Measuring Canopy Structure

Direct Methods

Canopy access

Once the canopy is accessed, the researcher has many methods to choose from, depending on the level of aggregation and goals of the research. For a detailed analysis of the spatial distribution of plant parts, special devices to measure leaf area (see Figure 2), leaf angle and azimuth (see Figure 1), stem angle and size, and more are available (such as the compass-protractor pictured below). These techniques are described fully in the canopy architecture literature (Ross 1981, Kvet and Marshall 1971, Lang 1973).

Figure 1. A compass-protractor used to measure leaf azimuth and direction (from Norman and Campbell 1999).	Figure 2. The LI-COR 3000A planimeter is used to measure leaf area in the field without destructive sampling (from http://www.licor.com)

For less detail on exact placement or orientation of parts, systematic destructive sampling of an entire tree in height categories can allow measurement of leaf area, stem sizes, biomass, and fruit and flower numbers at a particular height or distance from the trunk.

For many researches of canopy structure that involve direct access, a stratified sampling approach is taken whereby a limited number of individuals are sampled in detail, and fewer variables are collected for a much larger sample. This smaller set of variables often includes the tree height, the heights of the upper and lower canopy limits, and some measurement of the projected crown area, and the diameter at breast height (dbh). With an appropriate model derived from more detailed sampling, these summary variables often can provide good estimates of leaf area index, total foliar area, biomass, and many other "canopy structure" variables of interest.