Multi-species wasp groups?

I've been taking late afternoon walks in the McCrory Gardens in Brookings, SD after class the last few days, collecting bugs on my way, and noticed an oddity over the last 2 days. On October 2nd, I walked past a spruce tree on one of the paths, and noticed that a large number of yellowjackets were congregating on the needles. I whipped out a few bottles and caught one of the workers. After looking at the wasps, later identified as Eastern Yellowjackets (Vespula maculifrons), I noticed one with more yellow on the abdomen. I caught this one, looked a little longer at the mass of yellowjackets, ants and the occasional Paper wasp (Polistes sp.) on the spruce. After I brought the wasps back to my makeshift lab in my dorm, I identified the second, lighter yellowjacket as the German Yellowjacket (Vespula germanica). I was a little confused, thinking that maybe I had misidentified it. But I looked again in the guide to yellowjackets on this site and yep, it was a German Yellowjacket. I went for another walk today, October 3rd, and immediately searched out the spruce tree again. I recognized the Eastern Yellow jackets right away, comprizing about 97% of the specimens, and after a while noticed one other German Yellowjacket, which I collected. Then I saw another yellowjacket with darker markings further up the tree. I went and got a branch off the ground and knocked the wasp down onto a closer branch (it was chilly, he moved pretty slow). After reasurring passers-by that I was just catching a wasp, I put it in a vial and went to collect some scale insects off a Mugo Pine. When I brought the new wasp back to my dorm, I identified it as yet another type of yellowjacket, the Northern Ariel Yellowjacket (Dolichovespula norvegicoides). What is going on? Is it normal for yellowjackets of different species, that alone different genera, to congregate on the same tree. I understand it is getting colder, and they'll probably huddle together with whoever they can (even with the lone Polistes I found...they were pretty close). Also, if anyone knows what kind of scale I might have found on the Mugo Pine, ID would be appreciated. Thanks for reading!