Not an answer for sure, but the process for war dead in both World Wars was most often temporary burial with wooden or temporary grave markers, and eventual disinterment and distribution of bodies to permanent burial, which could have been to a designated permanent cemetery or to individual cemeteries determined by families, governments, organizations. The crosses would then have been removed and the land reverted to normal use. We can't know for sure if that is the case here without more information.
If you know the names of the original burials you might search those names on the internet, places like FindAGrave, other archives related to those buried.
Dear Ms. Gerber,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located the series General Records, 1945-1948 in the Records of U.S. Occupation Headquarters, World War II (Record Group 260) that includes records related to monuments for mass graves that may be relevant to your research. The series Records Related to the Allied Control Authority, 1945-1949 in Record Group 260 includes 3 files related to grave care and monuments as well. We also located 5 additional series related to graves and grave registration in Record Group 260 that may be of interest to you. These records have not been digitized. Please contact the National Archives at College Park - Textual Reference (RDT2) at firstname.lastname@example.org for access to these and similar records.
If you can share more information, such as the name and location of the forced labor camp or the military unit responsible for liberating the camp, then we may be able to locate additional relevant records.
Due to the continued impact of COVID-19, you may experience a delay in receiving an initial acknowledgment as well as a substantive response to your reference request from RDT2. We apologize for this inconvenience and appreciate your understanding and patience as we balance mission-critical work and the safety of our staff during the pandemic. Please check NARA’s web page about COVID-19 updates for the latest information.
The United States Holocaust Memorial Museum provides some information regarding the Recognition of U.S. Liberating Army Units on their website, along with numerous records related to grave markers that you may wish to review. We suggest that you contact them directly for further assistance.
We hope this is helpful. Best of luck with your research!