This additional constraint actually makes the puzzle much easier, whereas I had found it to be one of the hardest before.

You have a grid of squares, some of which contain trees. Your aim is to place tents in some of the remaining squares, in such a way that the following conditions are met:

* There are exactly as many tents as trees
* The tents and trees can be matched up in such a way that each tent is directly adjacent
(horizontally or vertically, but not diagonally) to its own tree. However, a tent may be adjacent to other trees as well as its own
* No two tents are adjacent horizontally, vertically or diagonally
* The number of tents in each row, and in each column, matches the numbers given round the sides of the grid

thanks!