Creating artificial natural communities

I have always been interested in understanding how plant communities are structured and assembled. That’s why I’ve spent the last half decade tromping around in old-fields, shrublands and woodlands, collecting, counting and measuring plants. While most of my research has involved surveys of different types of natural plant communities, in 2013 I was trying to understand the structure of communities when all plants were the same age. This meant that the established habitats I was used to studying were no longer suitable. I had to start my own communities from scratch.

One of my beautiful old-field sites.

The easy option would have been to collect seeds from an already existing herbaceous plant community and create a new community in a controlled greenhouse setting. But I didn’t want to do that. When you start moving experiments to a “controlled” greenhouse setting, things can often end up more complicated than you ever imagined. Greenhouse disasters I have witnessed in my time in graduate school include aphid/spider/mite outbreaks, extended water outages/contamination, issues with heat/lighting control, sabotage by angry colleagues and even, I kid you not, the panes of glass on the roof smashing. (Incidentally, those panes of glass are 1.5 inches thick…and the offending object was never found… can anyone say UFO???) In addition to having little control in these supposed controlled experiments, when you use a greenhouse setting, you are also introducing other sources of variation that you wouldn’t see naturally. For example, the water/ fertilizer you apply is different from a plant’s natural environment, as is access to sunlight, and often plants end up root-bound and limited by their pot size.

So, for me, the obvious solution was to take the hard route, and attempt to set up my own communities in the field.  To create these communities, I installed aluminum cylinders into the ground (about 9 inches deep) to ensure neighbouring roots couldn’t access them. I then applied a herbicide to the resident plants in those plots, and after they died, I cleared the dead vegetation out. At one site I installed 100 cylinders and just left them as they were after clearing the dead vegetation. This allowed seeds from the natural seed bank to germinate and grow and eventually reproduce. The issue with this site though, was that I had no idea how many seeds of each species were present in each plot. So for the second site, I spent the entire summer of 2013 collecting seeds. I chose species that didn’t overlap with those already at the field site, but had been found growing in similar habitats and had a wide range in body size, flowering time and life history strategy (annual, biennial, perennial). I ended up collecting seeds of 46 species, and putting 200 seeds of each of the 46 species into each of the 100 plots. I followed these communities over the next three growing seasons, and the results were amazing.

Early growing season plot (early May) versus mid-June

In the site without introduced species (just from the seedbank), the first year plots were filled with species I didn’t recognize. This site is normally dominated by perennial wildflower and grass species, but suddenly all sorts of annuals were popping up again. In the site with introduced species, I saw tonnes of beautiful annuals flowering in year one. In year two, the plots were exploding with biennials and in year 3 finally a perennial dominance was seen. The interesting part is that now this experiment is in year 4, and although we aren’t monitoring or collecting any data, we see the resident species starting to slowly make their way back into these plots. So even though we planted tens of thousands of seeds from introduced species at the site, the resident species seeds from the seed bank and plants surrounding the plots are slowly starting to take over again. This is the perfect example of how plant community dynamics are always changing.

So taking the hard route really did pay off in the end. That doesn’t mean that there weren’t a whole slew of hideous disasters that could have affected my natural plant communities. But I could definitely sleep better at night knowing that these experimental plant communities were experiencing as close to natural conditions as possible!


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