Blog: Definitions of Forest in Remote Sensing and Climate Change

In the forestry, ecology, climate change, conservation, and remote sensing fields, accurately defining what constitutes a forest is essential for effective monitoring, dynamics assessment, and policy formulation in areas focused on carbon offsetting and tracking. A clear, general, and comprehensive understanding of forest characteristics is, therefore, necessary for establishing baselines for reforestation, tracking deforestation, mapping ecological dynamics, and accurately quantifying the achievements of carbon offset goals. In different fields, the forest is defined based on structural, ecological, and functional criteria, and some definitions also consider the socioeconomic benefits that forests provide. Most definitions of forests focus on tree cover, canopy density, area covered, and tree heights [7]. For instance, the Food and Agriculture Organization (FAO) defines forests as areas with a tree cover of more than 10%, a minimum height of 5 meters, and an area of at least 0.5 hectares. In another aspect, the United Nations Framework Convention on Climate Change (UNFCCC) defines forests based on national definitions, with thresholds for canopy cover, tree height, and land use. In remote sensing, the forest definition is based on spectral indices such as the Normalized Difference Vegetation Index (NDVI) threshold ranging from 0.2 for the sparse forest to 1.0 for the dense forest for low and medium-resolution satellite images. In contrast, for high-resolution images (less than 1-meter resolution), the forest is defined based on individual tree counts as in this case a single tree can be identified. In general, more than 1000 definitions [6] exist both at the national level and in the organization level with some countries having more than a single definition under consideration. 

Some research studies have reviewed the importance of accurately defining forests in remote sensing and climate change research. [4], uses high-resolution satellite imagery to analyze global forest cover changes, highlighting and reviewing inconsistencies in definitions used by different areas of climate change and environmental and ecological research. [8] emphasizes the impact of inconsistent definitions on land-use classification and deforestation assessments. The reports of [3, 5] provide more information on international forest definitions and their implications for conservation policies. [1], emphasized the role of remote sensing in standardizing forest assessments for climate agreements. In contrast, [2] reported how forest definitions affect carbon sequestration estimates and emissions accounting in climate change models.

With the importance highlighted in the research, it is clear that the lack of a general definition of forests across various research fields is a challenge to climate change monitoring, global conservation initiatives, and land cover classification. Differences in definitions are most likely to affect forest monitoring, land cover mapping, and policy implementation, leading to inconsistencies, underestimation, and overestimation of achievement in climate commitments and biodiversity conservation strategies. Generalizing these definitions across different research fields is essential to improving the accuracy of restoration efforts quantification, forest mapping, and supporting the development of more effective policy-making in the carbon credit markets.

References

[1] Frederic Achard, Sandra Brown, Michael Brady, Ruth DeFries, Giacomo Grassi, Martin Herold, Danilo Mollicone, Brice Mora, Devendra Pandey, Carlos Souza, et al. A sourcebook of methods and procedures for monitoring and reporting anthropogenic greenhouse gas emissions and removals associated with deforestation, gains and losses of carbon stocks in forests remaining forests, and forestation.: Gofc-gold report version cop18-1.
2012. URL: https://discovery.dundee.ac.uk/en/publications/a-sourcebook-of-methods-and-procedures-for-monitoring-and-reporti.

[2] IPCC Climate Change. Land: an ipcc special report on climate change. Desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems, 41, 2019.

[3] Food and Agriculture Organization of the United Nations (FAO). Global forest resources assessment 2020 – interactive platform, 2020. Accessed: 2025-02-26. URL: https://www.fao.org/interactive/forest-resources-assessment/2020/en/.

[4] Matthew C Hansen, Peter V Potapov, Rebecca Moore, Matt Hancher, Svetlana A Turubanova, Alexandra Tyukavina, David Thau, Stephen V Stehman, Scott J Goetz, Thomas R Loveland, et al. High-resolution global maps of 21st-century forest cover change. science, 342(6160):850–853, 2013.

[5] Rodney J Keenan, Gregory A Reams, Fr´ed´eric Achard, Joberto V de Freitas, Alan Grainger, and Erik Lindquist. Dynamics of global forest area: Results from the fao global forest resources assessment 2015. Forest ecology and management, 352:9–20, 2015. URL: https://www.sciencedirect.com/science/article/pii/S0378112715003400.

[6] H Gyde Lund. National definitions of forest/forestland listed by country. Web: http://home.comcast.net/˜gyde/national.definitions.of.forest.pdf. Accessed, 10, 2013.

[7] Viviana Zalles, Nancy Harris, Fred Stolle, and Matthew C. Hansen. How rethinking ‘what is a forest’ can result in more effective conservation. World Resources Institute, November 2024. Accessed: 2025-02-26. URL: https://www.wri.org/insights/rethinking-definition-forest-monitoring

[8] Joseph O Sexton, Praveen Noojipady, Xiao-Peng Song, Min Feng, DanXia Song, Do-Hyung Kim, Anupam Anand, Chengquan Huang, Saurabh Channan, Stuart L Pimm, et al. Conservation policy and the measurement of forests. Nature Climate Change, 6(2):192–196, 2016. URL: https://www.nature.com/articles/nclimate2816. 

- Written by Angela John