Measuring herbivory

Meg Lowman and leaf samples

Meg Lowman, in fact, pioneered single rope climbing as a canopy access technique in the 1980’s. She sewed her first harness out of seatbelt webbing and used her gear to sample leaves in the canopy. She was interested in looking at herbivory rates of leaves. She has been collecting data about herbivory in 300 species on 4 continents for 30 years. Here in Ethiopia, as in any other place she finds herself collecting data, she has sampled a handful of trees. She collects 30 leaves randomly from different species at different heights. Meg mostly used trees that were also being used by other members of our team just to simplify collection (meaning that trees that were already being climbed for other reasons – collecting epiphytes, soils, etc. – would also be collected from).

Tracing leaves onto graphing paper

Tools of the trade: data sheet, metric ruler, graphing paper

Again, measuring herbviory is pretty low tech. The 30 leaves are numbered with a sharpie. Each leaf is traced, holes and all. The length and width of each leaf is recorded in centimeters (of course). Measurements of the potential leaf area (PLA) – the area of the leaf if it were whole – and the actual leaf area (ALA) are taken. If no herbivory has taken place, these numbers are the same. The percent  herbivory can be derived from the difference between the PLA and the ALA. Meg likes to see how good her eye is by comparing her eyeball estimate to the number found through the tracing. Percent mining is also recorded. Though mining is a type of herbivory, it by definition, is the consumption of only a few tissue layers. Lepidoptera larvae (caterpillars) and coleoptera larvae (beetle larvae) are common miners.

An example of leaf mining: the caterpillar is only eating a few tissue layers (photo: Phil Wittman)