How to get the treeInstances around the player?

Is there another way to get the tree IDs of terrain trees with a specific distance to the player? I ask this because the current script causes every second a game freeze. Would be nice if someone can help.

greets Vecidive

     var distance : float;
     var cplayer : CharacterController;
     var vecreal : Vector3;
     var treelist = new ArrayList(); 
     var aTerrain : Terrain;
     
     function Start () {
     aTerrain = Terrain.activeTerrain;
     StartCoroutine("FindTrees");
     cplayer = GameObject.FindObjectOfType(CharacterController);
     
     }
     
     function FindTrees()
     {
     
      
     while(true)
     {
     yield WaitForSeconds(1);
     treelist.Clear();
     
     for(var treenumber=0; treenumber < aTerrain.terrainData.treeInstances.Length; treenumber++)
     {
     vecreal = Vector3.Scale(aTerrain.terrainData.treeInstances[treenumber].position,
     aTerrain.terrainData.size) + aTerrain.transform.position;
     distance = Vector3.Distance (cplayer.transform.position, vecreal);
     
     if(distance<40)
     {
     treelist.Add(treenumber);
     }
     }
     
     }
     
     }