How long does an experiment take in biology?

A potential student asked this question, a good question, but the answer isn't easy.  It takes however long it takes for the treatments to result in significant results, or until you are quite certain that nothing significant is going to happen.  In the area of community ecology, this can take years depending upon what you are recording.  This is particularly significant this Monday AM because along with a collaborator and a couple of students field work is planned, maintenance really, on an experiment that was started in 2006.  Publishable results in terms of differences in biomass were forthcoming at the end of the third year, but we remain uncertain if species composition has actually changed.  Prairie perennials are long-lived plants and while their sizes may be plastic, changeable, based on different environmental conditions and different competitions, they do not come and go quickly, except for perhaps one invasive species.  Short term experiments are like a snap shot in ecological/evolutionary time.  This is sort of like looking at one still photo and trying to understand the whole movie.  But long-term experiments eat up your time and resources.  My friends and colleagues the Clarks, Deb and David, have been running an experiment, or really monitoring rain forest tree growth for what is going on 30 years, and their data is perfectly parallel to carbon dioxide concentrations and warmer temperatures, and these are not encouraging data.  But anything of shorter duration would not have shown these trends.  They have been working with people around the world to set up similar long-term projects.  The Phactor doubts that anyone will want to inherit our project, and we remain uncertain how long it will be maintained.  The data and scholarly productivity output have been small in comparison to the labor involved, but we remain reluctant to cut and run just yet.  In part, we'd like to see is species composition is actually changing, so we will gather more data next spring and summer to find out.  Science isn't necessarily fast.  Damn those microbiologists!