The question posed in this exercise is whether photographs of a work of 'land art' are the documentation of the art or the art itself.
After working through the readings associated with this portion of the course (such as John A. Walker's piece on "Context as a Determinant of Photographic Meaning"), I am not sure that this is an 'either-or' question. Given the role that context plays in understanding the layers of meaning for a particular piece, it seems to me that the proper response is 'both-and.'
The original work of land art or installation is certainly a work of art, but so is the subsequent recording or documenting of the piece or installation. The original piece had its context—place, time, etc.—but any resulting photographs of the piece contain the results of decisions made about format, light, focal length, angle of view and framing. Artistic decisions have been made about what to include, what to leave in and how to present it. And the results of these decisions are then seen in a new frame, and a range of new contexts (particularly if the photographs appear in different settings and times), particularly when photographic processes are used to introduce the perspective of time to the way the work is viewed.
A good example of this is Keith Arnatt’s Self-burial (Television Interference Project). In this case, the performance doesn't really make sense unless it is seen as a series of photographs. A spectator watching the development of Arnatt's self-burial would have seen the artist climbing in and out of a hole that was being progressively deepened. It would have taken a long time and might well have been incomprehensible. Viewed as a planned sequence, however, the work takes on greater meaning as a coherent whole—as a photographic work more than as a live performance.
If anything, then, the photographs of a work of a land art are a new thing: based on the land art and sharing a kind of heritage or lineage with it, but a work with its own integrity and layers of meaning.