At 40 NEON sites in 2013–2024, non-native plant cover did not increase overall, and native richness did not fall within plots where non-native cover rose, though it was lower in more invaded plots

Question: did non-native plants increase on permanent NEON plots, and did plots lose native species when non-native cover increased? Data: NEON plant presence and percent cover (DP1.10058.001, RELEASE-2026, via neonDivData), 45 sites, 1,494 plots of 400 m2, 10,283 cover surveys and 6,391 full species lists, 2013–2024; crop plots excluded. Method: site trends from plot plus year fixed effects, with standard errors from year effects; random-effects summary over sites; within-plot and between-plot models of native richness on non-native cover with site-year effects and a site bootstrap; first-to-last colonisation and loss counts. Results: the non-native share of cover increased at 21 sites and decreased at 19 (random-effects mean +0.7 pp per decade, 95% CI −0.7 to +2.1). Non-native richness increased by 0.39 species per decade (0.13 to 0.65), but native richness increased more (5.6 per decade), so the non-native share of species did not change. In the same site and year, plots with 10 pp more non-native cover had 1.94 fewer native species (−2.70 to −1.11), but within plots a 10 pp increase came with +0.11 native species (−0.23 to +0.59); long-difference and lagged tests agree. Plot occurrences of non-native species increased by 9.2% and of native species by 15.7% (difference −6.3 pp, −14.4 to +3.1). Woody invaders of eastern forests (Celastrus orbiculatus, Euonymus fortunei, Ligustrum sinense) gained plots, and ruderal annual herbs lost plots, after a genus-level check for identification changes. Limits: 6 to 12 years per site; observer effects within site-years are not removed; part of the richness increase occurred in the first network years and can be a learning effect; the results are associations at the 400 m2 scale.

non-native plants · plant invasion · NEON · native species richness · percent cover · within-plot change · space-for-time · invasion paradox · long-term monitoring · United States