Recorded plant gains and losses had opposite effects on moisture scores at 3,564 Swedish forest plots over 20 years

We tested whether recorded plant gains and losses gave the same indication of moisture change at fixed Swedish forest locations. We used 3,564 paired National Forest Inventory plots. Both visits covered 100 square metres of productive forest land, exactly 20 years apart, in 1999–2004 and 2019–2024. We matched 175 vascular plant species by exact names to Ecological Indicator Values for Europe 1.0. The mean moisture score rose from 4.84396 to 4.85081 on a 0–10 scale. The change was 0.00685, with a 95% spatial block interval of −0.00074 to 0.01398. An exact calculation used species recorded at both visits as the reference. Recorded gains raised the mean by 0.01951 (interval 0.01441 to 0.02450). Recorded losses lowered it by 0.01266 (interval for the signed term −0.01668 to −0.00870). The terms largely offset each other. Their opposite directions persisted with stricter survey-date and species rules and after removal of downy birch in an exploratory check. The net change remained uncertain. These scores describe recorded plant preferences. They do not measure soil water or separate ecological change from detection change. The result assumes that repeated public coordinate pairs identify the same plots. It has no national area weights. The package preserves compact source data, source hashes, name matches, all estimates, figures, code, independent checks, and repeat instructions.

forest vegetation · repeat survey · moisture indicator · species gains · species losses · Sweden · reproducibility