What are the trends in land cover and their effects on human health and the environment?
Importance of Land Cover
Land cover—the surface components of land that are physically present and visible—provides a means to examine landscape patterns and characteristics, which are important in understanding:
- The extent, availability, and condition of lands.
- Ecological system extent, structure, and condition.
- The potential for dispersion and effects of chemicals and other pollutants in and on the environment.
Land cover represents a starting point from which a variety of monitoring activities can be performed. EPA uses land cover information for many key purposes, such as assessing nonpoint sources of pollution, understanding landscape variables for ecological analyses, assessing the behavior of chemicals, and analyzing the effects of air pollution.
Forces Affecting Land Cover
Land cover, in its naturally occurring condition, integrates and reflects a given site's climate, geology and soils, and available biota over a time span of decades or longer. Over shorter time scales, land cover can be affected by naturally occurring disturbances (e.g., storms, floods, fires, volcanic eruptions, insects, landslides) and human activities (such as population change, industrial and urban development, deforestation or reforestation, water diversion, and road building).
These changes can be perceived as improvements or degradations of the state of land cover, depending on one's perspective.
Land cover affects or influences environmental conditions in many ways, by:
- Affecting other environmental variables including water quality, watershed hydrology, habitat and species composition, climate, and carbon storage.
- Influencing the mass and energy exchanges between the surface and the atmosphere and thus influencing weather and climate.1
- By affecting species habitat and distribution, as a primary ingredient of ecological structure and function.
- Altering hydrologic regimes, runoff patterns, and flood buffering in watersheds.2
The question of trends in and effects of land cover is addressed by two national-scale indicators: Land Cover and Forest Extent and Type. Coordinating, integrating, and using data collected at a variety of scales and based on diverse data sources and classifications poses significant challenges in tracking trends in and effects of land cover.
- Measurements of land cover characteristics can vary depending on the scale of mapping or measurement.
- Measuring land cover characteristics at a level of detail useful for differentiation of habitat types can be very difficult to do consistently on a national (as opposed to local) scale.
- The classification systems used to describe land cover vary by agency and by each agency's needs. Many different categories of land cover have been defined at very different levels of detail, making comparability among data sets and across time frames difficult.
- Technology is changing what can be measured, mapped, and classified. Data collected from ground surveys or in some cases inferred from aerial photos—such as understory species—are seen differently in automated satellite data processing.
 Marland, G., R.A. Pielke, Sr., M. Apps, R. Avissar, R.A. Betts, K.J. Davis, et al. 2003. The climatic impacts of land surface change and carbon management, and the implications for climate-change policy. Clim. Pol. 3:149-157.
 de Sherbinin, A. 2002. Land-use and land-cover change: A CIESIN thematic guide. Palisades, NY: Center for International Earth Science Information Network of Columbia University.