Full-sib progeny and clonal trials to evaluate family and clone performance
were simulated on a test site with various patterns of environmental varia
tion to examine the effectiveness of randomized incomplete block designs (I
CBs) under different design parameters (constant block size, variable block
size, block shape and orientation, and family size). Simulations showed th
at blocks of fixed size 5-20 were effective in removing most site variation
in a test with 120 full-sib families of three seedlings per family. Slight
variations in block size did not affect the precision of mean estimations
much when blocks were considered random. Square blocks were more effective
than either column or row blocks in removing both patchy variation and grad
ients in one direction. With blocks of fixed size 10, increasing family siz
e from 3 to 12 (at the expense of family number, which dropped from 120 to
30) reduced the average variance of family mean contrasts by 75%; most of t
his reduction (> 50%) was achieved at 6 seedlings per family. The differenc
es in precision of mean estimation between full-sib progeny and clonal tria
ls were small with respect to the design parameters and patterns of site va
riation examined.