Off the cuff I’d say “yes” simply on the principle that to rest would mean you need to disengage your mind too much to hold a spell. The strict letter of the feature in the PHB is: “Elves don’t need to sleep. Instead, they meditate deeply, remaining semiconscious, for 4 hours a day. (The Common word for such meditation is “trance.”) While meditating, you can dream after a fashion; such dreams are actually mental exercises that have become reflexive through years of practice. After resting in this way, you gain the same benefit that a human does from 8 hours of sleep.” I’d say “semi-conscious” is sufficiently unfocused to drop concentration, but there’s no hard mechanical language one way or the other.
No. An elf who is in a trance is nothing like a human who has fallen asleep (incapacitated and therefore cannot concentrate on spells.) It states you don't need sleep and magic can't put you to sleep. You can finish a long rest in 4 hours if you spend those hours in a trancelike meditation, during which you retain consciousness.
If you retain consciousness then you are able to keep concentration on a spell.
No. An elf who is in a trance is nothing like a human who has fallen asleep (incapacitated and therefore cannot concentrate on spells.) It states you don't need sleep and magic can't put you to sleep. You can finish a long rest in 4 hours if you spend those hours in a trancelike meditation, during which you retain consciousness.
If you retain consciousness then you are able to keep concentration on a spell.
You retain consciousness while subject to Tasha’s Hideous Laughter, but that doesn’t mean you can concentrate while under the effect. Granted, in that case there’s clear mechanical language that isn’t present for Trance, but the use of “semiconscious” in the description and lack of any mechanically relevant language one way or the other gives a DM a solid case for ruling against.
No. An elf who is in a trance is nothing like a human who has fallen asleep (incapacitated and therefore cannot concentrate on spells.) It states you don't need sleep and magic can't put you to sleep. You can finish a long rest in 4 hours if you spend those hours in a trancelike meditation, during which you retain consciousness.
If you retain consciousness then you are able to keep concentration on a spell.
You retain consciousness while subject to Tasha’s Hideous Laughter, but that doesn’t mean you can concentrate while under the effect. Granted, in that case there’s clear mechanical language that isn’t present for Trance, but the use of “semiconscious” in the description and lack of any mechanically relevant language one way or the other gives a DM a solid case for ruling against.
RAW, I would say that an elf can maintain concentration while in their trance. A DM can house rule whatever they like but in this case, there is no RAW supporting that an elf would lose concentration during a trance.
What causes concentration to be lost?
"Normal activity, such as moving and attacking, doesn’t interfere with concentration. The following factors can break concentration:
Casting another spell that requires concentration. You lose concentration on a spell if you cast another spell that requires concentration. You can’t concentrate on two spells at once.
Taking damage. Whenever you take damage while you are concentrating on a spell, you must make a Constitution saving throw to maintain your concentration. The DC equals 10 or half the damage you take, whichever number is higher. If you take damage from multiple sources, such as an arrow and a dragon’s breath, you make a separate saving throw for each source of damage.
Being incapacitated or killed. You lose concentration on a spell if you are incapacitated or if you die.
The DM might also decide that certain environmental phenomena, such as a wave crashing over you while you’re on a storm-tossed ship, require you to succeed on a DC 10 Constitution saving throw to maintain concentration on a spell."
The rules are very explicit about what can break concentration on a spell - Incapacitated is a specific condition caused by various spells or by being asleep if you are a species that sleeps.
Semi-conscious isn't on the list.
In addition, the warforged version is:
"Sentry’s Rest. When you take a long rest, you must spend at least six hours in an inactive, motionless state, rather than sleeping. In this state, you appear inert, but it doesn’t render you unconscious, and you can see and hear as normal."
In this case, the description mentions that they are not unconscious and can see and hear as normal.
Neither of these examples (Trance or Sentry's Rest) cause the creature to be incapacitated while resting. RAW, neither of these features would cause a creature to lose concentration on a spell.
I know when you fall asleep you become incapacitated and therefore cannot concentrate on spells.
Does the same thing happen when an Elf trances?
Off the cuff I’d say “yes” simply on the principle that to rest would mean you need to disengage your mind too much to hold a spell. The strict letter of the feature in the PHB is: “Elves don’t need to sleep. Instead, they meditate deeply, remaining semiconscious, for 4 hours a day. (The Common word for such meditation is “trance.”) While meditating, you can dream after a fashion; such dreams are actually mental exercises that have become reflexive through years of practice. After resting in this way, you gain the same benefit that a human does from 8 hours of sleep.” I’d say “semi-conscious” is sufficiently unfocused to drop concentration, but there’s no hard mechanical language one way or the other.
No. An elf who is in a trance is nothing like a human who has fallen asleep (incapacitated and therefore cannot concentrate on spells.) It states you don't need sleep and magic can't put you to sleep. You can finish a long rest in 4 hours if you spend those hours in a trancelike meditation, during which you retain consciousness.
If you retain consciousness then you are able to keep concentration on a spell.
You retain consciousness while subject to Tasha’s Hideous Laughter, but that doesn’t mean you can concentrate while under the effect. Granted, in that case there’s clear mechanical language that isn’t present for Trance, but the use of “semiconscious” in the description and lack of any mechanically relevant language one way or the other gives a DM a solid case for ruling against.
RAW, I would say that an elf can maintain concentration while in their trance. A DM can house rule whatever they like but in this case, there is no RAW supporting that an elf would lose concentration during a trance.
What causes concentration to be lost?
"Normal activity, such as moving and attacking, doesn’t interfere with concentration. The following factors can break concentration:
The DM might also decide that certain environmental phenomena, such as a wave crashing over you while you’re on a storm-tossed ship, require you to succeed on a DC 10 Constitution saving throw to maintain concentration on a spell."
The rules are very explicit about what can break concentration on a spell - Incapacitated is a specific condition caused by various spells or by being asleep if you are a species that sleeps.
Semi-conscious isn't on the list.
In addition, the warforged version is:
"Sentry’s Rest. When you take a long rest, you must spend at least six hours in an inactive, motionless state, rather than sleeping. In this state, you appear inert, but it doesn’t render you unconscious, and you can see and hear as normal."
In this case, the description mentions that they are not unconscious and can see and hear as normal.
Neither of these examples (Trance or Sentry's Rest) cause the creature to be incapacitated while resting. RAW, neither of these features would cause a creature to lose concentration on a spell.
I see nothing in Trance that would specifically prevent concentration.
If it interest you, while not official ruling, the Dev also chimed in on this in the past;