Vegetation dynamics refer to changes in vegetation over time, with temporal scales ranging from diurnal to seasonal, annual, decadal, and beyond. Changes can be relatively slow or fast, catastrophic or more subtle, depending on the cause. A variety of forces induces vegetation change, including seasonal variation (seasonal vegetation change is known as phenology), interannual meteorological differences, longer-term climate change, human activity (deforestation, burning of fossil fuel, acid rain, pollution), geologic events such as volcanic eruptions, and over geologic time the moving of lithospheric plates.

2.1 Why Study Global Vegetation?

The study of vegetation is of interest to numerous scientific (and other) disciplines, including but not limited to biology, ecology, forestry, agronomy, hydrology, meteorology, and some social sciences. Diverse questions require and utilize vegetation analyses. For example, an agricultural specialist might use satellite images to monitor wheat crops while a sociologist could use the same images to study land use practices. Foresters could look at forest extent to estimate timber amount while ecologists might need to use similar spatial areas in studies of nutrient cycling.

Global vegetation and its dynamics play significant roles in energy and water budgets, atmospheric composition, land surface stabilization and roughness, land surface albedos (brightness or reflectance), animal habitats, and the production of food, materials and pharmaceuticals. Understanding changes in vegetation patterns and compositions through time, both in the short- and long-term, is crucial for assessments and predictions of global ecological conditions and sustainability of life-enhancing resources. The consequences of vegetation variability, whether caused by anthropogenic and/or naturally occurring forces, need to be considered as human population grows and presumably peaks in the 21st century. The last chapter in this series details the interaction between land-cover change and human activity.

2.2 The Role of Remote Sensing in Global Vegetation Studies

Remote sensing technologies employing satellites provide the ability to repeatedly image and monitor vegetation dynamics over large areas, including the entire globe. This makes the task of studying vegetation change on a global basis an attainable one.

In order to use remote sensing effectively in any particular subject discipline, knowledge of relevant remote sensing techniques is required. A variety of satellite sensors exist, and researchers need to know which instruments and techniques provide data suitable for addressing specific research questions. Basic concepts fundamental to remote sensing are introduced in Chapter 5 followed by information about various sensor systems.

2.3 Human Interactions With the Environment

Human interactions with the environment are directly and indirectly connected to vegetation dynamics. The connections go both ways, since vegetation dynamics affect humans just as human activity modifies vegetation. These links involve physical as well as social processes. Social and Earth scientists working together in a multidisciplinary approach try to accurately predict cause-and-effect scenarios involving resources on which humans and other life depend for their existence. Chapters 7 and 8 discuss the study of vegetation change and how humans interact with the environment.