Select range of clips in Kdenlive
I didn't find a way of selecting a range of clips but the main problem is solved by the spacer tool which can be invoked by pressing M. One then grabs the left end of the clip to the right of a gap and drags it to the left until the gab is closed. By doing so, all clips to the right are automatically moved to the left as well.

When browsing through the different tools, I incorrectly assumed the spacer tool to be a restricted version of the selection tool because of its mouse pointer symbol: I assumed one could use it to expand clips to the left or to the right like with the selection tool (but not select clips).