n = 4;
        trees = new Tree[n][n];
      	int treeCount = 0;
        Random rand = new Random();

	int randomNumTrees = rand.nextInt(n*n/2)+n*n/2;
        while(treeCount <= randomNumTrees){
            int i = rand.nextInt(n);
            int j = rand.nextInt(n);
            if(trees[i][j] == null){
		if(rand.nextInt(2) == 0){
                	trees[i][j] = new Ash();
            	}
           	else{
             		trees[i][j] = new Beech();
            	}
            treeCount++;
            }
        }