I hate it when people use a lopper to control saplings...
The very best thing to do... wait for the ground to be moist...
then most trees are fairly easy to hand pull.
When they don't immediately release? I use a shovel right next to the trunk... push in with foot... pry tree out with leverage of shovel and hand gripping tree.
No dangerous toxins required.
I have no clue what your trees are based on an individual leaf.
Please take pic of tree.
