Conserving our planet's botanical resources and ecosystems

Herbivory – Using Leaf Damage to Teach Students about Statistics and Experimental Design

The data was collected from a single Eucalyptus tree in the early 80s by Margaret Lowman in conjunction with an Earthwatch expedition. The leaves were gathered from the top down with the aid of a cherry picker, bagged, weighed, and sorted. Since all of the leaves were removed at roughly the same period in the tree’s life this creates a snapshot of that tree’s foliage. Originally the data was used to determine the distribution of insect damage in its foliage, as well as the distribution of the that foliage over the whole of the tree. The current work we are doing with the data set, represented by the 3-D graph, is to determine how much of a tree’s canopy needs to be sampled in order to obtain an accurate picture of it’s health with the intent of harvesting only as much as is statistically needed. A recent analysis of the data shows that much of the insect damage is concentrated at the lowest heights of foliage and the areas close to the trunk. The damage shows a trend of becoming less severe out into the branches. From this graph, one can therefore determine that it would be an inaccurate sampling technique to gather only the most easily accessible leaves to represent that tree. They would have a higher probability of suffering from more damage as compared to the rest of the canopy. It is in our hopes that students can use this data set as a real world example to learn some of the principles of good sampling techniques and statistical analysis.

Lowman M.D., Burgess A.D., and Higgins W.D. 1987. The biomass of New England peppermint (Eucalyptus nova-anglica) in relation to insect damage associated with rural dieback. Australian Journal of Ecology (12): 361-371