil nitrogen components and its vertical distribution to rainfall redistribution during Robinia pseudoacasia forest restoration on the Loess Plateau. Ecological Indicators, 155, 111036.
• Dash, P., Sanders, S.L., Parajuli, P., Quyang, Y., 2023. Improving the accuracy of land use land cover classification of landsat data in an agricultural watershed. Remote Sensing, 15 (16): 4020.
• FAO, 2020. The State of the World’s Forests: Forests, biodiversity and people. Food and Agriculture Organization of the United Nations, Rome, http://www.fao.org/state-of-forests/en/ Accessed: 13.03.2024.
• FORMECU, 1996. The World Resources Institute’s Global Forest Watch: Programme and Projects: An Overview of Forestry Development. FORMECU, Yaoundé, Cameroon.
• Foley, J. A., DeFries, R., Asner, G. P., Barford, C., Bonan, G., Carpenter, S. R., Helkowski, J. H., 2005. Global consequences of land use. Science, 309(5734): 570-574.
• Gómez-Brandón, M., Lores, M., Domínguez, J., 2018. Long-term impact of human land-Use on soil microbial communities in a Mediterranean area. Science of the Total Environment, 619-620: 103-112. doi: 10.1016/j.scitotenv.2017.11.174.
• Hansen, M. C., Potapov, P. V. Moore, R., Hancher, M., Turubanova, S. A., Tyukavina, A., Townshend, J. R., 2013. High-resolution global maps of 21st-century forest cover change. Science, 342(6160): 850-853.
• Hido, A., Teka, A., Alemayehu, A., 2023. Analysis of charcoal producers perception of its production, forest degradation, and governance in Wolaita, Southern Ethiopia’s Dry Afromontane Forests. International Journal of Forestry Research, 2023(1): 3352702.
• Hou, X., Niu, Z., Gao, S., Huang, N., 2013. Monitoring vegetation phenology in farming pastoral zone using SPOT-VGT NDVI data. Transactions of the Chinese Society of Agricultural Engineering, 29(1): 142-140.
• Lambin, E. F., Meyfroidt, P., 2011. Global land use change, economic globalization, and the looming land scarcity. Proceedings of the National Academy of Sciences, 108(9): 3465-3472.
• Li, W., Ciais, P., MacBean, N., Peng, S., Defourny, P., Bontemps, S. 2016. Major forest changes and landcover transitions based on plant functional types derived from the ESA CCI Land Cover product. International Journal of Applied Earth Observation and Geoinformation, 47, 30-39.
• Mather, P., Tso, B. 2010. Classification Methods for Remotely Sensed Data. (Ed: Second). CRC Press. Boca Raton.
• Milchunas, D. G., Lauenroth, W. K., 1993. Quantitative effects of grazing on vegetation and soils over a global range of environments. Ecological Monographs, 63(4): 327-366.
• Naumann, G., Barbosa, P., Garrote, L., Iglesias, A., Vogt, J. V., Prompt, E., 2014. Global changes in drought conditions under different levels of warming. Wiley Interdisciplinary Reviews: Climate Change, 5(2): 219-232.
• Odekunle, J. F., Akindele, D. B., Adebayo, G. O., 2019. The problems and challenges of development control in Abeokuta-West zonal planning area, Ogun State, Nigeria. African Journal of Economics and Sustainable Development, 2(1): 9-27.
• Ogundele, F. T., Okeola, O. G., Ogunwale, A. B., Oladapo, A. A., 2016. Assessment of the dynamics of forest cover changes in Nigeria. Journal of Environmental Science and Water Resources, 5(6): 164-174.
• Ohwo, O., Abotutu, A., 2015. Environmental impact of urbanization in Nigeria. British Journal of Applied Science and Technology, 9(3): 212 – 221.
