To put it mildly, we were a bit surprised by the findings of the initial study, and decided it would be a good idea to conduct some follow-up work. Visitation can influence plant growth . For several species, final biomass was strongly correlated with initial size. However - this was true only if the plants were visited every week. When plants were left alone for the duration of the experiment, there was no such correlation.
Visitation influences community structure.
These findings have very serious implications for those studies based upon the study of long-term permanent plots. In a local grassland, simply visiting permanent plots and measuring percent cover by species influences species diversity and abundances. In short, in just one season of study we found the act of monitoring plots itself alters community structure. In a Pennsylvania old-field, we found that weekly walks through a field significantly alters insect community structure. The diversity and abundance of several taxa increased, while that of other taxa decreased.