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Population viability analyses (predicting the future of small populations) have developed concepts relating largely to genetic threats, although environmental and demographic factors may be of greater immediate concern. Using twenty-eight published empirically derived projection matrices of various perennial herbs and trees, I model the behavior of plant populations by introducing temporal variation (stochasticity) in demographic parameters (mortality, growth, reproductive status, and reproductive output) into matrix projections of stage-structured populations. Stochastic modeling of population behavior allows estimation of extinction probabilities and minimum viable population.

Demographic stochasticity (DS) generates little variation in population dynamics. In contrast, moderate environmental stochasticity (ES) causes extinction risk for many populations with positive population growth under …