Revisiting and resurveying historical vegetation plots has become a central tool for
documenting changes in plant communities. However, theoretical studies suggest that
reliable detection of long-term trends from a single resurvey is nearly impossible
for species with high stochastic population fluctuations, though it may be relatively
informative in more stable plant communities dominated by perennial species. To empirically
test how well data from a single resurvey align with estimated long-term trends in
species richness and community turnover in European grasslands, we compiled permanent-plot
time series from dry to wet grasslands that were sampled multiple times (most often
annually) during the monitoring period. We then extracted pairs of surveys (baseline
survey and one resurvey) from the individual time series and compared changes inferred
from these pairs with trends inferred from the full time series using Bayesian multilevel
regressions. We found that in studied grasslands, data from a single resurvey can
reliably reflect long-term trends in community turnover but deliver less reliable
inferences of trends in species richness. Synthesis. Despite limitations, single resurveys
remain a useful tool for describing and understanding changes in plant diversity,
at least in perennial grasslands. However, they should be used cautiously, especially
regarding changes in species richness. In general, trend inference becomes more accurate
as the number of resurveys increases and the monitoring period lengthens. Unfortunately,
such long-term, multiple-resurvey schemes still remain scarce.
