"There are many wild animals in the forest."

Translation: W lesie jest dużo dzikich zwierząt.

[Klaudialk]

Why is it "jest", not "są" here?

[immery]

Polish quantifiers and numerals. Dużo like most quantifiers needs specific construction.

Dużo + noun in genitive plural + verb in 3rd person singular neuter.

[Klaudialk]

Dziękuje bardzo! There's always more Polish grammar to learn...

[Mudkip20]

Why can one not use 'ma' here? Or is this only for negations, like in 'nie ma nikogo w domu'?

[alik1989]

Yes, only for negations. On its own it just means "have".

[Mudkip20]

Nice dziękuję

[Ubeogesh]

I think Duolingo should allow me to use to/ta in polish when there is a "the" in English.

[alik1989]

It usually does. "W tym lesie" is accepted here.

[Tato1966]

Jest dużo dzikich zwierząt w lesie, shouldn't this be accepted?

[Jellei]

Well, sentences starting with "There is/There are" generally start with the location in Polish. However, your suggestion sounds good enough for me. Maybe because it's more of a general truth, forests are (usually) full of wild animals...