A size-classified transition matrix model of the demography of Arisaema triphyllum, a perennial herb of temperate deciduous forest, was constructed from 3 yr of field data from two dif~ere.nt sites. Ar!sa~n:za is quite unusual in that individuals change sex in a pattern determined by thetr stzes: small mdtvtduals do not flower, larger individuals reproduce as males, and the largest as females. As plants increase or decrease in size, they also may change sex.Though demographic parameters varied with the site and with the year, some consistent patterns were seen. Mortality rates ranged from 20 to 4()%,/yr for small, nonflowering plants, but decreased to ~uch lower levels as plants reached reproductive size. For these large plants, mortality rates did not dtffer between sexes or among size-classes. Because rates of sexual reproduction were severely pollinator limited, levels of seed production were low (averaging 7 seeds·female-'·yr-1 ) and were not correlated with plant size. All plants engaged in clonal reproduction, regardless of their size.. Transition matrices based on these data were compared statistically and were found to vary in ttme, as a result of year-to-year environmental variability. No population had achieved a stable size distribution. The classical method of calculating rate of increase, A., was therefore rejected, and an alternative method incorporating temporal stochasticity substituted. A sensitivity analysis was performed to evaluate the effect on population growth of changing various life history parameters. J:?ifferences in ra!es of individual growth and of clonal reproduction were found to be largely responsible for the relative success of the two populations, one of which was increasing, the other declining. Arisaema's status as a climax-forest herb suggests that temporally varying transition matrices might be common even in environments traditionally regarded as "stable." The prevalence of temporal variability has consequences both for the future direction of demographic theory and for the design and analysis of field studies.

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Matrix projection models are among the most widely used tools in plant ecology. However, the way in which plant ecologists use and interpret these models differs from the way in which they are presented in the broader academic literature. In contrast to calls from earlier reviews, most studies of plant populations are based on < 5 matrices and present simple metrics such as deterministic population growth rates. However, plant ecologists also cautioned against literal interpretation of model predictions. Although academic studies have emphasized testing quantitative model predictions, such forecasts are not the way in which plant ecologists find matrix models to be most useful. Improving forecasting ability would necessitate increased model complexity and longer studies. Therefore, in addition to longer term studies with better links to environmental drivers, priorities for research include critically evaluating relative ⁄ comparative uses of matrix models and asking how we can use many short-term studies to understand long-term population dynamics.

SUMMARYInformation is reviewed on the life histories and demographic patterns of shade-tolerant herbs of temperate deciduous forest. Most of the species that have been studied are deciduous perennials. These species generally have a juvenile (non-flowering) period of several years followed by an extended period of flower and seed production. About half the species reviewed are self-incompatible, the others are at least partially self-compatible. Although vegetative reproduction is common, replacement does not always occur by vegetative spread; many species appear to be able to replace themselves by seed. Sexual reproductive effort ratiges from 15 to 50 % among the species reviewed; seed weight averages 2-6 mg. Short dormancy periods (one season) are most common, with germination rates getierally below 50%.Mortality rates of small plants are high, but decline as plant size increases. 'Ageing' does not appear to occur. No information exists on population growth rates of temperate deciduous forest herbs, or on the temporal stability of their population sizes or structures. The transition matrix model is suggested as a promising approach to future studies in plant demography.