Specify How To Delete Only Certain Amount Of Objects On Screen In Graphics Window

I have a question about how to delete only a certain amount of objects on screen in a graphics window. I have a method that will enable me to get rid of every object of the same type off screen, for example this method:

Java Code:

public void deleteTrees() {
//clears all tree trunks and leaves
for (Iterator<GRect> it = historyT.iterator(); it.hasNext();) {
GObject gobj = it.next();
this.remove(gobj);

[Code] ....

That Will delete all trees.

Now In my main method I populate the screen with trees by doing this

Java Code:

for (int xpos = 10; xpos < getWidth() - 40; xpos += getWidth() / 8) {
drawTree(150, 200, xpos, getHeight() / 2.0 - 50);
historyT.add(trunk);
historyL.add(leave);

} mh_sh_highlight_all('java');

My question is how to specify only deleting x amount of trees instead of the whole thing. I pretty sure I need to use something like history.remove(trunk) and to iterate through the amount of trees specified, but not sure how to implement that.