Constraints to seed production: temperate and tropical forest trees.

Reforestation requires a constant supply of high quality seed. Different methods have been used to measure seed and fruit production as a proportion of that which potentially could be produced. These estimates coupled with developmental studies permit determination of when and to what extent different biological constraints reduce seed and fruit production. These vary among species, years and sites. Overcoming biological constraints may be possible in seed orchards and seed production areas. Biological constraints include: (1) periodic or inadequate floral initiation, (2) asynchronous development and flowering, (3) floral abortion, (4) ovule abortion, (5) embryo abortion, and (6) failure of seeds and fruits to mature and our inability to determine maturity. Solutions to these constraints are varied but all must begin with an understanding of reproductive biology of each species.