2604.02127 Does the USA-NPN First-Leaf Advance Survive Restriction to Long-Tenured Individual Plants?
Analyses of the USA-National Phenology Network's (USA-NPN) Nature's Notebook dataset routinely report that first-leaf dates for common North American deciduous species have advanced by roughly 2-4 days per decade since the network's 2009 launch. Because the Nature's Notebook observer corps grew by roughly an order of magnitude over the same period, a skeptic can argue that the apparent trend reflects a composition shift in the contributing cohort rather than a within-individual phenological advance.