You would then add your DEX modifier, right?

No.  The spell just means that when you work out AC whatever the result, if that result is below 16, it becomes 16.

Barkskin does not work together with anything: here is the Sage Advice ruling regarding Barkskin (which was a reversal of a prior statement on using it with equipped shields) -

How does barkskin work with shields, cover, and other modifiers to AC?

Barkskin specifies that your AC can’t be lower than 16 while you are affected by the spell. This means you effectively ignore any modifiers to your AC—including your Dexterity modifier, your armor, a shield, and cover—unless your AC is higher than 16. For example, if your AC is normally 14, it’s 16 while barkskin is on you. If your AC is 15 and you have half cover, your AC is 17; barkskin isn’t relevant in this case, because your AC is now higher than 16.

Since Barkskin is 2nd level, one hour duration, and $#@!*&% CONCENTRATION, I suggest everyone consider using Mage Armor instead, perhaps by asking nicely the Sorcerer or Wizard in your party. In exchange you'll get a 1st level spell, EIGHT hour duration, no concentration; and you can use mage armor with a shield which would bring it up to 15+DexB.

"I fed an AI all of the most nerfed spells in the whole history of D&D and this is what it came up with."

Does anyone know if barkskin requires you to have armor on me and a couple of DM Buddies we're having this discussion and we could not come to a consensus

Eh, it's an okay spell to have if you cast it before using wildshape, as lots of animal forms have poor AC.

Quote from Davidqu >>

Does anyone know if barkskin requires you to have armor on me and a couple of DM Buddies we're having this discussion and we could not come to a consensus

The spell’s description states regardless of armor, so there’s no equipment prerequisite. Its true use is for Druids and their Wild Shape, or a stand-in for Mage Armor if an arcane caster isn’t present.

The spell could be good if it didn’t require concentration and its duration was extended... 

The spell would be good if you could use a shield with it and it didn't require concentration. The duration is not a problem. 

I was poorly stacking it against Mage Armor...1, level 1 spell slot can get you through the day, as opposed to a level 2 spell that last 1/8 the duration and can be lost on the first hit you take. 

Quote from corisande >>

The spell would be good if you could use a shield with it and it didn't require concentration. The duration is not a problem. 

 I think you’re meant to cast it on someone else, like a rogue, who doesn’t normally get shields or good armor.

Quote from Dr_Frederick >>

Quote from corisande >>

The spell would be good if you could use a shield with it and it didn't require concentration. The duration is not a problem. 

 I think you’re meant to cast it on someone else, like a rogue, who doesn’t normally get shields or good armor.

 A rogue with 45 gold to buy Studded Leather and 18 Dexterity will have 16 AC and get no bonus from this.  A Rogue with 16 Dexterity and Studded Leather will have 15 AC and will only get +1 AC from this.  It's not worth the concentration of a full spellcaster to give +1 AC to an ally.

And you're not really ever going to find a Rogue with less than 16 Dexterity or a Rogue that can't afford Studded Leather.

Quote from gabrielrockman >>

Quote from Dr_Frederick >>

Quote from corisande >>

The spell would be good if you could use a shield with it and it didn't require concentration. The duration is not a problem. 

 I think you’re meant to cast it on someone else, like a rogue, who doesn’t normally get shields or good armor.

 A rogue with 45 gold to buy Studded Leather and 18 Dexterity will have 16 AC and get no bonus from this.  A Rogue with 16 Dexterity and Studded Leather will have 15 AC and will only get +1 AC from this.  It's not worth the concentration of a full spellcaster to give +1 AC to an ally.

And you're not really ever going to find a Rogue with less than 16 Dexterity or a Rogue that can't afford Studded Leather.

You’re right.  I should have said “wizard”.  Or, a druid in animal form (since beastshape doesn’t brake concentration).

That still may not make it a “good” spell, but it has a use.

Casting word is:

Teflus Malium

And I'm assuming this also wouldnt synergize with Shield of Faith, or regular Shield? I mean really, whats the point of this other than to punish druids and rangers for not sorcerers or wizards?? If they gotta make a worse Mage Armor, at least take off the concentration and make it a 1st level, smh

A lot of people are calling this worse than Mage Armor, and while I agree that it is more niche, I do not believe it is inherently worse. Barkskin works with Druid Wild Shape forms in a way that Mage Armor does not, and is arguably better in many situations.

The best example I can give is that a Moon Druid that Wild Shapes into a Brown Bear gets a good deal more benefit from Barkskin than from Mage Armor. Since Mage Armor and Natural Armor cannot stack, the Brown Bear only gets a +2 AC bump. Since the druid is likely wearing armor (they have light armor proficiency, after all), Mage Armor can only be cast on the druid after wild shaping (which means the druid has to sit and wait for Mage Armor after wild shaping, or the wizard or sorc has to run into melee to cast it), and ends when the wild shape ends: "The spell ends if the target dons armor".

Barkskin gives a +5 AC bump to Brown Bear (each point AC is ~5% decreased chance to be hit, 15% less chance to be hit vs Mage Armor is not insignificant), does not end when Wild Shape ends and provides a benefit outside of Wild Shape since the druid can continue to wear armor. Yes, it is concentration, but generally wild shapes will often provide a bump to Concentration saves, so the risk here is reduced.

Are there better spells for the druid to concentrate while wild shaping? Yes, in most cases there are. But the druid can also play from a distance and keep barkskin up on a squishier character too. It may be niche, but it certainly isn't worthless and synergizes well with the druid's kit

This seems more the kinda of spell you would prepare when you know there is a scort mission coming up.

Quote from JohnCarney >>

"I fed an AI all of the most nerfed spells in the whole history of D&D and this is what it came up with."

 Nerfed? What was the previous version like?

I think the concentration requirement really reduces its effectiveness for Moon Druids. You're using the spell to help mix it up in melee, but it could drop at any moment. Also, most of the good Druid combat spells are concentration (e.g., call lightning, flaming sphere, fairie fire, conjure/summons) and you're giving up on all of those. It's not complete garbage, but it is underwhelming. 

Yes it should be like that