В этом парке много деревьев звучит более правильно но на английском это будет звучать как There are many trees in the park. This park has many trees - У этого парка много деревьев

"В этом парке много деревьев" is correctly. But in English this phrase is "There are many trees in this park". If you say "This park has many trees" - "У этого парка много деревьев" - you are doing little false. We don't say about place "It has anything material". Place can has beautiful and other immaterial things. For example, "У этого парка есть своя, особенная красота". In this phrase we mean "it is for our soul". If you say about material, its are in the place, place don't alive and can't has any material things. And already we don't say "есть", we mean it. For example "I have a problem" - "У меня проблема". We don't say "есть", because everyone understands, that we mean it. But you can say it. It's not a false. About case "деревья". If you say "много", "мало" etc., you saying "деревьев", "людей", "страниц". The question "Есть много чего?" Answer - "Деревьев". Есть что? Деревья. If you say about quantity, you're saying word in roditelniy case. It answer on questions "кого? чего?". Case "Деревья" is imenitelniy case. It answer on questions "кто? что?". Sorry for my bad English.

This park has many trees. = There are many trees in this park. = В этом парке много деревьев. I absolutely disagree with the previous answerer, who suggest the usage of the preposition "у" in your example. It sounds illiterate and awkward. We use the preposition "у" when someone or something owns something but it can be separated. e.g. У меня есть семья/сын/жена/работа/квартира/машина/книга/яблоко etc У человека есть голова, две руки и две ноги. У стула четыре ножки, а у табуретки — три. As for the nouns like "парк", "лес", we ONLY use the preposition "в" when we mean that a park or a forest has trees as the trees in themselves ARE the forest. Their summation IS the forest. As for your initial question, describing a place, we usually omit the verb "есть" unless it necessary to emphasize something or for the sake of "smoothness" and coherence. E.g. Рядом с моим домом есть парк. // Рядом с моим домом находится парк. (we state existence of a park for the first time in the speech) В нём много деревьев. // Там много деревьев. (omitted as it's clear that we are talking about the park) Ещё там есть мини-зоопарк, игровые площадки для детей, велодорожка и танцевальная площадка. // Также там есть мини-зоопарк, игровые площадки для детей, велодорожка и танцевальная площадка. (we list the things which are in the park... the verb is needed for smothness but could be omitted as well.) А бассейн там есть? // А бассейн? (the verb is neccessary for the sake of clearness of the question; however, it could be omitted as the both speakers understand what they are talking about) Нет, к сожалению, нет. // Нет, к сожалению, бассейна там нет.

Б 1. Use есть, when the main idea of the sentence is possessing, having, existence of something, rather than its quality or other features. 2. Omit есть, when the emphasis of the sentence is quality or features of the posessed thing. When we describe appearance, we usually don't use "есть", since the emphasis is on the colours, sizes and other features. - Извините, здесь есть туалет? - Да, туалет есть. У киоска - the emphasis is on the fact that the toilet exists (you can find it, it's provided), and the info about where it is located is just additional. - Извините, где здесь туалет? - Туалет у киоска. - the emphasis is on the location (feauture) of the kiosk, but not on the fact that it exists. From the context we figure out it's clear that both speakers know that the toilet exists somewhere here, and the question is just WHERE it's located. У него тёмные волосы и голубые глаза - He's got dark hair. The main idea is not the fact that he posesses hair, but to describe its feature (colour). So we omit "есть". Depending on the emphasis "есть" can be omitted or not, so often both alternatives are possible. - В этом доме (есть) 4 подъезда. - В этом театре есть много комедий* - There are comedies here. A lot. the emphasis is on the possession, existence of the comedies (additional info: there are a lot of them) - В этом театре много комедий* - The comedies are numerous. Emphasis is on the feature (quantity), existence is clear for the speaker and listener 3. Exception: diseases. We omit "есть". У него астма. - disease THE ANSWER: В ЭТОМ ПАРКЕ (ЕСТЬ) МНОГО ДЕРЕВЬЕВ (depending on the emphasis) *The words (не)много, (не)мало require genitive case after them

A) how to choose в/у B) how to choose whether to add "есть" or to omit it. A 1. When talking about a place, preferably to use "в+place" (in the place) rather than "у". Note that with some places you will have to use "на" instead of "в" (на стадионе). Use "у" only if you mean "next to (the place), near". В этом парке... in this park У парка... by the park, next to the park В парке нет магазина, но у парка есть (магазин). Туалет (есть) у киоска - the toilet is next to the kiosk We address a park as an animate object (and use "У"), but probably you don't need such structures at the beginner's level, so my advice is to stick to "в/на" when talking about the places.