Grain
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This article was researched and written by a student at the University of Vermont participating in the Encyclopedia of Earth's (EoE) Student Science Communication Project. The project encourages students in undergraduate and graduate programs to write about timely scientific issues under close faculty guidance. All articles have been reviewed by internal EoE editors, and by independent experts on each topic.
Introduction
In landscape ecology, grain describes the size of the smallest homogeneous unit of study and determines the resolution at which a landscape is studied. It is equivalent to minimum mapping unit in cartography. A pixel in a digital image is analogous to a grain in a landscape.
Both grain and extent determine the scale at which a landscape is described in a study. The choice of scale is important in determining the resolution of a study and constrains any inferences or extrapolations from the study. In studies of landscape, no pattern can be detected beyond the extent or below the grain of the study. Patches, boundaries, and landscape heterogeneity can disappear from view at spatial resolutions that are too fine or too broad. If the grain size is large, spatial heterogeneity can be masked as discontinuities are averaged across the measurement (Measurement system) units. Likewise, if the extent is too small, patterns may occur across a wider range than that visible within the spatial bounds of the study.
Related Terms
Grain size- Grain size of a landscape refers to the average size (diameter or area) of all the patches. A "coarse-grained" landscape would contain primarily large patches and is monotonous within patches (i.e. landscape diversity may be high, but site diversity is low). A "fine-grained" landscape contains many small patches dominated by edge conditions, which is best suited to generalist species that do not require large patches of a single habitat type.
Extent - Extent encompasses the overall area included in an investigation or the area within the landscape boundary. Extent refers to both the physical area as well as the time period for which a landscape or population process occurs.
Spatial Scaling- Spatial scaling involves changing either grain, extent, or both and leads to the translation of information across scales or organizational levels.
Further Reading
- Farina, A. 2006. Principles and Methods in Landscape Ecology: Towards a Science of Landscape. Springer, New York, NY.
- Forman, R.T.T., and M. Godron. 1986. Landscape Ecology. John Wiley & Sons, New York, NY.
- Gergel, S. E., and M. G. Turner. 2001. Learning Landscape Ecology. Springer, New York, 316 pp.
- Mayer, A.L. and G.N. Cameron. 2003. Consideration of grain and extent in landscape studies of terrestrial vertebrate ecology. Landscape and Urban Planning 65(4):201-217.
- Turner, M.G., R.V. O'Neill, R.H. Gardner, and B.T. Milne. 1989. Effects of changing spatial scale on the analysis of landscape pattern. Landscape Ecology 3: 153-162
- Wu, J. and R.J. Hobbs. 2007. Key Topics in Landscape Ecology. Cambridge University Press, Cambridge, MA.
