A Multistage Approach
to Population Monitoring for Rare Plant Populations
Tom Philippi, Beverly
Collins and Stephanie Guisti Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802 USA
Philip M. Dixon Department of Statistics, 125 Snedecor Hall, Iowa State University, Ames, IA
50011-1210 USA
ABSTRACT: Monitoring populations of endangered,
threatened, or sensitive species to
provide information on population status and trends is often mandated.Monitoring plant
population size over time is not trivial, even though plants are stationary.Demographic
status often must be included in monitoring information
because individuals of different
status contribute differentially to population
dynamics.However, the important
status
may be difficult to census, and resource limitations may preclude complete
demographic
monitoring of all but the smallest and most important populations.Further, the duration
of the census activity controls the power to detect a trend, so comparability
with any prior
data increases the current value of any monitoring
program.The optimal monitoring
protocol need not be a single methodology and intensity
applied to the entire population.In some cases, multistage sampling, combining extensive
plant counts with intensive
demographic monitoring of subsets of individuals, can
provide more powerful monitoring and simultaneously allow continued use of prior
data.The key to this possibility is
using reproductive values, estimated from intensively
sampled subsets, as weights for the
extensive plant counts.
Index terms: demographic monitoring, Echinacea
laevigata, multistage sampling, rare
plants, reproductive value
SREL Reprint #2504
Philippi, T.,
B. Collins, S. Guisti, and P. M. Dixon. 2001. A multistage approach to
population monitoring for rare plant populations. Natural Areas Journal
21:111-116.
