About 25 years ago (1990 or so), I started a hardcover book about a team of interstellar explorers who touch down on a heavily forested planet. They soon realize that the plant life is carnivorous and all life forms are predatory.
I believe the main character's name was something like Mark Markham — the first name could be different. There was a tree with purple vines that took a moose-like animal and popped it into its mouth.
Probably Planet of Death by Robert Silverberg. The main character's name is Roy Crawford, but he pretends to be a scientist named Paul Markham to get on the expedition [to escape being framed for a crime].
The planet is full of huge and deadly carnivores. A tree with grasping vines tries to eat one of the characters, but the vines are green (not purple) and I don't see anything described as moose-like.
EDIT: just saw your comment about the acid pool. One of the characters falls into a trapdoor spider / underground nest thing full of acid -
"Then he yelled and slipped out of sight. He went right into a big hole in the ground."
"A trap, you mean?" Hendrin asked.
"I think so. He thought he was stepping on solid ground. But it wasn't solid. He went right through.
[...]
He said, "I reached in and yanked Grover out. Some of the stuff spilled on my hands. It was like acid, sir. Like acid. He must have died right away."
I'm not sure, but your description (especially the comment) reminds me of Redliners by David Drake. It is available as a free ebook here, so you can check the fit if you want. It was published in 1997, so a little late but perhaps not terribly so.
The story follows a colonizing expedition formed up of a residence's worth of random high-class civilians, a company of soldiers retired for psychological issues, and a high ranking administrator and his aid running a social test on re-integration of war veterans.
Anyway, the points that seem to fit your description are that the ground where they land is very heavily forested, and initially looks peaceful - but they quickly discover that everything is dangerous, carnivorous, and willing to prey on them. There is a hidden acid pool, which has an inch or so of water over something caustic, which a soldier tests by dipping a thorn into it (because he did in fact suspect everything was out to get them, yes, personally). There are trees that spit thorns like bullets, and ones that drop explosives, and ones that spray sap which traps someone like a fly in amber, and also slowly dissolves them for the plant to eat. There are lots of violent and dangerous plants, more than I've mentioned, so even though I cant call up a mention of purple vines offhand, I would believe it.
Also, in terms of "all life forms are predatory" - the answer in this story is very specifically yes, they are all predatory and out to get them... which becomes a plot point
the administrator figures out the malevolence is directed, therefore artificial, finds the control center, and gains not just control of the forest but also of the bio-engineering knowledge its creators left behind. Handily winning the war the soldiers were veterans of.
Things that don't fit so well - like I said, can't recall purple vines though they may be there - I think there's a creeper vine, but I don't think its color or what it would have done is described, in the same scene with the acid pool. I don't think there was a moose-like animal, I recall a large species but they're described as humanoid. There isn't a Markson, Mark or otherwise, there is a Meyers and a Matthew if that helps - actually, there are an awful lot of named characters, each with subplots, it's a real tapestry rather than single-character oriented. It is also a bit later than you recall, 1997 instead of 1990.
I'm not sure if this is the right book, but it seemed close enough to be worth mentioning. I hope you find it.
