Yes, property laws. Slightly different depending on who owns the property (and yes, all property is owned by someone). If it's private property like the woods behind someone's house, or a privately owned preserve or organization you need the express consent of said person or organization to traipse across their land and dig up stuff - usually you have to state what and how many, you can't just grab whatever strikes your fancy that day.
Forests, parks, and the side of the road are all town/state owned. If it's owned by one of these governmental bodies, you need permission and a permit for collection. In CT the link to the permit is here through the Dept. of Energy and Environmental Protection - http://www.ct.gov/deep/cwp/view.asp?a=2709&q=324230&deepNav_GID=1643
Collection without a permit is trespassing on state property and poaching of a natural resource - and trust me, you don't want to be on DEEP's "naughty list" - we had some guy poaching beaver on our wetlands several years ago, they came out in camo and hid to catch the guy!
Forgot to add that many permits are issued on a "scientific research" basis, i.e. you need to have a better reason than "I want to put it in a pot so it looks pretty" to dig up something on state property. The only time I would consider getting a permit to dig up something in this state was if it was an absolutely, undeniably, unequivocally amazing piece of material - a once in a lifetime tree - something that would be worth all the legal red tape (and trust me, CT has plenty). It's just not worth the whole permitting process to grab a random sapling on the side of the road.
Oh, and wetlands - I would only ever try collecting from wetlands on private property, not state. They're pretty touchy about mucking around in wetlands around here.