Мост ‧ Mast ‧ cognates ‧ [ mast, pole, stick, aggregate of timbers/boards ] ‧ ‧ en.wiktionary.org/wiki/Reconstruction:Proto-Slavic/mostъ ‧ ‧ en.wiktionary.org/wiki/mast#English ‧ ‧ en.wikipedia.org/wiki/Corduroy_road
1792 ‧ bridges we everywhere met ‧ across creeks (very small rivers) or swamps ‧ corduroy bridge ‧ corduroy road ‧ a stretch of road made passable by a surface of transversely placed logs ‧ dchp.ca/DCHP-1/Entries/view/corduroy%20bridge ‧ ‧ en.wikipedia.org/wiki/Corduroy_road ‧ ‧ www.alamy.com/stock-photo/corduroy-bridge.html ‧ ‧ dchp.ca/DCHP-1/entries/view/log%20crossway
It depens solely on what you mean. If you rather mean "The forest has a bridge somwhere inside", you use есть here, which is a likely situation—and this is our main translation.
If you point at the fact that there's bridge, so this is why we can cross the river, you can omit есть. In such situation the identitiy of the object "bridge" is very important for your message (it might have been a shallow place, or a ferry, or a long tree across the river).
You can imagine other situations where you clarify what kind of object is inside the forest while downplaying the fact of its existence.
Exactly. Most such nouns have only one syllable, except берег, ветер and аэропорт, the latter included in the class in the 20th century by analogy with порт (which had been there already).
The exact circumstances where such forms are use are yet to be explained properly: some of these nouns only use the non-standard form with one of the prepositions (eg., на свету).
To explain what Shady said, есть is stating the existence of the bridge. So anyone you would say this to would just now be learning about this bridge, otherwise you wouldn't need to state it's existence. The article "the" doesn't make sense in this context, because "the" assumes your audience has prior knowledge about a certain bridge.
"A" bridge is in the forest might work but it seems like a random statement. It doesn't connect to anything very well.
As stated previously on this comments page.....The Russian sentence is indicating the existence of a bridge in the forest which was hitherto unknown to the audience. The bridge indicates you are talking about the location of a particular bridge which is the subject of interest in the conversation.
A brief search and it seems that locative nouns are modified by determiners/adjectives in the prepositional case rather than having a special locative conjugation. That's disappointing, I'm so used to precise Russian agreement between words that this feels very out of place. I wonder if there's an archaic locative declension for adjectives that allowed for better agreement.