Hello Todd. Tardigrades most likely will be found on lichens, rather on the exposed bark itself. Collect lichen and soak it in water for at least 24 hours, to rehydrate dessicated specimens. Distilled water is preffered for this step. Discard excess water, and collect the trapped water from the lichen clumps on a Petri dish (you may just simply squeeze the clumps). Examine the water for scpecimens; since tardigrades range from about 0.5mm to 1.2mm a stereoscope magnifier should be enough. You can use a micropipette to collect individuals.
Yes, we have collected and gotten many tardigrades from lichens; however, we want to see if we can find them on tree bark as well. I've heard from another collector they can be found on bark, but we don't have sampling protocol.
I collected bark from a Catalpa tree and put the bark into distilled water for about 18-20 hours and was able to find Tardigrades, Paramecium and some Nematodes