In the 1970s, people were fascinated by the thought that talking to houseplants could increase their growth. Now, a team of ecologists has discovered that touching plants in the field may alter the chance that insects will feed upon the plants' leaves. Their discoveries appear in a study published in the February issue of Ecology (volume 82 number 2). More than a novelty, this study may change the way future ecological studies are conducted.
James Cahill (now at the University of Alberta, formerly at the University of Delaware) together with Jeff Castelli and Brenda Casper (University of Pennsylvania) were studying plants in an abandoned hayfield and along a forest floor when they noticed that plants they had marked for study were experiencing extremely high rates of attack by insects. The scientists hypothesized that they, the human visitors, were somehow causing this to occur.
To test their theory, the ecologists marked 605 plants within 12 plots in an abandoned hayfield in Pennsylvania's Brandywine Valley. Six plots were visited weekly, while the remaining six plots were left unvisited as controls. When plants were visited, they were stroked once from base to tip, with care taken not to damage the plant body. This handling was designed to mimic what occurs when scientists typically take repeated measurements of plants in field studies.
One of the species studied, Indianhemp (Apocynum cannabinum) was negatively affected by visitation, experiencing high rates of leaf area loss due to insects. A second species, Sulphur Cinquefoil (Potentilla recta), seemed to benefit, as the plants experienced less leaf area loss when visited than when unvisited. The third species, commonly known as Butter and Eggs (Linaria vulgaris), also tended to fare better when visited. Fewer plants of this species died when visited than did their unvisited control counterparts.