Basal Gap Intercept

contributed by Karen Colson and Jason Karl

Method Type

Cover – Quantitative

Other Names

None known

Description and Uses

Basal Gap Intercept measures the proportion of the line covered by large gaps between plant bases. It is important as an indicator of runoff and water erosion. Basal cover is measured along a line intercept transect by recording the beginning and end of each gap between plant bases (therefore measures only the proportion of the plant that extends into the soil).

Advantages and Limitations

Cover is one of the most commonly used measures when conducting community monitoring. It can be used to measure a variety of life-forms (i.e., moss, annual forbs, shrubs, trees), it is strongly related to biomass and ecosystem processes, it does not require determining the number of individuals within a species, and it can easily be used to measure plants, mosses, or lichens at the ground surface. Unlike most measures of cover, basal gap does not vary greatly depending on climatic conditions and is not affected by utilization of animals. However, this method can be difficult to measure for plants with a single, small stem.


Video Instructions/Demonstration

Basal Gap Intercept

Similar Approaches

Canopy Gap Intercept measurements represent the proportion of a line covered by large gaps between plant canopies and is an important indicator of the potential for wind erosion and weed invasion. Canopy cover is measured along a line intercept transect by documenting the point along the tape at which the canopy begins and ends. Herrick et al. 2005 suggest using both the canopy and gap intercept methods together in combination with the cover indicators from the line point intercept and the soil stability to help determine whether observed erosion changes are due to loss of cover, changes in spatial distribution of vegetation or reduced soil stability.

Data Forms

Printable data forms for the Basal Gap Intercept method can be downloaded from

Electronic data forms can be found at the following sites

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