There are many synonyms for a collection of trees:
grove
A small group of trees is called a "Grove".
It is called a forest.
a group of trees is called a forest of trees
A group of trees that ends with "ump" is called a "clump." A clump typically refers to a small group of trees or plants growing close together. This term is often used in landscaping and ecology to describe a dense collection of vegetation.
a bundel of bamboo
In the U.K. a small group of trees is a 'copse', a slightly larger group is a 'woodland/woods'. and a very large group of trees is a 'forest'.
A group of trees is a stand or a grove. An area that produces fruit trees is an orchard.
http://wiki.answers.com/Q/Why_are_Fir_trees_in_a_different_group_to_oak_trees_but_daisies_are_in_the_same_group_as_oak_trees"
A group of trees is commonly referred to as a "forest."
I would call that a "stand of trees"
a grove of trees