However, careful documentation of provenances has been done for only a few species. The results of centralized screening and performance trials may
be misleading due to biased selection or uncertainty about provenances being
included in a trial. Results may be confounded by high variation within a
single seed lot. On-station species screening trials may also fail to meet
development objectives, since on farms the effects of establishment techniques
and conditions often outweigh the innate inter-species differences in
early survival and growth rates demonstrated under ideal growing conditions.
More decentralized, on-farm monitoring of unfamiliar species and provenances
under a range of environments, may provide more realistic guidelines
for species introduction.