P. Lesica et Bm. Steele, A METHOD FOR MONITORING LONG-TERM POPULATION TRENDS - AN EXAMPLE USING RARE ARCTIC-ALPINE PLANTS, Ecological applications, 6(3), 1996, pp. 879-887
Populations of arctic-alpine plants at the southern periphery of their
range should respond rapidly to projected global warming. We establis
hed a study to monitor the density and reproductive effort of six such
species in tundra of Glacier National Park, Montana to help project t
he fate of these species in the center of their range. For many specie
s, detecting long-term population trends is confounded by short-term v
ariation. Our study design employs temporal resampling of permanent pl
ots on multiple sites and a repeated-measures model that accommodates
the effects of high frequency variation and allows assessment of the s
ignificance of long-term trends. Statistical analysis compares site-sp
ecific estimates of annual mean density between two time periods and u
ses between-plot, within-site, within-year variation to estimate error
. Power calculations using data from the 3-yr baseline period indicate
that measurements of fecundity will be less sensitive for detecting l
ong-term trends than measurements of plant density. Furthermore, our r
esults suggest that perennial species of closed-turf communities may b
e better bioassays of long-term change than annuals or species of open
, ephemeral microsites.