American Fern Journal 90(2):60-76 (2000) Patterns of Growth and Reproduction in a Natural Population of the Fern Polystichum acrostichoides Gary K. Greer Department of Biology. West Virginia State College, Institute. WV 25112-1000 Brian C. McCarthy Department of Environmental and Plant Biology, Ohio University, Athens, OH 45701 Abstract. — Patterns of growth and reproduction were documented in a natural population of Polystichum acrostichoides in southeastern Ohio during the 1994 and 1995 growing seasons. The proportion of biomass allocated to fronds increased with plant biomass, indicating fronds are an increasingly dominant component of the body of P. acrostichoides. Regression analysis indicated a minimum size threshold exists at which this species first becomes reproductive. Both repro- ductivestatusandfrequencyofreproductionwerepositivelyassociatedwithgreaterplantbiomass and above-ground growth rates. A cost of reproduction to growth was apparent; above-ground growth rates increased during non-reproductive years among individuals that reproduced in only 1994. Minor increases in reproductive effort were associated with increasing plant biomass; rang- ing from approximately 0.01% to 2.11%. Nevertheless, reproductive effort may be plastic in R acrostichoides;thefrequencyofreproductioncorrelatednegativelywithcationconcentrationsand positively with phosphorous concentrations, and reproductive effort increased with decreasing canopy cover. Together, these observations suggest reproduction in P. acrostichoides only occurs when resources are sufficient to offset it*s cost to future growth; a life history that may optimize the advantages of early reproduction and life-time fecundity in a species whose colonizing phases (i.e., gametophyte and juvenile sporophyte) have high risks of mortality. Patterns of vegetative growth and reproduction are major components of plant life history evolution. They are the basis for investigating the relation- ships betvi^een age, size, growth, and reproduction, as well as the roles of ge- notypic and allometric constraints versus plasticity in allocation patterns (Harper, 1977; Stearns, 1992). According to resource allocation theory, repro- duction and growth compete for the same pool of resources and, therefore, occur at the expense of the other (Schaffer and Rosenzweig, 1977; Harper, 1977; Watson, 1984). The size of an individual's resource pool is a function of its capacities for storage and acquisition balanced against its current and past expenditures. Life history theory predicts that, within the boundaries set by genetic and allometric constraints, a species allocation pattern will evolve to maximize it's contribution to the gene pool (Harper, 1977; Stearns, 1992). In populations where juvenile mortality rates are lower than adult mortality rates, selection will favor the demographic advantage conferred by early reproduc- tion. Conversely, in populations where juvenile mortality rates are higher than adult mortality rates, life time fecundity will be favored. Among angiosperms and gymnosperms, the challenge of studying patterns of resource allocation is compounded by a number of factors, including the existence of structures that serve both reproductive and vegetative functions (e.g., petals, pedicels, bracts, and ovary walls), loss of meristems to reproduc-