Can we trust vegetation resurveys?

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.