Hi David,
It makes a lot of sense 
, thank you. I turned l_veg_compete to false, but the model failed with the following message.
{MPI Task 5} [FATAL ERROR] init_frac: No file name provided
It seemed to me that the model was reading the jules_frac from ./app/jules/rose-app.conf and no from ./app/jules/opt/rose-app-notriffid.conf. The first is indeed empty, while the second has the desired document. So I just added the datasets I want to prescribe on ./app/jules/rose-app.conf. I hope that works; at least it is now in the spinup3, which was not reached before in this process. The model has been very slow, possibly due to Jasmin, as each task takes one day to be submitted.
Best wishes,
Maria Paula