Abstract
The Normalized Difference Vegetation Index (NDVI) is a measure of vegetation greenness derived from a radiometric sensor carried by a satellite or aircraft. Global NDVI data have been available since the early 1980s and have been used in a large number of studies mostly related to the detection of land cover, including its variability over time. Variations in NDVI agree with variations in a number of vegetation measures such as above ground (green) biomass, dendrochronological data and vegetation cover fraction. Examples where analysis of NDVI data have led to changes in our understanding of the biosphere are the monitoring of desert margins and thereby exposing the myth of the ‘marching (Sahara) desert’ and the detection of increased vegetation greenness in temperate northern latitudes over time as a result of earlier, warmer springs and increased atmospheric CO2 concentrations. Global NDVI data are increasingly being used in climate models and ecosystem models to simulate the global carbon cycle and hydrological cycle. Global NDVI data are available at 8 km spatial resolution and 10-day, 15-day or monthly temporal resolution from August 1981 to the present; 1 km data are available for selected regions and times with continuous global coverage for most of the last two decades and 60 m or higher resolutions have erratic coverage in space and time (since 1972) with density of coverage improving over time.
The book The Normalized Difference Vegetation Index describes a wide range of applications of NDVI data. The focus is predominantly on ecological applications, but other aspects such as the relationship between NDVI and climate are also discussed. The book contains a very impressive list of references and covers a very wide range of topics. Putting this book together has clearly been a labour of love.
The book is organized in 11 chapters. The introduction puts the book in a wider perspective and shows how it fits in with global change, climate research, vegetation monitoring, land-cover change, food security, species diversity and ecological research pertaining to plant and animal distributions and interactions. A brief introduction is provided of vegetation remote sensing. The second and third chapters provide information on a wide range of vegetation indices with a focus on the NDVI. The chapters explain that the NDVI continues to be the vegetation index of choice for a wide range of applications because of its simplicity, robustness and a clear understanding of its strengths and weaknesses. Links are provided to a range of other global environmental data sets that can be used in conjunction with NDVI data. The book also gives a brief summary of an ongoing discussion about the usefulness of an alternative vegetation index, the Enhanced Vegetation Index (EVI), which performs better than the NDVI in some cases but can lead to spurious results in others (cf. Morton et al., 2014). Chapter 4 provides a discussion of linkages between NDVI and climate (precipitation, temperature and ocean temperatures). It provides a discussion of monitoring of desert margins and how NDVI changes in response to climate oscillators such as the El Niño – Southern Oscillation – of importance for rainfall patterns in, and to some extent outside the tropics – and the North Atlantic Oscillation which affects weather in mid to high northern latitudes. Specific examples for each continent (with the exception of the Antarctic) are provided. Chapter 5 gives an overview of vegetation monitoring, mostly at the sub-continental scale, and its use for famine early warning systems, ecological mapping and detection of disturbances linked to fires and outbreaks of pests and diseases. Chapters 6 through 8 provide examples where NDVI is used to obtain key information for research in plant ecology, wildlife management and conservation biology. In these chapters, NDVI is linked to aspects such as species richness, plant mortality, leaf nitrogen content, agricultural use, plant physiology and wildlife distribution. Spatial and temporal resolutions appear as important factors in the success of various applications. Chapter 9 discusses caveats and potential pitfalls in using NDVI and emphasizes the importance of a good understanding of processes and relationships. The closing chapters highlight implications for policy and legal issues, and give a future outlook.
Overall, the book provides a rich introduction into the use of satellite data for vegetation monitoring and gives the reader a better understanding of the data, their many applications and an appreciation of potential pitfalls. The book is not a textbook on the techniques of remote sensing of vegetation as such. For this purpose, Jones and Vaughan (2010) would be an excellent choice (see Los, 2011). The general focus of the book is on the application of NDVI data for ecological studies in the widest sense. As such, it is probably of greater interest to The Holocene readership than a more technical treatise of remote sensing.
The number of publications reviewed for this book is very impressive, and the author has done a stellar job putting all this work together. Examples of research range from the global to the local scale for a wide range of applications. What stands out is that multiple fields of research have seen tremendous developments over the past 20 years as a result of a simple index. The book provides an excellent introduction to the relevant literature and is highly recommended.