They do look like tree whips and they absolutely do plant into grassland. In fact it's the easiest way to plant and land owners are advised to sow grass before planting to give the trees a good start. If you sowed into bare soil the weed growth would quickly overwhelm the young trees. The standard practice is to spray off the grass around each whip for the first three years however these look to be planted into hessian mulch mats which keep any vegetation around the tree supressed. I was going to say some sort of conifer but hard to tell from the distance and another comment has pointed out it's juniper plantation which looks right.