I was using the latest stable Windows build and had an odd situation occur. It seems like a bug.
Basically, I established a base in a Public Works that was about 12 map squares south of a Triffid Grove. I went up there and took care of the grove by killing the Heart, which I was given to understand would mean that the local Triffid population would eventually die out.
Instead, I found that there were more Triffids than ever around my base when I returned. I took off exploring another area of the map so that they would de-spawn. When I came back, there still seemed to be a few Triffids around, but not so many that I was concerned.
So I retired to my base to read and then went to sleep. I got woken up in the middle of the night by a Triffid which had either spawned inside the closed room I was using as bedroom or had somehow learned to use doors.
After killing it, I turned on a flashlight to see that 95% of the visible local map was covered in forests & shrubs. My makeshift bed was on one of the half-dozen squares within sight range that was not converted to forest. There was a Triffid Queen within view and at least 6 more nearby, and their forest effect had literally covered the entire area around my character. It was a massive rectangle (the spawnable zone around me, I guess?) of shrubbery that used to be a Public Works and part of a Road. All while I was sleeping.
Now, I understand that “Dynamic Spawn” only affects Zombies, and Triffids spawn based on noise, but what noise was being made while I was sleeping?
And why, after I had supposedly done what was required to decrease their spawning, were there so many more Triffids than before? I used the debug reveal map option to see that there were no other Triffid groves nearby. Was it just a fluke? Or does clearing out the grove have no effect on spawning really, and I just got unlucky?