• Okorondu, J., Umar, N. A., Ulor, C. O., Onwuagba, C. G., Diagi, B. E., Ajiere, S. I.,Nwaogu, C., 2022. Anthropogenic activities as primary drivers of environmental pollution and loss of biodiversity: A review.. International Journal of Trend in Science, Resources and Development, 6: 621-643.
• Ola, A.B., Adewale, Y.Y., Raheem, W. A., Afonja, A.A., 2020. Anthropogenic activities and their impacts on biodiversity survival in Ifelodun Area, Kwara State, Nigeria.
• Olayiwola, A. M., Lawal, M. O., 2018. Mapping urban growth and its impact on agricultural land in Abeokuta, Nigeria: 1966 – 2016. Interdisciplinary Environmental Review, 19(3-4): 289-305.
• Quaranta, G., Salvia, R., Salvati, L., Paola, V.D., Coluzzi, R., Imbrenda, V., Simoniello, T., 2020. Long-term impacts of grazing management on land degradation in a rural community of Southern Italy: Depopulation matters. Land Degradation and Development, 31(16): 2379 – 2394.
• Rawat, J. S., Kumar, M., 2015. Monitoring landuse/landcover change using remote sensing and GIS technique: a case study of Hawalbagh block, district Almora, Uttarakhand, India. Egyptian Journal of Remote Sensing and Space Science, 18(1): 77-84.
• Roby, C., 1991. An overview of deforestation in Nigeria. Landscape and Urban Planning, 20(4): 265-275.
• Rojas, O., Senay, G., Singh, R. K., Verdin, J. P., 2011. Developing an operational drought monitoring system for Somalia. Journal of Arid Environments, 75(12): 1266-1272.
• Seifollahi-Aghmiuni, S., Kalantari, Z., Egidi, G., Gaburova, L., Salvati, L., 2022. Urbanisation-driven land degradation and socioeconomic challenges in peri-urban areas: Insights from Southern Europe. Ambio, 51 (6): 1446 – 1458.
• Seto, K. C., Güneralp, B., Hutyra, L. R., 2012. Global forecasts of urban expansion to 2030 and direct impacts on biodiversity and carbon pools. Proceedings of the National Academy of Sciences, 109(40): 16083-16088.
• Skakun, S., Lucanus, O., Fraser, R., 2016. Towards operational vegetation stress monitoring using Landsat surface reflectance data. Remote Sensing of Environment, 184: 557-575.
• Son, N. T., Chen, C. F., Chen, C. R., Chang, L. Y., 2012. Evaluating the MODIS LAI product using MODIS and Landsat data fusion. International Journal of Remote Sensing, 33(1): 67-89.
• Srivastava, P.K., Han, D., Rico-Ramirez, M.A., Bray, M., Islam, T. 2012. Selection of classification tecniques for land use/land cover change investigation. Advances in Space Research, 50(9): 1250 – 1265.
• Twumasi, N. Y. D., Shao, Z., Altan, 2019. Mapping built-up areas using two band ratio on Landsat imagery of ACCRA in Ghana from 1980 to 2017. Applied Ecology & Environmental Research, 17(6).
• Xu, Y., Tang, O., Fan, J., Bennett, S. J., Li, Y. (2011). Assessing construction land potential and its spatial pattern in China. Landscape and Urban Planning, 103(2), 207-216.
• Yang, Y., Li, M., Feng, X., Yan., H., Su, M., Wu, M., 2021.Spatiotemporal variation of essential ecosystem services and trade-off/synergy along with rapid urbanization in the Lower Pearl River Basin, China. Ecological Indicators, 133: 108439.
• Ying, L., 2019. Traditional land use systems, agrobiodiversity conservation, and sustainable development in China's ecological fragile areas. Journal of Cleaner Production, 237: 117835. doi: 10.1016/j.jclepro.2019.117835.
• Zhe, M., Zhang, X., 2021. Time-lag effects of NDVI responses to climate change in the Yamzhog Yumco Basin, South Tibet.Ecological Indicators, 124: 107431.