Flower production and floral ratios of a southwestern riparian tree, Arizona walnut (Juglans major)

Trees on drier terraces allocate significantly more resources to male flowering and less to female flowering than those on wet streambanks, but have equal dry weight allocation to reproduction. At the driest sites, many trees produce only male flowers. Male and female flower production fluctuates among years, but male flower number decreases less than female flower number in stress years, resulting in low female:male floral ratios. Increased male flowering on terraces and in stress years appears to be a result of reduced competition between male and female flowers. -from Authors