WordNet sense 1 (the ratio of live births in an area to the population of that area; expressed per 1000 population per year):

birthrate, natality, fertility rate

WordNet sense 2 (the state of being fertile; capable of producing offspring):

fecundity

WordNet sense 3 (the property of producing abundantly and sustaining vigorous and luxuriant growth):

rankness, richness, prolificacy