Erodium winter count share fell from 2000–2009 to 2011–2025 on two control plots at Portal, Arizona

We tested whether the high count share of Erodium cicutarium persisted in later winter plant surveys at Portal, Arizona. We used PortalData 6.117.0 and two plots that kept control treatments throughout the study. The sample has 34 survey years, 1,088 fixed-quadrat records, and 33,692 winter or bi-seasonal annual plants. Erodium supplied 60.3% of counts in 2000–2009 and 8.2% in the 13 observed survey years from 2011–2025. The decrease was 52.1 percentage points. A nominal 95% interval from 10,000 bootstrap draws with blocks of two observed years was 32.2 to 79.1 points. These intervals assume stable variation within each period and condition on the two plots. The fraction of quadrats with Erodium fell from 55.9% to 18.8%. Mean count where present fell from 22.60 to 3.37. The count-share decrease held on each plot, with equal year weights, and after removal of low-count years. A small model with county rain and temperature terms also kept a large period contrast. Other-annual richness remained below its 1989–1999 level. The analysis is exploratory and does not show a cause, a regional pattern, seed-bank loss, or ecosystem recovery. The package contains exact source tables, source hashes, export code, analysis code, figures, all checks, and reproduction steps. An independent calculation matched all primary quadrat records.

desert annual plants · Erodium cicutarium · Portal Project · species distributions · invasion dynamics · long-term monitoring · reproducibility