Seasonal structure, multi-scale variance, and inter-annual consistency of plant phenology in a Neotropical perhumid forest.

Plant phenology is a key determinant of the productivity and trophic dynamics of tropical forests, yet the multi-scale variance structure and inter-annual consistency of community-level phenological patterns in perhumid systems remain poorly characterized. We analyzed 10 years of weekly phenological recordings from 480 trees across 20 transects in a perhumid forest fragment at Los Tuxtlas (Mexico), characterizing the seasonal patterns, multi-scale variance structure, inter-annual consistency, and temporal covariation of five phenophases: young leaves, mature leaves, unripe fruits, ripe fruits, and flowers. All phenophases deviated significantly from uniform annual distributions (Rayleigh test, all p < 0.05), with flowers showing the highest seasonal concentration (mean vector length r = 0.52, Fourier peak April, R2 = 0.93) and mature leaves the lowest (r = 0.08). Mixed-effects variance partitioning revealed that month-within-year (seasonal) variance dominated total phenological variation across all phenophases, while between-year variance was negligible for four of five phenophases and significant only for mature leaves (18.0%). Annual phenological profiles showed moderate to high inter-annual repeatability (ICC(2,1) = 0.58-0.88), with flowers and unripe fruits exhibiting the most consistent profiles and tightest peak timing (circular SD ≤ 2.7 weeks). Young leaves and flowers showed significant positive covariation across years (mean r = 0.72, range 0.39-0.86 across all 10 years, p FDR < 0.001), with simultaneous above-average availability for 15 consecutive weeks. These results reveal that even in a perhumid climate with near year-round rainfall, seasonal forcing drives the dominant structure of plant phenological variation, producing a predictable community-level phenological calendar.