When the lurker on the other side moved on, Randy relaxed his stance some.  He is keeping the bow out and an arrow nocked, just not drawn now.

He listens to what Ulmwin says. " Hmmph. Makes sense. It could  be almost like a weed taking root.  Get rid of the 'roots' and the portal looses it's grip on our plane. You say you can track these things by their auras?"  He looks doubtfully at the boggy soil. "Probably be more reliable than trying to physically track them."

Ulmwin nods. "Well, more like, I can see wisps of it, like roots almost, stretching out from the portal... I think trying to follow those is our best bet for now."

"Well if it is somehow corrupting this sides wildlife or plants, I'm all for doing what I can to fix that.  Just tell me what will help."

Coljin now is more interested in looking around at the plantlife and seeing if it looks odd.

"Well, I was thinking of defaulting to the good ol' adventurer standby first, and see if that does anything."

He waves his rapier just to emphasize. Even if he barely uses it in favor of spellcasting.

"May work.  Might have to throw 'em back across the portal to get the thing to close, so we probably want to keep the bodies intact.  No disintegrations."

((So looking to hack off plants and toss them back? I'd take Survival checks, or if you want to roll an Attack to hit with a slashing weapon instead, we can use that.))

"So, should aye cut plants or watch the portal?"

Dornikal asks doubtfully.

If told to cut plants, he will cut plants and toss them back over.

Attack: 20 Damage: 5

(Oh, are they all relatively close by/in sight? I presumed the strands of magic trailed further along, but if they are)

Ulmwin nods. "Seems like the best bet. Of course, it's possible that there's also some vegetation local to our plane on the other side, but... I don't think we can do anything about that part."

"Yeah, I'm not volunteering to go play gardener  on the other side.  Be a better than average chance that it would close and leave you marooned.  Whatever is over there is going to have to take it's chances."  Randy switches to his rapier and checks over the closest prospect before he begins cutting.

Survival:24

Dornikal starts hacking (24, advantage for Ulmwin being able to direct you), while Randy (12 same reasoning) notices an otherwise normal looking sapling has roots that are an unusual red color, and rightly surmises that it has been affected by proximity to the portal.

It takes a bit of work, but between UImwin directing to where he sees tendrils wiggling, Randy's knowledge about vegetation and growth patterns, and Dornikal's willing blade, you manage to clear what you think is all of the affected vegetation around the portal, and toss it back through.

(does the portal look notably less stable?) 

Dornikal steps back from the portal and gives Ulmwin a 'Well?' look.

The chaotic tendrils seem untethered, twisting through the portal, the pulses coming quicker with stronger amplitude.

Randy reaches out with planar warrior to see if he can lock on to the tendrils.

Not seeing any of this, Dornikal looks around impatiently.

"If I didn't know better, I'd say it almost seems... Angry, really. It's pulsing stronger and faster, but it is untethered. I feel like that might lead to it burning itself out faster, but I'm not sure..."

Arcana? 17

Ulmwin might have somewhat of an idea on the portal stability, hopefully. While mulling over what stories and texts he remembers, he contemplates further.

"We might need to create some dissonance between the two planes in order to fully sever the connection. Starting a fire seems easy enough... I could try and light a fire on the other side? Not only might that destroy some of the tethers on that side, but..."

Randy can't quite make out the tendrils the same way Ulmwin can, but feels the portal shimmering in front of him, and can sense its instability, a tension building. It's certainly an oversimplification, but he pictures coating a hand in pine sap and placing his palms together before trying to pull them apart. The sense he gets of things is that the connection is at the planar equivalent of the skin and sap pulling, but not quite releasing.

Ulmwin realizes that inherent to his suggestion is making sure any such fire doesn't blow back and start a fire on this side, or it may have the opposite of the desired effect, strengthening the resonance between these two locations... but if they can manage that, it may help make things less easily aligned.

Dornikal steps back from the portal and gestures towards the portal,

"Light it up then."