Summer, summer. The busiest and probably the most fun time of the year in terms of research. There’s lots to do out on the green roofs now that all the plants are growing and the pollinators are flying, but this is what I look forward to all winter long when I’m in the lab or working on my computer.
This past month, I visited all five of my green roof research sites. I measured all the plants to see which ones had survived the winter and how much taller they were since last year at this time. I’m happy to say that there were a lot of survivors. Many of the plants are starting to bloom and some are bigger than last year. My prairie plots are actually starting to look like short grass prairies! After working on them for years, it’s quite nice to see!
This month, I also continued to work on some experiments with my green roof trays. I measured the transpiration rate in the experimental trays again – that’s a measurement of how fast water evaporates from the growing media and leaves the plants through their leaves. So far it looks like the prairie mixes in the trays are able to hold on to water in the same way that trays planted with non-native succulent plants can. This is a good sign because it means that native plants would still be useful for green roofs that are designed to hold rainwater.
Some people think that using the non-native succulent plants will help prevent unwanted weeds from growing on a green roof, so this summer I’m measuring that too. It’s not too difficult but a little time consuming to measure this. Basically, I just pull out all the weeds, wash the soil from their roots, dry them in an oven and weigh the dried plant tissue. So far it looks like the common idea holds true – the trays that have succulent plants have fewer weeds. I’ll keep measuring this over the summer so I can make sure this trend is supported all year long (or maybe not… we’ll see).
And in June I also added a new experiment to see if pollinators are moving between my plants of interest on the roof and gardens on the ground. To do this, I placed some potted plants called Penstemon hirsutus or “hairy beardtongue” (I know – what a funny name!) on a green roof and at the base of the building on the ground. Then I painted the flowers on these plants with a powdered fluorescent dye. I returned to the plants at the end of the day with a UV light that helps me see even small specks of dye to see if any dye has been moved from the ground to the roof or vice versa. So far, there’s no evidence that this has happened but I’ll keep looking. If I see that the dye has been moved then I’ll know that a pollinator has been to both of my hairy beardtongue populations. I’ve got my fingers crossed!