What's the problem with groves? In Exodus 34:13, Deuteronomy 7:5, Deuteronomy 12:3, God states laws against idolatry, and God says to cut down or burn groves:


  Exodus 34:13 KJV
  But ye shall destroy their altars, break their
  images, and cut down their groves:
  
  Deuteronomy 7:5 KJV
  But thus shall ye deal with them; ye shall
  destroy their altars, and break down their images, and cut down their
  groves, and burn their graven images with fire.
  
  Deuteronomy 12:3 KJV
  And ye shall overthrow their altars, and break
  their pillars, and burn their groves with fire; and ye shall hew down
  the graven images of their gods, and destroy the names of them out of
  that place.


Some kings, fighting against idolatry, accomplished that commandment, like Hezekiah
:


  2 Kings 18:4 KJV
  He removed the high places, and brake the images,
  and cut down the groves, and brake in pieces the brasen serpent that
  Moses had made: for unto those days the children of Israel did burn
  incense to it: and he called it Nehushtan.


In my native language (portuguese), "grove" is translated as a "forest". So I thought: What's the problem with some trees? What's related to idolatry on groves? 

Using strong, the "grove" word is H842 (happy; asherah (or Astarte) a Phoenician goddess; also an image of the same). God was fighting the idolatry about that goddess?
Sacred groves are a common feature of ancient pagan religion. 

A particularly accessible Western example might be Oedipus at Colonus, which is the middle play in the Theban cycle of Sophocles (following Oedipus Rex and preceding Antigone).

A great deal of the action in Oedipus at Colonus takes place in a grove outside Colonus that is consecrated to the "Erinyes" (goddesses of vengeance).

It's also not uncommon in the legends of early-medieval Western saints for the saint to cut down a sacred tree in the presence of pagan clerics and dignitaries, in a sort of recapitulation of 1 Kings 18 -- e.g., Boniface and the Donar Oak.